The potential source of lead in the Permian Kupferschiefer bed of Europe and some selected Paleozoic mineral deposits in the Federal Republic of Germany

USGS Publications Warehouse

Wedepohl, K.H.; Delevaux, M.H.; Doe, B.R.

1978-01-01

New lead isotopic compositions have been measured for Paleozoic bedded and vein ore deposits of Europe by the high precision thermal emission (triple filament) technique. Eleven samples have been analyzed from the Upper Permian Kupferschiefer bed with representatives from Poland to England, three samples from the Middle Devonian Rammelsberg deposit and one from the Middle Devonian Meggen deposit, both of which are conformable ore lenses and are in the Federal Republic of Germany (FRG); and also two vein deposits from the FRG were analyzed, from Ramsbeck in Devonian host rocks and from Grund in Carboniferous host rocks. For Kupferschiefer bed samples from Germany, the mineralization is of variable lead isotopic composition and appears to have been derived about 250 m.y. ago from 1700 m.y. old sources, or detritus of this age, in Paleozoic sedimentary rocks. Samples from England, Holland, and Poland have different isotopic characteristics from the German samples, indicative of significantly different source material (perhaps older). The isotopic variability of the samples from the Kupferschiefer bed in Germany probably favors the lead containing waters coming from shoreward (where poor mixing is to be expected) rather than basinward (where better mixing is likely) directions. The data thus support the interpretation of the metal source already given by Wedepohl in 1964. Data on samples from Rammelsberg and Meggen tend to be slightly less radiogenic than for the Kupferschiefer, about the amount expected if the leads were all derived from the same source material but 100 to 150 m.y. apart in time. The vein galena from Ramsbeck is similar to that from Rammelsberg conformable ore lenses, both in rocks of Devonian age; vein galena from Grund in Upper Carboniferous country rocks is similar to some bedded Kupferschiefer mineralization in Permian rocks, as if the lead composition was formed at about the same time and from similar source material as the bedded deposits. Although heat has played a more significant role in the formation of some of these deposits (veins and Rammelsberg-Meggen) than in others (Kupferschiefer), there is no indication of radically different sources for the lead, all apparently coming from sedimentary source material containing Precambrian detritus. One feldspar lead sample from the Brocken-Oker Granite is not the same in isotopic composition as any of the ores analyzed. ?? 1978 Springer-Verlag.

The Inskip Formation, the Harmony Formation, and the Havallah Sequence of Northwestern Nevada - An Interrelated Paleozoic Assemblage in the Home of the Sonoma Orogeny

USGS Publications Warehouse

Ketner, Keith B.

2008-01-01

An area between the towns of Winnemucca and Battle Mountain in northwestern Nevada, termed the arkosic triangle, includes the type areas of the middle to upper Paleozoic Inskip Formation and Havallah sequence, the Upper Devonian to Mississippian Harmony Formation, the Sonoma orogeny, and the Golconda thrust. According to an extensive body of scientific literature, the Havallah sequence, a diverse assemblage of oceanic rocks, was obducted onto the continent during the latest Permian or earliest Triassic Sonoma orogeny by way of the Golconda thrust. This has been the most commonly accepted theory for half a century, often cited but rarely challenged. The tectonic roles of the Inskip and Harmony Formations have remained uncertain, and they have never been fully integrated into the accepted theory. New, and newly interpreted, data are incompatible with the accepted theory and force comprehensive stratigraphic and tectonic concepts that include the Inskip and Harmony Formations as follows: middle to upper Paleozoic strata, including the Inskip, Harmony, and Havallah, form an interrelated assemblage that was deposited in a single basin on an autochthonous sequence of Cambrian, Ordovician, and lowest Silurian strata of the outer miogeocline. Sediments composing the Upper Devonian to Permian sequence entered the basin from both sides, arkosic sands, gravel, limestone olistoliths, and other detrital components entered from the west, and quartz, quartzite, chert, and other clasts from the east. Tectonic activity was expressed as: (1) Devonian uplift and erosion of part of the outer miogeocline; (2) Late Devonian depression of the same area, forming a trough, probably fault-bounded, in which the Inskip, Harmony, and Havallah were deposited; (3) production of intraformational and extrabasinal conglomerates derived from the basinal rocks; and (4) folding or tilting of the east side of the depositional basin in the Pennsylvanian. These middle to upper Paleozoic deposits were compressed in the Jurassic, causing east-verging thrusts in the eastern part of the depositional basin (Golconda thrust) and west-verging thrusts and folds in the western part. Hypotheses involving a far-traveled allochthon that was obducted from an ocean or back-arc basin are incompatible with modern observations and concepts.

Structural evolution and petroleum productivity of the Baltic basin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ulmishek, G.F.

The Baltic basin is an oval depression located in the western part of the Russian craton; it occupies the eastern Baltic Sea and adjacent onshore areas. The basin contains more than 5,000 m of sedimentary rocks ranging from latest Proterozoic to Tertiary in age. These rocks consist of four tectonostratigraphic sequences deposited during major tectonic episodes of basin evolution. Principal unconformities separate the sequences. The basin is underlain by a rift probably filled with Upper Proterozoic rocks. Vendian and Lower Cambrian rocks (Baikalian sequence) form two northeast-trending depressions. The principal stage of the basin development was during deposition of amore » thick Middle Cambrian-Lower Devonian (Caledonian) sequence. This stage was terminated by the most intense deformations in the basin history. The Middle Devonian-Carboniferous (Hercynian) and Permian-Tertiary (Kimmerian-Alpine) tectonic and depositional cycles only slightly modified the basin geometry and left intact the main structural framework of underlying rocks. The petroleum productivity of the basin is related to the Caledonian tectonostratigraphic sequence that contains both source rocks and reservoirs. However, maturation of source rocks, migration of oil, and formation of fields took place mostly during deposition of the Hercynian sequence.« less

The north-subducting Rheic Ocean during the Devonian: consequences for the Rhenohercynian ore sites

NASA Astrophysics Data System (ADS)

von Raumer, Jürgen F.; Nesbor, Heinz-Dieter; Stampfli, Gérard M.

2017-10-01

Base metal mining in the Rhenohercynian Zone has a long history. Middle-Upper Devonian to Lower Carboniferous sediment-hosted massive sulfide deposits (SHMS), volcanic-hosted massive sulfide deposits (VHMS) and Lahn-Dill-type iron, and base metal ores occur at several sites in the Rhenohercynian Zone that stretches from the South Portuguese Zone, through the Lizard area, the Rhenish Massif and the Harz Mountain to the Moravo-Silesian Zone of SW Bohemia. During Devonian to Early Carboniferous times, the Rhenohercynian Zone is seen as an evolving rift system developed on subsiding shelf areas of the Old Red continent. A reappraisal of the geotectonic setting of these ore deposits is proposed. The Middle-Upper Devonian to Early Carboniferous time period was characterized by detrital sedimentation, continental intraplate and subduction-related volcanism. The large shelf of the Devonian Old Red continent was the place of thermal subsidence with contemporaneous mobilization of rising thermal fluids along activated Early Devonian growth faults. Hydrothermal brines equilibrated with the basement and overlying Middle-Upper Devonian detrital deposits forming the SHMS deposits in the southern part of the Pyrite Belt, in the Rhenish Massif and in the Harz areas. Volcanic-hosted massive sulfide deposits (VHMS) formed in the more eastern localities of the Rhenohercynian domain. In contrast, since the Tournaisian period of ore formation, dominant pull-apart triggered magmatic emplacement of acidic rocks, and their metasomatic replacement in the apical zones of felsic domes and sediments in the northern part of the Iberian Pyrite belt, thus changing the general conditions of ore precipitation. This two-step evolution is thought to be controlled by syn- to post-tectonic phases in the Variscan framework, specifically by the transition of geotectonic setting dominated by crustal extension to a one characterized by the subduction of the supposed northern slab of the Rheic Ocean preceding the general Late Variscan crustal shortening and oroclinal bending.

Stable isotope analysis of Dacryoconarid carbonate microfossils: a new tool for Devonian oxygen and carbon isotope stratigraphy.

PubMed

Frappier, Amy Benoit; Lindemann, Richard H; Frappier, Brian R

2015-04-30

Dacryoconarids are extinct marine zooplankton known from abundant, globally distributed calcite microfossils in the Devonian, but their shell stable isotope composition has not been previously explored. Devonian stable isotope stratigraphy is currently limited to less common invertebrates or bulk rock analyses of uncertain provenance. As with Cenozoic planktonic foraminifera, isotopic analysis of dacryoconarid shells could facilitate higher-resolution, geographically widespread stable isotope records of paleoenvironmental change, including marine hypoxia events, climate changes, and biocrises. We explored the use of Dacryoconarid isotope stratigraphy as a viable method in interpreting paleoenvironments. We applied an established method for determining stable isotope ratios (δ(13) C, δ(18) O values) of small carbonate microfossils to very well-preserved dacryoconarid shells. We analyzed individual calcite shells representing five common genera using a Kiel carbonate device coupled to a MAT 253 isotope ratio mass spectrometer. Calcite shell δ(13) C and δ(18) O values were compared by taxonomic group, rock unit, and locality. Single dacryoconarid calcite shells are suitable for stable isotope analysis using a Kiel-IRMS setup. The dacryoconarid shell δ(13) C values (-4.7 to 2.3‰) and δ(18) O values (-10.3 to -4.8‰) were consistent across taxa, independent of shell size or part, but varied systematically through time. Lower fossil δ(18) O values were associated with warmer water temperature and more variable δ(13) C values were associated with major bioevents. Dacryoconarid δ(13) C and δ(18) O values differed from bulk rock carbonate values. Dacryoconarid individual microfossil δ(13) C and δ(18) O values are highly sensitive to paleoenvironmental changes, thus providing a promising avenue for stable isotope chemostratigraphy to better resolve regional to global paleoceanographic changes throughout the upper Silurian to the upper Devonian. Our results warrant further exploration of dacryoconarid stable isotope proxy sensitivity, the isotopic contrast among dacryoconarids, other taxa, and bulk rock, as well as other potential dacryoconarid proxies (Mg/Ca, Sr/Ca, (87) Sr/(86) Sr, microlaser and ion microprobe isotope techniques, and clumped isotopes) for stratigraphic research. Copyright © 2015 John Wiley & Sons, Ltd.

Devonian rocks and Lower and Middle Devonian pelecypods of Guangxi, China, and the Traverse Group of Michigan

USGS Publications Warehouse

Pojeta, John

1986-01-01

A state-of-the-art summary of the Devonian rocks of China, correlation of the Lower and Middle Devonian of the Guangxi Autonomous Region with the European Standards, and detailed lithologic descriptions of the major Lower and Middle Devonian sections in Guangxi from which pelecypods were collected. Systematic descriptions are given for the Lower and Middle Devonian pelecypods of Guangxi. The Chinese pelecypods are principally compared with the previously little studied Givetian pelecypods of Michigan, which are also described.

Geologic map of the Nelson quadrangle, Lewis and Clark County, Montana

USGS Publications Warehouse

Reynolds, Mitchell W.; Hays, William H.

2003-01-01

The geologic map of the Nelson quadrangle, scale 1:24,000, was prepared as part of the Montana Investigations Project to provide new information on the stratigraphy, structure, and geologic history of an area in the geologically complex southern part of the Montana disturbed belt. In the Nelson area, rocks ranging in age from Middle Proterozoic through Cretaceous are exposed on three major thrust plates in which rocks have been telescoped eastward. Rocks within the thrust plates are folded and broken by thrust faults of smaller displacement than the major bounding thrust faults. Middle and Late Tertiary sedimentary and volcaniclastic rocks unconformably overlie the pre-Tertiary rocks. A major normal fault displaces rocks of the western half of the quadrangle down on the west with respect to strata of the eastern part. Alluvial and terrace gravels and local landslide deposits are present in valley bottoms and on canyon walls in the deeply dissected terrain. Different stratigraphic successions are exposed at different structural levels across the quadrangle. In the northeastern part, strata of the Middle Cambrian Flathead Sandstone, Wolsey Shale, and Meagher Limestone, the Middle and Upper Cambrian Pilgrim Formation and Park Shale undivided, the Devonian Maywood, Jefferson, and lower part of the Three Forks Formation, and Lower and Upper Mississippian rocks assigned to the upper part of the Three Forks Formation and the overlying Lodgepole and Mission Canyon Limestones are complexly folded and faulted. These deformed strata are overlain structurally in the east-central part of the quadrangle by a succession of strata including the Middle Proterozoic Greyson Formation and the Paleozoic succession from the Flathead Sandstone upward through the Lodgepole Limestone. In the east-central area, the Flathead Sandstone rests unconformably on the middle part of the Greyson Formation. The north edge, northwest quarter, and south half of the quadrangle are underlain by a succession of rocks that includes not only strata equivalent to those of the remainder of the quadrangle, but also the Middle Proterozoic Newland, Greyson, and Spokane Formations, Pennsylvanian and Upper Mississippian Amsden Formation and Big Snowy Group undivided, the Permian and Pennsylvanian Phosphoria and Quadrant Formations undivided, the Jurassic Ellis Group and Lower Cretaceous Kootenai Formation. Hornblende diorite sills and irregular bodies of probable Late Cretaceous age intrude Middle Proterozoic, Cambrian and Devonian strata. No equivalent intrusive rocks are present in structurally underlying successions of strata. In this main part of the quadrangle, the Flathead Sandstone cuts unconformably downward from south to north across the Spokane Formation into the upper middle part of the Greyson Formation. Tertiary (Miocene?) strata including sandstone, pebble and cobble conglomerate, and vitric crystal tuff underlie, but are poorly exposed, in the southeastern part of the quadrangle where they are overlain by late Tertiary and Quaternary gravel. The structural complexity of the quadrangle decreases from northeast to southwest across the quadrangle. At the lowest structural level (Avalanche Butte thrust plate) exposed in the canyon of Beaver Creek, lower and middle Paleozoic rocks are folded in northwest-trending east-inclined disharmonic anticlines and synclines that are overlain by recumbently folded and thrust faulted Devonian and Mississippian rocks. The Mississippian strata are imbricated adjacent to the recumbent folds. In the east-central part of the quadrangle, a structurally overlying thrust plate, likely equivalent to the Hogback Mountain thrust plate of the Hogback Mountain quadrangle adjacent to the east (Reynolds, 20xx), juxtaposes recumbently folded Middle Proterozoic and unconformably overlying lower Paleozoic rocks on the complexly folded and faulted rocks of the Avalanche Butte thrust plate. The highest structural plate, bounded below

Provenance of upper Triassic sandstone, southwest Iberia (Alentejo and Algarve basins): tracing variability in the sources

NASA Astrophysics Data System (ADS)

Pereira, M. F.; Ribeiro, C.; Gama, C.; Drost, K.; Chichorro, M.; Vilallonga, F.; Hofmann, M.; Linnemann, U.

2017-01-01

Laser ablation ICP-MS U-Pb analyses have been conducted on detrital zircon of Upper Triassic sandstone from the Alentejo and Algarve basins in southwest Iberia. The predominance of Neoproterozoic, Devonian, Paleoproterozoic and Carboniferous detrital zircon ages confirms previous studies that indicate the locus of the sediment source of the late Triassic Alentejo Basin in the pre-Mesozoic basement of the South Portuguese and Ossa-Morena zones. Suitable sources for the Upper Triassic Algarve sandstone are the Upper Devonian-Lower Carboniferous of the South Portuguese Zone (Phyllite-Quartzite and Tercenas formations) and the Meguma Terrane (present-day in Nova Scotia). Spatial variations of the sediment sources of both Upper Triassic basins suggest a more complex history of drainage than previously documented involving other source rocks located outside present-day Iberia. The two Triassic basins were isolated from each other with the detrital transport being controlled by two independent drainage systems. This study is important for the reconstruction of the late Triassic paleogeography in a place where, later, the opening of the Central Atlantic Ocean took place separating Europe from North America.

Carbonate rocks of the Seward Peninsula, Alaska: Their correlation and paleogeographic significance

USGS Publications Warehouse

Dumoulin, Julie A.; Harris, Alta; Repetski, John E.

2014-01-01

Paleozoic carbonate strata deposited in shallow platform to off-platform settings occur across the Seward Peninsula and range from unmetamorphosed Ordovician–Devonian(?) rocks of the York succession in the west to highly deformed and metamorphosed Cambrian–Devonian units of the Nome Complex in the east. Faunal and lithologic correlations indicate that early Paleozoic strata in the two areas formed as part of a single carbonate platform. The York succession makes up part of the York terrane and consists of Ordovician, lesser Silurian, and limited, possibly Devonian rocks. Shallow-water facies predominate, but subordinate graptolitic shale and calcareous turbidites accumulated in deeper water, intraplatform basin environments, chiefly during the Middle Ordovician. Lower Ordovician strata are mainly lime mudstone and peloid-intraclast grainstone deposited in a deepening upward regime; noncarbonate detritus is abundant in lower parts of the section. Upper Ordovician and Silurian rocks include carbonate mudstone, skeletal wackestone, and coral-stromatoporoid biostromes that are commonly dolomitic and accumulated in warm, shallow to very shallow settings with locally restricted circulation. The rest of the York terrane is mainly Ordovician and older, variously deformed and metamorphosed carbonate and siliciclastic rocks intruded by early Cambrian (and younger?) metagabbros. Older (Neoproterozoic–Cambrian) parts of these units are chiefly turbidites and may have been basement for the carbonate platform facies of the York succession; younger, shallow- and deep-water strata likely represent previously unrecognized parts of the York succession and its offshore equivalents. Intensely deformed and altered Mississippian carbonate strata crop out in a small area at the western edge of the terrane. Metacarbonate rocks form all or part of several units within the blueschist- and greenschist-facies Nome Complex. The Layered sequence includes mafic meta¬igneous rocks and associated calcareous metaturbidites of Ordovician age as well as shallow-water Silurian dolostones. Scattered metacarbonate rocks are chiefly Cambrian, Ordovician, Silurian, and Devonian dolostones that formed in shallow, warm-water settings with locally restricted circulation and marbles of less constrained Paleozoic age. Carbonate metaturbidites occur on the northeast and southeast coasts and yield mainly Silurian and lesser Ordovician and Devonian conodonts; the northern succession also includes debris flows with meter-scale clasts and an argillite interval with Late Ordovician graptolites and lenses of radiolarian chert. Mafic igneous rocks at least partly of Early Devonian age are common in the southern succession. Carbonate rocks on Seward Peninsula experienced a range of deformational and thermal histories equivalent to those documented in the Brooks Range. Conodont color alteration indices (CAIs) from Seward Peninsula, like those from the Brooks Range, define distinct thermal provinces that likely reflect structural burial. Penetratively deformed high-pressure metamorphic rocks of the Nome Complex (CAIs ≥5) correspond to rocks of the Schist belt in the southern Brooks Range; both record subduction during early stages of the Jurassic–Cretaceous Brooks Range orogeny. Weakly metamorphosed to unmetamorphosed strata of the York terrane (CAIs mainly 2–5), like Brooks Range rocks in the Central belt and structural allochthons to the north, experienced moderate to shallow burial during the main phase of the Brooks Range orogeny. The nature of the contact between the York terrane and the Nome Complex is uncertain; it may be a thrust fault, an extensional surface, or a thrust fault later reactivated as an extensional fault. Lithofacies and biofacies data indicate that, in spite of their divergent Mesozoic histories, rocks of the York terrane and protoliths of the Nome Complex formed as part of the same lower Paleozoic carbonate platform. Stratigraphies in both

U-Pb (zircon) and geochemical constraints on the age, origin, and evolution of Paleozoic arc magmas in the Oyu Tolgoi porphyry Cu-Au district, southern Mongolia

USGS Publications Warehouse

Wainwright, A.J.; Tosdal, R.M.; Wooden, J.L.; Mazdab, F.K.; Friedman, R.M.

2011-01-01

Uranium-Pb (zircon) ages are linked with geochemical data for porphyry intrusions associated with giant porphyry Cu-Au systems at Oyu Tolgoi to place those rocks within the petrochemical framework of Devonian and Carboniferous rocks of southern Mongolia. In this part of the Gurvansayhan terrane within the Central Asian Orogenic Belt, the transition from Devonian tholeiitic marine rocks to unconformably overlying Carboniferous calc-alkaline subaerial to shallow marine volcanic rocks reflects volcanic arc thickening and maturation. Radiogenic Nd and Pb isotopic compositions (??Nd(t) range from +3.1 to +7.5 and 206Pb/204Pb values for feldspars range from 17.97 to 18.72), as well as low high-field strength element (HFSE) contents of most rocks (mafic rocks typically have <1.5% TiO2) are consistent with magma derivation from depleted mantle in an intra-oceanic volcanic arc. The Late Devonian and Carboniferous felsic rocks are dominantly medium- to high-K calc-alkaline and characterized by a decrease in Sr/Y ratios through time, with the Carboniferous rocks being more felsic than those of Devonian age. Porphyry Cu-Au related intrusions were emplaced in the Late Devonian during the transition from tholeiitic to calc-alkaline arc magmatism. Uranium-Pb (zircon) geochronology indicates that the Late Devonian pre- to syn-mineral quartz monzodiorite intrusions associated with the porphyry Cu-Au deposits are ~372Ma, whereas granodiorite intrusions that post-date major shortening and are associated with less well-developed porphyry Cu-Au mineralization are ~366Ma. Trace element geochemistry of zircons in the Late Devonian intrusions associated with the porphyry Cu-Au systems contain distinct Th/U and Yb/Gd ratios, as well as Hf and Y concentrations that reflect mixing of magma of distinct compositions. These characteristics are missing in the unmineralized Carboniferous intrusions. High Sr/Y and evidence for magma mixing in syn- to late-mineral intrusions distinguish the Late Devonian rocks associated with giant Cu-Au deposits from younger magmatic suites in the district. ?? 2010 Elsevier B.V.

Diagenesis and evolution of microporosity of Middle-Upper Devonian Kee Scarp reefs, Norman Wells, Northwest Territories, Canada: Petrographic and chemical evidence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Al-Aasm, I.S.; Azmy, K.K.

The Middle-Upper Devonian Kee Scarp reef complexes of Norman Wells, Northwest Territories, Canada, are oil-producing, stromatoporoid-dominated carbonates. Episodic increases in the rate of sea level rise produced multiple cycles of reef growth that exhibit backstepping characteristics. These carbonates, composed of invariably altered limestones, have original interskeletal, intraskeletal, and intergranular porosity, mostly occluded by nonferroan, dull luminescent cements. Secondary porosity, represented by micropores of various types, developed during diagenesis by aggrading neomorphism and dissolution. The micropores represent the main reservoir porosity in the Kee Scarp limestone. Petrographic, chemical, and isotopic studies of Kee Scarp reef components reveal a complex diagenetic historymore » involving marine fluids modified by increasing water/rock interaction and burial. Neomorphic stabilization of skeletal components caused further depletion in {gamma}{sup 18}O but very little change in {gamma}{sup 13}C, an argument for modification of the original marine fluids with increasing burial. Variations in magnitude of water/rock interaction with depth, facies changes, and porosity modifications probably exerted some control on fractionation and distribution of stable isotopes and trace elements in reef components.« less

Reconnaissance geology of the Central Mastuj Valley, Chitral State, Pakistan

USGS Publications Warehouse

Stauffer, Karl W.

1975-01-01

The Mastuj Valley in Chitral State is a part of the Hindu Kush Range, and is one of the structurally most complicated areas in northern Pakistan. Sedimentary rocks ranging from at least Middle Devonian to Cretaceous, and perhaps Early Tertiary age lie between ridge-forming granodiorite intrusions and are cut by thrust faults. The thrust planes dip 10? to 40? to the north- west. Movement of the upper thrust plates has been toward the southeast relative to the lower blocks. If this area is structurally typical of the Hindu-Kush and Karakoram Ranges, then these mountains are much more tectonically disturbed than previously recorded, and suggest compression on a scale compatible with the hypothesis that the Himalayan, Karakoram, and Hindu Kush Ranges form part of a continental collision zone. The thrust faults outline two plates consisting of distinctive sedimentary rocks. The lower thrust plate is about 3,000 feet thick and consists of the isoclinally folded Upper Cretaceous to perhaps lower Tertiary Reshun Formation. It has overridden the Paleozoic metasedimentary rocks of the Chitral Slate unit. This thrust plate is, in turn, overridden by an 8,000-foot thick sequence consisting largely of Devonian to Carboniferous limestones and quartzites. A key factor in the tectonic processes has been the relatively soft and plastic lithology of the siltstone layers in the Reshun Formation which have acted as lubricants along the principal thrust faults, where they are commonly found today as fault slices and smears. The stratigraphic sequence, in the central Mastuj Valley was tentatively divided into 9 mapped units. The fossiliferous shales and carbonates of the recently defined Shogram Formation and the clastlcs of the Reshun Formation have been fitted into a sequence of sedimentary rocks that has a total thick- ness of at least 13,000 feet and ranges in age from Devonian to Neogene. Minerals of potential economic significance include antimony sulfides which have been mined elsewhere in Chitral, the tungstate, scheelite, which occurs in relatively high concentrations in heavy-mineral fractions of stream sands, and an iron-rich lateritic rock.

Stratigraphy of lower to middle Paleozoic rocks of northern Nevada and the Antler orogeny

USGS Publications Warehouse

Ketner, Keith B.

2013-01-01

Commonly accepted concepts concerning the lower Paleozoic stratigraphy of northern Nevada are based on the assumption that the deep-water aspects of Ordovician to Devonian siliceous strata are due to their origin in a distant oceanic environment, and their presence where we find them is due to tectonic emplacement by the Roberts Mountains thrust. The concept adopted here is based on the assumption that their deep-water aspects are the result of sea-level rise in the Cambrian, and all of the Paleozoic strata in northern Nevada are indigenous to that area. The lower part of the Cambrian consists mainly of shallow-water cross-bedded sands derived from the craton. The upper part of the Cambrian, and part of the Ordovician, consists mainly of deep-water carbonate clastics carried by turbidity currents from the carbonate shelf in eastern Nevada, newly constructed as a result of sea-level rise. Ordovician to mid-Devonian strata are relatively deep-water siliceous deposits, which are the western facies assemblage. The basal contact of this assemblage on autochthonous Cambrian rocks is exposed in three mountain ranges and is clearly depositional in all three. The western facies assemblage can be divided into distinct stratigraphic units of regional extent. Many stratigraphic details can be explained simply by known changes in sea level. Upper Devonian to Mississippian strata are locally and westerly derived orogenic clastic beds deposited disconformably on the western facies assemblage. This disconformity, clearly exposed in 10 mountain ranges, indicates regional uplift and erosion of the western facies assemblage and absence of local deformation. The disconformity represents the Antler orogeny.

Geochemical Aspects of Formation of Large Oil Deposits in the Volga-Ural Sedimentary Basin

NASA Astrophysics Data System (ADS)

Plotnikova, I.; Nosova, F.; Pronin, N.; Nosova, J.; Budkevich, T.

2012-04-01

The study of the rocks domanikoid type in the territory of the Ural-Volga region has an almost century-long history, beginning with the first studies of A.D. Archangelsky in the late 20's of last century. But nevertheless the question of the source of oil that formed the industrial deposits of Volga-Ural oil and gas province (OGP), where Romashkinskoye oil field occupies a special place, remains unresolved and topical. According to the sedimentary-migration theory of origin of oil and gas, it is supposed that the primary source of hydrocarbons in this area are the deposits of domanikoid type that contain a large ammount of sapropel organic matter (OM). Semiluki (domanik) horizon of srednefranski substage of the Upper Devonian is considered to be a typical domanikoid stratum. Investigation of the OM of the rocks and oils of the sedimentary cover on the basis of chromato-mass spectrometry method allows us to study the correlations between rock and oil and to assess the location (or absence) of the sources of hydrocarbons in the Paleozoic sedimentary cover. The results of geochemical study of dispersed organic matter (DOM) of rocks from Semiluksky horizon of the Upper Devonian and of the oil from Pashiysky horizon of the Middle Devonian form the basis of this paper. The objectives of this study were the following: to determine the original organic matter of the rocks, which would indicate the conditions of sedimentation of the supposed rock-oil sources; the study of chemofossils (biomarkers) in oil from Pashiyskiy horizon; and the identification of genetic association of DOM rocks from Semiluksky horizon with this oil on the basis of the oil-DOM correlation. The study of biomarkers was carried out with the help of chromato-mass spectrometry in the Laboratory of Geochemistry of Fossil Fuels (Kazan Federal University). In this study we used several informative parameters characterizing the depositional environment, the type of source OM and its maturity: STER / PENT, hC35/hC34, GAM / HOP, S27/S28/S29 (steranes), DIA / REG, Ts / Tm, MOR / HOP, NOR / HOP, TET / TRI, C29SSR, C29BBAA, C31HSR, S30STER, TRI / PENT, TRI / HOP. Comparison in the rock-oil system was performed primarily according to the parameters indicating the depositional environment of the source rock that contains syngenetic DOM - according to the coefficients that determine lithological conditions for the formation of the supposed oil-source bed strata (DIA / REG, Ts / Tm, NOR / HOP, TRI / HOP and STER / PENT). Biomarker ratios indicate a different type of sedimentation basins. Sediments, which accumulated DOM from Semilukskiy horizon, can be characterized by low clay content, or its absence, that is consistent with the carbonate type of cut of the horizon. The bacterial material that was accumulated under reducing conditions of sedimentation appeared to be the source of syngenetic OM. Chemofossils found in oils from Pashiyskiy horizon are typical of sedimentary strata that contain clay - for clastic rocks, which in the study area are mainly represented by deposits and Eyfel Givetian layers of the Middle Devonian and lowfransk substage of the Upper Devonian. The study of correlations obtained for the different coefficients of OM and oils showed that only the relationships between Ts/Tm and DIA/REG and between NOR/HOP and TRI/HOP are characteristic of close, almost similar values of correlation both for the dispersed organic matter and for oil. In all other cases, the character of the correlation of OM is significantly different from that of oil. The differences in values and ranges of biomarker ratios as well as the character of their correlation indicates the absence of genetic connection between the oil from Pashiyskiy horizon for the dispersed organic matter from Semilukskiy horizon. This conclusion is based on the study of five biomarker parameters (DIA/REG, Ts/Tm, NOR/HOP, TRI/HOP and STER/PENT). The research results described in the article clearly indicate the need for further studies of geochemical features of the organic matter of the Paleozoic mantle rocks and the underlying sedimentary and crystalline complexes of Precambrian.

Stratigraphic and palaeoenvironmental summary of the south-east Georgia Embayment: a correlation of exploratory wells

USGS Publications Warehouse

Poppe, L.J.; Popenoe, P.; Poag, C.W.; Swift, B.A.

1995-01-01

A Continental Offshore Stratigraphic Test (COST) well and six exploratory wells have been drilled in the south-east Georgia embayment. The oldest rocks penetrated are weakly metamorphosed Lower Ordovician quartz arenites and Silurian shales and argillites in the Transco 1005-1 well and Upper Devonian argillites in the COST GE-1 well. The Palaeozoic strata are unconformably overlain by interbedded non-marine Jurassic sandstones and shales and marginal marine Lower Cretaceous rocks. Together, these rocks are stratigraphically equivalent to the onshore Fort Pierce and Cotton Valley(?) Formations and rocks of the Lower Cretaceous Comanchean Provincial Series. The Upper Cretaceous part of the section is composed mainly of neritic calcareous shales and shaley limestones stratigraphically equivalent to the primarily marginal marine facies of the onshore Atkinson, Cape Fear and Middendorf Formations and Black Creek Group, and to limestones and shales of the Lawson Limestone and Peedee Formations. Cenozoic strata are also described. -from Authors

Aquifer Characteristics Data Report for the Weldon Spring Site chemical plant/raffinate pits and vicinity properties for the Weldon Spring Site Remedial Action Project, Weldon Spring, Missouri

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1990-11-01

This report describes the procedures and methods used, and presents the results of physical testing performed, to characterize the hydraulic properties of the shallow Mississippian-Devonian aquifer beneath the Weldon Spring chemical plant, raffinate pits, and vicinity properties. The aquifer of concern is composed of saturated rocks of the Burlington-Keokuk Limestone which constitutes the upper portion of the Mississippian-Devonian aquifer. This aquifer is a heterogeneous anisotropic medium which can be described in terms of diffuse Darcian flow overlain by high porosity discrete flow zones and conduits. Average hydraulic conductivity for all wells tested is 9.6E-02 meters/day (3.1E-01 feet/day). High hydraulic conductivitymore » values are representative of discrete flow in the fractured and weathered zones in the upper Burlington-Keokuk Limestone. They indicate heterogeneities within the Mississippian-Devonian aquifer. Aquifer heterogeneity in the horizontal plane is believed to be randomly distributed and is a function of fracture spacing, solution voids, and preglacial weathering phenomena. Relatively high hydraulic conductivities in deeper portions of the aquifer are though to be due to the presence of widely spaced fractures. 44 refs., 27 figs., 9 tabs.« less

A search for stratiform massive-sulfide exploration targets in Appalachian Devonian rocks; a case study using computer-assisted attribute-coincidence mapping

USGS Publications Warehouse

Wedow, Helmuth

1983-01-01

The empirical model for sediment-associated, stratiform, exhalative, massive-sulfide deposits presented by D. Large in 1979 and 1980 has been redesigned to permit its use in a computer-assisted search for exploration-target areas in Devonian rocks of the Appalachian region using attribute-coincidence mapping (ACM). Some 36 gridded-data maps and selected maps derived therefrom were developed to show the orthogonal patterns, using the 7-1/2 minute quadrangle as an information cell, of geologic data patterns relevant to the empirical model. From these map and data files, six attribute-coincidence maps were prepared to illustrate both variation in the application of ACM techniques and the extent of possible significant exploration-target areas. As a result of this preliminary work in ACM, four major (and some lesser) exploration-target areas needing further study and analysis have been defined as follows: 1) in western and central New York in the outcrop area of lowermost Upper Devonian rocks straddling the Clarendon-Linden fault; 2) in western Virginia and eastern West Virginia in an area largely coincident with the well-known 'Oriskany' Mn-Fe ores; 3) an area in West Virginia, Maryland, and Virginia along and nearby the trend of the Alabama-New York lineament of King and Zietz approximately between 38- and 40-degrees N. latitude; and 4) an area in northeastern Ohio overlying an area coincident with a significant thickness of Silurian salt and high modern seismic activity. Some lesser, smaller areas suggested by relatively high coincidence may also be worthy of further study.

Lithostratigraphic, conodont, and other faunal links between lower Paleozoic strata in northern and central Alaska and northeastern Russia

USGS Publications Warehouse

Dumoulin, Julie A.; Harris, Anita G.; Gagiev, Mussa; Bradley, Dwight C.; Repetski, John E.

2002-01-01

Lower Paleozoic platform carbonate strata in northern Alaska (parts of the Arctic Alaska, York, and Seward terranes; herein called the North Alaska carbonate platform) and central Alaska (Farewell terrane) share distinctive lithologic and faunal features, and may have formed on a single continental fragment situated between Siberia and Laurentia. Sedimentary successions in northern and central Alaska overlie Late Proterozoic metamorphosed basement; contain Late Proterozoic ooid-rich dolostones, Middle Cambrian outer shelf deposits, and Ordovician, Silurian, and Devonian shallow-water platform facies, and include fossils of both Siberian and Laurentian biotic provinces. The presence in the Alaskan terranes of Siberian forms not seen in wellstudied cratonal margin sequences of western Laurentia implies that the Alaskan rocks were not attached to Laurentia during the early Paleozoic.The Siberian cratonal succession includes Archean basement, Ordovician shallow-water siliciclastic rocks, and Upper Silurian–Devonian evaporites, none of which have counterparts in the Alaskan successions, and contains only a few of the Laurentian conodonts that occur in Alaska. Thus we conclude that the lower Paleozoic platform successions of northern and central Alaska were not part of the Siberian craton during their deposition, but may have formed on a crustal fragment rifted away from Siberia during the Late Proterozoic. The Alaskan strata have more similarities to coeval rocks in some peri-Siberian terranes of northeastern Russia (Kotelny, Chukotka, and Omulevka). Lithologic ties between northern Alaska, the Farewell terrane, and the peri-Siberian terranes diminish after the Middle Devonian, but Siberian afµnities in northern and central Alaskan biotas persist into the late Paleozoic.

Ocean plateau-seamount origin of basaltic rocks, Angayucham terrane, central Alaska

USGS Publications Warehouse

Barker, F.; Jones, D.L.; Budahn, J.R.; Coney, P.J.

1988-01-01

The Angayucham terrane of north-central Alaska (immediately S of the Brooks Range) is a large (ca. 500 km E-W), allochthonous complex of Devonian to Lower Jurassic pillow basalt, diabase sills, gabbro plutons, and chert. The mafic rocks are transitional normal-to-enriched, mid-ocean-ridge (MORB) type tholeiites (TiO2 1.2-3.4%, Nb 7-23 ppm, Ta 0.24-1.08 ppm, Zr 69-214 ppm, and light REE's slightly depleted to moderately enriched). Geologic and geochemical constraints indicate that Angayucham terrane is the upper "skin' (ca. 3-4 km thick) of a long-lived (ca. 170-200 ma) oceanic plateau whose basaltic-gabbroic rocks are like those of seamounts of the East Pacific Rise. -Authors

Regional stratigraphy and petroleum potential, Ghadames basin, Algeria

DOE Office of Scientific and Technical Information (OSTI.GOV)

Emme, J.J.; Sunderland, B.L.

1991-03-01

The Ghadames basin in east-central Algeria extends over 65,000 km{sup 2} (25,000 mi{sup 2}), of which 90% is covered by dunes of the eastern Erg. This intracratonic basin consists of up to 6000 m (20,000 ft) of dominantly clastic Paleozoic through Mesozoic strata. The Ghadames basin is part of a larger, composite basin complex (Ilizzi-Ghadames-Triassic basins) where Paleozoic strata have been truncated during a Hercynian erosional event and subsequently overlain by a northward-thickening wedge of Mesozoic sediments. Major reservoir rocks include Triassic sandstones that produce oil, gas, and condensate in the western Ghadames basin, Siluro-Devonian sandstones that produce mostly oilmore » in the shallower Ilizzi basin to the south, and Cambro-Ordovician orthoquartzites that produce oil at Hassi Messaoud to the northwest. Organic shales of the Silurian and Middle-Upper Devonian are considered primary source rocks. Paleozoic shales and Triassic evaporite/red bed sequences act as seals for hydrocarbon accumulations. The central Ghadames basin is underexplored, with less than one wildcat well/1700 km{sup 2} (one well/420,000 ac). Recent Devonian and Triassic oil discoveries below 3500 m (11,500 ft) indicate that deep oil potential exists. Exploration to date has concentrated on structural traps. Subcrop and facies trends indicate that potential for giant stratigraphic or combination traps exists for both Siluro-Devonian and Triassic intervals. Modern seismic acquisition and processing techniques in high dune areas can be used to successfully identify critical unconformity-bound sequences with significant stratigraphic trap potential. Advances in seismic and drilling technology combined with creative exploration should result in major petroleum discoveries in the Ghadames basin.« less

Distribution and variation of the inorganic fraction of Devonian to Bashkirian black shales in the north-western part of the Dniepr-Donets Basin, Ukraine

NASA Astrophysics Data System (ADS)

Wegerer, Eva; Sachsenhofer, Reinhard; Misch, David; Aust, Nicolai

2016-04-01

Mineralogical data of 112 core samples from 12 wells are used to investigate lateral and vertical variations in the lithofacies of Devonian to Bashkirian black shales in the north-western part of the Dniepr-Donets-Basin. Sulphur and carbonate contents as well as organic geochemical parameters, including TOC and Hydrogen Index have been determined on the same sample set within the frame of an earlier study (Sachsenhofer et al. 2010). This allows the correlation of inorganic and organic composition of the black shales. Aims of the study are to distinguish between detrital and authigenic minerals, to relate the lithofacies of the black shales with the tectono-stratigraphic sequences of the Dniepr-Donets Basin, to contribute to the reconstruction of the depositional environment and to relate diagenetic processes with the thermal history of the basin. Mineral compositions were determined primarily using XRD-measurements applying several measurement procedures, e.g. chemical and temperature treatment, and specific standards. Major differences exist in the mineralogical composition of the black shales. For example, clay mineral contents range from less than 20 to more than 80 Vol%. Kaolinite contents are significantly higher in rocks with a Tournaisian or Early Visean age than in any other stratigraphic unit. This is also true for two Lower Visean coal samples from the shallow north-westernmost part of the basin. Chlorite contents reach maxima in uppermost Visean and overlying rocks. Quartz contents are often high in Upper Visean rocks and reach maxima in Bashkirian units. Feldspar-rich rocks are observed in Devonian sediments from the north-western part of the study area and may reflect the proximity to a sediment source. Carbonate contents are typically low, but reach very high values in some Tournaisian, Lower Visean and Serpukhovian samples. Pyrite contents reach maxima along the basin axis in Tournaisian and Visean rocks reflecting anoxic conditions. Mixed layer minerals are dominated by illite. Their presence in samples from depth exceeding 5 km reflects the low thermal overprint of Paleozoic rocks in the north-western Dniepr-Donets-Basin.

The pre-Devonian tectonic framework of Xing'an-Mongolia orogenic belt (XMOB) in north China

NASA Astrophysics Data System (ADS)

Xu, Bei; Zhao, Pan; Wang, Yanyang; Liao, Wen; Luo, Zhiwen; Bao, Qingzhong; Zhou, Yongheng

2015-01-01

A new tectonic division of the Xing'an-Mongolia orogenic belt (XMOB) in north China has been presented according to our research and a lot of new data of tectonics, geochronology and geochemistry. Four blocks and four sutures have been recognized in the XMOB, including the Erguna (EB), Xing'an-Airgin Sum (XAB), Songliao-Hunshandake (SHB), and Jiamusi (JB), and Xinlin-Xiguitu (XXS), Xilinhot-Heihe (XHS), Mudanjiang (MS) and Ondor Sum-Yongji sutures (OYS). The framework of the XMOB is characterized by a tectonic collage of the blocks and orogenic belts between them. Different Precambrian basements have been found in the blocks, including the Neoproterozoic metamorphic rocks and plutons in the EB, the Neoproterozoic metamorphic rocks in western and eastern of segments of the XAB, Mesoproterozoic and Neoproterozoic metamorphic rocks in middle segments of the XAB, respectively, the Neoproterozoic metamorphic rocks and Mesoproterozoic volcanic rocks and plutons in the SHB, and Neoproterozoic metamorphic rocks in the JB. The XXS resulted from a northwestward subduction of the XAB beneath the EB during the Cambrian, which was followed by the forming of the XHS and OYS in the northwest and south margins of the SHB in the Silurian, respectively. The MS was caused by a westward subduction of the JB beneath the east margin of the SHB during the middle Devonian. The three Cambrian, Silurian and middle Devonian events indicate that the XMOB belongs to a pre-middle Devonian multiple orogenic belt in the Central Asian Orogenic Belt (CAOB). Forming of the XMOB suggests that the southeast part of the Paleo Asian Ocean closed before the middle Devonian.

Assessment of Paleozoic terrane accretion along the southern central Andes using detrital zircon geochronology

NASA Astrophysics Data System (ADS)

McKenzie, R.; Horton, B. K.; Fuentes, F.; Fosdick, J. C.; Capaldi, T.; Stockli, D. F.; Alvarado, P. M.

2015-12-01

Two distinct Paleozoic terranes known as Cuyania and Chilenia occupy the southern central Andes of Argentina and Chile. Because the proposed terrane boundaries coincide with major structural elements of the modern Andean system at 30-36°S, it is important to understand their origins and potential role in guiding later Andean deformation. The Cuyania terrane of western Argentina encompasses the Precordillera (PC) and a thick-skinned thrust block of the western Sierras Pampeanas, persisting southward to the San Rafael Basin (SRB). Although recently challenged, Cuyania has been long considered a piece of southern Laurentia that rifted away during the early Cambrian and collided with the Argentine margin during the Ordovician. Chilenia is situated west of Cuyania and includes the Frontal Cordillera (FC) and Andean magmatic arc. This less-studied terrane was potentially accreted during an enigmatic Devonian orogenic event. We present new detrital zircon U-Pb age data from siliciclastic sedimentary rocks that span the entire Paleozoic to Triassic from the FC, PC, and SRB. Cambrian rocks of the PC exhibit similar zircon age distributions with prominent ~1.4 and subordinate ~1.1 Ga populations, which are distinct from other Paleozoic strata. Plutonic rocks with these ages are common in southern Laurentia, whereas ~1.4 Ga zircons are uncommon in South American age distributions. This supports a Laurentian origin for Cuyania in isolation from Argentina during the Cambrian. Upper Paleozoic strata from the PC, FC, and SRB all yield similar age data suggesting shared provenance across the proposed Cuyania-Chilenia suture. Age distributions also notably lack Devonian-age grains. The regional paucity of Devonian plutonic rocks and detrital zircon casts doubt on a possible arc system between these terranes at this time, a key requisite for the mid-Paleozoic transfer and accretion of Chilenia to the Argentine margin. Collectively, these data question the precise boundaries of the Chilenia terrane.

Trace Metal Characterization and Ion Exchange Capacity of Devonian to Pennsylvanian Age Bedrock in New York and Pennsylvania in Relation to Drinking Water Quality

NASA Astrophysics Data System (ADS)

Spradlin, J.; Fiorentino, A. J., II; Siegel, D. I.

2014-12-01

We report the results of an evaluation of the trace and major metal composition of shallow sedimentary rock formations in the Appalachian Basin that control the quality of potable water produced in domestic and other wells. In particular, we quantify the mobile and total metals for which there are health concerns related to unconventional gas exploitation; Fe, Mn, Sr, Ba, As, and Pb. To do this, we sampled the upper 400 feet of Devonian to Pennsylvanian aged bedrock from Marcellus, NY to State College, PA. We used a variation of the U.S. Geological Survey Field Leach Test to assess water reactivity and leaching potential. Al, Zn, and U potentially can be leached from aquifer rocks naturally under acidic conditions, such as where pyrite might oxidize, to above current allowable regulatory values for these metals (2 mg/L, 5 mg/L, and 0.03 mg/L respectively) from some of the clay-rich formations. Groundwater analyses from both New York and Pennsylvania show that natural ion exchange occurs along flow paths from ridges to valleys. We find the laboratory cation exchange capacity (CEC) spans what might be expected for illite and chlorite commonly found in these rocks. Given the low surface area of the mineral surfaces of the fractures through which most of the water moves, the observed ion exchange in these rocks is not well understood. Along with this broad scale study area we investigated a Devonian outcrop 4 miles North of Cortland, NY to evaluate small-scale trace metal heterogeneity within a single stratigraphic section. Together these two studies provide important information to determine the extent to which ground water might be naturally high in trace metal composition, either because of geochemical conditions or entrainment of suspended material not removed prior to sampling.

Reevaluation of the Piermont-Frontenac allochthon in the Upper Connecticut Valley: Restoration of a coherent Boundary Mountains–Bronson Hill stratigraphic sequence

USGS Publications Warehouse

Rankin, Douglas W.; Tucker, Robert D.; Amelin, Yuri

2013-01-01

The regional extent and mode and time of emplacement of the Piermont-Frontenac allochthon in the Boundary Mountains–Bronson Hill anticlinorium of the Upper Connecticut Valley, New Hampshire–Vermont, are controversial. Moench and coworkers beginning in the 1980s proposed that much of the autochthonous pre–Middle Ordovician section of the anticlinorium was a large allochthon of Silurian to Early Devonian rocks correlated to those near Rangeley, Maine. This ∼200-km-long allochthon was postulated to have been transported westward in the latest Silurian to Early Devonian as a soft-sediment gravity slide on a hypothesized Foster Hill fault. New mapping and U-Pb geochronology do not support this interpretation. The undisputed Rangeley sequence in the Bean Brook slice is different from the disputed sequence in the proposed larger Piermont-Frontenac allochthon, and field evidence for the Foster Hill fault is lacking. At the type locality on Foster Hill, the postulated “fault” is a stratigraphic contact within the Ordovician Ammonoosuc Volcanics. The proposed Foster Hill fault would place the Piermont-Frontenac allochthon over the inverted limb of the Cornish(?) nappe, which includes the Emsian Littleton Formation, thus limiting the alleged submarine slide to post-Emsian time. Mafic dikes of the 419 Ma Comerford Intrusive Complex intrude previously folded strata attributed to the larger Piermont-Frontenac allochthon as well as the autochthonous Albee Formation and Ammonoosuc Volcanics. The Lost Nation pluton intruded and produced hornfels in previously deformed Albee strata. Zircons from an apophysis of the pluton in the hornfels have a thermal ionization mass spectrometry 207Pb/206Pb age of 444.1 ± 2.1 Ma. Tonalite near Bath, New Hampshire, has a zircon sensitive high-resolution ion microprobe 206Pb/238U age of 492.5 ± 7.8 Ma. The tonalite intrudes the Albee Formation, formerly interpreted as the Silurian Perry Mountain Formation of the proposed allochthon. Collectively, these features indicate that the large Piermont-Frontenac allochthon gravity slide of Silurian-Devonian strata, as previously proposed, cannot exist. Allochthonous rocks are restricted to a 25 km2 klippe, the Bean Brook slice, emplaced by hard-rock thrusting in the post-Emsian Devonian. The Albee Formation, the oldest unit in the study area, is older than the Late Cambrian tonalite at Bath. The correlation and apparent continuity along strike to the northeast of the Albee Formation with the Dead River Formation suggest that the Albee Formation, like the Dead River Formation, is of Ganderian affinity and that the Bronson Hill magmatic arc in the Upper Connecticut Valley was built on Ganderian crust. The Dead River Formation is unconformably overlain by Middle and Upper Ordovician volcanic units; the unconformity is attributed to the pre-Arenig Penobscottian orogeny. Some of the pre-Silurian deformation in the Upper Connecticut Valley may be Penobscottian rather than Taconian. New stratigraphic units defined herein include the pelitic Scarritt Member of the Albee Formation, the Ordovician Washburn Brook Formation consisting of synsedimentary breccia and coticule, chert, and ironstone, and the Devonian–Silurian Sawyer Mountain Formation, probably correlative with the Frontenac Formation. The Partridge Formation is partially coeval with the Ammonoosuc Volcanics.

The Bolivian source rocks: Sub Andean Zone-Madre de Dios-Chaco

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moretti, I.; Montemurro, G.; Aguilera, E.

A complete study of source rocks has been carried out in the Bolivian foothills and foreland (Sub Andean Zone, Chaco and Madre de Dios) in order to quantify the petroleum potential of the area. Besides the classical mid-Devonian source rocks (Tequeje Formation in the north, Limoncito Formation in the center and Los Monos Formation in the south), others are important: the Tomachi Formation (late Devonian) in the north and the Copacabana Formation (Upper Carboniferous-lower Permian) in the northern Sub Andean Zone. Both show an excellent potential with S{sub 2} over 50 mg HC/g and average values higher than 10 mgmore » HC/g over few hundred meters. The Latest Cretaceous Flora Formation present locally a high potential but is very thin. Almost all the source rocks matured during the Neogene due to the subsidence in the Andean foreland and in the piggyback basins, and are thus involved on the current petroleum system. Silurian and Lower Paleozoic units also contain thick shale beds, but these source rocks were mature before the Jurassic in the south of the country. In the center, the Silurian is not nowadays overmature and may play an important role. The different zones are compared based on their Source Potential Index which indicates that the richest areas are the northern Sub Andean Zone and the Madre de Dios basin with SPI greater than 10 t/m{sup 2}. Since these two areas remain almost unexplored, these results allow us to be optimistic about the possibilities for future exploration.« less

Devonian post-orogenic extension-related volcano-sedimentary rocks in the northern margin of the Tibetan Plateau, NW China: Implications for the Paleozoic tectonic transition in the North Qaidam Orogen

NASA Astrophysics Data System (ADS)

Qin, Yu; Feng, Qiao; Chen, Gang; Chen, Yan; Zou, Kaizhen; Liu, Qian; Jiao, Qianqian; Zhou, Dingwu; Pan, Lihui; Gao, Jindong

2018-05-01

The Maoniushan Formation in the northern part of the North Qaidam Orogen (NQO), NW China, contains key information on a Paleozoic change in tectonic setting of the NQO from compression to extension. Here, new zircon U-Pb, petrological, and sedimentological data for the lower molasse sequence of the Maoniushan Formation are used to constrain the timing of this tectonic transition. Detrital zircons yield U-Pb ages of 3.3-0.4 Ga with major populations at 0.53-0.4, 1.0-0.56, 2.5-1.0, and 3.3-2.5 Ga. The maximum depositional age of the Maoniushan Formation is well constrained by a youngest detrital zircon age of ∼409 Ma. Comparing these dates with geochronological data for the region indicates that Proterozoic-Paleozoic zircons were derived mainly from the NQO as well as the Oulongbuluk and Qaidam blocks, whereas Archean zircons were probably derived from the Oulongbuluk Block and the Tarim Craton. The ∼924, ∼463, and ∼439 Ma tectonothermal events recorded in this region indicate that the NQO was involved in the early Neoproterozoic assembly of Rodinia and early Paleozoic microcontinental convergence. A regional angular unconformity between Devonian and pre-Devonian strata within the NQO suggests a period of strong mountain building between the Oulongbuluk and Qaidam blocks during the Silurian, whereas an Early Devonian post-orogenic molasse, evidence of extensional collapse, and Middle to Late Devonian bimodal volcanic rocks and Carboniferous marine carbonate rocks clearly reflect long-lived tectonic extension. Based on these results and the regional geology, we suggest that the Devonian volcano-sedimentary rocks within the NQO were formed in a post-orogenic extensional setting similar to that of the East Kunlun Orogen, indicating that a major tectonic transition from compression to extension in these two orogens probably commenced in the Early Devonian.

Birth and demise of the Rheic Ocean magmatic arc(s): Combined U-Pb and Hf isotope analyses in detrital zircon from SW Iberia siliciclastic strata

NASA Astrophysics Data System (ADS)

Pereira, M. F.; Gutíerrez-Alonso, G.; Murphy, J. B.; Drost, K.; Gama, C.; Silva, J. B.

2017-05-01

Paleozoic continental reconstructions indicate that subduction of Rheic oceanic lithosphere led to collision between Laurussia and Gondwana which was a major event in the formation of the Ouachita-Appalachian-Variscan orogenic belt and the amalgamation of Pangea. However, arc systems which record Rheic Ocean subduction are poorly preserved. The preservation of Devonian detrital zircon in Late Devonian-Early Carboniferous siliciclastic rocks of SW Iberia, rather than arc-related igneous rocks indicates that direct evidence of the arc system may have been largely destroyed by erosion. Here we report in-situ detrital zircon U-Pb isotopic analyses of Late Devonian-Early Carboniferous siliciclastic rocks from the Pulo do Lobo Zone, which is a reworked Late Paleozoic suture zone located between Laurussia and Gondwana. Detrital zircon age spectra from the Pulo do Lobo Zone Frasnian formations show striking similarities, revealing a wide range of ages dominated by Neoproterozoic and Paleoproterozoic grains sourced from rocks typical of peri-Gondwanan terranes, such as Avalonia, the Meguma terrane and the Ossa-Morena Zone. Pulo do Lobo rocks also include representative populations of Mesoproterozoic and Early Silurian zircons that are typical of Avalonia and the Meguma terrane which are absent in the Ossa-Morena Zone. The Famennian-Tournaisian formations from the Pulo do Lobo Zone, however, contain more abundant Middle-Late Devonian zircon indicating the contribution from a previously unrecognized source probably related to the Rheic Ocean magmatic arc(s). The Middle-Late Devonian to Early Carboniferous zircon ages from the siliciclastic rocks of SW Iberia (South Portuguese, Pulo do Lobo and Ossa-Morena zones) have a wide range in εHfT values (- 8.2 to + 8.3) indicating the likely crystallization from magmas formed in a convergent setting. The missing Rheic Ocean arc was probably built on a Meguma/Avalonia type basement. We propose for the Pulo do Lobo Zone that the Frasnian sedimentation occurred through the opening of a back-arc basin formed along the Laurussian active margin during Rheic Ocean subduction, as has been recently proposed for the Rhenohercynian Zone in Central Europe. Detrital zircon ages in the Frasnian siliciclastic rocks indicate provenance in the Meguma terrane, Avalonia and Devonian Rheic Ocean arc(s). As a result of back-arc basin inversion, the Frasnian formations underwent deformation, metamorphism and denudation and were unconformably overlain by Famennian to Visean siliciclastic strata (including the Phyllite-Quartzite Formation of the South Portuguese Zone). The Latest Devonian-Early Carboniferous detritus were probably shed to the Pulo do Lobo Zone (Represa and Santa Iria formations) by recycling of Devonian siliciclastic rocks, from the South Portuguese Zone (Meguma terrane) and from a new distinct source with Baltica/Laurentia derivation (preserved in the Horta da Torre Formation and Alajar Mélange).

Petrological, geochemical, isotopic, and geochronological constraints for the Late Devonian-Early Carboniferous magmatism in SW Gondwana (27-32°LS): an example of geodynamic switching

NASA Astrophysics Data System (ADS)

Dahlquist, Juan A.; Alasino, Pablo H.; Basei, Miguel A. S.; Morales Cámera, Matías M.; Macchioli Grande, Marcos; da Costa Campos Neto, Mario

2018-04-01

We report a study integrating 13 new U-Pb LA-MC-ICP-MS zircon ages and Hf-isotope data from dated magmatic zircons together with complete petrological and whole-rock geochemistry data for the dated granitic rocks. Sample selection was strongly based on knowledge reported in previous investigations. Latest Devonian-Early Carboniferous granite samples were collected along a transect of 900 km, from the inner continental region (present-day Eastern Sierras Pampeanas) to the magmatic arc (now Western Sierras Pampeanas and Frontal Cordillera). Based on these data together with ca. 100 published whole-rock geochemical analyses we conclude that Late Devonian-Early Carboniferous magmatism at this latitude represents continuous activity (ranging from 322 to 379 Ma) on the pre-Andean margin of SW Gondwana, although important whole-rock and isotopic compositional variations occurred through time and space. Combined whole-rock chemistry and isotope data reveal that peraluminous A-type magmatism started in the intracontinental region during the Late Devonian, with subsequent development of synchronous Carboniferous peraluminous and metaluminous A-type magmatism in the retro-arc region and calc-alkaline magmatism in the western paleomargin. We envisage that magmatic evolution was mainly controlled by episodic fluctuations in the angle of subduction of the oceanic plate (between flat-slab and normal subduction), supporting a geodynamic switching model. Subduction fluctuations were relatively fast (ca. 7 Ma) during the Late Devonian and Early Carboniferous, and the complete magmatic switch-off and switch-on process lasted for 57 Ma. Hf T DM values of zircon (igneous and inherited) from some Carboniferous peraluminous A-type granites in the retro-arc suggest that Gondwana continental lithosphere formed during previous orogenies was partly the source of the Devonian-Carboniferous granitic magmas, thus precluding the generation of the parental magmas from exotic terranes.

Rifting along the northern Gondwana margin and the evolution of the Rheic Ocean: A Devonian age for the El Castillo volcanic rocks (Salamanca, Central Iberian Zone)

NASA Astrophysics Data System (ADS)

Gutiérrez-Alonso, G.; Murphy, J. B.; Fernández-Suárez, J.; Hamilton, M. A.

2008-12-01

Exposures of volcanic rocks (El Castillo) in the Central Iberian Zone near Salamanca, Spain, are representative of Paleozoic volcanic activity along the northern Gondwanan passive margin. Alkaline basalts and mafic volcaniclastic rocks of this sequence are structurally preserved in the core of the Variscan-Tamames Syncline. On the basis of the occurrence of graptolite fossils in immediately underlying strata, the El Castillo volcanics traditionally have been regarded as Lower Silurian in age. In contrast, most Paleozoic volcanic units in western Iberia are rift-related mafic to felsic rocks emplaced during the Late Cambrian-Early Ordovician, and are attributed to the opening of the Rheic Ocean. We present new zircon U-Pb TIMS data from a mafic volcaniclastic rock within the El Castillo unit. These data yield a near-concordant, upper intercept age of 394.7 ± 1.4 Ma that is interpreted to reflect a Middle Devonian (Emsian-Eifelian) age for the magmatism, demonstrating that the El Castillo volcanic rocks are separated from underlying lower Silurian strata by an unconformity. The U-Pb age is coeval with a widespread extensional event in Iberia preserved in the form of a generalized paraconformity surface described in most of the Iberian Variscan realm. However, in the inner part of the Gondwanan platform, the Cantabrian Zone underwent a major, coeval increase in subsidence and the generation of sedimentary troughs. From this perspective, the eruption age reported here probably represents a discrete phase of incipient rifting along the southern flank of the Rheic Ocean. Paleogeographic reconstructions indicate that this rifting event was coeval with widespread orogeny and ridge subduction along the conjugate northern flank of the Rheic Ocean, the so called Acadian "orogeny". We speculate that ridge subduction resulted in geodynamic coupling of the northern and southern flanks of the Rheic Ocean, and that the extension along the southern flank of the Rheic Ocean is a manifestation of slab pull along the northern flank. This scenario provides a uniform explanation for many features that form at ca. 395 Ma along the Gondwanan margin and has implications for the origin of the coeval oceanic Devonian mafic rocks currently exposed in the Variscan suture of NW Iberia.

Stratigraphic and structural distribution of reservoirs in Romania

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stefanescu, M.O.

1991-08-01

In Romania, there are reservoirs at different levels of the whole Cambrian-Pliocene interval, but only some of these levels have the favorable structural conditions to accumulate hydrocarbons in commercial quantities. These levels are the Devonian, Triassic, Middle Jurassic, Lower Cretaceous (locally including the uppermost Jurassic), Eocene, Oligocene-lower Miocene, middle and upper Miocene, and Pliocene. The productive reservoirs are represented either by carbonate rocks (in Devonian, Middle Triassic and uppermost Jurassic-Lower Cretaceous) or by detrital rocks (in Lower and Upper Triassic, Middle Jurassic, Eocene, Oligocene, Miocene, and Pliocene). From the structural point of view, the Romanian territory is characterized by themore » coexistence both of platforms (East European, Scythian, and Moesian platforms) and of the strongly tectonized orogenes (North Dobrogea and Carpathian orogenes). Each importance crust shortening was followed by the accumulation of post-tectonic covers, some of them being folded during subsequently tectonic movements. The youngest post-tectonic cover is common both for the platforms (foreland) and Carpathian orogene, representing the Carpathian foredeep. Producing reservoirs are present in the East European and Moesian platforms, in the outer Carpathian units (Tarcau and Marginal folds nappes) and in certain post-tectonic covers which fill the Carpathian foredeep and the Transylvanian and Pannonian basins. In the platforms, hydrocarbons accumulated both in calcareous and detrital reservoirs, whereas in the Carpathian units and in their reservoirs, whereas in the Carpathian units and in their post-tectonic covers, hydrocarbons accumulated only in detrital reservoirs.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Negus-De Wys, J.; Dixon, J. M.; Evans, M. A.

This document consists of the following papers: inorganic geochemistry studies of the Eastern Kentucky Gas Field; lithology studies of upper Devonian well cuttings in the Eastern Kentucky Gas Field; possible effects of plate tectonics on the Appalachian Devonian black shale production in eastern Kentucky; preliminary depositional model for upper Devonian Huron age organic black shale in the Eastern Kentucky Gas Field; the anatomy of a large Devonian black shale gas field; the Cottageville (Mount Alto) Gas Field, Jackson County, West Virginia: a case study of Devonian shale gas production; the Eastern Kentucky Gas Field: a geological study of the relationshipsmore » of Ohio Shale gas occurrences to structure, stratigraphy, lithology, and inorganic geochemical parameters; and a statistical analysis of geochemical data for the Eastern Kentucky Gas Field.« less

Geologic framework of pre-Cretaceous rocks in the Southern Ute Indian Reservation and adjacent areas, southwestern Colorado and northwestern New Mexico

USGS Publications Warehouse

Condon, Steven M.

1992-01-01

This report is a discussion and summary of Jurassic and older rocks in the Southern Ute Indian Reservation and adjacent areas, southwestern Colorado and northwestern New Mexico, and is based on analysis of geophysical logs and observations of outcrops. The Reservation, which is located in the northern San Juan Basin, has been the site of deposition of sediments for much of the Phanerozoic. Geologic times represented on the Reservation are the Precambrian, Cambrian, Devonian, Mississippian, Pennsylvanian, Permian, Triassic, Jurassic, Cretaceous, Tertiary, and Quaternary. Rocks of Ordovician and Silurian age have not been reported in this region. Thicknesses of pre-Cretaceous sedimentary rocks range from about 750 feet (229 meters) on the Archuleta arch, east of the Reservation, to more than 8,300 feet (2,530 meters) just northwest of the Reservation. About 5,500 feet (1,676 meters) of pre-Cretaceous sedimentary rocks occur in the central part of the Reservation, near Ignacio. At Ignacio the top of the Jurassic lies at a depth of 7,600 feet (2,316 meters) below the surface, which is composed of Tertiary rocks. As much as 2,500 feet (762 meters) of Tertiary rocks occur in the area. More than 10,000 feet (3,048 meters) of Cretaceous and younger rocks, and 15,600 feet (4,755 meters) of all Phanerozoic sedimentary rocks occur in the vicinity of the Reservation. In the early Paleozoic the area that includes the Southern Ute Reservation was on the stable western shelf of the craton. During this time sediments that compose the following shallow-marine clastic and carbonate rocks were deposited: the Upper Cambrian Ignacio Quartzite (0-150 feet; 0-46 meters), Upper Devonian Elbert Formation (50-200 feet; 15-61 meters), Upper Devonian Ouray Limestone (10-75 feet; 3-23 meters), and Mississippian Leadville Limestone (0-250 feet; 0-76 meters). Mixed carbonate and clastic deposition, which was punctuated by a unique episode of deposition of evaporite sediments, continued through the Pennsylvanian after a significant episode of erosion at the end of the Mississippian. Pennsylvanian rocks on the Reservation are the Molas Formation (20-100 feet; 6-30 meters) and Hermosa Group (400-2,800 feet; 122-853 meters), which consists of the Pinkerton Trail Formation (40-120 feet; 12-36 meters), Paradox Formation and equivalent rocks (200-1,800 feet; 61-549 meters), and Honaker Trail Formation (200-1,300 feet; 61-396 meters). A unit that is transitional between the Pennsylvanian and Permian is the Rico Formation, which is about 200 feet (61 meters) thick across most of the Reservation area. The close of the Paleozoic Era was marked by a great influx of arkosic clastic sediments from uplifted highlands to the north of the Reservation area during the Permian. Near the paleomountain front the Cutler Formation (presently as thick as 8,000 feet; 2,438 meters) formed as a result of deposition of arkosic sediments; however, the original thickness of the Cutler is unknown due to an unconformity at its top. In the area of the Reservation the Cutler has group status and has been divided into several formations: the Halgaito Formation (350-800 feet; 107-244 meters), Cedar Mesa Sandstone and equivalent rocks (150-350 feet; 46-107 meters), Organ Rock Formation (500-900 feet; 152-274 meters), and De Chelly Sandstone (0-100 feet; 0-30 meters). The sediments of these formations were deposited in a variety of environments, including eolian, mud-flat, and fluvial systems. Following an episode of erosion in the Early and Middle(?) Triassic, deposition in the area of the Southern Ute Reservation continued during the Mesozoic. Sediments of the Upper Triassic Dolores and correlative Chinle Formations were deposited in fluvial, lacustrine, and minor eolian environments. On the Reservation the Dolores is 500-1,200 feet (152-366 meters) thick. Lower Jurassic eolian and fluvial deposits may have been present in much of the Reservation area but have been removed

Radon-222 content of natural gas samples from Upper and Middle Devonian sandstone and shale reservoirs in Pennsylvania—preliminary data

USGS Publications Warehouse

Rowan, E.L.; Kraemer, T.F.

2012-01-01

Samples of natural gas were collected as part of a study of formation water chemistry in oil and gas reservoirs in the Appalachian Basin. Nineteen samples (plus two duplicates) were collected from 11 wells producing gas from Upper Devonian sandstones and the Middle Devonian Marcellus Shale in Pennsylvania. The samples were collected from valves located between the wellhead and the gas-water separator. Analyses of the radon content of the gas indicated 222Rn (radon-222) activities ranging from 1 to 79 picocuries per liter (pCi/L) with an overall median of 37 pCi/L. The radon activities of the Upper Devonian sandstone samples overlap to a large degree with the activities of the Marcellus Shale samples.

Paleozoic and Mesozoic deformations in the central Sierra Nevada, California

USGS Publications Warehouse

Nokleberg, Warren J.; Kistler, Ronald Wayne

1980-01-01

Analysis of structural and stratigraphic data indicates that several periods of regional deformation, consisting of combined folding, faulting, cataclasis, and regional metamorphism, occurred throughout the central Sierra Nevada during Paleozoic and Mesozoic time. The oldest regional deformation occurred alono northward trends during the Devonian and Mississippian periods in most roof pendants containing lower Paleozoic metasedimentary rocks at the center and along the crest of the range. This deformation is expressed in some roof pendants by an angular unconformity separating older thrice-deformed from younger twice-deformed Paleozoic metasedimentary rocks. The first Mesozoic deformation, which consisted of uplift and erosion and was accompanied by the onset of Andean-type volcanism during the Permian and Triassic, is expressed by an angular unconformity in several roof pendants from the Saddlebag Lake to the Mount Morrison areas. This unconformity is defined by Permian and Triassic andesitic to rhyolitic metavolcanic rocks unconformably overlying more intensely deformed Pennsylvanian, Permian(?), and older metasedimentary rocks. A later regional deformation occurred during the Triassic along N. 20?_30? W. trends in Permian and Triassic metavolcanic rocks of the Saddlebag Lake and Mount Dana roof pendants, in upper Paleozoic rocks of the Pine Creek roof pendant, and in the Calaveras Formation of the western metamorphic belt; the roof pendants are crosscut by Upper Triassic granitic rocks of the Lee Vining intrusive epoch. A still later period of Early and Middle Jurassic regional deformation occurred along N. 30?-60? E. trends in upper Paleozoic rocks of the Calaveras Formation of the western metamorphic belt. A further period of deformation was the Late Jurassic Nevadan orogeny, which occurred along N. 20?_40? W. trends in Upper Jurassic rocks of the western metamorphic belt that are crosscut by Upper Jurassic granitic rocks of the Yosemite intrusive epoch. Structures of similar age occur in intensely deformed oceanic-lithospheric and syntectonic plutonic rocks of the lower Kings River area, in Jurassic metavolcanic rocks of the Ritter Range roof pendant, and in Triassic metasedimentary rocks of the Mineral King roof pendant. The final Mesozoic deformation occurred along N. 50?-80? W. trends in both high-country roof pendants and the lower Kings River area; structures of this generation are crosscut by relatively undeformed Upper Cretaceous granitic rocks of the Cathedral Range intrusive epoch.

Geology of the Cupsuptic quadrangle, Maine

USGS Publications Warehouse

Harwood, David S.

1966-01-01

The Cupsuptic quadrangle, in west-central Maine, lies in a relatively narrow belt of pre-Silurian rocks extending from the Connecticut River valley across northern New Hampshire to north-central Maine. The Albee Formation, composed of green, purple, and black phyllite with interbedded-quartzite, is exposed in the core of a regional anticlinorium overlain to the southeast by greenstone of the Oquossoc Formation which in turn is overlain by black slate of the Kamankeag Formation. In the northern part of the quadrangle the Albee Formation is overlain by black slate, feldspathic graywacke, and minor greenstone of the Dixville Formation. The Kamankeag Formation is dated as 1-ate Middle Ordovician by graptolites (zone 12) found near the base of the unit. The Dixville Formation is correlated with the Kamankeag Formation and Oquossoc Formation and is considered to be Middle Ordovician. The Albee Formation is considered to be Middle to Lower Ordovician from correlations with similar rocks in northeastern and southwestern Vermont. The Oquossoc and Kamankeag Formations are correlated with the Amonoosuc and Partridge Formations of northern New Hampshire. The pre-Silurian rocks are unconformably overlain by unnamed rocks of Silurian age in the southeast, west-central, and northwest ninths of the quadrangle. The basal Silurian units are boulder to cobble polymict conglomerate and quartz-pebble conglomerate of late Lower Silurian (Upper Llandovery) age. The overlying rocks are either well-bedded slate and quartzite, silty limestone, or arenaceous limestone. Thearenaceous limestone contains Upper Silurian (Lower Ludlow) brachiopods. The stratified rocks have been intruded by three stocks of biotite-muscovite quartz monzonite, a large body of metadiorite and associated serpentinite, smaller bodies of gabbro, granodiorite, and intrusive felsite, as well as numerous diabase and quartz monzonite dikes. The metadiorite and serpentinite, and possibly the gabbro and granodiorite are Late Ordovician in age. The quartz monzonite is considered to be Late Devonian. Five tectonic events are inferred from the structural features in the area. The earliest was a period of folding producing tightly-appressed, northeast-trending folds in the rocks of pre-Silurian age. In the second stage the folded pre-Silurian rocks were uplifted, eroded, and truncated to produce a major unconformity between the Middle Ordovician and Lower Silurian rocks. These events constitute the Taconic orogeny. The third tectonic event was a period of folding, probably of Middle Devonian age, that warped the unconformity and overlying rocks into open, gently-plunging, east-trending folds. This period of folding undoubtedly changed the attitude of the early folds in the pre-Silurian units but it did not produce any recognizable, cross-cutting planar features in the older rocks. The fourth tectonic event was a period of igneous intrusion that locally deformed the northeast-trending folds in the pre-Silurian rocks into a macroscopic drag fold plunging at 80 degrees in a direction S.10?w. A north-trending, subvertical slip cleavage was produced locally during this period of Late Devonian (?) deformation. A period of faulting, possibly of Triassic age, dislocated some of the earlier features. The rocks are in the chlorite zone of regional metamorphism, but have been contact metamorphosed to sillimanite-bearing hornfels adjacent to the quartz monzonite stocks. The chemical changes in chlorite, biotite, garnet, cordierite, and muscovite in the chlorite, biotite, andalusite, and sillimanite zones have been-studied by optical and x-ray methods and by partial chemical analyses. The progressive changes in mineral assemblages have been graphically portrayed on quaternary diagrams and ternary projections.

Bedrock geologic map of the Littleton and Lower Waterford quadrangles, Essex and Caledonia Counties, Vermont, and Grafton County, New Hampshire

USGS Publications Warehouse

Rankin, Douglas W.

2018-06-13

The bedrock geologic map of the Littleton and Lower Waterford quadrangles covers an area of approximately 107 square miles (277 square kilometers) north and south of the Connecticut River in east-central Vermont and adjacent New Hampshire. This map was created as part of a larger effort to produce a new bedrock geologic map of Vermont through the collection of field data at a scale of 1:24,000. A large part of the map area consists of the Bronson Hill anticlinorium, a post-Early Devonian structure that is cored by metamorphosed Cambrian to Devonian sedimentary, volcanic, and plutonic rocks. The northwestern part of the map is divided by the Monroe fault which separates Early Devonian rocks of the Connecticut Valley-Gaspé trough from rocks of the Bronson Hill anticlinorium.The Bronson Hill anticlinorium is the apex of the Middle Ordovician to earliest-Silurian Bronson Hill magmatic arc that contains the Ammonoosuc Volcanics, Partridge Formation, and Oliverian Plutonic suite, and extends from Maine, down the eastern side of the Connecticut River in New Hampshire, to Long Island Sound. The deformed and partially eroded arc is locally overlain by a relatively thin Silurian section of metasedimentary rocks (Clough Quartzite and Fitch Formation) that thickens to the east. The Silurian section near Littleton is disconformably overlain by a thicker, Lower Devonian section that includes mostly metasedimentary rocks and minor metavolcanic rocks of the Littleton Formation. The Bronson Hill anticlinorium is bisected by a series of northeast-southwest trending Mesozoic normal faults. Primarily among them is the steeply northwest-dipping Ammonoosuc fault that divides older and younger units (upper and lower sections) of the Ammonoosuc Volcanics. The Ammonoosuc Volcanics are lithologically complex and predominantly include interlayered and interfingered rhyolitic to basaltic volcanic and volcaniclastic rocks, as well as lesser amounts of metamorphic and metasedimentary rocks. The Ammonoosuc Volcanics overlies the Albee Formation that consists of interlayered feldspathic sandstone, siltstone, pelite, and slate.During the Late Ordovician, a series of arc-related plutons intruded the Ammonoosuc Volcanics, including the Whitefield pluton to the east, the Scrag granite of Billing (1937) in the far southeastern corner of the map, the Highlandcroft Granodiorite just to the west of the Ammonoosuc fault, and the Joslin Turn tonalite (just north of the Connecticut River). To the east of the Monroe fault lies the late Silurian Comerford Intrusive Complex, which consists of metamorphosed gabbro, diorite, tonalite, aplitic tonalite, and crosscutting diabase dikes. Abundant mafic dikes of the Comerford Intrusive Complex intruded the Albee Formation and Ammonoosuc Volcanics well east of the Monroe fault.This report consists of a single geologic map sheet and an online geographic information systems database that includes contacts of bedrock geologic units, faults, outcrops, and structural geologic information.

The geology of a part of Acadia and the nature of the Acadian orogeny across Central and Eastern Maine

USGS Publications Warehouse

Tucker, R.D.; Osberg, P.H.; Berry, H.N.

2001-01-01

The zone of Acadian collision between the Medial New England and Composite Avalon terranes is well preserved in Maine. A transect from northwest (Rome) to southeast (Camden) crosses the eastern part of Medial New England comprising the Central Maine basin, Liberty-Orrington thrust sheet, and Fredericton trough, and the western part of Composite Avalon, including the Graham Lake, Clarry Hill, and Clam Cove thrust sheets. U-Pb geochronology of events before, during, and after the Acadian orogeny helps elucidate the nature and distribution of tectonostrati& graphic belts in this zone and the timing of some Acadian events in the Northern Appalachians. The Central Maine basin consists of sedimentary and volcanic rocks of Middle Ordovician (???470 to ???460 Ma) age overlain with probable conformity by latest Ordovician(?) through earliest Devonian marine rift and flysch sedimentary rocks; these are intruded by weakly to undeformed plutonic rocks of Early and Middle Devonian age (???399??378 Ma). The Fredericton trough consists of Early Silurian gray pelite and sandstone to earliest Late Silurian calcareous turbidite, deformed and variably metamorphosed prior to the emplacement of Late Silurian (???422 Ma) and Early to Late Devonian (???418 to ???368 Ma) plutons. The Liberty-Orrington thrust sheet consists of Cambrian(?)-Ordovician (>???474 to ???469 Ma and younger) clastic sedimentary and volcanic rocks intruded by highly deformed Late Silurian (???424 to ???422 Ma) and Devonian (???418 to ???389 Ma) plutons, possibly metamorphosed in Late Silurian time (prior to ???417 Ma), and metamorphosed to amphibolite facies in Early to Middle Devonian time (???400 to ???381 Ma). The Graham Lake thrust sheet contains possible Precambrian rocks, Cambrian sedimentary rocks with a volcanic unit dated at ???503 Ma, and Ordovician rocks with possible Caradocian Old World fossils, metamor& phosed and deformed in Silurian time and intruded by mildly to undeformed Late Silurian (???421 Ma) and Late Devonian (???371 to ???368 Ma) plutons. The Clarry Hill thrust sheet consists of poorly studied, highly metamorphosed Cambrian(?) rocks. The Clam Cove thrust sheet contains highly deformed Precambrian limestone, shale, sandstone, and conglomerate, metamorphosed to epidote amphibolite facies and intruded by a mildly deformed pluton dated at ???421 Ma. Metamorphism, deformation, and voluminous intrusive igneous activity of Silu& rian age are common to both the most southeastern parts of Medial New England and the thrust sheets of Composite Avalon. In contrast to Medial New England, the thrust sheets of Composite Avalon show only modest effects of Devonian deformation and metamorphism. Regional stratigraphic relations, paleontologic findings, and U-Pb geochronology suggest that the Graham Lake, Clarry Hill, and Clam Cove thrust sheets are far-traveled allochthons that were widely separated from Medial New England in the Silurian.

Stratigraphy and Mesozoic–Cenozoic tectonic history of northern Sierra Los Ajos and adjacent areas, Sonora, Mexico

USGS Publications Warehouse

Page, William R.; Gray, Floyd; Iriondo, Alexander; Miggins, Daniel P.; Blodgett, Robert B.; Maldonado, Florian; Miller, Robert J.

2010-01-01

Geologic mapping in the northern Sierra Los Ajos reveals new stratigraphic and structural data relevant to deciphering the Mesozoic–Cenozoic tectonic evolution of the range. The northern Sierra Los Ajos is cored by Proterozoic, Cambrian, Devonian, Mississippian, and Pennsylvanian strata, equivalent respectively to the Pinal Schist, Bolsa Quartzite and Abrigo Limestone, Martin Formation, Escabrosa Limestone, and Horquilla Limestone. The Proterozoic–Paleozoic sequence is mantled by Upper Cretaceous rocks partly equivalent to the Fort Crittenden and Salero Formations in Arizona, and the Cabullona Group in Sonora, Mexico.Absence of the Upper Jurassic–Lower Cretaceous Bisbee Group below the Upper Cretaceous rocks and above the Proterozoic–Paleozoic rocks indicates that the Sierra Los Ajos was part of the Cananea high, a topographic highland during the Late Jurassic and Early Cretaceous. Deposition of Upper Cretaceous rocks directly on Paleozoic and Proterozoic rocks indicates that the Sierra Los Ajos area had subsided as part of the Laramide Cabullona basin during Late Cretaceous time. Basal beds of the Upper Cretaceous sequence are clast-supported conglomerate composed locally of basement (Paleozoic) clasts. The conglomerate represents erosion of Paleozoic basement in the Sierra Los Ajos area coincident with development of the Cabullona basin.The present-day Sierra Los Ajos reaches elevations of greater than 2600 m, and was uplifted during Tertiary basin-and-range extension. Upper Cretaceous rocks are exposed at higher elevations in the northern Sierra Los Ajos and represent an uplifted part of the inverted Cabullona basin. Tertiary uplift of the Sierra Los Ajos was largely accommodated by vertical movement along the north-to-northwest-striking Sierra Los Ajos fault zone flanking the west side of the range. This fault zone structurally controls the configuration of the headwaters of the San Pedro River basin, an important bi-national water resource in the US-Mexico border region.

Devonian of the Northern Rocky Mountains and plains

USGS Publications Warehouse

Sandberg, Charles A.; Mapel, William J.

1967-01-01

5. Undivided uppermost Devonian (Famennian, to V-VI) and lowermost Mississippian (Tournaisian, cuI-lower cuIIα) carbonaceous and clastic rocks deposited in six shallow basins interspersed among areas uplifted during the penecontemporaneous Antler orogeny.

Emsian synorogenic paleogeography of the Maine Applachians

USGS Publications Warehouse

Bradley, D.; Tucker, R.

2002-01-01

The Acadian deformation front in the northern Appalachians of Maine and New Hampshire can now be closely located during the early Emsian (Early Devonian; 408-406 Ma). Tight correlations between paleontologically and isotopically dated rocks are possible only because of a new 408-Ma time scale tie point for the early Emsian. The deformation front lay between a belt of Lower Devonian flysch and molasse that were deposited in an Acadian foreland basin and had not yet been folded and a belt of early Emsian plutons that intruded folded Lower Devonian rocks. This plutonic belt includes the newly dated Ore Mountain gabbro (U/Pb; 406 Ma), which hosts magmatic-sulfide mineralization. Along the deformation front, a 407-Ma pluton that locally truncates Acadian folds (Katahdin) was the feeder to volcanic rocks (Traveler Rhyolite; 406-407 Ma) that are part of the foreland-basin succession involved in these same folds. The Emsian igneous rocks thus define a syncollisional magmatic province that straddled the deformation front. These findings bear on three alternative subduction geometries for the Acadian collision.

Assessment of undiscovered continuous gas resources in Upper Devonian Shales of the Appalachian Basin Province, 2017

USGS Publications Warehouse

Enomoto, Catherine B.; Trippi, Michael H.; Higley, Debra K.; Rouse, William A.; Dulong, Frank T.; Klett, Timothy R.; Mercier, Tracey J.; Brownfield, Michael E.; Leathers-Miller, Heidi M.; Finn, Thomas M.; Marra, Kristen R.; Le, Phuong A.; Woodall, Cheryl A.; Schenk, Christopher J.

2018-04-19

Using a geology-based assessment methodology, the U.S. Geological Survey estimated mean undiscovered, technically recoverable continuous resources of 10.7 trillion cubic feet of natural gas in Upper Devonian shales of the Appalachian Basin Province.

Organic metamorphism in the Lower Mississippian-Upper Devonian Bakken shales-II: Soxhlet extraction.

USGS Publications Warehouse

Price, L.C.; Ging, T.; Love, A.; Anders, D.

1986-01-01

We report on Soxhlet extraction (and subsequent related analyses) of 39 Lower Mississippian-Upper Devonian Bakken shales from the North Dakota portion of the Williston Basin, and analyses of 28 oils from the Basin. Because of the influence of primary petroleum migration, no increase in the relative or absolute concentrations of hydrocarbons or bitumen was observed at the threshold of intense hydrocarbon generation (TIHG), or during mainstage hydrocarbon generation in the Bakken shales. Thus, the maturation indices that have been so useful in delineating the TIHG and mainstage hydrocarbon generation in other studies were of no use in this study, where these events could clearly be identified only by Rock-Eval pyrolysis data. The data of this study demonstrate that primary petroleum migration is a very efficient process. Four distinctive classes of saturated hydrocarbon gas chromatograms from the Bakken shales arose from facies, maturation, and primary migration controls. As a consequence of maturation, the % of saturated hydrocarbons increased in the shale extract at the expense of decreases in the resins and asphaltenes. Measurements involving resins and asphaltenes appear to be excellent maturation indices in the Bakken shales. Two different and distinct organic facies were present in immature Bakken shales. -from Authors

A new reconstruction of the Paleozoic continental margin of southwestern North America: Implications for the nature and timing of continental truncation and the possible role of the Mojave-Sonora megashear

USGS Publications Warehouse

Stevens, C.H.; Stone, P.; Miller, J.S.

2005-01-01

Data bearing on interpretations of the Paleozoic and Mesozoic paleogeography of southwestern North America are important for testing the hypothesis that the Paleozoic miogeocline in this region has been tectonically truncated, and if so, for ascertaining the time of the event and the possible role of the Mojave-Sonora megashear. Here, we present an analysis of existing and new data permitting reconstruction of the Paleozoic continental margin of southwestern North America. Significant new and recent information incorporated into this reconstruction includes (1) spatial distribution of Middle to Upper Devonian continental-margin facies belts, (2) positions of other paleogeographically significant sedimentary boundaries on the Paleozoic continental shelf, (3) distribution of Upper Permian through Upper Triassic plutonic rocks, and (4) evidence that the southern Sierra Nevada and western Mojave Desert are underlain by continental crust. After restoring the geology of western Nevada and California along known and inferred strike-slip faults, we find that the Devonian facies belts and pre-Pennsylvanian sedimentary boundaries define an arcuate, generally south-trending continental margin that appears to be truncated on the southwest. A Pennsylvanian basin, a Permian coral belt, and a belt of Upper Permian to Upper Triassic plutons stretching from Sonora, Mexico, into westernmost central Nevada, cut across the older facies belts, suggesting that truncation of the continental margin occurred in the Pennsylvanian. We postulate that the main truncating structure was a left-lateral transform fault zone that extended from the Mojave-Sonora megashear in northwestern Mexico to the Foothills Suture in California. The Caborca block of northwestern Mexico, where Devonian facies belts and pre-Pennsylvanian sedimentary boundaries like those in California have been identified, is interpreted to represent a missing fragment of the continental margin that underwent ???400 km of left-lateral displacement along this fault zone. If this model is correct, the Mojave-Sonora megashear played a direct role in the Pennsylvanian truncation of the continental margin, and any younger displacement on this fault has been relatively small. ?? 2005 Geological Society of America.

Bedrock geologic map of the Nashua South quadrangle, Hillsborough County, New Hampshire, and Middlesex County, Massachusetts

USGS Publications Warehouse

Walsh, Gregory J.; Jahns, Richard H.; Aleinikoff, John N.

2013-01-01

The bedrock geology of the 7.5-minute Nashua South quadrangle consists primarily of deformed Silurian metasedimentary rocks of the Berwick Formation. The metasedimentary rocks are intruded by a Late Silurian to Early Devonian diorite-gabbro suite, Devonian rocks of the Ayer Granodiorite, Devonian granitic rocks of the New Hampshire Plutonic Suite including pegmatite and the Chelmsford Granite, and Jurassic diabase dikes. The bedrock geology was mapped to study the tectonic history of the area and to provide a framework for ongoing hydrogeologic characterization of the fractured bedrock of Massachusetts and New Hampshire. This report presents mapping by G.J. Walsh and R.H. Jahns and zircon U-Pb geochronology by J.N. Aleinikoff. The complete report consists of a map, text pamphlet, and GIS database. The map and text pamphlet are only available as downloadable files (see frame at right). The GIS database is available for download in ESRITM shapefile and Google EarthTM formats, and includes contacts of bedrock geologic units, faults, outcrops, structural geologic information, photographs, and a three-dimensional model.

The Valley and Ridge Province of eastern Pennsylvania - stratigraphic and sedimentologic contributions and problems ( USA).

USGS Publications Warehouse

Epstein, J.B.

1986-01-01

The rocks in the area, which range from Middle Ordovician to Late Devonian in age, are more than 7620 m thick. This diversified group of sedimentary rocks was deposited in many different environments, ranging from deep sea, through neritic and tidal, to alluvial. In general, the Middle Ordovician through Lower Devonian strata are a sedimentary cycle related to the waxing and waning of Taconic tectonism. The sequence began with a greywacke-argillite suite (Martinsburg Formation) representing synorogenic basin deepening. This was followed by basin filling and progradation of a sandstone-shale clastic wedge (Shawangunk Formation and Bloomsburg Red Beds) derived from the erosion of the mountains that were uplifted during the Taconic orogeny. The sequence ended with deposition of many thin units of carbonate, sandstone, and shale on a shelf marginal to a land area of low relief. Another tectonic-sedimentary cycle, related to the Acadian orogeny, began with deposition of Middle Devonian rocks. Deep-water shales (Marcellus Shale) preceded shoaling (Mahantango Formation) and turbidite sedimentation (Trimmers Rock Formation) followed by another molasse (Catskill Formation). -from Author

Eastern Madre de Dios Devonian generated large volumes of oil

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peters, K.E.; Wagner, J.B.; Carpenter, D.G.

This is the second part of an article giving details of a Mobil Corp. regional geological, geophysical, and geochemical study of the Madre de Dios basin. The assessment covered the distribution, richness, depositional environment, and thermal maturity of Devonian source rocks.

Middle Devonian to Early Carboniferous event stratigraphy of Devils Gate and Northern Antelope Range sections, Nevada, U.S.A

USGS Publications Warehouse

Sandberg, C.A.; Morrow, J.R.; Poole, F.G.; Ziegler, W.

2003-01-01

The classic type section of the Devils Gate Limestone at Devils Gate Pass is situated on the eastern slope of a proto-Antler forebulge that resulted from convergence of the west side of the North American continent with an ocean plate. The original Late Devonian forebulge, the site of which is now located between Devils Gate Pass and the Northern Antelope Range, separated the continental-rise to deep-slope Woodruff basin on the west from the backbulge Pilot basin on the east. Two connections between these basins are recorded by deeper water siltstone beds at Devils Gate; the older one is the lower tongue of the Woodruff Formation, which forms the basal unit of the upper member of the type Devils Gate, and the upper one is the overlying, thin lower member of the Pilot Shale. The forebulge and the backbulge Pilot basin originated during the middle Frasnian (early Late Devonian) Early hassi Zone, shortly following the Alamo Impact within the punctata Zone in southern Nevada. Evidence of this impact is recorded by coeval and reworked shocked quartz grains in the Northern Antelope Range and possibly by a unique bypass-channel or megatsunami-uprush sandy diamictite within carbonate-platform rocks of the lower member of the type Devils Gate Limestone. Besides the Alamo Impact and three regional events, two other important global events are recorded in the Devils Gate section. The semichatovae eustatic rise, the maximum Late Devonian flooding event, coincides with the sharp lithogenetic change at the discordant boundary above the lower member of the Devils Gate Limestone. Most significantly, the Devils Gate section contains the thickest and most complete rock record in North America across the late Frasnian linguiformis Zone mass extinction event. Excellent exposures include not only the extinction shale, but also a younger. Early triangularis Zone tsunamite breccia, produced by global collapse of carbonate platforms during a shallowing event that continued into the next younger Famennian Stage. The Northern Antelope Range section is located near the top of the west side of the proto-Antler forebulge. Because of its unusual, tectonically active location, unmatched at any other Nevada localities, this section records only four regional and global events during a timespan slightly longer than that of the Devils Gate section. The global semichatovae rise and late Frasnian mass extinction event are largely masked because of the depositional complexities resulting from this location.

Late Ordovician (post-Sardic) rifting branches in the North Gondwanan Montagne Noire and Mouthoumet massifs of southern France

NASA Astrophysics Data System (ADS)

Javier Álvaro, J.; Colmenar, Jorge; Monceret, Eric; Pouclet, André; Vizcaïno, Daniel

2016-06-01

Upper Ordovician-Lower Devonian rocks of the Cabrières klippes (southern Montagne Noire) and the Mouthoumet massif in southern France rest paraconformably or with angular discordance on Cambrian-Lower Ordovician strata. Neither Middle-Ordovician volcanism nor associated metamorphism is recorded, and the subsequent Middle-Ordovician stratigraphic gap is related to the Sardic phase. Upper Ordovician sedimentation started in the rifting branches of Cabrières and Mouthoumet with deposition of basaltic lava flows and lahar deposits (Roque de Bandies and Villerouge formations) of continental tholeiite signature (CT), indicative of continental fracturing. The infill of both rifting branches followed with the onset of (1) Katian (Ka1-Ka2) conglomerates and sandstones (Glauzy and Gascagne formations), which have yielded a new brachiopod assemblage representative of the Svobodaina havliceki Community; (2) Katian (Ka2-Ka4) limestones, marlstones, and shales with carbonate nodules, reflecting development of bryozoan-echinoderm meadows with elements of the Nicolella Community (Gabian and Montjoi formations); and (3) the Hirnantian Marmairane Formation in the Mouthoumet massif that has yielded a rich and diverse fossil association representative of the pandemic Hirnantia Fauna. The sealing of the subaerial palaeorelief generated during the Sardic phase is related to Silurian and Early Devonian transgressions leading to onlapping patterns and the record of high-angle discordances.

Palaeomagnetism and geochemistry of Early Palaeozoic rocks of the Barrandian (Teplé-Barrandian Unit, Bohemian Massif): palaeotectonic implications

NASA Astrophysics Data System (ADS)

Patočka, F.; Pruner, P.; Štorch, P.

The Barrandian area (the Teplá-Barrandian unit, Bohemian Massif) provided palaeomagnetic results on Early Palaeozoic rocks and chemical data on siliciclastic sediments of both Middle Cambrian and Early Ordovician to Middle Devonian sedimentary sequences; an outcoming interpretation defined source areas of clastic material and palaeotectonic settings of the siliciclastic rock deposition. The siliciclastic rocks of the earliest Palaeozoic sedimentation cycle, deposited in the Cambrian Příbram-Jince Basin of the Barrandian, were derived from an early Cadomian volcanic island arc developed on Neoproterozoic oceanic lithosphere and accreted to a Cadomian active margin of northwestern Gondwana. Inversion of relief terminated the Cambrian sedimentation, and a successory Prague Basin subsided nearby since Tremadocian. Source area of the Ordovician and Early Silurian shallow-marine siliciclastic sediments corresponded to progressively dissected crust of continental arc/active continental margin type of Cadomian age. Since Late Ordovician onwards both synsedimentary within-plate basic volcanics and older sediments had been contributing in recognizable proportions to the siliciclastic rocks. The siliciclastic sedimentation was replaced by deposition of carbonate rocks throughout late Early Silurian to Early Devonian period of withdrawal of the Cadomian clastic material source. Above the carbonates an early Givetian flysch-like siliciclastic suite completed sedimentation in the Barrandian. In times between Middle Cambrian and Early/Middle Devonian boundary interval an extensional tectonic setting prevailed in the Teplá-Barrandian unit. The extensional regime was related to Early Palaeozoic large-scale fragmentation of the Cadomian belt of northwestern Gondwana and origin of Armorican microcontinent assemblage. The Teplá-Barrandian unit was also engaged in a peri-equatorially oriented drift of Armorican microcontinent assemblage throughout the Early Palaeozoic: respective palaeolatitudes of 58°S (Middle Cambrian) and 17°S (Middle Devonian) were inferred for the Barrandian rocks. The Middle Devonian flysch-like siliciclastics of the Prague Basin suggest a reappearance of the deeply dissected Cadomian source area in a proximity of the Barrandian due to early Variscan convergences and collisions of the Armorican microcontinents. Significant palaeotectonic rotations are palaeomagnetically evidenced to take place during oblique convergence and final docking of the Teplá-Barrandian microplate within the Variscan terrane mosaic of the Bohemian Massif.

New Insights into Arctic Tectonics: Uranium-Lead, (Uranium-Thorium)/Helium, and Hafnium Isotopic Data from the Franklinian Basin, Canadian Arctic Islands

NASA Astrophysics Data System (ADS)

Anfinson, Owen Anthony

More than 2300 detrital zircon uranium-lead (U-Pb) ages, 32 176Hf/177Hf (eHf) isotopic values, 37 apatite helium (AHe) ages, and 72 zircon helium (ZHe) ages represent the first in-depth geochronologic and thermochronologic study of Franklinian Basin strata in the Canadian Arctic and provide new insight on >500 M.y. of geologic history along the northern Laurentian margin (modern orientation). Detrital zircon U-Pb age data demonstrate that the Franklinian Basin succession is composed of strata with three distinctly different provenance signatures. Neoproterozoic and Lower Cambrian formations contain detrital zircon populations consistent with derivation from Archean to Paleoproterozoic gneisses and granites of the west Greenland--northeast Canadian Shield. Lower Silurian to Middle Devonian strata are primarily derived from foreland basin strata of the East Greenland Caledonides (Caledonian orogen). Middle Devonian to Upper Devonian strata also contain detrital zircon populations interpreted as being primarily northerly derived from the continental landmass responsible for the Ellesmerian Orogen (often referred to as Crockerland). U-Pb age data from basal turbidites of the Middle to Upper Devonian clastic succession suggest Crockerland contributed sediment to the northern Laurentian margin by early-Middle Devonian time and that prior to the Ellesmerian Orogeny Crockerland had a comparable geologic history to the northern Baltica Craton. Detrital zircon U-Pb ages in Upper Devonian strata suggest Crockerland became the dominant source by the end of Franklinian Basin sedimentation. Mean eHf values from Paleozoic detrital zircon derived from Crockerland suggest the zircons were primarily formed in either an island arc or continental arc built on accreted oceanic crust setting. ZHe cooling ages from Middle and Upper Devonian strata were not buried deeper than 7 km since deposition and suggest Crockerland was partially exhumed during the Caledonian Orogen. AHe cooling ages are partially reset since deposition and experienced varying burial histories depending on stratigraphic and geographic location within the basin. AHe ages from Middle Devonian strata from the western margin of the basin indicate episodes of exhumation associated with clastic influxes of sediment into the Sverdrup Basin during the Late Jurassic-Early Cretaceous and Late Cretaceous.

Biostratigraphy and structure of paleozoic host rocks and their relationship to Carlin-type gold deposits in the Jerritt Canyon mining district, Nevada

USGS Publications Warehouse

Peters, S.G.; Armstrong, A.K.; Harris, A.G.; Oscarson, R.L.; Noble, P.J.

2003-01-01

The Jerritt Canyon mining district in the northern Independence Range, northern Nevada, contains multiple, nearly horizontal, thrust masses of platform carbonate rocks that are exposed in a series of north- to northeast-elongated, tectonic windows through rocks of the Roberts Mountains allochthon. The Roberts Mountains allochthon was emplaced during the Late Devonian to Early Mississippian Antler orogeny. These thrust masses contain structurally and stratigraphically controlled Carlin-type gold deposits. The gold deposits are hosted in tectonically truncated units of the Silurian to Devonian Hanson Creek and Roberts Mountains Formations that lie within structural slices of an Eastern assemblage of Cambrian to Devonian carbonate rocks. In addition, these multiply thrust-faulted and folded host rocks are structurally interleaved with Mississippian siliciclastic rocks and are overlain structurally by Cambrian to Devonian siliciclastic units of the Roberts Mountains allochthon. All sedimentary rocks were involved in thrusting, high-angle faulting, and folding, and some of these events indicate substantial late Paleozoic and/or Mesozoic regional shortening. Early Pennsylvanian and late Eocene dikes also intrude the sedimentary rocks. These rocks all were uplifted into a northeast-trending range by subsequent late Cenozoic Basin and Range faulting. Eocene sedimentary and volcanic rocks flank part of the range. Pathways of hydrothermal fluid flow and locations of Carlin-type gold orebodies in the Jerritt Canyon mining district were controlled by structural and host-rock geometries within specific lithologies of the stacked thrust masses of Eastern assemblage rocks. The gold deposits are most common proximal to intersections of northeast-striking faults, northwest-striking dikes, and thrust planes that lie adjacent to permeable stratigraphic horizons. The host stratigraphic units include carbonate sequences that contained primary intercrystalline permeability, which provided initial pathways for fluid flow and later served as precipitation sites for ore minerals. Alteration, during, and perhaps prior to mineralization, enhanced primary permeability by dissolution, by removal of calcite, and by formation of dolomite. Ore-stage sulfide minerals and alteration minerals commonly precipitated in pore spaces among dolomite grains. Microveinlets and microbrecciation in zones of intense alteration also provided networks of secondary permeability that further enhanced fluid flux and produced additional sites for ore deposition.

Leaf evolution in early-diverging ferns: insights from a new fern-like plant from the Late Devonian of China

PubMed Central

Wang, De-Ming; Xu, Hong-He; Xue, Jin-Zhuang; Wang, Qi; Liu, Le

2015-01-01

Background and Aims With the exception of angiosperms, the main euphyllophyte lineages (i.e. ferns sensu lato, progymnosperms and gymnosperms) had evolved laminate leaves by the Late Devonian. The evolution of laminate leaves, however, remains unclear for early-diverging ferns, largely represented by fern-like plants. This study presents a novel fern-like taxon with pinnules, which provides new insights into the early evolution of laminate leaves in early-diverging ferns. Methods Macrofossil specimens were collected from the Upper Devonian (Famennian) Wutong Formation of Anhui and Jiangsu Provinces, South China. A standard degagement technique was employed to uncover compressed plant portions within the rock matrix. Key Results A new fern-like taxon, Shougangia bella gen. et sp. nov., is described and represents an early-diverging fern with highly derived features. It has a partially creeping stem with adventitious roots only on one side, upright primary and secondary branches arranged in helices, tertiary branches borne alternately or (sub)oppositely, laminate and usually lobed leaves with divergent veins, and complex fertile organs terminating tertiary branches and possessing multiple divisions and numerous terminal sporangia. Conclusions Shougangia bella provides unequivocal fossil evidence for laminate leaves in early-diverging ferns. It suggests that fern-like plants, along with other euphyllophyte lineages, had independently evolved megaphylls by the Late Devonian, possibly in response to a significant decline in atmospheric CO2 concentration. Among fern-like plants, planate ultimate appendages are homologous with laminate pinnules, and in the evolution of megaphylls, fertile organs tend to become complex. PMID:25979918

Lithologies of the basement complex (Devonian and older) in the National Petroleum Reserve - Alaska

USGS Publications Warehouse

Dumoulin, Julie A.; Houseknecht, David W.

2001-01-01

Rocks of the basement complex (Devonian and older) were encountered in at least 30 exploratory wells in the northern part of the NPRA. Fine-grained, variably deformed sedimentary rocks deposited in a slope or basinal setting predominate and include varicolored (mainly red and green) argillite in the Simpson area, dark argillite and chert near Barrow, and widespread gray argillite. Chitinozoans of Middle-Late Ordovician and Silurian age occur in the dark argillite and chert unit. Sponge spicules and radiolarians establish a Phanerozoic age for the varicolored and gray argillite units, both of which contain local interbeds of chert-rich sandstone and silt-stone. Conglomerate and sandstone, also chert-rich but interbedded with mudstone and coal and of Early-Middle Devonian age, occur in the Topagoruk area; these strata formed in a fluvial environment. At East Teshekpuk, granite of probable Devonian age was penetrated. Brecciated, quartz-veined rock of uncertain protolith that may be part of the basement complex was encountered in the Ikpikpuk well. Seismic data indicate that angular unconformities truncate all sedimentary units of the basement complex in NPRA. Rocks correlative in age and lithofacies with the dark argillite and chert unit occur in the subsurface near Prudhoe Bay. Other argillite units in NPRA have similarities to basement rocks in the subsurface adjacent to ANWR and the Ordovician-Silurian Iviagik Group at Cape Lisburne, but lack the interbedded limestones found in the ANWR strata, and are less metamorphosed than, and compositionally distinct from, the Iviagik. The Topagoruk conglomerate and the East Teshekpuk granite resemble the Ulungarat formation and the Okpilak batholith, respectively, in the northeastern Brooks Range.

Underplating generated A- and I-type granitoids of the East Junggar from the lower and the upper oceanic crust with mixing of mafic magma: Insights from integrated zircon U-Pb ages, petrography, geochemistry and Nd-Sr-Hf isotopes

NASA Astrophysics Data System (ADS)

Liu, Wei; Liu, Xiu-Jin; Liu, Li-Juan

2013-10-01

Whole rock major and trace element, Nd-Sr and zircon Hf isotopic compositions and secondary-ion mass spectrometry zircon U-Pb ages of eleven granitoid intrusions and dioritic rocks from the East Junggar (NW China) were analyzed in this study. The East Junggar granitoids were emplaced during terminal Early to Late Carboniferous (325-301 Ma) following volcanic eruption of the Batamayi Formation. Zircons from the East Junggar granitoids yielded 210 concordant 206Pb/238U ages which are all younger than 334 Ma and exhibit ɛHf(t) values distinctly higher than Devonian arc volcanic-rocks. Seismic P-wave velocities of deep crust of the East Junggar proper resemble those of oceanic crust (OC). These characteristics suggest absence of volcanic rock and volcano-sedimentary rock of Devonian and Early Carboniferous from the source region. The East Junggar granitoids show ɛNd(t) and initial 87Sr/86Sr values substantially overlapping those of the Armantai ophiolite in the area. The Early Paleozoic OC with seamount-like composition as the Zhaheba-Armantai ophiolites remained in the lower crust and formed main source rock of the East Junggar granitoids. Based on petrography and geochemistry, the East Junggar granitoids are classified into peralkaline A-type in the northern subarea, I-type (I1 and I2 subgroups) mainly in the north and A-type in the south of the southern subarea. The perthitic or argillated core and oligoclasic rim with an argillated boundary of feldspar phenocrysts and inclusion of perthites or its overgrowth by matrix plagioclase, in the monzogranites (northern subarea), suggest mixing of peralkaline granitic magma with mafic magma. In the north of the southern subarea, the presence of magmatic microdioritic enclaves (MMEs) in the I1 subgroup granitoids, transfer of plagioclase phenocrysts and hornblendes between host granodiorite and the MME across the boundary and a prominent resorption surface in the plagioclase phenocrysts indicate mixing of crustal magma (I2 subgroup granitoids) with mafic magma. Magma mixing shifted (87Sr/86Sr)i of the I1 subgroup granitoids towards the mantle array. Two generations of hornblende with zonal distribution and similar mineral and geochemical compositions of quartz monzodiorite and hosted MME with unfractionated rare earth elements (REE) suggest extended magma mixing with onset probably at or near source region. These observations imply concurrency of mantle input and the crustal melting and, hence, a causal relationship between underplating/intraplating and the lower OC/upper OC melting. The I-type granitoids experienced plagioclase and hornblende fractionations, whereas fractionated phases of the two groups of A-type granites were alkali feldspar and albite-oligoclase with significant involvement of F--rich fluid. Granodioritic parent magmas of the I2 subgroup granitoids stemmed from the hydrous upper OC. Parent magmas of the two A-type groups possess syenogranitic or quartz syenitic compositions. The peralkaline A-type granites stemmed from the lower OC, whereas the A-type granites from dehydrated upper OC left behind after extensive partial melting and extraction of I-type granitoids. Based on comparison in the ternary system Mg2SiO4-CaAl2SiO6-SiO2, most of the Batamayi volcanic rocks with affinity to ocean-island basalts were derived from asthenospheric upwelling. The gabbro-dioritic rocks with higher light to heavy REE ratios stemmed from metasomatized lithospheric mantle. Both of the above mafic rocks contain subducted slab component.

A Systems Approach to Identifying Exploration and Development Opportunities in the Illinois Basin: Digital Portifolio of Plays in Underexplored Lower Paleozoic Rocks [Part 1 of 2

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seyler, Beverly; Harris, David; Keith, Brian

2008-06-30

This study examined petroleum occurrence in Ordovician, Silurian and Devonian reservoirs in the Illinois Basin. Results from this project show that there is excellent potential for additional discovery of petroleum reservoirs in these formations. Numerous exploration targets and exploration strategies were identified that can be used to increase production from these underexplored strata. Some of the challenges to exploration of deeper strata include the lack of subsurface data, lack of understanding of regional facies changes, lack of understanding the role of diagenetic alteration in developing reservoir porosity and permeability, the shifting of structural closures with depth, overlooking potential producing horizons,more » and under utilization of 3D seismic techniques. This study has shown many areas are prospective for additional discoveries in lower Paleozoic strata in the Illinois Basin. This project implemented a systematic basin analysis approach that is expected to encourage exploration for petroleum in lower Paleozoic rocks of the Illinois Basin. The study has compiled and presented a broad base of information and knowledge needed by independent oil companies to pursue the development of exploration prospects in overlooked, deeper play horizons in the Illinois Basin. Available geologic data relevant for the exploration and development of petroleum reservoirs in the Illinois Basin was analyzed and assimilated into a coherent, easily accessible digital play portfolio. The primary focus of this project was on case studies of existing reservoirs in Devonian, Silurian, and Ordovician strata and the application of knowledge gained to future exploration and development in these underexplored strata of the Illinois Basin. In addition, a review of published reports and exploration in the New Albany Shale Group, a Devonian black shale source rock, in Illinois was completed due to the recent increased interest in Devonian black shales across the United States. The New Albany Shale is regarded as the source rock for petroleum in Silurian and younger strata in the Illinois Basin and has potential as a petroleum reservoir. Field studies of reservoirs in Devonian strata such as the Geneva Dolomite, Dutch Creek Sandstone and Grassy knob Chert suggest that there is much additional potential for expanding these plays beyond their current limits. These studies also suggest the potential for the discovery of additional plays using stratigraphic concepts to develop a subcrop play on the subkaskaskia unconformity boundary that separates lower Devonian strata from middle Devonian strata in portions of the basin. The lateral transition from Geneva Dolomite to Dutch Creek Sandstone also offers an avenue for developing exploration strategies in middle Devonian strata. Study of lower Devonian strata in the Sesser Oil Field and the region surrounding the field shows opportunities for development of a subcrop play where lower Devonian strata unconformably overlie Silurian strata. Field studies of Silurian reservoirs along the Sangamon Arch show that opportunities exist for overlooked pays in areas where wells do not penetrate deep enough to test all reservoir intervals in Niagaran rocks. Mapping of Silurian reservoirs in the Mt. Auburn trend along the Sangamon Arch shows that porous reservoir rock grades laterally to non-reservoir facies and several reservoir intervals may be encountered in the Silurian with numerous exploration wells testing only the uppermost reservoir intervals. Mapping of the Ordovician Trenton and shallower strata at Centralia Field show that the crest of the anticline shifted through geologic time. This study illustrates that the axes of anticlines may shift with depth and shallow structure maps may not accurately predict structurally favorable reservoir locations at depth.« less

Chapter 1: An overview of the petroleum geology of the Arctic

USGS Publications Warehouse

Spencer, A.M.; Embry, A.F.; Gautier, D.L.; Stoupakova, A.V.; Sorensen, K.

2011-01-01

Nine main petroleum provinces containing recoverable resources totalling 61 Bbbl liquids + 269 Bbbloe of gas are known in the Arctic. The three best known major provinces are: West Siberia-South Kara, Arctic Alaska and Timan-Pechora. They have been sourced principally from, respectively, Upper Jurassic, Triassic and Devonian marine source rocks and their hydrocarbons are reservoired principally in Cretaceous sandstones, Triassic sandstones and Palaeozoic carbonates. The remaining six provinces except for the Upper Cretaceous-Palaeogene petroleum system in the Mackenzie Delta have predominantly Mesozoic sources and Jurassic reservoirs. There are discoveries in 15% of the total area of sedimentary basins (c. 8 ?? 106 km2), dry wells in 10% of the area, seismic but no wells in 50% and no seismic in 25%. The United States Geological Survey estimate yet-to-find resources to total 90 Bbbl liquids + 279 Bbbloe gas, with four regions - South Kara Sea, Alaska, East Barents Sea, East Greenland - dominating. Russian estimates of South Kara Sea and East Barents Sea are equally positive. The large potential reflects primarily the large undrilled areas, thick basins and widespread source rocks. ?? 2011 The Geological Society of London.

Bedrock Geologic Map of the Old Lyme Quadrangle, New London and Middlesex Counties, Connecticut

USGS Publications Warehouse

Walsh, Gregory J.; Scott, Robert B.; Aleinikoff, John N.; Armstrong, Thomas R.

2009-01-01

The bedrock geology of the Old Lyme quadrangle consists of Neoproterozoic and Permian gneisses and granites of the Gander and Avalon terranes, Silurian metasedimentary rocks of the Merrimack terrane, and Silurian to Devonian metasedimentary rocks of uncertain origin. The Avalon terrane rocks crop out within the Selden Neck block, and the Gander terrane rocks crop out within the Lyme dome. The Silurian to Devonian rocks crop out between these two massifs. Previous mapping in the Old Lyme quadrangle includes the work by Lawrence Lundgren, Jr. Lundgren's work provides an excellent resource for rock descriptions and detailed modal analyses of rock units that will not be duplicated in this current report. New research that was not covered in detail by Lundgren is the focus of this report and includes (1) evaluation of the rocks in the core of the Lyme dome in an effort to subdivide units in this area; (2) structural analysis of foliations and folds in and around the Lyme dome; (3) geochronology of selected units within the Lyme dome; and (4) analysis of joints and the fracture properties of the rocks.

Silurian and Devonian in Vietnam—Stratigraphy and facies

NASA Astrophysics Data System (ADS)

Thanh, Tống Duy; Phương, Tạ Hoàng; Janvier, Philippe; Hùng, Nguyễn Hữu; Cúc, Nguyễn Thị Thu; Dương, Nguyễn Thùy

2013-09-01

Silurian and Devonian deposits in Viet Nam are present in several zones and regions, including Quang Ninh, East Bac Bo, and West Bac Bo Zones of the Bac Bo Region, the Dien Bien-Nghe An and Binh Tri Thien Zones of the Viet-Lao Region, and the South Trung Bo, and Western Nam Bo Zones of the South Viet Nam Region (Fig. 1). The main lithological features and faunal composition of the Silurian and Devonian Units in all these zones are briefly described. The Silurian consists of deep-water deposits of the upper parts of the Co To and Tan Mai Formations in the Quang Ninh Zone, the upper parts of the Phu Ngu Formation in the East Bac Bo Zone and the upper parts of the Long Dai and Song Ca Formations in the Viet-Lao Region. Shallow water facies Silurian units containing benthic faunas are more widely distributed, including the upper part of the Sinh Vinh and Bo Hieng Formations in the West Bac Bo Zone, the Kien An Formation in the Quang Ninh Zone, and, in the Viet-Lao Region, the Dai Giang Formation and the upper part of the Tay Trang Formation. No Lower and Middle Devonian deposits indicate deep water facies, but they are characterized by different shallow water facies. Continental to near shore, deltaic facies characterize the Lower Devonian Song Cau Group in the East Bac Bo Zone, the Van Canh Formation in the Quang Ninh Zone, and the A Choc Formation in the Binh Tri Thien Zone. Similar facies also occur in the Givetian Do Son Formation of the Quang Ninh Zone, and the Tan Lap Formation in the East Bac Bo Zone, and consist of coarse terrigenous deposits—cross-bedded conglomerates, sandstone, etc. Most Devonian units are characterized by shallow marine shelf facies. Carbonate and terrigenous-carbonate facies dominate, and terrigenous facies occur in the Lower and Middle Devonian sections in some areas only. The deep-water-like facies is characteriztic for some Upper Devonian formations in the Bac Bo (Bang Ca and Toc Tat Formations) and Viet-Lao Regions (Thien Nhan and Xom Nha Formations). These formations contain cherty shale or siliceous limestone, and fossils consist of conodonts, but there are also brachiopods and other benthos. They were possibly deposited in a deep water environment on the slope of the continental shelf. Most Devonian units distributed in the North and the Central Viet Nam consist of self shallow water sediments, and apparently they were deposited in a passive marginal marine environment. The coarse clastic continental or subcontinental deposits are distributed only in some areas of the East Bac Bo and of the Quang Ninh zones of the Bac Bo Region, and in the south of the Binh Tri Thien Zone. This situation suggests the influence of the Caledonian movement at the end of the Silurian period that called the Guangxi movement in South China.

Bedrock geologic map of the Lisbon quadrangle, and parts of the Sugar Hill and East Haverhill quadrangles, Grafton County, New Hampshire

USGS Publications Warehouse

Rankin, Douglas W.

2018-04-20

The bedrock geologic map of the Lisbon quadrangle, and parts of the Sugar Hill and East Haverhill quadrangles, Grafton County, New Hampshire, covers an area of approximately 73 square miles (189 square kilometers) in west-central New Hampshire. This map was created as part of a larger effort to produce a new bedrock geologic map of Vermont through the collection of field data at a scale of 1:24,000. A large part of the map area consists of the Bronson Hill anticlinorium, a post-Early Devonian structure that is cored by metamorphosed Cambrian to Devonian sedimentary, volcanic, and plutonic rocks.The Bronson Hill anticlinorium is the apex of the Middle Ordovician to earliest-Silurian Bronson Hill magmatic arc that contains the Ammonoosuc Volcanics, Partridge Formation, and Oliverian Plutonic Suite, and extends from Maine, through western New Hampshire (down the eastern side of the Connecticut River), through southern New England to Long Island Sound. The deformed and partially eroded arc is locally overlain by a relatively thin Silurian section of metasedimentary rocks (Clough Quartzite and Fitch Formation) that thickens to the east. The Silurian section near Littleton is disconformably overlain by a thicker, Lower Devonian section that includes mostly metasedimentary and minor metavolcanic rocks of the Littleton Formation. The Bronson Hill anticlinorium is bisected by a series of northeast-southwest trending Mesozoic normal faults. Primarily among them is the steeply northwest-dipping Ammonoosuc fault that divides older and younger units (lower and upper sections) of the Ammonoosuc Volcanics. The Ammonoosuc Volcanics are lithologically complex and predominantly include interlayered and interfingered rhyolitic to basaltic volcanic and volcaniclastic rocks, as well as lesser amounts of slate, phyllite, ironstone, chert, sandstone, and pelite. The Albee Formation underlies the Ammonoosuc Volcanics and is predominantly composed of interbedded metamorphosed sandstone, siltstone, and phyllite.During the Late Ordovician, a series of arc-related plutons intruded the Ammonoosuc Volcanics including the Moody Ledge pluton and the Scrag granite of Billings (1937). Subsequent plutonism related to the Acadian orogeny occurred after volcanism and deposition resulted in the Littleton Formation during the Late Devonian, including the intrusion of the Haverhill pluton and French Pond Granite found in the southern part of the map.This report consists of a geologic map and an online geographic information systems database that includes contacts of bedrock geologic units, faults, outcrops, and structural geologic information. The geologic map is intended to serve as a foundation for applying geologic information to problems involving land use decisions, groundwater availability and quality, earth resources such as natural aggregate for construction, assessment of natural hazards, and engineering and environmental studies for waste disposal sites and construction projects.

Paleozoic subduction complex and Paleozoic-Mesozoic island-arc volcano-plutonic assemblages in the northern Sierra terrane

USGS Publications Warehouse

Hanson, Richard E.; Girty, Gary H.; Harwood, David S.; Schweickert, Richard A.

2000-01-01

This field trip provides an overview of the stratigraphic and structural evolution of the northern Sierra terrane, which forms a significant part of the wall rocks on the western side of the later Mesozoic Sierra Nevada batholith in California. The terrane consists of a pre-Late Devonian subduction complex (Shoo Fly Complex) overlain by submarine arc-related deposits that record the evolution of three separate island-arc systems in the Late Sevonian-Early Mississippian, Permian, and Late Triassic-Jurassic. The two Paleozoic are packages and the underlying Shoo Fly Complex have an important bearing on plate-tectonic processes affecting the convergent margin outboard of the Paleozoic Cordilleran miogeocline, although their original paleogeographic relations to North America are controversial. The third arc package represents an overlap assemblage that ties the terrane to North America by the Late Triassic and helps constrain the nature and timing of Mesozoic orogenesis. Several of the field-trip stops examine the record of pre-Late Devonian subduction contained in the Shoo Fly Complex, as well as the paleovolcanology of the overlying Devonian to Jurassic arc rocks. Excellent glaciated exposures provide the opportunity to study a cross section through a tilted Devonian volcano-plutonic association. Additional stops focus on plutonic rocks emplaced during the Middle Jurassic arc magmatism in the terrane, and during the main pulse of Cretaceous magmatism in the Sierra Nevada batholith to the east.

Devonian volcanic rocks of the southern Chinese Altai, NW China: Petrogenesis and implication for a propagating slab-window magmatism induced by ridge subduction during accretionary orogenesis

NASA Astrophysics Data System (ADS)

Ma, Xiaomei; Cai, Keda; Zhao, Taiping; Bao, Zihe; Wang, Xiangsong; Chen, Ming; Buslov, M. M.

2018-07-01

Ridge-trench interaction is a common tectonic process of the present-day Pacific Rim accretionary orogenic belts, and this process may facilitate "slab-window" magmatism that can produce significant thermal anomalies and geochemically unusual magmatic events. However, ridge-trench interaction has rarely been well-documented in the ancient geologic record, leading to grossly underestimation of this process in tectonic syntheses of plate margins. The Chinese Altai was inferred to have undergone ridge subduction in the Devonian and a slab-window model is proposed to interpret its high-temperature metamorphism and geochemically unique magmatic rocks, which can serve as an excellent and unique place to refine the tectonic evolution associated with ridge subduction in an ancient accretionary orogeny. For this purpose, we carried out geochemical and geochronological studies on Devonian basaltic rocks in this region. Secondary ion mass spectrometry (SIMS) zircon U-Pb dating results yield an age of 376.2 ± 2.4 Ma, suggesting an eruption at the time of Late Devonian. Geochemically, the samples in this study have variable SiO2 (43.3-58.3 wt%), low K2O (0.02-0.07 wt%) and total alkaline contents (2.16-5.41 wt%), as well as Fe2O3T/MgO ratios, showing typical tholeiitic affinity. On the other hand, the basaltic rocks display MORB-like REE patterns ((La/Yb)N = 0.90-2.57) and (Ga/Yb)N = 0.97-1.28), and have moderate positive εNd(t) values (+4.4 to +5.4), which collectively suggest a derivation from a mixing source comprising MORB-like mantle of a mature back-arc basin and subordinate arc mantle wedge. These basaltic rocks are characterized by Low La/Yb (1.26-3.69), Dy/Yb (1.51-1.77) and Sm/Yb (0.83-1.32) ratios, consistent with magmas derived from low degree (∼10%) partial melting of the spinel lherzolite source at a quite shallow mantle depth. Considering the distinctive petrogenesis of the basaltic rocks in this region, the Late Devonian basalts in the southern Chinese Altai is suggested to have witnessed the propagating process of slab-window magmatism that was induced by ridge subduction in a nascent rifting stage of a back-arc basin.

Bedrock geologic map of the Montpelier and Barre West quadrangles, Washington and Orange Counties, Vermont

USGS Publications Warehouse

Walsh, Gregory J.; Kim, Jonathan; Gale, Marjorie H.; King, Sarah M.

2010-01-01

The bedrock geology of the Montpelier and Barre West quadrangles consists of Silurian and Devonian metasedimentary rocks of the Connecticut Valley-Gaspe synclinorium (CVGS) and metasedimentary, metavolcanic, and metaintrusive rocks of the Cambrian and Ordovician Moretown and Cram Hill Formations. Devonian granite dikes occur throughout the two quadrangles but are more abundant in the Silurian and Devonian rocks. The pre-Silurian rocks are separated from the rocks of the CVGS by the informally named 'Richardson Memorial Contact,' historically interpreted as either an unconformity or a fault. The results of this report represent mapping by G.J. Walsh, Jonathan Kim, and M.H. Gale from 2002 to 2005. S.M. King assisted Kim and Gale from 2002 to 2003. A.M. Satkoski (Indiana University) assisted Walsh, and L.R. Pascale (University of Vermont) and C.M. Orsi (Middlebury College) assisted Kim and Gale as summer interns in 2003. This study was designed to map the bedrock geology in the area. This map supersedes a preliminary map of the Montpelier quadrangle (Kim, Gale, and others, 2003). A companion study in the Barre West quadrangle (Walsh and Satkoski, 2005) determined the levels of naturally occurring radioactivity in the bedrock from surface measurements at outcrops during the course of 1:24,000-scale geologic mapping to identify which rock types were potential sources of radionuclides. Results of that study indicate that the carbonaceous phyllites in the CVGS have the highest levels of natural radioactivity.

Carbon isotope chemostratigraphy and precise dating of middle Frasnian (lower Upper Devonian) Alamo Breccia, Nevada, USA

USGS Publications Warehouse

Morrow, J.R.; Sandberg, C.A.; Malkowski, K.; Joachimski, M.M.

2009-01-01

At Hancock Summit West, Nevada, western USA, uppermost Givetian (upper Middle Devonian) and lower and middle Frasnian (lower Upper Devonian) rocks of the lower Guilmette Formation include, in stratigraphic sequence, carbonate-platform facies of the conodont falsiovalis, transitans, and punctata Zones; the type Alamo Breccia Member of the middle punctata Zone; and slope facies of the punctata and hassi Zones. The catastrophically deposited Alamo Breccia and related phenomena record the ~ 382??Ma Alamo event, produced by a km-scale bolide impact into a marine setting seaward of an extensive carbonate platform fringing western North America. Re-evaluation of conodonts from the lower Guilmette Formation and Alamo Breccia Member, together with regional sedimentologic and conodont biofacies comparisons, now firmly locates the onset of the Johnson et al. (1985) transgressive-regressive (T-R) cycle IIc, which occurred after the start of the punctata Zone, within a parautochthonous megablock low in the Alamo Breccia. Whole-rock carbon isotope analyses through the lower Guilmette Formation and Alamo Breccia Member reveal two positive ??13Ccarb excursions: (1) a small, 3??? excursion, which is possibly correlative with the falsiovalis Event previously identified from sections in Western Europe and Australia, occurs below the breccia in the Upper falsiovalis Zone to early part of the transitans Zone; and (2) a large, multi-part excursion, dominated by a 6??? positive shift, begins above the start of the punctata Zone and onset of T-R cycle IIc and continues above the Alamo Breccia, ending near the punctata- hassi zonal boundary. This large excursion correlates with the punctata Event, a major positive ??13C excursion previously recognized in eastern Laurussia and northern Gondwana. Consistent with previous studies, at Hancock Summit West the punctata Event is apparently not associated with any regional extinctions or ecosystem reorganizations. In the study area, onset of the main punctata Event began after the start of both the punctata Zone and T-R cycle IIc, and preceded the Alamo impact by less than 650??k.y., as inferred from conodont biochronologic and regional rock-accumulation rate estimates. Although complicated by the heterolithic, high-energy deposits of the Alamo Breccia, the carbon isotope record of the breccia and post-breccia beds does not indicate a major impact-correlative perturbation to the carbon cycle. This study extends recognition of the punctata Event to western Laurussia, further reinforcing the potential global scale of the event and its potential importance to understanding early to middle Frasnian marine geochemistry and palaeoenvironments. Based on previous models and our observations, increased tectonic activity, increased nutrient flux to oceans, increased marine bioproductivity, widespread anoxia, and increased organic carbon burial were all likely key factors in driving the punctata Event excursion. Furthermore, periodic eustatic and regional relative sea-level rises may have played an important role in promoting organic carbon burial and in maintaining a link between the primary open-marine geochemical signal and that recorded on the shallow-marine, lower Guilmette carbonate platform. ?? 2009 Elsevier B.V. All rights reserved.

Geometry of the neoproterozoic and paleozoic rift margin of western Laurentia: Implications for mineral deposit settings

USGS Publications Warehouse

Lund, K.

2008-01-01

The U.S. and Canadian Cordilleran miogeocline evolved during several phases of Cryogenian-Devonian intracontinental rifting that formed the western mangin of Laurentia. Recent field and dating studies across central Idaho and northern Nevada result in identification of two segments of the rift margin. Resulting interpretations of rift geometry in the northern U.S. Cordillera are compatible with interpretations of northwest- striking asymmetric extensional segments subdivided by northeast-striking transform and transfer segments. The new interpretation permits integration of miogeoclinal segments along the length of the western North American Cordillera. For the U.S. Cordillera, miogeoclinal segments include the St. Mary-Moyie transform, eastern Washington- eastern Idaho upper-plate margin, Snake River transfer, Nevada-Utah lower-plate margin, and Mina transfer. The rift is orthogonal to most older basement domains, but the location of the transform-transfer zones suggests control of them by basement domain boundaries. The zigzag geometry of reentrants and promontories along the rift is paralleled by salients and recesses in younger thrust belts and by segmentation of younger extensional domains. Likewise, transform transfer zones localized subsequent transcurrent structures and igneous activity. Sediment-hosted mineral deposits trace the same zigzag geometry along the margin. Sedimentary exhalative (sedex) Zn-Pb-Ag ??Au and barite mineral deposits formed in continental-slope rocks during the Late Devonian-Mississippian and to a lesser degree, during the Cambrian-Early Ordovician. Such deposits formed during episodes of renewed extension along miogeoclinal segments. Carbonate-hosted Mississippi Valley- type (MVT) Zn-Pb deposits formed in structurally reactivated continental shelf rocks during the Late Devonian-Mississippian and Mesozoic due to reactivation of preexisting structures. The distribution and abundance of sedex and MVT deposits are controlled by the polarity and kinematics of the rift segment. Locally, discrete mineral belts parallel secondary structures such as rotated crustal blocks at depth that produced sedimentary subbasins and conduits for hydrothermal fluids. Where the miogeocline was overprinted by Mesozoic and Cenozoic deformation and magmatism, igneous rock-related mineral deposits are common. ??2008 Geological Society of America.

Sequence stratigraphy and a revised sea-level curve for the Middle Devonian of eastern North America

USGS Publications Warehouse

Brett, Carlton E.; Baird, G.C.; Bartholomew, A.J.; DeSantis, M.K.; Ver Straeten, C.A.

2011-01-01

The well-exposed Middle Devonian rocks of the Appalachian foreland basin (Onondaga Formation; Hamilton Group, Tully Formation, and the Genesee Group of New York State) preserve one of the most detailed records of high-order sea-level oscillation cycles for this time period in the world. Detailed examination of coeval units in distal areas of the Appalachian Basin, as well as portions of the Michigan and Illinois basins, has revealed that the pattern of high-order sea-level oscillations documented in the New York-Pennsylvania section can be positively identified in all areas of eastern North America where coeval units are preserved. The persistence of the pattern of high-order sea-level cycles across such a wide geographic area suggests that these cycles are allocyclic in nature with primary control on deposition being eustatic sea-level oscillation, as opposed to autocylic controls, such as sediment supply, which would be more local in their manifestation. There is strong evidence from studies of cyclicity and spectral analysis that these cycles are also related to Milankovitch orbital variations, with the short and long-term eccentricity cycles (100. kyr and 405. kyr) being the dominant oscillations in many settings. Relative sea-level oscillations of tens of meters are likely and raise considerable issues about the driving mechanism, given that the Middle Devonian appears to record a greenhouse phase of Phanerozoic history. These new correlations lend strong support to a revised high-resolution sea-level oscillation curve for the Middle Devonian for the eastern portion of North America. Recognized third-order sequences are: Eif-1 lower Onondaga Formation, Eif-2: upper Onondaga and Union Springs formations; Eif-Giv: Oatka Creek Formation; Giv-1: Skaneateles, Giv-2: Ludlowville, Giv-3: lower Moscow, Giv-4: upper Moscow-lower Tully, and Giv-5: middle Tully-Geneseo formations. Thus, in contrast with the widely cited eustatic curve of Johnson et al. (1985), which recognizes just one major transgressive-regressive (T-R) cycle in the early-mid Givetian (If) prior to the major late Givetian Taghanic unconformity (IIa, upper Tully-Geneseo Shale), we recognize four T-R cycles: If (restricted), Ig, Ih, and Ii. We surmise that third-order sequences record eustatic sea-level fluctuations of tens of meters with periodicities of 0.8-2. myr, while their medial-scale (fourth-order) subdivisions record lesser variations primarily of 405. kyr duration (long-term eccentricity). This high-resolution record of sea-level change provides strong evidence for high-order eustatic cycles with probable Milankovitch periodicities, despite the fact that no direct evidence for Middle Devonian glacial sediments has been found to date. ?? 2010.

Leaf evolution in early-diverging ferns: insights from a new fern-like plant from the Late Devonian of China.

PubMed

Wang, De-Ming; Xu, Hong-He; Xue, Jin-Zhuang; Wang, Qi; Liu, Le

2015-06-01

With the exception of angiosperms, the main euphyllophyte lineages (i.e. ferns sensu lato, progymnosperms and gymnosperms) had evolved laminate leaves by the Late Devonian. The evolution of laminate leaves, however, remains unclear for early-diverging ferns, largely represented by fern-like plants. This study presents a novel fern-like taxon with pinnules, which provides new insights into the early evolution of laminate leaves in early-diverging ferns. Macrofossil specimens were collected from the Upper Devonian (Famennian) Wutong Formation of Anhui and Jiangsu Provinces, South China. A standard degagement technique was employed to uncover compressed plant portions within the rock matrix. A new fern-like taxon, SHOUGANGIA BELLA GEN ET SP NOV: , is described and represents an early-diverging fern with highly derived features. It has a partially creeping stem with adventitious roots only on one side, upright primary and secondary branches arranged in helices, tertiary branches borne alternately or (sub)oppositely, laminate and usually lobed leaves with divergent veins, and complex fertile organs terminating tertiary branches and possessing multiple divisions and numerous terminal sporangia. Shougangia bella provides unequivocal fossil evidence for laminate leaves in early-diverging ferns. It suggests that fern-like plants, along with other euphyllophyte lineages, had independently evolved megaphylls by the Late Devonian, possibly in response to a significant decline in atmospheric CO2 concentration. Among fern-like plants, planate ultimate appendages are homologous with laminate pinnules, and in the evolution of megaphylls, fertile organs tend to become complex. © The Author 2015. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

Middle Devonian to Late Mississippian event stratigraphy of Overthrust belt region, western United States.

USGS Publications Warehouse

Sandberg, C.A.; Gutschick, R.C.; Johnson, J.G.; Poole, F.G.; Sando, W.J.

1986-01-01

Twenty eustatic and epeirogenic events mainly dated by conodonts are distinguished between the Middle Devonian and the lower Upper Mississippian in Great Basin, in Rocky Mountains and in the Overthrust belt regions.-Journal Editors

Petroleum geology and resources of the North Caspian Basin, Kazakhstan and Russia

USGS Publications Warehouse

Ulmishek, Gregory F.

2001-01-01

The North Caspian basin is a petroleum-rich but lightly explored basin located in Kazakhstan and Russia. It occupies the shallow northern portion of the Caspian Sea and a large plain to the north of the sea between the Volga and Ural Rivers and farther east to the Mugodzhary Highland, which is the southern continuation of the Ural foldbelt. The basin is bounded by the Paleozoic carbonate platform of the Volga-Ural province to the north and west and by the Ural, South Emba, and Karpinsky Hercynian foldbelts to the east and south. The basin was originated by pre-Late Devonian rifting and subsequent spreading that opened the oceanic crust, but the precise time of these tectonic events is not known. The sedimentary succession of the basin is more than 20 km thick in the central areas. The drilled Upper Devonian to Tertiary part of this succession includes a prominent thick Kungurian (uppermost Lower Permian) salt formation that separates strata into the subsalt and suprasalt sequences and played an important role in the formation of oil and gas fields. Shallow-shelf carbonate formations that contain various reefs and alternate with clastic wedges compose the subsalt sequence on the 1 basin margins. Basinward, these rocks grade into deep-water anoxic black shales and turbidites. The Kungurian salt formation is strongly deformed into domes and intervening depressions. The most active halokinesis occurred during Late Permian?Triassic time, but growth of salt domes continued later and some of them are exposed on the present-day surface. The suprasalt sequence is mostly composed of clastic rocks that are several kilometers thick in depressions between salt domes. A single total petroleum system is defined in the North Caspian basin. Discovered reserves are about 19.7 billion barrels of oil and natural gas liquids and 157 trillion cubic feet of gas. Much of the reserves are concentrated in the supergiant Tengiz, Karachaganak, and Astrakhan fields. A recent new oil discovery on the Kashagan structure offshore in the Caspian Sea is probably also of the supergiant status. Major oil and gas reserves are located in carbonate reservoirs in reefs and structural traps of the subsalt sequence. Substantially smaller reserves are located in numerous fields in the suprasalt sequence. These suprasalt fields are largely in shallow Jurassic and Cretaceous clastic reservoirs in salt dome-related traps. Petroleum source rocks are poorly identified by geochemical methods. However, geologic data indicate that the principal source rocks are Upper Devonian to Lower Permian deep-water black-shale facies stratigraphically correlative to shallow-shelf carbonate platforms on the basin margins. The main stage of hydrocarbon generation was probably in Late Permian and Triassic time, during deposition of thick orogenic clastics. Generated hydrocarbons migrated laterally into adjacent subsalt reservoirs and vertically, through depressions between Kungurian salt domes where the salt is thin or absent, into suprasalt clastic reservoirs. Six assessment units have been identified in the North Caspian basin. Four of them include Paleozoic subsalt rocks of the basin margins, and a fifth unit, which encompasses the entire total petroleum system area, includes the suprasalt sequence. All five of these assessment units are underexplored and have significant potential for new discoveries. Most undiscovered petroleum resources are expected in Paleozoic subsalt carbonate rocks. The assessment unit in subsalt rocks with the greatest undiscovered potential occupies the south basin margin. Petroleum potential of suprasalt rocks is lower; however, discoveries of many small to medium size fields are expected. The sixth identified assessment unit embraces subsalt rocks of the central basin areas. The top of subsalt rocks in these areas occurs at depths ranging from 7 to 10 kilometers and has not been reached by wells. Undiscovered resources of this unit did not rec

Tectonics of Antarctica

USGS Publications Warehouse

Hamilton, W.

1967-01-01

Antarctica consists of large and wholly continental east Antarctica and smaller west Antarctica which would form large and small islands, even after isostatic rebound, if its ice cap were melted. Most of east Antarctica is a Precambrian Shield, in much of which charnockites are characteristic. The high Transantarctic Mountains, along the Ross and Weddell Seas, largely follow a geosyncline of Upper Precambrian sedimentary rocks that were deformed, metamorphosed and intruded by granitic rocks during Late Cambrian or Early Ordovician time. The rocks of the orogen were peneplained, then covered by thin and mostly continental Devonian-Jurassic sediments, which were intruded by Jurassic diabase sheets and overlain by plateau-forming tholeiites. Late Cenozoic doming and block-faulting have raised the present high mountains. Northeastern Victoria Land, the end of the Transantarctic Mountains south of New Zealand, preserves part of a Middle Paleozoic orogen. Clastic strata laid unconformably upon the Lower Paleozoic plutonic complex were metamorphosed at low grade, highly deformed and intruded by Late Devonian or Early Carboniferous granodiorites. The overlying Triassic continental sedimentary rocks have been broadly folded and normal-faulted. Interior west Antarctica is composed of miogeosynclinal clastic and subordinate carbonate rocks which span the Paleozoic Era and which were deformed, metamorphosed at generally low grade, and intruded by granitic rocks during Early Mesozoic time and possibly during other times also. Patterns of orogenic belts, if systematic, cannot yet be defined; but fragmentation and rotation of crustal blocks by oroclinal folding and strike-slip faulting can be suggested. The Ellsworth Mountains, for example, consist of Cambrian-Permian metasedimentary rocks that strike northward toward the noncorrelative and latitudinally striking Mesozoic terrane of the Antarctic Peninsula in one direction and southward toward that of the Lower Paleozoic: terrane of the Transantarctic Mountains in the other; the three regions may be separated by great strike-slip faults. The Antarctic Peninsula in west Antarctica, south of South America, consists of metavolcanic and metasedimentary rocks intruded by Late Cretaceous quartz diorite. The pre-granitic rocks are of Jurassic and Early Cretaceous ages wherever they have been dated by fossils, although some crystalline complexes may be older. The S-shape of the peninsula may represent oroclinal bending within Cenozoic time as part of a motion system in which a narrow continental bridge between South America and Antarctica was deformed and ruptured. Perhaps this bridge lagged behind as the larger continental plates drifted into the Pacific Ocean Basin. ?? 1967.

Upper Devonian outcrop stratigraphy, southwestern Virginia and southeastern West Virginia

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dennison, J.M.; Filer, J.K.; Rossbach, T.J.

Ongoing outcrop studies are resulting in the extension of existing formal lithostratigraphic units and revision of previously less refined subdivisions of Upper Devonian strata in southwestern Virginia and southeastern West Virginia. A 425 km (263 mi) long stratigraphic cross-section has been constructed primarily from the outcrop belt along the Allegheny Structural Front, supplemented by sections from nearby outcrop belts. This NE-SW striking cross-section is oblique to the nearly due N-S depositional strike of the Upper Devonian Acadian orogenic wedge. To the southwest, the Upper Devonian section thins from 2,100 meters (6,900 feet) to 230 meters (756 feet) as progressively moremore » distal deposits are encountered. An integrated approach has been taken to establish chronostratigraphic control within the cross-section. The best time markers include particularly regressive parasequences which can be identified across facies boundaries (especially the Pound and Briery Gap Sandstones and their equivalents), volcanic ashes, and an organic-rich shale zone marking the base of a major transgression (equivalent to the base of the Huron Shale in Ohio and the Dunkirk Shale of New York). These tools provide chronostratigraphic correlation through the undivided Brallier Formation. Supplemental control includes biostratigraphic markers as well as marine dull redbeds within the Foreknobs which parallel other time lines and may represent partially reduced influxes of oxidized coastal plain sediments during minor parasequence scale regressions.« less

Geochemical and stable isotopic data on barren and mineralized drill core in the Devonian Popovich Formation, Screamer sector of the Betze-Post gold deposit, northern Carlin trend, Nevada

USGS Publications Warehouse

Christiansen, William D.; Hofstra, Albert H.; Zohar, Pamela B.; Tousignant, Gilles

2011-01-01

The Devonian Popovich Formation is the major host for Carlin-type gold deposits in the northern Carlin trend of Nevada. The Popovich is composed of gray to black, thin-bedded, calcareous to dolomitic mudstone and limestone deposited near the carbonate platform margin. Carlin-type gold deposits are Eocene, disseminated, auriferous pyrite deposits characterized by acid leaching, sulfidation, and silicification that are typically hosted in Paleozoic calcareous sedimentary rocks exposed in windows through siliceous sedimentary rocks of the Roberts Mountains allochthon. The Carlin trend currently is the largest gold producer in the United States. The Screamer ore zone is a tabular body on the periphery of the huge Betze-Post gold deposit. Screamer is a good place to study both the original lithogeochemistry of the Popovich Formation and the effects of subsequent alteration and mineralization because it is below the level of supergene oxidation, mostly outside the contact metamorphic aureole of the Jurassic Goldstrike stock, has small, high-grade ore zones along fractures and Jurassic dikes, and has intervening areas with lower grade mineralization and barren rock. In 1997, prior to mining at Screamer, drill core intervals from barren and mineralized Popovich Formation were selected for geochemical and stable isotope analysis. The 332, five-foot core samples analyzed are from five holes separated by as much as 2000 feet (600 meters). The samples extend from the base of the Wispy unit up through the Planar and Soft sediment deformation units into the lower part of the upper Mud unit of the Popovich Formation.

Thermal maturity patterns in New York State using CAI and %Ro

USGS Publications Warehouse

Weary, D.J.; Ryder, R.T.; Nyahay, R.E.

2001-01-01

New conodont alteration index (CAI) and vitrinite reflectance (%Ro) data collected from drill holes in the Appalachian basin of New York State allow refinement of thermal maturity maps for Ordovician and Devonian rocks. CAI isotherms on the new maps show a pattern that approximates that published by Harris et al. (1978) in eastern and western New York, but it differs in central New York, where the isotherms are shifted markedly westward by more than 100 km and are more tightly grouped. This close grouping of isograds reflects a steeper thermal gradient than previously noted by Harris et al. (1978) and agrees closely with the abrupt west-to-east increase in thermal maturity across New York noted by Johnsson (1986). These data show, in concordance with previous studies, that thermal maturity levels in these rocks are higher than can be explained by simple burial heating beneath the present thickness of overburden. The Ordovician and Devonian rocks of the Appalachian Basin in New York must have been buried by very thick post-Devonian sediments (4-6 km suggested by Sarwar and Friedman 1995) or were exposed to a higher-than-normal geothermal flux caused by crustal extension, or a combination of the two.

Alligator ridge district, East-Central Nevada: Carlin-type gold mineralization at shallow depths

USGS Publications Warehouse

Nutt, C.J.; Hofstra, A.H.

2003-01-01

Carlin-type deposits in the Alligator Ridge mining district are present sporadically for 40 km along the north-striking Mooney Basin fault system but are restricted to a 250-m interval of Devonian to Mississippian strata. Their age is bracketed between silicified ca. 45 Ma sedimentary rocks and unaltered 36.5 to 34 Ma volcanic rocks. The silicification is linked to the deposits by its continuity with ore-grade silicification in Devonian-Mississippian strata and by its similar ??18O values (_e1???17???) and trace element signature (As, Sb, Tl, Hg). Eocene reconstruction indicates that the deposits formed at depths of ???300 to 800 m. In comparison to most Carlin-type gold deposits, they have lower Au/Ag, Au grades, and contained Au, more abundant jasperoid, and textural evidence from deposition of an amorphous silica precursor in jasperoid. These differences most likely result from their shallow depth of formation. The peak fluid temperature (_e1???230??C) and large ??18OH2O value shift from the meteroric water line (_e1???20???) suggest that ore fluids were derived from depths of 8 km or more. A magnetotelluric survey indicates that the Mooney Basin fault system penetrates to mid-crustal depths. Deep circulation of meteoric water along the Mooney Basin fault system may have been in response to initial uplift of the East Humboldt-Ruby Mountains metamorphic core complex; convection also may have been promoted by increased heat flow associated with large magnitude extension in the core complex and regional magmatism. Ore fluids ascended along the fault system until they encountered impermeable Devonian and Mississippian shales, at which point they moved laterally through permeable strata in the Devonian Guilmette Formation, Devonian-Mississippian Pilot Shale, Mississippian Joana Limestone, and Mississippian Chainman Shale toward erosional windows where they ascended into Eocene fluvial conglomerates and lake sediments. Most gold precipitated by sulfidation of host-rock Fe and mixing with local ground water in zones of lateral fluid flow in reactive strata, such as the Lower Devonian-Mississippian Pilot Shale.

Geologic Map of the Warm Spring Canyon Area, Death Valley National Park, Inyo County, California, With a Discussion of the Regional Significance of the Stratigraphy and Structure

USGS Publications Warehouse

Wrucke, Chester T.; Stone, Paul; Stevens, Calvin H.

2007-01-01

Warm Spring Canyon is located in the southeastern part of the Panamint Range in east-central California, 54 km south of Death Valley National Park headquarters at Furnace Creek Ranch. For the relatively small size of the area mapped (57 km2), an unusual variety of Proterozoic and Phanerozoic rocks is present. The outcrop distribution of these rocks largely resulted from movement on the east-west-striking, south-directed Butte Valley Thrust Fault of Jurassic age. The upper plate of the thrust fault comprises a basement of Paleoproterozoic schist and gneiss overlain by a thick sequence of Mesoproterozoic and Neoproterozoic rocks, the latter of which includes diamictite generally considered to be of glacial origin. The lower plate is composed of Devonian to Permian marine formations overlain by Jurassic volcanic and sedimentary rocks. Late Jurassic or Early Cretaceous plutons intrude rocks of the area, and one pluton intrudes the Butte Valley Thrust Fault. Low-angle detachment faults of presumed Tertiary age underlie large masses of Neoproterozoic dolomite in parts of the area. Movement on these faults predated emplacement of middle Miocene volcanic rocks in deep, east-striking paleovalleys. Excellent exposures of all the rocks and structural features in the area result from sparse vegetation in the dry desert climate and from deep erosion along Warm Spring Canyon and its tributaries.

Earth observation taken by the Expedition 20 crew

NASA Image and Video Library

2009-07-25

ISS020-E-026195 (25 July 2009) --- Aorounga Impact Crater is featured in this image photographed by an Expedition 20 crew member on the International Space Station. Aorounga Impact Crater is located in the Sahara Desert of north-central Chad and is one of the best preserved impact structures in the world. According to scientists, the crater is thought to be middle or upper Devonian to lower Mississippian (approximately 345 ? 370 million years old) based on the age of the sedimentary rocks deformed by the impact. Spaceborne Imaging Radar (SIR) data collected in 1994 suggests that Aorounga is one of a set of three craters formed by the same impact event. The other two suggested impact structures are buried by sand deposits. The concentric ring structure of the Aorounga crater ? renamed Aorounga South in the multiple-crater interpretation of SIR data ? is clearly visible in this detailed photograph. The central highland, or peak, of the crater is surrounded by a small sand-filled trough; this in turn is surrounded by a larger circular trough. Linear rock ridges alternating with light orange sand deposits cross the image from upper left to lower right; these are called yardangs by geomorphologists. Yardangs form by wind erosion of exposed rock layers in a unidirectional wind field. The wind blows from the northeast at Aorounga, and sand dunes formed between the yardangs are actively migrating to the southwest.

Geology of the Devonian black shales of the Appalachian Basin

USGS Publications Warehouse

Roen, J.B.

1984-01-01

Black shales of Devonian age in the Appalachian Basin are a unique rock sequence. The high content of organic matter, which imparts the characteristic lithology, has for years attracted considerable interest in the shales as a possible source of energy. The recent energy shortage prompted the U.S. Department of Energy through the Eastern Gas Shales Project of the Morgantown Energy Technology Center to underwrite a research program to determine the geologic, geochemical, and structural characteristics of the Devonian black shales in order to enhance the recovery of gas from the shales. Geologic studies by Federal and State agencies and academic institutions produced a regional stratigraphic network that correlates the 15 ft black shale sequence in Tennessee with 3000 ft of interbedded black and gray shales in central New York. These studies correlate the classic Devonian black shale sequence in New York with the Ohio Shale of Ohio and Kentucky and the Chattanooga Shale of Tennessee and southwestern Virginia. Biostratigraphic and lithostratigraphic markers in conjunction with gamma-ray logs facilitated long-range correlations within the Appalachian Basin. Basinwide correlations, including the subsurface rocks, provided a basis for determining the areal distribution and thickness of the important black shale units. The organic carbon content of the dark shales generally increases from east to west across the basin and is sufficient to qualify as a hydrocarbon source rock. Significant structural features that involve the black shale and their hydrocarbon potential are the Rome trough, Kentucky River and Irvine-Paint Creek fault zone, and regional decollements and ramp zones. ?? 1984.

Rock-inhabiting fungi originated during periods of dry climate in the late Devonian and middle Triassic.

PubMed

Gueidan, Cécile; Ruibal, Constantino; de Hoog, G S; Schneider, Harald

2011-10-01

Non-lichenized rock-inhabiting fungi (RIF) are slow-growing melanized ascomycetes colonizing rock surfaces in arid environments. They possess adaptations, which allow them to tolerate extreme abiotic conditions, such as high UV radiations and extreme temperatures. They belong to two separate lineages, one consisting in the sister classes Dothideomycetes and Arthoniomycetes (Dothideomyceta), and the other consisting in the order Chaetothyriales (Eurotiomycetes). Because RIF often form early diverging groups in Chaetothyriales and Dothideomyceta, the ancestors of these two lineages were suggested to most likely be rock-inhabitants. The lineage of RIF related to the Chaetothyriales shows a much narrower phylogenetic spectrum than the lineage of RIF related to Dothideomyceta, suggesting a much more ancient origin for the latter. Our study aims at investigating the times of origin of RIF using a relaxed clock model and several fossil and secondary calibrations. Our results show that the RIF in Dothideomyceta evolved in the late Devonian, much earlier than the RIF in Chaetothyriales, which originated in the middle Triassic. The origin of the chaetothyrialean RIF correlates well with a period of recovery after the Permian-Triassic mass extinction and an expansion of arid landmasses. The period preceding the diversification of the RIF related to Dothideomyceta (Silurian--Devonian) is also characterized by large arid landmasses, but temperatures were much cooler than during the Triassic. The paleoclimate record provides a good explanation for the diversification of fungi subjected to abiotic stresses and adapted to life on rock surfaces in nutrient-poor habitats. Copyright © 2011 British Mycological Society. Published by Elsevier Ltd. All rights reserved.

Cyclostratigraphic calibration of the Famennian stage (Late Devonian, Illinois Basin, USA)

NASA Astrophysics Data System (ADS)

Pas, Damien; Hinnov, Linda; Day, James E. (Jed); Kodama, Kenneth; Sinnesael, Matthias; Liu, Wei

2018-04-01

The Late Devonian biosphere was affected by two of the most severe biodiversity crises in Earth's history, the Kellwasser and Hangenberg events near the Frasnian-Famennian (F-F) and the Devonian-Carboniferous (D-C) boundaries, respectively. Current hypotheses for the causes of the Late Devonian extinctions are focused on climate changes and associated ocean anoxia. Testing these hypotheses has been impeded by a lack of sufficient temporal resolution in paleobiological, tectonic and climate proxy records. While there have been recent advances in astronomical calibration that have improved the accuracy of the Frasnian time scale and part of the Famennian, the time duration of the entire Famennian Stage remains poorly constrained. During the Late Devonian, a complete Late Frasnian-Early Carboniferous succession of deep-shelf deposits accumulated in the epieric sea in Illinois Basin of the central North-American mid-continent. A record of this sequence is captured in three overlapping cores (H-30, Sullivan and H-32). The H-30 core section spans the F-F boundary; the Sullivan section spans almost all of the Famennian and the H-32 section sampled spans the interval of the Upper Famennian and the D-C boundary. To have the best chance of capturing Milankovitch cycles, 2000 rock samples were collected at minimum 5-cm-interval across the entire sequence. Magnetic susceptibility (MS) was measured on each sample and the preservation of climatic information into the MS signal was verified through geochemical analyses and low-temperature magnetic susceptibility acquisition. To estimate the duration of the Famennian Stage, we applied multiple spectral techniques and tuned the MS signal using the highly stable 405 kyr cycle for Sullivan and the obliquity cycle for the H-30 and H-32 cores. Based on the correlation between the cores we constructed a Famennian floating astronomical time scale, which indicates a duration of 13.5 ± 0.5 myr. An uncertainty of 0.5 myr was estimated for the uncertainties arising from the errors in the stratigraphic position of the F-F and D-C boundaries, and the 405 kyr cycle counting. Interpolated from the high-resolution U-Pb radiometric ages available for the Devonian-Carboniferous boundary we recalibrated the Frasnian-Famennian boundary numerical age to 372.4 ± 0.9 Ma.

On the fossil faunas of the Upper Devonian: The Genesee section, New York

USGS Publications Warehouse

Williams, Henry Shaler

1887-01-01

I have the honor to transmit herewith for publication as a bulletin a second contribution to the study of Devonian paleontology, Bulletin No. 3, "On the Fossil Faunas of the Upper Devonian," having been designed as the first of a series of papers on the comparative paleontology of the Devonian and Carboniferous.In that paper I gave the results of a study of the section along the meridian of Ithaca and Cayuga Lake, running southward, which may be called the Cayuga section.In 1883 examination was made south along the meridian running through Genesee County, New York, into McKean County, Pennsylvania, where the Alton coal beds were reached. The general results of this survey were communicated to the Director of the United States Geological Survey and an abstract of my communication was published in Science, Vol. II, pp. 836, 837, December 28, 1883. The present paper is a detailed report of the study of the materials of this Genesee section.Since the field work was done several additional sections have been examined: in 1884, sections through Western New York (and adjoining Pennsylvania) from Chautauqua County westward and into Ohio as far as the meridian of Cleveland; and in 1885 the region between the Cayuga section and those of Delaware and Otsego Counties, as far as Oneonta, were examined. The materials are under investigation and will be reported upon as soon as their study is completed.The sections are made along meridians, in order to make them more readily and simply comparable. Each long meridional section runs through the same stratigraphical series of deposits and is made up of a series of small local sections, such as the individual outcrop of the rocks renders possible.It is not supposed that in any case these sections are exhaustive, but it is intended that so far as they go the relative position of the faunas in the sections shall be precise and the association of species in each horizon shall be given as it is, so that the faunas can be identified, and thus, while they will leave much to be added, these studies, it is hoped, will give an outline of the geographical distribution and geological range of faunas and their species which will make a comparative study of the faunas possible.Respectfully yours, HENRY S. WILLIAMS.

Sea-level and environmental changes around the Devonian-Carboniferous boundary in the Namur-Dinant Basin (S Belgium, NE France): A multi-proxy stratigraphic analysis of carbonate ramp archives and its use in regional and interregional correlations

NASA Astrophysics Data System (ADS)

Kumpan, Tomáš; Bábek, Ondřej; Kalvoda, Jiří; Matys Grygar, Tomáš; Frýda, Jiří

2014-08-01

The paper focuses on high-resolution multidisciplinary research on three Devonian-Carboniferous boundary sections in shallow-water carbonate rocks in the Namur-Dinant Basin (Belgium, France). The aim of the study is to provide palaeo-environmental reconstructions and correlations supported by several independent quantitative proxies. We describe several correlative horizons and provide their sequence-stratigraphic interpretation based on facies analysis, spectral gamma-ray data, element concentrations (XRF) and δ13Ccarb, with foraminifer-biostratigraphy age control. The most prominent surface is a basal surface of forced regression, which is indicated by a sharp basinwards facies shift and a drop in clay-gamma-ray values and Al concentrations at the base of the Hastière and Avesnelles formations in more distal settings. In proximal settings, this surface merges with a hiatus at the Devonian-Carboniferous boundary inferred from foraminifer biostratigraphy. This hiatus can be correlated with the global Hangenberg sandstone event, which indicates a glacioeustatic sea-level fall. Increasing values of Zr/Al, K/Al, Sr/Al and Mn/Al coincide with the proximal facies of the falling stage system tract and lowstand system tract in the Hastière and Avesnelles formations as a consequence of the enhanced input of siliciclastics and nutrients during low sea levels. The top of the middle Hastière member is interpreted as the maximum regression surface, which is overlain by transgressive system tract of the upper Hastière member. The patterns of gamma-ray, δ13Ccarb, Th/K, Al and Zr/Al curves are well correlated between the studied sections. The δ13Ccarb excursions are correlated with the unnamed excursion in the Upper expansa conodont zone (Carnic Alps) and with the global Hangenberg event s.l. excursion in the kockeli conodont zone. This sequence-stratigraphic framework is used for correlations with deltaic successions from the Tafilalt Basin, Morocco. The basal surface of the forced regression equivalent to the Hangenberg sandstone event, which is typical for deeper-water settings, is easily recognisable and correlatable with gaps in more-shallow water settings. We suggest that it should be taken into account as a possible candidate for the “natural solution” of the Devonian-Carboniferous boundary in discussions concerning its redefinition.

Assessment of Appalachian basin oil and gas resources: Devonian gas shales of the Devonian Shale-Middle and Upper Paleozoic Total Petroleum System: Chapter G.9 in Coal and petroleum resources in the Appalachian basin: distribution, geologic framework, and geochemical character

USGS Publications Warehouse

Milici, Robert C.; Swezey, Christopher S.; Ruppert, Leslie F.; Ryder, Robert T.

2014-01-01

This report presents the results of a U.S. Geological Survey (USGS) assessment of the technically recoverable undiscovered natural gas resources in Devonian shale in the Appalachian Basin Petroleum Province of the eastern United States. These results are part of the USGS assessment in 2002 of the technically recoverable undiscovered oil and gas resources of the province. This report does not use the results of a 2011 USGS assessment of the Devonian Marcellus Shale because the area considered in the 2011 assessment is much greater than the area of the Marcellus Shale described in this report. The USGS assessment in 2002 was based on the identification of six total petroleum systems, which include strata that range in age from Cambrian to Pennsylvanian. The Devonian gas shales described in this report are within the Devonian Shale-Middle and Upper Paleozoic Total Petroleum System, which extends generally from New York to Tennessee. This total petroleum system is divided into ten assessment units (plays), four of which are classified as conventional and six as continuous. The Devonian shales described in this report make up four of these continuous assessment units. The assessment results are reported as fully risked fractiles (F95, F50, F5, and the mean); the fractiles indicate the probability of recovery of the assessment amount. The products reported are oil, gas, and natural gas liquids. The mean estimates for technically recoverable undiscovered hydrocarbons in the four gas shale assessment units are 12,195.53 billion cubic feet (12.20 trillion cubic feet) of gas and 158.91 million barrels of natural gas liquids

Paleomagnetism of Devonian dykes in the northern Kola Peninsula and its bearing on the apparent polar wander path of Baltica in the Precambrian

NASA Astrophysics Data System (ADS)

Veselovskiy, Roman V.; Bazhenov, Mikhail L.; Arzamastsev, Andrey A.

2016-04-01

Mafic dykes and large alkaline and carbonatite intrusions of Middle-Late Devonian age are widespread on the Kola Peninsula in NE Fennoscandia. These magmatic rocks are well characterized with petrographic, geochemical and geochronological data but no paleomagnetic results have been reported yet. We studied dolerite dykes from the northern part of the Peninsula and isolated three paleomagnetic components in these rocks. A low-temperature component is aligned along the present-day field, while a major constituent of natural remanent magnetization is an intermediate-temperature component (Decl. = 79.6°, Inc. = 78.5°, α95 = 5,9°, N = 17 sites) that is present in most Devonian dykes but is found in some baked metamorphic rocks and Proterozoic dykes too. Finally, a primary Devonian component could be reliably isolated from two dykes only. Rock-magnetic studies point to presumably primary low-Ti titanomagnetite and/or pure magnetite as the main remanence carriers but also reveal alteration of the primary minerals and the formation of new magnetic phases. The directions of a major component differ from the Middle Paleozoic reference data for Baltica but closely match those for the 190 ± 10 Ma interval recalculated from the apparent polar wander path of the craton. We assume that this Early Jurassic component is a low-temperature overprint of chemical origin. The main impact of the new results is not to mid-Paleozoic or Early Mesozoic times but to much older epochs. Analysis of paleomagnetic data shows that the directionally similar remanences are present in objects with the ages ranging from 500 Ma to 2 Ga over entire Fennoscandia. Hence we argue that an Early Jurassic remagnetization is of regional extent but cannot link it to a certain process and a certain tectonic event. If true, this hypothesis necessitates a major revision of the APWP for Baltica over a wide time interval.

Petrophysical, Lithological and Mineralogical Characteristics of the Shale Strata of the Volga- Ural Region

NASA Astrophysics Data System (ADS)

Morozov, Vladimir P.; Plotnikova, Irina N.; Pronin, Nikita V.; Nosova, Fidania F.; Pronina, Nailya R.

2014-05-01

The objects of the study are Upper Devonian carbonate rocks in the territory of South-Tatar arch and Melekess basin in the Volga- Urals region. We studied core material of Domanicoid facies from the sediments of Mendymski and Domanik horizons of middle substage of Frasnian stage of the Upper Devonian. Basic analytical research methods included the following: study of the composition, structural and textural features of the rocks, the structure of their voids, filter and reservoir properties and composition of the fluid. The complex research consisted of macroscopic description of the core material, optical microscopy analysis, radiographical analysis, thermal analysis, x-ray tomography, electron microscopy, gas-liquid chromatography, chromate-mass spectrometry, light hydrocarbons analysis using paraphase assay, adsorbed gases analysis, and thermal vacuum degassing method. In addition, we performed isotopic studies of hydrocarbons saturating shale rocks. Shale strata are mainly represented by carbonate-chert rocks. They consist mainly of calcite and quartz. The ratio of these rock-forming minerals varies widely - from 25 to 75 percent. Pyrite, muscovite, albite, and microcline are the most common inclusions. Calcareous and ferruginous dolomite (ankerite), as well as magnesian calcite are tracked down as secondary minerals. While performing the tests we found out that the walls of open fractures filled with oil are stacked by secondary dolomite, which should be considered as an indication moveable oil presence in the open-cut. Electron microscopy data indicate that all the studied samples have porosity - both carbonates and carbonate-siliceous rocks. Idiomorphism of the rock-forming grains and pores that are visible under a microscope bring us to that conclusion. The analysis of the images indicates that the type of reservoir is either porous or granular. The pores are distributed evenly in the volume of rock. Their size is very unstable and varies from 0.5 microns to 100 microns. The lowest value are observed in long carbonate-siliceous rocks, the highest values are found in carbonate rocks. The latter is caused by the fact that there is a very strong recrystallization of calcite and its dolomite substitution in carbonates. Open porosity ranges from 0.65 to 7.98 percent, average value is 4.1percent . Effective porosity has an average value of 0.44 percent, ranging from 0.22 to 1.97. Permeability varies from 0.043 to 1.49 mD, average value is 0,191 mD. Organic matter was found in all samples. Its content varies within the section. The fluctuation range of from 1.0 to 20 percent. The lowest content of carbonates is found in carbonates, while the highest is observed in carbonate-siliceous rocks with a high content of chalcedony. Average organic matter content is 5-7 percent. According to Rock-Eval studies of the core, the catagenetic maturity of organic matter corresponds to MK1 - MK2 degree. We found a connection between the type of organic matter and the composition of adsorbed gas. We also could see that the samples with humic organics present in their organic matter and can be characterized by a fair dominance of methane over other gases. There is a clear relationship between organic matter content and the intensity of the gas saturation of the rock. Organic matter is characteristic mainly of the most siliceous formations. In "pure" carbonates, which are represented by micro-layers with different capacities, OM is not observed at all or its content is quite low.

Geology and total petroleum systems of the Paradox Basin, Utah, Colorado, New Mexico, and Arizona

USGS Publications Warehouse

Whidden, Katherine J.; Lillis, Paul G.; Anna, Lawrence O.; Pearson, Krystal M.; Dubiel, Russell F.

2014-01-01

The most studied source intervals are the Pennsylvanian black shales that were deposited during relative high stands in an otherwise evaporitic basin. These black shales are the source for most of the discovered hydrocarbons in the Paradox Basin. A second oil type can be traced to either a Mississippian or Permian source rock to the west, and therefore requires long-distance migration to explain its presence in the basin. Upper Cretaceous continental to nearshore-marine sandstones are interbedded with coal beds that have recognized coalbed methane potential. Precambrian and Devonian TPSs are considered hypothetical, as both are known to have organic-rich intervals, but no discovered hydrocarbons have been definitively typed back to either of these units.

Total petroleum systems of the Illizi Province, Algeria and Libya; Tanezzuft-Illizi

USGS Publications Warehouse

Klett, T.R.

2000-01-01

Undiscovered conventional oil and gas resources were assessed within a total petroleum system of the Illizi Province (2056) as part of the U.S. Geological Survey World Petroleum Assessment 2000. The Illizi Province is in eastern Algeria and a small portion of western Libya. The province and its total petroleum system coincide with the Illizi Basin. Although several total petroleum systems may exist within the Illizi Province, only one “composite” total petroleum system is identified. This total petroleum system comprises a single assessment unit. The main source rocks are the Silurian Tanezzuft Formation (or lateral equivalents) and Middle to Upper Devonian mudstone. The total petroleum system was named after the oldest major source rock and the basin in which it resides. The estimated means of the undiscovered conventional petroleum volumes in the Tanezzuft-Illizi Total Petroleum System are 2,814 million barrels of oil (MMBO), 27,785 billion cubic feet of gas (BCFG), and 873 million barrels of natural gas liquids (MMBNGL).

Material composition of the basalt-trachyte series of the early Devonian of the Saralin graben-rift

NASA Astrophysics Data System (ADS)

Grinev, O. M.; Grinev, R. O.; Bogorodov, A. A.; Adylbaev, R. R.

2017-12-01

The article clarifies the structural-tectonic position of the Saralin graben. It is determined that, along with the Balyksinsky graben located to the south and the Goryachegorsky volcanic plateau to the north, they are the connecting structural links between the Kuznetsk-Alatau alkaline province and the adjacent Minusinsk trough. In the early Devonian, the alkaline province was formed as a vaulted-block structure (the “shoulder” of the rift), and the Minusinsk deflection as a depression with the dominant volcanism in it. The boundary between these positive and negative structures was the deep Balyksinsko-Saralinsky fault. In the stratigraphic section of the graben, the lower molassoid part (Ustkundustylskaya stratum), the middle trachybasaltoid stratum (Bazarskay) and the upper problematic Ashpanian stratum are distinguished. In addition to analcime basalts, a large extrusive-subvolcanic dome-shaped construction of trachytes is considered. By petrographic and material composition, volcanites of graben are represented by the dominant basalt-trachyte series in the composition of basanites, trachybasalts, trachyandesites, trachytes. The rocks of the basalt-andesibasalt-andesite series are limited. Foidites are rare. Geochemical data indicate the genetic relationship of the volcanics of the studied series. Geochemically, they are clearly specialized in Sc, Ti, Zn, Zr, Th, U, Mn and P. According to the content of some of these elements, the rocks may have an industrial potential. In geodynamic and genetic plans, graben and its volcanics were formed during plume-tectonic processes involving mantle plume, enriched mantle, and recycling processes of these formations with the substance of the consolidated PR-PZ1 cortex.

Geologic summary of the Appalachian Basin, with reference to the subsurface disposal of radioactive waste solutions

USGS Publications Warehouse

Colton, G.W.

1962-01-01

The Appalachian basin is an elongate depression in the crystalline basement complex< which contains a great volume of predominantly sedimentary stratified rocks. As defined in this paper it extends from the Adirondack Mountains in New York to central Alabama. From east to west it extends from the west flank of the Blue Ridge Mountains to the crest of the Findlay and Cincinnati arches and the Nashville dome. It encompasses an area of about 207,000 square miles, including all of West Virginia and parts of New York, New Jersey, Pennsylvania, Ohio, Maryland, Virginia, Kentucky, Tennessee, North Carolina, Georgia, and Alabama. The stratified rocks that occupy the basin constitute a wedge-shaped mass whose axis of greatest thickness lies close to and parallel to the east edge of the basin. The maximum thickness of stratified rocks preserved in any one part of the basin today is between 35,000 and 40,000 feet. The volume of the sedimentary rocks is approximately 510,000 cubic miles and of volcanic rocks is a few thousand cubic miles. The sedimentary rocks are predominantly Paleozoic in age, whereas the volcanic rocks are predominantly Late Precambrian. On the basis of gross lithology the stratified rocks overlying the crystalline basement complex can be divided into nine vertically sequential units, which are designated 'sequences' in this report. The boundaries between contiguous sequences do not necessarily coincide with the commonly recognized boundaries between systems or series. All sequences are grossly wedge shaped, being thickest along the eastern margin of the basin and thinnest along the western margin. The lowermost unit--the Late Precambrian stratified sequence--is present only along part of the eastern margin of the basin, where it lies unconformably on the basement complex. It consists largely of volcanic tuffs and flows but contains some interbedded sedimentary rocks. The Late Precambrian sequence is overlain by the Early Cambrian clastic sequence. Where the older sequence is absent, the Early Cambrian sequence rests on the basement complex. Interbedded fine- to coarse-grained noncarbonate detrital rocks comprise the bulk of the sequence, but some volcanic and carbonate rocks are included. Next above is the Cambrian-Ordovician carbonate sequence which consists largely of limestone and dolomite. Some quartzose sandstone is present in the lower part in the western half of the basin, and much shale is present in the upper part in the southeast part of the basin. The next higher sequence is the Late Ordovician clastic sequence, which consists largely of shale, siltstone, and sandstone. Coarse-grained light-gray to red rocks are common in the sequence along the eastern side of the basin, whereas fine-grained dark-gray to black calcareous rocks are common along the west side. The Late Ordovician clastic sequence is overlain--unconformably in many places--by the Early Silurian clastic sequence. The latter comprises a relatively thin wedge of coarse-grained clastic rocks. Some of the most prolific oil- and gas-producing sandstones in the Appalachian basin are included. Among these are the 'Clinton' sands of Ohio, the Medina Sandstones of New York and Pennsylvania, and the Keefer or 'Big Six' Sandstone of West Virginia and Kentucky. Conformably overlying the Early Silurian clastic sequence is the Silurian-Devonian carbonate sequence, which consists predominantly of limestone and dolomite. It also contains a salt-bearing unit in the north-central part of the basin and a thick wedge of coarse-grained red beds in the northeastern part. The sequence is absent in much of the southern part of the basin. Large volumes of gas and much oil are obtained from some of its rocks, especially from the Oriskany Sandstone and the Huntersville Chert. The Silurian-Devonian carbonate sequence is abruptly overlain by the Devonian clastic sequence--a thick succession of interbedded shale, mudrock, siltstone, and sandstone. Colors range f

The pre-Mesozoic tectonic unit division of the Xing-Meng orogenic belt (XMOB)

NASA Astrophysics Data System (ADS)

Xu, Bei; Zhao, Pan

2014-05-01

According to the viewpoint that the paleo-Asian ocean closed by the end of early Paleozoic and extended during the late Paleozoic, a pre-Mesozoic tectonic unit division has been suggested. Five blocks and four sutures have been recognized in the pre-Devonia stage, the five blocks are called Erguna (EB), Xing'an (XB), Airgin Sum-Xilinhot (AXB), Songliao-Hunshandak (SHB) and Jiamusi (JB) blocks and four sutures, Xinlin-Xiguitu (XXS), Airgin Sum-Xilinhot-Heihe (AXHS), Ondor Sum-Jizhong-Yanji (OJYS) and Mudanjiang (MS) sutures. The EB contains the Precambrian base with the ages of 720-850Ma and ɛHf(T)=+2.5to +8.1. The XB is characterized by the Paleoproterozoic granitic gneiss with ɛHf(T)=-3.9 to -8.9. Several ages from 1150 to 1500 Ma bave been acquired in the AXB, proving presence of old block that links with Hutag Uul block in Mongolia to the west. The Paleoproterozoic (1.8-1.9Ga) and Neoproterozoic (750-850Ma) ages have been reported from southern and eastern parts of the SHB, respectively. As a small block in east margin of the XMOB, the JB outcrops magmatite and granitic gneiss bases with ages of 800-1000Ma. The XXS is marked by blueschists with zircon ages of 490-500Ma in Toudaoqiao village, ophiolites in Xiguitu County and granite with ages of about 500Ma along the northern segment of XXS. The AXHS is characterized by the early Paleozoic arc magmatic rocks with ages from 430Ma to 490Ma, mélange and the late Devonia molass basins, which indicates a northward subduction of the SHB beneath the AXB during the early-middle Paleozoic. The OJYS is composed of the early Paleozoic volcanic rocks, diorites and granites with ages of 425-475Ma, blueschists, ophiolitic mélange, the late Silurian flysch and Early-Middle Devonian molasses in western segment, granites (420-450Ma) in middle segment, and plagiogranites (443Ma) and the late Silurian molasses in eastern segment. This suture was caused by a southward subduction of the SHB beneath the North China block. The MS is between the SHB and JB, marked by the three phase granites of 485, 450 and 425Ma in the SHB. Tectonic units of the middle Devonian-Carboniferous tectonic stage include the middle-late Devonian continental basin, Carboniferious continental and epeiric sea basin, intrusive and irruptive igneous rock belt with ages from 300Ma to 330Ma containing granites, diorites, gabbros and biomodal volcanic rocks, and early Carboniferious ophiolites of 330-350Ma in Hegenshan and Erenhot. The Permian tectonic units can be divided into continental rift belt, ophiolite belt, alkaline rock belt and "red sea"-like ocean basin, which indicates an continuous extension environment during the Permian. The continental rift belt is composed of thick continental sedimentary rocks containing plant fossils, biomodal volcanic rocks (270-290Ma). The alkaline rocks can be divided into north and south belts by their distribution. The Solonker ophiolite is a thrust sheet that is inserted in a thrust stack containing the Upper Carboniferious epeiric sea clastic rocks and carbornates. The "red sea"-like ocean basin is characterized by basalt sequences with ages of 246-260Ma, which shows an affinity to E-MORB and a tendency towards OIB.

Hydrocarbon potential of Upper Devonian black shale, eastern Kentucky

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnston, I.M.; Frankie, W.T.; Moody, J.R.

The gas-producing Upper Devonian black shales of eastern Kentucky represent cycles of organic units alternating with less-organic units that were dominated by an influx of clastics from a northeastern source. This pattern of sedimentation is typical throughout the southern Appalachian basin in areas basinal to, yet still influenced by, the Catskill delta to the northwest. These black shales, which thin westward onto the Cincinnati arch, dip eastward into the Appalachian basin. To evaluate the future gas potential of Devonian shale, a data base has been compiled, consisting of specific geologic and engineering information from 5920 Devonian shale wells in Letcher,more » Knott, Floyd, Martin, and Pike Counties, Kentucky. The first successful gas completion in eastern Kentucky was drilled in Martin County in 1901. Comparison of initial open-flow potential (IP) and long-term production data for these wells demonstrates that higher IP values generally indicate wells of higher production potential. Areas of higher IP are aligned linearly, and these lineaments are interpreted to be related to fracture systems within the Devonian shale. These fractures may be basement influenced. Temperature log analyses indicate that the greatest number of natural gas shows occur in the lower Huron Member of the Ohio Shale. Using both the temperature log to indicate gas shows and the gamma-ray log to determine the producing unit is a workable method for selecting the interval for treatment.« less

The stratigraphic utility of the trace fossil Pteridichnites biseriatus in the Upper Devonian of eastern West Virginia and western Virginia, USA

USGS Publications Warehouse

McDowell, R.R.; Avary, K.L.; Matchen, D.L.; Britton, J.Q.

2007-01-01

Similar lithologies and lithofacies are present in two Upper Devonian siliciclastic units, the Brallier and Foreknobs formations, in eastern West Virginia and western Virginia, USA. Specimens of an unusual trace fossil, Pteridichnites biseriatus, occur in variable numbers throughout both stratigraphic units. P. biseriatus is present in abundance in the lowermost Brallier and this abundance-zone serves as a local stratigraphic marker for the Brallier. The trace fossil, originally suggested as an indication of polychaete or arthropod locomotion, is herein proposed as the locomotion trace of an unidentified ophiuroid.

Stratigraphic and palaeoenvironmental summary of the south-east Georgia embayment: a correlation of exploratory wells

USGS Publications Warehouse

Poppe, Lawrence J.; Popenoe, Peter; Poag, C. Wylie; Swift, B. Ann

1995-01-01

A Continental Offshore Stratigraphic Test (COST) well and six exploratory wells have been drilled in the south-east Georgia embayment. The oldest rocks penetrated are weakly metamorphosed Lower Ordovician quartz arenites and Silurian shales and argillites in the Transco 1005-1 well and Upper Devonian argillites in the COST GE-1 well. These marine strata, which are equivalent to the Tippecanoe sequence in Florida, underlie the post-rift unconformity and represent part of a disjunct fragment of Gondwana that was sutured to the North American craton during the late Palaeozoic Alleghanian orogeny. The Palaeozoic strata are unconformably overlain by interbedded non-marine Jurassic (Bajocian and younger) sandstones and shales and marginal marine Lower Cretaceous sandstones, calcareous shales and carbonates, which contain scattered beds of coal and evaporite. Together, these rocks are stratigraphically equivalent to the onshore Fort Pierce and Cotton Valley(?) Formations and rocks of the Lower Cretaceous Comanchean Provincial Series. The abundance of carbonates and evaporites in this interval, which reflects marine influences within the embayment, increases upwards, eastwards and southwards. The Upper Cretaceous part of the section is composed mainly of neritic calcareous shales and shaley limestones stratigraphically equivalent to the primarily marginal marine facies of the onshore Atkinson, Cape Fear and Middendorf Formations and Black Creek Group, and to limestones and shales of the Lawson Limestone and Peedee Formations. Cenozoic strata are primarily semiconsolidated marine carbonates. Palaeocene to middle Eocene strata are commonly cherty; middle Miocene to Pliocene strata are massive and locally phosphatic and glauconitic; Quaternary sediments are dominated by unconsolidated carbonate sands. The effects of eustatic changes and shifts in the palaeocirculation are recorded in the Upper Cretaceous and Tertiary strata.

Protolith relations of the Gravina belt and Yukon-Tanana terrane in central southeastern Alaska

DOE Office of Scientific and Technical Information (OSTI.GOV)

McClelland, W.C.; Gehrels, G.E.; Patchett, P.J.

1992-01-01

Metamorphic rocks west of the Coast Mountains batholith in central southeastern Alaska are divided into the Gravina belt, Taku terrane, and newly defined Ruth assemblage. The Ruth assemblage comprises metapelite, quartzose metaclastic strata, quartzite, marble, felsic metatuff, mafic metavolcanic rocks, and orthogneiss. Depositional and emplacement ages of 367 {plus minus} 10 Ma and 345 {plus minus} 13 Ma inferred from discordant U/Pb zircon analyses on felsic metatuff and granodioritic orthogneiss, respectively, require that at least portions of the Ruth assemblage be Late Devonian and early Mississippian in age. The assemblage is similar in age and protolith to, and thus correlatedmore » with, the Yukon-Tanana terrane. The Gravina belt is characterized by upper Jurassic and lower Cretaceous mafic volcanic rocks and tuffaceous turbiditic clastic strata that unconformably overlie the Alexander terrane. Metamorphic rocks that structurally underlie the Taku terrane and Rugh assemblage are included in this assemblage. Trace element geochemistry and the abundance of pyroclastic flows associated with tuffaceous turbidites suggest that the Gravina belt evolved in an intra-arc basinal setting. In central southeastern Alaska, the mid-Cretaceous structure that currently separates the Ruth assemblage (Yukon-Tanana correlative) from the Gravina belt marks the fundamental boundary between the Alexander-Wrangellia terrane and inboard Yukon-Tanana and Stikine terranes.« less

Formation resistivity as an indicator of oil generation in black shales

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hester, T.C.; Schmoker, J.W.

1987-08-01

Black, organic-rich shales of Late Devonian-Early Mississippi age are present in many basins of the North American craton and, where mature, have significant economic importance as hydrocarbon source rocks. Examples drawn from the upper and lower shale members of the Bakken Formation, Williston basin, North Dakota, and the Woodford Shale, Anadarko basin, Oklahoma, demonstrate the utility of formation resistivity as a direct in-situ indicator of oil generation in black shales. With the onset of oil generation, nonconductive hydrocarbons begin to replace conductive pore water, and the resistivity of a given black-shale interval increases from low levels associated with thermal immaturitymore » to values approaching infinity. Crossplots of a thermal-maturity index (R/sub 0/ or TTI) versus formation resistivity define two populations representing immature shales and shales that have generated oil. A resistivity of 35 ohm-m marks the boundary between immature and mature source rocks for each of the three shales studied. Thermal maturity-resistivity crossplots make possible a straightforward determination of thermal maturity at the onset of oil generation, and are sufficiently precise to detect subtle differences in source-rock properties. For example, the threshold of oil generation in the upper Bakken shale occurs at R/sub 0/ = 0.43-0.45% (TTI = 10-12). The threshold increases to R/sub 0/ = 0.48-0.51% (TTI = 20-26) in the lower Bakken shale, and to R/sub 0/ = 0.56-0.57% (TTI = 33-48) in the most resistive Woodford interval.« less

Some contrasting biostratigraphic links between the Baker and Olds Ferry Terranes, eastern Oregon

USGS Publications Warehouse

Nestell, Merlynd K.; Blome, Charles D.

2016-01-01

New stratigraphic and paleontologic data indicate that ophiolitic melange windows in the Olds Ferry terrane of eastern Oregon contain limestone blocks and chert that are somewhat different in age than those present in the adjacent Baker terrane melange. The melange windows in the Olds Ferry terrane occur as inliers in the flyschoid Early and Middle Jurassic age Weatherby Formation, which depositionally overlies the contact between the melange-rich Devonian to Upper Triassic rocks of the Baker terrane on the north, and Upper Triassic and Early Jurassic volcanic arc rocks of the Huntington Formation on the south. The Baker terrane and Huntington Formation represent fragments of a subduction complex and related volcanic island arc, whereas the Weatherby Formation consists of forearc basin sedimentary deposits. The tectonic blocks in the melange windows of the Weatherby Formation (in the Olds Ferry terrane) are dated by scarce biostratigraphic evidence as Upper Pennsylvanian to Lower Permian and Upper Triassic. In contrast, tectonic blocks of limestone in theBaker terrane yield mostly fusulinids and small foraminifers of Middle Pennsylvanian Moscovian age at one locality.Middle Permian (Guadalupian) Tethyan fusulinids and smaller foraminifers (neoschwagerinids and other Middle Permian genera) are present at a few other localities. Late Triassic conodonts and bryozoans are also present in a few of the Baker terrane tectonic blocks. These limestone blocks are generally embedded in Permian and Triassic radiolarian bearing chert or argillite. Based on conodont, radiolarian and fusulinid data, the age limits of the meange blocks in the Weatherby Formation range from Pennsylvanian to Late Triassic.

Pre-lithification tectonic foliation development in a clastic sedimentary sequence

NASA Astrophysics Data System (ADS)

Meere, Patrick; Mulchrone, Kieran; McCarthy, David; Timmermann, Martin; Dewey, John

2016-04-01

The current view regarding the timing of regionally developed penetrative tectonic fabrics in sedimentary rocks is that their development postdates lithification of those rocks. In this case fabric development is achieved by a number of deformation mechanisms including grain rigid body rotation, crystal-plastic deformation and pressure solution (wet diffusion). The latter is believed to be the primary mechanism responsible for shortening and the domainal structure of cleavage development commonly observed in low grade metamorphic rocks. In this study we combine field observations with strain analysis and modelling to fully characterise considerable (>50%) mid-Devonian Acadian crustal shortening in a Devonian clastic sedimentary sequence from south west Ireland. Despite these high levels of shortening and associated penetrative tectonic fabric there is a marked absence of the expected domainal cleavage structure and intra-clast deformation, which are expected with this level of deformation. In contrast to the expected deformation processes associated with conventional cleavage development, fabrics in these rocks are a product of translation, rigid body rotation and repacking of extra-formational clasts during deformation of an un-lithified clastic sedimentary sequence.

Syngenetic Au on the Carlin trend: Implications for Carlin-type deposits

USGS Publications Warehouse

Emsbo, P.; Hutchinson, R.W.; Hofstra, A.H.; Volk, J.A.; Bettles, K.H.; Baschuk, G.J.; Johnson, C.A.

1999-01-01

A new type of gold occurrence recently discovered in the Carlin trend, north-central Nevada, is clearly distinct from classic Carlin-type gold ore. These occurrences are interpreted to be of sedimentary exhalative (sedex) origin because they are stratiform and predate compaction and lithification of their unaltered Devonian host rocks. They contain barite that exhibits ??34S and ??18O values identical to sulfate in Late Devonian seawater and sedex-type barite deposits. Abrupt facies changes in the host rocks strongly suggest synsedimentary faulting and foundering of the carbonate shelf during mineralization, as is characteristic of sedex deposits. Gold occurs both as native inclusions in synsedimentary base-metal sulfides and barite, and as chemical enrichments in sulfide minerals. The absence of alteration and lack of ??13C and ??18O isotopic shift of primary carbonates in these rocks is strong evidence that this gold was not introduced with classic Carlin-type mineralization. Collectively, these features show that the Devonian strata were significantly enriched in gold some 300 m.y. prior to generation of the mid-Tertiary Carlin-type deposits. These strata may have been an important, perhaps even vital, source of gold for the latter. Although gold is typically low in most Zn-Pb-rich sedex deposits, our evidence suggests that transport of gold in basinal fluids, and its subsequent deposition in the sedex environment, can be significant.

In situ FTIR and flash pyrolysis/GC-MS characterization of Protosalvinia (Upper Devonian, Kentucky, USA): Implications for maceral classification

USGS Publications Warehouse

Mastalerz, Maria; Hower, J.C.; Carmo, A.

1998-01-01

Protosalvinia from Devonian rocks in Kentucky has been analyzed using petrographic and in situ FTIR and flash pyrolysis/GC-MS techniques in order to discuss its origin and placement in organic matter classification. In reflected light, Protosalvinia resembles cutinite in shape, color and reflectance, whereas in fluorescent mode it reveals yellow-green fluorescence, reminiscent of alginite. Alkylbenzenes, alkylnaphthalenes, and n-alkanes are the principal compounds in the pyrolyzates, whereas alkylphenols and n-alk-l-enes are present in minor concentrations. FTIR results show that aliphatic bands (both in stretching and bending modes) are prominent. Protosalvinia also reveals well developed aromatic bands in the out-of-plane region. Such a mixture of aliphatic and aromatic components is not known in documented organic matter types of either marine or terrestrial origin. It is suggested that Protosalvinia might belong to rare marine organisms that yield aromatic pyrolyzates. Based on morphological features and optical properties Protosalvinia should be classified as a maceral of the liptinite group. It does not, however, fit precisely within any of the established categories of the liptinite macerals.Protosalvinia from Devonian rocks in Kentucky has been analyzed using petrographic and in situ FTIR and flash pyrolysis/GC-MS techniques in order to discuss its origin and placement in organic matter classification. In reflected light, Protosalvinia resembles cutinite in shape, color and reflectance, whereas in fluorescent mode it reveals yellow-green fluorescence, reminiscent of alginite. Alkylbenzenes, alkylnaphthalenes, and n-alkanes are the principal compounds in the pyrolyzates, whereas alkylphenols and n-alk-l-enes are present in minor concentrations. FTIR results show that aliphatic bands (both in stretching and bending modes) are prominent. Protosalvinia also reveals well developed aromatic bands in the out-of-plane region. Such a mixture of aliphatic and aromatic components is not known in documented organic matter types of either marine or terrestrial origin. It is suggested that Protosalvinia might belong to rare marine organisms that yield aromatic pyrolyzates. Based on morphological features and optical properties Protosalvinia should be classified as a maceral of the liptinite group. It does not, however, fit precisely within any of the established categories of the liptinite macerals.

Petrology, geochemistry and Sm-Nd analyses on the Balkan-Carpathian Ophiolite (BCO - Romania, Serbia, Bulgaria): Remnants of a Devonian back-arc basin in the easternmost part of the Variscan domain

NASA Astrophysics Data System (ADS)

Plissart, Gaëlle; Monnier, Christophe; Diot, Hervé; Mărunţiu, Marcel; Berger, Julien; Triantafyllou, Antoine

2017-04-01

The pre-Alpine basement of the Southern Carpathians/Western Balkans contains four ophiolitic massifs dismembered by Alpine tectonics, which define the ;Balkan-Carpathian Ophiolite; (BCO) for which the tectonic setting and age of formation are still debated (Precambrian or Early Devonian). In this contribution, we demonstrate that, in light of a Pre-Alpine restoration, the four massifs belonged to a unique slice of very complete, obducted oceanic lithosphere and we re-evaluate its tectonic setting. Large chromitite volumes with Al-rich spinel compositions (Cr# = 0.39-0.48), as well as major and trace geochemical results on basalts (slightly enriched N-MORBs with low negative Nb anomaly associated with calk-alkaline BABBs), point to a formation in a back-arc basin. Mantle spinel composition (Cr# = 0.49-0.51) and melting modeling indicate mean melting extents of 8.5-11% favouring intermediate spreading rate. New Sm-Nd dating on lower gabbroic rocks give a whole rock isochron, interpreted as the age of formation of the BCO crust at 409 ± 38 Ma, thus confirming an Early Devonian oceanic crust. The previous ∼563 Ma U-Pb zircon age can be interpreted as casual inheritance indicating the proximity of an old continental lithosphere. Taking into account the lithological evidences and paleocontinental affinities of the two recognized terranes separated by the BC oceanic basin (Balkans and Sredna Gora) and by analogy with other Variscan ophiolites in Western/Central Europe, we suggest that the BC ophiolite belong to the ∼400 Ma ophiolites group obducted between West and East Galatia and belonging to the southern Variscan suture. However, the BC ophiolite is the only one of this group obducted to the north and not involved in the Lower Allochthon/ophiolite/Upper Allochthon thrust pile, likely explaining its exceptional preservation. Finally, we tentatively propose a new unifying tectonic model where different terrane drift rates and highly oblique displacements create two Rheic branches, the ;Rheic; and the ;Galicia-Brittany-Massif Central;.

Textural and Rb-Sr isotopic evidence for late Paleozoic mylonitization within the Honey Hill fault zone southeastern Connecticut

DOE Office of Scientific and Technical Information (OSTI.GOV)

O'Hara, K.D.; Gromet, L.P.

A petrographic and Rb-Sr isotopic study of rocks within and near the Honey Hill fault zone places important constraints on its history of movement. Rb-Sr apparent ages for micas and plagioclase from these rocks have been reset and range from Permian to Triassic, considerably younger than the minimum stratigraphic age (Ordovician) of the rocks studied or of Acadian (Devonian) regional metamorphism. Permian Rb-Sr ages of dynamically recrystallized muscovite date the development of mylonite fabric. An older age is precluded by the excellent preservation of unrecovered quartz, which indicates that these rocks did not experience temperatures high enough to anneal quartzmore » or thermally reset Rb-Sr isotopic systems in muscovite since the time of mylonitization. Metamorphic mineral assemblages and mineral apparent ages in rocks north of the fault zone indicate recrystallization under similar upper greenschist-lower amphibolite grade conditions during Permian to Triassic time. Collectively these results indicate that the Honey Hill fault zone was active during the Late Paleozoic and that ductile deformation and metamorphism associated with the Alleghanian orogeny extend well into southern Connecticut. An Alleghanian age for mylonitization within the Honey Hill fault zone suggests it should be considered as a possible site for the major Late Paleozoic strike-slip displacements inferred from paleomagnetic studies for parts of coastal New England and maritime Canada.« less

Paleozoic carbonate buildup (reef) inventory, central and southeastern Idaho

DOE Office of Scientific and Technical Information (OSTI.GOV)

Isaacson, P.E.

1987-08-01

Knowledge of central and southeastern Idaho's Paleozoic rocks to date suggest that three styles of buildup (reef) complexes occur in Late Devonian, Mississippian, and Pennsylvanian-Permian time. The Late Devonian Jefferson Formation has stromatoporoid and coral (both rugosan and tabulate) organisms effecting a buildup in the Grandview Canyon vicinity; Early Mississippian Waulsortian-type mud mounds occur in the Lodgepole formation of southeastern Idaho; there are Late Mississippian Waulsortian-type mounds in the Surrett Canyon Formation of the Lost River Range; and cyclic Pennsylvanian-Permian algal and hydrozoan buildups occur in the Juniper gulch Member of the Snaky Canyon Formation in the Arco Hills andmore » Lemhi Range. Late Devonian (Frasnian) carbonates of the Jefferson formation show buildup development on deep ramp sediments.« less

Metals in Devonian kerogenous marine strata at Gibellini and Bisoni properties in southern Fish Creek Range, Eureka County, Nevada

USGS Publications Warehouse

Desborough, George A.; Poole, F.G.; Hose, R.K.; Radtke, A.S.

1979-01-01

A kerogen-rich sequence of siliceous mudstone, siltstone, and chert as much as 60 m thick on ridge 7129 in the southern Fish Creek Range, referred to as Gibellini facies of the Woodruff Formation, has been evaluated on the surface and in drill holes principally for its potential resources of vanadium, zinc, selenium, molybdenum, and syncrude oil content. The strata are part of a strongly deformed allochthonous mass of eugeosynclinal Devonian marine rocks that overlie deformed allochthonous Mississippian siliceous rocks and relatively undeformed autochthonous Mississippian Antler flysch at this locality. The vanadium in fresh black rocks obtained from drill holes and fresh exposures in trenches and roadcuts occurs chiefly in organic matter. Concentrations of vanadium oxide (V2O5) in unoxidized samples range from 3,000 to 7,000 ppm. In oxidized and bleached rock that is prevalent at the surface, concentrations of vanadium oxide range from 6,000 to 8,000 ppm, suggesting a tendency toward enrichment due to surficial weathering and ground-water movement. Zinc occurs in sphalerite, and selenium occurs in organic matter; molybdenum appears to occur both in molybdenite and in organic matter. Concentrations of zinc in unoxidized rock range from 4,000 to 18,000 ppm, whereas in oxidized rock they range from 30 to 100 ppm, showing strong depletion due to weathering. Concentrations of selenium in unoxidized rock range from 30 to 200 ppm, whereas in oxidized rock they range from 200 to 400 ppm, indicating some enrichment upon weathering. Concentrations of molybdenum in unoxidized rock range from 70 to 960 ppm, whereas in oxidized rock they range from 30 to 80 ppm, indicating strong depletion upon weathering. Most fresh black rock is low-grade oil shale, and yields as much as 12 gallons/short ton of syncrude oil. Metahewettite is the principal vanadium mineral in the oxidized zone, but it also occurs sparsely as small nodules and fillings of microfractures in unweathered strata. In fresh rock, bluish-white opaline-like silica (chalcedonic quartz) fills microfractures, and is believed to have originated by diagenetic mobilization of opaline silica from radiolarian tests and sponge spicules. As revealed by microscopic study, the Gibellini facies originally consisted of siliceous muds, slimes, and oozes high in organic constituents. The organic matter is amorphous flaky and stringy sapropel, and probably includes remains of bacteria, phytoplankton, zooplankton, and minor higher plants. Recognizable organic remnants include radiolarian tests, sponge spicules, conodonts, brachiopod shells, algae, and humic debris. Diagnostic radiolarians indicate a Late Devonian age for the Gibellini facies of the Woodruff Formation. Some pyrite is disseminated through the rock and may be primary (syngenetic) but significant pyrite and marcasite occur in chalcedonic quartz veinlets and appear to be diagenetic. In fresh rock, black solid bitumen and liquid oil fill voids and microfractures. These early phase hydrocarbons probably were released during diagenesis from complex nonhydrocarbon molecular structures originating from living organisms, and formed without any major thermal degradation of the kerogen. Gas chromatographic analysis of the saturated hydrocarbon fraction indicates a very complex mixture dominated by branched and cyclic compounds. Conodont and palynomorph color alteration, vitrinite reflectance, and other organic geochemical data suggest that the organic matter in the rock is thermally immature and has not been subjected to temperatures greater than 60?C since deposition in Devonian time. All of these characteristics are consistent with the interpretation of a relatively low temperature and a shallow-burial history for the Gibellini facies on ridge 7129.

Concordant paleolatitudes for Neoproterozoic ophiolitic rocks of the Trinity Complex, Klamath Mountains, California

USGS Publications Warehouse

Mankinen, E.A.; Lindsley-Griffin, N.; Griffin, J.R.

2002-01-01

New paleomagnetic results from the eastern Klamath Mountains of northern California show that Neoproterozoic rocks of the Trinity ophiolitic complex and overlying Middle Devonian volcanic rocks are latitudinally concordant with cratonal North America. Combining paleomagnetic data with regional geologic and faunal evidence suggests that the Trinity Complex and related terranes of the eastern Klamath plate were linked in some fashion to the North American craton throughout that time, but that distance between them may have varied considerably. A possible model that is consistent with our paleomagnetic results and the geologic evidence is that the Trinity Complex formed and migrated parallel to paleolatitude in the basin between Laurasia and Australia-East Antarctica as the Rodinian supercontinent began to break up. It then continued to move parallel to paleolatitude at least through Middle Devonian time. Although the eastern Klamath plate served as a nucleus against which more western components of the Klamath Mountains province amalgamated, the Klamath superterrane was not accreted to North America until Early Cretaceous time.

The Fossil Fauna of the Islands Region of Western Lake Erie.

ERIC Educational Resources Information Center

Bowe, Lulu M., Comp.

The islands of western Lake Erie are rock-bound isles that abound in rocky outcrops and quarries. The rocks of these islands are of two distinct types, Silurian dolomites and Devonian limestones. The dolomites, exposed in the Bass Islands and Sister Islands are virtually devoid of fossils. Conversely, the limestones of Johnson Island, Marblehead,…

Geology of quadrangles H-12, H-13, and parts of I-12 and I-13, (zone III) in northeastern Santander Department, Colombia

USGS Publications Warehouse

Ward, Dwight Edward; Goldsmith, Richard; Cruz, Jaime B.; Restrepo, Hernan A.

1974-01-01

A program of geologic mapping and mineral investigation in Colombia was undertaken cooperatively by the Colombian Instituto Nacional de Investigaciones Geologico-Mineras (formerly known as the Inventario Minero Nacional), and the U. S. Geological Survey; by the Government of Colombia and the Agency for International Development, U. S. Department of State. The purpose was to study, and evaluate mineral resources (excluding of petroleum, coal, emeralds, and alluvial gold) of four selected areas, designated Zones I to IV, that total about 70,000 km2. The work in Zone III, in the Cordillera Oriental, was done from 1965 to 1968. The northeast trend of the Cordillera Oriental of Colombia swings abruptly to north-northwest in the area of this report, and divides around the southern end of the Maracaibo Basin. This section of the Cordillera Oriental is referred to as the Santander Massif. Radiometric age determinations indicate that the oldest rocks of the Santander massif are Precambrian and include high-grade gneiss, schist, and migmatite of the Bucaramanga Formation. These rocks were probably part of the Precambrian Guayana Shield. Low- to medium-grade metamorphic rocks of late Precambrian to Ordovician age .include phyllite, schist, metasiltstone, metasandstone, and marble of the Silgara Formation, a geosynclinal series of considerable extent in the Cordillera Oriental and possibly the Cordillera de Merida of Venezuela. Orthogneiss ranging from granite to tonalite is widely distributed in the high- and medium-grade metamorphic rocks of the central core of the massif and probably represents rocks of two ages, Precambrian and Ordovician to Early Devonian. Younger orthogneiss and the Silgara are overlain by Middle Devonian beds of the Floresta Formation which show a generally low but varying degree of metamorphism. Phyllite and argillite are common, and infrequent marble and other calcareous beds are fossiliferous. Except for recrystallization in limestones of !the Permian-Carboniferous Diamante Formation, sedimentary rocks younger than Devonian are unmetamorphosed. The effects of Precambrian regional dynamothermal metamorphism and plutonism on Precambrian geosynclinal deposits reached the upper amphibolite facies in the Bucaramanga Gneiss. The geosynclinal Silgara Formation was subjected to similar conditions in Late Ordovician and Early Silurian time but reached only the greenschist or lower amphibolite facies. Orthogneisses generally show a concordance of foliation and lineation with the neighboring Silgara Formation and the Bucaramanga Gneiss as well as similarities in grade of metamorphism. Regional dynamothermal metamorphism in Late Permian and Triassic time reached, low grade in the Floresta Formation and caused recrystallization of limestone of the Diamante Formation. The Bucaramanga and Silgara metamorphic rocks show evidence of metrogressive metamorphism accompanied by high activity or potassium and water, but whether this occurred at the time the Floresta was metamorphosed or later is not clear. Batholiths, plutons, and stocks of igneous rocks in the Santander massif range from diorite to granite. Radioactive age data indicate that most belong to a single plutonic interval. These are referred to as the Santander Plutoniq Group and are Jurassic and Jurassic-Triassic- Two suites of this group are pink granite and quartz monzonite, and gray quartz monzonite and granodiorite. Contact relations indicate that the pink and more granitic rocks are younger than the gray and more mafic rocks, but radioactive age data are in conflict with this. Undated plutonic rocks that are not clearly related to the group are assigned to relatively older or younger age positions. West of the Bucanamanga fault rhyolite makes up a small body at one locality and forms an intrusive sheet with granophyre and intrusive breccias in Triassic sedimentary rocks at another locality. Its age is unknown, but it probably is younger than the

Timing and pacing of the Late Devonian mass extinction event regulated by eccentricity and obliquity.

PubMed

De Vleeschouwer, David; Da Silva, Anne-Christine; Sinnesael, Matthias; Chen, Daizhao; Day, James E; Whalen, Michael T; Guo, Zenghui; Claeys, Philippe

2017-12-22

The Late Devonian envelops one of Earth's big five mass extinction events at the Frasnian-Famennian boundary (374 Ma). Environmental change across the extinction severely affected Devonian reef-builders, besides many other forms of marine life. Yet, cause-and-effect chains leading to the extinction remain poorly constrained as Late Devonian stratigraphy is poorly resolved, compared to younger cataclysmic intervals. In this study we present a global orbitally calibrated chronology across this momentous interval, applying cyclostratigraphic techniques. Our timescale stipulates that 600 kyr separate the lower and upper Kellwasser positive δ 13 C excursions. The latter excursion is paced by obliquity and is therein similar to Mesozoic intervals of environmental upheaval, like the Cretaceous Ocean-Anoxic-Event-2 (OAE-2). This obliquity signature implies coincidence with a minimum of the 2.4 Myr eccentricity cycle, during which obliquity prevails over precession, and highlights the decisive role of astronomically forced "Milankovitch" climate change in timing and pacing the Late Devonian mass extinction.

Devonian-Carboniferous boundary succession in Eastern Taurides, Turkey

NASA Astrophysics Data System (ADS)

Atakul-Özdemir, Ayşe; Altıner, Demir; Özkan-Altıner, Sevinç

2015-04-01

The succession covering the Devonian-Carboniferous boundary in Eastern Taurides comprises mainly limestones, shales and siltstones. The studied section starts at the base with bioturbated limestones alternating with shales and is followed upwards by platy limestones, and continues with the alternations of bioturbated and platy limestones. Towards the upper part of the succession the alternations of limestone, shales and siltstones reappear again and the top of the section is capped by quartz arenitic sandstone. The studied section spanning the Uppermost Devonian-Lower Carboniferous interval yields a not very abundant, but quite important assemblage of conodont taxa including species of Bispathodus, Polygnathus, Palmatolepis, Spathognathodus and Vogelgnathus. The uppermost Devonian part of the succession is characterized by the presence of Bispathodus costatus, Bispathodus aculeatus aculeatus, Polygnathus communis communis, Palmatolepis gracilis gracilis and Spathognathodus sp.. The Lower Carboniferous in the studied section is represented by the appearance of Polygnathus inornatus and Polygnathus communis communis. Based on the recovered conodont assemblages, Devonian-Carboniferous boundary in Eastern Turides has been determined by the appearance and disappearance of major conodont species.

Fluid evolution during burial and Variscan deformation in the Lower Devonian rocks of the High-Ardenne slate belt (Belgium): sources and causes of high-salinity and C-O-H-N fluids

NASA Astrophysics Data System (ADS)

Kenis, I.; Muchez, Ph.; Verhaert, G.; Boyce, A.; Sintubin, M.

2005-08-01

Fluid inclusions in quartz veins of the High-Ardenne slate belt have preserved remnants of prograde and retrograde metamorphic fluids. These fluids were examined by petrography, microthermometry and Raman analysis to define the chemical and spatial evolution of the fluids that circulated through the metamorphic area of the High-Ardenne slate belt. The earliest fluid type was a mixed aqueous/gaseous fluid (H2O-NaCl-CO2-(CH4-N2)) occurring in growth zones and as isolated fluid inclusions in both the epizonal and anchizonal part of the metamorphic area. In the central part of the metamorphic area (epizone), in addition to this mixed aqueous/gaseous fluid, primary and isolated fluid inclusions are also filled with a purely gaseous fluid (CO2-N2-CH4). During the Variscan orogeny, the chemical composition of gaseous fluids circulating through the Lower Devonian rocks in the epizonal part of the slate belt, evolved from an earlier CO2-CH4-N2 composition to a later composition enriched in N2. Finally, a late, Variscan aqueous fluid system with a H2O-NaCl composition migrated through the Lower Devonian rocks. This latest type of fluid can be observed in and outside the epizonal metamorphic part of the High-Ardenne slate belt. The chemical composition of the fluids throughout the metamorphic area, shows a direct correlation with the metamorphic grade of the host rock. In general, the proportion of non-polar species (i.e. CO2, CH4, N2) with respect to water and the proportion of non-polar species other than CO2 increase with increasing metamorphic grade within the slate belt. In addition to this spatial evolution of the fluids, the temporal evolution of the gaseous fluids is indicative for a gradual maturation due to metamorphism in the central part of the basin. In addition to the maturity of the metamorphic fluids, the salinity of the aqueous fluids also shows a link with the metamorphic grade of the host-rock. For the earliest and latest fluid inclusions in the anchizonal part of the High-Ardenne slate belt the salinity varies respectively between 0 and 3.5 eq.wt% NaCl and between 0 and 2.7 eq.wt% NaCl, while in the epizonal part the salinity varies between 0.6 and 17 eq.wt% NaCl and between 3 and 10.6 eq.wt% for the earliest and latest aqueous fluid inclusions, respectively. Although high salinity fluids are often attributed to the original sedimentary setting, the increasing salinity of the fluids that circulated through the Lower Devonian rocks in the High-Ardenne slate belt can be directly attributed to regional metamorphism. More specifically the salinity of the primary fluid inclusions is related to hydrolysis reactions of Cl-bearing minerals during prograde metamorphism, while the salinity of the secondary fluid inclusions is rather related to hydration reactions during retrograde metamorphism. The temporal and spatial distribution of the fluids in the High-Ardenne slate belt are indicative for a closed fluid flow system present in the Lower Devonian rocks during burial and Variscan deformation, where fluids were in thermal and chemical equilibrium with the host rock. Such a closed fluid flow system is confirmed by stable isotope study of the veins and their adjacent host rock for which uniform δ180 values of both the veins and their host rock demonstrate a rock-buffered fluid flow system.

Bedrock geology of the Mount Carmel and Southington quadrangles, Connecticut

USGS Publications Warehouse

Fritts, Crawford Ellswroth

1962-01-01

New data concerning the geologic structure, stratigraphy, petrography, origin, and ages of bedrock formations in an area of approximately 111 square miles in south-central Connecticut were obtained in the course of detailed geologic mapping from 1957 to 1960. Mapping was done at a scale of 1:24,000 on topographic base maps having a 10-foot contour interval. Bedrock formations are classified in two principal categories. The first includes metasedimentary, meta-igneous, and igneous rocks of Precambrian to Devonian age, which crop out in the western parts of both quadrangles. The second includes sedimentary and igneous rocks of the Newark Group of Late Triassic age, which crop out in the eastern parts of the quadrangles. Diabase dikes, which are Late Triassic or younger in age, intruded rocks in both the western and eastern parts of the map area. Rocks in the western part of the area underwent progressive regional metamorphism in Middle to Late Devonian time. The arrangement of the chlorite, garnet, biotite, staurolite, and kyanite zones here is approximately the mirror-image of metamorphic zones in Dutchess County, New York. However, garnet appeared before biotite in politic rocks in the map area, because the ration MgO/FeO is low. Waterbury Gneiss and the intrusive Woodtick Gneiss are parts of a basement complex of Precambrian age, which forms the core of the Waterbury dome. This structure is near the southern end of a line of similar domes that lie along the crest of a geanticline east of the Green Mountain anticlinorium. The Waterbury Gneiss is believed to have been metamorphosed in Precambrian time as well as in Paleozoic time. The Woodtick Gneiss also may have been metamorphosed more than once. In Paleozoic time, sediments were deposited in geosynclines during two main cycles of sedimentation. The Straits, Southington Mountain, and Derby Hill Schists, which range in age from Cambrian to Ordovician, reflect a transition from relatively clean politic sediments to thinly layered sediments that contained rather high percentages of fine-grained volcanic debris. Metadiabase and metabasalt extrusives above Derby Hill Schist south of the map area represent more intense volcanic activity before or during the early stages of the Taconic disturbance in Late Ordovician time. Impure argillaceous, siliceous, and minor calcareous sediments of the Wepawaug Schist, which is Silurian and Devonian in age, were deposited unconformably on older rocks during renewed subsidence of a geosyncline. The Wepawaug now occupies the trough of a tight syncline, which formed before and during progressive regional metamorphism at the time of the Acadian orogeny in middle to Late Devonian time. Felsic igneous rocks were intruded into the metasedimentary formations of Paleozoic age before the climax of the latest progressive regional metamorphism. Intrusives that gave rise to the Prospect and Ansonia Gneisses were emplaced mainly in the Southington Mountain Schist, and the igneous rocks as well as the host rocks were metamorphosed in the staurolite zone. Although it is possible that these two intrusives were emplaced during the Taconic disturbance, the writer believes it more likely that the igneous rocks from which the Prospect and Ansonia Gneisses formed were emplaced during the Acadian orogeny. Woodbridge Granite, which intruded the Wepawaug Schist, is Devonian in age and undoubtedly was emplaced during the Acadian orogeny. In this area the granite is essentially unmetamorphosed, because it is in the chlorite, garnet, and biotite zones. Southwest of the map area, however, metamorphic equivalents of the Woodbridge are found in Wepawaug Schist in the staurolite zone. The Ansonia Gneiss, therefore, may be a metamorphic equivalent of the Woodbridge Granite. Rocks of Late Triassic age formerly covered the entire map area, but were eroded from the western part after tilting and faulting in Late Triassic time. The New Haven Arkose of the Newark

Reported middle Paleozoic fossils and new geochronological data from the southern and central Appalachians: Disposable outrageous hypothesis or justification for major revision of tectonic history

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hatcher, R.D. Jr.

Recently published interpretations of fossil fragments from the Walden Creek Group (Ocoee Supergroup) suggesting that these rocks are middle Paleozoic (Devonian to Early Carboniferous), and new geochronological data that yield late Paleozoic age dates on rocks and major faults in the Blue Ridge and piedmont, if taken alone, would permit speculation that most of the deformation and metamorphism affecting this part of the orogen is Alleghanian. The two Ordovician clastic wedges (Sevier, Llanvirn, and Martinsburg, Caradoc-Ashgill) and the Carboniferous-Permian wedge(s), along with many radiometric ages on plutons, indicate uplift and sediment dispersal from the interior of the southern and centralmore » Appalachians (SCA) that may have resulted from Taconian and Alleghanian deformation. Combining the reproducible fossil evidence, including that from Alabama and a recently discovered crinoid fragment from the upper part of the Murphy belt sequence, with the most current geochronological data requires that peak metamorphism and penetrative deformation be at least Devonian or younger at the southwestern end of the orogen, and Late Ordovician or younger in the Carolinas and northern Georgia. Zircon ages reported from large thrust and dextral strike-slip faults bounding the Pine Mountain window indicate all of the faults there may be Alleghanian, except the younger sinistral Mesozoic faults, and requires that both metamorphism and penetrative deformation there also be Alleghanian. As in New England, the southern Appalachian Alleghanian metamorphic core is now known to be much more extensive. The older data require that the Taconian and perhaps the Acadian orogenies were significant events in the SCA, but these new data reconfirm the dominance of Alleghanian continent-continent collision processes here.« less

Unconventional shallow biogenic gas systems

USGS Publications Warehouse

Shurr, G.W.; Ridgley, J.L.

2002-01-01

Unconventional shallow biogenic gas falls into two distinct systems that have different attributes. Early-generation systems have blanketlike geometries, and gas generation begins soon after deposition of reservoir and source rocks. Late-generation systems have ringlike geometries, and long time intervals separate deposition of reservoir and source rocks from gas generation. For both types of systems, the gas is dominantly methane and is associated with source rocks that are not thermally mature. Early-generation biogenic gas systems are typified by production from low-permeability Cretaceous rocks in the northern Great Plains of Alberta, Saskatchewan, and Montana. The main area of production is on the southeastern margin of the Alberta basin and the northwestern margin of the Williston basin. The huge volume of Cretaceous rocks has a generalized regional pattern of thick, non-marine, coarse clastics to the west and thinner, finer grained marine lithologies to the east. Reservoir rocks in the lower part tend to be finer grained and have lower porosity and permeability than those in the upper part. Similarly, source beds in the units have higher values of total organic carbon. Patterns of erosion, deposition, deformation, and production in both the upper and lower units are related to the geometry of lineament-bounded basement blocks. Geochemical studies show that gas and coproduced water are in equilibrium and that the fluids are relatively old, namely, as much as 66 Ma. Other examples of early-generation systems include Cretaceous clastic reservoirs on the southwestern margin of Williston basin and chalks on the eastern margin of the Denver basin. Late-generation biogenic gas systems have as an archetype the Devonian Antrim Shale on the northern margin of the Michigan basin. Reservoir rocks are fractured, organic-rich black shales that also serve as source rocks. Although fractures are important for production, the relationships to specific geologic structures are not clear. Large quantities of water are coproduced with the gas, and geochemical data indicate that the water is fairly fresh and relatively young. Current thinking holds that biogenic gas was generated, and perhaps continues to be, when glacial meltwater descended into the plumbing system provided by fractures. Other examples of late-generation systems include the Devonian New Albany Shale on the eastern margin of the Illinois basin and the Tertiary coalbed methane production on the northwestern margin of the Powder River basin. Both types of biogenic gas systems have a similar resource development history. Initially, little technology is used, and gas is consumed locally; eventually, sweet spots are exploited, widespread unconventional reservoirs are developed, and transport of gas is interstate or international. However, drilling and completion techniques are very different between the two types of systems. Early-generation systems have water-sensitive reservoir rocks, and consequently water is avoided or minimized in drilling and completion. In contrast, water is an important constituent of late-generation systems; gas production is closely tied to dewatering the system during production. Existing production and resource estimates generally range from 10 to 100 tcf for both types of biogenic gas systems. Although both system types are examples of relatively continuous accumulations, the geologic frameworks constrain most-economic production to large geologic structures on the margins of basins. Shallow biogenic gas systems hold important resources to meet the increased domestic and international demands for natural gas.

Geologic map of the White Hall quadrangle, Frederick County, Virginia, and Berkeley County, West Virginia

USGS Publications Warehouse

Doctor, Daniel H.; Orndorff, Randall C.; Parker, Ronald A.; Weary, David J.; Repetski, John E.

2010-01-01

The White Hall 7.5-minute quadrangle is located within the Valley and Ridge province of northern Virginia and the eastern panhandle of West Virginia. The quadrangle is one of several being mapped to investigate the geologic framework and groundwater resources of Frederick County, Va., as well as other areas in the northern Shenandoah Valley of Virginia and West Virginia. All exposed bedrock outcrops are clastic and carbonate strata of Paleozoic age ranging from Middle Cambrian to Late Devonian. Surficial materials include unconsolidated alluvium, colluvium, and terrace deposits of Quaternary age, and local paleo-terrace deposits possibly of Tertiary age. The quadrangle lies across the northeast plunge of the Great North Mountain anticlinorium and includes several other regional folds. The North Mountain fault zone cuts through the eastern part of the quadrangle; it is a series of thrust faults generally oriented northeast-southwest that separate the Silurian and Devonian clastic rocks from the Cambrian and Ordovician carbonate rocks and shales. Karst development in the quadrangle occurs in all of the carbonate rocks. Springs occur mainly near or on faults. Sinkholes occur within all of the carbonate rock units, especially where the rocks have undergone locally intensified deformation through folding, faulting, or some combination.

Hydrogeology and simulation of ground-water flow in the Silurian-Devonian aquifer system, Johnson County, Iowa

USGS Publications Warehouse

Tucci, Patrick; McKay, Robert M.

2006-01-01

The greatest limitation to the model is the lack of measured or estimated water-budget components for comparison to simulated water-budget components. Because the model is only calibrated to measured water levels, and not to water-budget components, the model results are nonunique. Other model limitations include the relatively coarse grid scale, lack of detailed information on pumpage from the quarry and from private developments and domestic wells, and the lack of separate water-level data for the Silurian- and Devonian-age rocks.

Sedimentology and stratigraphy of the Kanayut Conglomerate, central and western Brooks Range, Alaska; report of 1981 field season

USGS Publications Warehouse

Nilsen, T.H.; Moore, T.E.

1982-01-01

The Upper Devonian and Lower Mississippian(?) Kanayut Conglomerate forms a major stratigraphic unit along the crest of the Brooks Range of northern Alaska. It crops out for an east-west distance of about 900 km and a north-south distance of about 65 km. The Kanayut is wholly allochthonous and has probably been transported northward on a series of thrust plates. The Kanayut is as thick as 2,600 m in the east-central Brooks Range. It thins and fines to the south and west. The Kanayut forms the middle part of the allochthonous sequence of the Endicott Group, an Upper Devonian and Mississippian clastic sequence underlain by platform limestones of the Baird Group and overlain by platform limestone, carbonaceous shale, and black chert of the Lisburne Group. The Kanayut overlies the marine Upper Devonian Noatak Sandstone or, where it is missing, the marine Upper Devonian Hunt Fork Shale. It is overlain by the marine Mississippian Kayak Shale. The Kanayut Conglomerate forms the fluvial part of a large, coarse-grained delta that prograded to the southwest in Late Devonian time and retreated in Early Mississippian time. Four sections of the Kanayut Conglomerate in the central Brooks Range and five in the western Brooks Range were measured in 1981. The sections from the western Brooks Range document the presence of fluvial cycles in the Kanayut as far west as the shores of the Chukchi Sea. The Kanayut in this area is generally finer grained than it is in the central and eastern Brooks Range, having a maximum clast size of 3 cm. It is probably about 300 m thick. The upper and lower contacts of the Kanayut are gradational. The lower Kanayut contains calcareous, marine-influenced sandstone within channel deposits, and the upper Kanayut contains probable marine interdistributary-bay shale sequences. The members of the Kanayut Conglomerate cannot be differentiated in this region. In the central Brooks Range, sections of the Kanayut Conglomerate at Siavlat Mountain and Kakivilak Creek are typically organized into fining-upward fluvial cycles. The maximum clast size is about 3 cm in this area. The Kanayut in this region is 200-500 m thick and can be divided into the Ear Peak, Shainin Lake, and Stuver Members. The upper contact of the Kanayut with the Kayak Shale is very gradational at Kakivilak Creek and very abrupt at Siavlat Mountain. Paleocurrents from fluvial strata of the Kanayut indicate sediment transport toward the west and south in both the western and central Brooks Range. The maximum clast size distribution generally indicates westward fining from the Shainin Lake region.

Assessment of Undiscovered Technically Recoverable Oil and Gas Resources of the Bakken Formation, Williston Basin, Montana and North Dakota, 2008

USGS Publications Warehouse

Pollastro, R.M.; Roberts, L.N.R.; Cook, T.A.; Lewan, M.D.

2008-01-01

The U.S. Geological Survey (USGS) has completed an assessment of the undiscovered oil and associated gas resources of the Upper Devonian to Lower Mississippian Bakken Formation in the U.S. portion of the Williston Basin of Montana and North Dakota and within the Williston Basin Province. The assessment is based on geologic elements of a total petroleum system (TPS), which include (1) source-rock distribution, thickness, organic richness, maturation, petroleum generation, and migration; (2) reservoir-rock type (conventional or continuous), distribution, and quality; and (3) character of traps and time of formation with respect to petroleum generation and migration. Framework studies in stratigraphy and structural geology and modeling of petroleum geochemistry, combined with historical exploration and production analyses, were used to estimate the undiscovered, technically recoverable oil resource of the Bakken Formation. Using this framework, the USGS defined a Bakken-Lodgepole TPS and seven assessment units (AU) within the system. For the Bakken Formation, the undiscovered oil and associated gas resources were quantitatively estimated for six of these AUs.

Mid to late Devonian back-arc rift basins in the Brooks Range, AK, and across the Arctic: a possible paleogeographic piercing point for Arctic reconstructions

NASA Astrophysics Data System (ADS)

Hoiland, C. W.; Miller, E. L.; Hourigan, J. K.

2013-12-01

The westernmost Brooks Range, Alaska, is underlain by basement of probable Baltic or Timanian affinity (e.g. Miller et al., 2011; Amato et al., 2009), while the eastern Brooks Range is underlain by Laurentian affinity basement (e.g. Strauss et al., 2013). A post-Timanian and pre-Mississippian suture or contact is thus required based on continuity of late Devonian and younger strata across the Brooks Range (e.g. Dumoulin et al., 2002). This inferred juxtaposition has been proposed as the distal and diachronous (though possibly non-collisional) continuation of the Caledonian orogen (e.g. Moore et al., 2012) but the actual location and character of this suture within basement rocks of the Brooks Range remain speculative. New laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb single grain detrital zircon (DZ) geochronology of basement rocks from the Cosmos Hills, Slate Creek, and Wiseman regions suggest that metamorphic rocks in these regions are Devonian, not pre-Devonian. New SHRIMP-RG analyses of the Kogoluktuk orthogneiss (Cosmos) (zircon: 383 Ma × 5 Ma, 2-sigma errors, consistent with Dillon et al. 1980) revealed no inherited cores from which to infer basement affinity. DZ spectra from metasedimentary and metavolcanic wall rock contain youngest detrital zircon populations with ages (390 Ma) just barely older than the cross-cutting intrusive age, providing tight bracketing of depositional age. These zircon ages are noticeably younger than Caledonian magmatic ages (430-420 Ma) suggesting deposition in a volcanically and tectonically active setting (likely extensional) as originally suggested by Hitzman et al (1986). Zircon spectra (Cosmos) contain notable amounts of "Timanian" age zircons (c. 700-550 Ma), and a spread of zircons from 1-2 Ga (including 1.5-1.6 Ga ages of the Laurentian "magmatic gap', e.g. Grove et al. 2008) more typical of derivation from Baltic rather than Laurentian sources. East in the Wiseman and Slate Creek localities, the detrital signature becomes characteristically Laurentian, with a notable absence of Timanian and "magmatic gap" ages. A youngest age population of 390 Ma still provides a maximum depositional age, but minimum age is poorly constrained. The coarse and feldspathic nature of many of these intercalated volcanic and clastic sequences suggests a proximal provenance, thus serving as a proxy for local pre-Devonian basement ages and affinity. We might, therefore, infer a non-Laurentian basement for the AACM at least as far east as the Cosmos Hills but not further east than the Wiseman region. These Devonian-age volcanic/rift basins may be related to slab roll-back and induced backarc rifting that occurred obliquely across a 'Caledonian' suture, possibly in response to global plate re-organization. Rifting, accompanied by bimodal volcanism (the Ambler Sequence), may have aided the removal and translation of peri-Baltic terranes to a position outboard of the proto-Cordilleran margin ('Northwestern Passage' of Colpron & Nelson, 2009). Further correlations might be drawn with the Sakmarian-Magnitogorsk arcs of the pre-Uralian margin of Europe. These Devonian backarc rift sequences - more widespread than previously thought - may serve as critical additional tie-points for paleogeographic reconstructions of the Arctic.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Potter, P.E.; Maynard, J.B.; Pryor, W.A.

Studies of shales in the Appalachian area are reported (mainly in the form of abstracts of reports or manuscripts). They discuss the geology, lithology, stratigraphy, radioactivity, organic matter, the isotopic abundance of carbon and sulfur isotopes, etc. of shales in this area with maps. One report discusses Devonian paliocurrents in the central and northern Appalachian basin. Another discusses sedimentology of the Brallier Formation. The stratigraphy of upper Devonian shales along the southern shore of Lake Erie was also studied. (LTN)

Water resources of the Clarion River and Redbank Creek basins, northwestern Pennsylvania

USGS Publications Warehouse

Buckwalter, Theodore F.; Dodge, C.H.; Schiner, G.R.; Koester, H.F.

1981-01-01

The Clarion River and Redbank Creek basin occupy 1,280 and 545 square miles, respectively, in northwatern Pennsylvania. The area is mostly in Clerion, Elk, and Jefferson Counties and is approximately 70 miles long and 30 miles wide. All drainage is to the Allegheny River. Sedimentary rocks of Late Devionian Early Mississippian, and Pennsylvanian age underlie the area. Rocks of Late Devonian age underlie the entire area and crop out in the deep stream valleys in the north. Lower Mississippian rocks generally crop out in strips along major stream valleys; the strips are narrow in the south and broaden northward. Pennsylvanian rocks cover most of the interfluvial areas between major streams. The Upper Devonian and Lower Mississippian rocks are composed mostly of alternating sandstone and shale. Sandstone may intertongue laterally with shale. The Pennsylvanian rocks are most heterogeneous and contain many commercial coal beds. The major mineral resources are bituminous coal, petroleum, and natural gas. Narly all coal production is from strip mining in Clarion, Elk, and Jefferson Counties. Total coal production exceeded 8 million short tons in 1976. The basins are south and east of the major oil-producing regions in Pennsylvania, but more than 50,000 barrels of crude oil were produced here in 1975. Commercial quantities of natural gas are also obtained. Thirty-three public water-supply systems furnish about two-thirds of the water for domestic use. Surface water is the source of about 90 percent of public-supply water. The remainder is from wells and springs. In an average year, 64 percent of the precipitation in the Clarion River basin and 60 percent in the Redbank Creek basin leave the area as streamflow. The percentage of annuual discharge from each basin that is base runoff averaged 53 and 51 percent, respectively, during 1972-75. Only 4 of 10 stream-gaging stations recorded an average 10-year, 7-consecutive day low flow of at least 0.15 cubic feet per second per square mile. Most wells are completed on bedrock. Yields of bedrock wells are affected mostly by rock type, type of overburden, topography, depth of water-bearing zones, and by the rate and duration of pumping. Water in the bedrock occurs chiefly along fractures and bedding planes. Most wells get water from several zones. Yielding zones occur less frequently as depth increases, but are reported as much as 400 feet below land surface. Optimum well depth is about 350 feet. Well yields range from less than 1 to more than 550 gallons per minute. The best bedrock aquifers are the Lower Mississippian rocks, which have a median specific capacity of 4.3 gallons per minute per foot of drawdown compared to median between 0.38 and 0.67 in the Conemaugh, Allegheny, and Pottsville Groups. The major water-qualitty problems are due to high concentrations of iron, manganese, hardness, and acidity. Some of these problems are related to coal mining that has degraded water quality in parts of Clarion, Clearfield, Elk, and Jefferson Counties. Water-quality problems result from the rock composition. Many streams have low alkalinity concentrations and, consequently, have little capacity to neutralize the acid water from coal mines. Large forested areas, with little development, in Elk, Forest, and Jefferson Counties, have good quality water. The water from over three-quarters of the bedrock wells sampled has dissolved-solids concentratins less than 250 milligrams per liter. Water from aqufers of Pennsylvanian age is generally lower in dissolved solids than that from Lower Mississippian aquifers. Salt water is not a problem, except locally in Devonian rocks. Water from wells on hilltops is generally of better quality than that from wells in valleys (median dissolved solids 140 versus 340 millgrams per liter). In many valleys in Clarion and Jefferson Counties, old abandoned flowing oil and gas wells contribute high

Lithogeochemistry of Carlin-type gold mineralization in the Gold Bar district, Battle Mountain-Eureka trend, Nevada

USGS Publications Warehouse

Yigit, O.; Hofstra, A.H.

2003-01-01

The Gold Bar district contains five Carlin-type gold deposits and four resources for a combined gold endowment of 1.6 M oz [50 t]. The gold deposits are hosted in Devonian carbonate rocks below parautochthonous and allochthonous Paleozoic siliciclastic rocks emplaced during the Early Mississippian Antler orogeny. The district is in the Battle Mountain-Eureka trend, a long-lived structural feature that localized intrusions and ore deposits of different types and ages. The whole-rock geochemistry of four different mineralized and unmineralized Devonian carbonate rock units (two favorable and two unfavorable) were determined and interpreted in the context of the regional geology. A combination of basic statistics, R-mode factor analysis, isocon plots, and alteration diagrams were utilized to (1) identify favorable geochemical attributes of the host rocks, (2) characterize alteration and associated element enrichments and depletions, and (3) identify the mechanism of gold precipitation. This approach also led to the recognition of other types of alteration and mineralization in host rocks previously thought to be solely affected by Carlin-type mineralization. Unit 2 of the Upper Member of the Denay Formation, with the highest Al2O3, Fe2O3 and SiO2 contents and the lowest CaO content, is the most favorable host rock. Based on the high regression coefficients of data arrays on X-Y plots that project toward the origin, Al2O3 and TiO2 were immobile and K2O and Fe2O3 were relatively immobile during alteration and mineralization. Specific element associations identified by factor analysis are also prominent on isocon diagrams that compare the composition of fresh and altered equivalents of the same rock units. The most prominent associations are: Au, As, Sb, SiO2, TI, -CaO and -LOI, the main gold mineralizing event and related silicification and decalcification; Cd, Zn, Ag, P, Ni and Tl, an early base metal event; and MgO, early dolomitization. Alteration diagrams, consisting of X-Y plots of SiO2/Al2O3, K2O/Al2O3, CO2/Al2O3, that documented in classic Carlin-type gold deposits in the region, but the size of the deposits and the intensity of alteration and mineralization are less. The presence of other types of mineralization in the Gold Bar district is also common to most of the other Carlin-type districts located in major mineral belts. The approach used in this study is well suited to the interpretation of multi-element geochemical data from other study areas with superimposed alteration and mineralization. ?? 2002 Elsevier Science B.V. All rights reserved.

Upper Paleozoic Marine Shale Characteristics and Exploration Prospects in the Northwestern Guizhong Depression, South China

NASA Astrophysics Data System (ADS)

Zhu, Zhenhong; Yao, Genshun; Lou, Zhanghua; Jin, Aimin; Zhu, Rong; Jin, Chong; Chen, Chao

2018-05-01

Multiple sets of organic-rich shales developed in the Upper Paleozoic of the northwestern Guizhong Depression in South China. However, the exploration of these shales is presently at a relatively immature stage. The Upper Paleozoic shales in the northwestern Guizhong Depression, including the Middle Devonian Luofu shale, the Nabiao shale, and the Lower Carboniferous Yanguan shale, were investigated in this study. Mineral composition analysis, organic matter analysis (including total organic carbon (TOC) content, maceral of kerogen and the vitrinite reflection (Ro)), pore characteristic analysis (including porosity and permeability, pore type identification by SEM, and pore size distribution by nitrogen sorption), methane isothermal sorption test were conducted, and the distribution and thickness of the shales were determined, Then the characteristics of the two target shales were illustrated and compared. The results show that the Upper Paleozoic shales have favorable organic matter conditions (mainly moderate to high TOC content, type I and II1 kerogen and high to over maturity), good fracability potential (brittleness index (BI) > 40%), multiple pore types, stable distribution and effective thickness, and good methane sorption capacity. Therefore, the Upper Paleozoic shales in the northern Guizhong Depression have good shale gas potential and exploration prospects. Moreover, the average TOC content, average BI, thickness of the organic-rich shale (TOC > 2.0 wt%) and the shale gas resources of the Middle Devonian shales are better than those of the Lower Carboniferous shale. The Middle Devonian shales have better shale gas potential and exploration prospects than the Lower Carboniferous shales.

Geochronology and geochemistry of basaltic rocks from the Sartuohai ophiolitic mélange, NW China: Implications for a Devonian mantle plume within the Junggar Ocean

NASA Astrophysics Data System (ADS)

Yang, Gaoxue; Li, Yongjun; Santosh, M.; Yang, Baokai; Yan, Jing; Zhang, Bing; Tong, Lili

2012-10-01

The West Junggar domain in NW China is a distinct tectonic unit of the Central Asian Orogenic Belt (CAOB). It is composed of Paleozoic ophiolitic mélanges, arcs and accretionary complexes. The Sartuohai ophiolitic mélange in the eastern West Junggar forms the northeastern part of the Darbut ophiolitic mélange, which contains serpentinized harzburgite, pyroxenite, dunite, cumulate, pillow lava, abyssal radiolarian chert and podiform chromite, overlain by the Early Carboniferous volcano-sedimentary rocks. In this paper we report new geochronological and geochemical data from basaltic and gabbroic blocks embedded within the Sartuohai ophiolitic mélange, to assess the possible presence of a Devonian mantle plume in the West Junggar, and evaluate the petrogenesis and implications for understanding of the Paleozoic continental accretion of CAOB. Zircon U-Pb analyses from the alkali basalt and gabbro by laser ablation inductively coupled plasma mass spectrometry yielded weighted mean ages of 375 ± 2 Ma and 368 ± 11 Ma. Geochemically, the Sartuohai ophiolitic mélange includes at least two distinct magmatic units: (1) a Late Devonian fragmented ophiolite, which were produced by ca. 2-10% spinel lherzolite partial melting in arc-related setting, and (2) contemporary alkali lavas, which were derived from 5% to 10% garnet + minor spinel lherzolite partial melting in an oceanic plateau or a seamount. Based on detailed zircon U-Pb dating and geochemical data for basalts and gabbros from the Sartuohai ophiolitic mélange, in combination with previous work, indicate a complex evolution by subduction-accretion processes from the Devonian to the Carboniferous. Furthermore, the alkali basalts from the Sartuohai ophiolitic mélange might be correlated to a Devonian mantle plume-related magmatism within the Junggar Ocean. If the plume model as proposed here is correct, it would suggest that mantle plume activity significantly contributed to the crustal growth in the CAOB.

Gold Veins near Great Falls, Maryland

USGS Publications Warehouse

Reed, John Calvin; Reed, John C.

1969-01-01

Small deposits of native gold are present along an anastomosing system of quartz veins and shear zones just east of Great Falls, Montgomery County, Md. The deposits were discovered in 1861 and were worked sporadically until 1951, yielding more than 5,000 ounces of gold. The vein system and the principal veins within it strike a few degrees west of north, at an appreciable angle to foliation and fold axial planes in enclosing rocks of the Wissahickon Formation of late Precambrian (?) age. The veins cut granitic rocks of Devonian or pre-Devonian age and may be as young as Triassic. Further development of the deposits is unlikely under present economic conditions because of their generally low gold content and because much of the vein system lies on park property, but study of the Great Falls vein system may be useful in the search for similar deposits elsewhere in the Appalachian Piedmont.

A new model for the provenance of the Upper Devonian Old Red Sandstone (UORS) of southern Ireland

NASA Astrophysics Data System (ADS)

Ennis, Meg; Meere, Pat; Timmerman, Martin

2010-05-01

The geology of Southern Ireland is dominated by the influence of both the Caledonian and Variscan orogenies which have shaped the landscape of today. The Old Red Sandstone (ORS) sequences of the Middle - Upper Devonian Munster Basin have traditionally been viewed as a post-orogenic molasse deposit sourced from the Caledonides (Friend et al. 2000 & references therein), which were subsequently deformed by the Late Carboniferous Variscan Orogeny. This model does not take into account the potential impact of the Acadian Orogeny, an Early to Mid Devonian transpressional tectonic event which culminated in Mid Emsian times and resulted in the deformation and inversion of Lower ORS (LORS) basins across Britain and Ireland (Soper & Woodcock 2003; Meere & Mulchrone 2006). Evidence of Acadian deformation in Southern Ireland is recorded in the LORS sequence of the Lower-Middle Devonian basin, the Dingle Basin. Meere & Mulchrone (2006) show that penetrative deformation visible in the LORS of the Dingle Basin has an Acadian signature and is not associated with Late Carboniferous Variscan compression (Parkin 1976; Todd 2000). The role of the Acadian Orogeny in the tectono-sedimentary evolution of Southern Ireland has been analyzed in this study using a multidisciplinary approach. Petrographic analysis of both the LORS and Upper ORS (UORS) of southern Ireland suggests an alternative provenance model in which there is a direct genetic link between the two Devonian deposits. There is a fining-up relationship between the two basins and the volcanic lithic fragments - while extremely limited in occurrence in the Munster Basin - are strikingly similar in both units. The absence of conglomeratic units at the base of the Munster Basin provide further evidence that the UORS does not represent a classic molasse deposit. This is supported by EMPA data from both basins which indicates identical mica chemistries in both the LORS and UORS. A comparison with the white mica chemistries from a variety of source areas suggests that the mica chemistry is similar to both the Irish Caledonides and also to the Scandian micas; therefore the ultimate source area of the ORS detritus remains ambiguous. This relationship is confirmed by the 40Ar/39Ar step-heating and total fusion age dating which yields Acadian apparent ages for the detrital white mica component in both basins; apparent ages for the Munster Basin micas are in the range 403 to 388 Ma. The Dingle Basin micas yield ages in the range 405 to 385 Ma. The presence of Acadian age micas in both basins and the similarity in mica chemistry suggest an alternative provenance model in which the LORS deposits of the Dingle Basin are inverted and recycled southwards into the UORS Munster Basin. References: Friend, P.F., Williams, B.P.J. and Williams, E.A. 2000. Kinematics and dynamics of Old Red Sandstone basins. In: Friend, P.F., and Williams, B.P.J. (eds.). New Perspectives on the Old Red Sandstone. Geological Society of London Special Publications, 180, 29-60. Meere, P.A. and Mulchrone, K.F. 2006. Timing of deformation within the Old Red Sandstone lithologies from the Dingle Peninsula, SW Ireland. Journal of the Geological Society of London, 163, 461-469. Parkin, J. 1976. Silurian rocks of the Bull's Head, Annascaul and Derrymore Glen inliers, Co. Kerry. Proceedings of the Royal Irish Academy 76B, 577-606. Soper, N.J., and Woodcock, N.H., 2003, The lost Lower Old Red Sandstone of England and Wales: a record of post-Iapetan flexure or Early Devonian transtension? Geological Magazine, 140, 627-647. Todd, S.P., Connery, C., Higgs, K.T. and Murphy, F.C. 2000. An Early Ordovician age for the Annascaul Formation of the SE Dingle Peninsula, SW Ireland. Journal of the Geological Society of London, 157, 823-833.

The geology and petroleum potential of the North Afghan platform and adjacent areas (northern Afghanistan, with parts of southern Turkmenistan, Uzbekistan and Tajikistan)

NASA Astrophysics Data System (ADS)

Brookfield, Michael E.; Hashmat, Ajruddin

2001-10-01

The North Afghan platform has a pre-Jurassic basement unconformably overlain by a Jurassic to Paleogene oil- and gas-bearing sedimentary rock platform cover, unconformably overlain by Neogene syn- and post-orogenic continental clastics. The pre-Jurassic basement has four units: (1) An ?Ordovician to Lower Devonian passive margin succession developed on oceanic crust. (2) An Upper Devonian to Lower Carboniferous (Tournaisian) magmatic arc succession developed on the passive margin. (3) A Lower Carboniferous (?Visean) to Permian rift-passive margin succession. (4) A Triassic continental magmatic arc succession. The Mesozoic-Palaeogene cover has three units: (1) A ?Late Triassic to Middle Jurassic rift succession is dominated by variable continental clastics. Thick, coarse, lenticular coal-bearing clastics were deposited by braided and meandering streams in linear grabens, while bauxites formed on the adjacent horsts. (2) A Middle to Upper Jurassic transgressive-regressive succession consists of mixed continental and marine Bathonian to Lower Kimmeridgian clastics and carbonates overlain by regressive Upper Kimmeridgian-Tithonian evaporite-bearing clastics. (3) A Cretaceous succession consists of Lower Cretaceous red beds with evaporites, resting unconformably on Jurassic and older deposits, overlain (usually unconformably) by Cenomanian to Maastrichtian shallow marine limestones, which form a fairly uniform transgressive succession across most of Afghanistan. (4) A Palaeogene succession rests on the Upper Cretaceous limestones, with a minor break marked by bauxite in places. Thin Palaeocene to Upper Eocene limestones with gypsum are overlain by thin conglomerates, which pass up into shales with a restricted brackish-water ?Upper Oligocene-?Lower Miocene marine fauna. The Neogene succession consists of a variable thickness of coarse continental sediments derived from the rising Pamir mountains and adjacent ranges. Almost all the deformation of the North Afghan platform began in the Miocene. Oil and gas traps are mainly in Upper Jurassic carbonates and Lower Cretaceous sandstones across the entire North Afghan block. Upper Jurassic carbonate traps, sealed by evaporites, occur mainly north of the southern limit of the Upper Jurassic salt. Lower Cretaceous traps consist of fine-grained continental sandstones, sealed by Aptian-Albian shales and siltstones. Upper Cretaceous-Palaeocene carbonates, sealed by Palaeogene shales are the main traps along the northern edge of the platform and in the Tajik basin. Almost all the traps are broad anticlines related to Neogene wrench faulting, in this respect, like similar traps along the San Andreas fault. Hydrocarbon sources are in the Mesozoic section. The Lower-Middle Jurassic continental coal-bearing beds provide about 75% of the hydrocarbons; the Callovian-Oxfordian provides about 10%; the Neocomian a meagre 1%, and the Aptian-Albian about 14%. The coal-bearing source rocks decrease very markedly in thickness southwards cross the North Afghan platform. Much of the hydrocarbon generation probably occurred during the Late Cretaceous-Paleogene and migrated to structural traps during Neogene deformation. Since no regional structural dip aids southward hydrocarbon migration, and since the traps are all structural and somewhat small, then there is little chance of very large petroleum fields on the platform. Nevertheless, further studies of the North Afghan platform should be rewarding because: (a) the traps of strike-slip belts are difficult to find without detailed exploration; (b) the troubles of the last 20 years mean that almost no exploration has been done; and, (c) conditions may soon become more favorable. There should be ample potential for oil, and particularly gas, discoveries especially in the northern and western parts of the North Afghan platform.

Eastern Devonian shales: Organic geochemical studies, past and present

USGS Publications Warehouse

Breger, I.A.; Hatcher, P.G.; Romankiw, L.A.; Miknis, F.P.

1983-01-01

The Eastern Devonian shales are represented by a sequence of sediments extending from New York state, south to the northern regions of Georgia and Alabama, and west into Ohio and to the Michigan and Ilinois Basins. Correlatives are known in Texas. The shale is regionally known by a number of names: Chattanooga, Dunkirk, Rhinestreet, Huron, Antrim, Ohio, Woodford, etc. These shales, other than those in Texas, have elicited much interest because they have been a source of unassociated natural gas. It is of particular interest, however, that most of these shales have no associated crude oil, in spite of the fact that they have some of the characteristics normally attributed to source beds. This paper addresses some of the organic geochemical aspects of the kerogen in these shales, in relation to their oil generating potential. Past organic geochemical studies on Eastern Devonian shales will be reviewed. Recent solid state 13C NMR studies on the nature of the organic matter in Eastern Devonian shales show that Eastern Devonian shales contain a larger fraction of aromatic carbon in their chemical composition. Thus, despite their high organic matter contents, their potential as a petroleum source rock is low, because the kerogen in these shales is of a "coaly" nature and hence more prone to producing natural gas.

Eastern Devonian shales: Organic geochemical studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Berger, I.A.; Hatchner, P.G.; Miknis, F.P.

The Eastern Devonian shales are represented by a sequence of sediments extending from New York state, south to the northern regions of Georgia and Alabama, and west into Ohio and to the Michigan and Illinois Basins. Correlatives are known in Texas. The shale is regionally known by a number of names: Chattanooga, Dunkirk, Rhinestreet, Huron, Antrim, Ohio, Woodford, etc. These shales, other than those in Texas, have elicited much interest because they have been a source of unassociated natural gas. It is of particular interest, however, that most of these shales have no associated crude oil, in spite of themore » fact that they have some of the characteristics normally attributed to source beds. This paper addresses some of the organic geochemical aspects of the kerogen in these shales, in relation to their oil generating potential. Past organic geochemical studies on Eastern Devonian shales are reviewed. Recent solid state /sup 13/C NMR studies on the nature of the organic matter in Eastern Devonian shales show that Eastern Devonian shales contain a larger fraction of aromatic carbon in their chemical composition. Thus, despite their high organic matter contents, their potential as a petroleum source rock is low, because the kerogen in these shales is of a ''coaly'' nature and hence more prone to producing natural gas.« less

Thermal maturity of northern Appalachian Basin Devonian shales: Insights from sterane and terpane biomarkers

USGS Publications Warehouse

Hackley, Paul C.; Ryder, Robert T.; Trippi, Michael H.; Alimi, Hossein

2013-01-01

To better estimate thermal maturity of Devonian shales in the northern Appalachian Basin, eleven samples of Marcellus and Huron Shale were characterized via multiple analytical techniques. Vitrinite reflectance, Rock–Eval pyrolysis, gas chromatography (GC) of whole rock extracts, and GC–mass spectrometry (GCMS) of extract saturate fractions were evaluated on three transects that lie across previously documented regional thermal maturity isolines. Results from vitrinite reflectance suggest that most samples are immature with respect to hydrocarbon generation. However, bulk geochemical data and sterane and terpane biomarker ratios from GCMS suggest that almost all samples are in the oil window. This observation is consistent with the presence of thermogenic gas in the study area and higher vitrinite reflectance values recorded from overlying Pennsylvanian coals. These results suggest that vitrinite reflectance is a poor predictor of thermal maturity in early mature areas of Devonian shale, perhaps because reported measurements often include determinations of solid bitumen reflectance. Vitrinite reflectance interpretations in areas of early mature Devonian shale should be supplanted by evaluation of thermal maturity information from biomarker ratios and bulk geochemical data.

Significance of detrital zircons in upper Devonian ocean-basin strata of the Sonora allochthon and Lower Permian synorogenic strata of the Mina Mexico foredeep, central Sonora, Mexico

USGS Publications Warehouse

Poole, F.G.; Gehrels, G.E.; Stewart, John H.

2008-01-01

U-Pb isotopic dating of detrital zircons from a conglomeratic barite sandstone in the Sonora allochthon and a calciclastic sandstone in the Mina Mexico foredeep of the Minas de Barita area reveals two main age groups in the Upper Devonian part of the Los Pozos Formation, 1.73-1.65 Ga and 1.44-1.42 Ga; and three main age groups in the Lower Permian part of the Mina Mexico Formation, 1.93-1.91 Ga, 1.45-1.42 Ga, and 1.1-1.0 Ga. Small numbers of zircons with ages of 2.72-2.65 Ga, 1.30-1.24 Ga, ca. 2.46 Ga, ca. 1.83 Ga, and ca. 0.53 Ga are also present in the Los Pozos sandstone. Detrital zircons ranging in age from 1.73 to 1.65 Ga are considered to have been derived from the Yavapai, Mojave, and Mazatzal Provinces and their transition zones of the southwestern United States and northwestern Mexico. The 1.45-1.30 Ga detrital zircons were probably derived from scattered granite bodies within the Mojave and Mazatzal basement rocks in the southwestern United States and northwestern Mexico, and possibly from the Southern and Eastern Granite-Rhyolite Provinces of the southern United States. The 1.24-1.0 Ga detrital zircons are believed to have been derived from the Grenville (Llano) Province to the east and northeast or from Grenvilleage intrusions or anatectites to the north. Several detrital zircon ages ranging from 2.72 to 1.91 Ga were probably derived originally from the Archean Wyoming Province and Early Paleoproterozoic rocks of the Lake Superior region. These older detrital zircons most likely have been recycled one or more times into the Paleozoic sandstones of central Sonora. The 0.53 Ga zircon is believed to have been derived from a Lower Cambrian granitoid or meta-morphic rock northeast of central Sonora, possibly in New Mexico and Colorado, or Oklahoma. Detrital zircon geochronology suggests that most of the detritus in both samples was derived from Laurentia to the north, whereas some detritus in the Permian synorogenic foredeep sequence was derived from the evolving accretionary wedge to the south. Compositional and sedimentological differences between the continental-rise Los Pozos conglomeratic barite sandstone and the foredeep Mina Mexico calciclastic sandstone imply different depositional and tectonic settings. ?? 2008 The Geological Society of America.

Lead in the Getchell-Turquoise ridge Carlin-type gold deposits from the perspective of potential igneous and sedimentary rock sources in Northern Nevada: Implications for fluid and metal sources

USGS Publications Warehouse

Tosdal, R.M.; Cline, J.S.; Fanning, C.M.; Wooden, J.L.

2003-01-01

Lead isotope compositions of bulk mineral samples (fluorite, orpiment, and realgar) determined using conventional techniques and of ore-stage arsenian pyrite using the Sensitive High Resolution Ion-Microprobe (SHRIMP) in the Getchell and Turquoise Ridge Carlin-type gold deposits (Osgood Mountains) require contribution from two different Pb sources. One Pb source dominates the ore stage. It has a limited Pb isotope range characterized by 208Pb/206Pb values of 2.000 to 2.005 and 207Pb/206Pb values of 0.8031 to 0.8075, as recorded by 10-??m-diameter spot SHRIMP analyses of ore-stage arsenian pyrite. These values approximately correspond to 206Pb/204Pb of 19.3 to 19.6, 207Pb/204Pb of 15.65 to 15.75, and 208Pb/204Pb of 39.2 to 39.5. This Pb source is isotopically similar to that in average Neoproterozoic and Cambrian elastic rocks but not to any potential magmatic sources. Whether those clastic rocks provided Pb to the ore fluid cannot be unequivocally proven because their Pb isotope compositions over the same range as in ore-stage arsenian pyrite are similar to those of Ordovician to Devonian siliciclastic and calcareous rocks. The Pb source in the calcareous rocks most likely is largely detrital minerals, since that detritus was derived from the same sources as the detritus in the Neoproterozoic and Cambrian clastic rocks. The second Pb source is characterized by a large range of 206Pb/204Pb values (18-34) with a limited range of 208Pb/204Pb values (38.1-39.5), indicating low but variable Th/U and high and variable U/Pb values. The second Pb source dominates late and postore-stage minerals but is also found in preore sulfide minerals. These Pb isotope characteristics typify Ordovician to Devonian siliciclastic and calcareous rocks around the Carlin trend in northeast Nevada. Petrologically similar rocks host the Getchell and Turquoise Ridge deposits. Lead from the second source was either contributed from the host sedimentary rock sequences or brought into the hydrothermal system by oxidized ground water as the system collapsed. Late ore- and postore-stage sulfide minerals (pyrite, orpiment, and stibnite) from the Betze-Post and Meikle deposits in the Carlin trend and from the Jerritt Canyon mining district have Pb isotope characteristics similar to those determined in Getchell and Turquoise Ridge. This observation suggests that the Pb isotope compositions of their ore fluids may be similar to those at Getchell and Turquoise Ridge. Two models can explain the Pb isotope compositions of the ore-stage arsenian pyrite versus the late ore or postore sulfide minerals. In either model, Pb from the Ordovician to Devonian siliciclastic and calcareous rock source enters the hydrothermal system late in the ore stage but not to any extent during the main stage of ore deposition. In one model, ore-stage Pb was derived from a source with Pb isotope compositions similar to those of the Neoproterozoic and Cambrian clastic sequence, transported as part of the ore fluid and then deposited in the ore-stage arsenian pyrite and fluorite. The second model is based on the observation that the Pb isotope characteristics of the ore-stage minerals also are found in some Ordovician to Devonian calcareous and siliciclastic rocks. Hence, ore-stage Pb could have been derived locally and simply concentrated during the ore stage. Critical to the second model is the removal of all high 206Pb/204Pb (>20) material during alteration. It Also requires the retention of only the low 206Pb/204Pb component of the Ordovician to Devonian sedimentary rocks. This critical step is possible only if the high 206Pb/204Pb values are contained in readily dissolvable mineral phases, whereas the low 206Pb/204Pb values are found only in refractory minerals that released Pb during a final alteration stage just prior deposition of auriferous arsenian pyrite. Distinguishing between Pb transported with the ore fluid or inherited from the site of mineral deposition is not straightforward

Petrology and sedimentology of the Horlick Formation (Lower Devonian), Ohio Range, Transantarctic Mountains

USGS Publications Warehouse

McCartan, Lucy; Bradshaw, Margaret A.

1987-01-01

The Horlick Formation of Early Devonian age is as thick as 50 m and consists of subhorizontal, interbedded subarkosic sandstone and chloritic shale and mudstone. The Horlick overlies an erosion surface cut into Ordovician granitic rocks and is, in turn, overlain by Carboniferous and Permian glacial and periglacial deposits. Textures, sedimentary structures, and ubiquitous marine body fossils and animal traces suggest that the Horlick was deposited on a shallow shelf having moderate wave energy and a moderate tidal range. The source terrane probably lay to the north, and longshore transport was toward the west.

Bedrock Geology and Asbestos Deposits of the Upper Missisquoi Valley and Vicinity, Vermont

USGS Publications Warehouse

Cady, Wallace Martin; Albee, Arden Leroy; Chidester, A.H.

1963-01-01

The upper Missisquoi Valley and vicinity as described in this report covers an area of about 250 square miles at the headwaters of the Missisquoi River in north-central Vermont. About 90 percent of the area is forested and the remainder is chiefly farm land. The topography reflects the geologic structure and varied resistance of the bedrock to erosion. Most of the area is on the east limb of the Green Mountain anticlinorium, which is the principal structural feature of Vermont. The bedrock is predominantly sedimentary and volcanic rock that has been regionally metamorphosed. It was intruded before metamorphism by mafic and ultramafic igneous rocks, and after metamorphism by felsic and mafic igneous rocks. The metamorphosed sedimentary and volcanic rocks range in age from Cambrian(?) to Middle Silurian, the intrusive igneous rocks from probably Late Ordovician to probably late Permian. Metamorphism and principal folding in the region occurred in Middle Devonian time. The metamorphosed sedimentary and volcanic rocks make up a section at least 25,000 feet thick and can be divided into nine formations. The Hazens Notch formation of Cambrian(?) and Early Cambrian age is characterized by carbonaceous schist. It is succeeded in western parts of the area by the Jay Peak formation of Early Cambrian age, which is chiefly a schist that is distinguished by the general absence of carbonaceous zones; in central parts of the area the Hazens Notch formation is followed by the Belvidere Mountain amphibolite, probably the youngest of the formations of Early Cambrian age. The Ottauquechee formation, composed of carbonaceous phyllite and quartzite, and phyllitic graywacke, is of Middle Cambrian age. The Stowe formation of Late Cambrian(?) and Early(?) Ordovician age overlies the Ottauquechee and is predominantly noncarbonaceous schist, though it also contains greenstone and carbonaceous schist and phyllite. The Umbrella Hill formation of Middle Ordovician age is characteristically a conglomerate in which the mineral chloritoid is common. The overlying Moretown formation, also of Middle Ordovician age, contains granulite and slate, also greenstone and amphibolite of the Coburn Hill volcanic member. The Shaw Mountain formation, made up of conglomerate, phyllite, and limestone, is the oldest Silurian unit. The Shaw Mountain formation is succeeded by the Northfield slate of Middle Silurian age. The igneous rocks of the region include various ultramafic plutonic rocks, such as dunite, peridotite, and serpentinite, probably of Late Ordovician age; sills and nearly concordant dikes of metagabbro of Late Ordovician age; biotite granite plutons or Middle or Late Devonian age, most notably on Eltey Mountain; and hypabyssallamprophyre, probably of late Permian age. Metamorphic zoning is shown by the distribution of rocks of the epidote-amphibolite facies and the greenschist facies in and near the Green Mountains, and near Coburn Hill and Eltey Mountain. Metasomatism related to regional metamorphism has produced porphyroblasts and quartz segregations in the sedimentary and volcanic rocks, and steatitization and carbonatization of serpentinite. Contact metamorphism has formed rocks of the epidote-amphibolite facies near granite plutons, and probably calc-silicate rock at the contacts of ultramafic plutons. The axial anticline of the Green Mountain anticlinorium and other anticlines and synclines to the east are the major longitudinal structural features of the area. These structures are complicated by transverse folds, particularly a syncline in the vicinity of Tillotson Peak. Early minor cross folds that are best developed in the Hazens Notch formation are believed to be genetically related to the transverse folds. The axial planes of the cross folds are folded about the axes of the later longitudinal folds of the Green Mountain anticlinorium. The longitudinal and transverse fold systems probably formed in the same episode of defor

The Paleotethys suture in Central Iran

NASA Astrophysics Data System (ADS)

Bagheri, S.; Stampfli, G. M.

2003-04-01

The Triassic rocks of the Nakhlak area have been used to justify the hypothesis of the rotation of the Central-East Iranian microplate, mainly based on paleomagnetic data. Davoudzadeh and his coworkers (1981) pointed out the existing contrast between the Nakhlakh succession and the time-equivalent lithostratigraphic units exposed in the surrounding regions and compared them with the Triassic rocks of the Aghdarband area on the southern edge of the Turan plate. We recently gathered evidences that this part of central Iran effectively belongs to the Northern Iranian Paleo-Tethys suture zone and related Variscan terrains of the Turan plate. This is the case for the northwestern part of central Iran, where the Anarak-Khur belt (Anarak schists and their thick Cretaceous-Paleocene sedimentary cover) presents all the elements of an orogenic zone such as dismembered ophiolites and silisiclastics, calcareous and volcanic cover which has been deformed and metamorphosed. This belt is separated to the northwest from the Alborz microcontinent by the Great Kavir fault and Cretaceous ophiolite mélanges. To the southeast it is bounded by the Biabanak fault and serpentinites and the Biabanak block, part of the central-east Iranian plate. The later zone is formed by Proterozoic metamorphic basement and marine sedimentary cover, nearly continuous from the Ordovician to the Triassic, at the uppermost part upper Triassic-lower Jurassic bauxites and silisiclastics are observed. Excepted the Ordovician angular unconformities and the boundary between lower Jurassic and younger layers, this sequence displays no significant main unconformities and can be attributed to the Cimmerian super-terrain. Thus, this sequences represents the classical evolution of the southern Paleo-Tethys passive margin, as found in the Alborz microcontinent or the Band-e Bayan zone of Afghanistan and is the witness of large scale duplication of the Paleo-Tethys suture zone through major Alpine strike-slip faults. Within the Anarak-Khur belt limit and to the northeast of the Nakhlak succession, the area of Godar-e Siah of Jandaq, remnants of the Eurasian active margin are found, represented by: 1- A lower Paleozoic to upper Devonian unit consisting mainly of metamorphosed rocks including ophiolitic rocks, pelagic sediments, flysch-like deposits and shallow-water limestones of Devonian age belonging to the Anarak and Kabudan areas. Folding and thrusting was pre-Carboniferous and all geochronological dating based on K/Ar for the Anarak and Kaboudan schists placed this metamorphic event between middle Devonian and Visean. 2- the main part of the lower Carboniferous unit consists of a volcano-sedimentary complex with intercalations of limestone containing Coral, Brachiopod and Foraminiferas. Pyroclastic deposits are followed by continental red beds containing a great variety of grain types, such as hypabyssal to several types of granitoid rock fragments derived from the arc, accompanied by pebbles of chert, fossiliferous carbonate and serpentinite recycled from the accretionary complex, pointing to a fore-arc environment of deposition. 3- The middle Carboniferous to Permian unit consists of coarse littoral conglomerate and sandstones derived from ophiolitic to felsic material with some platform limestones. They represent the final infill of the fore-arc basin and rest unconformably on both the metamorphites and Lower Carboniferous units. These tectono-stratigraphic units are similar to the western Hindu Kush sequences of Afghanistan and Tuarkyr in Turkmenistan and belong to the northern active margin of Paleo-Tethys. Therefore, the Anarak-Khur belt was part of the Variscan terranes located along this margin. Volcano-sedimentary strata with Conodont-bearing limestones of Permian to Triassic age have been found in direct contact with the Biabanak fault which, therefore, is most likely following and reactivating the Paleo-Tethys suture zone.

Sulfur-, oxygen-, and carbon-isotope studies of Ag-Pb-Zn vein-breccia occurrences, sulfide-bearing concretions, and barite deposits in the north-central Brooks Range, with comparisons to shale-hosted stratiform massive sulfide deposits: A section in Geologic studies in Alaska by the U.S. Geological Survey, 1998

USGS Publications Warehouse

Kelley, Karen D.; Leach, David L.; Johnson, Craig A.

2000-01-01

Stratiform shale-hosted massive sulfide deposits, sulfidebearing concretions and vein breccias, and barite deposits are widespread in sedimentary rocks of Late Devonian to Permian age in the northern Brooks Range. All of the sulfide-bearing concretions and vein breccias are hosted in mixed continental-marine clastic rocks of the Upper Devonian to Lower Mississippian Endicott Group. The clastic rocks and associated sulfide occurrences underlie chert and shale of Mississippian-Pennsylvanian(?) age that contain large stratiform massive sulfide deposits like that at Red Dog. The relative stratigraphic position of the vein breccias, as well as previously published mineralogical, geochemical, and lead-isotope data, suggest that the vein breccias formed coevally with overlying shale-hosted massive sulfide deposits and that they may represent pathways of oreforming hydrothermal fluids. Barite deposits are hosted either in Mississippian chert and limestone (at essentially the same stratigraphic position as the shale-hosted massive sulfide deposits) or Permian chert and shale. Although most barite deposits have no associated base-metal mineralization, barite occurs with massive sulfide deposits at the Red Dog deposit.Galena and sphalerite from most vein breccias have δ34S values from –7.3 to –0.7‰ (per mil) and –5.1 to 3.6‰, respectively; sphalerite from sulfide-bearing concretions have δ34S values of 0.7 and 4.7‰. This overall range in δ34S values largely overlaps with the range previously determined for galena and sphalerite from shale-hosted massive sulfide deposits at Red Dog and Drenchwater. The Kady vein-breccia occurrence is unusual in having higher δ34S values for sphalerite (12.1 to 12.9‰) and pyrite (11.3‰), consistent with previously published values for the shale-hosted Lik deposit. The correspondence in sulfur isotopic compositions between the stratiform and vein-breccia deposits suggests that they share a common source of reduced sulfur, or derived reduced sulfur by similar geochemical processes. Most likely, the reduced sulfur was derived by biogenic sulfate reduction (BSR) or thermochemical sulfate reduction (TSR) of seawater sulfate during Devonian-Mississippian time.The δ18O values of quartz from the vein breccias are between 16.6 and 19.9‰. Using the sphalerite-galena sulfur isotopic temperature of 188°±25°C, the calulated hydrothermal fluids had δ18O values of 4.2 to 7.5‰. The calculated range of δ18O values of the fluids is similar to that of pore fluids in equilibrium with sedimentary rocks during diagenesis at 100°– 190°C.

Overview of the potential and identified petroleum source rocks of the Appalachian basin, eastern United States: Chapter G.13 in Coal and petroleum resources in the Appalachian basin: distribution, geologic framework, and geochemical character

USGS Publications Warehouse

Coleman, James L.; Ryder, Robert T.; Milici, Robert C.; Brown, Stephen; Ruppert, Leslie F.; Ryder, Robert T.

2014-01-01

The Appalachian basin is the oldest and longest producing commercially viable petroleum-producing basin in the United States. Source rocks for reservoirs within the basin are located throughout the entire stratigraphic succession and extend geographically over much of the foreland basin and fold-and-thrust belt that make up the Appalachian basin. Major source rock intervals occur in Ordovician, Devonian, and Pennsylvanian strata with minor source rock intervals present in Cambrian, Silurian, and Mississippian strata.

Utility of palmatolepids and icriodontids in recognizing Upper Devonian Series, Stage, and possible substage boundaries

USGS Publications Warehouse

Ziegler, W.; Sandberg, C.A.

2000-01-01

Conodonts are accepted internationally to define Devonian Series and Stage boundaries. Hence, the evolution and taxonomy of pelagic palmatolepids, primarily Palmatolepis and its direct ancestor Mesotaxis, and shallow-water icriodontids, Icriodus, Pelekysgnathus, and "Icriodus", are the major tools for recognizing subdivisions of the Upper Devonian. Palmatolepids are the basis for the Late Devonian Standard Conodont Zonation (ZIEGLER & SANDBERG 1990), whereas icriodontids are the basis for the alternative, integrated shallow-water zonation (SANDBERG & DREESEN 1984). However, an alternative palmatolepid taxonomy for some Frasnian species has been employed recently by some conodont workers using the Montagne Noire (M.N.) zonation, shape analyses of Pa elements, and multielement reconstructions of KLAPPER (1989), KLAPPER & FOSTER (1993); and KLAPPER et al. (1996). Herein, the evolution of palmatolepids and icriodontids is summarized in terms of our zonation and some of the taxonomic differences with the alternative M.N. zonation are exemplified. One of the problems in relating the Standard and M.N. zonations arises from previous errors of interpretation and drafting of the Martenberg section in Germany. This section was designated the reference section for the Frasnian transitans through jamieae Zones by ZIEGLER & SANDBERG (1990). Herein, the early and middle Frasnian zonal boundaries at Martenberg are improved by re-study of our old and recent collections from three profiles, spaced only 4 m apart. Serious problems exist with the Global Stratotype Sections and Points (GSSP's), selected by the Subcommission on Devonian Stratigraphy, following the paleontologic definition of the bases of the Frasnian, Famennian, and Tournaisian Stages, because of the difficulty in making global correlations from these GSSP's. Our summary of these problems should be helpful if future workers decide to relocate these GSSP's.

Benefits of applying technology to Devonian shale wells. Topical report, July-December 1992

DOE Office of Scientific and Technical Information (OSTI.GOV)

Voneiff, G.W.; Gatens, J.M.

1993-01-01

The report summarizes the benefits of applying technology to Devonian Shales wells in the Appalachian Basin. The results of the work suggest that an intermediate level of technology application, with an incremental cost of $6,700/well, is best for routine application in the Devonian Shales. The technology level uses conventional well tests, rock mechanical properties logs, a borehole camera, and a moderate logging suite. Most of these tools and technologies should be used on only a portion of the wells in multi-well projects, reducing the per well cost of the technology. Determining the correct reservoir description is critical to optimizing themore » stimulation treatment. The most critical reservoir properties are bulk and matrix permeabilities, net pay, stress profile, and natural fracture spacing in the direction perpendicular to induced hydraulic fractures. Applying technology to improve the accuracy of the reservoir description can significantly increase well profitability.« less

The New Albany Shale Petroleum System, Illinois Basin - Data and Map Image Archive from the Material-Balance Assessment

USGS Publications Warehouse

Higley, Debra K.; Henry, M.E.; Lewan, M.D.; Pitman, Janet K.

2003-01-01

The data files and explanations presented in this report were used to generate published material-balance approach estimates of amounts of petroleum 1) expelled from a source rock, and the sum of 2) petroleum discovered in-place plus that lost due to 3) secondary migration within, or leakage or erosion from a petroleum system. This study includes assessment of cumulative production, known petroleum volume, and original oil in place for hydrocarbons that were generated from the New Albany Shale source rocks.More than 4.00 billion barrels of oil (BBO) have been produced from Pennsylvanian-, Mississippian-, Devonian-, and Silurian-age reservoirs in the New Albany Shale petroleum system. Known petroleum volume is 4.16 BBO; the average recovery factor is 103.9% of the current cumulative production. Known petroleum volume of oil is 36.22% of the total original oil in place of 11.45 BBO. More than 140.4 BBO have been generated from the Upper Devonian and Lower Mississippian New Albany Shale in the Illinois Basin. Approximately 86.29 billion barrels of oil that was trapped south of the Cottage Grove fault system were lost by erosion of reservoir intervals. The remaining 54.15 BBO are 21% of the hydrocarbons that were generated in the basin and are accounted for using production data. Included in this publication are 2D maps that show the distribution of production for different formations versus the Rock-Eval pyrolysis hydrogen-indices (HI) contours, and 3D images that show the close association between burial depth and HI values.The primary vertical migration pathway of oil and gas was through faults and fractures into overlying reservoir strata. About 66% of the produced oil is located within the generative basin, which is outlined by an HI contour of 400. The remaining production is concentrated within 30 miles (50 km) outside the 400 HI contour. The generative basin is subdivided by contours of progressively lower hydrogen indices that represent increased levels of thermal maturity and generative capacity of New Albany Shale source rocks. The generative basin was also divided into seven oil-migration catchments. The catchments were determined using a surface-flow hydrologic model with contoured HI values as input to the model.

The New Albany shale in Illinois: Emerging play or prolific source

USGS Publications Warehouse

Crockett, Joan; Morse, David E.

2010-01-01

The New Albany shale (Upper Devonian) in the Illinois basin is the primary hydrocarbon source rock for the basins nearly 4 billion bbl of oil production to date. The gas play is well-established in Indiana and Western Kentucky. One in-situ oil producing well was reported in a multiply competed well in the New Albany at Johnsonville field in Wayne County, Illinois. The Illinois gas and oil wells at Russellville, in Lawrence County are closely associated with the 0.6% reflectance contour, which suggests a higher level of thermal maturity in this area. Today, only one field, Russellville in eastern Lawrence County has established commercial production in the Ness Albany in Illinois. Two wildcat wells with gas shows were drilled in recent years in southern Saline County, where the New Albany is relatively deeply buried and close to faults associated with the Fluorspar District.

Bedrock geologic map of the Miles Pond and Concord quadrangles, Essex and Caledonia Counties, Vermont, and Grafton County, New Hampshire

USGS Publications Warehouse

Rankin, Douglas W.

2018-04-20

The bedrock geologic map of the Miles Pond and Concord quadrangles covers an area of approximately 107 square miles (276 square kilometers) in east-central Vermont and adjacent New Hampshire, north of and along the Connecticut River. This map was created as part of a larger effort to produce a new bedrock geologic map of Vermont through the collection of field data at a scale of 1:24,000. The majority of the map area consists of the Bronson Hill anticlinorium, a post-Early Devonian structure that is cored by metamorphosed Cambrian to Silurian sedimentary, volcanic, and plutonic rocks. A major feature on the map is the Monroe fault, interpreted to be a west-directed, steeply dipping Late Devonian (Acadian) thrust fault. To the west of the Monroe fault, rocks of the Connecticut Valley-Gaspé trough dominate and consist primarily of metamorphosed Silurian and Devonian sedimentary rocks. To the north, the Victory pluton intrudes the Bronson Hill anticlinorium. The Bronson Hill anticlinorium consists of the metamorphosed Albee Formation, the Ammonoosuc Volcanics, the Comerford Intrusive Complex, the Highlandcroft Granodiorite, and the Joselin Turn tonalite. The Albee Formation is an interlayered, feldspathic metasandstone and pelite that is locally sulfidic. Much of the deformed metasandstone is tectonically pinstriped. In places, one can see compositional layering that was transposed by a steeply southeast-dipping foliation. The Ammonoosuc Volcanics are lithologically complex and predominantly include interlayered and interfingered rhyolitic to basaltic volcanic and volcaniclastic rocks, as well as lesser amounts of siltstone, phyllite, graywacke, and grit. The Comerford Intrusive Complex crops out east of the Monroe fault and consists of metamorphosed gabbro, diorite, tonalite, aplitic tonalite, and crosscutting diabase dikes. Abundant mafic dikes from the Comerford Intrusive Complex intruded the Albee Formation and Ammonoosuc Volcanics east of the Monroe fault. The Highlandcroft Granodiorite and Joslin Turn tonalite plutons intruded during the Middle to Late Ordovician.West of the Monroe fault, the Connecticut Valley-Gaspé trough consists of the Silurian and Devonian Waits River and Gile Mountain Formations. The Waits River Formation is a carbonaceous muscovite-biotite-quartz (±garnet) phyllite containing abundant beds of micaceous quartz-rich limestone. The Gile Mountain Formation consists of interlayered metasandstone and graphitic (and commonly sulfidic) slate, along with minor calcareous metasandstone and ironstone. Graded bedding is common in the Gile Mountain Formation. Rocks of the Devonian New Hampshire Plutonic Suite intruded as plutons, dikes, and sills. The largest of these is the Victory pluton, which consists of weakly foliated, biotite granite and granodiorite. The Victory pluton also intruded a large part of the Albee Formation to the north.This report consists of a geologic map and an online geographic information systems database that includes contacts of bedrock geologic units, faults, outcrops, and structural geologic information. The geologic map is intended to serve as a foundation for applying geologic information to problems involving land use decisions, groundwater availability and quality, earth resources such as natural aggregate for construction, assessment of natural hazards, and engineering and environmental studies for waste disposal sites and construction projects.

Hydrology, water quality, and effects of drought in Monroe County, Michigan

USGS Publications Warehouse

Nicholas, J.R.; Rowe, Gary L.; Brannen, J.R.

1996-01-01

Monroe County relies heavily on its aquifers and streams for drinking water, irrigation, and other ~ses; however, increased water use, high concentrations of certain constituents in ground water, and droughts may limit the availability of water resources. Although the most densely populated parts of the county use water from the Great Lakes, large amounts of ground water are withdrawn for quarry dewatering, domestic supply, and irrigation.Unconsolidated deposits and bedrock of Silurian and Devonian age underlie Mon_roe County. The unconsolidated deposits are mostly clayey and less than 50 feet thick. Usable amounts of ground water generally are obtained from thin, discontinuous surficial sand deposits or, in the northwestern part of the county, from deep glaciofluvial deposits. In most of the county, however, ground water in unconsolidated deposits is highly susceptible to effects of droughts and to contamination.The bedrock is mostly carbonate rock, and usable quantities of ground water can be obtained from fractures and other secondary openings throughout the county. Transmissivities of the Silurian-Devonian aquifer range from 10 to 6,600 feet squared per day. Aquifer tests and historical informati.on indicate that the Silurian-Devonian aquifer is confmed throughout most of the county. The major recharge area for the Silurian-Devonian aquifer in Monroe County is in the southwest, and groundwater flow is mostly southeastward toward Lake Erie. In the northeastern and southeastern parts of the county, the potentiometric surface of the SilurianDevonian aquifers has been lowered by pumpage to below the elevation of Lake Erie.Streams and artificial drains in Monroe County are tributary to Lake Erie. Most streams are perennial because of sustained discharge from the sand aquifer and the Silurian-Devonian aquifer; however, the lower reaches of River Raisin and Plum Creek lost water to the Silurian-Devonian aquifer in July 1990.The quality of ground water and of streamwater at low flow is suitable for most domestic u~es, irrigation, and recreation. In ground water, dissolved solids and hydrogen sulfide are present at concentrations objectionable to some users. Indicators of ground-water contamination from agricultural activities-pesticides and nitrates-were not present at detectable concentrations or were below U.S. Environmental Protection Agency (USEPA) limits. In streamwater, some treatment to remove bacteria may be necessary in summer months; nitrate concentrations, however, were found to be below USEPA limits.Tritium concentrations indicative of recent recharge to the Silurian-Devonian aquifer are present in a southwest-to-northeast-trending band from Whiteford to Berlin Townships. Generally, where glacial deposits are thicker than 30 feet, rech~rge.takes more than 40 years. Carbon isotope data md1cate that some of the ground water in the Silurian-Devonian aquifer is more than 14,000 years old.Mild droughts are common in Michigan, but long severe droughts, such as those during 1930-37 and 1960-67, are infrequent. The most recent drought, during 1988, was severe but short. Ground-water levels declined throughout the county; the largest declines were probably in the southwest. Shallow bedrock wells completed in only the upper part of the Silurian-Devonian aquifer and near large uses of ground water were especially susceptible to the effects of drought. Deep bedrock wells continued to produce water through the drought of 1988.During droughts, streamflow is reduced because of low ground-water levels and high consumptive uses of surface water. In 1988, annual discharge on the River Raisin was near normal, but monthly averages were below normal from March through August. The quality of surface water during droughts is similar to that during normal lowflow conditions.

U-Pb detrital zircon dates and provenance data from the Beaufort Group (Karoo Supergroup) reflect sedimentary recycling and air-fall tuff deposition in the Permo-Triassic Karoo foreland basin

NASA Astrophysics Data System (ADS)

Viglietti, Pia A.; Frei, Dirk; Rubidge, Bruce S.; Smith, Roger M. H.

2018-07-01

Detrital zircon U-Pb age dating was used for provenance determination and maximum age of deposition for the Upper Permian (upper Teekloof and Balfour formations) and Lower Triassic (Katberg Formation) lithostratigraphic subdivisions of the Beaufort Group of South Africa's Karoo Basin. Ten samples were analysed using laser ablation - single collector - magnetic sectorfield - inductively coupled plasma - mass spectrometry (LA-SF-ICP-MS). The results reveal a dominant Late Carboniferous-Late Permian population (250 ± 5 Ma - 339 ± 5 Ma), a secondary Cambrian-Neoproterozoic (489 ± 5 Ma to 878 ± 24 Ma) population, a minor Mesoproterozoic (908 ± 24 Ma to 1308 ± 23) population, and minor occurrences of Devonian, Ordovician, Proterozoic and Archean zircon grains. Multiple lines of evidence (e.g. roundness and fragmentary nature of zircons, palaeo-current directions, and previous work), suggest the older zircon populations are related to sedimentary recycling in the Gondwanide Orogeny. The youngest and dominant population contain elongate euhedral grains interpreted to be directly derived from their protolith. Since zircons form in felsic igneous rocks, and no igneous rocks of Late Permian age occur in the Karoo Basin, these findings suggest significant input of volcanic material by ash falls. These results support sedimentological and palaeontological data for a Lopingian (Late Permian) age for the upper Beaufort Group, but contradict previous workers who retrieved Early Triassic dates from zircons in ashes for the Beaufort and Ecca Groups. Pb-loss not revealed by resolvable discordance on the concordia diagram, and metamictization of natural zircons are not factored into the conclusions of earlier workers.

A paleolatitude reconstruction of the South Armenian Block (Lesser Caucasus) for the Late Cretaceous: Constraints on the Tethyan realm

NASA Astrophysics Data System (ADS)

Meijers, Maud J. M.; Smith, Brigitte; Kirscher, Uwe; Mensink, Marily; Sosson, Marc; Rolland, Yann; Grigoryan, Araik; Sahakyan, Lilit; Avagyan, Ara; Langereis, Cor; Müller, Carla

2015-03-01

The continental South Armenian Block - part of the Anatolide-Tauride South Armenian microplate - of Gondwana origin rifted from the African margin after the Triassic and collided with the Eurasian margin after the Late Cretaceous. During the Late Cretaceous, two northward dipping subduction zones were simultaneously active in the northern Neo-Tethys between the South Armenian Block in the south and the Eurasian margin in the north: oceanic subduction took place below the continental Eurasian margin and intra-oceanic subduction resulted in ophiolite obduction onto the South Armenian Block in the Late Cretaceous. The paleolatitude position of the South Armenian Block before its collision with Eurasia within paleogeographic reconstructions is poorly determined and limited to one study. This earlier study places the South Armenian Block at the African margin in the Early Jurassic. To reconstruct the paleolatitude history of the South Armenian Block, we sampled Upper Devonian-Permian and Cretaceous sedimentary rocks in Armenia. The sampled Paleozoic rocks have likely been remagnetized. Results from two out of three sites sampled in Upper Cretaceous strata pass fold tests and probably all three carry a primary paleomagnetic signal. The sampled sedimentary rocks were potentially affected by inclination shallowing. Therefore, two sites that consist of a large number of samples (> 100) were corrected for inclination shallowing using the elongation/inclination method. These are the first paleomagnetic data that quantify the South Armenian Block's position in the Tethys ocean between post-Triassic rifting from the African margin and post-Cretaceous collision with Eurasia. A locality sampled in Lower Campanian Eurasian margin sedimentary rocks and corrected for inclination shallowing, confirms that the corresponding paleolatitude falls on the Eurasian paleolatitude curve. The north-south distance between the South Armenian Block and the Eurasian margin just after Coniacian-Santonian ophiolite obduction was at most 1000 km.

Geochemical character and origin of oils in Ordovician reservoir rock, Illinois and Indiana, USA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guthrie, J.M.; Pratt, L.M.

1995-11-01

Twenty-three oils produced from reservoirs within the Ordovician Galena Group (Trenton equivalent) and one oil from the Mississippian Ste. Genevieve Limestone in the Illinois and Indiana portions of the Illinois basin are characterized. Two end-member oil groups (1) and (2) and one intermediate group (1A) are identified using conventional carbon isotopic analysis of whole and fractionated oils, gas chromatography (GC) of saturated hydrocarbon fractions, isotope-ratio-monitoring gas chromatography/mass spectrometry (irm-GC/MS) of n-alkanes ranging from C{sub 15} to C{sub 25}, and gas chromatography/mass spectrometry (GC/MS) of the aromatic hydrocarbon fractions. Group 1 is characterized by high odd-carbon predominance in mid-chain n-alkanes (C{submore » 15}-C{sub 19}), low abundance Of C{sub 20+}, n-alkanes, and an absence of pristane and phytane. Group IA is characterized by slightly lower odd-carbon predominance of mid-chain n-alkanes, greater abundance of C{sub 20+} n-alkanes compared to group 1, and no pristane and phytane. Conventional correlations of oil to source rock based on carbon isotopic-type curves and hopane (m/z 191) and sterane (m/z 217) distributions are of limited use in distinguishing Ordovician-reservoired oil groups and determining their origin. Oil to source rock correlations using the distribution and carbon isotopic composition of n-alkanes and the m/z 133 chromatograms of n-alkylarenes show that groups 1 and 1A originated from strata of the Upper Ordovician Galena Group. Group 2 either originated solely from the Upper Ordovician Maquoketa Group or from a mixture of oils generated from the Maquoketa Group and the Galena Group. The Mississippian-reservoired oil most likely originated from the Devonian New Albany Group. The use of GC, irm-GC/MS, and GC/MS illustrates the value of integrated molecular and isotopic approaches for correlating oil groups with source rocks.« less

Integration of new geologic mapping and satellite-derived quartz mapping yields insights into the structure of the Roberts Mountains allochthon applicable to assessments for concealed Carlin-type gold deposits

USGS Publications Warehouse

Holm-Denoma, Christopher S.; Hofstra, Albert H.; Rockwell, Barnaby W.; Noble, Paula J.

2012-01-01

Geologic mapping and remote sensing across north-central Nevada enable recognition of a thick sheet of Middle and Upper Ordovician Valmy Formation quartzite that structurally overlies folded and faulted Ordovician through Devonian stratigraphic units of the Roberts Mountains allochthon. In the northern Independence Mountains and nearby Double Mountain area, the Valmy Formation is in fault contact with Ordovician through Silurian, predominantly clastic, sedimentary rocks of the Roberts Mountains allochthon that were deformed prior to, or during, emplacement of the Valmy thrust sheet. Similar structural relations are recognized discontinuously for 200 kilometers along the strike of the Roberts Mountains allochthon in mapping guided by regional remote-sensing-based (ASTER) quartz maps. Overall thicknesses of deformed Roberts Mountains allochthon units between the base of the Valmy and the top of underlying carbonate rocks that host large Carlin-type gold deposits varies on the order of hundreds of meters but is not known to exceed 700 meters. The base of the Valmy thrust sheet is a complimentary datum in natural resource exploration and mineral resource assessment for concealed Carlin-type gold deposits.

Late Proterozoic-Paleozoic evolution of the Arctic Alaska-Chukotka terrane based on U-Pb igneous and detrital zircon ages: Implications for Neoproterozoic paleogeographic reconstructions

USGS Publications Warehouse

Amato, J.M.; Toro, J.; Miller, E.L.; Gehrels, G.E.; Farmer, G.L.; Gottlieb, E.S.; Till, A.B.

2009-01-01

The Seward Peninsula of northwestern Alaska is part of the Arctic Alaska-Chukotka terrane, a crustal fragment exotic to western Laurentia with an uncertain origin and pre-Mesozoic evolution. U-Pb zircon geochronology on deformed igneous rocks reveals a previously unknown intermediate-felsic volcanic event at 870 Ma, coeval with rift-related magmatism associated with early breakup of eastern Rodinia. Orthogneiss bodies on Seward Peninsula yielded numerous 680 Ma U-Pb ages. The Arctic Alaska-Chukotka terrane has pre-Neoproterozoic basement based on Mesoproterozoic Nd model ages from both 870 Ma and 680 Ma igneous rocks, and detrital zircon ages between 2.0 and 1.0 Ga in overlying cover rocks. Small-volume magmatism occurred in Devonian time, based on U-Pb dating of granitic rocks. U-Pb dating of detrital zircons in 12 samples of metamorphosed Paleozoic siliciclastic cover rocks to this basement indicates that the dominant zircon age populations in the 934 zircons analyzed are found in the range 700-540 Ma, with prominent peaks at 720-660 Ma, 620-590 Ma, 560-510 Ma, 485 Ma, and 440-400 Ma. Devonian- and Pennsylvanian-age peaks are present in the samples with the youngest detrital zircons. These data show that the Seward Peninsula is exotic to western Laurentia because of the abundance of Neoproterozoic detrital zircons, which are rare or absent in Lower Paleozoic Cordilleran continental shelf rocks. Maximum depositional ages inferred from the youngest detrital age peaks include latest Proterozoic-Early Cambrian, Cambrian, Ordovician, Silurian, Devonian, and Pennsylvanian. These maximum depositional ages overlap with conodont ages reported from fossiliferous carbonate rocks on Seward Peninsula. The distinctive features of the Arctic Alaska-Chukotka terrane include Neoproterozoic felsic magmatic rocks intruding 2.0-1.1 Ga crust overlain by Paleozoic carbonate rocks and Paleozoic siliciclastic rocks with Neoproterozoic detrital zircons. The Neoproterozoic ages are similar to those in the peri-Gondwanan Avalonian-Cadomian arc system, the Timanide orogen of Baltica, and other circum-Arctic terranes that were proximal to Arctic Alaska prior to the opening of the Amerasian basin in the Early Cretaceous. Our Neoproterozoic reconstruction places the Arctic Alaska-Chukotka terrane in a position near Baltica, northeast of Laurentia, in an arc system along strike with the Avalonian-Cadomian arc terranes. Previously published faunal data indicate that Seward Peninsula had Siberian and Laurentian links by Early Ordovician time. The geologic links between the Arctic Alaska-Chukotka terrane and eastern Laurentia, Baltica, peri-Gondwanan arc terranes, and Siberia from the Paleoproterozoic to the Paleozoic help to constrain paleogeographic models from the Neoproterozoic history of Rodinia to the Mesozoic opening of the Arctic basin. ?? 2009 Geological Society of America.

Discovery of the fossiliferous Cu Brei Formation (Lower Devonian) in the Kon Tum Block (South Viet Nam)

NASA Astrophysics Data System (ADS)

Thanh, Tong-Dzuy; Duyen, Than Duc; Hung, Nguyen Huu; My, Bui Phu

2007-01-01

Lower Devonian corals and stromatoporoids have recently been discovered in limestones among low grade metamorphic rocks on the western margin of the Kon Tum Block (South Viet Nam). This unit has been identified as the Cu Brei Formation. Coral and stromatoporoid species have been described including Squameofavosites aff. spongiosus, Parallelostroma cf. multicolumnum, Amphipora cf. rasilis, A. cf. raritalis, Simplexodictyon cf. artyschtense, Stromatopora cf. boriarchinovi and Stromatopora sp. indet. The Cu Brei Formation is exposed in a small area 6 km in length and 3 km wide at the foot of Cu Brei Mountain (Sa Thay District, Kon Tum Province). As this formation is in marine shelf facies it is probable that further exposures of Lower Devonian sediments may be discovered in the Kon Tum Block. This discovery raises the question of the tectonic history of the metamorphic Kon Tum Block. It is possible that the block was not an area of positive uplift from the beginning of Paleozoic as has been supposed, but was submerged in a marine environment, at least on its outer margins, in the Devonian, and possibly even earlier, in Early Paleozoic.

Magmatic record of Late Devonian arc-continent collision in the northern Qiangtang, Tibet: Implications for the early evolution of East Paleo-Tethys Ocean

NASA Astrophysics Data System (ADS)

Dan, Wei; Wang, Qiang; Zhang, Xiu-Zheng; Zhang, Chunfu; Tang, Gong-Jian; Wang, Jun; Ou, Quan; Hao, Lu-Lu; Qi, Yue

2018-05-01

Recognizing the early-developed intra-oceanic arc is important in revealing the early evolution of East Paleo-Tethys Ocean. In this study, new SIMS zircon U-Pb dating, O-Hf isotopes, and whole-rock geochemical data are reported for the newly-discovered Late Devonian-Early Carboniferous arc in Qiangtang, central Tibet. New dating results reveal that the eastern Riwanchaka volcanic rocks were formed at 370-365 Ma and were intruded by the 360 Ma Gangma Co alkali feldspar granites. The volcanic rocks consist of basalts, andesites, dacites, and rhyodacites, whose geochemistry is similar to that typical of subduction-related volcanism. The basalts and andesites were generated by partial melting of the fluid and sediment-melt metasomatized mantle, respectively. The rhyodacites and dacites were probably derived from the fractional crystallization of andesites and from partial melting of the juvenile underplated mafic rocks, respectively. The Gangma Co alkali feldspar granites are A-type granites, and were possibly derived by partial melting of juvenile underplated mafic rocks in a post-collisional setting. The 370-365 Ma volcanic arc was characterized by basalts with oceanic arc-like Ce/Yb ratios and by rhyodacites with mantle-like or slightly higher zircon δ18O values, and it was associated with the contemporary ophiolites. Thus, we propose that it is the earliest intra-oceanic arc in the East Paleo-Tethys Ocean, and was accreted to the Northern Qiangtang Terrane during 365-360 Ma.

The Anarak, Jandaq and Posht-e-Badam metamorphic complexes in central Iran: New geological data, relationships and tectonic implications

NASA Astrophysics Data System (ADS)

Bagheri, Sasan; Stampfli, Gérard M.

2008-04-01

The Anarak, Jandaq and Posht-e-Badam metamorphic complexes occupy the NW part of the Central-East Iranian Microcontinent and are juxtaposed with the Great Kavir block and Sanandaj-Sirjan zone. Our recent findings redefine the origin of these complexes, so far attributed to the Precambrian-Early Paleozoic orogenic episodes, and now directly related to the tectonic evolution of the Paleo-Tethys Ocean. This tectonic evolution was initiated by Late Ordovician-Early Devonian rifting events and terminated in the Triassic by the Eocimmerian collision event due to the docking of the Cimmerian blocks with the Asiatic Turan block. The "Variscan accretionary complex" is a new name we proposed for the most widely distributed metamorphic rocks connected to the Anarak and Jandaq complexes. This accretionary complex exposed from SW of Jandaq to the Anarak and Kabudan areas is a thick and fine grain siliciclastic sequence accompanied by marginal-sea ophiolitic remnants, including gabbro-basalts with a supra-subduction-geochemical signature. New 40Ar/ 39Ar ages are obtained as 333-320 Ma for the metamorphism of this sequence under greenschist to amphibolite facies. Moreover, the limy intercalations in the volcano-sedimentary part of this complex in Godar-e-Siah yielded Upper Devonian-Tournaisian conodonts. The northeastern part of this complex in the Jandaq area was intruded by 215 ± 15 Ma arc to collisional granite and pegmatites dated by ID-TIMS and its metamorphic rocks are characterized by some 40Ar/ 39Ar radiometric ages of 163-156 Ma. The "Variscan" accretionary complex was northwardly accreted to the Airekan granitic terrane dated at 549 ± 15 Ma. Later, from the Late Carboniferous to Triassic, huge amounts of oceanic material were accreted to its southern side and penetrated by several seamounts such as the Anarak and Kabudan. This new period of accretion is supported by the 280-230 Ma 40Ar/ 39Ar ages for the Anarak mild high-pressure metamorphic rocks and a 262 Ma U-Pb age for the trondhjemite-rhyolite association of that area. The Triassic Bayazeh flysch filled the foreland basin during the final closure of the Paleo-Tethys Ocean and was partly deposited and/or thrusted onto the Cimmerian Yazd block. The Paleo-Tethys magmatic arc products have been well-preserved in the Late Devonian-Carboniferous Godar-e-Siah intra-arc deposits and the Triassic Nakhlak fore-arc succession. On the passive margin of the Cimmerian block, in the Yazd region, the nearly continuous Upper Paleozoic platform-type deposition was totally interrupted during the Middle to Late Triassic. Local erosion, down to Lower Paleozoic levels, may be related to flexural bulge erosion. The platform was finally unconformably covered by Liassic continental molassic deposits of the Shemshak. One of the extensional periods related to Neo-Tethyan back-arc rifting in Late Cretaceous time finally separated parts of the Eocimmerian collisional domain from the Eurasian Turan domain. The opening and closing of this new ocean, characterized by the Nain and Sabzevar ophiolitic mélanges, finally transported the Anarak-Jandaq composite terrane to Central Iran, accompanied by large scale rotation of the Central-East Iranian Microcontinent (CEIM). Due to many similarities between the Posht-e-Badam metamorphic complex and the Anarak-Jandaq composite terrane, the former could be part of the latter, if it was transported further south during Tertiary time.

Publications - PIR 2004-3A | Alaska Division of Geological & Geophysical

Science.gov Websites

; Bedrock; Bedrock Geology; Cambrian; Caribou Fossils; Cascaden Ridge Unit; Cenozoic; Colluvial Deposits ; Cretaceous; Devonian; Eolian; Fox Fossils; Generalized; Geochemistry; Geochronology; Geologic Map; Geology ; Holocene; Horse Fossils; Igneous Rocks; K-Ar; Livengood Bench; Livengood Dome Chert; Lost Creek Unit

Total petroleum systems of the Bonaparte Gulf Basin area, Australia; Jurassic, Early Cretaceous-Mesozoic; Keyling, Hyland Bay-Permian; Milligans-Carboniferous, Permian

USGS Publications Warehouse

Bishop, M.G.

1999-01-01

The Bonaparte Gulf Basin Province (USGS #3910) of northern Australia contains three important hydrocarbon source-rock intervals. The oldest source-rock interval and associated reservoir rocks is the Milligans-Carboniferous, Permian petroleum system. This petroleum system is located at the southern end of Joseph Bonaparte Gulf and includes both onshore and offshore areas within a northwest to southeast trending Paleozoic rift that was initiated in the Devonian. The Milligans Formation is a Carboniferous marine shale that sources accumulations of both oil and gas in Carboniferous and Permian deltaic, marine shelf carbonate, and shallow to deep marine sandstones. The second petroleum system in the Paleozoic rift is the Keyling, Hyland Bay-Permian. Source rocks include Lower Permian Keyling Formation delta-plain coals and marginal marine shales combined with Upper Permian Hyland Bay Formation prodelta shales. These source-rock intervals provide gas and condensate for fluvial, deltaic, and shallow marine sandstone reservoirs primarily within several members of the Hyland Bay Formation. The Keyling, Hyland Bay-Permian petroleum system is located in the Joseph Bonaparte Gulf, north of the Milligans-Carboniferous, Permian petroleum system, and may extend northwest under the Vulcan graben sub-basin. The third and youngest petroleum system is the Jurassic, Early Cretaceous-Mesozoic system that is located seaward of Joseph Bonaparte Gulf on the Australian continental shelf, and trends southwest-northeast. Source-rock intervals in the Vulcan graben sub-basin include deltaic mudstones of the Middle Jurassic Plover Formation and organic-rich marine shales of the Upper Jurassic Vulcan Formation and Lower Cretaceous Echuca Shoals Formation. These intervals produce gas, oil, and condensate that accumulates in, shallow- to deep-marine sandstone reservoirs of the Challis and Vulcan Formations of Jurassic to Cretaceous age. Organic-rich, marginal marine claystones and coals of the Plover Formation (Lower to Upper Jurassic), combined with marine claystones of the Flamingo Group and Darwin Formation (Upper Jurassic to Lower Cretaceous) comprise the source rocks for the remaining area of the system. These claystones and coals source oil, gas, and condensate accumulations in reservoirs of continental to marine sandstones of the Plover Formation and Flamingo Group. Shales of the regionally distributed Lower Cretaceous Bathurst Island Group and intraformational shales act as seals for hydrocarbons trapped in anticlines and fault blocks, which are the major traps of the province. Production in the Bonaparte Gulf Basin Province began in 1986 using floating production facilities, and had been limited to three offshore fields located in the Vulcan graben sub-basin. Cumulative production from these fields totaled more than 124 million barrels of oil before the facilities were removed after production fell substantially in 1995. Production began in 1998 from three offshore wells in the Zone of Cooperation through floating production facilities. After forty years of exploration, a new infrastructure of pipelines and facilities are planned to tap already discovered offshore reserves and to support additional development.

Source rock contributions to the Lower Cretaceous heavy oil accumulations in Alberta: a basin modeling study

USGS Publications Warehouse

Berbesi, Luiyin Alejandro; di Primio, Rolando; Anka, Zahie; Horsfield, Brian; Higley, Debra K.

2012-01-01

The origin of the immense oil sand deposits in Lower Cretaceous reservoirs of the Western Canada sedimentary basin is still a matter of debate, specifically with respect to the original in-place volumes and contributing source rocks. In this study, the contributions from the main source rocks were addressed using a three-dimensional petroleum system model calibrated to well data. A sensitivity analysis of source rock definition was performed in the case of the two main contributors, which are the Lower Jurassic Gordondale Member of the Fernie Group and the Upper Devonian–Lower Mississippian Exshaw Formation. This sensitivity analysis included variations of assigned total organic carbon and hydrogen index for both source intervals, and in the case of the Exshaw Formation, variations of thickness in areas beneath the Rocky Mountains were also considered. All of the modeled source rocks reached the early or main oil generation stages by 60 Ma, before the onset of the Laramide orogeny. Reconstructed oil accumulations were initially modest because of limited trapping efficiency. This was improved by defining lateral stratigraphic seals within the carrier system. An additional sealing effect by biodegraded oil may have hindered the migration of petroleum in the northern areas, but not to the east of Athabasca. In the latter case, the main trapping controls are dominantly stratigraphic and structural. Our model, based on available data, identifies the Gordondale source rock as the contributor of more than 54% of the oil in the Athabasca and Peace River accumulations, followed by minor amounts from Exshaw (15%) and other Devonian to Lower Jurassic source rocks. The proposed strong contribution of petroleum from the Exshaw Formation source rock to the Athabasca oil sands is only reproduced by assuming 25 m (82 ft) of mature Exshaw in the kitchen areas, with original total organic carbon of 9% or more.

The Neoacadian orogenic core of the souther Appalachians: a Geo-traverse through the migmatitic inner Piedmont from the Brushy Mountains to Lincolnton, North Carolina

USGS Publications Warehouse

Merschat, Arthur J.; Hatcher, Robert D.; Byars, Heather E.; Gilliam, William G.; Eppes, Martha Cary; Bartholomew, Mervin J.

2012-01-01

The Inner Piedmont extends from North Carolina to Alabama and comprises the Neoacadian (360–345 Ma) orogenic core of the southern Appalachian orogen. Bordered to west by the Blue Ridge and the exotic Carolina superterrane to the east, the Inner Piedmont is cored by an extensive region of migmatitic, sillimanite-grade rocks. It is a composite of the peri-Laurentian Tugaloo terrane and mixed Laurentian and peri-Gondwanan affinity Cat Square terrane, which are exposed in several gentle-dipping thrust sheets (nappes). The Cat Square terrane consists of Late Silurian to Early Devonian pelitic schist and metagraywacke intruded by several Devonian to Mississippian peraluminous granitoids, and juxtaposed against the Tugaloo terrane by the Brindle Creek fault. This field trip through the North Carolina Inner Piedmont will examine the lithostratigraphies of the Tugaloo and Cat Square terranes, deformation associated with Brindle Creek fault, Devonian-Mississippian granitoids and charnockite of the Cat Square terrane, pervasive amphibolite-grade Devonian-Mississippian (Neoacadian) deformation and metamorphism throughout the Inner Piedmont, and existence of large crystalline thrust sheets in the Inner Piedmont. Consistent with field observations, geochronology and other data, we have hypothesized that the Carolina superterrane collided obliquely with Laurentia near the Pennsylvania embayment during the Devonian, overrode the Cat Square terrane and Laurentian margin, and squeezed the Inner Piedmont out to the west and southwest as an orogenic channel buttressed against the footwall of the Brevard fault zone.

The Devonian Marcellus Shale and Millboro Shale

USGS Publications Warehouse

Soeder, Daniel J.; Enomoto, Catherine B.; Chermak, John A.

2014-01-01

The recent development of unconventional oil and natural gas resources in the United States builds upon many decades of research, which included resource assessment and the development of well completion and extraction technology. The Eastern Gas Shales Project, funded by the U.S. Department of Energy in the 1980s, investigated the gas potential of organic-rich, Devonian black shales in the Appalachian, Michigan, and Illinois basins. One of these eastern shales is the Middle Devonian Marcellus Shale, which has been extensively developed for natural gas and natural gas liquids since 2007. The Marcellus is one of the basal units in a thick Devonian shale sedimentary sequence in the Appalachian basin. The Marcellus rests on the Onondaga Limestone throughout most of the basin, or on the time-equivalent Needmore Shale in the southeastern parts of the basin. Another basal unit, the Huntersville Chert, underlies the Marcellus in the southern part of the basin. The Devonian section is compressed to the south, and the Marcellus Shale, along with several overlying units, grades into the age-equivalent Millboro Shale in Virginia. The Marcellus-Millboro interval is far from a uniform slab of black rock. This field trip will examine a number of natural and engineered exposures in the vicinity of the West Virginia–Virginia state line, where participants will have the opportunity to view a variety of sedimentary facies within the shale itself, sedimentary structures, tectonic structures, fossils, overlying and underlying formations, volcaniclastic ash beds, and to view a basaltic intrusion.

Devonian salt dissolution-collapse breccias flooring the Cretaceous Athabasca oil sands deposit and development of lower McMurray Formation sinkholes, northern Alberta Basin, Western Canada

NASA Astrophysics Data System (ADS)

Broughton, Paul L.

2013-01-01

The sub-Cretaceous paleotopography underlying giant Lower Cretaceous Athabasca oil sands, northern Alberta, has an orthogonal lattice pattern of troughs up to 50 km long and 100 m deep between pairs of cross-cutting lineaments. These structures are interpreted to have been inherited from a similar pattern of dissolution collapse-subsidence troughs in the underlying Middle Devonian salt beds. Removal of more than 100 m of halite salt fragmented the overlying Upper Devonian strata into fault blocks and collapse breccias that subsided into the underlying dissolution troughs. The unusually low 1:2 to 1:3 thickness ratios of halite salts to the overlying strata resulted in the Upper Devonian strata collapse-subsidence into underlying salt dissolution troughs being more cataclysmic during the first phase of salt removal. The second phase of slower but complete salt removal between the earlier troughs resulted in a more gradual subsidence of the overlying strata. This obliterated the earlier pattern of giant cross-cutting dissolution troughs bounded by major lineaments. The collapse breccia fabrics underlying the earlier troughs differ from those from areas between the troughs. Collapse breccias underlying the large troughs often have crushed fabrics distributed in zones that rapidly pinched out between fault blocks. Breccias between troughs developed as giant mosaics of detached carbonate blocks that formed breccia pipe complexes. Multiple sinkholes up to 100 m deep aligned along multi-km linear valley trends that dissected the sub-Cretaceous paleotopography. These sinkhole trends formed orthogonal patterns inherited from underlying lattice of NW-SE and NE-SW salt structured lineaments. These cross-cutting sinkhole trends have a smaller 5 km scale reticulate pattern similar to the giant 50 km scale pattern of collapse-subsidence troughs. Other sinkholes developed as lower McMurray strata sagged when underlying Devonian fault blocks and breccia pipes differentially subsided.

New U-Pb zircon ages and the duration and division of Devonian time

USGS Publications Warehouse

Tucker, R.D.; Bradley, D.C.; Ver Straeten, C.A.; Harris, A.G.; Ebert, J.R.; McCutcheon, S.R.

1998-01-01

Newly determined U-Pb zircon ages of volcanic ashes closely tied to biostratigraphic zones are used to revise the Devonian time-scale. They are: 1) 417.6 ?? 1.0 Ma for an ash within the conodont zone of Icriodus woschmidti/I. w. hesperius Lochkovian); 2) 408.3 ?? 1.9 Ma for an ash of early Emsian age correlated with the conodont zones of Po. dehiscens--Lower Po. inversus; 3) 391.4 ?? 1.8 Ma for an ash within the Po. c. costatus Zone and probably within the upper half of the zone (Eifelian); and 4) 381.1 ?? 1.3 Ma for an ash within the range of the Frasnian conodont Palmatolepis punctata (Pa. punctata Zone to Upper Pa. hassi Zone). U-Pb zircon ages for two rhyolites bracketing a palyniferous bed of the pusillites-lepidophyta spore zone, are dated at 363.8 ?? 2.2 Ma and 363 ?? 2.2 Ma and 363.4 ?? 1.8 Ma, respectively, suggesting an age of ~363 Ma for a level within the late Famennian Pa. g. expansa Zone. These data, together with other published zircon ages, suggest that the base and top of the Devonian lie close to 418 Ma and 362 Ma, respectively, thus lengthening the period of ~20% over current estimates. We suggest that the duration of the Middle Devonian (Eifelian and Givitian) is rather brief, perhaps no longer than 11.5 Myr (394 Ma-382.5 Ma), and that the Emsian and Famennian are the longest stages in the period with estimated durations of ~15.5 Myr and 14.5 Myr, respectively.

Geology of the Stroudsburg quadrangle and Adjacent areas, Pennsylvania--New Jersey

USGS Publications Warehouse

Epstein, Jack Burton

1971-01-01

The Stroudsburg area is within the Valley and Ridge and Great Valley physiographic provinces, Northampton and Monroe Counties, Pennsylvania, and Warren County, New Jersey. The northeast-trending subparallel valleys and ridges resulted from erosion of folded heterogeneous sedimentary rocks. These are Middle Ordovician to Middle Devonian in age and are more than 17,000 feet thick. Deposition of a thick flysch sequence (Martinsburg Formation of Ordovician age) accompanied onset of Taconic orogenesis. It was followed by deposition of a thick molasse sequence of Silurian and Early Devonian age (continental and marginal-marine clastics--Shawangunk Formation and Bloomsburg Red Beds--overlain by predominantly marginal-marine and subtidal limestone, dolomite, shale, and sandstone--Poxono Island Formation through Oriskany Group). Basin deepening and gradual shallowing occurred during Esopus through Mahantango deposition, heralding the Acadian clastic wedge exposed north of the Stroudsburg area. Interpretation of sedimentary structures and regional stratigraphic relations suggest that the Silurian and Devonian rocks were deposited in the following environments: A1luviated coastal plain (meandering and braided streams), tidal flats (supratidal and intertidal), barrier zone, and neritic zone (upper and lower). The rock stratigraphic units have been grouped into four lithotectonic units, each having a different style of deformation. Folds produced in these rocks are disharmonic, and it is believed that each rock sequence is set off from units above and below by decollements, or zones of detachment. Movement was northwest into the Appalachian basin, primarily by gravitational sliding. The contact between the Shawangunk Formation of Silurian age and Martinsburg Formation of Ordovician age, is one zone of detachment as well as an angular unconformity. Deformational effects of the Middle to Late Ordovician Taconic orogeny are elusive, but it appears that the folds and most minor structures, including the prominent regional cleavage, were produced during the late Paleozoic Appalachian orogeny and are superimposed upon larger Taconic folds and faults. Field relations and microscopic study suggest that the regional cleavage in the Stroudsburg area is due to laminar flow of pelitic material along cleavage folia accompanied by mechanical reorientation of platy and elongate minerals and neocrystallization of mica, quartz, chlorite, and probably albite. Numerous lines of evidence point to the conclusion that cleavage developed after the rock was indurated and formed at, and Just below, conditions of low-grade metamorphism. Intensity of cleavage development increases to the southeast across the area. Second-generation slip cleavage, also believed to be Appalachian in age, formed by mechanical reorientation of minerals as well as by limited new mineral growth. The topography had a profound effect on the direction of movement of the Wisconsin glacier, as well as the manner of its retreat and the deposits that were formed. Till and stratified drift of Wisconsin age and till of Illinoian(?) age are common in the area. Wisconsin deglaciation occurred by northeastward retreat and by stagnation. A conspicuous terminal moraine marks the limit of Wisconsin ice movement. Lake Sciota was dammed between the retreating ice, the moraine, and the surrounding ridges north of Godfrey Ridge. Several deltas mark ice stand positions during the retreat of the ice. Lake-bottom and kame deposits are locally common in Cherry Valley. South of Kittatinny Mountain, on the other hand, melt water was freely discharged to the south. The wind and water gaps in the Stroudsburg area (including Delaware Water Gap and Wind Gap) are structurally controlled; specifically they are located where folds die out in short distances, where folding is locally more intense, or where resistant rocks dip steeply and have a narrow width of outcrop. This conclusion is contrary to

Geologic map of the Hogback Mountain quadrangle, Lewis and Clark and Meagher Counties, Montana

USGS Publications Warehouse

Reynolds, Mitchell W.

2003-01-01

The geologic map of the Hogback Mountain quadrangle, scale 1:24,000, was made as part of the Montana Investigations Project to provide new information on the stratigraphy, structure, and geologic history of an area in the geologically complex southern part of the Montana disturbed belt. In the Hogback Mountain area, rocks ranging in age from Middle Proterozoic through Cretaceous are strongly folded within and under thrust plates of equivalent rocks. Continental rocks of successive thrust plates have been telescoped eastward over a buttress of the stable continent. Erosional remnants of Oligocene andesitic basalt lie on highest surfaces eroded across the strongly deformed older rocks; younger erosion has dissected the terrain deeply, producing Late Tertiary and Quaternary deposits of alluvium, colluvium, and local landslide debris in the valleys and canyons. Different stratigraphic successions are exposed at different structural levels across the quadrangle. In the northeastern part of the quadrangle at the lowest structural level, rocks of the Upper Mississippian Big Snowy Group, including the Kibbey Formation and the undivided Otter and Heath Formations, the overlying Pennsylvanian Amsden and undivided Quadrant and Phosphoria Formations, the Ellis Group, and the Kootenai Formation, are folded and broken by thrust faults. The next higher structural level, the Avalanche Butte thrust plate, exposes strongly folded and, in places, attenuated strata of Cambrian (Flathead Sandstone, Wolsey Shale, Meagher Limestone, and undivided Pilgrim Formation and Park Shale), Devonian (Maywood Formation, Jefferson Formation, and most of the Three Forks Formation), and Mississippian (uppermost part of the Three Forks Formation and Lodgepole and Mission Canyon Limestones) ages. The overlying Hogback Mountain thrust plate contains strongly folded rocks ranging in age from the Middle Proterozoic Greyson Formation to the Upper and Lower Mississippian Mission Canyon Limestone and Cretaceous diorite sills. The highest structural level, the Moors Mountain thrust plate, contains the Middle Proterozoic Greyson and Newland Formations and discontinuous Upper Proterozoic diabase sills. Rocks are complexly folded and faulted across the quadrangle. At the lowest level in the northeastern part of the quadrangle, Upper Mississippian and younger strata are folded along northwest-trending axes and broken by thrust faults that at outcrop level displace the same rocks. The central core of the quadrangle is formed by the Avalanche Butte thrust plate, which contains recumbently folded and thrust faulted Paleozoic rocks. A succession of four tight recumbent folds within the plate have axial traces that trend northwest and north-northwest, and that are both arched and downfolded along east- and northeast-trending axes. Carbonate rocks of the Mission Canyon and Lodgepole Limestones in the upper part of the Avalanche Butte thrust plate exposed in the canyon of Trout Creek are folded and attenuated in stacked east-directed recumbent folds that developed as a succession of folded duplex thrust slices. The exposed remnant of the next higher structural level, the Hogback Mountain thrust plate, contains northeast- and east-trending folds that are inverted on the upper overturned limb of a younger northwest-trending recumbent fold. The Hogback Mountain thrust fault is itself folded and, in its northernmost exposures, is overturned to dip west beneath the overlying Moors Mountain thrust plate. During post-middle Tertiary deformation, the Hogback Mountain thrust fault moved as a normal fault, down on the east. The structurally highest Moors Mountain thrust plate rests on the Avalanche Butte thrust plate in the southwestern part of the quadrangle and across both the Avalanche Butte and Hogback Mountain thrust plates along the northwest edge of the quadrangle. In the central eastern part of the map area, the edge of a large klippen of the Moors Mounta

New insight on petroleum system modeling of Ghadames basin, Libya

NASA Astrophysics Data System (ADS)

Bora, Deepender; Dubey, Siddharth

2015-12-01

Underdown and Redfern (2008) performed a detailed petroleum system modeling of the Ghadames basin along an E-W section. However, hydrocarbon generation, migration and accumulation changes significantly across the basin due to complex geological history. Therefore, a single section can't be considered representative for the whole basin. This study aims at bridging this gap by performing petroleum system modeling along a N-S section and provides new insights on source rock maturation, generation and migration of the hydrocarbons using 2D basin modeling. This study in conjunction with earlier work provides a 3D context of petroleum system modeling in the Ghadames basin. Hydrocarbon generation from the lower Silurian Tanezzuft formation and the Upper Devonian Aouinet Ouenine started during the late Carboniferous. However, high subsidence rate during middle to late Cretaceous and elevated heat flow in Cenozoic had maximum impact on source rock transformation and hydrocarbon generation whereas large-scale uplift and erosion during Alpine orogeny has significant impact on migration and accumulation. Visible migration observed along faults, which reactivated during Austrian unconformity. Peak hydrocarbon expulsion reached during Oligocene for both the Tanezzuft and the Aouinet Ouenine source rocks. Based on modeling results, capillary entry pressure driven downward expulsion of hydrocarbons from the lower Silurian Tanezzuft formation to the underlying Bir Tlacsin formation observed during middle Cretaceous. Kinetic modeling has helped to model hydrocarbon composition and distribution of generated hydrocarbons from both the source rocks. Application of source to reservoir tracking technology suggest some accumulations at shallow stratigraphic level has received hydrocarbons from both the Tanezzuft and Aouinet Ouenine source rocks, implying charge mixing. Five petroleum systems identified based on source to reservoir correlation technology in Petromod*. This Study builds upon the original work of Underdown and Redfern, 2008 and offers new insights and interpretation of the data.

Evaluation of shale gas potential based on organic matter characteristics and gas concentration in the Devonian Horn River Formation, Canada

NASA Astrophysics Data System (ADS)

Choi, Jiyoung; Hong, Sung Kyung; Lee, Hyun Suk

2017-04-01

In this study, we investigate organic matter characteristics from the analysis of Rock-Eval6 and biomarker, and estimate methane concentration from headspace method in the Devonian Horn River Formation, which is one of the largest shale reservoir in western Canada. The Horn River Formation consists of the Evie, Otterpark and Muskwa members in ascending stratigraphic order. Total Organic Carbon (TOC) ranges from 0.34 to 7.57 wt%, with an average of 2.78 wt%. The Evie, middle Otterpark and Muskwa members have an average TOC of more than 3%, whereas those of the lower and upper Otterpark Member are less than 2%. Based on Pristane/n-C17 (0.2 0.6) and Phytane/n-C18 (0.3 0.9) ratios, the organic matter in the Evie, middle Otterpark and Muskwa members mainly consists of type II kerogen which are formed in reducing marine environment. Thermal maturity were examined through the use of the distributions of Phenanthrene (P) and Methylphenantrenes (MP) based on m/z 178 and 192 mass chromatograms, respectively (Radke et al., 1982). The methylphenanthrene index (MPI-1) are calculated as follows : MPI-1 = 1.5 × (2MP+3MP)/(P+1MP+9MP), and Ro are calculated as follows : Ro = -0.6 × MPI-1 + 2.3. Estimated Ro ranges between 1.88 and 1.93%, which indicates the last stage of wet gas generation. The methane concentrations in headspace range from 15 to 914 ppmv, with an average of 73.5 ppmv. The methane concentrations in the Evie, middle Otterpark and Muskwa members (up to 914 ppmv) are higher than those of the lower and upper Otterpark Member (up to 75 ppmv). Considering the organic geochemical characteristics and gas concentrations, the shale gas potentials of the Evie, middle Otterpark and Muskwa members are higher than those of other members.

The rise of fire: Fossil charcoal in late Devonian marine shales as an indicator of expanding terrestrial ecosystems, fire, and atmospheric change

USGS Publications Warehouse

Rimmer, Susan M.; Hawkins, Sarah J.; Scott, Andrew C.; Cressler, Walter L.

2015-01-01

Fossil charcoal provides direct evidence for fire events that, in turn, have implications for the evolution of both terrestrial ecosystems and the atmosphere. Most of the ancient charcoal record is known from terrestrial or nearshore environments and indicates the earliest occurrences of fire in the Late Silurian. However, despite the rise in available fuel through the Devonian as vascular land plants became larger and trees and forests evolved, charcoal occurrences are very sparse until the Early Mississippian where extensive charcoal suggests well-established fire systems. We present data from the latest Devonian and Early Mississippian of North America from terrestrial and marine rocks indicating that fire became more widespread and significant at this time. This increase may be a function of rising O2 levels and the occurrence of fire itself may have contributed to this rise through positive feedback. Recent atmospheric modeling suggests an O2 low during the Middle Devonian (around 17.5%), with O2 rising steadily through the Late Devonian and Early Mississippian (to 21–22%) that allowed for widespread burning for the first time. In Devonian-Mississippian marine black shales, fossil charcoal (inertinite) steadily increases up-section suggesting the rise of widespread fire systems. There is a concomitant increase in the amount of vitrinite (preserved woody and other plant tissues) that also suggests increased sources of terrestrial organic matter. Even as end Devonian glaciation was experienced, fossil charcoal continued to be a source of organic matter being introduced into the Devonian oceans. Scanning electron and reflectance microscopy of charcoal from Late Devonian terrestrial sites indicate that the fires were moderately hot (typically 500–600 °C) and burnt mainly surface vegetation dominated by herbaceous zygopterid ferns and lycopsids, rather than being produced by forest crown fires. The occurrence and relative abundance of fossil charcoal in marine black shales are significant in that these shales may provide a more continuous record of fire than is preserved in terrestrial environments. Our data support the idea that major fires are not seen in the fossil record until there is both sufficient and connected fuel and a high enough atmospheric O2 content for it to burn.

Detrital zircon geochronology of pre- and syncollisional strata, Acadian orogen, Maine Appalachians

USGS Publications Warehouse

Bradley, Dwight C.; O'Sullivan, Paul B.

2017-01-01

The Central Maine Basin is the largest expanse of deep-marine, Upper Ordovician to Devonian metasedimentary rocks in the New England Appalachians, and is a key to the tectonics of the Acadian Orogeny. Detrital zircon ages are reported from two groups of strata: (1) the Quimby, Rangeley, Perry Mountain and Smalls Falls Formations, which were derived from inboard, northwesterly sources and are supposedly older; and (2) the Madrid, Carrabassett and Littleton Formations, which were derived from outboard, easterly sources and are supposedly younger. Deep-water deposition prevailed throughout, with the provenance shift inferred to mark the onset of foredeep deposition and orogeny. The detrital zircon age distribution of a composite of the inboard-derived units shows maxima at 988 and 429 Ma; a composite from the outboard-derived units shows maxima at 1324, 1141, 957, 628, and 437 Ma. The inboard-derived units have a greater proportion of zircons between 450 and 400 Ma. Three samples from the inboard-derived group have youngest age maxima that are significantly younger than the nominal depositional ages. The outboard-derived group does not share this problem. These results are consistent with the hypothesised provenance shift, but they signal potential problems with the established stratigraphy, structure, and (or) regional mapping. Shallow-marine deposits of the Silurian to Devonian Ripogenus Formation, from northwest of the Central Maine Basin, yielded detrital zircons featuring a single age maximum at 441 Ma. These zircons were likely derived from a nearby magmatic arc now concealed by younger strata. Detrital zircons from the Tarratine Formation, part of the Acadian foreland-basin succession in this strike belt, shows age maxima at 1615, 980 and 429 Ma. These results are consistent with three episodes of zircon recycling beginning with the deposition of inboard-derived strata of the Central Maine Basin, which were shed from post-Taconic highlands located to the northwest. Next, southeasterly parts of this succession were deformed in the Acadian orogeny, shedding detritus towards the northwest into what remained of the basin. Finally, by Pragian time, all strata in the Central Maine Basin had been deformed and detritus from this new source accumulated as the Tarratine Formation in a new incarnation of the foreland basin. Silurian-Devonian strata from the Central Maine Basin have similar detrital zircon age distributions to coeval rocks from the Arctic Alaska and Farewell terranes of Alaska and the Northwestern terrane of Svalbard. We suggest that these strata were derived from different segments of the 6500-km-long Appalachian-Caledonide orogen.

Low Pressure-High Temperature Metamorphism and the Advection of Heat to the Continental Crust: A Case Study from Northwest New Guinea

NASA Astrophysics Data System (ADS)

Jost, B.; Webb, M.; White, L. T.

2017-12-01

In northwest New Guinea, Palaeozoic basement rocks forming part of the northern margin of the Australian continent are exposed in a rugged mountain range. This remote and understudied region provides a unique window into the complex Palaeozoic evolution and tectonic history of this region, which we help unravel with new field, petrographic, geochemical, and geochronological data. The basement rocks consist of extensive meta-turbidites that were subject to low pressure-high temperature metamorphism along their eastern margin. They are cross-cut by predominantly acidic granitoids. U-Pb zircon dating reveals that these granitoids intruded in three episodes in the Devonian-Carboniferous, the Carboniferous, and the Triassic. The first episode has not previously been reported in the region. The granitoids are strongly peraluminous, suggesting that partial melting of the meta-sedimentary country rock contributed to their petrogenesis (S-type). The occurrence and character of country rock xenoliths and migmatites supports this interpretation. Equilibrium thermodynamic modelling of the metapelites and the migmatites indicates that a substantial amount of heat was added to the lower and middle crust to cause partial melting and regional metamorphism at relatively low pressure. We propose repeated intrusion of hot magma as the mechanism responsible for advecting the necessary heat from the mantle. This likely occurred in an active continental margin setting during the Devonian-Carboniferous and the Triassic, possibly separated by an interval of magmatic quiescence during most of the Permian. New biostratigraphic and low-temperature thermochronological data reveal very recent Pliocene-Pleistocene uplift and unroofing of these basement rocks.

The Mesozoic and Palaeozoic granitoids of north-western New Guinea

NASA Astrophysics Data System (ADS)

Jost, Benjamin M.; Webb, Max; White, Lloyd T.

2018-07-01

A large portion of the Bird's Head Peninsula of NW New Guinea is an inlier that reveals the pre-Cenozoic geological history of the northern margin of eastern Gondwana. The peninsula is dominated by a regional basement high exposing Gondwanan ('Australian') Palaeozoic metasediments intruded by Palaeozoic and Mesozoic granitoids. Here, we present the first comprehensive study of these granitoids, including field and petrographic descriptions, bulk rock geochemistry, and U-Pb zircon age data. We further revise and update previous subdivisions of granitoids in the area. Most granitoids were emplaced as small to medium-scale intrusions during two episodes in the Devonian-Carboniferous and the Late Permian-Triassic, separated by a period of apparent magmatic quiescence. The oldest rocks went unrecognised until this study, likely due to the younger intrusive events resetting the K-Ar isotopic system used in previous studies. Most of the Palaeozoic and Mesozoic granitoids are peraluminous and in large parts derived from partial melts of the country rock. This is corroborated by local migmatites and country rock xenoliths. Although rare, metaluminous and mafic rocks show that partial melts of mantle-derived material played a minor role in granitoid petrogenesis, especially during the Permian-Triassic. The Devonian-Carboniferous granitoids and associated volcanics are locally restricted, whereas the Permian-Triassic intrusions are found across NW New Guinea and further afield. The latter were likely part of an extensive active continental margin above a subduction system spanning the length of what is now New Guinea and potentially extending southward through eastern Australia and Antarctica.

Hydrologic properties and ground-water flow systems of the Paleozoic rocks in the upper Colorado River basin in Arizona, Colorado, New Mexico, Utah, and Wyoming, excluding the San Juan Basin

USGS Publications Warehouse

Geldon, Arthur L.

2003-01-01

The hydrologic properties and ground-water flow systems of Paleozoic sedimentary rocks in the Upper Colorado River Basin were investigated under the Regional Aquifer-System Analysis (RASA) program of the U.S. Geological Survey in anticipation of the development of water supplies from bedrock aquifers to fulfill the region's growing water demands. The study area, in parts of Arizona, Colorado, New Mexico, Utah, and Wyoming, covers about 100,000 square miles. It includes parts of four physiographic provinces--the Middle Rocky Mountains, Wyoming Basin, Southern Rocky Mountains, and Colorado Plateaus. A variety of landforms, including mountains, plateaus, mesas, cuestas, plains, badlands, and canyons, are present. Altitudes range from 3,100 to 14,500 feet. Precipitation is distributed orographically and ranges from less than 6 inches per year at lower altitudes to more than 60 inches per year in some mountainous areas. Most of the infrequent precipitation at altitudes of less than 6,000 feet is consumed by evapotranspiration. The Colorado and Green Rivers are the principal streams: the 1964-82 average discharge of the Colorado River where it leaves the Upper Colorado River Basin is 12,170 cubic feet per second (a decrease of 5,680 cubic feet per second since construction of Glen Canyon Dam in 1963). On the basis of their predominant lithologic and hydrologic properties, the Paleozoic rocks are classified into four aquifers and three confining units. The Flathead aquifer, Gros Ventre confining unit, Bighorn aquifer, Elbert-Parting confining unit, and Madison aquifer (Redwall-Leadville and Darwin-Humbug zones) make up the Four Corners aquifer system. A thick sequence, composed mostly of Mississippian and Pennsylvanian shale, anhydrite, halite, and carbonate rocks--the Four Corners confining unit (Belden-Molas and Paradox-Eagle Valley subunits)--overlies the Four Corners aquifer system in most areas and inhibits vertical ground-water flow between the Four Corners aquifer system and the overlying Canyonlands aquifer. Composed of the uppermost Paleozoic rocks, the Canyonlands aquifer consists, in ascending order, of the Cutler-Maroon, Weber-De Chelly, and Park City-State Bridge zones. The Paleozoic rocks are underlain by a basal confining unit consisting of Precambrian sedimentary, igneous, and metamorphic rocks and overlain throughout most of the Upper Colorado River Basin by the Chinle-Moenkopi confining unit, which consists of Triassic formations composed mostly of shale. The largest values of porosity, permeability, hydraulic conductivity, transmissivity, and artesian yield are exhibited by the Redwall-Leadville zone of the Madison aquifer and the Weber-De Chelly zone of the Canyonlands aquifer. The former consists almost entirely of Devonian and Mississippian carbonate rocks: the latter consists mostly of Pennsylvanian and Permian quartz sandstone. Unit-averaged porosity in hydrogeologic units composed of Paleozoic rocks ranges from less than 1 to 28 percent. Permeability ranges from less than 0.0001 to 3,460 millidarcies. Unit-averaged hydraulic conductivity ranges from 0.000005 to 200 feet per day. The composite transmissivity of Paleozoic rocks ranges from 0.0005 to 47,000 feet squared per day. Artesian yields to wells and springs (excluding atypical springflows) from these hydrogeologic units range from less than 1 to 10,000 gallons per minute. The permeability and watersupply capabilities of all hydrogeologic units progressively decrease from uplifted areas to structural basins. Recharge to the Paleozoic rocks is provided by direct infiltration of precipitation, leakage from streams, and ground-water inflows from structurally continuous areas west and north of the Upper Colorado River Basin. The total recharge available flom ground-water systems in the basin from direct precipitation and stream leakage is estimated to be 6,600,000 acre-feet per year. However, little of this recharge directly enters the Paleozoic rocks

Continental crust melting induced by subduction initiation of the South Tianshan Ocean: Insight from the Latest Devonian granitic magmatism in the southern Yili Block, NW China

NASA Astrophysics Data System (ADS)

Bao, Zihe; Cai, Keda; Sun, Min; Xiao, Wenjiao; Wan, Bo; Wang, Yannan; Wang, Xiangsong; Xia, Xiaoping

2018-03-01

The Tianshan belt of the southwestern Central Asian Orogenic Belt was generated by Paleozoic multi-stage subduction and final closure of several extinct oceans, including the South Tianshan Ocean between the Kazakhstan-Yili and Tarim blocks. However, the subduction initiation and polarity of the South Tianshan Ocean remain issues of highly debated. This study presents new zircon U-Pb ages, geochemical compositions and Sr-Nd isotopes, as well as zircon Hf isotopic data of the Latest Devonian to Early Carboniferous granitic rocks in the Wusun Mountain of the Yili Paleozoic convergent margin, which, together with the spatial-temporal distributions of regional magmatic rocks, are applied to elucidate their petrogenesis and tectonic linkage to the northward subduction initiation of the South Tianshan Ocean. Our zircon U-Pb dating results reveal that these granites were emplaced at the time interval of 362.0 ± 1.2-360.3 ± 1.9 Ma, suggesting a marked partial melting event of the continental crust in the Latest Devonian to Early Carboniferous. These granites, based on their mineral compositions and textures, can be categorized as monzogranites and K-feldspar granites. Geochemically, both monzogranites and K-feldspar granites have characters of I-type granites with high K2O contents (4.64-4.83 wt.%), and the K-feldspar granites are highly fractionated I-type granites, while the monzogranites have features of unfractionated I-type granites. Whole-rock Sr-Nd isotopic modeling results suggest that ca. 20-40% mantle-derived magmas may be involved in magma mixing with continental crust partial melts to generate the parental magmas of the granites. The mantle-derived basaltic magmas was inferred not only to be a major component of magma mixture but also as an important heat source to fuse the continental crust in an extensional setting, which is evidenced by the high zircon saturation temperatures (713-727 °C and 760-782 °C) of the studied granites. The Latest Devonian to Early Carboniferous extensional setting in the Wusun Mountain region of the Yili Paleozoic convergent margin is addressed by the subduction initiation of the South Tianshan Ocean and constituted a late Paleozoic nascent arc- back-arc system in the southwestern CAOB.

Paleozoic intrusive rocks from the Dunhuang tectonic belt, NW China: Constraints on the tectonic evolution of the southernmost Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Zhao, Yan; Sun, Yong; Diwu, Chunrong; Zhu, Tao; Ao, Wenhao; Zhang, Hong; Yan, Jianghao

2017-05-01

The Dunhuang tectonic belt (DTB) is of great importance for understanding the tectonic evolution of the southernmost Central Asian Orogenic Belt (CAOB). In this study, the temporal-spatial distribution, petrogenesis and tectonic setting of the Paleozoic representative intrusive rocks from the DTB were systematically investigated to discuss crustal evolution history and tectonic regime of the DTB during Paleozoic. Our results reveal that the Paleozoic magmatism within the DTB can be broadly divided into two distinct episodes of early Paleozoic and late Paleozoic. The early Paleozoic intrusive rocks, represented by a suite metaluminous-slight peraluminous and medium- to high-K calc-alkaline I-type granitoids crystallized at Silurian (ca. 430-410 Ma), are predominantly distributed along the northern part of the DTB. They were probably produced with mineral assemblage of eclogite or garnet + amphibole + rutile in the residue, and were derived from magma mixing source of depleted mantle materials with various proportions of Archean-Mesoproterozoic continental crust. The late Paleozoic intrusive rocks can be further subdivided into two stages of late Devonian stage (ca. 370-360 Ma) and middle Carboniferous stage (ca. 335-315 Ma). The former stage is predominated by metaluminous to slight peraluminous and low-K tholeiite to high-K calc-alkaline I-type granitic rocks distributed in the central part of the DTB. They were also generated with mineral assemblage of amphibolite- to eclogite-facies in the residue, and originated from magma source of depleted mantle materials mixed with different degrees of old continental crust. The later stage is represented by adakite and alkali-rich granite exposed in the southern part of the DTB. The alkali-rich granites studied in this paper were possibly produced with mineral assemblage of granulite-facies in the residue and were generated by partial melting of thickened lower continental crust. Zircon Hf isotopes and field distribution of those Paleozoic intrusive rocks reveal that both the Silurian and the late Devonian magmatic activities predominantly represent crustal growth processes in the DTB, accompanied by different degrees of reworking of pre-existing continental crust. However, the middle Carboniferous (ca. 335-315 Ma) magmatic activity reflects a crustal reworking process. The Silurian and late Devonian intrusive rocks were most likely formed in the arc-related subduction zones, whereas, the middle Carboniferous intrusive rocks were possibly formed in a transitional tectonic setting from compression to extension, representing the final stage of Paleozoic orogeny in the DTB. These Paleozoic magmatic rocks further suggest that the DTB has reactivated from a stable block to an orogen and undergone two episodes (the early Paleozoic and the late Paleozoic) of orogeny during Paleozoic. It represents a Paleozoic accretionary orogen of the southernmost margin of the CAOB between the Tarim Craton and North China Craton, and tectonically extends northward to the Beishan orogen and westward to the eastern South Tianshan Belt.

Provenance and paleogeography of the Devonian Durazno Group, southern Parana Basin in Uruguay

NASA Astrophysics Data System (ADS)

Uriz, N. J.; Cingolani, C. A.; Basei, M. A. S.; Blanco, G.; Abre, P.; Portillo, N. S.; Siccardi, A.

2016-03-01

A succession of Devonian cover rocks occurs in outcrop and in the subsurface of central-northern Uruguay where they were deposited in an intracratonic basin. This Durazno Group comprises three distinct stratigraphic units, namely the Cerrezuelo, Cordobés and La Paloma formations. The Durazno Group does not exceed 300 m of average thickness and preserves a transgressive-regressive cycle within a shallow-marine siliciclastic shelf platform, and is characterized by an assemblage of invertebrate fossils of Malvinokaffric affinity especially within the Lower Devonian Cordobés shales. The sedimentary provenance of the Durazno Group was determined using petrography, geochemistry, and morphological studies of detrital zircons as well as their U-Pb ages. Sandstone petrography of Cerrezuelo and La Paloma sequences shows that they have a dominantly quartz-feldspathic composition with a minor contribution of other minerals. Whole-rock geochemical data indicate that alteration was strong in each of the three formations studied; chondritic-normalized REE patterns essentially parallel to PAAS, the presence of a negative Eu-anomaly, and Th/Sc and La/Hf ratios point to an average source composition similar to UCC or slightly more felsic. Within the Cerrezuelo Formation, recycling of older volcano-metasedimentary sources is interpreted from Zr/Sc ratios and high Hf, Zr, and REE concentrations. U-Pb detrital zircon age populations of the Cerrezuelo and La Paloma formations indicate that the principal source terranes are of Neoproterozoic age, but include also minor populations derived from Mesoproterozoic and Archean-Paleoproterozoic rocks. A provenance from the Cuchilla Dionisio-Dom Feliciano, Nico Pérez and Piedra Alta terranes of Uruguay and southern Brazil is likely. This study establishes an intracratonic extensional tectonic setting during Durazno time. Considering provenance age sources, regional paleocurrent distributions and the established orogenic history recorded in SW Gondwana, we suggest that the basin fill was derived from paleohighs located in what is currently SE Uruguay.

Geology and hydrocarbon potential of the Oued Mya Basin, Algeria

DOE Office of Scientific and Technical Information (OSTI.GOV)

Benamrane, O.; Messaoudi, M.; Messelles, H.

1992-01-01

The hydrocarbon System Ourd Mya is located in the Sahara Basin. It is one of the producing basin in Algeria. The stratigraphic section consists of Paleozoic and Mesosoic, it is about 5000m thick. In the eastern part, the basin is limited by the Hassi-Messaoud high zone which is a giant oil field producing from the Cambrian sands. The western part is limited by Hassi R'mel which is one of the biggest gas field in the world, it is producing from the triassic sands. The Mesozoic section is laying on the lower Devonian and in the eastern part, on the Cambrian.more » The main source rock is the Silurian shale with an average thickness of 50m and a total organic matter of 6% (14% in some cases). Results of maturation modeling indicate that the lower Silurian source is in the oil window. The Ordovician shales are also a source rock, but in a second order. Clastic reservoirs are in the Triassic sequence which is mainly fluvial deposits with complex alluvial channels, it is the main target in the basin. Clastic reservoirs within the lower Devonian section have a good hydrocarbon potential in the east of the basin through a southwest-northeast orientation. The late Triassic-Early Jurassic evaporites overlie the Triassic clastic interval and extend over the entire Oued Mya Basin. This is considered as a super-seal evaporate package, which consists predominantly of anhydrite and halite. For Paleozoic targets, a large number of potential seals exist within the stratigraphic column. The authors infer that a large amount of the oil volume generated by the Silurian source rock from the beginning of Cretaceous until now, still not discovered could be trapped within structure closures and mixed or stratigraphic traps related to the fluvial Triassic sandstones, marine Devonian sands and Cambro-Ordovician reservoirs.« less

Geology of the Volga-Ural petroleum province and detailed description of the Ramashkino and Arlan oil fields

USGS Publications Warehouse

Peterson, James A.; Clarke, James W.

1983-01-01

The Volga-Ural petroleum province is in general coincident with the Volga-Ural regional high, a broad upwarp of the east-central part of the Russian (East European) platform. The central part of the province is occupied by the Tatar arch, which contains the major share of the oil fields of the province. The Perm-Bashkir arch forms the northeastern part of the regional high, and the Zhigulevsko-Orenburg arch makes up the southern part. These arches are separated from one another by elongate downwarps. The platform cover overlies an Archean crystalline basement and consists of seven main sedimentation cycles as follows: 1) Riphean (lower Bavly) continental sandstone, shale, and conglomerate beds from 500 to 5,000 m thick deposited in aulacogens. 2) Vendian (upper Bavly) continental and marine shale and sandstone up to 3,000 m thick. 3) Middle Devonian-Tournaisian transgressive deposits, which are sandstone, siltstone, and shale in the lower part and carbonates with abundant reefs in the upper; thickness is 300-1,000 m. In the upper carbonate part is the Kamsko-Kinel trough system, which consists of narrow interconnected deep-water troughs. 4) The Visean-Namurian-Bashkirian cycle, which began with deposition of Visean clastics that draped over reefs of the previous cycle and filled in an erosional relief that had formed in some places on the sediments of the previous cycle. The Visean clastics are overlain by marine carbonates. Thickness of the cycle is 50-800 m. 5) Early Moscovian-Early Permian terrigenous clastic deposits and marine carbonate beds 1,000-3,000 m thick. 6) The late Early Permian-Late Permian cycle, which reflects maximum growth of the Ural Mountains and associated Ural foredeep. Evaporites were first deposited, then marine limestones and dolomites, which intertongue eastward with clastic sediments from the Ural Mountains. 7) Continental redbeds of Triassic age and mixed continental and marine elastic beds of Jurassic and Cretaceous age, which were deposited on the southern, southwestern, and northern margins of the Russian platform; they are generally absent in the Volga-Ural province, however. The Volga-Ural oil and gas basin is a single artesian system that contains seven aquifers separated by seals. The areas of greatest hydraulic head are in the eastern parts of the basin near areas where the aquifers crop out on the western slopes of the Ural Mountains. The Peri-Caspian basin is the principal drainage area of the artesian system. Approximately 600 oil and gas fields and 2,000 pools have been found in the Volga-Ural province. Nine productive sequences are recognized as follows: 1) Upper Proterozoic (Bavly beds), which are promising but not yet commercial. 2) Clastic Devonian, which contains the major reserves and includes the main pays of the super-giant Romashkino field. 3) Carbonate Upper Devonian and lowermost Carboniferous, which is one of the main reef-bearing intervals. 4) Visean (Lower Carboniferous) elastics, which are the main pays in the super-giant Arian field. 5) Carbonate Lower and Middle Carboniferous. 6) Clastic Middle Carboniferous Moscovian. 7) Carbonate Middle and Upper Carboniferous. 8) Carbonate-evaporite Lower Permian, which contains the major gas reserves and the lower part of the Melekess tar deposits. 9) Clastic-carbonate Upper Permian, which contains the major part of the Melekess tar deposits. The Volga-Ural province is divided into several productive regions on a basis of differences in structure, distribution of reservoir and source-rock facies, and general composition of the petroleum accumulations. These regions are the Tatar arch, Birsk saddle, Upper Kama depression, Perm-Bashkir arch, Ufa-Orenburg monocline, Melekess-Sernovodsko-Abdulino basin, Zhligulevsko-Orenburg arch, Ural foredeep, and north borders of the Peri-Casplan depression. Exploration activity has declined in recent years; however, interest remains high in several parts of the province, particula

Metamorphism and plutonism around the middle and south forks of the Feather River, California

USGS Publications Warehouse

Hietanen, Anna Martta

1976-01-01

The area around the Middle and South Forks of the Feather River provides information on metamorphic and igneous processes that bear on the origin of andesitic and granitic magmas in general and on the variation of their potassium content in particular. In the north, the area joins the Pulga and Bucks Lake quadrangles studied previously. Tectonically, this area is situated in the southern part of an arcuate segment of the Nevadan orogenic belt in the northwestern Sierra Nevada. The oldest rocks are metamorphosed calcalkaline island-arc-type andesite, dacite, and sodarhyolite with interbedded tuff layers (the Franklin Canyon Formation), all probably correlative with Devonian rocks in the Klamath Mountains. Younger rocks form a sequence of volcanic, volcaniclastic, and sedimentary rocks including some limestone (The Horseshoe Bend Formation), probably Permian in age. All the volcanic and sedimentary rocks were folded and recrystallized to the greenschist facies during the Nevadan (Jurassic) orogeny and were invaded by monzotonalitic magmas shortly thereafter. A second lineation and metamorphism to the epidote-amphibolite facies developed in a narrow zone around the plutons. In light of the concept of plate tectonics, it is suggested that the early (Devonian?) island-arc-type andesite, dacite, and sodarhyolite (the Franklin Canyon Formation) were derived from the mantle above a Benioff zone by partial melting of peridotite in hydrous conditions. The water was probably derived from an oceanic plate descending to the mantle. Later (Permian?) magmas were mainly basaltic; some discontinuous layers of potassium-rich rhyolite indicate a change into anhydrous conditions and a deeper level of magma generation. The plutonic magmas that invaded the metamorphic rocks at the end of the Jurassic may contain material from the mantle, the subducted oceanic lithosphere, and the downfolded metamorphic rocks. The ratio of partial melts from these three sources may have changed with time, giving rise to the diversity in composition of magmas.

Metallogeny of the Mont-de-l'Aigle IOCG deposit, Gaspé Peninsula, Québec, Canada

NASA Astrophysics Data System (ADS)

Simard, M.; Beaudoin, G.; Bernard, J.; Hupé, A.

2006-09-01

The Mont-de-l’Aigle deposit is located in the northern part of Dome Lemieux, in the Connecticut Valley-Gaspé Synclinorium, Gaspé Peninsula, Québec. The Dome Lemieux is a subcircular antiform of Siluro-Devonian sedimentary rocks that is cut by numerous mafic and felsic sills and dikes of Silurian to Late Devonian age. Plutonism occurred in a continental within-plate extensional setting typical of orogenic collapse. The Cu-Fe (± Au) mineralization of Mont-de-l’Aigle occurs in veins, stockworks, and breccias. Mineralization is located near or within N-S and NW-SE faults cutting sedimentary rocks. IOCG mineralization postdates intrusions, skarns, hornfels, and epithermal mineralization typical of the southern part of the Dome Lemieux. The paragenetic sequence comprises: (1) pervasive sodic, potassic, chlorite, and silica alteration, (2) hematite, quartz, pyrite, magnetite, and chalcopyrite veins, stockworks and breccias and, (3) dolomite ± hematite veins and veinlets cutting the earlier mineralization. Intrusions display proximal sodic and potassic alteration, whereas sedimentary rocks have proximal decalcification, silicification, and potassic alteration. Both intrusive and sedimentary rocks are affected by a pervasive distal chlorite (± silica) alteration. The sulfur isotope composition of pyrite and chalcopyrite (δ34S=-1.5 to 4.8‰) suggests that sulfur was derived mainly from igneous rocks. Fluid δ18O (-0.4 to 2.65‰) indicates meteoric or seawater that reacted with the country rocks. Mixing of hot magmatic fluids with a cooler fluid, perhaps meteoric or seawater is suggested for mineral deposition and alteration of the Mont-de-l’Aigle deposit. The mineralogy, alteration, and sulfur isotope composition of the Mont-de-l’Aigle deposit compare well with IOCG deposits worldwide, making the Mont-de-l’Aigle deposit a rare example of Paleozoic IOCG mineralization, formed at shallow depth, within a low metamorphic grade sedimentary rock sequence.

Rotational and accretionary evolution of the Klamath Mountains, California and Oregon, from Devonian to present time

USGS Publications Warehouse

Irwin, William P.; Mankinen, Edward A.

1998-01-01

The purpose of this report is to show graphically how the Klamath Mountains grew from a relatively small nucleus in Early Devonian time to its present size while rotating clockwise approximately 110°. This growth occurred by the addition of large tectonic slices of oceanic lithosphere, volcanic arcs, and melange during a sequence of accretionary episodes. The Klamath Mountains province consists of eight lithotectonoic units called terranes, some of which are divided into subterranes. The Eastern Klamath terrane, which was the early Paleozoic nucleus of the province, is divided into the Yreka, Trinity, and Redding subterranes. Through tectonic plate motion, usually involving subduction, the other terranes joined the early Paleozoic nucleus during seven accretionary episodes ranging in age from Early Devonian to Late Jurassic. The active terrane suture is shown for each episode by a bold black line. Much of the western boundary of the Klamath Mountains is marked by the South Fork and correlative faults along which the Klamath terranes overrode the Coast Range rocks during an eighth accretionary episode, forming the South Fork Mountain Schist in Early Cretaceous time.

Dutrochus, a new microdomatid (Gastropoda) genus from the Middle Devonian (Eifelian) of west-central Alaska

USGS Publications Warehouse

Blodgett, R.B.

1993-01-01

A new gastropod genus, Dutrochus, is established for members of the family Microdomatidae that are characterized by a reticulate ornament of spiral cords and intersecting, finer collabral threads, with all but one spiral cord being of nearly equal strength, and the single remaining cord being of stronger (nearly twice the order) magnitude and being situated at the periphery. It is represented by the type and only known species, Dutrochus alaskensis n. gen. and sp., from the upper part (lower Eifelian) of the Lower? and Middle Devonian Cheeneetnuk Limestone. The genus is very close and nearly homeomorphic to the Permian microdomatid genus Glyptospira. -from Author

Origins and relationships of colonial Heliophyllum in the upper Middle Devonian (Givetian) of New York

USGS Publications Warehouse

Oliver, W.A.

1997-01-01

Heliophyllum halli Milne-Edwards and Haime is common to abundant in many Lower and Middle Devonian stratigraphic units in New York. Most Heliophyllum are solitary, but both branching and massive colonies are known. Four 'populations' of colonial Heliophyllum in the Givetian part of the sequence are distinct, as is a fifth form that occurs through the section. Each of the colonial forms is interpreted as an independent derivative of solitary forms of H. halli. The relationships appear to range from infrasubspecific to specific, and it is suggested that the complex should be recognized as the Heliophyllum halli species group.

A reconnaissance Rb-Sr, Sm-Nd, U-Pb, and K-Ar study of some host rocks and ore minerals in the West Shasta Cu- Zn district, California ( USA).

USGS Publications Warehouse

Kistler, R.W.; McKee, E.H.; Futa, K.; Peterman, Z.E.; Zartman, R.E.

1985-01-01

The Copley Greenstone, Balaklala Rhyolite, and Mule Mountain stock in the West Shasta Cu-Zn district, California, have Rb-Sr, Sm-Nd, U-Pb, and K-Ar systematics that indicate they are a cogenetic suite of ensimatic island-arc rocks about 400 Ma. Pervasive alteration and mineralization of these rocks, for the most part, was syngenetic and the major component of the mineralizing fluid was Devonian seawater. K-Ar ages of quarz-sericite concentrates from ore horizons and Rb-Sr systematics of a few rock and ore specimens record a later thermal and mineralizing event in the district of about 260 Ma. Contamination of some rocks with pelagic sediments is indicated by the Sm-Nd data. -Authors

A late Devonian impact event and its association with a possible extinction event on Eastern Gondwana

NASA Technical Reports Server (NTRS)

Wang, K.; Geldsetzer, H. H. J.

1992-01-01

Evidence from South China and Western Australia for a 365-Ma impact event in the Lower crepida conodont zone of the Famennian stage of the Late Devonian (about 1.5 Ma after the Frasnian/Famennian extinction event) includes microtektitelike glassy microspherules, geochemical anomalies (including a weak Ir), a probable impact crater (greater than 70 k) at Taihu in South China, and an Ir anomaly in Western Australia. A brachiopod faunal turnover in South China, and the 'strangelove ocean'-like c-delta 13 excursions in both Chinese and Australian sections indicate that at least a regional-scale extinction might have occurred at the time of the impact. A paleoreconstruction shows that South China was very close to and facing Western Australia in the Late Devonian. The carbon isotopic excursions, which occur at the same stratigraphic level in both South China and Western Australia cannot be explained as being coincidental. The c-delta 13 excursions and the brachiopod faunal turnover in South China indicate that there might have been at least a regional (possibly global) extinction in the Lower crepida zone. The impact-derived microspherules and geochemical anomalies (especially the Ir) indicate a Lower crepida zone impact event on eastern Gondwana. The location, type of target rocks, and possibly age of the Taihu Lake crater qualify as the probable site of this Late Devonian impact.

Evolution of groundwater composition in the depression cone of Riga region

NASA Astrophysics Data System (ADS)

Raga, B.; Kalvans, A.; Delina, A.; Perkone, E.; Retike, I.

2012-04-01

Riga is the capital of Latvia with around 0.9 million inhabitants where the main water supply is centralised and decentralised, mostly from groundwater sources, that is from the the Arukilas-Amatas multi-aquifer system, which consists of sandstones and siltstone. These rocks belong to the middle and upper Devonian and have good properties for groundwater extraction: they have high permeability and are widely spread. Below this system lies the middle Devonian Narvas aquitard, that consists of marl and clay. But in the southern and western part of Riga this system covers the upper Devonian Salaspils formation which consists of marl and gypsum. In the second half of the 20th century an intensive groundwater extraction from the Arukilas-Amtas multi-aquifer system took place in Riga, causing sharp and significant lowering of piezometric surfaces. The maximal decline of groundwater level was observed in 1972, when it was 16 m lower than the average. From the end of 80's started a regeneration of water table, when the volume of water usage began to decrease. Nowadays piezometric surface in the Arukilas-Amatas multi-aquifer system is being renewed and fluctuations are insignificant. The territory, where natural regime of groundwater has changed and that is induced by antropogenic effect is called "Large Riga". To track chemical changes and evolution in the Arukila-Amata multi-aquifer system long - term monitoring data is used. Data on major ions and piezometric surfaces from 45 monitoring wells that groups in 17 monitoring stations is being analysed. The area is dived into three zones - central, middle and periphery, which differ from each other by the volume of the groundwater level decline. These zones are determined from maps, that shows the piezometric surface difference between two periods: 1949-1951, that describes the natural situation, and 1970-1972, where the minimal groundwater level in the Gauja aquifer was observed. On this basis it was studied how rapidly water chemistry change in aquifers shows up and how these trends change. It was found out that the sources of water with high SO42- which worsen the quality of water in deeper aquifers, are from the Salaspils aquifer, because the first signs were observed in aquifers, that lie below the Salaspils formation. The same water composition changes in deeper aquifers with a time lag. When piezometric surface rised up, the mixing from different aquifers ended, that can be clearly observed in the upper Devonian Plavinu aquifer where, in the latest samples, is an increasing concentration of HCO3- ion. These are the first signs that the situation in this multi-aquifer system begins to return into natural conditions. Despite that Riga is lying near the sea, the lowering of water table in the Arukilas-Amatas multi-aquifer system hasn't induced intensive intrusion of sea water. This process is observed only in some areas, where intrusion occurs through the bed of river Daugava where the Plavinas aquifer dolomites are situated. The significant water composition changes are observed in the central part, where the greatest piezometric surface lowering is, which was sufficient enough to cause stronger downward flow from upper aquifers, that induced the mixing water from different aquifers in this territory. As a result, in this zone there are great water composition changes. Also the first signs about water composition changes show up very quickly, but the return to the natural situation is relatively slow. This study is supported by the European Social Fund project No. 2009/0212/1DP/1.1.1.2.0/09/APIA/VIAA/060

The carpenter fork bed, a new - and older - Black-shale unit at the base of the New Albany shale in central Kentucky: Characterization and significance

USGS Publications Warehouse

Barnett, S.F.; Ettensohn, F.R.; Norby, R.D.

1996-01-01

Black shales previously interpreted to be Late Devonian cave-fill or slide deposits are shown to be much older Middle Devonian black shales only preserved locally in Middle Devonian grabens and structural lows in central Kentucky. This newly recognized - and older -black-shale unit occurs at the base of the New Albany Shale and is named the Carpenter Fork Bed of the Portwood Member of the New Albany Shale after its only known exposure on Carpenter Fork in Boyle County, central Kentucky; two other occurrences are known from core holes in east-central Kentucky. Based on stratigraphic position and conodont biostratigraphy, the unit is Middle Devonian (Givetian: probably Middle to Upper P. varcus Zone) in age and occurs at a position represented by an unconformity atop the Middle Devonian Boyle Dolostone and its equivalents elsewhere on the outcrop belt. Based on its presence as isolated clasts in the overlying Duffin Bed of the Portwood Member, the former distribution of the unit was probably much more widespread - perhaps occurring throughout western parts of the Rome trough. Carpenter Fork black shales apparently represent an episode of subsidence or sea-level rise coincident with inception of the third tectophase of the Acadian orogeny. Deposition, however, was soon interrupted by reactivation of several fault zones in central Kentucky, perhaps in response to bulge migration accompanying start of the tectophase. As a result, much of central Kentucky was uplifted and tilted, and the Carpenter Fork Bed was largely eroded from the top of the Boyle, except in a few structural lows like the Carpenter Fork graben where a nearly complete record of Middle to early Late Devonian deposition is preserved.

Paleozoic strata of the Dyckman Mountain area, northeastern Medfra quadrangle, Alaska: A section in Geologic studies in Alaska by the U.S. Geological Survey, 1998

USGS Publications Warehouse

Dumoulin, Julie A.; Bradley, Dwight C.; Harris, Anita G.

2000-01-01

Paleozoic rocks in the Dyckman Mountain area (northeastern Medfra quadrangle; Farewell terrane) include both shallowand deep-water lithologies deposited on and adjacent to a carbonate platform. Shallow-water strata, which were recognized by earlier workers but not previously studied in detail, consist of algal-laminated micrite and skeletal-peloidal wackestone, packstone, and lesser grainstone. These rocks are, at least in part, of Early and (or) Middle Devonian age but locally could be as old as Silurian; they accumulated in shallow subtidal to intertidal settings with periodically restricted water circulation. Deepwater facies, reported here for the first time, are thin, locally graded beds of micrite and calcisiltite and subordinate thick to massive beds of lime grainstone and conglomerate. Conodonts indicate an age of Silurian to Middle Devonian; the most tightly dated intervals are early Late Silurian (early to middle Ludlow). These strata formed as hemipelagic deposits, turbidites, and debris flows derived from shallow-water lithologies of the Nixon Fork subterrane. Rocks in the Dyckman Mountain area are part of a broader facies belt that is transitional between the Nixon Fork carbonate platform to the west and deeper water, basinal lithologies (Minchumina “terrane”) to the east. Transitional facies patterns are complex because of Paleozoic shifts in the position of the platform margin, Mesozoic shortening, and Late Cretaceous-Tertiary disruption by strike-slip faulting.

Geologic structure and occurrence of gas in part of southwestern New York. Part 1, Structure and gas possibilities of the Oriskany sandstone in Steuben, Yates, and parts of the adjacent counties

USGS Publications Warehouse

Bradley, W.H.; Pepper, J.F.

1941-01-01

The area covered by this report is in southwestern New York and includes a little more than 3,000 square miles in Steuben and Yates counties and parts of the six adjacent counties. This area has been mapped to determine the structural attitude of the exposed rocks, so as to aid those interested in prospecting for natural gas in the Oriskany sandstone of Lower Devonian age.Because of the gentle regional dip toward the southwest, the youngest beds are exposed in the southwest corner of the area, and progressively older beds crop out northeastward in successive bands that strike generally northwest. All the exposed rocks are of Upper Devonian age except those in a narrow belt at the extreme north edge of the area, where a small thickness of Middle Devonian rocks crops out. The maximum thickness of beds so exposed is nearly 4,000 feet, of which the lower part is predominantly soft dark shale and the upper part predominantly fine-grained sandstone and gray shale. All the beds are marine except a few tongues of continental deposits red shale and sandstone and gray mudstone in the youngest beds. All the beds thicken southeastward, so that there is a northwestward convergence between any two lithologic units in the series. More than 30 key horizons that are persistent and distinctive were mapped, and altitudes on these key horizons served as a basis for constructing the structure contour map. Many of the key horizons are formation or member boundaries, but others are the tops or bottoms of limestone or sandstone beds within formations. All the stratigraphic units mapped are purely lithologic. (See pi. 2.)The Tully limestone, which crops out along the northern border of the area, is an easily recognizable and therefore valuable key bed for subsurface correlations in this part of the State. Below the Tully limestone is a thick body of Middle Devonian shales of the Hamilton group which rests on another valuable key bed, the hard, cherty Onondaga limestone, also of Middle Devonian age. Below the Onondaga limestone is the Lower Devonian Oriskany sandstone, which is the gas-producing bed. Unlike the Onondaga, the Oriskany is locally thin or absent.The structure of most of the area is shown by contour lines at 25-foot intervals, but where key horizons are lacking the structure is indicated by dip symbols. Upon the regional south and southwest dip are superposed numerous gentle folds whose axes trend approximately northeastward in the greater part of the area but more nearly eastward in the eastern part. The folds generally tend to become narrower and steeper, and therefore more closely spaced, southwestward. Many of the anticlines fork southwestward, whereas the synclines. tend to fork northeastward. All the folds have a westward or southwestward plunge. Throughout the area the rocks are jointed in two dominant sets one that trends northwest and the other east or northeast. No evident relation .between these joints, which were measured only in the hard, relatively brittle beds, and the individual folds or domes was discernible.The faults are concentrated in the northeastern and southwestern parts of the area and trend either northeastward or northwestward. Some are nearly vertical normal faults; others are steep reverse faults. Subsurface data show that most of the faults increase in throw downward and also that many subsurface faults do not reach the surface. A group of faults in the northwestern part of the Greenwood quadrangle and the southwestern part of the Hornell quadrangle were active during Upper Devonian time, while the Gowanda shale and overlying beds were being deposited. At this stratigraphic horizon the beds in a zone a few hundred feet thick are highly deformed in a wide belt on both sides of the faults. Sandstone layers are thinned out into long stringers or swollen into thick masses and in places are bent acutely without fracture. Thin layers of shale, coquina, and sand have flowed together into intricately plicated zones that lack cleavage and joints. These features show that the sediments were deformed while wet and plastic and buried only a little way below the sea floor. The beds that were laid down over these disturbed zones were not involved in this deformation. Many of the sharper flexures and most of the faults are not evident in the beds several hundred feet stratigraphically higher. Accordingly, broad, gentle folds in these higher beds in parts of the area south and west of the northwest corner of the Greenwood quadrangle may conceal, at considerable depths below them, narrow folds separated by abrupt flexures or faults.Several of the larger streams and rivers occupy strike valleys, and their j courses swing to follow the changing strike of the rocks where they cross ( successive folds. But, with few exceptions, the small streams are not adjusted to the bedrock structure. Domes likely to serve as traps for natural gas are concentrated in the northeastern and southwestern parts of the area. The Wayne-Dundee gas field is in the northeastern part. All the other potentially valuable domes in this part of the area have been drilled and found valueless except one small structural feature in the southern part of the Ovid quadrangle, which, if the Oriskany is present, may trap a small quantity of gas.In the Greenwood quadrangle in the southwestern part of the area there is one gas field and four well-defined domes, all of which may be productive if the Oriskany sandstone is present. In the northwest corner of the quadrangle the dips indicate at least two domes that can be adequately defined and evaluated only by geophysical prospecting. The State Line gas field is in tbe Wellsville quadrangle. In the southeast corner of this quadrangle there are three other domes of comparable size that may also be productive if underlain by the Oriskany sandstone. At other places in the Wellsville quadrangle the dips suggest several anticlinal axes on which analogous productive domes maybe found. The structural features in this quadrangle, however, are defined by contours only in the southeastern part. In the Woodhull quadrangle a large dome east of Jasper may be productive, and the western top of the large Woodhull dome in the southwestern part of the quadrangle seems to warrant drilling, despite the absence of the Oriskany in a well on the eastern top. Two wells drilled in 1936 and 1937 a little northeast of a broad, nearly flat-topped dome in the Hornell quadrangle, a few miles east of Hornell,, struck small flows of gas, suggesting that wells drilled higher on this dome may be productive.In much of the southwestern part of the area seismograph surveys should be of great value in determining the structure at the Tully and Onondaga horizons. Without abundant subsurface control of this sort, the danger of drilling into subsurface faults can hardly be overemphasized. Three closed or nearly closed synclines in the Greenwood and Wellsville quadrangles appear to be favorable places to drill for oil in the shallow sands presumably parts of the Dunkirk sandstone.

Geologic structure and occurrence of gas in part of southwestern New York

USGS Publications Warehouse

Bradley, Wilmot H.; Pepper, James F.; Richardson, G.B.

1941-01-01

The area covered by this report is in southwestern New York and includes a little more than 3,000 square miles in Steuben and Yates counties and parts of the six adjacent counties. This area has been mapped to determine the structural attitude of the exposed rocks, so as to aid those interested in prospecting for natural gas in the Oriskany sandstone of Lower Devonian age.Because of the gentle regional dip toward the southwest, the youngest beds are exposed in the southwest corner of the area, and progressively older beds crop out northeastward in successive bands that strike generally northwest. All the exposed rocks are of Upper Devonian age except those in a narrow belt at the extreme north edge of the area, where a small thickness of Middle Devonian rocks crops out. The maximum thickness of beds so exposed is nearly 4,000 feet, of which the lower part is predominantly soft dark shale and the upper part predominantly fine-grained sandstone and gray shale. All the beds are marine except a few tongues of continental deposits—red shale and sandstone and gray mudstone—in the youngest beds. All the beds thicken southeastward, so that there is a northwestward convergence between any two lithologic units in the series. More than 30 key horizons that are persistent and distinctive were mapped, and altitudes on these key horizons served as a basis for constructing the structure contour map. Many of the key horizons are formation or member boundaries, but others are the tops or bottoms of limestone or sandstone beds within formations. All the stratigraphic units mapped are purely lithologic. (See pl. 2.)The Tully limestone, which crops out along the northern border of the area, is an easily recognizable and therefore valuable key bed for subsurface correlations in this part of the State. Below the Tully limestone is a thick body of Middle Devonian shales of the Hamilton group which rests on another valuable key bed, the hard, cherty Onondaga limestone, also of Middle Devonian age. Below the Onondaga limestone is the Lower Devonian Oriskany sandstone, which is the gas-producing bed. Unlike the Onondaga, the Oriskany is locally thin or absent.The structure of most of the area is shown by contour lines at 25-foot intervals, but, where key horizons are lacking the structure is indicated by dip symbols. Upon the regional south and southwest dip are superposed numerous gentle folds whose axes trend approximately northeastward in the greater part of the area but more nearly eastward in the eastern part. The folds generally tend to become narrower and steeper, and therefore more closely spaced, southwestward. Many of the anticlines fork southwestward, whereas the synclines tend to fork northeastward. All the folds have a westward or southwestward plunge.Throughout the area the rocks are jointed in two dominant sets—one that trends northwest and the other east or northeast. No evident relation between these joints, which were measured only in the hard, relatively brittle beds, and the individual folds or domes was discernible.The faults are concentrated in the northeastern and southwestern parts of the area and trend either northeastward or northwestward. Some are nearly vertical normal faults ; others are steep reverse faults. Subsurface data show that most of the faults increase in throw downward and also that many subsurface faults do not reach the surface. A group of faults in the northwestern part of the Greenwood quadrangle and the southwestern part of the Hornell quadrangle were active during Upper Devonian time, while the Gowanda shale and overlying beds were being deposited. At this stratigraphic horizon the beds in a zone a few hundred feet thick are highly deformed in a wide belt on both sides of the faults. Sandstone layers are thinned out into long stringers or swollen into thick masses and in places are bent acutely without fracture. Thin layers of shale, coquina, and sand have flowed together into intricately plicated zones that lack cleavage and joints. These features show that the sediments were deformed while wet and plastic and buried only a little way below the sea floor. The beds that were laid down over these disturbed zones were not involved in this deformation. Many of the sharper flexures and most of the faults are not evident in the beds several hundred feet stratigraphically higher. Accordingly, broad, gentle folds in these higher beds in parts of the area south and west of the northwest corner of the Greenwood quadrangle may conceal, at considerable depths below them, narrow folds separated by abrupt flexures or faults.Several of the larger streams and rivers occupy strike valleys, and their courses swing to follow the changing strike of the rocks where they cross successive folds. But, with few exceptions, the small streams are not adjusted to the bedrock structure.Domes likely to serve as traps for natural gas are concentrated in the northeastern and southwestern parts of the area. The Wayne-Dundee gas field is in the northeastern part. All the other potentially valuable domes in this part of the area have been drilled and found valueless except one small structural feature in the southern part of the Ovid quadrangle, which, if the Oriskany is present, may trap a small quantity of gas.In the Greenwood quadrangle in the southwestern part of the area there is one gas field and four well-defined domes, all of which may be productive if the Oriskany sandstone is present. In the northwest corner of the quadrangle the dips indicate at least two domes that can be adequately defined and evaluated only by geophysical prospecting. The State Line gas field is in the Wellsville quadrangle. In the southeast corner of this quadrangle there are three other domes of comparable size that may also be productive if underlain by the Oriskany sandstone. At other places in the Wellsville quadrangle the dips suggest several anticlinal axes on which analogous productive domes may be found. The structural features in this quadrangle, however, are defined by contours only in the southeastern part. In the Woodhull quadrangle a large dome east of Jasper may be productive, and the western top of the large Wood-hull dome in the southwestern part of the quadrangle seems to warrant drilling, despite the absence of the Oriskany in a well on the eastern top. Two wells drilled in 1936 and 1937 a little northeast of a broad, nearly flat-topped dome in the Hornell quadrangle, a few miles east of Hornell, struck small flows of gas, suggesting that wells drilled higher on this dome may be productive.In much of the southwestern part of the area seismograph surveys should be of great value in determining the structure at the Tully and Onondaga horizons. Without abundant subsurface control of this sort, the danger of drilling into subsurface faults can hardly be overemphasized.Three closed or nearly closed synclines in the Greenwood and Wellsville quadrangles appear to be favorable places to drill for oil in the shallow sands— presumably parts of the Dunkirk sandstone.

Mineral and whole-rock compositions of seawater-dominated hydrothermal alteration at the Arctic volcanogenic massive sulfide prospect, Alaska

USGS Publications Warehouse

Schmidt, J.M.

1988-01-01

The Arctic volcanogenic massive sulfide prospect, located in the Ambler mineral district of northwestern Alaska, includes three types of hydrothermally altered rocks overlying, underlying, and interlayered with semimassive sulfide mineralization. Hydrothermal alteration of wall rocks and deposition of sulfide and gangue minerals were contemporaneous with Late Devonian of Early Mississippian basalt-rhyolite volcanism. Alteration developed asymmetrically around a linear fissure, suggesting fracture control of ore fluids rather than a point source. Microprobe analyses of phyllosilicates from the Arctic area indicate two discrete mineral populations. These differences in mineral chemistry are the result of differences in protolith composition caused by hydrothermal alteration-metasomatism. -from Author

Geology of the Devonian black shales of the Appalachian basin

USGS Publications Warehouse

Roen, J.B.

1983-01-01

Black shales of Devonian age in the Appalachian basin are a unique rock sequence. The high content of organic matter, which imparts the characteristic lithology, has for years attracted considerable interest in the shales as a possible source of energy. Concurrent with periodic and varied economic exploitations of the black shales are geologic studies. The recent energy shortage prompted the U.S. Department of Energy through the Eastern Gas Shales Project of the Morgantown Energy Technology Center to underwrite a research program to determine the geologic, geochemical, and structural characteristics of the Devonian black shales in order to enhance the recovery of gas from the shales. Geologic studies produced a regional stratigraphic network that correlates the 15-foot sequence in Tennessee with 3,000 feet of interbedded black and gray shales in central New York. The classic Devonian black-shale sequence in New York has been correlated with the Ohio Shale of Ohio and Kentucky and the Chattanooga Shale of Tennessee and southwestern Virginia. Biostratigraphic and lithostratigraphic markers in conjunction with gamma-ray logs facilitated long range correlations within the Appalachian basin and provided a basis for correlations with the black shales of the Illinois and Michigan basins. Areal distribution of selected shale units along with paleocurrent studies, clay mineralogy, and geochemistry suggests variations in the sediment source and transport directions. Current structures, faunal evidence, lithologic variations, and geochemical studies provide evidence to support interpretation of depositional environments. In addition, organic geochemical data combined with stratigraphic and structural characteristics of the shale within the basin allow an evaluation of the resource potential of natural gas in the Devonian shale sequence.

Provenance and petrofacies, Upper Devonian sandstones, Philip Smith Mountains and Arctic quandrangles, Brooks Range, Alaska: Final report, Project No. 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, A.V.; Coney, P.J.

1987-11-01

Late Devonian sandstone beds are exposed as allochthonous sequences that extend for over 1000 km along the east-west strike of the Brooks Range in northern Alaska. These horizons, at least in part, record Late Devonian tectonism and deposition along the southern margin of the Arctic Alaska block. This study identifies clastic petrofacies in the western Philip Smith Mountains and southern Arctic quadrangles and infers the composition of the source terrane. The paleogeography is not known and the original distribution of lithofacies is uncertain, owing to the extensive post-depositional tectonism. In the study area the sandstones are exposed along rugged mountainmore » tops and high ridges. Although exposures are excellent, access is often difficult. Samples were collected from exposures near the western end of the Chandalar Shelf, Atigun Pass, and the Atigun River valley in the Philip Smith Mountains quadrangle and from the Crow Nest Creek and Ottertail Creek areas in the Arctic quadrangle. 34 refs., 17 figs.« less

New geological data of New Siberian Archipelago

NASA Astrophysics Data System (ADS)

Sobolev, Nikolay; Petrov, Evgeniy

2014-05-01

The area of New Siberian Archipelago (NSA) encompasses different tectonic blocks is a clue for reconstruction of geological structure and geodynamic evolution of East Arctic. According to palaeomagnetic study two parts of the archipelago - Bennett and Anjou Islands formed a single continental block at least from the Early Palaeozoic. Isotope dating of De Long Islands igneous and sedimentary rocks suggests Neoproterozoic (Baikalian) age of its basement. The De Long platform sedimentary cover may be subdivided into two complexes: (1) intermediate of PZ-J variously deformed and metamorphosed rocks and (2) K-KZ of weakly lithified sediments. The former complex comprises the Cambrian riftogenic volcanic-clastic member which overlain by Cambrian-Ordovician turbiditic sequence, deposited on a continental margin. This Lower Palaeozoic complex is unconformably overlain by Early Cretaceous (K-Ar age of c.120 Ma) basalts with HALIP petrochemical affinities. In Anjou Islands the intermediate sedimentary complex encompasses the lower Ordovician -Lower Carboniferous sequence of shallow-marine limestone and subordinate dolomite, mudstone and sandstone that bear fossils characteristic of the Siberian biogeographic province. The upper Mid Carboniferous - Jurassic part is dominated by shallow-marine clastic sediments, mainly clays. The K-KZ complex rests upon the lower one with angular unconformity and consists mainly of coal-bearing clastic sediments with rhyolite lavas and tuffs in the bottom (117-110 Ma by K-Ar) while the complexe's upper part contains intraplate alkalic basalt and Neogene-Quaternary limburgite. The De-Long-Anjou block's features of geology and evolution resemble those of Wrangel Island located some 1000 km eastward. The Laptev Sea shelf outcrops in intrashelf rises (Belkovsky and Stolbovoy Islands) where its geology and structure may be observed directly. On Belkovsky Island non-dislocated Oligocene-Miocene sedimentary cover of littoral-marine coal-bearing unconformably overlies folded basement. The latter encompasses two sedimentary units: the Middle Devonian shallow-marine carbonate and Late-Devonian-Permian olistostrome - flysch deposited in transitional environment from carbonate platform to passive margin. Dating of detrital zircons suggests the Siberian Platform and Taimyr-Severnaya Zemlya areas as the most possible provenance. The magmatic activity on Belkovsky Island resulted in formation of Early Triassic gabbro-dolerite similar to the Siberian Platform traps. Proximity of Belkovsky Island to the north of Verkhoyansk foldbelt allows continuation of the latter into the Laptev Sea shelf. The geology of Bolshoy Lyakhovsky Island is discrepant from the rest of the NSA. In the south of Bolshoy Lyakhovsky Island the ophiolite crops complex out: it is composed of tectonic melange of serpentinized peridotite, bandedf gabbro, pillow-basalt, and pelagic sediments (black shales and cherts). All the rocks underwent epidot - amphibolite, glaucophane and greenschist facies metamorphism. The ophiolite is intruded by various in composition igneous massifs - from gabbro-diorite to leuco-granite, which occurred at 110-120 Ma. The Bolshoy Lyakhovsky Island structure is thought to be a westerly continuation of the South Anui suture of Chukchi.

A resource evaluation of the Bakken Formation (Upper Devonian and Lower Mississippian) continuous oil accumulation, Williston Basin, North Dakota and Montana

USGS Publications Warehouse

Schmoker, J.W.

1996-01-01

The Upper Devonian and Lower Mississippian Bakken Formation in the United States portion of the Williston Basin is both the source and the reservoir for a continuous oil accumulation - in effect a single very large field - underlying approximately 17,800 mi2 (46,100 km2) of North Dakota and Montana. Within this area, the Bakken Formation continuous oil accumulation is not significantly influenced by the water column and cannot be analyzed in terms of conventional, discrete fields. Rather, the continuous accumulation can be envisioned as a collection of oil-charged cells, virtually all of which are capable of producing some oil, but which vary significantly in their production characteristics. Better wellperformance statistics are linked regionally to higher levels of thermal maturity and to lower levels of reservoir heterogeneity. Although portions of the Bakken Formation continuous oil accumulation have reached a mature stage of development, the accumulation as a whole is far from depleted.

Late Devonian conodonts and event stratigraphy in northwestern Algerian Sahara

NASA Astrophysics Data System (ADS)

Mahboubi, Abdessamed; Gatovsky, Yury

2015-01-01

Conodonts recovered from the Late Devonian South Marhouma section comprise 5 genera with 31 species (3 undetermined). The fauna establishes the presence of MN Zones 5, undifferentiated 6/7, 8/10 for the Middle Frasnian, the MN Zones 11, 12, 13 for the Upper Frasnian as well as the Early through Late triangularis Zones in the basal Famennian. The outcropping lithological succession is one of mostly nodular calcilutites alternating with numerous marly and shaly deposits, which, in the lower and upper part, comprise several dysoxic dark shale intervals. Among these the Upper Kellwasser horizon can be precisely dated and as such the presence of the terminal Frasnian Kellwasser Event is recognized for the first time in Algeria. Both the Middlesex and Rhinestreet Events cannot yet be precisely located, but supposedly occur among the dark shale horizons in the lower part of the section. However, their assignment to a precise level has so far not been established. Though poor in conodont abundance the South Marhouma section provides first evidence of the presence of several Montagne Noire conodont zones within the so far widely unstudied Frasnian of the Ougarta Chain. As such it is considered representative for the northwestern Algerian Saoura region.

Tectonics and hydrocarbon potential of the Barents Megatrough

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baturin, D.; Vinogradov, A.; Yunov, A.

1991-08-01

Interpretation of geophysical data shows that the geological structure of the Eastern Barents Shelf, named Barents Megatrough (BM), extends sublongitudinally almost from the Baltic shield to the Franz Josef Land archipelago. The earth crust within the axis part of the BM is attenuated up to 28-30 km, whereas in adjacent areas its thickness exceeds 35 km. The depression is filled with of more than 15 km of Upper Paleozoic, Mesozoic, and Cenozoic sediments overlying a folded basement of probable Caledonian age. Paleozoic sediments, with exception of the Upper Permian, are composed mainly of carbonates and evaporites. Mesozoic-Cenozoic sediments are mostlymore » terrigenous. The major force in the development of the BM was due to extensional tectonics. Three rifting phases are recognizable: Late Devonian-Early Carboniferous, Early Triassic, and Jurassic-Early Cretaceous. The principal features of the geologic structure and evolution of the BM during the late Paleozoic-Mesozoic correlate well with those of the Sverdup basin, Canadian Arctic. Significant quantity of Late Jurassic-Early Cretaceous basaltic dikes and sills were intruded within Triassic sequence during the third rifting phase. This was probably the main reason for trap disruption and hydrocarbon loss from Triassic structures. Lower Jurassic and Lower Cretaceous reservoir sandstones are most probably the main future objects for oil and gas discoveries within the BM. Upper Jurassic black shales are probably the main source rocks of the BM basin, as well as excellent structural traps for hydrocarbon fluids from the underlying sediments.« less

Detrital zircon U-Pb geochronology of Cambrian to Triassic miogeoclinal and eugeoclinal strata of Sonora, Mexico

USGS Publications Warehouse

Gehrels, G.E.; Stewart, John H.

1998-01-01

One hundred and eighty two individual detrital zircon grains from Cambrian through Permian miogeoclinal strata, Ordovician eugeoclinal rocks, and Triassic post-orogenic sediments in northwestern Sonora have been analyzed. During Cambrian, Devonian, Permian, and Triassic time, most zircons accumulating along this part of the Cordilleran margin were shed from 1.40-1.45 and 1.62-1.78 Ga igneous rocks that are widespread in the southwestern United States and northwestern Mexico. Zircons with ages of approximately 1.11 Ga are common in Cambrian strata and were apparently shed from granite bodies near the sample site. The sources of 225-280 Ma zircons in our Triassic sample are more problematic, as few igneous rocks of these ages are recognized in northwestern Mexico. Such sources may be present but unrecognized, or the grains could have been derived from igneous rocks of the appropriate ages to the northwest in the Mojave Desert region, to the east in Chihuahua and Coahuila, or to the south in accreted(?) arc-type terranes. Because the zircon grains in our Cambrian and Devonian to Triassic samples could have accumulated in proximity to basement rocks near their present position or in the Death Valley region of southern California, our data do not support or refute the existence of the Mojave-Sonora megashear. Ordovician strata of both miogeoclinal and eugeoclinal affinity are dominated by >1.77 Ga detrital zircons, which are considerably older than most basement rocks in the region. Zircon grains in the miogeoclinal sample were apparently derived from the Peace River arch area of northwestern Canada and transported southward by longshore currents. The eugeoclinal grains may also have come from the Peace River arch region, with southward transport by either sedimentary or tectonic processes, or they may have been shed from off-shelf slivers of continents (perhaps Antarctica?) removed from the Cordilleran margin during Neoproterozoic rifting. It is also possible that the Ordovician eugeoclinal strata are far traveled and exotic to North America.

Confirmation of the southwest continuation of the Cat Square terrane, southern Appalachian Inner Piedmont, with implications for middle Paleozoic collisional orogenesis

USGS Publications Warehouse

Huebner, Matthew T.; Hatcher, Robert D.; Merschat, Arthur J.

2017-01-01

Detailed geologic mapping, U-Pb zircon geochronology and whole-rock geochemical analyses were conducted to test the hypothesis that the southwestern extent of the Cat Square terrane continues from the northern Inner Piedmont (western Carolinas) into central Georgia. Geologic mapping revealed the Jackson Lake fault, a ∼15 m-thick, steeply dipping sillimanite-grade fault zone that truncates lithologically distinct granitoids and metasedimentary units, and roughly corresponds with a prominent aeromagnetic lineament hypothesized to represent the southern continuation of the terrane-bounding Brindle Creek fault. Results of U-Pb SHRIMP geochronology indicate Late Ordovician to Silurian granitoids (444–439 Ma) occur exclusively northwest of the fault, whereas Devonian (404–371 Ma) granitoids only occur southeast of the fault. The relatively undeformed Indian Springs granodiorite (three individual bodies dated 317–298 Ma) crosscuts the fault and occurs on both sides, which indicates the Jackson Lake fault is a pre-Alleghanian structure. However, detrital zircon signatures from samples southeast of the Jackson Lake fault reveal dominant Grenville provenance, in contrast to Cat Square terrane detrital zircon samples from the northern Inner Piedmont, which include peri-Gondwanan (600–500 Ma) and a prominent Ordovician-Silurian (∼430 Ma) signature. We interpret the rocks southeast of the Jackson Lake fault to represent the southwestern extension of the Cat Square terrane primarily based on the partitioning of granitoid ages and lithologic distinctions similar to the northern Inner Piedmont.Data suggest Cat Square terrane metasedimentary rocks were initially deposited in a remnant ocean basin setting and developed into an accretionary prism in front of the approaching Carolina superterrane, ultimately overridden by it in Late Devonian to Early Mississippian time. Burial to >20 km resulted in migmatization of lower plate rocks, forming an infrastructure beneath the Carolina superterrane suprastructure. Provenance patterns support ∼250 km of Devonian dextral translation of the composite Inner Piedmont, which places the northern portion of the Inner Piedmont adjacent to a suite of ∼430 Ma plutons in the Virginia Blue Ridge during deposition. The megascopic thrust-nappe structural style of the northern Inner Piedmont, combined with southwest-directed lateral extrusion at mid-crustal depths, may reconcile differences in timing of metamorphism between the Carolina and central Georgia Inner Piedmont and structural contrasts between the Brindle Creek and Jackson Lake faults.

Thermal maturity of type II kerogen from the New Albany Shale assessed by13C CP/MAS NMR

USGS Publications Warehouse

Werner-Zwanziger, U.; Lis, G.; Mastalerz, Maria; Schimmelmann, A.

2005-01-01

Thermal maturity of oil and gas source rocks is typically quantified in terms of vitrinite reflectance, which is based on optical properties of terrestrial woody remains. This study evaluates 13C CP/MAS NMR parameters in kerogen (i.e., the insoluble fraction of organic matter in sediments and sedimentary rocks) as proxies for thermal maturity in marine-derived source rocks where terrestrially derived vitrinite is often absent or sparse. In a suite of samples from the New Albany Shale (Middle Devonian to the Early Mississippian, Illinois Basin) the abundance of aromatic carbon in kerogen determined by 13C CP/MAS NMR correlates linearly well with vitrinite reflectance. ?? 2004 Elsevier Inc. All rights reserved.

40Ar/39Ar Dating of Zn-Pb-Ag Mineralization in the Northern Brooks Range, Alaska

USGS Publications Warehouse

Werdon, Melanie B.; Layer, Paul W.; Newberry, Rainer J.

2004-01-01

The 40Ar/39Ar laser step-heating method potentially can be used to provide absolute ages for a number of formerly undatable, low-temperature ore deposits. This study demonstrates the use of this method by determining absolute ages for Zn-Pb-Ag sediment-hosted massive sulfide deposits and vein-breccia occurrences found throughout a 300-km-long, east-west-trending belt in the northern Brooks Range, Alaska. Massive sulfide deposits are hosted by Mississippian to Pennsylvanian(?) black carbonaceous shale, siliceous mudstone, and lesser chert and carbonate turbidites of the Kuna Formation (e.g., Red Dog, Anarraaq, Lik (Su), and Drenchwater). The vein-breccia occurrences (e.g., Husky, Story Creek, West Kivliktort Mountain, Vidlee, and Kady) are hosted by a deformed but only weakly metamorphosed package of Upper Devonian to Lower Mississippian mixed continental and marine clastic rocks (the Endicott Group) that stratigraphically underlie the Kuna Formation. The vein-breccias are mineralogically similar to, but not spatially associated with, known massive sulfide deposits. The region's largest shale-hosted massive sulfide deposit is Red Dog; it has reserves of 148 Mt grading 16.6 percent zinc, 4.5 percent lead, and 77 g of silver per tonne. Hydrothermally produced white mica in a whole-rock sample from a sulfide-bearing igneous sill within the Red Dog deposit yielded a plateau age of 314.5 Ma. The plateau age of this whole-rock sample records the time at which temperatures cooled below the argon closure temperature of the white mica and is interpreted to represent the minimum age limit for massive sulfide-related hydrothermal activity in the Red Dog deposit. Sulfide-bearing quartz veins at Drenchwater crosscut a hypabyssal intrusion with a maximum biotite age of 337.0 Ma. Despite relatively low sulfide deposition temperatures in the vein-breccia occurrences (162°-251°C), detrital white mica in sandstone immediately adjacent to large vein-breccia zones was partially to completely recrystallized. The 40Ar/39Ar age spectra and inverse isochron plots of the multicomponent whole-rock sandstone samples are more complex than those of single minerals. However, different minerals have different Ca/K and Cl/K ratios and closure temperatures, and these properties were used to identify portions of spectra dominated by argon release from specific minerals. 40Ar/39Ar laser step-heating analyses of Late Devonian sandstone whole rocks produced spectra that record a two-stage resetting history: a Carboniferous hydrothermal event first and later Mesozoic to Tertiary events, which are in agreement with geologic constraints. The 40Ar/39Ar ages and the similar mineralogy, lead isotope composition, and relative stratigraphic positions support the interpretation that the shale-hosted massive sulfide deposits and most vein-breccia occurrences are temporally and genetically related, and that they are different expressions of Carboniferous basinal dewatering.

Sedimentary records on the subduction-accretion history of the Russian Altai, northwestern Central Asian Orogenic Belt

NASA Astrophysics Data System (ADS)

Chen, Ming; Sun, Min

2017-04-01

The Russian Altai, comprising the northern segment of the Altai-Mongolian terrane (AM) in the south, the Gorny Altai terrane (GA) in the north and the intervening Charysh-Terekta-Ulagan-Sayan suture zone, is a key area of the northwestern Central Asian Orogenic Belt (CAOB). A combined geochemical and detrital zircon study was conducted on the (meta-)sedimentary sequences from the Russian Altai to reveal the tectono-magmatic history of these two terranes and their amalgamation history, which in turn place constraints on the accretionary orogenesis and crustal growth in the CAOB. The Cambrian-Ordovician meta-sedimentary rocks from the northern AM are dominated by immature sediments possibly sourced from intermediate-felsic igneous rocks. Geochemical data show that the sediments were likely deposited in a continental arc-related setting. Zircons separated from these rocks are mainly 566-475 Ma and 1015-600 Ma old, comparable to the magmatic records of the Tuva-Mongolian terrane and surrounding island arcs in the western Mongolia. The similar source nature, provenance and depositional setting of these rocks to the counterparts from the Chinese Altai (i.e., the southern AM) imply that the whole AM possibly represents a coherent accretionary prism of the western Mongolia in the early Paleozoic rather than a Precambrian continental block with passive marginal deposition as previously thought. In contrast, the Cambrian to Silurian (meta-)sedimentary rocks from the GA are characterized by a unitary zircon population with ages of 640-470 Ma, which were potentially sourced from the Kuznetsk-Altai intra-oceanic island arc in the east of this terrane. The low abundance of 640-540 Ma zircons (5%) may attest that this arc was under a primitive stage in the late Neoproterozoic, when mafic igneous rocks dominated. However, the voluminous 530-470 Ma zircons (95%) suggest that this arc possibly evolved toward a mature one in the Cambrian to early Ordovician with increasing amount of intermediate-felsic igneous rocks, highlighting both crustal growth and recycling. Importantly, a significant amount of additional 2431-772 Ma zircons occur in the early Devonian sedimentary sequence of the GA. These detrital zircons possibly have the same source as their counterpart from the AM. This implies that the two terranes with countrary evolutionary history, i.e. the GA and AM, amalgamated before the early Devonian. To summary, the AM and GA represented two separated subduction-accretion systems in the early Paleozoic and subsequently amalgamated prior to the early Devonian, documenting complicated accretionary orogenesis and significant lateral crustal growth in the CAOB. Acknowledgement This study is financially supported by the Major Research Project of the Ministry of Science and Technology of China (2014CB44801 and 2014CB448000), Hong Kong Research Grant Council (HKU705313P and HKU17303415), National Science Foundation of China (41273048) and the Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan) (162301132731).

Organic metamorphism in the Lower Mississippian-Upper Devonian Bakken shales. Part 1: Rock-Eval pyrolysis and vitrinite reflectance.

USGS Publications Warehouse

Price, L.C.; Daws, T.; Pawlewicz, M.

1986-01-01

The Williston basin is an intracratonic basin extending across parts of several states, principally North Dakota, on the US/Canadian frontier. A sequence of up to 16 000 ft of Phanerozoic rocks exists in the basin; the Bakken formation is a relatively thin clastic unit composed of three members, of which the middle one is a black shale. Both core chip and cutting chip samples from a series of widely-distributed well locations were taken for laboratory analysis. Pyrolysis data showed 'wide variations' in maturity indices in samples from equivalent depths at different well locations. This suggests that a number of different palaeoheat-flow regimes have existed in the basin, resulting in the optimization of hydrocarbon formation processes at varying depths at different localities. The vitrinite reflectance profiles presented illustrate the expected trend of linearly-increasing maturity with depth to around 6500 ft. Between 6700 and 10 000 ft, however, this trend is interrupted by two 'reversals'. It is suggested that these reversals are due to suppression of the vitrinite reflectance values in samples with high concentrations of H-rich organic matter, and that they may therefore be associated with transitions from 'terrestrial-derived' to marine-depositional conditions. Consequently, the precise identification of the thresholds of intense hydrocarbon generation within the basin is problematic.-J.M.H.

Structural controls on Carlin-type gold mineralization in the gold bar district, Eureka County, Nevada

USGS Publications Warehouse

Yigit, O.; Nelson, E.P.; Hitzman, M.W.; Hofstra, A.H.

2003-01-01

The Gold Bar district in the southern Roberts Mountains, 48 km northwest of Eureka, Nevada, contains one main deposit (Gold Bar), five satellite deposits, and other resources. Approximately 0.5 Moz of gold have been recovered from a resource of 1,639,000 oz of gold in Carlin-type gold deposits in lower plate, miogeoclinal carbonate rocks below the Roberts Mountains thrust. Host rocks are unit 2 of the Upper Member of the Devonian Denay Formation and the Bartine Member of the McColley Canyon Formation. Spatial and temporal relations between structures and gold mineralization indicate that both pre-Tertiary and Tertiary structures were important controls on gold mineralization. Gold mineralization occurs primarily along high-angle Tertiary normal faults, some of which are reactivated reverse faults of Paleozoic or Mesozoic age. Most deposits are localized at the intersection of northwest- and northeast-striking faults. Alteration includes decalcification, and to a lesser extent, silicification along high-angle faults. Jasperoid (pervasive silicification), which formed along most faults and in some strata-bound zones, accounts for a small portion of the ore in every deposit. In the Gold Canyon deposit, a high-grade jasperoid pipe formed along a Tertiary normal fault which was localized along a zone of overturned fault-propagation folds and thrust faults of Paleozoic or Mesozoic age.

Tectonic overprint on magnetic fabric of the Ordovician Thetford Mines Ophiolite (Canada)

NASA Astrophysics Data System (ADS)

Di Chiara, Anita; Morris, Antony; Anderson, Mark W.; Menegon, Luca

2017-04-01

Studies in modern oceanic settings suggest locally along low-spreading ridges both lower crust and upper mantle peridotites may be exhumed to the seafloor in features known as oceanic core complexes (OCC). Examples of OCC on geological record can be preserved in ophiolites, relict of oceanic crust obducted onto continental margins, as for example the Jurassic Mirdita Ophiolite (Albania), suggesting that this spreading mode was active in the past. In order to understand such dynamics further, we investigated the OCC preserved in the Thetford Mines Ophiolite (TMO). TMO is part of the Southern Quebec ophiolites in the Canadian Appalachians (Quebec region), divided into three lithotectonic assemblages: The Humber Zone, a remnant of the Laurentian continental margin; The Cambrian-Ordovician Dunnage Zone, a remnant of the Iapetus Ocean and including the TMO and other ophiolites; and Silurian-Devonian Gaspé Belt, the sedimentary cover sequence. These were subjected to polyphase deformation, experiencing two Paleozoic orogenies: The Ordovician Taconian Orogeny (the Humber and Dunnage zones were amalgamated) and the Devonian Acadian orogeny which deformed and metamorphosed both the Dunnage Zone and the overlying Gaspe Belt. Here we present results from 12 paleomagnetic sites sampled on Humber zone on pillow lavas, dykes, layered gabbros and serpentinized dunites. Our results from AMS experiments show that these rocks, formed by fundamentally different magmatic processes, share a common magnetic fabric, with a kmin axis NW-SE orientated and the kmax steeply plunging to the NE. Additional processing of acquired BSE images and chemical mapping analyses at the SEM show that the kmax of the magnetic fabric is parallel to the elongation of magnetic particles (Iron rich minerals). This remarkably consistent fabric has a tectonic origin and is consistent with shortening perpendicular to the regional trend of fold axes.

The structural evolution of the Ghadames and Illizi basins during the Paleozoic, Mesozoic and Cenozoic: Petroleum implications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gauthier, F.J.; Boudjema, A.; Lounis, R.

1995-08-01

The Ghadames and Illizi basins cover the majority of the eastern Sahara of Algeria. Geologicaly, this part of the Central Saharan platform has been influenced by a series of structural arches and {open_quotes}moles{close_quotes} (continental highs) which controlled sedimentation and structure through geologic time. These features, resulting from and having been affected by nine major tectonic phases ranging from pre-Cambrian to Tertiary, completely bound the Ghadames and Illizi Basins. During the Paleozoic both basins formed one continuous depositional entity with the Ghadames basin being the distal portion of the continental sag basin where facies and thickness variations are observed over largemore » distances. It is during the Mesozoic-Cenozoic that the Ghadames basin starts to evolve differently from the Illizi Basin. Eustatic low-stand periods resulted in continental deposition yielding the major petroleum-bearing reservoir horizons (Cambrian, Ordovician, Siluro-Devonian and Carboniferous). High-stand periods corresponds to the major marine transgressions covering the majority of the Saharan platform. These transgressions deposited the principal source rock intervals of the Silurian and Middle to Upper Devonian. The main reservoirs of the Mesozoic and Cenozoic are Triassic sandstone sequences which are covered by a thick evaporite succession forming a super-seal. Structurally, the principal phases affecting this sequence are the extensional events related to the breakup of Pangea and the Alpine compressional events. The Ghadames and Illizi basins, therefore, have been controlled by a polphase tectonic history influenced by Pan African brittle basement fracturing which resulted in complex structures localized along the major basin bounding trends as well as several subsidiary trends within the basin. These trends, as demonstrated with key seismic data, have been found to contain the majority of hydrocarbons trapped.« less

Fractographic logging for determination of pre-core and core-induced fractures: Nicholas Combs No. 7239 well, Hazard, Kentucky

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kulander, B.R.; Dean, S.L.; Barton, C.C.

1977-01-01

Methods results, and conclusions formulated during a prototype fractographic logging study of seventy-five feet of oriented Devonian shale core are summarized. The core analyzed is from the Nicholas Combs No. 7239 well located twelve miles due north of Hazard, Kentucky. The seventy-five foot core length was taken from a cored section lying between 2369.0 feet (subsea) and 2708.0 feet (subsea). Total core length is 339.0 feet. The core was extracted from the upper Devonian Ohio and Olentangy shale formations. Results indicate that there are few tectonic (pre-core) fractures within the studied core section. The region may nevertheless be cut atmore » core sample depth by well-defined vertical or inclined tectonic fractures that the vertically drilled test core didn't intersect. This is likely since surface Plateau systematic fractures in other Plateau areas are vertical to sub-vertical and seldom have a frequency of less than one major fracture per foot. The remarkable directional preference of set three fractures about strikes of N 40/sup 0/ E, N 10/sup 0/ W, N 45/sup 0/ W, suggests some incipient pre-core rock anisotropy or stored directional strain energy. If this situation exists, the anisotropy strike change or stored strain variance from N 40/sup 0/ E to N 45/sup 0/ W downcore remains an unanswered question. Tectonic features, indicating local and/or regional movement plans, are present on and within the tectonichorizontal fracture set one. Slickensides had a preferred orientation within several core levels, and fibrous-nonfibrous calcite serves as fracture fillings.« less

Post-early cretaceous landform evolution along the western margin of the banca~nnia trough, western nsw

USGS Publications Warehouse

Gibson, D.L.

2000-01-01

Previously undated post-Devonian sediments outcropping north of Fowlers Gap station near the western margin of the Bancannia Trough are shown by plant macro- and microfossil determinations to be of Early Cretaceous (most likely Neocomian and/or Aptian) age, and thus part of the Eromanga Basin. They are assigned to the previously defined Telephone Creek Formation. Study of the structural configuration of this unit and the unconformably underlying Devonian rocks suggests that the gross landscape architecture of the area results from post-Early Cretaceous monoclinal folding along blind faults at the western margin of the trough, combined with the effects of differential erosion. This study shows that, while landscape evolution in the area has been dynamic, the major changes that have occurred are on a geological rather than human timescale.

Traces in the dark: sedimentary processes and facies gradients in the upper shale member of the Upper Devonian-Lower Mississippian Bakken Formation, Williston Basin, North Dakota, U.S.A.

USGS Publications Warehouse

Egenhoff, Sven O.; Fishman, Neil S.

2013-01-01

Black, organic-rich rocks of the upper shale member of the Upper Devonian–Lower Mississippian Bakken Formation, a world-class petroleum source rock in the Williston Basin of the United States and Canada, contain a diverse suite of mudstone lithofacies that were deposited in distinct facies belts. The succession consists of three discrete facies associations (FAs). These comprise: 1) siliceous mudstones; 2) quartz- and carbonate-bearing, laminated mudstones; and 3) macrofossil-debris-bearing massive mudstones. These FAs were deposited in three facies belts that reflect proximal to distal relationships in this mudstone system. The macrofossil-debris-bearing massive mudstones (FA 3) occur in the proximal facies belt and contain erosion surfaces, some with overlying conodont and phosphate–lithoclast lag deposits, mudstones with abundant millimeter-scale siltstone laminae showing irregular lateral thickness changes, and shell debris. In the medial facies belt, quartz- and carbonate-bearing, laminated mudstones dominate, exhibiting sub-millimeter-thick siltstone layers with variable lateral thicknesses and localized mudstone ripples. In the distal siliceous mudstone facies belt, radiolarites, radiolarian-bearing mudstones, and quartz- and carbonate-bearing, laminated mudstones dominate. Overall, total organic carbon (TOC) contents range between about 3 and 10 wt %, with a general proximal to distal decrease in TOC content. Abundant evidence of bioturbation exists in all FAs, and the lithological and TOC variations are paralleled by changes in burrowing style and trace-fossil abundance. While two horizontal traces and two types of fecal strings are recognized in the proximal facies belt, only a single horizontal trace fossil and one type of fecal string characterize mudstones in the distal facies belt. Radiolarites intercalated into the most distal mudstones are devoid of traces and fecal strings. Bedload transport processes, likely caused by storm-induced turbidity currents, were active across all facies belts. Suspended sediment settling from near the ocean surface, however, most likely played a role in the deposition of some of the mudstones, and was probably responsible for deposition of the radiolarites. The distribution pattern of high-TOC sediments in proximal and lower-TOC deposits in some distal facies is interpreted as a function of higher accumulation rates during radiolarian depositional events leading to a decrease in suspension-derived organic carbon in radiolarite laminae. The presence of burrows in all FAs and nearly all facies in the upper Bakken shale member indicates that dysoxic conditions prevailed during its deposition. This study shows that in intracratonic high-TOC mudstone successions such as the upper Bakken shale member bed-load processes most likely dominated sedimentation, and conditions promoted a thriving infaunal benthic community. As such, deposition of the upper Bakken shale member through dynamic processes in an overall dysoxic environment represents an alternative to conventional anoxic depositional models for world-class source rocks.

MX Siting Investigation. Water Resources Program Progress Report.

DTIC Science & Technology

1981-02-13

avoided. o Limestones and dolomites (carbonates) of Devonian age appear to be the major regional aquifers which hydrologically con- nect many valleys...that of the aquifer itself. Carbonate Aquifer. A aquifer, contained in limestone or dolomite rock, which occurs beneath the unconsolidated valley-fill...sediments and in the mountain ranges. Flow is believed to be primarily through fracture and solution openings rather than through normal inter

The ancient environment of the Beartooth Butte Formation (Devonian) in Wyoming and Montana: combining paleontological inquiry with federal management needs

Treesearch

Anthony R. Fiorillo

2000-01-01

The Beartooth Butte Formation is found in many mountain ranges throughout central Montana and northern Wyoming. This study combines a variety of geologic data to provide a clearer understanding of the fossil fauna and environmental setting of this rock unit. Results show not all exposures of this unit are fossil-bearing and where present, faunal...

Geological Structure of the Basement of Western and Eastern Parts of the West-Siberian Plain

ERIC Educational Resources Information Center

Ivanov, Kirill S.; Erokhin, Yuriy V.; Ponomarev, Vladimir S.; Pogromskaya, Olga E.; Berzin, Stepan V.

2016-01-01

The U-Pb dating (SHRIMP-II on zircon) was obtained for the first time from the basement of the West Siberian Plain in the Western half of the region. It is established that a large part of the protolith of the metamorphic depth in the Shaim-Kuznetsov meganticlinorium contained sedimentary late- and middle-Devonian rocks (395-358 million years).…

Late Devonian Anoxia Events in the Central Asian Orogenic Belt: a Global Phenomenon

NASA Astrophysics Data System (ADS)

Carmichael, S. K.; Waters, J. A.; Suttner, T. J.; Kido, E.; DeReuil, A. A.; Moore, L. M.; Batchelor, C. J.

2013-12-01

Atmospheric CO2 values decreased dramatically during the Middle Devonian due to the rapid rise of land plants. These changing environmental conditions resulted in widespread anoxia and extinction events throughout the Late Devonian, including the critical Kellwasser and Hangenberg anoxia events, which are associated with major mass extinctions at both the beginning and end of the Famennian Stage of the Late Devonian. Fammenian sediments in northwestern Xinjiang Province, China, represent a highly fossiliferous shallow marine setting associated with a Devonian oceanic island arc complex. Analysis of multiple geochemical proxies (such as U/Th, Ba, normalized P2O5, V/Cr, Zr), magnetic susceptibility, and mineralogical data (biogenic apatite and pyrite framboids) indicates that these Famennian sequences record not only the Upper Kellwasser Anoxic Event at the Frasnian/Famennian (F/F) boundary but also the rebound from the F/F extinction event. Preliminary evidence suggests that the Hangenberg Anoxic Event can also be recognized in the same sequence, although our biostratigraphic control is less precise. Previous studies of the Kellwasser and Hangenberg Events have been performed on continental shelf environments of Laurussia, Gondwana, Siberia, and South China. The Devonian formations of northwest Xinjiang in this study, however, are part of the Central Asian Orogenic Belt (CAOB), which is thought to have formed as part of a complex amalgamation of intra-oceanic island arcs and continental fragments prior to the end of the latest Carboniferous. These results allow us to confirm the presence of the Kellwasser and Hangenberg Events in the open oceanic part of Paleotethys, indicating that both events were global in scope. The presence of an abundant diverse Famennian fauna between these anoxia/extinction events suggests that the shallow marine ecosystems in the CAOB were somewhat protected due to their tectonic location and relative isolation within an open ocean system. Our new data puts the Late Devonian anoxic events recognized in the CAOB into a global rather than regional context, and helps constrain the nature of ocean anoxia during this period by analysis of locations outside subequatorial North America and Europe.

Tracing source terranes using U-Pb-Hf isotopic analysis of detrital zircons: provenance of the Orhanlar Unit of the Palaeotethyan Karakaya subduction-accretion complex, NW Turkey

NASA Astrophysics Data System (ADS)

Ustaömer, Timur; Ayda Ustaömer, Petek; Robertson, Alastair; Gerdes, Axel

2016-04-01

Sandstones of the Late Palaeozoic-Early Mesozoic Karakaya Complex are interpreted to have accumulated along an active continental margin related to northward subduction of Palaeotethys. The age of deposition and provenance of the sandstones are currently being determined using radiometric dating of detrital zircons, coupled with dating of potential source terranes. Our previous work shows that the U-Pb-Hf isotopic characteristics of the sandstones of all but one of the main tectonostratigraphic units of the Karakaya Complex are compatible with a provenance that was dominated by Triassic and Permo-Carboniferous magmatic arc-type rocks, together with a minor contribution from Lower to Mid-Devonian igneous rocks (Ustaömer et al. 2015). However, one of the tectono-stratigraphic units, the Orhanlar Unit, which occurs in a structurally high position, differs in sedimentary facies and composition from the other units of the Karakaya Complex. Here, we report new isotopic age data for the sandstones of the Orhanlar Unit and also from an extensive, associated tectonic slice of continental metamorphic rocks (part of the regional Sakarya Terrane). Our main aim is to assess the provenance of the Orhanlar Unit sandstones in relation to the tectonic development of the Karakaya Complex as a whole. The Orhanlar Unit is composed of shales, sandstone turbidites and debris-flow deposits, which include blocks of Devonian radiolarian chert and Carboniferous and Permian neritic limestones. The sandstones are dominated by rock fragments, principally volcanic and plutonic rocks of basic-to-intermediate composition, metamorphic rocks and chert, together with common quartz, feldspar and mica. This modal composition contrasts significantly with the dominantly arkosic composition of the other Karakaya Complex sandstones. The detrital zircons were dated by the U-Pb method, coupled with determination of Lu-Hf isotopic compositions using a laser ablation microprobe attached to a multicollector-inductively coupled plasma-mass spectrometer (LA-MC-ICP-MS) at Goethe University, Frankfurt. A total of 399 U-Pb spot analyses were carried out on zircons from the sandstones of the Orhanlar Unit. 84% of the data yielded Precambrian ages, which is in marked contrast with the typical arkosic sandstones of the Karakaya Complex in which Precambrian zircons form only 10% of the population. Three zircon grains of Ladinian age suggest a maximum depositional age for the Orhanlar Unit. The most prominent zircon population is of Ediacaran-Cryogenian age (31%). The second largest population is Tonian-Stenian (22%), the third largest Cryogenian-Tonian (9%) and the fourth Devonian-Carboniferous (7%). There are also minor zircon populations of Palaeoproterozoic and Neo-Archean ages. The Precambrian zircon populations in the Orhanlar Unit sandstones are identical to those in the schists of the Sakarya continental crust (P.A. Ustaömer et al. 2012; this study). Their Hf isotope compositions also overlap, suggesting that the Sakarya continental crust could be a source for the sandstones of the Orhanlar Unit. On the other hand, the Hf(t) values of most of the Devonian and Carboniferous detrital zircons differ from those of the Devonian and Carboniferous granites that intrude the Sakarya continental crust. The Karakaya Complex as a whole appears to have been derived from two different source terranes, of which the Orhanlar Unit sandstones represent a minor, but significant component. Possible explanations are that two different source terranes already existed in the same region but that these were not exposed to erosion at the same time or, if exposed simultaneously, experienced different depositional pathways (without mixing); alternatively, the Orhanar Unit represents part of a different tectono-stratigraphic terrane from the other Karakaya Complex units, with which it was tectonically amalgamated prior to Early Jurassic deposition of a common sedimentary cover. Ustaömer PA, Ustaömer T, Robertson AHF (2012), Turkish Journal of Earth Sciences, doi:10.3906/yer-1103-1 Ustaömer T, Ustaömer PA, Robertson AHF, Gerdes A (2015), International Journal of Earth Sciences, DOI 10.1007/s00531-015-1225-8. This work was supported by TUBITAK, Project no 111R015

Development of a new software for analyzing 3-D fracture network

NASA Astrophysics Data System (ADS)

Um, Jeong-Gi; Noh, Young-Hwan; Choi, Yosoon

2014-05-01

A new software is presented to analyze fracture network in 3-D. Recently, we completed the software package based on information given in EGU2013. The software consists of several modules that play roles in management of borehole data, stochastic modelling of fracture network, construction of analysis domain, visualization of fracture geometry in 3-D, calculation of equivalent pipes and production of cross-section diagrams. Intel Parallel Studio XE 2013, Visual Studio.NET 2010 and the open source VTK library were utilized as development tools to efficiently implement the modules and the graphical user interface of the software. A case study was performed to analyze 3-D fracture network system at the Upper Devonian Grosmont Formation in Alberta, Canada. The results have suggested that the developed software is effective in modelling and visualizing 3-D fracture network system, and can provide useful information to tackle the geomechanical problems related to strength, deformability and hydraulic behaviours of the fractured rock masses. This presentation describes the concept and details of the development and implementation of the software.

Ordovician "sphinctozoan" sponges from Prince of Wales Island, southeastern Alaska

USGS Publications Warehouse

Rigby, J.K.; Karl, Susan M.; Blodgett, R.B.; Baichtal, J.F.

2005-01-01

A faunule of silicified hypercalcified "sphinctozoan" sponges has been recovered from a clast of Upper Ordovician limestone out of the Early Devonian Karheen Formation on Prince of Wales Island in southeastern Alaska. Included in the faunule are abundant examples of the new genus Girtyocoeliana, represented by Girtyocoeliana epiporata (Rigby and Potter), and Corymbospongia adnata Rigby and Potter, along with rare Corymbospongia amplia n. sp., and Girtyocoelia(?) sp., plus common Amblysiphonella sp. 1 and rare Amblysiphonella(?) sp. 2. The assemblage is similar to that from Ordovician clasts from the eastern Klamath Mountains of northern California. This indicates that the Alexander terrane of southeastern Alaska is related paleogeographically to the lithologically and paleontologically similar terrane of the eastern Klamath Mountains. This lithology and fossil assemblage of the clast cannot be tied to any currently known local rock units on Prince of Wales Island. Other clasts in the conglomerate appear to have been locally derived, so it is inferred that the limestone clasts were also locally derived, indicating the presence of a previously undocumented Ordovician limestone unit on northern Prince of Wales Island. 

Paracontinuous boundaries within the Devonian Columbus Limestone and Delaware Formation of central Ohio

DOE Office of Scientific and Technical Information (OSTI.GOV)

Conkin, J.E.; Conkin, B.M.

1994-04-01

Internal units within the Columbus Limestone (Early Devonian Emsian [Schoharie] to Middle Devonian Eifelian [late Onesquethawan]) and the Delaware Formation (Middle Devonian early Givetian [Cazenovian]) of central Ohio are separated by disconformities of the magnitude of paracontinuities. Stauffer (1909) divided the Columbus Limestone into zones A--H and the Delaware Formation into zones I--M. Within the Columbus, the A Zone (conglomerate at the base of Bellepoint Member) disconformably overlies Late Silurian beds. The D zone at top of the Bellepoint Member (bearing the Kawkawlin Metabentonite horizon) is overlain paracontinuously by the Marblehead Member (Lower Paraspirifer acuminatus-Spirifer macrothyris to Brevispirifer gregarius-Moellerina greeneimore » zones [= E--G zones]), with the Onondagan Indian Nation Metabentonite in the top of the G Zone. The Marblehead Member is overlain paracontinuously by a bone bed at base of the Venice Member (H zone = Upper Paraspirifer acuminatus- Spirifer duodenarius'' Zone). I Zone (Dublin Shale=Marcellus) of the Delaware Formation overlies the Columbus and has two bone beds at its base; Tioga Metabentonite (restricted) overlies the I Zone bone beds and is a few tenths to 1.85 feet above the base of the I Zone. Paracontinuities and bone beds occur at the bases of J, K, and L zones. Conkin and Conkin (1975) have shown Stauffer's (1909) M Zone is an extension of his L Zone. The Olentangy paracontinuously overlies the L Zone.« less

Geochronology and geochemistry of late Paleozoic-early Mesozoic igneous rocks of the Erguna Massif, NE China: Implications for the early evolution of the Mongol-Okhotsk tectonic regime

NASA Astrophysics Data System (ADS)

Li, Yu; Xu, Wen-Liang; Wang, Feng; Tang, Jie; Zhao, Shuo; Guo, Peng

2017-08-01

We undertook geochemical and geochronological studies on late Paleozoic-early Mesozoic igneous rocks from the Erguna Massif with the aim of constraining the early evolution of the Mongol-Okhotsk tectonic regime. Zircon crystals from nine representative samples are euhedral-subhedral, display oscillatory growth zoning, and have Th/U values of 0.14-6.48, indicating a magmatic origin. U-Pb dating of zircon using SIMS and LA-ICP-MS indicates that these igneous rocks formed during the Late Devonian (∼365 Ma), late Carboniferous (∼303 Ma), late Permian (∼256 Ma), and Early-Middle Triassic (246-238 Ma). The Late Devonian rhyolites, together with coeval A-type granites, formed in an extensional environment related to the northwestwards subduction of the Heihe-Nenjiang oceanic plate. Their positive εHf(t) values (+8.4 to +14.4) and Hf two-stage model ages (TDM2 = 444-827 Ma) indicate they were derived from a newly accreted continental crustal source. The late Carboniferous granodiorites are geochemically similar to adakites, and their εHf(t) values (+10.4 to +12.3) and Hf two-stage model ages (TDM2 = 500-607 Ma) suggest they were sourced from thickened juvenile lower crustal material, this thickening may be related to the amalgamation of the Erguna-Xing'an and Songnen-Zhangguangcai Range massifs. Rocks of the late Permian to Middle Triassic suite comprise high-K calc-alkaline monzonites, quartz monzonites, granodiorites, and monzogranites. These rocks are relatively enriched in light rare earth elements and large ion lithophile elements, and depleted in heavy rare earth elements and high field strength elements. They were emplaced, together with coeval porphyry-type ore deposits, along an active continental margin where the Mongol-Okhotsk oceanic plate was subducting beneath the Erguna Massif.

Geology and geochemistry of the Arctic prospect, Ambler District, Alaska

NASA Astrophysics Data System (ADS)

Schmidt, J. M.

The Arctic volcanogenic massive sulfide prospect is the largest known (40 million ton) deposit hosted by the low greenschist grade, latest Devonian Ambler Sequence of bimodal, basaltic and rhyolitic volcanic and volcanoclastic rocks, pelitic, graphitic and calcareous metasediments. Detailed field mapping, core logging, petrography, X-ray diffractometry, electron microprobe analyses and whole-rock major element analyses of hydrothermally altered rocks were used to determine the emplacement history and setting of sulfide deposition. Low greenschist grade metamorphism was essentially isochemical on a macroscopic scale, and preserved volcanic compositions, the major element chemistry of alteration and the compositions of individual metamorphic, alteration and relict igneous minerals. Mineralization at Arctic was formed along a synvolcanic fault in a tectonically and volcanically active basin within a rifted continental margin, possibly related to an actively spreading oceanic rift.

First Record of Soft Tissue Preservation in the Upper Devonian of Poland

PubMed Central

Zatoń, Michał; Broda, Krzysztof

2015-01-01

Soft tissue preservation is reported from Upper Devonian deposits of the Holy Cross Mountains, central Poland, for the first time. The preserved soft tissues are muscles associated with arthropod cuticle fragments. The muscles are phosphatized with variable states of preservation. Well-preserved specimens display the typical banding of striated muscles. Other muscle fragments are highly degraded and/or recrystallized such that their microstructure is barely visible. The phosphatized muscles and associated cuticle are fragmented, occur in patches and some are scattered on the bedding plane. Due to the state of preservation and the lack of diagnostic features, the cuticle identification is problematic; however, it may have belonged to a phyllocarid crustacean. Taphonomic features of the remains indicate that they do not represent fossilized fecal matter (coprolite) but may represent a regurgitate, but the hypothesis is difficult to test. Most probably they represent the leftover remains after arthropod or fish scavenging. The present study shows that soft tissues, which even earlier were manipulated by scavenger, may be preserved if only special microenvironmental conditions within and around the animal remains are established. PMID:26559060

First Record of Soft Tissue Preservation in the Upper Devonian of Poland.

PubMed

Zatoń, Michał; Broda, Krzysztof

2015-01-01

Soft tissue preservation is reported from Upper Devonian deposits of the Holy Cross Mountains, central Poland, for the first time. The preserved soft tissues are muscles associated with arthropod cuticle fragments. The muscles are phosphatized with variable states of preservation. Well-preserved specimens display the typical banding of striated muscles. Other muscle fragments are highly degraded and/or recrystallized such that their microstructure is barely visible. The phosphatized muscles and associated cuticle are fragmented, occur in patches and some are scattered on the bedding plane. Due to the state of preservation and the lack of diagnostic features, the cuticle identification is problematic; however, it may have belonged to a phyllocarid crustacean. Taphonomic features of the remains indicate that they do not represent fossilized fecal matter (coprolite) but may represent a regurgitate, but the hypothesis is difficult to test. Most probably they represent the leftover remains after arthropod or fish scavenging. The present study shows that soft tissues, which even earlier were manipulated by scavenger, may be preserved if only special microenvironmental conditions within and around the animal remains are established.

Correlation of LANDSAT lineaments with Devonian gas fields in Lawrence County, Ohio

NASA Technical Reports Server (NTRS)

Johnson, G. O.

1981-01-01

In an effort to locate sources of natural gas in Ohio, the fractures and lineaments in Black Devonian shale were measured by: (1) field mapping of joints, swarms, and fractures; (2) stereophotointerpretation of geomorphic lineaments with precise photoquads; and (3) by interpreting the linear features on LANDSAT images. All results were compiled and graphically represented on 1:250,000 scale maps. The geologic setting of Lawrence County was defined and a field fracture map was generated and plotted as rose patterns at the exposure site. All maps were compared, contrasted, and correlated by superimposing each over the other as a transparency. The LANDSAT lineaments had significant correlation with the limits of oil and gas producing fields. These limits included termination of field production as well as extensions to other fields. The lineaments represent real rock fractures with zones of increased permeability in the near surface bedrock.

Indirect and direct tensile behavior of Devonian oil shales

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chong, K.P.; Chen, J.L.; Dana, G.F.

1984-03-01

Ultimate indirect tensile strengths of Devonian oil shales across the bedding planes is a mechanical property parameter important to predicting how oil shale will break. This is particularly important to in-situ fragmentation. The Split Cylinder Test was used to determine the indirect tensile strengths between the bedding planes. Test specimens, cored perpendicular to the bedding planes, representing oil shales of different oil yields taken from Silver Point Quad in DeKalb County, Tennessee and Friendship in Scioto County, Ohio, were subjected to the Split Cylinder Test. Linear regression equations relating ultimate tensile strength across the bedding planes to volume percent ofmore » organic matter in the rock were developed from the test data. In addition, direct tensile strengths were obtained between the bedding planes for the Tennessee oil shales. This property is important for the design of horizontal fractures in oil shales. Typical results were presented.« less

Root evolution at the base of the lycophyte clade: insights from an Early Devonian lycophyte

PubMed Central

Matsunaga, Kelly K. S.; Tomescu, Alexandru M. F.

2016-01-01

Background and Aims The evolution of complex rooting systems during the Devonian had significant impacts on global terrestrial ecosystems and the evolution of plant body plans. However, detailed understanding of the pathways of root evolution and the architecture of early rooting systems is currently lacking. We describe the architecture and resolve the structural homology of the rooting system of an Early Devonian basal lycophyte. Insights gained from these fossils are used to address lycophyte root evolution and homology. Methods Plant fossils are preserved as carbonaceous compressions at Cottonwood Canyon (Wyoming), in the Lochkovian–Pragian (∼411 Ma; Early Devonian) Beartooth Butte Formation. We analysed 177 rock specimens and documented morphology, cuticular anatomy and structural relationships, as well as stratigraphic position and taphonomic conditions. Key Results The rooting system of the Cottonwood Canyon lycophyte is composed of modified stems that bear fine, dichotomously branching lateral roots. These modified stems, referred to as root-bearing axes, are produced at branching points of the above-ground shoot system. Root-bearing axes preserved in growth position exhibit evidence of positive gravitropism, whereas the lateral roots extend horizontally. Consistent recurrence of these features in successive populations of the plant preserved in situ demonstrates that they represent constitutive structural traits and not opportunistic responses of a flexible developmental programme. Conclusions This is the oldest direct evidence for a rooting system preserved in growth position. These rooting systems, which can be traced to a parent plant, include some of the earliest roots known to date and demonstrate that substantial plant–substrate interactions were under way by Early Devonian time. The morphological relationships between stems, root-bearing axes and roots corroborate evidence that positive gravitropism and root identity were evolutionarily uncoupled in lycophytes, and challenge the hypothesis that roots evolved from branches of the above-ground axial system, suggesting instead that lycophyte roots arose as a novel organ. PMID:26921730

Contrasting tectonothermal domains and faulting in the Potomac terrane, Virginia-Maryland - Discrimination by 40Ar/39Ar and fission-track thermochronology

USGS Publications Warehouse

Kunk, Michael J.; Wintsch, R.P.; Naeser, C.W.; Naeser, N.D.; Southworth, C.S.; Drake, Avery A.; Becker, J.L.

2005-01-01

New 40Ar/39Ar data reveal ages and thermal discontinuities that identify mapped and unmapped fault boundaries in the Potomac terrane in northern Virginia, thus confirming previous interpretations that it is a composite terrane. The rocks of the Potomac terrane were examined along the Potomac River, where it has been previously subdivided into three units: the Mather Gorge, Sykesville, and Laurel Formations. In the Mather Gorge Formation, at least two metamorphic thermal domains were identified, the Blockhouse Point and Bear Island domains, separated by a fault active in the late Devonian. Early Ordovician (ca. 475 Ma) cooling ages of amphibole in the Bear Island domain reflect cooling from Taconic metamorphism, whereas the Blockhouse Point domain was first metamorphosed in the Devonian. The 40Ar/39Ar data from muscovites in a third (eastern) domain within the Mather Gorge Formation, the Stubblefield Falls domain, record thrusting of the Sykesville Formation over the Mather Gorge Formation on the Plummers Island fault in the Devonian. The existence of two distinctly different thermal domains separated by a tectonic boundary within the Mather Gorge argues against its status as a formation. Hornblende cooling ages in the Sykesville Formation are Early Devonian (ca. 400 Ma), reflecting cooling from Taconic and Acadian metamorphism. The ages of retrograde and overprinting muscovite in phyllonites from domain-bounding faults are late Devonian (Acadian) and late Pennsylvanian (Alleghanian), marking the time of assembly of these domains and subsequent movement on the Plummers Island fault. Our data indicate that net vertical motion between the Bear Island domain of the Mather Gorge complex and the Sykesville Formation across the Plummers Island fault is east-side-up. Zircon fission-track cooling ages demonstrate thermal equillbrium across the Potomac terrane in the early Permian, and apatite fission-track cooling ages record tilting of the Potomac terrane in the Cretaceous or later with the west side up at least 1 km. ?? 2005 Geological Society of America.

Magnetic properties and anomalies related to eclogite- and high-pressure granulite-facies mafic rocks: What do they tell about magnetization of deep-crustal lithosphere?

NASA Astrophysics Data System (ADS)

McEnroe, S. A.; Robinson, P.

2012-12-01

The magnetic response of crustal rocks is directly related to type and abundance of oxides in the rock bodies. About 800 samples from mafic bodies and mantle peridotites from the eclogite-facies part of the Western Gneiss Region, Norway, were studied for magnetic properties and oxide mineralogy, and show strong variations. Many eclogites are paramagnetic, while adjacent gabbros from which the eclogites were derived during high-pressure (HP) recrystallization, either preserved or formed magnetite during HP metamorphism or during the following exhumation. Phase petrology indicates many of these rocks were subjected to 4 Gpa and possibly to 6 Gpa equivalent to depths of 125 and 200 km during the Scandian (Upper Silurian - Lower Devonian) continental subduction. Likely conditions in intermediate stages of exhumation were temperature (T) > 700C and pressure (P) of 1 GPa. When magnetite dominates in these samples, the primary control on magnetization is abundance, because magnetite in coarse-grained igneous and high-grade metamorphic rocks is commonly of multi-domain size, close to end-member, and with few microstructures. With few features to stabilize the NRM, the magnetic response is dominated by induced magnetization (Ji). When exsolved members of the rhombohedral ilmenite-hematite solid solution are present, commonly in more oxidized rocks, the response is dominated by the NRM (Jr), and NRM intensity is more complicated than in magnetite-bearing rocks. Important here, in addition to the amount of oxide, are the orientation of the oxide grains relative to the magnetizing field, and the amount of exsolution lamellae, mostly produced during cooling from HP conditions, leading to lamellar magnetism. Where there is no coexisting magnetite, these rocks have high Q values (Jr/Ji) because the induced magnetization (Ji) is low. For such more oxidized rocks, remanent anomalies are generally more common than for more reduced magnetite-bearing rocks formed under the same conditions. Mafic rocks from the Southwest Swedish Granulite Region contain high-pressure granulite-facies assemblages produced during Sveconorwegian (early Neoproterozoic) metamorphism with peak T of 770C and P 0.75-1.05 GPa. Here, the assemblages commonly indicate more oxidized compositions than prevailing in the Western Gneiss Region. Thus, the NRM is dominant, and resultant magnetic vectors are controlled by NRM vectors, nearly opposite to the Earth's present magnetic field, giving rise to striking negative anomalies. Both regions offer insights and show strong variations in the magnetic properties of lower crustal rocks.

Total Petroleum Systems of the North Carpathian Province of Poland, Ukraine, Czech Republic, and Austria

USGS Publications Warehouse

Pawlewicz, Mark

2006-01-01

Three total petroleum systems were identified in the North Carpathian Province (4047) that includes parts of Poland, Ukraine, Austria, and the Czech Republic. They are the Isotopically Light Gas Total Petroleum System, the Mesozoic-Paleogene Composite Total Petroleum System, and the Paleozoic Composite Total Petroleum System. The Foreland Basin Assessment Unit of the Isotopically Light Gas Total Petroleum System is wholly contained within the shallow sedimentary rocks of Neogene molasse in the Carpathian foredeep. The biogenic gas is generated locally as the result of bacterial activity on dispersed organic matter. Migration is also believed to be local, and gas is believed to be trapped in shallow stratigraphic traps. The Mesozoic-Paleogene Composite Total Petroleum System, which includes the Deformed Belt Assessment Unit, is structurally complex, and source rocks, reservoirs, and seals are juxtaposed in such a way that a single stratigraphic section is insufficient to describe the geology. The Menilite Shale, an organic-rich rock widespread throughout the Carpathian region, is the main hydrocarbon source rock. Other Jurassic to Cretaceous formations also contribute to oil and gas in the overthrust zone in Poland and Ukraine but in smaller amounts, because those formations are more localized than the Menilite Shale. The Paleozoic Composite Total Petroleum System is defined on the basis of the suspected source rock for two oil or gas fields in western Poland. The Paleozoic Reservoirs Assessment Unit encompasses Devonian organic-rich shale believed to be a source of deep gas within the total petroleum system. East of this field is a Paleozoic oil accumulation whose source is uncertain; however, it possesses geochemical similarities to oil generated by Upper Carboniferous coals. The undiscovered resources in the North Carpathian Province are, at the mean, 4.61 trillion cubic feet of gas and 359 million barrels of oil. Many favorable parts of the province have been extensively explored for oil and gas. The lateral and vertical variability of the structure, the distribution and complex geologic nature of source rocks, and the depths of potential exploration targets, as well as the high degree of exploration, all indicate that future discoveries in this province are likely to be numerous but in small fields.

Sedimentology, conodonts and ostracods of the Devonian - Carboniferous strata of the Anseremme railway bridge section, Dinant Basin, Belgium

USGS Publications Warehouse

Casier, J.-G.; Mamet, B.; Preat, A.; Sandberg, C.A.

2004-01-01

Seven major carbonate microfacies are defined in the Devonian - Carboniferous (D/C) strata (50 m) of the Anseremme railway bridge section, south of Dinant. They permit recognition of several levels encompassing the Etroeungt and Hastie??re formations. "Bathymetric" sequences range from open marine, below the storm wave base, to semi-restricted lagoon. This sequence records a shallowing-upward trend of the relative sea level, from environments below the storm wave base to strongly eroded supraticial pre-evaporitic environments. Faunal components (echinoderms, brachiopods...) indicate open-marine domain for the first six microfacies located within the dysphoticeuphotic zone in relatively shallow waters. The textures of the rocks (mudstones to rudstones) associated with lamination characteristics indicate the position of the storm (SWB) and the fair-weather (FWWB) wave bases. Microfacies seven suggests a semi-restricted platform with salinity fluctuations from hypersaline brines to brackish waters. Thus, the boundary of the Etroeungt/Hastie??re formations is marked by an abrupt drop in sea level. Carbonate micro-conglomerates recording an important erosive phase and a sedimentary hiatus. The environment is again open marine in the upper part of the Hastie??re Formation. Our conclusion is that the Anseremme section is not a reliable continuous succession for the study of the D/C boundary. This confirms the VAN STEENWINKEL (1988, 1993 hypothesis based on other arguments. Conodont faunas demonstrate that the Devonian sequence spans the five youngest conodont zones, but that two of these zones are not represented. The Epinette Formation is dated as the youngest part of the Middle expansa Zone. Thus, the boundary with the Late praesulcata Zone probably coincides with the sharp sedimentological change at the base of the Etroeungt Formation, which is interpreted to belong entirely to this zone. The disconformably overlying basal bed 159 of the Hastie??re Formation is dated as Late praesulcata Zone, with the Early and Middle praesulcata Zones unrepresented because of an hiatus or unconformity. Sparse conodont faunas suggest that only the two next-to-oldest Carboniferous duplicata and sandbergi Zones are represented in the higher part of the Hastie??re Formation. The oldest Carboniferous sulcata Zone and possibly part ofthe duplicata Zone are unrepresented because of an hiatus or unconformity above bed 159. Ostracods are abundant and diversified at most levels in the Anseremme railway bridge section and sixty taxa, the majority in open nomenclature, have been identified and nearly all of them are figured. The ostracod fauna is indicative of shallow-marine environments between fair-weather and storm wave bases in the Etroeungt Formation, and to shallower water conditions periodically subjected to minor salinity variations in the base of the Hastie??re Formation. The upper part of the Hastie??re Formation is marked by a sea-level rise associated with a moderate decrease of the oxygenation of bottom waters. The intra-Devonian hiatus at the Etroeungt-Hastie??re boundary shows no abnormal extinctions and no appearance of new taxa. Thus, the Hangenberg Event is not recognizable in the studied section. Neither the sedimentological analysis nor the palaeontological study of the Bocahut quarry in the Avesnois and of the Anseremme railway bridge section confirm the hypothesis of a highstand for the Hastie??re Formation.

Crustal implications of bedrock geology along the Trans-Alaska Crustal Transect (TACT) in the Brooks Range, northern Alaska

USGS Publications Warehouse

Moore, Thomas E.; Wallace, W.K.; Mull, C.G.; Adams, K.E.; Plafker, G.; Nokleberg, W.J.

1997-01-01

Geologic mapping of the Trans-Alaska Crustal Transect (TACT) project along the Dalton Highway in northern Alaska indicates that the Endicott Mountains allochthon and the Hammond terrane compose a combined allochthon that was thrust northward at least 90 km in the Early Cretaceous. The basal thrust of the combined allochthon climbs up section in the hanging wall from a ductile shear zone, in the south through lower Paleozoic rocks of the Hammond terrane and into Upper Devonian rocks of the Endicott Mountains allochthon at the Mount Doonerak antiform, culminating in Early Cretaceous shale in the northern foothills of the Brooks Range. Footwall rocks north of the Mount Doonerak antiform are everywhere parautochthonous Permian and Triassic shale of the North Slope terrane rather than Jurassic and Lower Cretaceous strata of the Colville Basin as shown in most other tectonic models of the central Brooks Range. Stratigraphic and structural relations suggest that this thrust was the basal detachment for Early Cretaceous deformation. Younger structures, such as the Tertiary Mount Doonerak antiform, deform the Early Cretaceous structures and are cored by thrusts that root at a depth of about 10 to 30 km along a deeper detachment than the Early Cretaceous detachment. The Brooks Range, therefore, exposes (1) an Early Cretaceous thin-skinned deformational belt developed during arc-continent collision and (2) a mainly Tertiary thick-skinned orogen that is probably the northward continuation of the Rocky Mountains erogenic belt. A down-to-the-south zone of both ductile and brittle normal faulting along the southern margin of the Brooks Range probably formed in the mid-Cretaceous by extensional exhumation of the Early Cretaceous contractional deformation. copyright. Published in 1997 by the American Geophysical Union.

Beneath it all: bedrock geology of the Catskill Mountains and implications of its weathering.

PubMed

Ver Straeten, Charles A

2013-09-01

The Devonian-age bedrock of the Catskill Mountains has been the focus of many studies. This paper reviews the character and composition of the rocks of the Catskills, and examines weathering (rock decay) processes and their implications in the Catskills. Rocks of the Catskills and closest foothills consist of siliciclastic rocks (sandstones, mudrocks, conglomerates) with minimal, locally dispersed carbonate rocks. The former are dominated by quartz, metamorphic and sedimentary rock fragments, and clay minerals. Other minor sediment components include cements, authigenic and heavy minerals, and fossil organic matter. Physical, chemical, and biological weathering of the Catskill bedrock since uplift of the Appalachian region, combined with glaciation, have dissected a plateau of nearly horizontally layered rocks into a series of ridges, valleys, and peaks. The varied weathering processes, in conjunction with many factors (natural and anthropogenic), fragment the rocks, forming sediment and releasing various elements and compounds. These may have positive, neutral, or negative implications for the region's soils, waters, ecology, and human usage. A new generation of studies and analyses of the Catskill bedrock is needed to help answer a broad set of questions and problems across various fields of interest. © 2013 New York Academy of Sciences.

Unusual central Nevada geologic terranes produced by Late Devonian Antler orogeny and Alamo impact

USGS Publications Warehouse

Poole, Forrest G.; Sandberg, Charles

2015-01-01

Detailed geologic maps at scales of 1:8,000 and 1:10,000 document the conclusions, interpretations, and hypotheses presented in Chapters 1 and 2, respectively. Identification and dating of Paleozoic rock units are accomplished by means of nearly a hundred acid-dissolved carbonate conodont samples and at least 50 collections of conodonts on siltstone bedding planes that were identified either in the field or later in the office.

The composition of fluid inclusions in ore and gangue minerals from the Silesian-Cracow Mississippi Valley-type Zn-Pb deposits Poland: Genetic and environmental implications

USGS Publications Warehouse

Viets, J.G.; Hofstra, A.H.; Emsbo, P.; Kozlowski, A.

1996-01-01

The composition of fluids extracted from ore and gangue sulfide minerals that span most of the paragenesis of the Silesian-Cracow district was determined using a newly developed ion chromatographic (IC) technique. Ionic species determined were Na+, NH+4, Ca2+, Mg2+, K+, Rb+, Sr2+, Ba2+, Cl-, Br-, F-, I-, PO3-4, CO2-3, HS-, S2O2-3, SO2-4, NO-3, and acetate. Mineral samples included six from the Pomorzany mine and one from the Trzebionka mine which are hosted in the Triassic Muschelkalk Formation, and two samples of drill core from mineralized Upper Devonian strata. Nine paragenetically identifiable sulfide minerals occur throughout the Silesian-Cracow district. These include from earliest to latest: early iron sulfides, granular sphalerite, early galena, light-banded sphalerite, galena, dark-banded sphalerite, iron sulfides, late dark-banded sphalerite with late galena, and late iron sulfides. Seven of the minerals were sampled for fluid inclusion analysis in this study. Only the early iron sulfides and the last galena stage were not sampled. Although the number of analyses are limited to nine samples and two replicates and there is uncertainty about the characteristics of the fluid inclusions analyzed, the data show clear temporal trends in the composition of the fluids that deposited these minerals. Fluid inclusions in minerals deposited later in the paragenesis have significantly more K+, Br-, NH+4, and acetate but less Sr2+ than those deposited earlier in the paragenesis. The later minerals are also characterized by isotopically lighter sulfur and significantly more Tl and As in the solid minerals. The change in ore-fluid chemistry is interpreted to reflect a major change in the hydrologic regime of the district. Apparently, the migrational paths of ore fluids from the Upper Silesian basin changed during ore deposition and the fluids which deposited early minerals reacted with aquifers with very different geochemical characteristics than those that deposited late minerals. The early fluids may have reacted primarily with Devonian and Lower Carboniferous carbonate aquifers deeper in the basin, whereas the later fluids appear to have had extensive contact with organic-rich rocks, probably the shallower Middle and Upper Carboniferous flysch associated with coal measures. High concentrations of toxic Tl and As occur in the readily oxidized marcasite and pyrite minerals deposited by the later fluids. In general, the geochemistry of both the early and late fluids may be explained by an evaporite related origin or by water-rock modification of a saline basinal brine. When compared to the composition of fluid inclusions in Mississippi Valley-type (MVT) ore minerals from the Ozark region of the United States, fluid inclusions in minerals from Silesian-Cracow are fundamentally different, containing more Ca2+, Mg2+, NH+4, Br-, Sr2+ and acetate in all mineral stages with significantly more K+ in later stage minerals. The differences in ore fluid chemistry between the two regions are consistent with the lithologic differences of the respective basins thought to be the source of the mineralizing brines.

Total petroleum systems of the Trias/Ghadames Province, Algeria, Tunisia, and Libya; the Tanezzuft-Oued Mya, Tanezzuft-Melrhir, and Tanezzuft-Ghadames

USGS Publications Warehouse

Klett, T.R.

2000-01-01

Undiscovered conventional oil and gas resources were assessed within total petroleum systems of the Trias/Ghadames Province (2054) as part of the U.S. Geological Survey World Petroleum Assessment 2000. The Trias/Ghadames Province is in eastern Algeria, southern Tunisia, and westernmost Libya. The province and its total petroleum systems generally coincide with the Triassic Basin. The province includes the Oued Mya Basin, Melrhir Basin, and Ghadames (Berkine) Basin. Although several total petroleum systems may exist within each of these basins, only three “composite” total petroleum systems were identified. Each total petroleum system occurs in a separate basin, and each comprises a single assessment unit.The main source rocks are the Silurian Tanezzuft Formation (or lateral equivalents) and Middle to Upper Devonian mudstone. Maturation history and the major migration pathways from source to reservoir are unique to each basin. The total petroleum systems were named after the oldest major source rock and the basin in which it resides.The estimated means of the undiscovered conventional petroleum volumes in total petroleum systems of the Trias/Ghadames Province are as follows [MMBO, million barrels of oil; BCFG, billion cubic feet of gas; MMBNGL, million barrels of natural gas liquids]:Tanezzuft-Oued Mya 830 MMBO 2,341 BCFG 110 MMBNGLTanezzuft-Melrhir 1,875 MMBO 4,887 BCFG 269 MMBNGLTanezzuft-Ghadames 4,461 MMBO 12,035 BCFG 908 MMBNGL

Total Petroleum Systems of the Carpathian - Balkanian Basin Province of Romania and Bulgaria

USGS Publications Warehouse

Pawlewicz, Mark

2007-01-01

The U.S. Geological Survey defined the Moesian Platform Composite Total Petroleum System and the Dysodile Schist-Tertiary Total Petroleum System, which contain three assessment units, in the Carpathian-Balkanian Basin Province of Romania and Bulgaria. The Moesian Platform Assessment Unit, contained within the Moesian Platform Composite Total Petroleum System, is composed of Mesozoic and Cenozoic rocks within the Moesian platform region of southern Romania and northern Bulgaria and also within the Birlad depression in the northeastern platform area. In Romania, hydrocarbon sources are identified as carbonate rocks and bituminous claystones within the Middle Devonian, Middle Jurassic, Lower Cretaceous, and Neogene stratigraphic sequences. In the Birlad depression, Neogene pelitic strata have the best potential for generating hydrocarbons. In Bulgaria, Middle and Upper Jurassic shales are the most probable hydrocarbon sources. The Romania Flysch Zone Assessment Unit in the Dysodile Schist-Tertiary Total Petroleum System encompasses three structural and paleogeographic subunits within the Pre-Carpathian Mountains region: (1) the Getic depression, a segment of the Carpathian foredeep; (2) the flysch zone of the eastern Carpathian Mountains (also called the Marginal Fold nappe); and (3) the Miocene zone (also called the Sub-Carpathian nappe). Source rocks are interpreted to be Oligocene dysodile schist and black claystone, along with Miocene black claystone and marls. Also part of the Dysodile Schist-Tertiary Total Petroleum System is the Romania Ploiesti Zone Assessment Unit, which includes a zone of diapir folds. This zone lies between the Rimnicu Sarat and Dinibovita valleys and between the folds of the inner Carpathian Mountains and the external flanks of the Carpathian foredeep. The Oligocene Dysodile Schist is considered the main hydrocarbon source rock and Neogene black marls and claystones are likely secondary sources; all are thought to be at their maximum thermal maturation. Undiscovered resources in the Carpathian-Balkanian Basin Province are estimated, at the mean, to be 2,076 billion cubic feet of gas, 1,013 million barrels of oil, and 116 million barrels of natural gas liquids.

Variscan tectonics in Dodecanese, Kalymnos island, Greece

NASA Astrophysics Data System (ADS)

Chatziioannou, Eleftheria; Grasemann, Bernhard; Schneider, David; Hubmann, Bernhard; Soukis, Konstantinos

2015-04-01

Kalymnos island is located in the Dodecanese, southeastern Aegean Sea, and geologically appears to be part of the external Hellenides. Pre-Alpidic basement rocks on the Dodecanese islands have been suggested to record compelling similarities with the basement rocks in Eastern Crete with respect to their lithologies and pre-Alpidic metamorphic evolution. The lithotectonic units experienced greenschist to amphibolite facies conditions during the Variscan orogeny. Whereas the rocks in Eastern Crete reveal Alpine high-pressure overprint, the Variscan basement units in the Dodecanese record no or low-grade Alpine metamorphism. A field study of basement rocks below Mesozoic limestones and dolomites in the NW part of Kalymnos near Emporios uncovered a complex history of metamorphism, folding and faulting. Three different tectonic units can be discriminated from top to bottom: a) a quartz-mica schist, b) a white-grey, fossiliferous coarse grained marble and c) a fine-grained fossiliferous blue-grey marble. In the marbles macrofossils such as brachiopods, ammonoid cephalopods (Goniatids?) and crinoids suggest a Middle-Upper Devonian deposition age (Givetian- Frasnian). Structural mapping the area resolved a dominant W-E shortening event, resulting in an overall inverted metamorphic gradient. The lowermost blue-grey marble unit is folded into large-scale upright folds, which are truncated by top-to-east overthrusting of the white-grey marble unit. Whereas deformation mechanisms in the blue-grey marble unit are dominated by dissolution-precipitation creep, the white-grey marble suffered intense crystal plastic deformation with localized high-strain mylonitic shear zones. The uppermost quartz-mica schist unit is separated from the lower units by a cataclastic phyllonitic shear zone. 40Ar/39Ar geochronological dating on white micas from the quartz-mica schists yielded cooling ages between 240 and 334 Ma indicative of Variscan cooling. Our data suggest that this part of the Dodecanese experienced intense Variscan deformation with no high-temperature Alpine overprint.

Geologic map of the Yucca Mountain region, Nye County, Nevada

USGS Publications Warehouse

Potter, Christopher J.; Dickerson, Robert P.; Sweetkind, Donald S.; Drake II, Ronald M.; Taylor, Emily M.; Fridrich, Christopher J.; San Juan, Carma A.; Day, Warren C.

2002-01-01

Yucca Mountain, Nye County, Nev., has been identified as a potential site for underground storage of high-level radioactive waste. This geologic map compilation, including all of Yucca Mountain and Crater Flat, most of the Calico Hills, western Jackass Flats, Little Skull Mountain, the Striped Hills, the Skeleton Hills, and the northeastern Amargosa Desert, portrays the geologic framework for a saturated-zone hydrologic flow model of the Yucca Mountain site. Key geologic features shown on the geologic map and accompanying cross sections include: (1) exposures of Proterozoic through Devonian strata inferred to have been deformed by regional thrust faulting and folding, in the Skeleton Hills, Striped Hills, and Amargosa Desert near Big Dune; (2) folded and thrust-faulted Devonian and Mississippian strata, unconformably overlain by Miocene tuffs and lavas and cut by complex Neogene fault patterns, in the Calico Hills; (3) the Claim Canyon caldera, a segment of which is exposed north of Yucca Mountain and Crater Flat; (4) thick densely welded to nonwelded ash-flow sheets of the Miocene southwest Nevada volcanic field exposed in normal-fault-bounded blocks at Yucca Mountain; (5) upper Tertiary and Quaternary basaltic cinder cones and lava flows in Crater Flat and at southernmost Yucca Mountain; and (6) broad basins covered by Quaternary and upper Tertiary surficial deposits in Jackass Flats, Crater Flat, and the northeastern Amargosa Desert, beneath which Neogene normal and strike-slip faults are inferred to be present on the basis of geophysical data and geologic map patterns. A regional thrust belt of late Paleozoic or Mesozoic age affected all pre-Tertiary rocks in the region; main thrust faults, not exposed in the map area, are interpreted to underlie the map area in an arcuate pattern, striking north, northeast, and east. The predominant vergence of thrust faults exposed elsewhere in the region, including the Belted Range and Specter Range thrusts, was to the east, southeast, and south. The vertical to overturned strata of the Striped Hills are hypothesized to result from successive stacking of three south-vergent thrust ramps, the lowest of which is the Specter Range thrust. The CP thrust is interpreted as a north-vergent backthrust that may have been roughly contemporaneous with the Belted Range and Specter Range thrusts. The southwest Nevada volcanic field consists predominantly of a series of silicic tuffs and lava flows ranging in age from 15 to 8 Ma. The map area is in the southwestern quadrant of the southwest Nevada volcanic field, just south of the Timber Mountain caldera complex. The Claim Canyon caldera, exposed in the northern part of the map area, contains thick deposits of the 12.7-Ma Tiva Canyon Tuff, along with widespread megabreccia deposits of similar age, and subordinate thick exposures of other 12.8- to 12.7-Ma Paintbrush Group rocks. An irregular, blocky fault array, which affects parts of the caldera and much of the nearby area, includes several large-displacement, steeply dipping faults that strike radially to the caldera and bound south-dipping blocks of volcanic rock. South and southeast of the Claim Canyon caldera, in the area that includes Yucca Mountain, the Neogene fault pattern is dominated by closely spaced, north-northwest- to north-northeast-striking normal faults that lie within a north-trending graben. This 20- to 25-km-wide graben includes Crater Flat, Yucca Mountain, and Fortymile Wash, and is bounded on the east by the 'gravity fault' and on the west by the Bare Mountain fault. Both of these faults separate Proterozoic and Paleozoic sedimentary rocks in their footwalls from Miocene volcanic rocks in their hanging walls. Stratigraphic and structural relations at Yucca Mountain demonstrate that block-bounding faults were active before and during eruption of the 12.8- to 12.7-Ma Paintbrush Group, and significant motion on these faults continued unt

Tectonic control of Middle Devonian reef building in the Mechra ben Abbou (northern Rehamna, Morocco)Contrôle tectonique de l'édification des récifs Dévonien moyen de Mechra ben Abbou (Rehamna, Maroc)

NASA Astrophysics Data System (ADS)

El Kamel, Fouad; El Hassani, Ahmed; Mohsine, Assia; Remmal, Toufik

2000-01-01

In the carbonated platform of Upper Emsian to Givetian age, the reef edification is previous to, and contemporaneous with, a tilted block tectonic that has favoured the bioconstruction in its upper part. The tectonic expression is illustrated by several instability marks, such as tension faults, progressive unconformity and the resulting landslide, observed in both the reef development zone and the external platform.

Detrital zircon age distribution from Devonian and Carboniferous sandstone in the Southern Variscan Fold-and-Thrust belt (Montagne Noire, French Massif Central), and their bearings on the Variscan belt evolution

NASA Astrophysics Data System (ADS)

Lin, Wei; Faure, Michel; Li, Xian-hua; Chu, Yang; Ji, Wenbin; Xue, Zhenhua

2016-05-01

In the Southern French Massif Central, the Late Paleozoic sedimentary sequences of the Montagne Noire area provide clues to decipher the successive tectonic events that occurred during the evolution of the Variscan belt. Previous sedimentological studies already demonstrated that the siliciclastic deposits were supplied from the northern part of the Massif Central. In this study, detrital zircon provenance analysis has been investigated in Early Devonian (Lochkovian) conglomerate and sandstone, and in Carboniferous (Visean to Early Serpukhovian) sandstone from the recumbent folds and the foreland basin of the Variscan Southern Massif Central in Montagne Noire. The zircon grains from all of the samples yielded U-Pb age spectra ranging from Neoarchean to Late Paleozoic with several age population peaks at 2700 Ma, 2000 Ma, 980 Ma, 750 Ma, 620 Ma, 590 Ma, 560 Ma, 480 Ma, 450 Ma, and 350 Ma. The dominant age populations concentrate on the Neoproterozoic and Paleozoic. The dominant concordant detrital zircon age populations in the Lochkovian samples, the 480-445 Ma with a statistical peak around 450 Ma, are interpreted as reflecting the rifting event that separated several continental stripes, such as Armorica, Mid-German Crystalline Rise, and Avalonia from the northern part of Gondwana. However, Ediacaran and Cambrian secondary peaks are also observed. The detrital zircons with ages at 352 - 340 Ma, with a statistical peak around 350 Ma, came from the Early Carboniferous volcanic and plutonic rocks similar to those exposed in the NE part of the French Massif Central. Moreover, some Precambrian grains recorded a more complex itinerary and may have experienced a multi-recycling history: the Archean and Proterozoic grains have been firstly deposited in Cambrian or Ordovician terrigenous rocks, and secondly re-sedimented in Devonian and/or Carboniferous formations. Another possibility is that ancient grains would be inherited grains, scavenged from an underlying but not exposed Precambrian basement.

Petrogenesis and tectonic setting of the Devonian Xiqin A-type granite in the northeastern Cathaysia Block, SE China

NASA Astrophysics Data System (ADS)

Cai, Da-wei; Tang, Yong; Zhang, Hui; Lv, Zheng-Hang; Liu, Yun-long

2017-06-01

Most Silurian-Devonian granites in South China are S- or I-type granites, which are suggested to be petrogenetically related to the Wuyi-Yunkai orogeny. In this paper, we present the detailed LA-ICP-MS zircon U-Pb dating, major and trace element geochemical, and Nd-Hf isotopic data for Xiqin A-type granites in the northeastern Cathaysia Block, SE China. Zircon U-Pb dating results show that the Xiqin granites were emplaced at about 410 Ma, indicating that they were generated at the end of Wuyi-Yunkai orogeny. These granites are high in K2O + Na2O (6.31-8.79 wt%), high field strength elements (Zr + Nb + Ce + Y = 427-699 ppm), rare earth elements (total REE = 221-361 ppm) as well as high Ga/Al ratios (10,000 Ga/Al = 2.50-3.10), and show characteristics typical of A-type granites. εHf(t) values of the Xiqin granites mainly vary from -0.4 to -3.1 and yield Mesoproterozoic T2DM(Hf) (mainly ranging from 1.29 to 1.45 Ga). The εNd(t) values are from -1.23 to -2.11 and T2DM(Nd) vary from 1.25 to 1.32 Ga. These isotopic data suggest that the Xiqin granites were generated by partial melting of metavolcanic rocks with minor metasedimentary rocks in the lower crust. Our data on the Xiqin granites, coupled with previous studies of Silurian-Devonian magmatism, suggest that the tectonic regime had changed to a strongly post-collisional extension environment in the Wuyi-Yunkai orogen at least since 410 Ma, and that delamination, which accounts for the change in stress from the compression to extension and asthenospheric upwelling during the early Paleozoic, plays a significant role in the generation of Xiqin A-type granites.

Towards a High-resolution Time Scale for the Early Devonian

NASA Astrophysics Data System (ADS)

Dekkers, M. J.; da Silva, A. C.

2017-12-01

High-resolution time scales are crucial to understand Earth's history in detail. The construction of a robust geological time scale, however, inevitably becomes increasingly harder further back in time. Uncertainties associated with anchor radiometric ages increase in size, not speaking of the mere presence of suitable datable strata. However, durations of stages can be tightly constrained by making use of cyclic expressions in sediments, an approach that revolutionized the Cenozoic time scale. When precisely determined durations are stitched together, ultimately, a very precise time scale is the result. For the Mesozoic and Paleozoic an astronomical solution as a tuning target is not available but the dominant periods of eccentricity, obliquity and precession are reasonably well constrained for the entire Phanerozoic which enables their detection by means of spectral analysis. Eccentricity is time-invariant and is used as the prime building block. Here we focus on the Early Devonian, on its lowermost three stages: the Lochkovian, Pragian and Emsian. The uncertainties on the Devonian stage boundaries are currently in the order of several millions of years. The preservation of climatic cycles in diagenetically or even anchimetamorphically affected successions, however, is essential. The fit of spectral peak ratios with those calculated for orbital cycles, is classically used as a strong argument for a preserved climatic signal. Here we use primarily the low field magnetic susceptibility (MS) as proxy parameter, supported by gamma-ray spectrometry to test for consistency. Continuous Wavelet Transform, Evolutive Harmonic Analysis, Multitaper Method, and Average Spectral Misfit are used to reach an optimal astronomical interpretation. We report on classic Early Devonian sections from the Czech Republic: the Pozar-CS (Lochkovian and Pragian), Pod Barrandovem (Pragian and Lower Emsian), and Zlichov (Middle-Upper Emsian). Also a Middle-Upper Emsian section from the US (Road 199 section, Kingston, New York) will be targeted. Strata display Milankovitch cycles to a varying visible degree but spectral analysis of MS with supporting magnetic property tests enables to constrain durations up to an order of magnitude more precise than in the current (2012) Geological Time Scale.

Late Devonian shale deposition based on known and predicted occurrence of Foerstia in Michigan basin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matthews, R.D.

The fossil Foerstia (Protosalvinia) marks a time zone within Late Devonian shale sequences in the eastern US. Its recent discovery in Michigan has led to more accurate correlations among the three large eastern basins. Subdivisions of the Devonian-Mississippi shale sequence in Michigan based on gamma-ray correlations reveal an idealized black shale geometry common to other eastern black shales, such as the Sunbury of Michigan and Ohio, the Clegg Creek of Indiana, the Dunkirk of Pennsylvania and New York, and the lower Huron of Ohio and West Virginia. In Michigan, Foerstia occurs at a stratigraphic position postulated to mark a majormore » change in depositional conditions and source areas. This position strengthens the physical and paleontologic evidence for a formal division of the Antrim. Isopach maps of the shale sequence above and below Foerstia show a relatively uniform and continuous black shale deposit (units 1A, 1B, and 1C) below Foerstia. This deposit is unlike the wedge of sediment found above Foerstia, which is composed of a western facies (Ellsworth) and an eastern facies (upper Antrim) that should be combined in a single stratigraphic unit conforming to Forgotson's concept of a format.« less

Affinities and architecture of Devonian trunks of Prototaxites loganii.

PubMed

Retallack, G J; Landing, Ed

2014-01-01

Devonian fossil logs of Prototaxites loganii have been considered kelp-like aquatic algae, rolled up carpets of liverworts, enormous saprophytic fungal fruiting bodies or giant lichens. Algae and rolled liverwort models cannot explain the proportions and branching described here of a complete fossil of Prototaxites loganii from the Middle Devonian (386 Ma) Bellvale Sandstone on Schunnemunk Mountain, eastern New York. The "Schunnemunk tree" was 8.83 m long and had six branches, each about 1 m long and 9 cm diam, on the upper 1.2 m of the main axis. The coalified outermost layer of the Schunnemunk trunk and branches have isotopic compositions (δ(13)CPDB) of -25.03 ± 0.13‰ and -26.17 ± 0.69‰, respectively. The outermost part of the trunk has poorly preserved invaginations above cortical nests of coccoid cells embraced by much-branched tubular cells. This histology is unlike algae, liverworts or vascular plants and most like lichen with coccoid chlorophyte phycobionts. Prototaxites has been placed within Basidiomycota but lacks clear dikaryan features. Prototaxites and its extinct order Nematophytales may belong within Mucoromycotina or Glomeromycota. © 2014 by The Mycological Society of America.

The Middle to Late Devonian Eden-Comerong-Yalwal Volcanic Zone of Southeastern Australia: An ancient analogue of the Yellowstone-Snake River Plain region of the USA

NASA Astrophysics Data System (ADS)

Dadd, K. A.

1992-11-01

The Middle to Late Devonian Yalwal Volcanics, Comerong Volcanics, Boyd Volcanic Complex and associated gabbroic and A-type granitic plutons form part of a continental volcano-tectonic belt, the Eden-Comerong-Yalwal Volcanic Zone (EVZ), located parallel to the coast of southeastern Australia. The EVZ is characterised by an elongate outcrop pattern, bimodal basalt-rhyolite volcanism, and a paucity of sedimentary rocks. Volcanic centres were located along the length of the volcanic zone at positions indicated by subvolcanic plutons, dykes, rhyolite lavas and other proximal vent indicators including surge bedforms in tuff rings, and hydrothermal alteration. Previous interpretations that suggested the volcanic zone was a fault bounded rift are rejected in favour of a volcano-tectonic belt. The Yellowstone-Snake River Plain region (Y-SRP) in the USA is an appropriate analogue. Both regions have basalt lavas which range in composition from olivine tholeiite to ferrobasalt, alkalic rhyolitic rocks enriched in Y, Zr and Th, large rhyolite lava flows, plains-type basalt lava flows, and a paucity of sedimentary rocks. The Y-SRP is inferred to have developed by migration of the American plate over a fixed hot spot leading to a northeast temporal progression of the focus of volcanic activity. Application of a similar hot spot model to the EVZ (using a length of 300 km and a time range for volcanic activity of 5-10 Ma), suggests that during the Middle to Late Devonian the Australian plate was moving at a rate of between 3 and 6 cm/yr relative to the hot spot and that the northern extent of the volcanic zone at any time was a topographically high region with rhyolitic activity, similar to present day Yellowstone. As the focus of activity moved northward, the high region subsided and the depression was flooded by basalt. The EVZ was much wider (up to 70 km) and much longer than the belt defined by present-day outcrop and was of comparable scale to the Y-SRP. The main difference between the two volcanic belts is the lack of large pyroclastic flows and identifiable caldera complexes in the EVZ.

Geology of the Deep Creek area, Washington, and its regional significance

USGS Publications Warehouse

Yates, Robert Giertz

1976-01-01

This report, although primarily concerned with the stratigraphy and structure of a lead-zinc mining district in northern Stevens County, Washington, discusses and integrates the geology of the region about the Deep Creek area. Although the study centers in an area of about 200 square miles immediately south of the International Boundary, the regional background comes from: (1)the previously undescribed Northport quadrangle to the west, (2) published reports and reconnaissance of the Metaline quadrangle to the east, and (3) from published reports and maps of a 16 mile wide area that lies to the north adjacent to these three quadrangles in British Columbia. The report is divided into three parts: (1) descriptions of rocks and structures of the Deep Creek area, (2) descriptions of the regional setting of the Deep Creek area, and (3) an analysis and interpretation of the depositional and tectonic events that produced the geologic features exposed today. In the Deep Creek area surficial deposits of sand and gravel of glacial origin cover much of the consolidated rocks, which range in age from greenschist of the late Precambrlan to albite granite of the Eocene. Three broad divisions of depositional history are represented: (1) Precambrian, (2) lower Paleozoic and (3) upper Paleozoic; the record of the Mesozoic and Eocene is fragmentary. The lower Paleozoic division is the only fossil-controlled sequence; the age of the other two divisions were established by less direct methods. Both Precambrian and upper Paleozoic sequences are dominated by fine-grained detrital sediments, the Precambrian tending towards the alumina-rich and the upper Paleozoic tending towards the black shale facies with high silica. Neither sequence has more than trivial amounts of coarse clastics. Both include limestones, but in minor abundance. The lower Paleozoic sequence, on the other hand, represents a progressive change in deposition. The sequence began during the very late Precambrian with the deposition of clean quartz sand. This was followed by the accumulation of a comparatively thin limestone unit succeeded by a thick shale. The shale grades into a thick carbonate unit which in turn is overlain by black graptolitic slates (Ordovician). This general order of deposition holds for the Cambro-Ordovician throughout the area. Precambrian rocks indigenous to the Deep Creek area, have undergone at least six tectonic events of greatly different intensities. The first three of these events are epeirogentic, the fourth involves intense folding, the fifth, crossfolding, and the sixth, block faulting without folding. These events are dated with varying degrees of precision. The two epeirogentic events of the Precambrian, one gentle folding at the beginning of Windermere time and the other high angle faulting and volcanism in mid-Windermere time, did little to deform or metamorphose the rocks. The third event consists of uplift of northern Idaho and adjacent Montana and westward decollement thrusting of essentially unfolded lower Paleozoic rocks. The decollement faulting is inferred to explain anomalous rock distribution and cannot be accurately dated. It occurred sometime after the Devonian and before the Jurassic. A late Paleozoic age is favored.

Rock Magnetic Properties of Remagnetised Devonian and Carboniferous Carbonate and Clastic Rocks From The NE Rhenish Massif, Germany

NASA Astrophysics Data System (ADS)

Zwing, A.; Matzka, J.; Bachtadse, V.; Soffel, H. C.

Previous studies on remagnetised carbonate rocks from the North American and Eu- ropean Variscides reported characteristic rock magnetic properties which are thought to be diagnostic for a chemical remagnetisation event. Their hysteresis properties with high ratios of Mrs/Ms and Hcr/Hc indicate the presence of a mixture of single-domain and superparamagnetic magnetite (Jackson, et al. 1990). In order to test if this fin- gerprint can be identified in remagnetised carbonate and clastic rocks from the NE Rhenish Massif, Germany, a series of rock magnetic experiments has been carried out. The hysteresis properties of the remagnetised clastic rocks indicate the domi- nance of large MD particles, as can be expected for detrital sediments. The carbon- ates yield significantly higher ratios of Mrs/Ms and Hcr/Hc than the clastic rocks, but only partly correspond to the characteristic properties of remagnetised carbon- ates described above. The latter might be attributed to detrital input into the carbonate platforms. Additional low-temperature remanence measurements show a wide vari- ety of phenomena, including Verwey transitions and indications for the presence of superparamagnetic grains. However, the low-temperature experiments do not allow a straightforward discrimination between the clastic and carbonate rocks and suggest more complex magnetomineralogies than expected from the hysteresis measurements alone.

Geochemistry and origin of regional dolomites

NASA Astrophysics Data System (ADS)

Hanson, G. N.; Meyers, W. J.

1989-12-01

The major goal of the carbonate research program at Stony Brook is to better understand the conditions and processes leading to regional diagenesis of carbonate rocks. Our research focuses on studies of ancient, massive dolostones, but we are also studying limestone diagenesis for its own importance, and as it relates to dolomitization. Our approach has been to carry out a very detailed petrographic and geochemical case study to the Mississippian Burlington-Keokuk Fms. of Iowa, Illinois and Missouri, and to develop this as a testing ground for new geochemical and modelling techniques, and for testing various models for regional dolomitization in epicontinental carbonates. The ideas and techniques developed in our Burlington-Keokuk studies are being expanded and applied to carbonate sequences of other ages (Devonian to Neogene), and other tectono-sedimentary settings. The emphasis of this report will be on new developments and results on the Burlington-Keokuk studies and on our diagenetic studies of other strata. Recent research on Burlington-Keokuk rocks include development and application of boron isotopes and the U--Th--Pb system to dolomite studies, investigations of porosity and permeability in the dolostones. Projects on other strata include dolomitization and limestones diagenesis of Devonian carbonates of Alberta and Western Australia, Miocene reefal carbonates of Spain, Neogene carbonates of Curacao and Bonaire, Waulsortian limestones of Ireland, modelling of trace elements and stable isotopes, and experimental growth of calcites to investigate crystallographic controls of trace element incorporation.

Variability over time in the sources of South Portuguese Zone turbidites: evidence of denudation of different crustal blocks during the assembly of Pangaea

NASA Astrophysics Data System (ADS)

Pereira, M. F.; Ribeiro, C.; Vilallonga, F.; Chichorro, M.; Drost, K.; Silva, J. B.; Albardeiro, L.; Hofmann, M.; Linnemann, U.

2014-07-01

This study combines geochemical and geochronological data in order to decipher the provenance of Carboniferous turbidites from the South Portuguese Zone (SW Iberia). Major and trace elements of 25 samples of graywackes and mudstones from the Mértola (Visean), Mira (Serpukhovian), and Brejeira (Moscovian) Formations were analyzed, and 363 U-Pb ages were obtained on detrital zircons from five samples of graywackes from the Mira and Brejeira Formations using LA-ICPMS. The results indicate that turbiditic sedimentation during the Carboniferous was marked by variability in the sources, involving the denudation of different crustal blocks and a break in synorogenic volcanism. The Visean is characterized by the accumulation of immature turbidites (Mértola Formation and the base of the Mira Formation) inherited from a terrane with intermediate to mafic source rocks. These source rocks were probably formed in relation to Devonian magmatic arcs poorly influenced by sedimentary recycling, as indicated by the almost total absence of pre-Devonian zircons typical of the Gondwana and/or Laurussia basements. The presence of Carboniferous grains in Visean turbidites indicates that volcanism was active at this time. Later, Serpukhovian to Moscovian turbiditic sedimentation (Mira and Brejeira Formations) included sedimentary detritus derived from felsic mature source rocks situated far from active magmatism. The abundance of Precambrian and Paleozoic zircons reveals strong recycling of the Gondwana and/or Laurussia basements. A peri-Gondwanan provenance is indicated by zircon populations with Neoproterozoic (Cadomian-Avalonian and Pan-African zircon-forming events), Paleoproterozoic, and Archean ages. The presence of late Ordovician and Silurian detrital zircons in Brejeira turbidites, which have no correspondence in the Gondwana basement of SW Iberia, indicates Laurussia as their most probable source.

Reconstruction of an early Paleozoic continental margin based on the nature of protoliths in the Nome Complex, Seward Peninsula, Alaska

USGS Publications Warehouse

Till, Alison B.; Dumoulin, Julie A.; Ayuso, Robert A.; Aleinikoff, John N.; Amato, Jeffrey M.; Slack, John F.; Shanks, W.C. Pat

2014-01-01

The Nome Complex is a large metamorphic unit that sits along the southern boundary of the Arctic Alaska–Chukotka terrane, the largest of several micro continental fragments of uncertain origin located between the Siberian and Laurentian cratons. The Arctic Alaska–Chukotka terrane moved into its present position during the Mesozoic; its Mesozoic and older movements are central to reconstruction of Arctic tectonic history. Accurate representation of the Arctic Alaska–Chukotka terrane in reconstructions of Late Proterozoic and early Paleozoic paleogeography is hampered by the paucity of information available. Most of the Late Proterozoic to Paleozoic rocks in the Alaska–Chukotka terrane were penetratively deformed and recrystallized during the Mesozoic deformational events; primary features and relationships have been obliterated, and age control is sparse. We use a variety of geochemical, geochronologic, paleontologic, and geologic tools to read through penetrative deformation and reconstruct the protolith sequence of part of the Arctic Alaska–Chukotka terrane, the Nome Complex. We confirm that the protoliths of the Nome Complex were part of the same Late Proterozoic to Devonian continental margin as weakly deformed rocks in the southern and central part of the terrane, the Brooks Range. We show that the protoliths of the Nome Complex represent a carbonate platform (and related rocks) that underwent incipient rifting, probably during the Ordovician, and that the carbonate platform was overrun by an influx of siliciclastic detritus during the Devonian. During early phases of the transition to siliciclastic deposition, restricted basins formed that were the site of sedimentary exhalative base-metal sulfide deposition. Finally, we propose that most of the basement on which the largely Paleozoic sedimentary protolith was deposited was subducted during the Mesozoic.

Suprasubduction volcanic rocks of the Char ophiolite belt, East Kazakhstan: new geochemical and first geochronological data

NASA Astrophysics Data System (ADS)

Safonova, Inna; Simonov, Vladimir; Seltmann, Reimar; Yamamoto, Shinji; Xiao, Wenjiao

2016-04-01

The Char ophiolite belt is located in the western Central Asian Orogenic Belt, a world largest accretionary orogen, which has evolved during more than 800 Ma. The Char belt formed during Kazakhstan - Siberia collision. It has been known for hosting fragments of Late Devonian-Early Carboniferous oceanic crust, MORB, OPB and OIB, of the Paleo-Asian Ocean (Safonova et al., 2012). The Char is surrounded by two Paleozoic island-arc terranes: Zharma-Saur in the west and Rudny Altai in the east, however, until recent times, no island-arc units have been found within it. We were the first to find island-arc units as tectonic sheets occurring adjacent to those consisting of oceanic rocks. In places, island-arc andesites cut oceanic basalts. The Char volcanic and subvolcanic rocks of a probable suprasubduction origin are basalt, microgabbro, dolerite, andesite, tonalite and dacite. The mafic to andesitic volcanics possessing low TiO2 (0.85 wt.%av.) and show MgO vs. major elements crystallization trends suggesting two magma series: tholeiitic and calc-alkaline. The tholeiitic varieties are less enriched in incompatible elements then the calc-alkaline ones. Two samples are high-Mg and low-Ti andesibasalts similar to boninites. The rocks possess moderately LREE enriched rare-earth element patterns and are characterized by negative Nb anomalies present on the multi-element spectra (Nb/Lapm = 0.14-0.47; Nb/Thpm = 0.7-1.6).The distribution of rare-earth elements (La/Smn = 0.8-2.3, Gd/Ybn = 0.7-1.9) and the results of geochemical modeling in the Nb-Yb system suggest high degrees of melting of a depleted harzburgite-bearing mantle source at spinel facies depths. Fractional crystallization of clinopyroxene, plagioclase and opaque minerals also affected the final composition of the volcanic rocks. Clinopyroxene monomineral thermometry indicates crystallization of melts at 1020-1180°C. Melt inclusion composition based numerical calculations show that primary melts were derived at 1350-1530°C and 14-26 kbar and crystallized at 1150-1190°C (Simonov et al., 2010). All these features are indicative of a supra-subduction origin of rocks. The age of gabbro, dolerite, andesite and tonalite was determined by LA ICP MS U-Pb zircon dating performed in the University of Kyoto, Japan. The andesites and tonalites yielded Carboniferous ages of ca. 322-336 Ma and the gabbro and dolerite appeared Devonian (387-395 Ma). Thus, the Char volcanic rocks possess geochemical signatures of supra-subduction magmas and could be derived at high degree melting of relatively shallow mantle sources. The volcanic units probably formed at one or two island-arcs or at an intra-oceanic arc and continental margin arc during the Middle Devonian - Mississippian. Later, the island-arc units were probably accreted to the active margin of the Kazakhstan continent. The work was supported by RFBR Project no. 16-05-00313. Contribution to IGCP#592 of UNESCO-IUGS. Safonova, I.Yu., Simonov V.A., Kurganskaya E.V., Obut O.T., Romer R.L., Seltmann R., 2012. Late Paleozoic oceanic basalts hosted by the Char suture-shear zone, East Kazakhstan: geological position, geochemistry, petrogenesis and tectonic setting. Journal of Asian Earth Sciences 49, 20-39. Simonov V.A., Safonova I.Yu., Kovyazin S.V., 2010. Petrogenesis of island-arc complexes of the Char zone, East Kazakhstan. Petrology 18, 59-72.

Late Paleozoic SEDEX deposits in South China formed in a carbonate platform at the northern margin of Gondwana

NASA Astrophysics Data System (ADS)

Qiu, Wenhong Johnson; Zhou, Mei-Fu; Liu, Zerui Ray

2018-05-01

SEDEX sulfide deposits hosted in black shale and carbonate are common in the South China Block. The Dajiangping pyrite deposit is the largest of these deposits and is made up of stratiform orebodies hosted in black shales. Sandstone interlayered with stratiform orebodies contains detrital zircon grains with the youngest ages of 429 Ma. Pyrite from the orebodies has a Re-Os isochron age of 389 ± 62 Ma, indicative of formation of the hosting strata and syngenetic pyrite ores in the mid-late Devonian. The hosting strata is a transgression sequence in a passive margin and composed of carbonaceous limestone in the lower part and black shales in the upper part. The ore-hosting black shales have high TOC (total organic carbon), Mo, As, Pb, Zn and Cd, indicating an anoxic-euxinic deep basin origin. The high redox proxies, V/(V + Ni) > 0.6 and V/Cr > 1, and the positive correlations of TOC with Mo and V in black shales are also consistent with an anoxic depositional environment. The Dajiangping deposit is located close to the NE-trending Wuchuan-Sihui fault, which was active during the Devonian. The mid-late Devonian mineralization age and the anoxic-euxinic deep basinal condition of this deposit thus imply that the formation of this deposit was causally linked to hydrothermal fluid exhalation in an anoxic fault-bounded basin that developed in a carbonate platform of the South China Block. The regional distribution of many Devonian, stratiform, carbonaceous sediment-hosted sulfide deposits along the NE-trending fault-bounded basins in South China, similar to the Dajiangping deposit, indicates that these deposits formed at a basin developed in the passive margin setting of the South China Block during the Devonian. This environment was caused by the break-up and northward migration of the South China Block from Gandwana.

A study of secondary fabrics in rocks from the lizard Peninsula and adjacent areas in southwest cornwall, england

NASA Astrophysics Data System (ADS)

Rathore, Jaswant Singh

1980-09-01

Magnetic susceptibility anisotropy techniques were applied to samples taken in selected areas of the Lizard Peninsula in order to study secondary fabrics due to: (1) the intrusion of granites into sediments; (2) the compression in the sediments to the north of the Lizard thrust boundary; and (3) the intrusion of serpentine into hornblende schists of the Lizard metamorphic block. The magnetic fabric around the Carnmenellis and Godolphin granite masses shows a strong compressional fabric, tending to suggest that the Devonian sediments were compressed radially as the granites intruded them. The high degree of anisotropy observed at the Lizard boundary falls, with increasing distance from the thrust, systematically down to low values in the Devonian sediments. The distinct changes in the fabric parameters at the north end of Church Cove-Landewednack and the southern end of Cadgwith Cove appear to be the remnant secondary fabrics due to the intrusion of serpentine into hornblende schists.

Root evolution at the base of the lycophyte clade: insights from an Early Devonian lycophyte.

PubMed

Matsunaga, Kelly K S; Tomescu, Alexandru M F

2016-04-01

The evolution of complex rooting systems during the Devonian had significant impacts on global terrestrial ecosystems and the evolution of plant body plans. However, detailed understanding of the pathways of root evolution and the architecture of early rooting systems is currently lacking. We describe the architecture and resolve the structural homology of the rooting system of an Early Devonian basal lycophyte. Insights gained from these fossils are used to address lycophyte root evolution and homology. Plant fossils are preserved as carbonaceous compressions at Cottonwood Canyon (Wyoming), in the Lochkovian-Pragian (∼411 Ma; Early Devonian) Beartooth Butte Formation. We analysed 177 rock specimens and documented morphology, cuticular anatomy and structural relationships, as well as stratigraphic position and taphonomic conditions. The rooting system of the Cottonwood Canyon lycophyte is composed of modified stems that bear fine, dichotomously branching lateral roots. These modified stems, referred to as root-bearing axes, are produced at branching points of the above-ground shoot system. Root-bearing axes preserved in growth position exhibit evidence of positive gravitropism, whereas the lateral roots extend horizontally. Consistent recurrence of these features in successive populations of the plant preserved in situ demonstrates that they represent constitutive structural traits and not opportunistic responses of a flexible developmental programme. This is the oldest direct evidence for a rooting system preserved in growth position. These rooting systems, which can be traced to a parent plant, include some of the earliest roots known to date and demonstrate that substantial plant-substrate interactions were under way by Early Devonian time. The morphological relationships between stems, root-bearing axes and roots corroborate evidence that positive gravitropism and root identity were evolutionarily uncoupled in lycophytes, and challenge the hypothesis that roots evolved from branches of the above-ground axial system, suggesting instead that lycophyte roots arose as a novel organ. © The Author 2016. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

75 FR 68974 - Drawbridge Operation Regulation; Upper Mississippi River, Rock Island, IL

Federal Register 2010, 2011, 2012, 2013, 2014

2010-11-10

... Operation Regulation; Upper Mississippi River, Rock Island, IL AGENCY: Coast Guard, DHS. ACTION: Notice of..., has issued a temporary deviation from the regulation governing the operation of the Rock Island Railroad and Highway Drawbridge across the Upper Mississippi River, mile 482.9, at Rock Island, Illinois...

75 FR 17561 - Drawbridge Operation Regulations; Upper Mississippi River, Rock Island, IL

Federal Register 2010, 2011, 2012, 2013, 2014

2010-04-07

...] Drawbridge Operation Regulations; Upper Mississippi River, Rock Island, IL AGENCY: Coast Guard, DHS. ACTION... issued a temporary deviation from the regulation governing the operations of the Rock Island Railroad and Highway Drawbridge across the Upper Mississippi River, Mile 482.9, Rock Island, Illinois. The deviation is...

76 FR 9224 - Drawbridge Operation Regulation; Upper Mississippi River, Rock Island, IL

Federal Register 2010, 2011, 2012, 2013, 2014

2011-02-17

...] Drawbridge Operation Regulation; Upper Mississippi River, Rock Island, IL AGENCY: Coast Guard, DHS. ACTION... issued a temporary deviation from the regulation governing the operation of the Rock Island Railroad and Highway Drawbridge across the Upper Mississippi River, mile 482.9, at Rock Island, Illinois. The deviation...

77 FR 3607 - Drawbridge Operation Regulation; Upper Mississippi River, Rock Island, IL

Federal Register 2010, 2011, 2012, 2013, 2014

2012-01-25

...] Drawbridge Operation Regulation; Upper Mississippi River, Rock Island, IL AGENCY: Coast Guard, DHS. ACTION... issued a temporary deviation from the regulation governing the operation of the Rock Island Railroad and Highway Drawbridge across the Upper Mississippi River, mile 482.9, at Rock Island, Illinois. The deviation...

77 FR 20716 - Drawbridge Operation Regulation; Upper Mississippi River, Rock Island, IL

Federal Register 2010, 2011, 2012, 2013, 2014

2012-04-06

...] Drawbridge Operation Regulation; Upper Mississippi River, Rock Island, IL AGENCY: Coast Guard, DHS. ACTION... issued a temporary deviation from the regulation governing the operation of the Rock Island Railroad and Highway Drawbridge across the Upper Mississippi River, mile 482.9, at Rock Island, Illinois. The deviation...

Extensional Late Paleozoic deformation on the western margin of Pangea, Patlanoaya area, Acatlán Complex, southern Mexico

NASA Astrophysics Data System (ADS)

Ramos-Arias, M. A.; Keppie, J. D.; Ortega-Rivera, A.; Lee, J. W. K.

2008-02-01

New mapping in the northern part of the Paleozoic Acatlán Complex (Patlanoaya area) records several ductile shear zones and brittle faults with normal kinematics (previously thought to be thrusts). These movement zones separate a variety of units that pass structurally upwards from: (i) blueschist-eclogitic metamorphic rocks (Piaxtla Suite) and mylonitic megacrystic granites (Columpio del Diablo granite ≡ Ordovician granites elsewhere in the complex); (ii) a gently E-dipping, listric, normal shear zone with top to the east kinematic indicators that formed under upper greenschist to lower amphibolite conditions; (iii) the Middle-Late Ordovician Las Minas quartzite (upper greenschist facies psammites with minor interbedded pelites intruded by mafic dikes and a leucogranite dike from the Columpio del Diablo granite) unconformably overlain by the Otate meta-arenite (lower greenschist facies psammites and pelites): roughly temporal equivalents are the Middle-Late Ordovician Mal Paso and Ojo de Agua units (interbedded metasandstone and slate, and metapelite and mafic minor intrusions, respectively) — some of these units are intruded by the massive, 461 ± 2 Ma, Palo Liso megacrystic granite: decussate, contact metamorphic muscovite yielded a 40Ar/ 39Ar plateau age of 440 ± 4 Ma; (iv) a steeply-moderately, E-dipping normal fault; (v) latest Devonian-Middle Permian sedimentary rocks (Patlanoaya Group: here elevated from formation status). The upward decrease in metamorphic grade is paralleled by a decrease in the number of penetrative fabrics, which varies from (i) three in the Piaxtla Suite, through (ii) two in the Las Minas unit (E-trending sheath folds deformed by NE-trending, subhorizontal folds with top to the southeast asymmetry, both associated with a solution cleavage), (iii) one in the Otate, Mal Paso, and Ojo de Agua units (steeply SE-dipping, NE-SW plunging, open-close folds), to (iv) none in the Patlanoaya Group. 40Ar/ 39Ar analyses of muscovite from the earliest cleavage in the Las Minas unit yielded a plateau age of 347 ± 3 Ma and show low temperature ages of ˜ 260 Ma. Post-dating all of these structures and the Patlanoaya Group are NE-plunging, subvertical folds and kink bands. An E-W, vertical normal fault juxtaposes the low-grade rocks against the Anacahuite amphibolite that is cut by megacrystic granite sheets, both of which were deformed by two penetrative fabrics. Amphibole from this unit has yielded a 40Ar/ 39Ar plateau age of 299 ± 6 Ma, which records cooling through ˜ 490 °C and is probably related to a Permo-Carboniferous reheating event during exhumation. The extensional deformation is inferred to have started in the latest Devonian (˜ 360 Ma) during deposition of the basal Patlanoaya Group, lasting through the rapid exhumation of the Piaxtla Suite at ˜ 350-340 Ma synchronous with cleavage development in the Las Minas unit, deposition of the Patlanoaya Group with active fault-related exhumation suggested by Mississippian and Early Permian conglomerates (˜ 340 and 300 Ma, respectively), and continuing at least into the Middle Permian (≡ 260 Ma muscovite ages). The continuity of Mid-Continent Mississippian fauna from the USA to southern Mexico suggests that this extensional deformation occurred on the western margin of Pangea after closure of the Rheic Ocean.

26. Photograph of a photograph in possession of Rock Island ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

26. Photograph of a photograph in possession of Rock Island Arsenal Historical Office. SERIES OF VIEWS BEFORE CONSTRUCTION OF LOCK AND DAM, SHOWING RAIL BED ON UPPER DECK (UPPER LEFT), SWING SPAN IN ROTATION (UPPER RIGHT), EAST ELEVATION OF SWING SPAN AND BALTIMORE TRUSSES (CENTER), VEHICULAR ROADWAY ON LOWER DECK (LOWER LEFT), AND DRAW PIER. ORIGINALLY PUBLISHED 1898. - Rock Island Arsenal, Rock Island Bridge, Fort Armstrong Avenue, Rock Island, Rock Island County, IL

78 FR 16411 - Drawbridge Operation Regulation; Upper Mississippi River, Rock Island, IL

Federal Register 2010, 2011, 2012, 2013, 2014

2013-03-15

... Operation Regulation; Upper Mississippi River, Rock Island, IL AGENCY: Coast Guard, DHS. ACTION: Notice of... operating schedule that governs the Rock Island Railroad and Highway Drawbridge across the Upper Mississippi River, mile 482.9, at Rock Island, Illinois. The deviation is necessary to allow the Quad City Heart...

78 FR 69995 - Drawbridge Operation Regulation; Upper Mississippi River, Rock Island, IL

Federal Register 2010, 2011, 2012, 2013, 2014

2013-11-22

... Operation Regulation; Upper Mississippi River, Rock Island, IL AGENCY: Coast Guard, DHS. ACTION: Notice of... operating schedule that governs the Rock Island Railroad and Highway Drawbridge across the Upper Mississippi River, mile 482.9, at Rock Island, Illinois. The deviation is necessary to allow the bridge owner time...

78 FR 15292 - Drawbridge Operation Regulations; Upper Mississippi River, Rock Island, IL

Federal Register 2010, 2011, 2012, 2013, 2014

2013-03-11

... Operation Regulations; Upper Mississippi River, Rock Island, IL AGENCY: Coast Guard, DHS. ACTION: Notice of... schedule that governs the Rock Island Railroad and Highway Drawbridge, across the Upper Mississippi River, mile 482.9, at Rock Island, Illinois. The deviation is necessary to allow the River Bandits 5K Run/Walk...

78 FR 18933 - Drawbridge Operation Regulations; Upper Mississippi River, Rock Island, IL

Federal Register 2010, 2011, 2012, 2013, 2014

2013-03-28

... Operation Regulations; Upper Mississippi River, Rock Island, IL AGENCY: Coast Guard, DHS. ACTION: Notice of... operating schedule that governs the Rock Island Railroad and Highway Drawbridge across the Upper Mississippi River, mile 482.9, at Rock Island, Illinois. The deviation is necessary to allow the Quad City Marathon...

78 FR 21537 - Drawbridge Operation Regulations; Upper Mississippi River, Rock Island, IL

Federal Register 2010, 2011, 2012, 2013, 2014

2013-04-11

... Operation Regulations; Upper Mississippi River, Rock Island, IL AGENCY: Coast Guard, DHS. ACTION: Notice of... operating schedule that governs the Rock Island Railroad and Highway Drawbridge across the Upper Mississippi River, mile 482.9, at Rock Island, Illinois. The deviation is necessary to allow the Front Street 5K Run...

Total petroleum systems of the Grand Erg/Ahnet Province, Algeria and Morocco; the Tanezzuft-Timimoun, Tanezzuft-Ahnet, Tanezzuft-Sbaa, Tanezzuft Mouydir, Tanezzuft-Benoud, and Tanezzuft-Bechar/Abadla

USGS Publications Warehouse

Klett, T.R.

2000-01-01

Undiscovered, conventional oil and gas resources were assessed within total petroleum systems of the Grand Erg/Ahnet Province (2058) as part of the U.S. Geological Survey World Petroleum Assessment 2000. The majority of the Grand Erg/ Ahnet Province is in western Algeria; a very small portion extends into Morocco. The province includes the Timimoun Basin, Ahnet Basin, Sbaa Basin, Mouydir Basin, Benoud Trough, Bechar/Abadla Basin(s), and part of the Oued Mya Basin. Although several petroleum systems may exist within each of these basins, only seven ?composite? total petroleum systems were identified. Each total petroleum system occurs in a separate basin, and each comprises a single assessment unit. The main source rocks are the Silurian Tanezzuft Formation (or lateral equivalents) and Middle to Upper Devonian mudstone. Maturation history and the major migration pathways from source to reservoir are unique to each basin. The total petroleum systems were named after the oldest major source rock and the basin in which it resides. The estimated means of the undiscovered conventional petroleum volumes in total petroleum systems of the Grand Erg/ Ahnet Province are as follows: [MMBO, million barrels of oil; BCFG, billion cubic feet of gas; MMBNGL, million barrels of natural gas liquids] Total Petroleum System MMBO BCFG MMBNGL Tanezzuft-Timimoun 31 1,128 56 Tanezzuft-Ahnet 34 2,973 149 Tanezzuft-Sbaa 162 645 11 Tanezzuft-Mouydir 12 292 14 Tanezzuft-Benoud 72 2,541 125 Tanezzuft-Bechar/Abadla 16 441 22

Geochemical characteristics and reservoir continuity of Silurian Acacus in Ghadames Basin, Southern Tunisia

NASA Astrophysics Data System (ADS)

Mahmoudi, S.; Mohamed, A. Belhaj; Saidi, M.; Rezgui, F.

2017-11-01

The present work is dealing with the study of lateral and vertical continuity of the multi-layers Acacus reservoir (Ghadames Basin-Southern Tunisia) using the distribution of hydrocarbon fraction. For this purpose, oil-oil and source rock-oil correlations as well as the composition of the light fractions and a number of saturate and aromatic biomarkers parameters, including C35/C34 hopanes and DBT/P, have been investigated. Based on the ratios of light fraction and their fingerprints, the Acacus reservoir from Well1 and Well2 have found to be laterally non-connected although the hydrocarbons they contain have the same source rock. Moreover, the two oil samples from two different Acacus reservoir layers crossed by Well3-A3 and A9, display a similar hydrocarbons distribution, suggesting vertical reservoir continuity. On the other hand, the biomarker distributions of the oils samples and source rocks assess a Silurian ;Hot shale; that is the source rock feeding the Acacus reservoir. The biomarker distribution is characterized by high tricyclic terpanes contents compared to hopanes for the Silurian source rock and the two crude oils. This result is also confirmed by the dendrogram that precludes the Devonian source rocks as a source rock in the study area.

U.S. Geological Survey 2013 assessment of undiscovered resources in the Bakken and Three Forks Formations of the U.S. Williston Basin Province

USGS Publications Warehouse

Gaswirth, Stephanie B.; Marra, Kristen R.

2014-01-01

The Upper Devonian Three Forks and Upper Devonian to Lower Mississippian Bakken Formations comprise a major United States continuous oil resource. Current exploitation of oil is from horizontal drilling and hydraulic fracturing of the Middle Member of the Bakken and upper Three Forks, with ongoing exploration of the lower Three Forks, and the Upper, Lower, and Pronghorn Members of the Bakken Formation. In 2008, the U.S. Geological Survey (USGS) estimated a mean of 3.65 billion bbl of undiscovered, technically recoverable oil resource within the Bakken Formation. The USGS recently reassessed the Bakken Formation, which included an assessment of the underlying Three Forks Formation. The Pronghorn Member of the Bakken Formation, where present, was included as part of the Three Forks assessment due to probable fluid communication between reservoirs. For the Bakken Formation, five continuous and one conventional assessment units (AUs) were defined. These AUs are modified from the 2008 AU boundaries to incorporate expanded geologic and production information. The Three Forks Formation was defined with one continuous and one conventional AU. Within the continuous AUs, optimal regions of hydrocarbon recovery, or “sweet spots,” were delineated and estimated ultimate recoveries were calculated for each continuous AU. Resulting undiscovered, technically recoverable resource estimates were 3.65 billion bbl for the five Bakken continuous oil AUs and 3.73 billion bbl for the Three Forks Continuous Oil AU, generating a total mean resource estimate of 7.38 billion bbl. The two conventional AUs are hypothetical and represent a negligible component of the total estimated resource (8 million barrels of oil).

Tectono-metamorphic evolution of the Chinese Altai, central Asia: new insights from microstructures

NASA Astrophysics Data System (ADS)

Jiang, Yingde; Zhang, Jian; Schulmann, Karel; Sun, Min; Zhao, Guochun

2013-04-01

The Altai Orogen, extending from Russia, through northeast Kazakhstan and northwest China, to western and southern Mongolia, occupies a pivotal position in understanding the accretionary process of the Central Asian Orogenic Belt and has drawn much attention in recent years. However, its orogenic evolution remains poorly constrained, because previous studies were mainly focused on the geochronological and geochemical signatures and much less work has been done on metamorphic and structural studies. Metamorphic rocks widely occur in the southern Altai Range and have previously been separated into high-T/low-P and medium-P types. Recent studies demonstrated that these two kinds of rocks may have similar protoliths, i.e. early Paleozoic arc-related assemblages, but experienced different metamorphic histories. The development of biotite, garnet, staurolite and kyanite metamorphic zonal sequences in the low- to medium- grade rocks, demonstrate typical medium-pressure metamorphism that has been suggested as a major consequence of the orogenesis. The high-T/low-P metamorphism, represented by the growth of garnet+cordierite+sillimanite+k-feldspar and was accompanied by extensive anatexis, remains its tectonic significance poorly constrained. Field structural investigation in the Chinese Altai reveals that the high-T/low-P metamorphic rocks have major S-L fabrics (defined by the strongly aligned biotite and sillimanite) exactly in the same orientations as those developed in the associated medium-P grade rocks. Geochronological studies constrain the major fabrics in both kinds of rocks developed during mid-Devonian, coeval with the strong magmatism in the region. Micro-structural investigation on both kinds of rocks show similar prograde metamorphic history featured by clockwise P-T path evolution. Phase equilibrium modeling in the MnNCKFMASH system indicates that the development of major fabrics in the medium-P metamorphic rocks mainly recorded the notable increase of pressure and that in the high-T rocks was featured by the significant increase of temperature. The pressure increase could attribute to the progressive crustal thickening that may be correlated to the accretionary regime of the southern Altai in the mid-Devonian and the high temperature conditions most likely imply a significant heat input from the deep depth, consistent with the syn-chronologically emplacement of juvenile magmas on a large scale. Our study indicates the development of high-T metamorphism was genetically linked with that of the medium-P metamorphism and suggests that the crustal thickening during the orogenic process of the Altai region was accompanied by large heat input. This study is supported by Hong Kong Research Grant Council (HKU705311P and HKU704712P), National Science Foundation of China (41273048), IGCP #592 Project "Continental construction in Central Asia" and Research grant of State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences (SKLIG-KF-12-06) .

75 FR 81125 - Drawbridge Operation Regulation; Upper Mississippi River, Rock Island, IL

Federal Register 2010, 2011, 2012, 2013, 2014

2010-12-27

... Operation Regulation; Upper Mississippi River, Rock Island, IL AGENCY: Coast Guard, DHS. ACTION: Notice of... the Upper Mississippi River, mile 481.4, at Rock Island, Illinois. The deviation is necessary to allow... Rock Island, Illinois to open on signal if at least 24 hours advance notice is given for 44 days from...

Algeria: structural evolution and hydrocarbon potential of a complicated Tectonic province

DOE Office of Scientific and Technical Information (OSTI.GOV)

Knudsen, H.W.

1985-02-01

During most of the pre-Carboniferous, Algeria was part of a stable foreland platform on which a thick clastic sequence was deposited. Caledonian tectonics were primarily epeirogenic, but they established structural alignments that were further reinforced by the much stronger movements of the Carboniferous Hercynian orogeny. In northern and eastern Algeria, a variable basal sandstone and a thick sequence of Triassic and Lower Jurassic evaporites were deposited over the eroded Hercynian surface. This provided a seal for subsequent hydrocarbon migration from the underlying Silurian and Devonian source rocks. Important epeirogenic events and tensional faulting occurred during the Jurassic and Cretaceous. Compressionalmore » forces in the tertiary culminated in the Alpine orogeny. A broad zone of uplift and southward-directed imbricate thrusting formed along the northern margins of Algeria obscuring much of the sub-Tertiary depositional and structural features. Hydrocarbon accumulation in Algeria has been predominantly controlled by the relationships among the Silurian-Devonian source rocks, the Hercynian unconformity, and the distribution of the overlying Triassic clastic and evaporite sequence. More than 65% of the recoverable oil reserves and 90% of the gas reserves are trapped immediately below or above the Hercynian unconformity, with the evaporites providing the seal. Heretofore, the complex geology of the Tertiary overthrust zone has been a deterrent to exploration in both the autochthonous Miocene basins and the sub-Tertiary sequence. However, improved seismic techniques and renewed interest in the potential of overthrust provinces point to increased activity in this area.« less

Geochemistry and origin of regional dolomites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hanson, G.N.; Meyers, W.J.

1989-12-01

The major goal of the carbonate research program at Stony Brook is to better understand the conditions and processes leading to regional diagenesis of carbonate rocks. Our research focuses on studies of ancient, massive dolostones, but we are also studying limestone diagenesis for its own importance, and as it relates to dolomitization. Our approach has been to carry out a very detailed petrographic and geochemical case study to the Mississippian Burlington-Keokuk Fms. of Iowa, Illinois and Missouri, and to develop this as a testing ground for new geochemical and modelling techniques, and for testing various models for regional dolomitization inmore » epicontinental carbonates. The ideas and techniques developed in our Burlington-Keokuk studies are being expanded and applied to carbonate sequences of other ages (Devonian to Neogene), and other tectono-sedimentary settings. The emphasis of this report will be on new developments and results on the Burlington-Keokuk studies and on our diagenetic studies of other strata. Recent research on Burlington-Keokuk rocks include development and application of boron isotopes and the U--Th--Pb system to dolomite studies, investigations of porosity and permeability in the dolostones. Projects on other strata include dolomitization and limestones diagenesis of Devonian carbonates of Alberta and Western Australia, Miocene reefal carbonates of Spain, Neogene carbonates of Curacao and Bonaire, Waulsortian limestones of Ireland, modelling of trace elements and stable isotopes, and experimental growth of calcites to investigate crystallographic controls of trace element incorporation. 118 refs., 46 figs.« less

Geology and hydrocarbon potential of the Hamada and Murzuq basins in western Libya

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kirmani, K.U.; Elhaj, F.

1988-08-01

The Hamada and Murzuq intracratonic basins of western Libya form a continuation of the Saharan basin which stretches from Algeria eastward into Tunisia and Libya. The tectonics and sedimentology of this region have been greatly influenced by the Caledonian and Hercynian orogenies. Northwest- and northeast-trending faults are characteristic of the broad, shallow basins. The Cambrian-Ordovician sediments are fluvial to shallow marine. The Silurian constitutes a complete sedimentary cycle, ranging from deep marine shales to shallow marine and deltaic sediments. The Devonian occupies a unique position between two major orogenies. The Mesozoic strata are relatively thin. The Triassic consists of well-developedmore » continental sands, whereas the Jurassic and Cretaceous sediments are mainly lagoonal dolomites, evaporites, and shales. Silurian shales are the primary source rock in the area. The quality of the source rock appears to be better in the deeper part of the basin than on its periphery. The Paleozoic has the best hydrocarbon potential. Hydrocarbons have also been encountered in the Triassic and Carboniferous. In the Hamada basin, the best-known field is the El Hamra, with reserves estimated at 155 million bbl from the Devonian. Significant accumulations of oil have been found in the Silurian. Tlacsin and Tigi are two fields with Silurian production. In the Murzuq basin the Cambrian-Ordovician has the best production capability. However, substantial reserves need to be established before developing any field in this basin. Large areas still remain unexplored in western Libya.« less

Sedimentology, CSFe relationships and stable isotopic compositions in Devonian black mudrocks, Mackenzie Mountains, Northwest Territories, Canada

NASA Astrophysics Data System (ADS)

Al-Aasm, I. S.; Morad, S.; Durocher, S.; Muir, I.

1996-11-01

An integrated approach combining CSFe relationships, stable isotopic compositions, and lithofacies characterization was utilized to constrain the palaeoenvironmental and early diagenetic conditions of Middle-Upper Devonian (Eifelian-Frasnian) mudrocks from the Mackenzie Mountains, Northwest Territories, Canada. These rocks include the Hare Indian Formation (informally subdivided into the lower Bluefish Member and the Hare Indian Upper Member), Carcajou Marker and Canol Formation. The Bluefish Member is dominated by black, laminated, organic-rich shales (TOC = 0.35-10.34 wt.%; av. 5.83 wt.) with moderate degrees of pyritization (DOP) of 0.34-0.67 (av. 0.55). These mudrocks were deposited in dysoxic marine bottom-waters that became progressively more oxygenated with time. Variations in TOC, DOP and organic matter δ 13C PDB values (-29.7% to -19.9%; av. -27.2%) are attributed to repeated clastic dilution and increased input of terrestrial organic matter in association with shallowing-upward ramp-clinothem cycles. Pyrite δ 34S CDT values (-32.7% to -18.8%; av. -24.9%) indicate an open system, bacteriogenic seawater-sulphate reduction. Conversely, the overlying Hare Indian Upper Member, characterized by clinothem facies, is composed of grey to green mudstone with minor argillaceous limestones and considerably less organic matter contents (TOC = 0.28-2.99 wt.%; δ 13C = -29.5% to -22.5%). Deposition occurred in oxic to slightly dysoxic waters (DOP = 0.20-0.54; δ 34S = -23.0% to -20.9%), depending on the palaeotopographic location along the depositional slope. A rapid rise in sea level drowned the carbonate 'ramp' member of the Ramparts Formation and produced the thin, organic-rich Carcajou Marker. Bottom-water stagnation that resulted from subdued ramp palaeotopography produced anoxic sea bottom. Black, laminated, organic-rich shales from the Canol Formation (TOC = 1.37-6.68 wt.%) are very similar to those of the Bluefish Member, and are likewise basinal sediments. However, TOC, DOP and organic-matter δ 13C PDB values (-29.1% to -20.8%; av. -26.2%) do not show pronounced variations and indicate that low-energy, quietwater conditions persisted over relatively long, uninterrupted periods of time. High DOP values (0.72-0.93) throughout the Canol Formation suggest that deposition occurred in anoxic bottom-waters, but as basin-fill conditions continued there was a shift to a dysoxic environment (DOP = 0.55-0.65), which grades into nearshore and offshore sequences of the overlying Imperial Formation. In contrast with the Hare Indian Formation, much heavier δ 34S CDT values of pyrite in Canol mudrocks (-11.1% to +5.3%; av. -3.1%) point to bacterial sulphate reduction in a closed to semi-closed system with respect to seawater sulphate.

Faulting at Thebes Gap, Mo. -Ill. : Implications for New Madrid tectonism

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harrison, R.W.; Schultz, A.P.

1992-01-01

Recent geologic mapping in the Thebes Gap area has identified numerous NNE- and NE-striking faults having a long-lived and complex structural history. The faults are located in an area of moderate recent seismicity at the northern margin of the Mississippi embayment, approximately 45 km north of the New Madrid seismic zone. Earliest deformation occurred along dextral strike-slip faults constrained as post-Devonian and pre-Cretaceous. Uplift and erosion of all Carboniferous strata suggest that this faulting is related to development of the Pascola arch (Ouachita orogeny). This early deformation is characterized by strongly faulted and folded Ordovician through Devonian rocks overlain inmore » places with angular unconformity by undeformed Cretaceous strata. Elsewhere, younger deformation involves Paleozoic, Cretaceous, Paleocene, and Eocene formations. These units have experienced both minor high-angle normal faulting and major, dextral strike-slip faulting. Quaternary-Tertiary Mounds Gravel is also involved in the latest episode of strike-slip deformation. Enechelon north-south folds, antithetic R[prime] shears, and drag folds indicate right-lateral motion. Characteristic positive and negative flower structures are commonly revealed in cross section. Right-stepping fault strands have produced pull-apart basins where Ordovician, Silurian, Devonian, Cretaceous, and Tertiary units are downdropped several hundreds of meters and occur in chaotic orientations. Similar fault orientations and kinematics, as well as recent seismicity and close proximity, clearly suggest a structural relationship between deformation at Thebes Gap and tectonism associated with the New Madrid area.« less

The Talas-Fergana Fault, Kirghiz and Kazakh, USSR

USGS Publications Warehouse

Wallace, R.E.

1976-01-01

The great Talas-Fergana fault transects the Soviet republic of Kirghiz in Soviet Central Asia and extends southeastward into China and northwestward into Kazakh SSR (figs. 1 and 2). This great rupture in the Earth's crust rivals the San Andreas fault in California; it is long (approximately 900 kilometers), complex, and possibly has a lateral displacement of hundreds of kilometers similar to that on the San Andreas fault. The Soviet geologist V. S. Burtman suggested that right-lateral offset of 250 kilometers has occurred, citing a shift of Devonian rocks as evidence (fig. 3). By no means do all Soviet geologists agree. Some hold the view that there is no lateral displacement along the Talas-Fergana fault and that the anomalous distribution of Paleozoic rocks is a result of the original position of deposition. 

Carbon and nitrogen isotopic analysis of coral-associated nitrogen in rugose corals of the Middle Devonian, implications for paleoecology and paleoceanography.

NASA Astrophysics Data System (ADS)

Hickey, A. N.; Junium, C. K.; Uveges, B. T.; Ivany, L. C.; Martindale, R. C.

2017-12-01

The Middle Devonian Appalachian Basin of Central New York hosts an extraordinary diversity of well-studied fossil invertebrates within the shallow marine sequences of the Givetian Age, Hamilton Group. Of particular interest are a series of aerially expansive coral beds with diverse assemblages of rugose corals. These well-preserved specimens provide an excellent opportunity to test the feasibility of δ15N and δ13C analyses in rugose corals in an effort to resolve outstanding issues regarding their paleoecology and ontogeny as well environmental dynamics within the Devonian Appalachian Basin. Here we present carbon and nitrogen isotope analyses of the rugose corals Heliophyllum and Siphonophrentis from the Joshua Coral Bed. Corals were cleaned of the host calcareous shale and sonicated sequentially in deionized water and methanol, and then oxidatively cleaned. Cleaned corals were sectioned into 0.5cm billets to obtain enough residual organic material for analysis. The organic content of the corals is low, but nanoEA allows for serial sampling of 5-10 samples per coral. Coral sections were decarbonated and the residual organic material is filtered and dried prior to analysis. Coral organic matter is analyzed in triplicate using nanoEA, which is a cryo-trapping, capillary focusing technique for δ15N and δ13C. The δ15N of organic matter extracted from rugose corals is, on average, enriched by 2-4‰ relative to the bulk nitrogen in the host rock. As well, the δ13C of organic carbon from the corals is 13C-enriched relative to the bulk rock, but to a lesser degree (no more than 1.5‰). Assuming that the bulk rock carbon and nitrogen are largely representative of the long-term primary production background, the modest enrichment is consistent with a trophic effect, and that rugose corals are likely planktivores. In an individual coral, δ15N ranges by 3-4‰ over its length, and when adjusted for trophic enrichment varies around the average δ15N of bulk sedimentary organic matter (+2.0‰). There is no apparent trajectory in the isotopic composition of organic matter, which suggests that over the sampled life history of the corals we cannot resolve any ontogenetic trends. Therefore, the variability in the δ15N of the coral organic matter likely reflects short-term variability in basinal conditions or changes in coral food supply.

Discovery of a Triassic magmatic arc source for the Permo-Triassic Karakaya subduction complex, NW Turkey

NASA Astrophysics Data System (ADS)

Ayda Ustaömer, Petek; Ustaömer, Timur; Gerdes, Axel; Robertson, Alastair H. F.; Zulauf, Gernold

2014-05-01

The Permo-Triassic Karakaya Complex is well explained by northward subduction of Palaeotethys but until now no corresponding magmatic arc has been identified in the region. With the aim of determining the compositions and ages of the source units, ten sandstone samples were collected from the mappably distinct Ortaoba, Hodul, Kendirli and Orhanlar Units. Zircon grains were extracted from these sandstones and >1300 were dated by the U-Pb method and subsequently analysed for the Lu-Hf isotopic compositions by LA-MC-ICPMS at Goethe University, Frankfurt. The U-Pb-Hf isotope systematics are indicative of two different sediment provenances. The first, represented by the Ortaoba, Hodul and Kendirli Units, is dominated by igneous rocks of Triassic (250-220 Ma), Early Carboniferous-Early Permian (290-340 Ma) and Early to Mid-Devonian (385-400 Ma) ages. The second provenance, represented by the Orhanlar Unit, is indicative of derivation from a peri-Gondwanan terrane. In case of the first provenance, the Devonian and Carboniferous source rocks exibit intermediate eHf(t) values (-11 to -3), consistent with the formation at a continental margin where juvenile mantle-derived magmas mixed with (recycled) old crust having Palaeoproterozoic Hf model ages. In contrast, the Triassic arc magma exhibits higher eHf(t) values (-6 to +6), consistent with the mixing of juvenile mantle-derived melts with (recycled) old crust perhaps somewhat rejuvanated during the Cadomian period. We have therefore identified a Triassic magmatic arc as predicted by the interpretation of the Karakaya Complex as an accretionary complex related to northward subduction (Carboniferous and Devonian granites are already well documented in NW Turkey). Possible explanations for the lack of any outcrop of the source magmatic arc are that it was later subducted or the Karakaya Complex was displaced laterally from its source arc (both post 220 Ma). Strike-slip displacement (driven by oblique subduction?) can also explain the presence of two different sandstone source areas as indicated by the combined U-Pb-Hf isotope and supporting petrographic data. This study was supported by TUBITAK, Project no: 111R015

Stratigraphy and lithofacies of Lisburne Group carbonate rocks (Carboniferous - Permian) in the National Petroleum Reserve - Alaska

USGS Publications Warehouse

Dumoulin, Julie A.; Bird, Kenneth J.; Houseknecht, David W.

2001-01-01

Carbonate rocks of the Lisburne Group (Carboniferous-Permian) occur widely throughout northern Alaska. In the NPRA, seismic mapping and well penetrations show that the Lisburne occurs throughout the subsurface except in northernmost NPRA where it is missing by depositional onlap. Lisburne strata encountered in 11 exploratory wells in the northern part of the NPRA are essentially undeformed, consist of limestone and lesser dolostone, sandstone, siltstone, and shale, encompass a wide array of chiefly shallow-water facies, and range in age from Early Mississippian to Permian. Basins and platforms that formed during Mississippian (and possibly Devonian) time greatly affected depositional patterns of the Lisburne. Total thickness of the Lisburne in northern NPRA wells varies from almost 4000 ft in the Ikpikpuk-Umiat Basin to 300 ft on the north edge of the Fish Creek Platform. Lisburne strata of Mississippian age are found in northeastern NPRA, comprise three subunits (lower limestone, middle dolostone, and upper limestone) and are oldest (Osagean) in the Ikpikpuk-Umiat Basin. All wells that penetrated the Lisburne in northern NPRA encountered rocks of Pennsylvanian age; these intervals are mainly limestone and characterized by decameter-scale shallowing-upward sequences. Lisburne sections of prob-able Early-middle Permian age range from thin (≤60 ft) intervals of dolostone and limestone in the Fish Creek Platform area to thick (500-1000 ft) successions of interbedded limestone and siliciclastic sediment in the Ikpikpuk-Umiat Basin and northwestern NPRA. Abundant non-carbonate detritus, primarily quartz and chert with locally notable plagioclase feldspar and metamorphic lithic clasts, occurs throughout the Lisburne Group in northern NPRA. Per-mian strata and a persistent non-carbonate detrital component are also seen in the Lisburne in subsurface beneath the Chukchi Sea (Hanna Trough) to the northwest, but are not found in Lisburne successions elsewhere in Alaska.

Geochemical and multi-isotopic (87Sr/86Sr, 143Nd/144Nd, 238U/235U) perspectives of sediment sources, depositional conditions, and diagenesis of the Marcellus Shale, Appalachian Basin, USA

NASA Astrophysics Data System (ADS)

Phan, Thai T.; Gardiner, James B.; Capo, Rosemary C.; Stewart, Brian W.

2018-02-01

We investigate sediment sources, depositional conditions and diagenetic processes affecting the Middle Devonian Marcellus Shale in the Appalachian Basin, eastern USA, a major target of natural gas exploration. Multiple proxies, including trace metal contents, rare earth elements (REE), the Sm-Nd and Rb-Sr isotope systems, and U isotopes were applied to whole rock digestions and sequentially extracted fractions of the Marcellus shale and adjacent units from two locations in the Appalachian Basin. The narrow range of εNd values (from -7.8 to -6.4 at 390 Ma) is consistent with derivation of the clastic sedimentary component of the Marcellus Shale from a well-mixed source of fluvial and eolian material of the Grenville orogenic belt, and indicate minimal post-depositional alteration of the Sm-Nd system. While silicate minerals host >80% of the REE in the shale, data from sequentially extracted fractions reflect post-depositional modifications at the mineralogical scale, which is not observed in whole rock REE patterns. Limestone units thought to have formed under open ocean (oxic) conditions have δ238U values and REE patterns consistent with modern seawater. The δ238U values in whole rock shale and authigenic phases are greater than those of modern seawater and the upper crust. The δ238U values of reduced phases (the oxidizable fraction consisting of organics and sulfide minerals) are ∼0.6‰ greater than that of modern seawater. Bulk shale and carbonate cement extracted from the shale have similar δ238U values, and are greater than δ238U values of adjacent limestone units. We suggest these trends are due to the accumulation of chemically and, more likely, biologically reduced U from anoxic to euxinic bottom water as well as the influence of diagenetic reactions between pore fluids and surrounding sediment and organic matter during diagenesis and catagenesis.

Determining the source and genetic fingerprint of natural gases using noble gas geochemistry: a northern Appalachian Basin case study

USGS Publications Warehouse

Hunt, Andrew G.; Darrah, Thomas H.; Poreda, Robert J.

2012-01-01

Silurian and Devonian natural gas reservoirs present within New York state represent an example of unconventional gas accumulations within the northern Appalachian Basin. These unconventional energy resources, previously thought to be noneconomically viable, have come into play following advances in drilling (i.e., horizontal drilling) and extraction (i.e., hydraulic fracturing) capabilities. Therefore, efforts to understand these and other domestic and global natural gas reserves have recently increased. The suspicion of fugitive mass migration issues within current Appalachian production fields has catalyzed the need to develop a greater understanding of the genetic grouping (source) and migrational history of natural gases in this area. We introduce new noble gas data in the context of published hydrocarbon carbon (C1,C2+) (13C) data to explore the genesis of thermogenic gases in the Appalachian Basin. This study includes natural gases from two distinct genetic groups: group 1, Upper Devonian (Marcellus shale and Canadaway Group) gases generated in situ, characterized by early mature (13C[C1  C2][13C113C2]: –9), isotopically light methane, with low (4He) (average, 1  103 cc/cc) elevated 4He/40Ar and 21Ne/40Ar (where the asterisk denotes excess radiogenic or nucleogenic production beyond the atmospheric ratio), and a variable, atmospherically (air-saturated–water) derived noble gas component; and group 2, a migratory natural gas that emanated from Lower Ordovician source rocks (i.e., most likely, Middle Ordovician Trenton or Black River group) that is currently hosted primarily in Lower Silurian sands (i.e., Medina or Clinton group) characterized by isotopically heavy, mature methane (13C[C1 – C2] [13C113C2]: 3), with high (4He) (average, 1.85  103 cc/cc) 4He/40Ar and 21Ne/40Ar near crustal production levels and elevated crustal noble gas content (enriched 4He,21Ne, 40Ar). Because the release of each crustal noble gas (i.e., He, Ne, Ar) from mineral grains in the shale matrix is regulated by temperature, natural gases obtain and retain a record of the thermal conditions of the source rock. Therefore, noble gases constitute a valuable technique for distinguishing the genetic source and post-genetic processes of natural gases.

Unroofing history of Late Paleozoic magmatic arcs within the ``Turan Plate'' (Tuarkyr, Turkmenistan)

NASA Astrophysics Data System (ADS)

Garzanti, E.; Gaetani, M.

2002-07-01

Stratigraphic, sedimentologic and petrographic data collected on the Kizilkaya sedimentary succession (Western Turkmenistan) demonstrate that the "Turan Plate" consists in fact of an amalgamation of Late Paleozoic to Triassic continental microblocks separated by ocean sutures. In the Kizilkaya area, an ophiolitic sequence including pyroxenite, gabbro, pillow basalt and chert, interpreted as the oceanic crust of a back-arc or intra-arc basin, is tectonically juxtaposed against volcaniclastic redbeds documenting penecontemporaneous felsic arc magmatism (Amanbulak Group). A collisional event took place around ?mid-Carboniferous times, when oceanic rocks underwent greenschist-facies metamorphism and a thick volcaniclastic wedge, with pyroclastic rocks interbedded in the lower part, accumulated (Kizilkaya Formation). The climax of orogenic activity is testified by arid fanglomerates shed from the rapid unroofing of a continental arc sequence, including Middle-Upper Devonian back-reef carbonates and cherts, and the underlying metamorphic and granitoid basement rocks (Yashmu Formation). After a short period of relative quiescence, renewed tectonic activity is indicated by a conglomeratic sequence documenting erosion of a sedimentary and metasedimentary succession including chert, sandstone, slate and a few carbonates. A final stage of rhyolitic magmatism took place during rapid unroofing of granitoid basement rocks (Kizildag Formation). Such a complex sequence of events recorded by the Kizilkaya episutural basin succession documents the stepwise assemblage of magmatic arcs and continental fragments to form the Turan microblock collage during the Late Paleozoic. Evolution of detrital modes is compatible with that predicted for juvenile to accreted and unroofed crustal blocks. The deposition of braidplain lithic arkoses in earliest Triassic time indicates that strong subsidence continued after the end of the volcanic activity, possibly in retroarc foreland basin settings. The occurrence of transgressive coquinas yielding endemic ammonoids ( Dorikranites) characteristic of the whole Caspian area suggests proximity to the southern margin of the newly formed Eurasian continent in the late Early Triassic. The Late Triassic Eo-Cimmerian Orogeny caused only mild tilting and rejuvenation of the underlying succession in the study area. Only at this time were the Turan blocks, a series of Indonesian-type terranes comprised between the Mashad Paleo-Tethys Suture in the south and the Mangyshlak belt in the north, finally incorporated into the Eurasian landmass.

Hunton Group core workshop and field trip

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johnson, K.S.

The Late Ordovician-Silurian-Devonian Hunton Group is a moderately thick sequence of shallow-marine carbonates deposited on the south edge of the North American craton. This rock unit is a major target for petroleum exploration and reservoir development in the southern Midcontinent. The workshop described here was held to display cores, outcrop samples, and other reservoir-characterization studies of the Hunton Group and equivalent strata throughout the region. A field trip was organized to complement the workshop by allowing examination of excellent outcrops of the Hunton Group of the Arbuckle Mountains.

Bedrock-surface altitude in the midwestern basins and arches region of Indiana, Ohio, Michigan, and Illinois

USGS Publications Warehouse

Bunner, Danny W.

1993-01-01

The Midwestern Basins and Arches Regional Aquifer-Systems Analysis (RASA) is one of 28 projects that were identified by Congress in 1978, after a period of severe drought, to be studied by the U.S. Geological Survey (Sun, 1984).  The Midwestern Basins and Arches RASA study area in parts of Indiana, Ohio, Michigan, and Illinois is defined by either the limestone-shale contact of rocks of Devonian age or by the contact of the land with surface-water bodies (fig. 1).

Composition and genesis of the Konevinsky gold deposit, Eastern Sayan, Russia

NASA Astrophysics Data System (ADS)

Damdinov, B. B.; Zhmodik, S. M.; Roshchektaev, P. A.; Damdinova, L. B.

2016-03-01

The Konevinsky gold deposit in southeast Eastern Sayan is distinguished from most known deposits in this region (Zun-Kholba, etc.) by the geological setting and composition of mineralization. To elucidate the cause of the peculiar mineralization, we have studied the composition, formation conditions, and origin of this deposit, which is related to the Ordovician granitoid pluton 445-441 Ma in age cut by intermediate and basic dikes spatially associated with metavolcanic rocks of the Devonian-Carboniferous Ilei Sequence. Four mineral assemblages are recognized: (1) quartz-pyrite-molybdenite, (2) quartz-gold-pyrite, (3) gold-polysulfide, and (4) telluride. Certain indications show that the ore was formed as a result of the superposition of two distinct mineral assemblages differing in age. The first stage dated at ~440 Ma is related to intrusions generating Cu-Mo-Au porphyry mineralization and gold-polysulfide veins. The second stage is controlled by dikes pertaining to the Devonian-Carboniferous volcanic-plutonic association. The second stage is characterized by gain of Hg and Te and formation of gold-mercury-telluride paragenesis.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Barron, L.S.; Ettensohn, F.R.

The Devonian-Mississippian black-shale sequence is one of the most prominent and well-known stratigraphic horizons in the Paleozoic of the United States, yet the paleontology and its paleoecologic and paleoenvironmental implications are poorly known. This is in larger part related to the scarcity of fossils preserved in the shale - in terms of both diversity and abundance. Nonetheless, that biota which is preserved is well-known and much described, but there is little synthesis of this data. The first step in such a synthesis is the compilation of an inclusive bibliography such as this one. This bibliography contains 1193 entries covering allmore » the major works dealing with Devonian-Mississippian black-shale paleontology and paleoecology in North America. Articles dealing with areas of peripheral interest, such as paleogeography, paleoclimatology, ocean circulation and chemistry, and modern analogues, are also cited. In the index, the various genera, taxonomic groups, and other general topics are cross-referenced to the cited articles. It is hoped that this compilation will aid in the synthesis of paleontologic and paleoecologic data toward a better understanding of these unique rocks and their role as a source of energy.« less

Timing of terrane accretion in eastern and east-central Maine

NASA Astrophysics Data System (ADS)

Ludman, Allan

1986-05-01

The Norumbega fault zone is often cited as a post-Acadian suture between exotic blocks, even though stratigraphic, structural, and metamorphic data indicate that there is little offset of the Silurian-Devonian strata that the zone cuts in eastern Maine. Similarly, the Kingman fault zone has been shown by gravity and geochemical studies to separate distinct crustal blocks, whereas mapping shows that it lies entirely within a Silurian turbidite package. These conflicts are resolved if the two fault zones represent boundaries between Ordovician or older crustal blocks that had accreted to form a composite terrane prior to deposition of the cover sequences. The faults now mapped within these younger rocks formed by reactivation of the pre-Silurian boundaries during late Acadian time; movement continued until the late Carboniferous. Most of the accretionary history of Maine had thus ended before the Silurian. A complex composite terrane may have formed during Cambrian-Ordovician time that (1) interacted with cratonic North America during the Taconian orogeny and (2) became the “basement” upon which the Silurian and Lower Devonian strata of eastern Maine were deposited.

Recognition and delineation of Paleokarst zones by the use of wireline logs in the bitumen-saturated upper Devonian Grosmont formation of Northeastern Alberta, Canada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dembicki, E.A.; Machel, H.G.

1996-05-01

The Upper Devonian Grosmont Formation in northeastern Alberta, Canada, is a shallow-marine carbonate platform complex that was subaerially exposed for hundreds of millions of years between the Mississippian(?) and Cretaceous. During this lengthy exposure period, an extensive karst system developed that is characterized by an irregular erosional surface, meter-size (several feet) dissolution cavities, collapse breccias, sinkholes, paleosols, and fractures. The karsted Grosmont Formation, which contains giant reserves of bitumen, sub-crops beneath Cretaceous clastic sediments of the giant Athabasca tar sands deposit. The paleokarst in the Grosmont Formation can be recognized on wireline logs in relatively nonargillaceous carbonate intervals (<30 APImore » units on the gamma-ray log) as excursions of the caliper log, off-scale neutron-density porosity readings, and severe cycle skipping of the acoustic log. The paleokarst is more prevalent in the upper units of the Grosmont Formation, and the effects of karstification decrease toward stratigraphically older and deeper units. The paleokarst usually occurs within 35 m (115 ft) of the erosional surface. The reservoir properties of the Grosmont Formation (e.g., thickness, porosity, permeability, and seal effectiveness) are significantly influenced by karstification. Depending upon the location, karstification has either benefited or degraded the reservoir characteristics. Benefits include porosity values greater than 40% (up to 100% in caverns) and permeability values of 30,000 md in severely fractured intervals. Detrimental reservoir characteristics include erosion, porosity and permeability reduction, and seal ineffectiveness.« less

187Re - 187Os nuclear geochronometry: age dating with permil precision

NASA Astrophysics Data System (ADS)

Roller, Goetz

2016-04-01

Recently, 187Re - 187Os nuclear geochronometry, a new dating method combining ideas of nuclear astrophysics with geochronology, has successfully been used to calculate two-point-isochron (TPI) ages for Devonian black gas shales using the isotopic signature of an r-process geochronometer as one data point in a TPI diagram [1]. Based upon a nuclear production ratio 187Re/188Os = 5.873, TPI ages were calculated for 12 SDO-1 (Devonian Ohio Shale, Appalachian Basin) aliquants, for which repeated Re-Os measurements are reported in the literature [2]. TPI ages range from 384.5 ± 2.7 Ma (187Os/188Osi = 0.29413 ± 0.00023) to 387.7 ± 2.1 Ma (187Os/188Osi = 0.29407 ± 0.00019) with a mean of 386.67 ± 1.79 Ma). The result is consistent with the isochronous age from the 12 aliquants alone (386 ± 16 Ma, 187Os/188Osi = 0.31±0.31), which is bracketed by U-Pb ages for the Belpre Ash (381.1 ± 3.3 Ma) and the Tioga Ash bed (390.0 ± 2.5 Ma) [3] from the Appalachian Basin. Hence, SDO-1 can be assigned to the Givetian stage (varcus-zone) of the Middle Devonian, close to the Eifelian/Givetian boundary (using the time-scale of [3] or [4]). If an age is calculated from an isochron diagram for the 12 aliquants including the nuclear geochronometer, a permil precision can be achieved, an interesting feature with respect to any effort towards calibrating the Geologic Timescale. Additionally, a Th/U evolution (or: Th/U-time) diagram can be plotted using U-Pb zircon age data and Th/U ratios from volcanic rocks and ashes reported in the literature [3] for specific Devonian samples from the Appalachian Basin. Since the Re-Os age obtained for SDO-1 can also be connected to its Th/U ratio, it turns out, that Th/U ratios might be helpful age indicators, as demonstrated for the Devonian using the U-Pb and Re-Os datasets. [1] Roller (2015), GSA Abstr. with Programs 47, #248-14. [2] Du Vivier et al. (2014), Earth Planet. Sci. Lett. 389, 23 - 33. [3] Tucker et al. (1998), Earth Planet. Sci. Lett. 158, 175 - 186. [4] Kaufmann (2006), Earth-Sci. Revs. 76, 175 - 190.

Devonian granitoids and their hosted mafic enclaves in the Gorny Altai terrane, northwestern Central Asian Orogenic Belt: crust-mantle interaction in a continental arc setting

NASA Astrophysics Data System (ADS)

Chen, Ming; Sun, Min

2016-04-01

Granitoids are a major component in the upper continental crust and hold key information on how did the continental crust grow and differentiate. This study focuses on the Yaloman intrusive complex from the Gorny Altai terrane, northwestern Central Asian Orogenic Belt (CAOB). The association of granitoids and mafic enclaves can provide important clues on the source nature, petrogenetic processes and geodynamic setting of the Yaloman intrusive complex, which in turn will shed light on the crustal evolution in the northwestern CAOB. Zircon U-Pb dating shows that the granitoids, including quartz diorites and granodiorites, were emplaced in ca. 389-387 Ma. The moderate Na2O + K2O contents and low A/CNK values indicate that these rocks belong to the sub-alkaline series with metaluminous to weakly peraluminous compositions. The granitoids yield two-stage zircon Hf model ages of ca. 0.79-1.07 Ga and whole-rock Nd model ages of ca. 0.90-0.99 Ga, respectively, implying that they were mainly sourced from Neoproterozoic juvenile crustal materials. The mafic enclaves show an almost identical crystallization age of ca. 389 Ma. The identification of coarse-grained xenocrysts and acicular apatites, together with the fine-grained texture, makes us infer that these enclaves are likely to represent magmatic globules commingled with the host magmas. The low SiO2 and high MgO contents of the mafic enclaves further suggest that substantial mantle-derived mafic melts were probably involved in their formation. Importantly, the SiO2 contents of the granitoids and mafic enclaves are well correlated with other major elements and most of the trace elements. Also a broadly negative correlation exists between the SiO2 contents and whole-rock epsilon Nd (390 Ma) values of the granitoids. Given the observation of reversely zoned plagioclases within the granitoids and the common occurrence of igneous mafic enclaves, we propose that magma mixing probably played an important role in the formation of the Yaloman intrusive complex. Our data imply that mantle-derived melts not only provided heat to melt the pre-existing Neoproterozoic crustal materials but also served as an important component in controlling the geochemical diversity of the granitoids. The mineral assemblages and compositions suggest that the Yaloman intrusive complex was possibly crystallized from a relatively oxidizing and water-enriched magma chamber, indicative of a continental-arc related tectonic setting in stead of a collisional origin as previously proposed. Collectively, our study suggests that the widespread Devonian granitoids within the Gorny Altai terrane signify significant vertical crustal growth and differentiation via underplating of subduction-related mafic melts. Acknowledgement This study is financially supported by the Major Research Project of the Ministry of Science and Technology of China (2014CB44801 and 2014CB448000), Hong Kong Research Grant Council (HKU705311P and HKU704712P) and National Science Foundation of China (41273048).

Stratigraphy and facies development of the marine Late Devonian near the Boulongour Reservoir, northwest Xinjiang, China

NASA Astrophysics Data System (ADS)

Suttner, Thomas J.; Kido, Erika; Chen, Xiuqin; Mawson, Ruth; Waters, Johnny A.; Frýda, Jiří; Mathieson, David; Molloy, Peter D.; Pickett, John; Webster, Gary D.; Frýdová, Barbora

2014-02-01

Late Devonian to Early Carboniferous stratigraphic units within the 'Zhulumute' Formation, Hongguleleng Formation (stratotype), 'Hebukehe' Formation and the Heishantou Formation near the Boulongour Reservoir in northwestern Xinjiang are fossil-rich. The Hongguleleng and 'Hebukehe' formations are biostratigraphically well constrained by microfossils from the latest Frasnian linguiformis to mid-Famennian trachytera conodont biozones. The Hongguleleng Formation (96.8 m) is characterized by bioclastic argillaceous limestones and marls (the dominant facies) intercalated with green spiculitic calcareous shales. It yields abundant and highly diverse faunas of bryozoans, brachiopods and crinoids with subordinate solitary rugose corals, ostracods, trilobites, conodonts and other fish teeth. The succeeding 'Hebukehe' Formation (95.7 m) consists of siltstones, mudstones, arenites and intervals of bioclastic limestone (e.g. 'Blastoid Hill') and cherts with radiolarians. A diverse ichnofauna, phacopid trilobites, echinoderms (crinoids and blastoids) together with brachiopods, ostracods, bryozoans and rare cephalopods have been collected from this interval. Analysis of geochemical data, microfacies and especially the distribution of marine organisms, which are not described in detail here, but used for facies analysis, indicate a deepening of the depositional environment at the Boulongour Reservoir section. Results presented here concern mainly the sedimentological and stratigraphical context of the investigated section. Additionally, one Late Devonian palaeo-oceanic and biotic event, the Upper Kellwasser Event is recognized near the section base.

Geochemical and strontium isotope characterization of produced waters from Marcellus Shale natural gas extraction.

PubMed

Chapman, Elizabeth C; Capo, Rosemary C; Stewart, Brian W; Kirby, Carl S; Hammack, Richard W; Schroeder, Karl T; Edenborn, Harry M

2012-03-20

Extraction of natural gas by hydraulic fracturing of the Middle Devonian Marcellus Shale, a major gas-bearing unit in the Appalachian Basin, results in significant quantities of produced water containing high total dissolved solids (TDS). We carried out a strontium (Sr) isotope investigation to determine the utility of Sr isotopes in identifying and quantifying the interaction of Marcellus Formation produced waters with other waters in the Appalachian Basin in the event of an accidental release, and to provide information about the source of the dissolved solids. Strontium isotopic ratios of Marcellus produced waters collected over a geographic range of ~375 km from southwestern to northeastern Pennsylvania define a relatively narrow set of values (ε(Sr)(SW) = +13.8 to +41.6, where ε(Sr) (SW) is the deviation of the (87)Sr/(86)Sr ratio from that of seawater in parts per 10(4)); this isotopic range falls above that of Middle Devonian seawater, and is distinct from most western Pennsylvania acid mine drainage and Upper Devonian Venango Group oil and gas brines. The uniformity of the isotope ratios suggests a basin-wide source of dissolved solids with a component that is more radiogenic than seawater. Mixing models indicate that Sr isotope ratios can be used to sensitively differentiate between Marcellus Formation produced water and other potential sources of TDS into ground or surface waters.

Discriminating signal from noise in the fossil record of early vertebrates reveals cryptic evolutionary history

PubMed Central

Sansom, Robert S.; Randle, Emma; Donoghue, Philip C. J.

2015-01-01

The fossil record of early vertebrates has been influential in elucidating the evolutionary assembly of the gnathostome bodyplan. Understanding of the timing and tempo of vertebrate innovations remains, however, mired in a literal reading of the fossil record. Early jawless vertebrates (ostracoderms) exhibit restriction to shallow-water environments. The distribution of their stratigraphic occurrences therefore reflects not only flux in diversity, but also secular variation in facies representation of the rock record. Using stratigraphic, phylogenetic and palaeoenvironmental data, we assessed the veracity of the fossil records of the jawless relatives of jawed vertebrates (Osteostraci, Galeaspida, Thelodonti, Heterostraci). Non-random models of fossil recovery potential using Palaeozoic sea-level changes were used to calculate confidence intervals of clade origins. These intervals extend the timescale for possible origins into the Upper Ordovician; these estimates ameliorate the long ghost lineages inferred for Osteostraci, Galeaspida and Heterostraci, given their known stratigraphic occurrences and stem–gnathostome phylogeny. Diversity changes through the Silurian and Devonian were found to lie within the expected limits predicted from estimates of fossil record quality indicating that it is geological, rather than biological factors, that are responsible for shifts in diversity. Environmental restriction also appears to belie ostracoderm extinction and demise rather than competition with jawed vertebrates. PMID:25520359

Devonian climate and reef evolution: Insights from oxygen isotopes in apatite

NASA Astrophysics Data System (ADS)

Joachimski, M. M.; Breisig, S.; Buggisch, W.; Talent, J. A.; Mawson, R.; Gereke, M.; Morrow, J. R.; Day, J.; Weddige, K.

2009-07-01

Conodonts, microfossils composed of carbonate-fluor apatite, are abundant in Palaeozoic-Triassic sediments and have a high potential to preserve primary oxygen isotope signals. In order to reconstruct the palaeotemperature history of the Devonian, the oxygen isotope composition of apatite phosphate was measured on 639 conodont samples from sequences in Europe, North America and Australia. The Early Devonian (Lochkovian; 416-411 Myr) was characterized by warm tropical temperatures of around 30 °C. A cooling trend started in the Pragian (410 Myr) with intermediate temperatures around 23 to 25 °C reconstructed for the Middle Devonian (397-385 Myr). During the Frasnian (383-375 Myr), temperatures increased again with temperatures to 30 °C calculated for the Frasnian-Famennian transition (375 Myr). During the Famennian (375-359 Myr), surface water temperatures slightly decreased. Reconstructed Devonian palaeotemperatures do not support earlier views suggesting the Middle Devonian was a supergreenhouse interval, an interpretation based partly on the development of extensive tropical coral-stromatoporoid communities during the Middle Devonian. Instead, the Devonian palaeotemperature record suggests that Middle Devonian coral-stromatoporoid reefs flourished during cooler time intervals whereas microbial reefs dominated during the warm to very warm Early and Late Devonian.

Geologic map of the Vail East quadrangle, Eagle County, Colorado

USGS Publications Warehouse

Kellogg, Karl S.; Bryant, Bruce; Redsteer, Margaret H.

2003-01-01

New 1:24,000-scale geologic mapping along the Interstate-70 urban corridor in western Colorado, in support of the State/USGS Cooperative Geologic Mapping Project, is contributing to a more complete understanding of the stratigraphy, structure, tectonic evolution, and hazard potential of this rapidly developing region. The 1:24,000-scale Vail East quadrangle straddles the Gore fault system, the western structural boundary of the Gore Range. The Gore fault system is a contractional structure that has been recurrently active since at least the early Paleozoic and marks the approximate eastern boundary of the Central Colorado trough, a thick late Paleozoic depocenter into which thousands of meters of clastic sediment were deposited from several uplifts, including the ancestral Front Range. The Gore fault was active during both the late Paleozoic and Upper Cretaceous-lower Tertiary (Laramide) deformations. In addition, numerous north-northwest faults that cut the crystalline rocks of the Gore Range were active during at least 5 periods, the last of which was related to Neogene uplift of the Gore Range and formation of the northern Rio Grande rift. Early Proterozoic crystalline rocks underlie the high Gore Range, north and east of the Gore fault system. These rocks consist predominantly of migmatitic biotite gneiss intruded by mostly granitic rocks of the 1.667-1.750 Ma Cross Creek batholith, part of the 1,667-1,750 Ma Routt Plutonic Suite (Tweto, 1987). Southwest of the Gore fault, a mostly gently south-dipping sequence of Pennsylvanian Mimturn Formation, as thick as 1,900 m, and the Permian and Pennsylvanian Maroon Formation (only the basal several hundred meters are exposed in the quadrangle)were shed from the ancestral Front Range and overlie a thin sequence of Devonian and Cambrian rocks. The Minturn Formation is a sequence of interlayered pink, maroon, and gray conglomerate, sandstone, shale, and marine limestone. The Maroon Formation is mostly reddish conglomerate and sandstone. Glacial till of both the middle Pleistocene Bull Lake and late Pleistocene Pinedale glaciations are well exposed along parts of the Gore Creek valley and its tributaries, although human development has profoundly altered the outcrop patterns along the Gore Creek valley bottom. Landslides, some of which are currently active, are also mapped.

Petrogenesis of the postcollisional Middle Devonian monzonitic to granitic magmatism of the Sierra de San Luis, Argentina

NASA Astrophysics Data System (ADS)

López de Luchi, Mónica G.; Siegesmund, Siegfried; Wemmer, Klaus; Nolte, Nicole

2017-09-01

Middle Devonian granitoids intruded the Eastern Sierras Pampeanas basement ca. 600 km east of the inferred proto-Pacific margin of Gondwana along which a ca. 390 Ma collisional event developed. In the Sierra de San Luis, voluminous Middle Devonian (393-382 Ma) batholiths are composed of I- to A-type hybrid Monzonite and Granite suites. Shoshonite and subordinated high-K series, stocks, synplutonic dikes and enclaves make up the Monzonite Suite; rocks are metaluminous alkali-calcic magnesian porphyritic or equigranular monzonite, quartz monzonite, monzodiorite and scarce monzogabbro. High-K and subordinated shoshonite series metaluminous to mildly peraluminous magnesian alkali-calcic to calc-alkalic porphyritic or equigranular quartz monzonite, granodiorite, monzogranite and equigranular leucomonzogranites make up the Granite Suite plutons and batholiths. Only a small group of highly evolved granites are ferroan. SiO2 (46-62%), Cr, Ni, V, Sc, LILE, LREE, Th, Zr and variable, Sr/Y, (La/Yb)N and (Tb/Yb)N, smooth Eu/Eu*, moderate Na2O (ca 3.5), and troughs at Nb and Ta for Monzonite Suite rocks suggest an subduction-related enriched lithospheric mantle source. Sm-Nd data (TDM 0.98-1.08 Ga, εNd(380 Ma) 0.66-1.47) and 87Sr/86Sri (0.703520-0.704203) are compatible with an enriched mantle source. The metaluminous porphyritic quartz monzonite-monzogranite and the mildly peraluminous equigranular biotite monzogranites of the Granite Suite are characterized by relatively moderate Al2O3, CaO, and 87Sr/86Sri, high LILE, Cr, variable Sr/Y, (La/Yb)N and Eu/Eu* and low Rb/Sr (< 1.2) suggest a mafic source. The porphyritic monzogranite (TDM 1.20-1.28 Ga, εNd(380Ma) - 3.02 to - 3.3, 87Sr/86Sri 0.706578-0.707027) and the biotite monzogranites (TDM 1.31 Ga, εNd(380Ma) - 3.3, 87Sr/86Sri 0.707782) would share a common source. The equigranular alkali-calcic leucomonzogranites are characterized by Rb/Sr > 1.5, ASI 1.05-1.18, and Ga/Al 2.6-3.9, εNd(380 Ma) - 3.74 to - 3.95 and (87Sr/86Sr)i 0.710743-0.712955 which would point to metasedimentary or felsic igneous crustal sources. Nevertheless their TDM 1.36-1.38 Ga is considerably younger than the mean 1.8-1.6 Ga Eastern Sierras Pampeanas crustal residence age and less radiogenic. Middle Devonian magmatism would record an episode of crustal growth by enriched mantle derived magma input and variable degrees of partial melting of a lower crustal source at the waning stages of the Achalian orogeny.

Association of deformation and fluid events in the central Brooks Range fold-and-thrust belt, Northern Alaska

USGS Publications Warehouse

Moore, Thomas E.; Potter, Christopher J.; O'Sullivan, Paul B.; Shelton, Kevin L.; Underwood, Michael B.

2003-01-01

Ocentral Brooks Range consists of two superposed north-directed contractional orogens, one formed between 140-120 Ma and the other at ~60-45 Ma. The older orogen was an arc-continent collisional zone characterized by far-traveled allochthons and relatively low structural relief. The younger orogen is a retroarc thrust belt with relatively low amounts of shortening and high structural relief. Folding and thrusting of the younger episode is superimposed on the thin-skinned deformational wedge of the earlier orogen and also produced a frontal triangle zone in a thick sequence of mid-Cretaceous foreland basin sediments to the north. Stable isotope compositions of calcite and quartz veins indicate two fluid events including: (1) an earlier, higher-temperature (~250-300° C) event that produced veins in deformed Devonian clastic rocks, and (2) a younger, lower-temperature (~150° C) event that deposited veins in deformed Mississippian through Albian strata. The fluids in the first event had variable d18O values, but nearly constant d13C values buffered by limestone lithologies. The vein-forming fluids in the second event had similarly variable d18O values, but with distinctly lower d13C values as a result of oxidation of organic matter and/or methane. Zircon fission track ages demonstrate cooling to temperatures below 200° C between 140-120 Ma for the Devonian rocks, whereas zircon and apatite fission track ages show that Mississippian to Albian rocks were never heated above 200° C and cooled below 110-90° C at ~60-45 Ma. These data are interpreted as indicating that the older, high-temperature fluid event was active during thrusting at 120-140 Ma, and the younger fluid event during deformation at ~60-45 Ma. The data and results presented in this poster will be published in early 2004 in Moore and others (in press).

Characteristics of the Late Devonian Tsagaan Suvarga Cu-Mo deposit, Southern Mongolia

NASA Astrophysics Data System (ADS)

Tungalag, Naidansuren; Jargalan, Sereenen; Khashgerel, Bat-Erdene; Mijiddorj, Chuluunbaatar; Kavalieris, Imants

2018-05-01

The Late Devonian Tsagaan Suvarga deposit (255 Mt at 0.55% Cu, 0.02% Mo) is located on the NW margin of the Tsagaan Suvarga Complex (TSC), which extends ENE over 15 × 10 km and comprises mainly medium-grained equigranular hornblende-biotite quartz monzonite and monzodiorite. Distinct mineralized intrusions are inferred from distribution of Cu-Mo mineralization but are not clearly discernible. The Tsagaan Suvarga Complex is a window within Carboniferous volcanic and sedimentary rocks, and wall rocks to the TSC are not known or exposed in the nearby district. Whole-rock analyses and Sr-Nd isotopes, 87Sr/86Sr0 = 0.7027 to 0.7038 (n = 12) and ɛNd0 = + 4.26 to + 2.77 (n = 12), show that the granitoids are subduction-related I-type, high K-calc-alkaline to shoshonitic series and derived from a mantle source. They exhibit fractionated light rare earth elements, without depleted Eu and depleted middle heavy rare earth elements and Y, typical of oxidized, fertile porphyry magmatic suites. Early porphyry-style quartz veins include A- and B-type. Molybdenite occurs in monomineralic veins (1-5 mm) or A veins. Copper mineralization occurs mainly as chalcopyrite and subordinate bornite, disseminated and associated with quartz-muscovite veins. Pyrite (vol%) content is less than chalcopyrite and bornite combined. Deep oxidation to about 50 m depth has formed zones of malachite and covellite in late fractures. The most important alteration is actinolite-biotite-chlorite-magnetite replacing hornblende and primary biotite. Quartz-K-feldspar alteration is minor. Late albite replaces primary K-feldspar and enhances sodic rims on plagioclase crystals. Quartz-muscovite (or sericitic alteration) overprints actinolite-biotite and porphyry-type quartz veins. Field observations and petrographic studies suggest that the bulk of the chalcopyrite-bornite mineralization at the Tsagaan Suvarga formed together with coarse muscovite alteration.

Seven 365-Million-Year-Old Trilobites Moulting within a Nautiloid Conch

NASA Astrophysics Data System (ADS)

Zong, Rui-Wen; Fan, Ruo-Ying; Gong, Yi-Ming

2016-10-01

A nautiloid conch containing many disarticulated exoskeletons of Omegops cornelius (Phacopidae, Trilobita) was found in the Upper Devonian Hongguleleng Formation of the northwestern margin of the Junggar Basin, NW China. The similar number of cephala, thoraces and pygidia, unbroken thoraces, explicit exuviae, and lack of other macrofossils in the conch, indicate that at least seven individual trilobites had moulted within the nautiloid living chamber, using the vacant chamber of a dead nautiloid as a communal place for ecdysis. This exuvial strategy manifests cryptic behaviour of trilobites, which may have resulted from the adaptive evolution induced by powerful predation pressure, unstable marine environments, and competition pressure of organisms occupying the same ecological niche in the Devonian period. The unusual presence of several trilobites moulting within a nautiloid conch is possibly associated with social behaviours in face of a serious crisis. New materials in this study open a window for understanding the survival strategy of marine benthic organisms, especially predator-prey interactions and the behavioural ecology of trilobites in the middle Palaeozoic.

Preliminary report on the clay mineralogy of the Upper Devonian Shales in the southern and middle Appalachian Basin

USGS Publications Warehouse

Hosterman, John W.; Loferski, Patricia J.

1978-01-01

The distribution of kaolinite in parts of the Devonian shale section is the most significant finding of this work. These shales are composed predominately of 2M illite and illitic mixed-layer clay with minor amounts of chlorite and kaolinite. Preliminary data indicate that kaolinite, the only allogenic clay mineral, is present in successively older beds of the Ohio Shale from south to north in the southern and middle parts of the Appalachian basin. This trend in the distribution of kaolinite shows a paleocurrent direction to the southwest. Three well-known methods of preparing the clay fraction for X-ray diffraction analysis were tested and evaluated. Kaolinite was not identified in two of the methods because of layering due to differing settling rates of the clay minerals. It is suggested that if one of the two settling methods of sample preparation is used, the clay film be thin enough for the X-ray beam to penetrate the entire thickness of clay.

Silurian extension in the Upper Connecticut Valley, United States and the origin of middle Paleozoic basins in the Québec embayment

USGS Publications Warehouse

Rankin, D.W.; Coish, R.A.; Tucker, R.D.; Peng, Z.X.; Wilson, S.A.; Rouff, A.A.

2007-01-01

Pre-Silurian strata of the Bronson Hill arch (BHA) in the Upper Connecticut Valley, NH-VT are host to the latest Ludlow Comerford Intrusive Suite consisting, east to west, of a mafic dike swarm with sheeted dikes, and an intrusive complex. The rocks are mostly mafic but with compositions ranging from gabbro to leucocratic tonalite. The suite is truncated on the west by the Monroe fault, a late Acadian thrust that carries rocks of the BHA westward over Silurian-Devonian strata of the Connecticut Valley-Gaspe?? trough (CVGT). Dikes intrude folded strata with a pre-intrusion metamorphic fabric (Taconian?) but they experienced Acadian deformation. Twenty fractions of zircon and baddeleyite from three sample sites of gabbrodiorite spanning nearly 40 km yield a weighted 207Pb/206Pb age of 419 ?? 1 Ma. Greenschist-facies dikes, sampled over a strike distance of 35 km, were tholeiitic basalts formed by partial melting of asthenospheric mantle, with little or no influence from mantle or crustal lithosphere. The dike chemistry is similar to mid-ocean ridge, within-plate, and back-arc basin basalts. Parent magmas originated in the asthenosphere and were erupted through severely thinned lithosphere adjacent to the CVGT. Extensive middle Paleozoic basins in the internides of the Appalachian orogen are restricted to the Que??bec embayment of the Laurentian rifted margin, and include the CVGT and the Central Maine trough (CMT), separated from the BHA by a Silurian tectonic hinge. The NE-trending Comerford intrusions parallel the CVGT, CMT, and the tectonic hinge, and indicate NW-SE extension. During post-Taconian convergence, the irregular margins of composite Laurentia and Avalon permitted continued collision in Newfoundland (St. Lawrence promontory) and coeval extension in the Que??bec embayment. Extension may be related to hinge retreat of the northwest directed Brunswick subduction complex and rise of the asthenosphere following slab break-off. An alternative hypothesis is that the basins originated as pull-apart basins between northwest-trending, left-stepping, sinistral strike-slip faults along the southern flanks of the New York and St. Lawrence promontories.

Geological Structure and History of the Arctic Ocean

NASA Astrophysics Data System (ADS)

Petrov, Oleg; Morozov, Andrey; Shokalsky, Sergey; Sobolev, Nikolay; Kashubin, Sergey; Pospelov, Igor; Tolmacheva, Tatiana; Petrov, Eugeny

2016-04-01

New data on geological structure of the deep-water part of the Arctic Basin have been integrated in the joint project of Arctic states - the Atlas of maps of the Circumpolar Arctic. Geological (CGS, 2009) and potential field (NGS, 2009) maps were published as part of the Atlas; tectonic (Russia) and mineral resources (Norway) maps are being completed. The Arctic basement map is one of supplements to the tectonic map. It shows the Eurasian basin with oceanic crust and submerged margins of adjacent continents: the Barents-Kara, Amerasian ("Amerasian basin") and the Canada-Greenland. These margins are characterized by strained and thinned crust with the upper crust layer, almost extinct in places (South Barents and Makarov basins). In the Central Arctic elevations, seismic studies and investigation of seabed rock samples resulted in the identification of a craton with the Early Precambrian crust (near-polar part of the Lomonosov Ridge - Alpha-Mendeleev Rise). Its basement presumably consists of gneiss granite (2.6-2.2 Ga), and the cover is composed of Proterozoic quartzite sandstone and dolomite overlain with unconformity and break in sedimentation by Devonian-Triassic limestone with fauna and terrigenous rocks. The old crust is surrounded by accretion belts of Timanides and Grenvillides. Folded belts with the Late Precambrian crust are reworked by Caledonian-Ellesmerian and the Late Mesozoic movements. Structures of the South Anuy - Angayucham ophiolite suture reworked in the Early Cretaceous are separated from Mesozoides proper of the Pacific - Verkhoyansk-Kolyma and Koryak-Kamchatka belts. The complicated modern ensemble of structures of the basement and the continental frame of the Arctic Ocean was formed as a result of the conjugate evolution and interaction of the three major oceans of the Earth: Paleoasian, Paleoatlantic and Paleopacific.

Petroleum geology and resources of the Nepa-Botuoba High, Angara-Lena Terrace, and Cis-Patom Foredeep, southeastern Siberian Craton, Russia

USGS Publications Warehouse

Ulmishek, Gregory F.

2001-01-01

Three structural provinces of this report, the Nepa-Botuoba High, the Angara-Lena Terrace, and the Cis-Patom Foredeep, occupy the southeastern part of the Siberian craton northwest of the Baikal-Patom folded region (fig. 1). The provinces are similar in many aspects of their history of development, stratigraphic composition, and petroleum geology characteristics. The sedimentary cover of the provinces overlies the Archean?Lower Proterozoic basement of the Siberian craton. Over most of the area of the provinces, the basement is covered by Vendian (uppermost Proterozoic, 650?570 Ma) clastic and carbonate rocks. Unlike the case in the more northwestern areas of the craton, older Riphean sedimentary rocks here are largely absent and they appear in the stratigraphic sequence only in parts of the Cis-Patom Foredeep province. Most of the overlying sedimentary section consists of Cambrian and Ordovician carbonate and clastic rocks, and it includes a thick Lower Cambrian salt-bearing formation. Younger rocks are thin and are present only in marginal areas. 1 A single total petroleum system (TPS) embraces all three provinces. The TPS is unique in two aspects: (1) its rich hydro-carbon reserves are derived from Precambrian source rocks and (2) preservation of oil and gas fields is extremely long owing to the presence of the Lower Cambrian undeformed salt seal. Discovered reserves of the TPS are about 2 billion barrels of oil and more than 30 trillion cubic feet of gas. The stratigraphic distribution of oil and gas reserves is narrow; all fields are in Vendian to lowermost Cambrian clastic and carbonate reservoirs that occur below Lower Cambrian salt. Both structural and stratigraphic traps are known. Source rocks are absent in the sedimentary cover of the provinces, with the possible exception of a narrow zone on the margin of the Cis-Patom Foredeep province. Source rocks are interpreted here to be Riphean and Vendian organic-rich shales of the Baikal-Patom folded region. These rocks presently are deformed and metamorphosed, but they generated oil and gas before the deformation occurred in Late Silurian and Devonian time. Generated hydrocarbons migrated updip onto the craton margin. The time of migration and formation of fields is constrained by the deposition of Lower Cambrian salt and by the Late Silurian or Devonian metamorphism of source rocks. This time frame indicates that the TPS is one of the oldest petroleum systems in the world. All three provinces are exploration frontiers, and available geologic data are limited; therefore, only one assessment unit has been identified. The largest undiscovered hydrocarbon resources are expected to be in Vendian clastic reservoirs in both structural and stratigraphic traps of the Nepa-Botuoba High province. The petroleum potential of Vendian?lowermost Cambrian carbonate reservoirs is smaller. Nevertheless, these reservoirs may contain significant resources. Gas is expected to dominate over oil in the resource base.

Strike-slip faulting at Thebes Gap, Missouri and Illinois; implications for New Madrid tectonism

USGS Publications Warehouse

Harrison, Richard W.; Schultz, Art

1994-01-01

Numerous NNE and NE striking strike-slip faults and associated normal faults, folds, and transtensional grabens occur in the Thebes Gap area of Missouri and Illinois. These structures developed along the northwestern margin of the buried Reelfoot rift of Precambrian-Cambrian age at the northern edge of the Mississippi embayment. They have had a long-lived and complex structural history. This is an area of recent moderate seismicity, approximately 45 km north of the New Madrid seismic zone. Stratigraphic evidence suggests that these faults were active during the Middle Ordovician. They were subsequently reactivated between the Early Devonian and Late Cretaceous, probably in response to both the Acadian and Ouachita orogenies. Deformation during this period was characterized by strongly faulted and folded Ordovician through Devonian rocks. In places, these deformed rocks are overlain with angular unconformity by undeformed Cretaceous strata. Fault motion is interpreted as dominantly strike slip. A still younger period of reactivation involved Late Cretaceous and Cenozoic formations as young as the Miocene or Pliocene Mounds Gravel. These formations have experienced both minor high-angle normal faulting and subsequent major, right-lateral strike-slip faulting. En echelon north-south folds, ENE striking normal faults, regional fracture patterns, and drag folds indicate the right-lateral motion for this major episode of faulting which predates deposition of Quaternary loess. Several nondefinitive lines of evidence suggest Quaternary faulting. Similar fault orientations and kinematics, as well as recent seismicity and proximity, clearly suggest a structural relationship between deformation at Thebes Gap and tectonism associated with the New Madrid area.

Paleozoic Assemblage of the Northern Sierra Terrane: New Geochronology And Geochemical Data From the Stitching Late Devonian - Early Carboniferous Bowman Lake Batholith, and Associated Rocks

NASA Astrophysics Data System (ADS)

Powerman, V.; Hanson, R. E.; Girty, G.; Tretiakov, A.

2016-12-01

Previous study (Grove et al., 2008) of detrital zircon ages and the timing of magmatism within the Northern Sierra terrane (NST) suggest that it is exotic relative to western Laurentia, and link it to the Paleozoic Arctic Realm, Baltica and Caledonides. NST is a composite terrane in the North America Cordillera, consisting of four distinct allochthons, thrusted upon each other. As a first step towards the understanding of the origin and tectonic development of the NST we have undertaken the SHRIMP-RG U-Pb zircon dating of the rocks from granites, granodiorites, trondhjemites, tonalites and hypabyssal intrusions, composing the Bowman Lake batholith. The batholith stitches the allochthons of the NST and its crystallization age signifies the timing of juxtaposition SHRIMP-RG analyses from 14 samples yielded an age range of ca. 352-369 Ma, which overlaps the Devonian-Mississipian boundary and constrains the minimum age for amalgamation. Additionally, we have acquired multiple XRF data, favoring the island arc provenance of the Bowman Lake batholith Batholith. Previously proposed ties between NST and Robert Mountains allochthon seem unlikely because the latter was accreted onto the western miogeocline of Laurentia during the Late Dev.-Early Miss. while the NST was most probably still situated within the Arctic Realm. This work has been supported by the grant #14.Z50.31.0017 of the Government of the Russian Federation and by the Russian Foundation for Basic Research grant #15-55-10055. We are grateful to Stanford-USGS SHRIMP-RG center, and personally to Marty Grove and Elizabeth Miller.

Stratigraphy of the Silurian outcrop belt on the east side of the Cincinnati Arch in Kentucky, with revisions in the nomenclature

USGS Publications Warehouse

McDowell, Robert C.

1983-01-01

Silurian rocks form a narrow arcuate outcrop belt about 100 mi long on the east side of the Cincinnati Arch in Kentucky. They range from as much as 300 ft thick in the north to a pinchout edge in the south. The nomenclature of this sequence is revised to reflect mappability and lithologic uniformity on the basis of detailed mapping at a scale of 1:24,000 by the U.S. Geological Survey in cooperation with the Kentucky Geological Survey. The Silurian rocks are divided into two parts: the Crab Orchard Group, raised in rank from Crab Orchard Formation and redefined, in the lower part of the Silurian section, and Bisher Dolomite in the upper part of the section. The Crab Orchard Group is subdivided into the Drowning Creek Formation (new name) at the base of the Silurian, overlain by the Alger Shale (adopted herein) south of Fleming County and by the Estill Shale (elevated to formational rank) north of Bath County. The Brassfield Member (reduced in rank from Brassfield Dolomite or Formation) and the Plum Creek Shale and Oldham Members of the former Crab Orchard Formation are included as members of the Drowning Creek; the Lulbegrud Shale, Waco, and Estill Shale Members of the former Crab Orchard Formation are now included in the Alger. The Drowning Creek Formation, 20 to 50 ft thick, is composed mainly of gray fine to coarse-grained dolomite with shale interbeds. The dolomite beds average several inches thick, with bedding surfaces that are locally smooth but generally irregular and are fossiliferous in many places; fossils include brachiopods, crinoid columnals, horn corals, colonial corals, trilobites, pelecypods, and bryozoans. The shale interbeds average several inches thick, except for its Plum Creek Shale Member which is entirely shale and as much as 12 ft thick, and are most abundant in the upper half of the formation. The members of the Drowning Creek intergrade and are indistinguishable in the northern part of the area. The Alger Shale, as much as 170 feet thick, is predominantly grayish-green clay shale with a thin (0.5-3 ft) dolomite member (the Waco, or its northern equivalent, the Dayton Dolomite Member, reduced in rank from Dayton Limestone) near the base. North of Bath County, the Lulbegrud Shale and Dayton Dolomite Members are reassigned to the underlying Drowning Creek Formation, the Estill Shale Member is elevated to formational status, and the Alger is dropped. The Bisher Dolomite, which overlies the Estill Shale in the northernmost part of the Silurian belt, ranges from 0 to 300 ft in thickness and is composed of medium-to coarse-grained, gray, fossiliferous dolomite. The Silurian section overlies Upper Ordovician rocks in apparent conformity, although faunal studies suggest a minor hiatus, and is overlain by Middle to Upper Devonian rocks in a regional angular unconformity that truncates the entire Silurian section at the southwest end of the outcrop belt, where it is nearest the axis of the Cincinnati Arch. All of the units recognized in the Silurian appear to thicken eastward, away from the axis of the arch and towards the Appalachian basin. This, with the presence of isolated remnants of the Brassfield near the axis, suggest that formation of the arch was initiated in Early Silurian time by subsidence of its eastern flank.

Assessment of Appalachian basin oil and gas resources:Devonian shale - Middle and Upper Paleozoic Total Petroleum System

USGS Publications Warehouse

Milici, Robert C.; Swezey, Christopher S.

2006-01-01

The U.S. Geological Survey (USGS) recently completed an assessment of the technically recoverable undiscovered hydrocarbon resources of the Appalachian Basin Province. The assessment province includes parts of New York, Pennsylvania, Ohio, Maryland, West Virginia, Virginia, Kentucky, Tennessee, Georgia and Alabama. The assessment was based on six major petroleum systems, which include strata that range in age from Cambrian to Pennsylvanian. The Devonian Shale-Middle and Upper Paleozoic Total Petroleum System (TPS) extends generally from New York to Tennessee. This petroleum system has produced a large proportion of the oil and natural gas that has been discovered in the Appalachian basin since the drilling of the Drake well in Pennsylvania in 1859. For assessment purposes, the TPS was divided into 10 assessment units (plays), 4 of which were classified as conventional and 6 as continuous. The results were reported as fully risked fractiles (F95, F50, F5 and the Mean), with the fractiles indicating the probability of recovery of the assessment amount. Products reported were oil (millions of barrels of oil, MMBO), gas (billions of cubic feet of gas, BCFG), and natural gas liquids (millions of barrels of natural gas liquids, MMBNGL). The mean estimates for technically recoverable undiscovered hydrocarbons in the TPS are: 7.53 MMBO, 31,418.88 BCFG (31.42 trillion cubic feet) of gas, and 562.07 MMBNGL.

Position of the Upper Devonian Frasnian--Famennian boundary in the central Appalachians

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rossbach, T.J.

Biostratigraphic analysis of eight Upper Devonian sections in VA and WV reveals that the section at Huttonsville, Randolph County, WV, is a key locality for determining the Frasnian-Famennian boundary. The Foreknobs Formation at Huttonsville indicates a higher stratigraphic placement of the Frasnian-Famennian boundary than has been generally assumed. Conodonts are not known within that section, so placement of the boundary uses the last occurrence of tentaculitids and the last and first occurrences of several species of brachiopods. It is believed that the Frasnian-Famennian boundary can be identified independently of the atrypoid brachiopods. Stratigraphic ranges of the cricoconarid Tentaculites discusses andmore » the brachiopod Tropidoleptus carinatus, both considered Frasnian marker fossils, indicate that the Frasnian extends well into the Red Lick Member of the Foreknobs Formation at Huttonsville, with T. carinatus occurring up to 70% of the stratigraphic thickness of the Red Lick. The Famennian marker fossils A. angelica and C. sulcifer are both found at Huttonsville above the last recorded occurrence of all the Frasnian marker fossils. To the northeast of Huttonsville the Frasnian-Famennian series boundary has been placed by other workers within or at the top of the Pound Member of the Foreknobs Formation. This discrepancy implies that either the Pound Member is diachronous or that to the northeast paleoecologic factors caused local disappearances of critical fossils before their extinction at Huttonsville.« less

Biogeography of late Silurian and devonian rugose corals

USGS Publications Warehouse

Oliver, W.A.

1977-01-01

Three marine benthic faunal realms can be recognized in the Early and Middle Devonian. The Eastern Americas Realm consisted of most of the eastern half of North America and South America north of the Amazon. This realm extended in a southwest direction from the Devonian equator to approximately 35??S and was an isolated epicontinental sea during much of its history. The Eastern Americas Realm was bounded on the west by the Transcontinental Arch, on the north by the Canadian Shield and on the east and southeast by a peninsular extension of the Old Red Continent. These barriers were emergent during much, but not all, of Devonian time. Seaways beyond these barriers belonged to the Old World Realm. The Malvinokaffric Realm that was farther south was apparently temperate to arctic in climate and latitudinal position and contained few corals. Rugose corals in the Eastern Americas Realm show increasing generic-level endemism from the Late Silurian through the Early Devonian; during the late Early Devonian, 92% of the rugosan genera are not known anywhere else in the world. Endemism decreased through the Middle Devonian to zero in the early Late Devonian. The Early Devonian increase in endemism paralleled, and was probably related to, the development of the Old Red Continent as a barrier between America and Africa-Europe. The waning of endemism in the Middle Devonian reflects the breaching of the land barriers. This permitted some migration in and out of the realm in early Middle Devonian time but greatest movements were in late Middle Devonian time. Principal migration directions were from western or Arctic North America into the Michigan-Hudson Bay area and from the southern Appalachian area into Africa. ?? 1977.

Geologic Map of the Weaverville 15' Quadrangle, Trinity County, California

USGS Publications Warehouse

Irwin, William P.

2009-01-01

The Weaverville 15' quadrangle spans parts of five generally north-northwest-trending accreted terranes. From east to west, these are the Eastern Klamath, Central Metamorphic, North Fork, Eastern Hayfork, and Western Hayfork terranes. The Eastern Klamath terrane was thrust westward over the Central Metamorphic terrane during early Paleozoic (Devonian?) time and, in Early Cretaceous time (approx. 136 Ma), was intruded along its length by the massive Shasta Bally batholith. Remnants of overlap assemblages of the Early Cretaceous (Hauterivian) Great Valley sequence and the Tertiary Weaverville Formation cover nearly 10 percent of the quadrangle. The base of the Eastern Klamath terrane in the Weaverville quadrangle is a peridotite-gabbro complex that probably is correlative to the Trinity ophiolite (Ordovician), which is widely exposed farther north beyond the quadrangle. In the northeast part of the Weaverville quadrangle, the peridotite-gabbro complex is overlain by the Devonian Copley Greenstone and the Mississippian Bragdon Formation. Where these formations were intruded by the Shasta Bally batholith, they formed an aureole of gneissic and other metamorphic rocks around the batholith. Westward thrusting of the Eastern Klamath terrane over an adjacent body of mafic volcanic and overlying quartzose sedimentary rocks during Devonian time formed the Salmon Hornblende Schist and the Abrams Mica Schist of the Central Metamorphic terrane. Substantial beds of limestone in the quartzose sedimentary unit, generally found near the underlying volcanic rock, are too metamorphosed for fossils to have survived. Rb-Sr analysis of the Abrams Mica Schist indicates a metamorphic age of approx. 380 Ma. West of Weavervillle, the Oregon Mountain outlier of the Eastern Klamath terrane consists mainly of Bragdon Formation(?) and is largely separated from the underlying Central Metamorphic terrane by serpentinized peridotite that may be a remnant of the Trinity ophiolite. The North Fork terrane is faulted against the west edge of the Central Metamorphic terrane, and its northerly trend is disrupted by major left-lateral offsets along generally west-northwest-trending faults. The serpentinized peridotite-gabbro complex that forms the western base of the terrane is the Permian North Fork ophiolite, which to the east is overlain by broken formation of mafic-volcanic rocks, red chert, siliceous tuff, argillite, minor limestone, and clastic sedimentary rocks. The chert and siliceous tuff contain radiolarians of Permian and Mesozoic ages, and some are as young as Early Jurassic (Pliensbachian). Similar Pliensbachian radiolarians are found in Franciscan rocks of the Coast Ranges. The Eastern Hayfork terrane is broken formation and melange of mainly chert, sandstone, argillite, and various exotic blocks. The cherts yield radiolarians of Permian and Triassic ages but none of clearly Jurassic age. Limestone bodies of the Eastern Hayfork terrane contain Permian microfaunas of Tethyan affinity. The Western Hayfork terrane, exposed only in a small area in the southwestern part of the quadrangle, consists dominantly of mafic tuff and dark slaty argillite. Sparse paleontologic data indicate a Mesozoic age for the strata. The terrane includes small bodies of diorite that are related to the nearby Wildwood pluton of Middle Jurassic age and probably are related genetically to the stratified rocks. The terrane is interpreted to be the accreted remnants of a Middle Jurassic volcanic arc. Shortly after intrusion by Shasta Bally batholith (approx. 136 Ma), much of the southern half of the Weaverville quadrangle was overlapped by Lower Cretaceous, dominantly Hauterivian, marine strata of the Great Valley sequence, and to a lesser extent later during Oligocene and (or) Miocene time by fluvial and lacustrine deposits of the Weaverville Formation. This map of the Weaverville Quadrangle is a digital rendition of U.S. Geological Survey Miscellaneous Field

Tectonic setting of synorogenic gold deposits of the Pacific Rim

USGS Publications Warehouse

Goldfarb, R.J.; Phillips, G.N.; Nokleberg, W.J.

1998-01-01

More than 420 million oz of gold were concentrated in circum-Pacific synorogenic quartz loades mainly during two periods of continental growth, one along the Gondwanan margin in the Palaeozoic and the other in the northern Pacific basin between 170 and 50 Ma. These ores have many features in common and can be grouped into a single type of lode gold deposit widespread throughout clastic sedimentary-rock dominant terranes. The auriferous veins contain only a few percent sulphide minerals, have gold:silver ratios typically greater than 1:1, show a distinct association with medium grade metamorphic rocks, and may be associated with large-scale fault zone. Ore fluids are consistently of low salinity and are CO2-rich. In the early and middle Palaeozoic in the southern Pacific basin, a single immense turbidite sequence was added to the eastern margin of Gondwanaland. Deformation of these rocks in southeastern Australia was accompanied by deposition of at least 80 million oz of gold in the Victorian sector of the Lachlan fold belt mainly during the Middle and Late Devonian. Lesser Devonian gold accumulations characterized the more northerly parts of the Gondwanan margin within the Hodgkinson-Broken River and Thomson fold belts. Additional lodes were emplaced in this flyschoid sequence in Devonian or earlier Palaeozoic times in what is now the Buller Terrane, Westland, New Zealand. Minor post-Devonian growth of Gondwanaland included terrane collision and formation of gold-bearing veins in the Permian in Australia's New England fold belt and in the Jurassic-Early Cretaceous in New Zealand's Otago schists. Collision and accretion of dozens of terranes for a 100-m.y.-long period against the western margin of North America and eastern margin of Eurasia led to widespread, lattest Jurassic to Eocene gold veining in the northern Pacific basin. In the former location, Late Jurassic and Early Cretaceous veins and related placer deposits along the western margin of the Sierra Nevada batholith have yielded more than 100 million oz of gold. Additional significant ore-forming events during the development of North America's Cordilleran orogen included those in the Klamath Mountains region, California in the Late Jurassic and Early Cretaceous; the Klondike district, Yukon by the Early Cretaceous; the Nome and Fairbanks districts, Alaska, and the Bridge River district, British Columbia in the middle Cretaceous; and the Juneau gold belt, Alaska in the Eocene. Gold-bearing veins deposited during the Late Jurassic and Early Cretaceous terrane collision that formed the present-day Russian Far East have been the source for more than 130 million oz of placer gold. The abundance of gold-bearing quartz-carbonate veins throughout the Gondwanan, North American and Eurasian continental margins suggests the migration and concentration of large fluid volumes during continental growth. Such volumes could be released during orogenic heating of hydrous silicate mineral phases within accreted marine strata. The common temporal association between gold veining and magmatism around the Pacific Rim reflects these thermal episodes. Melting of the lower thickened crust during arc formation, slab rollback and extensional tectonism, and subduction of a slab window beneath the seaward part of the forearc region can all provide the required heat for initation of the ore-forming processes.

Pre-lithification tectonic foliation development in a clastic sedimentary rock sequence from SW Ireland

NASA Astrophysics Data System (ADS)

Meere, Patrick; Mulchrone, Kieran; McCarthy, David

2017-04-01

The current orthodoxy regarding the development of regionally developed penetrative tectonic cleavage fabrics in sedimentary rocks is that it postdates lithification of those rocks. It is well established that fabric development under these circumstances is achieved by a combination of grain rigid body rotation, crystal-plastic deformation and pressure solution. The latter is believed to be the primary mechanism responsible for the domainal nature of cleavage development commonly observed in low grade metamorphic rocks. While there have been advocates for the development of tectonic cleavages before host rock lithification these are currently viewed as essentially local aberrations without regional significance. In this study we combine new field observations with strain analysis, element mapping and modelling to characterise Acadian (>50%) crustal shortening in a Devonian clastic sedimentary sequence from the Dingle Peninsula of south west Ireland. Fabrics in these rocks reflect significant levels of tectonic shortening are a product of grain translation, rigid body rotation and repacking of intra- and extra-formational clasts during deformation of an unconsolidated clastic sedimentary sequence. There is an absence of the expected domainal cleavage structure and intra-clast deformation expected with conventional cleavage formation. This study requires geologists to consider the possibility such a mechanism contributing to tectonic strain in a wide range of geological settings and to look again at field evidence that indicates early sediment mobility during deformation.

Collision of the Tacheng block with the Mayile-Barleik-Tangbale accretionary complex in Western Junggar, NW China: Implication for Early-Middle Paleozoic architecture of the western Altaids

NASA Astrophysics Data System (ADS)

Zhang, Ji'en; Xiao, Wenjiao; Luo, Jun; Chen, Yichao; Windley, Brian F.; Song, Dongfang; Han, Chunming; Safonova, Inna

2018-06-01

Western Junggar in NW China, located to the southeast of the Boshchekul-Chingiz (BC) Range and to the north of the Chu-Balkhash-Yili microcontinent (CBY), played a key role in the architectural development of the western Altaids. However, the mutual tectonic relationships have been poorly constrained. In this paper, we present detailed mapping, field structural geology, and geochemical data from the Barleik-Mayile-Tangbale Complex (BMTC) in Western Junggar. The Complex is divisible into Zones I, II and III, which are mainly composed of Cambrian-Silurian rocks. Zone I contains pillow lava, siliceous shale, chert, coral-bearing limestone, sandstone and purple mudstone. Zone II consists of basaltic lava, siliceous shale, chert, sandstone and mudstone. Zone III is characterized by basalt, chert, sandstone and mudstone. These rocks represent imbricated ocean plate stratigraphy, which have been either tectonically juxtaposed by thrusting or form a mélange with a block-in-matrix structure. All these relationships suggest that the BMTC is an Early-Middle Paleozoic accretionary complex in the eastern extension of the BC Range. These Early Paleozoic oceanic rocks were thrust onto Silurian sediments forming imbricate thrust stacks that are unconformably overlain by Devonian limestone, conglomerate and sandstone containing fossils of brachiopoda, crinoidea, bryozoa, and plant stems and leaves. The tectonic vergence of overturned folds in cherts, drag-related curved cleavages and σ-type structures on the main thrust surface suggests top-to-the-NW transport. Moreover, the positive εNd(t) values of volcanic rocks from the Tacan-1 drill-core, and the positive εHf(t) values and post-Cambrian ages of detrital zircons from Silurian and Devonian strata to the south of the Tacheng block indicate that its basement is a depleted and juvenile lithosphere. And there was a radial outward transition from coral-bearing shallow marine (shelf) to deep ocean (pelagic) environments, and from OIB/E-MORB to N-MORB lava geochemistry away from the Tacheng block. Comparisons with published data suggest that these positive isotopic values, stratigraphic, structural and geochemical relationships can be best understood as an analogue of the relationships between the Ontong Java oceanic plateau and the Pacific oceanic crust. Therefore we propose that the basement of the Tacheng block was an Early Paleozoic oceanic plateau. The southern part of the Tacheng block was an accretionary complex and the northern part was an oceanic basin in the Early Paleozoic, the configuration of which is similar to that of the present Ontong Java oceanic plateau situated on the Pacific oceanic crust, and its accretion into the Solomon accretionary complex. The presence of Ordovician SSZ-type ophiolites, early Paleozoic blueschist and Silurian SSZ-type intrusions in the BMTC, and Early-Middle Paleozoic continental arc-related intrusive rocks in the northern margin of the CBY provide further corroboration of a former subduction zone between the southern West Junggar and the northern margin of the CBY. Furthermore, consideration of the fact that the Kokchetav-North Tianshan range was collaged to the southern margin of the CBY in the Ordovician-Devonian indicates that both ranges were amalgamated synchronously with the CBY constructing the Early-Middle Paleozoic architecture of western Altaids.

18 CFR 270.306 - Devonian shale wells in Michigan.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 18 Conservation of Power and Water Resources 1 2011-04-01 2011-04-01 false Devonian shale wells in... PROCEDURES Requirements for Filings With Jurisdictional Agencies § 270.306 Devonian shale wells in Michigan. A person seeking a determination that natural gas is being produced from the Devonian Age Antrim...

18 CFR 270.306 - Devonian shale wells in Michigan.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 18 Conservation of Power and Water Resources 1 2014-04-01 2014-04-01 false Devonian shale wells in... PROCEDURES Requirements for Filings With Jurisdictional Agencies § 270.306 Devonian shale wells in Michigan. A person seeking a determination that natural gas is being produced from the Devonian Age Antrim...

18 CFR 270.306 - Devonian shale wells in Michigan.

Code of Federal Regulations, 2013 CFR

2013-04-01

... 18 Conservation of Power and Water Resources 1 2013-04-01 2013-04-01 false Devonian shale wells in... PROCEDURES Requirements for Filings With Jurisdictional Agencies § 270.306 Devonian shale wells in Michigan. A person seeking a determination that natural gas is being produced from the Devonian Age Antrim...

18 CFR 270.306 - Devonian shale wells in Michigan.

Code of Federal Regulations, 2012 CFR

2012-04-01

... 18 Conservation of Power and Water Resources 1 2012-04-01 2012-04-01 false Devonian shale wells in... PROCEDURES Requirements for Filings With Jurisdictional Agencies § 270.306 Devonian shale wells in Michigan. A person seeking a determination that natural gas is being produced from the Devonian Age Antrim...

18 CFR 270.303 - Natural gas produced from Devonian shale.

Code of Federal Regulations, 2013 CFR

2013-04-01

... from Devonian shale. A person seeking a determination that natural gas is produced from Devonian shale... 18 Conservation of Power and Water Resources 1 2013-04-01 2013-04-01 false Natural gas produced from Devonian shale. 270.303 Section 270.303 Conservation of Power and Water Resources FEDERAL ENERGY...

18 CFR 270.303 - Natural gas produced from Devonian shale.

Code of Federal Regulations, 2012 CFR

2012-04-01

... from Devonian shale. A person seeking a determination that natural gas is produced from Devonian shale... 18 Conservation of Power and Water Resources 1 2012-04-01 2012-04-01 false Natural gas produced from Devonian shale. 270.303 Section 270.303 Conservation of Power and Water Resources FEDERAL ENERGY...

18 CFR 270.303 - Natural gas produced from Devonian shale.

Code of Federal Regulations, 2014 CFR

2014-04-01

... from Devonian shale. A person seeking a determination that natural gas is produced from Devonian shale... 18 Conservation of Power and Water Resources 1 2014-04-01 2014-04-01 false Natural gas produced from Devonian shale. 270.303 Section 270.303 Conservation of Power and Water Resources FEDERAL ENERGY...

A new Late Devonian genus with seed plant affinities.

PubMed

Wang, Deming; Liu, Le

2015-02-26

Many ovules of Late Devonian (Famennian) seed plants have been well studied. However, because few taxa occur with anatomically preserved stems and/or petioles, the vascular system of these earliest spermatophytes is little understood and available data come mostly from Euramerica. There remains great controversy over the anatomical differentiation of Late Devonian and Carboniferous seed plant groups of Buteoxylonales, Calamopityales and Lyginopteridales. Protostele evolution of these early spermatophytes needs more research. A new taxon Yiduxylon trilobum gen. et sp. nov. with seed plant affinities has been discovered in the Upper Devonian (Famennian) Tizikou Formation of Hubei Province, China. It is represented by stems, helically arranged and bifurcate fronds with two orders of pinnae and planate pinnules. Both secondary pinnae and pinnules are borne alternately. Stems contain a small protostele with three primary xylem ribs possessing a single peripheral protoxylem strand. Thick secondary xylem displays multiseriate bordered pitting on the tangential and radial walls of the tracheids, and has biseriate to multiseriate and high rays. A narrow cortex consists of inner cortex without sclerotic nests and sparganum-type outer cortex with peripheral bands of vertically aligned sclerenchyma cells. Two leaf traces successively arise tangentially from each primary xylem rib and they divide once to produce four circular-oval traces in the stem cortex. Four vascular bundles occur in two C-shaped groups at each petiole base with ground tissue and peripheral bands of sclerenchyma cells. Yiduxylon justifies the assignment to a new genus mainly because of the protostele with protoxylem strands only near the periphery of primary xylem ribs, leaf trace origination and petiolar vascular supply structure. It shares many definitive characters with Calamopityales and Lyginopteridales, further underscoring the anatomical similarities among early seed plants. The primary vascular system, pycnoxylic-manoxylic secondary xylem with bordered pits on both tangential and radial walls of a tracheid and leaf trace divergence of Yiduxylon suggest transitional features between the early spermatophytes and ancestral aneurophyte progymnosperms.

Representatives of the family Actinostromatidae (Stromatoporoidea) in the Devonian of southern Poland and their ecological significance

NASA Astrophysics Data System (ADS)

Wolniewicz, Paweł

2016-09-01

Stromatoporoids of the family Actinostromatidae are common constituents of Givetian to Frasnian (Devonian) organic buildups. The species-level structure of actinostromatid assemblages from the Devonian of southern Poland is described in the present paper, with special emphasis on ecological factors that influenced species composition of the communities. Nine species of the genera Actinostroma and Bifariostroma are distinguished. Members of the family Actinostromatidae predominated in stromatoporoid assemblages within lower Frasnian carbonate buildup margins. The most diverse actinostromatid faunas were found within the middle Givetian Stringocephalus Bank, in the upper Givetian-lower Frasnian biostromal complex and in the lower Frasnian organic buildups. Species-level biodiversity was lowest within detrital facies which surrounded the Frasnian carbonate buildups. Species of Actinostroma with well-developed colliculi are commonest within the middle Givetian to early Frasnian coral-stromatoporoid biostromal complexes, whereas species with strongly reduced colliculi predominate early-middle Frasnian organic buildups. The skeletal structure of actinostromatids reflects environmental changes, documenting a transition from species with thin, close-set pillars and widely spaced laminae (common in the middle Givetian) to those with long, thick pillars and megapillars (in Bifariostroma), which were predominant during the early and middle Frasnian. The distribution of growth forms among species reveals a significant intraspecific variation. Species of Actinostroma can be either tabular or low domical, depending on the palaeoenvironmental setting. Thus, the present study confirms that stromatoporoid morphology was influenced by environmental conditions.

Magnetic susceptibilities measured on rocks of the upper Cook Inlet, Alaska

USGS Publications Warehouse

Alstatt, A.A.; Saltus, R.W.; Bruhn, R.L.; Haeussler, Peter J.

2002-01-01

We have measured magnetic susceptibility in the field on most of the geologic rock formations exposed in the upper Cook Inlet near Anchorage and Kenai, Alaska. Measured susceptibilities range from less than our detection limit of 0.01 x 10-3 (SI) to greater than 100 x 10-3 (SI). As expected, mafic igneous rocks have the highest susceptibilities and some sedimentary rocks the lowest. Rocks of the Tertiary Sterling Formation yielded some moderate to high susceptibility values. Although we do not have detailed information on the magnetic mineralogy of the rocks measured here, the higher susceptibilities are sufficient to explain the magnitudes of some short-wavelength aeromagnetic anomalies observed on recent surveys of the upper Cook Inlet.

Evolution of Devonian carbonate-shelf margin, Nevada

USGS Publications Warehouse

Morrow, J.R.; Sandberg, C.A.

2008-01-01

The north-trending, 550-km-long Nevada segment of the Devonian carbonate-shelf margin, which fringed western North America, evidences the complex interaction of paleotectonics, eustasy, biotic changes, and bolide impact-related influences. Margin reconstruction is complicated by mid-Paleozoic to Paleogene compressional tectonics and younger extensional and strike-slip faulting. Reports published during the past three decades identify 12 important events that influenced development of shelf-margin settings; in chronological order, these are: (1) Early Devonian inheritance of Silurian stable shelf inargin, (2) formation of Early to early Middle 'Devonian shelf-margin basins, (3) propradation of later Middle Devonian shelf margin, (4) late Middle Devonian Taghanic ondap and continuing long-term Frasnian transgression, (5) initiation of latest Middle Devonian to early Frasnian proto-Antler orogenic forebulge, (6) mid-Frasnian Alamo Impact, (7) accelerated development of proto-Antler forebulge and backbulge Pilot basin, (8) global late Frasnian sentichatovae sea-level rise, (9) end-Frasnian sea-level fluctuations and ensuing mass extinction, (10) long-term Famennian regression and continept-wide erosion, (11) late Famennian emergence: of Ahtler orogenic highlands, and (12) end-Devonian eustatic sea-level fall. Although of considerable value for understanding facies relationships and geometries, existing standard carbonate platform-margin models developed for passive settings else-where do not adequately describe the diverse depositional and, structural settings along the Nevada Devonian platform margin. Recent structural and geochemical studies suggest that the Early to Middle Devonian-shelf-margin basins may have been fault-bound and controlled by inherited Precambrian structure. Subsequently, the migrating latest Middle to Late Devonian Antler orogenic forebulge exerted a dominant control on shelf-margin position, morphology, and sedimentation. ??Geological Society of America.

Devonian Terrestrial Revolution: the palaeoenvironment of the oldest known tetrapod tracks, Zachełmie Quarry, Poland

NASA Astrophysics Data System (ADS)

Niedźwiedzki, G.

2012-04-01

Numerous trackways and isolated prints with digit impressions, which are similar to the foot anatomy of early tetrapods such as Ichthyostega, were found on the three dolomite bed-surfaces in the lower part of the Wojciechowice Formation exposed in the Zachełmie Quarry in the Holy Cross Mountains (south-central Poland), (Niedźwiedzki et al., 2010). The age of the tetrapod track-bearing strata is well-constrained, but the detailed sedimentology of the lower section with tetrapod ichnites is still under study. The Wojciechowice Formation represent one of the first carbonate stages of a transgressive succession that begins with Early Devonian continental to marginal marine clastics and culminates in the development of a Givetian coral-stromatoporoid carbonate platform. The tetrapod track-bearing complex is composed of grey to reddish, thin- to medium-bedded dolomitic shales and marly dolomite mudstones. These deposits from the tetrapod track-bearing horizon lack definitive marine body fossils, and may have formed in a marginal marine environment, e.g. around a coastal lagoon. Mudcracks, columnar peds, root traces, and microbially induced sedimentary structures were found in three distinct pedotypes of very weakly to weakly developed paleosols (Retallack, 2011). Conodonts of the costatus zone (mid-Eifelian) were found 20 m above the uppermost surface with tetrapod tracks in limestones of the upper Wojciechowice Formation, which contain also brachiopod and crinoidal debris. The overlying Kowala Formation is a marine coral limestone and dolostone. The parts of profile with tetrapod ichnites and invertebrate and conodont fossils contain also records of invertebrate traces. Seven ichnotaxa are distributed among four recognized ichnoassemblages. The recognized ichnocoenoses are typical for the shallow-marine (Cruziana ichnofacies) and land-water transitional (Skolithos/Psilonichnus ichnofacies) carbonate depositional environments. The ichnocoenoses are dominated by trace fossils produced by arthropods (probably crustaceans), a group that can create large and distinctive burrows. The palaeoecological information from the Zachełmie section has direct bearing on the interpretation of environmental aspects of tetrapod emergence and terrestrialization. It should be fully integrated with data from other Devonian tetrapod tracksites. Niedźwiedzki, G., Szrek P., Narkiewicz K., Narkiewicz M. and Ahlberg P.E. 2010. Tetrapod trackways from the early Middle Devonian period of Poland. Nature, 463: 43-48. Retallack, G.J. 2011. Woodland Hypothesis for Devonian Tetrapod Evolution. The Journal of Geology, 119, 3: 235-258

Arsenic in rocks and stream sediments of the central Appalachian Basin, Kentucky

USGS Publications Warehouse

Tuttle, Michele L.W.; Goldhaber, Martin B.; Ruppert, Leslie F.; Hower, James C.

2002-01-01

Arsenic (As) enrichment in coal and stream sediments has been documented in the southern Appalachian basin (see Goldhaber and others, submitted) and is attributed to interaction of rocks and coal with metamorphic fluids generated during the Allegheny Orogeny (late Paleozoic). Similarly derived fluids are expected to affect the coal and in the Kentucky Appalachian Basin to the north as well. In addition, similar processes may have influenced the Devonian oil shale on the western margin of the basin. The major goals of this study are to determine the effect such fluids had on rocks in the Kentucky Appalachian basin (fig. 1), and to understand the geochemical processes that control trace-metal source, residence, and mobility within the basin. This report includes data presented in a poster at the USGS workshop on arsenic (February 21 and 22, 2001), new NURE stream sediment data3 , and field data from a trip in April 2001. Although data for major and minor elements and all detectable trace metals are reported in the Appendices, the narrative of this report primarily focuses on arsenic.

Discovery of a Devonian mafic magmatism on the western border of the Murzuq basin (Saharan metacraton): Paleomagnetic dating and geodynamical implications

NASA Astrophysics Data System (ADS)

Derder, M. E. M.; Maouche, S.; Liégeois, J. P.; Henry, B.; Amenna, M.; Ouabadi, A.; Bellon, H.; Bruguier, O.; Bayou, B.; Bestandji, R.; Nouar, O.; Bouabdallah, H.; Ayache, M.; Beddiaf, M.

2016-03-01

Intraplate deformation is most often linked to major stress applied on plate margins. When such intraplate events are accompanied by magmatism, the use of several dating methods integrated within a multidisciplinary approach can bring constraints on the age, nature and source mobilized for generating the magma and in turn on the nature of the intraplate deformation. This study focuses on the large gabbro Arrikine sill (35 km in extension) emplaced within the Silurian sediments of the western margin of the Murzuq cratonic basin in southeastern Algeria. Its emplacement is dated during the early Devonian (415-400 Ma) through the determination of a reliable paleomagnetic pole by comparison with the Gondwana Apparent Polar Wander Path (APWP). This age can be correlated with deep phreatic eruptions before Pragian time thought to be at the origin of sand injections and associated circular structures in Algeria and Libya. For the sill, the K-Ar age of 325.6 ± 7.7 Ma is related to a K-rich aplitic phase that has K-enriched by more than 20% the Devonian gabbro. Laser-ICP-MS U-Pb method dates only inherited zircons mostly at c. 2030 Ma with additional ages at c. 2700 Ma and younger ones in the 766-598 Ma age range. The Arrikine sill is a high-Ti alkaline gabbro having the geochemical composition of a hawaiite akin to several intraplate continental and oceanic provinces, including the contemporaneous Aïr ring complexes province in Niger, but also to the Mauna Loa volcano in Hawaii. This peculiar composition akin to that of the contemporaneous Aïr province is in agreement with a lower Devonian age for the Arrikine sill. The lower Devonian Arrikine sill emplacement is related to a "Caledonian" transtensive reactivation of the western metacratonic boundary of the Murzuq craton. This event also generated in the Saharan platform the so-called "Caledonian unconformity" of regional extension, the Aïr ring complexes and magmatic rocks that produced sand injections. It could be related to rifting of the Hun terranes that occurred at the plate margin to the north (Stampfli and Borel, 2002, Blackey, 2008 and references therein). The mid-Carboniferous (c. 326 Ma) reactivation corresponds to Variscan compression on NW Africa generating aplitic fluids, but also to the major "Hercynian unconformity" of regional extension. The generation of the Arrikine magma is attributed to partial melting through adiabatic pressure release of uprising asthenosphere along tectonically reactivated mega-shear zones, here bordering the relictual Murzuq craton enclosed in the Saharan metacraton.

Petroleum systems of the Southeast Tertiary basins and Marbella area, Southeast Mexico

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fuentes, F.

1996-08-01

This study was done in an area where insufficient organic-rich rocks were available for a reliable oil-source rock correlation. However, oil-rock correlations, molecular characteristics of key horizons, paleofacies maps, maturation and potential migration pathways suggest the Tithonian as a major source rock. Moreover, there is good evidence of high quality source rocks in Oxfordian, Kimmeridgian, Middle-Upper Cretaceous and Paleogene (mainly in the Eocene). Plays were identified in Upper Jurassic oolitic sequences, Early-Middle Cretaceus carbonate platform rocks and breccias, Late Cretaceous basinal fracture carbonates, Paleogene carbonates and breccias, Early-Middle Miocene mounds and submarine fans and isolated carbonate platform sediments and Miocene-Recentmore » turbidites. Seal rocks are shaly carbonates and anhydrites from Tithonian, basinal carbonates and anhydrites from Middle-Upper Cretaceous, basinal carbonates and marls from Upper Cretaceous and Paleogene shales, and bathyal shales from Early Miocene-Recent. The first phase of oil migration from upper Jurassic-Early Cretaceous source rocks occurred in the Early-Middle Cretaceous. In the Upper Cretaceous the Chortis block collided with Chiapas, and as a result mild folding and some hydrocarbons were emplaced to the structural highs. The main phase of structuration and folding of the Sierra de Chiapas started in the Miocene, resulting in well-defined structural traps. Finally, in Plio-Pleistocene the Chortis block was separated, the major compressional period finished and the southern portion of Sierra de Chiapas was raised isostatically. As a result of major subsidence, salt withdrawal and increased burial depth, conditions were created for the generation of liquid hydrocarbons from the Paleogene shales.« less

The Grand St Bernard-Briançonnais Nappe System and the Paleozoic Inheritance of the Western Alps Unraveled by Zircon U-Pb Dating

NASA Astrophysics Data System (ADS)

Bergomi, M. A.; Dal Piaz, G. V.; Malusà, M. G.; Monopoli, B.; Tunesi, A.

2017-12-01

The continental crust involved in the Alpine orogeny was largely shaped by Paleozoic tectono-metamorphic and igneous events during oblique collision between Gondwana and Laurussia. In order to shed light on the pre-Alpine basement puzzle disrupted and reamalgamated during the Tethyan rifting and the Alpine orogeny, we provide sensitive high-resolution ion microprobe U-Pb zircon and geochemical whole rock data from selected basement units of the Grand St Bernard-Briançonnais nappe system in the Western Alps and from the Penninic and Lower Austroalpine units in the Central Alps. Zircon U-Pb ages, ranging from 459.0 ± 2.3 Ma to 279.1 ± 1.1 Ma, provide evidence of a complex evolution along the northern margin of Gondwana including Ordovician transtension, Devonian subduction, and Carboniferous-to-Permian tectonic reorganization. Original zircon U-Pb ages of 371 ± 0.9 Ma and 369.3 ± 1.5 Ma, from calc-alkaline granitoids of the Grand Nomenon and Gneiss del Monte Canale units, provide the first compelling evidence of Late Devonian orogenic magmatism in the Alps. We propose that rocks belonging to these units were originally part of the Moldanubian domain and were displaced toward the SW by Late Carboniferous strike-slip faulting. The resulting assemblage of basement units was disrupted by Permian tectonics and by Mesozoic opening of the Alpine Tethys. Remnants of the Moldanubian domain became either part of the European paleomargin (Grand Nomenon unit) or part of the Adriatic paleomargin (Gneiss del Monte Canale unit), to be finally accreted into the Alpine orogenic wedge during the Cenozoic.

Stratigraphy, structure, and lithofacies relationships of Devonian through Permian sedimentary rocks: Paradox Basin and adjacent areas - southeastern Utah. Technical report

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCleary, J.; Rogers, T.; Ely, R.

Geophysical well log analysis, literature review, and field work were conducted to develop isopach, structure contour, outcrop, and facies maps and cross sections for the Devonian through Permian strata of a 14,586-km/sup 2/ (5632-square-mile) area in southeastern Utah. The study area includes part of the Paradox Basin, the salt deposits of which are of interest in siting studies for a nuclear waste repository. For this reason hydrologic models of this area are needed. This study, part of which included the development of a three-dimensional stratigraphic computer model utilizing Geographic Information System software, can serve as a base for hydrologic ormore » other models for this area. Within and adjacent to the study area, 730 wells were screened to select the 191 wells analyzed for the study. It was found that the Elbert through Molas formations did not exhibit noticeable facies changes within the study area. The Pinkerton Trail Formation exhibits moderate changes: anhydrite and shale become somewhat more abundant toward the northeast. Facies changes in the Paradox Formation are more dramatic. Thick saline facies deposits are present in the northeast, grading to thinner anhydrite and then to carbonate facies in the south and west. The lithology of the Honaker Trail Formation appears to be fairly uniform throughout the area. Facies changes in the Cutler Group are numerous and sometimes dramatic, and generally correspond to the named formations of the group. Other factors that could affect groundwater flow, such as stratigraphic cover of fine-grained rocks, area of formation outcrops, and fracturing and faulting are discussed and delineated on maps.« less

S-type rhyolites from the Tolmie Igneous Complex, Australia: deep crust origins and shallow crustal evolution

NASA Astrophysics Data System (ADS)

Clemens, J. D.; Birch, W. D.

2010-05-01

The Late Devonian Tolmie Igneous Complex, in Central Victoria, Australia, is composed mainly of Ba-rich (up to 3000 ppm) S-type rhyolite ignimbrites with SiO2 varying from 69 to 79 wt% and low Mg#s (1 to 43). Two main ignimbrite flows fill the Wabonga Caldera, the Ryans Creek and the overlying Toombullup Ignimbrites, totalling 750 to 1000 km3 in volume. The tectonic environment is late post-tectonic continental extension, with rifting and normal faulting. However, the volcanism was unimodal, without associated mafic lavas or pyroclastic rocks. Devonian red-beds underlie the Complex, Carboniferous, red-bed basins overlie the volcanic rocks, and some mafic lavas are present in the overlying red-bed sequences. The presence of almandine-rich garnet phenocrysts with rutile, in the Ryans Creek, implies minimum pressures of magma generation of 0.9 - 1.0 GPa. The Toombullup Ignimbrite contains two generations of garnet phenocrysts and three of orthopyroxene. Grt+Opx assemblages in the Toombullup imply early magmatic temperatures near 1000 ° C. The early phenocryst assemblage of Grt+Opx+Pl+Qtz constrains early magmatic crystallisation to around 0.4 GPa. Later Grt+Opx+Crd+Pl+Bt+Qtz assemblages suggest crystallisation at around 0.3 GPa and 750 to 800 ° C. The presence of ferroan Opx+Fa as late microphenocrysts suggest continued crystallisation at around 0.15 GPa and 800 ° C. Thus the magmas may were generated by high-T contact anatectic partial melting of Ba-enriched quartzofeldspathic metasediments near the base of the continental crust, during extension and mantle upwelling. There is then a record of partial crystallisation during ascent to shallow crustal pressures, where the felsic magmas evolved and interacted prior to eruption. Geochemical variations in the Complex suggest that there are at least 3 separate magma groups. Mafic-felsic magma mixing and restite unmixing can be ruled out as processes responsible for the variation. The chemistry of the magmas is interpreted to be the result of a complex interplay between partial melting of heterogeneous source rocks, variable entrainment of peritectic phases formed during the melting reactions and some crystal fractionation involving garnet, orthopyroxene, plagioclase and accessory minerals (Ap, Mon, Ilm, Zrn). The implication of these rocks for the local geology is that pre-Palaeozoic supracrustal rocks must have been carried to the base of the crust but escaped high-grade metamorphism and partial melting for 100s of millions of years after the orogenic events that brought them to those depths.

Tin-polymetallic sulfide deposits in the eastern part of the Dachang tin field (South China) and the role of black shales in their origin

NASA Astrophysics Data System (ADS)

Pašava, Jan; Kříbek, Bohdan; Dobeš, Petr; Vavřín, Ivan; Žák, Karel; Delian, Fan; Tao, Zhang; Boiron, Marie-Christine

2003-01-01

The Dafulou and Huile vein and stratabound cassiterite-sulfide deposits and sheeted ore veins at the Kangma cassiterite-sulfide deposit are located in the eastern part of the Dachang tin field. These deposits are hosted in a sedimentary sequence containing significant concentrations of organic matter in the form of Lower Devonian calcareous black shales and hornfels. These rocks together with the younger intrusion of Longxianggai granite (91±2 Ma) actively participated in the formation of Sn-polymetallic deposits. The following three major stages have been distinguished in stratiform and vein-type orebodies at Dafulou, Huile and Kangma: stage I (cassiterite, pyrrhotite, arsenopyrite, tourmaline, carbonate), stage II - main sulfide stage (quartz, cassiterite, arsenopyrite, pyrrhotite, sphalerite, stannite, pyrite, carbonates) and stage III (native Bi, galena, electrum, sulfosalts). Stage IV (post-ore), recognized at Huile is represented by barren carbonates and zeolites. Whole rock geochemistry has revealed that at Dafulou, Bi and Cu correlate strongly with S, whereas V and Pb correlate well with Corg (organic carbon). The similar distribution patterns of selected elements in average slightly mineralized low-Ca black shales indicate a fluid composition similar for all deposits studied. Studies of graphitization of the organic matter in black shales adjacent to orebodies indicate that d(002) and FWHM (full width in half maximum)/peak height values gradually decrease in the following sequence: Dafulou deposit → Kangma deposit → Huile deposit. The pyrolysate of wall rocks at the Dafulou deposit is relatively enriched in asphaltenes and maltenes (55.6-72.0% of the pyrolysate) comparable with pyrolysate obtained from more distal black shales (19.2-28.5%). Typical GC-MS spectra of pyrolysate from distal black shales are dominated by alkanes in the n-C15 to n-C25 range, aromatic molecules being represented mostly by alkyl-naphthalenes. In contrast, only traces of aliphatic hydrocarbons in the n-C14 to n-C18 range and elemental sulfur were identified in pyrolysates from pyrrhotitized wall rocks. The earliest fluid inclusions of the studied system occur in the quartz-tourmaline-cassiterite assemblage of stage I at Dafulou. These inclusions are H2O-CO2-CH4-rich, with 10 to 20 vol% of aqueous phase. P-T conditions of the trapping of inclusions are estimated to be up to 400 °C and 1.3 to 2.0 kbar (between 5.0 and 7.5 km under lithostatic pressure). In contrast, the presence of a low density gaseous CO2-CH4 phase indicates relatively low pressures during the formation of the breccia-type quartz-calcite-cassiterite-sulfide mineralization (stage II), when P-T conditions probably reached approx. 380 to 400 °C and 0.6 kbar (up to 6 km under hydrostatic pressure). Fluid inclusion data and oxygen isotope thermometry indicate that cassiterite-sulfide ores of the main sulfide stage (stage II) formed from aqueous-carbonic fluid (CO2/CH4 =≈10) at temperatures of up to 390 °C at Dafulou and in a temperature range of 250 to 360 °C at Huile and 260 to 370 °C at Kangma. The δ34S values of sulfides from Dafulou range mostly between -1 and -6‰, whereas sulfides from the Kangma and Huile deposits are characterized by more negative δ34S values (between -8 and -11‰, and between -9 and -12‰, respectively). These data suggest that bacteriogenic sulfides of black shales were a dominant source of reduced sulfur for epigenetic (vein and replacement) mineralization. Oxygen isotopic compositions of five quartz-cassiterite pairs from Dafulou and Huile show a relatively narrow range of calculated oxygen isotope temperatures (250-320 °C, using the equation of Alderton 1989) and high δ18Ofluid values between +8 and +10‰ (SMOW), which are in agreement with fluid derivation from and/or high temperature equilibration with the Longxianggai granite. The carbon and oxygen isotope composition of carbonates reflects variable carbon sources. Stage I calcite is characterized by narrow ranges of δ13C (-7.0 to -9.5‰ PDB) and δ18O (+15.0 to +17.5‰ SMOW). This calcite shows ubiquitous deformation, evidenced by intense development of twins. Fluid compositions calculated at 330 °C for the Dafulou and Huile deposits and at 270-300 °C for the Kangma deposit (δ18Ofluid between +10.0 and +11.5‰ SMOW, δ13Cfluid between -5.5 and -7.5‰ PDB), agree with fluid derivation from and/or equilibration with the peraluminous, high-δ18O Longxianggai granite and suggest a significant influence of contact metasedimentary sequences (carbon derived from decomposition and/or alteration of organic matter of calcareous black shales). The δ13 C values of organic matter from the Lower to Upper Devonian host rocks at the Dafulou deposit (-24.0 and -28.0‰) fit with a marine origin from algae. However, organic matter adjacent to the host rock-ore contact displays a slight enrichment in 13C. The organic carbon from the Huile and Kangma deposits is even more 13C enriched (-24.6 to -23.5‰). The most heavy δ13 C values (-16.5‰) were detected in hornfels sampled at the contact of the Upper Devonian sediments with the Longxianggai granite. The δ13C data broadly correlate with the degree of structural ordering (degree of graphitization) of organic matter, which indicates that both variables are related to thermal overprint.

Factors controlling Li concentration and isotopic composition in formation waters and host rocks of Marcellus Shale, Appalachian Basin

USGS Publications Warehouse

Phan, Thai T.; Capo, Rosemary C; Stewart, Brian W.; Macpherson, Gwen; Rowan, Elisabeth L.; Hammack, Richard W.

2015-01-01

In Greene Co., southwest Pennsylvania, the Upper Devonian sandstone formation waters have δ7Li values of + 14.6 ± 1.2 (2SD, n = 25), and are distinct from Marcellus Shale formation waters which have δ7Li of + 10.0 ± 0.8 (2SD, n = 12). These two formation waters also maintain distinctive 87Sr/86Sr ratios suggesting hydrologic separation between these units. Applying temperature-dependent illitilization model to Marcellus Shale, we found that Li concentration in clay minerals increased with Li concentration in pore fluid during diagenetic illite-smectite transition. Samples from north central PA show a much smaller range in both δ7Li and 87Sr/86Sr than in southwest Pennsylvania. Spatial variations in Li and δ7Li values show that Marcellus formation waters are not homogeneous across the Appalachian Basin. Marcellus formation waters in the northeastern Pennsylvania portion of the basin show a much smaller range in both δ7Li and 87Sr/86Sr, suggesting long term, cross-formational fluid migration in this region. Assessing the impact of potential mixing of fresh water with deep formation water requires establishment of a geochemical and isotopic baseline in the shallow, fresh water aquifers, and site specific characterization of formation water, followed by long-term monitoring, particularly in regions of future shale gas development.

Mid-Permian Phosphoria Sea in Nevada and the Upwelling Model

USGS Publications Warehouse

Ketner, Keith B.

2009-01-01

The Phosphoria Sea extended at least 500 km westward and at least 700 km southwestward from its core area centered in southeastern Idaho. Throughout that extent it displayed many characteristic features of the core: the same fauna, the same unique sedimentary assemblage including phosphate in mostly pelletal form, chert composed mainly of sponge spicules, and an association with dolomite. Phosphoria-age sediments in Nevada display ample evidence of deposition in shallow water. The chief difference between the sediments in Nevada and those of the core area is the greater admixture of sandstone and conglomerate in Nevada. Evidence of the western margin of the Phosphoria Sea where the water deepened and began to lose its essential characteristics is located in the uppermost part of the Upper Devonian to Permian Havallah sequence, which has been displaced tectonically eastward an unknown distance. The relatively deep water in which the mid-Permian part of the Havallah was deposited was a sea of probably restricted east-west width and was floored by a very thick sequence of mainly terrigenous sedimentary rocks. The phosphate content of mid-Permian strata in western exposures tends to be relatively low as a percentage, but the thickness of those strata tends to be high. The core area in and near southeastern Idaho where the concentration of phosphate is highest was separated from any possible site of upwelling oceanic waters by a great expanse of shallow sea.

Survey of Hand and Upper Extremity Injuries Among Rock Climbers.

PubMed

Nelson, Clayton E; Rayan, Ghazi M; Judd, Dustin I; Ding, Kai; Stoner, Julie A

2017-07-01

Rock climbing first evolved as a sport in the late 18th century. With its growing popularity, the number of rock climbing-related injuries has potential to increase, spurring a rise in the number of articles associated with it. Despite the available literature, there remains a paucity of information about upper extremity injuries sustained by rock climbers, and no studies to date have focused on gender-specific injuries. A 24-question online survey was distributed to rock climbers about upper extremity injuries sustained during rock climbing. Statistical analysis was used to study association between participants' demographics and injuries. A total of 397 participants responded to the survey. Mean age was 32.5 years with males comprising 85%. No significant differences in demographics or climbing behaviors were found between males and females. Ninety percent of participants reported sustaining an upper extremity injury. Fingers were the most common injury followed by shoulder/arm and elbow/forearm. Our study found females to be more likely to report a rock climbing-related injury, and more likely to undergo surgery for it. Female rock climbers were significantly more likely to report a shoulder/upper arm injury and were also more likely to report undergoing surgery compared with males, where these differences were not due to age or climbing behaviors. Further investigation is warranted into the association between shoulder injuries and female athletes to determine how the gender differences relate to extent of injury as well as health service utilization behaviors.

Provenance of Carboniferous sedimentary rocks in the northern margin of Dabie Mountains, central China and the tectonic significance: constraints from trace elements, mineral chemistry and SHRIMP dating of zircons

NASA Astrophysics Data System (ADS)

Li, Renwei; Li, Shuangying; Jin, Fuquan; Wan, Yusheng; Zhang, Shukun

2004-04-01

A suite of slightly metamorphosed Carboniferous sedimentary strata occurs in the northern margin of the Dabie Mountains, central China. It consists, in ascending order, of the upper Huayuanqiang Formation (C 1), the Yangshan Formation (C 1), the Daorenchong Formation (C 1-2), the most widely distributed Huyoufang Formation (C 2) and the Yangxiaozhuang Formation (C 2). The provenance of the Carboniferous sedimentary rocks is constrained by the integration of trace elements, detrital mineral chemistry and sensitive high resolution ion microprobe (SHRIMP) dating of detrital zircons, which can help to understand the connection between the provenance and the Paleozoic tectonic evolution of the Qinling-Dabie Orogen. The trace element compositions indicate that the source terrain was probably a continental island arc. Detrital tourmalines were mainly derived from aluminous and Al-poor metapelites and metapsammites, and some are sourced from Li-poor granitoids, pegmatites and aplites. Detrital garnets, found only in the uppermost Huyoufang Formation, are almandine and Mn-almandine garnets, indicating probable sources mainly from garnetiferous schists, and partly from granitoid rocks. The detrital white K-micas are muscovitic in the Huayuanqiang, Daorenchong and Huyoufang Formations, and phengitic with Si contents (p.f.u.) from 3.20 up to max. 3.47-3.53 in the uppermost Huyoufang and the Yangxiaozhuang Formations, a meta-sedimentary source. Major components in the detrital zircon age structure for the Huyoufang Formation range from 506 to 363 Ma, centering on ˜400 and ˜480 Ma, which is characteristic of the Qinling and Erlangping Groups in the Qinling and Tongbai Mountains, central China. Evidently, the major source of the Carboniferous sedimentary rocks in the northern margin of Dabie Mountains was from the southern margin of the Sino-Korean Craton represented by the Qinling and Erlangping Groups. The source area was an island-arc system during the Early Paleozoic that collided with the Sino-Korea plate towards the end of the Early Paleozoic or during the Devonian. A prominent feature in the detrital zircon age structure of the Huyoufang Formation is the Neoproterozoic detritus, which could be derived only from the Yangtze Craton. Reasonable interpretation of the two distinct source materials for the Huyoufang Formation is that the two plates were juxtaposed through collision before the late Carboniferous.

Evidence for long-term climate change in Upper Devonian strata of the central Appalachians

USGS Publications Warehouse

Brezinski, D.K.; Cecil, C.B.; Skema, V.W.; Kertis, C.A.

2009-01-01

The highest 1 to 200 m of the Upper Devonian (Famennian) Catskill and equivalent Hampshire formations exhibit a noticeable vertical or stratigraphic change in color and a shift in lithologic character. The lower part of the unit is characterized by typically red, channel-phase sandstones and overbank siltstone and mudstone containing thin calcareous paleosols. These lithologies give way to greenish gray sandstone containing abundant coaly plant fragments, coalified logs, and pyrite, interbedded with thick intervals of non-calcareous paleo-vertisols. The increase in the prominence of preserved terrestrial organic matter suggests that there was a corresponding increase in the abundance of plants in terrestrial ecosystems. The stratigraphic change in lithology within the upper part of the Catskill-Hampshire succession suggests the onset of environmental conditions that became increasingly wet in response to elevated humid climatic conditions during the final stages of Catskill alluvial plain deposition. The sedimentological signature suggesting increased climatic wetness within the uppermost Catskill and Hampshire formations is nearly contemporaneous with the initiation of Late Devonian Gondwanan glaciation in the paleo-high-latitudes. The Appalachian climate record indicates that this change began during the Fa2c and continued through the latest Famennian, reaching its peak during the Fa2d when glacial deposits are recorded in the paleo-mid-latitudes of the Appalachian basin. Evidence of this late Famennian increase in precipitation also is recorded in the adjacent marine environments. Equivalent-age marine units in Ohio and Kentucky record progressive increases in both total organic carbon and the percentage of terrestrially-derived organic carbon. This suggests that there was a late Famennian increase in terrestrial organic matter productivity, and that during the late Famennian, there were elevated levels of runoff produced by the interpreted increase in precipitation that washed progressively higher amounts of terrestrial organic matter into the local marine environments. The late Famennian climate changes identified within the Appalachian basin strata have been recognizable globally, and appear to have had both positive and negative effects on the Earth's biota. Some marine groups exhibit sharp diversity drops or even extinction coincident with the maximum development of the late Famennian ice age. Conversely, terrestrial biota appears to have been more positively affected by the late Famennian increased wetness that accompanied this progressive climate change. Marked diversification and evolutionary innovation, which appear to coincide with this climatic deviation, can be recognized within terrestrial plant communities and early tetrapod amphibians. ?? 2009 Elsevier B.V. All rights reserved.

Composition, Age, and Origin of Cretaceous Granitic Magmatism on the Eastern Chukchi Peninsula

NASA Astrophysics Data System (ADS)

Luchitskaya, M. V.; Sokolov, S. D.; Pease, V.; Miller, E.; Belyatsky, B. V.

2018-05-01

New geochronological and isotopic geochemical data are given, which make it possible to recognize two types of granitic rocks on the eastern Chukchi Peninsula. Early Cretaceous Tkachen and Dolina granitic plutons with zircon ages (U-Pb SIMS) of 119-122 and 131-136 Ma are related to the first type. They cut through Devonian-Lower Carboniferous basement rocks and are overlain by the Aptian-Albian Etelkuyum Formation. Basal units of the latter contain fragments of granitic rocks. Late Cretaceous Provideniya and Rumilet granitic plutons, which contain zircons with ages of 94 and 85 Ma (U-Pb SIMS), respectively, belong to the second type. They cut through volcanic-sedimentary rocks of the Etelkuyum and Leurvaam formations pertaining to the Okhotsk-Chukotka Volcanic Belt. In petrographic and geochemical features, the Early Cretaceous granitic rocks of the Tkachen Pluton are commensurable with I-type granites, while Late Cretaceous granite of the Rumilet Pluton is comparable to A2-type granite. The Sr-Nd isotopic data provide evidence that from the Early Cretaceous Tkachen and Dolina plutons to the Late Cretaceous Provideniya and Rumilet plutons, the degree of crustal assimilation of suprasubduction mantle-derived melts increases up to partial melting of heterogeneous continental crust enriched in rubidium. An unconformity and various degrees of secondary alteration of volcanic-sedimentary rocks have been established in the Okhotsk-Chukotka Volcanic Belt, and this was apparently caused by transition of the tectonic setting from suprasubduction to a transform margin with local extension.

4D petroleum system model of the Mississippian System in the Anadarko Basin Province, Oklahoma, Kansas, Texas, and Colorado, U.S.A.

USGS Publications Warehouse

Higley, Debra K.

2013-01-01

The Upper Devonian and Lower Mississippian Woodford Shale is an important petroleum source rock for Mississippian reservoirs in the Anadarko Basin Province of Oklahoma, Kansas, Texas, and Colorado, based on results from a 4D petroleum system model of the basin. The Woodford Shale underlies Mississippian strata over most of the Anadarko Basin portions of Oklahoma and northeastern Texas. The Kansas and Colorado portions of the province are almost entirely thermally immature for oil generation from the Woodford Shale or potential Mississippian source rocks, based mainly on measured vitrinite reflectance and modeled thermal maturation. Thermal maturities of the Woodford Shale range from mature for oil to overmature for gas generation at present-day depths of about 5,000 to 20,000 ft. Oil generation began at burial depths of about 6,000 to 6,500 ft. Modeled onset of Woodford Shale oil generation was about 330 million years ago (Ma); peak oil generation was from 300 to 220 Ma.Mississippian production, including horizontal wells of the informal Mississippi limestone, is concentrated within and north of the Sooner Trend area in the northeast Oklahoma portion of the basin. This large pod of oil and gas production is within the area modeled as thermally mature for oil generation from the Woodford Shale. The southern boundary of the trend approximates the 99% transformation ratio of the Woodford Shale, which marks the end of oil generation. Because most of the Sooner Trend area is thermally mature for oil generation from the Woodford Shale, the trend probably includes short- and longer-distance vertical and lateral migration. The Woodford Shale is absent in the Mocane-Laverne Field area of the eastern Oklahoma panhandle; because of this, associated oil migrated from the south into the field. If the Springer Formation or deeper Mississippian strata generated oil, then the southern field area is within the oil window for associated petroleum source rocks. Mississippian fields along the western boundary of the study area were supplied by oil that flowed northward from the Panhandle Field area and westward from the deep basin.

Some aspects of lithological and exogenic control of sandstone morphology, the Świętokrzyskie (Holy Cross) Mts. case study, Poland

NASA Astrophysics Data System (ADS)

Urban, Jan; Górnik, Marek

2017-10-01

Various morphologies of cliffs built of different quartzose rocks in the Świętokrzyskie (Holy Cross) Mts. (upland region, central Poland) - from Cambrian quartzites and Devonian quartzitic sandstones to Triassic and Jurassic porous sandstones - were described in order to examine the constraints of their lithological and spatial occurrence. The quantitative study of the occurrence of these morphologies on cliffs makes it possible to distinguish two principal groups of morphologies: angular relief produced by rock splitting (crumbling), typical of quartzites indurated in silica and of open porosity less than 1.5%, and morphologies developed due to granular disintegration and exfoliation of sandstones of open porosity higher than 1.5%. Among the relief types of this second group, morphology reflecting sedimentary and diagenetic structures as well as smooth surfaces are the most common and are referred to sandstones of a wide range of porosity, whereas honeycombs and surfaces suffering fast granular decay and scaling are characteristic of rocks of specific porosity (respectively: 5-8% and 3.5-8%). The occurrence of honeycombs on rock surfaces is also conditioned by exogenic factors: sun, wind and rain, since this morphology tends to occur on cliffs with aspects ranging from south-east, through south, to west-north-west.

Hydrocarbon potential of Morocco

DOE Office of Scientific and Technical Information (OSTI.GOV)

Achnin, H.; Nairn, A.E.M.

1988-08-01

Morocco lies at the junction of the African and Eurasian plates and carries a record of their movements since the end of the Precambrian. Four structural regions with basins and troughs can be identified: Saharan (Tarfaya-Ayoun and Tindouf basins); Anti-Atlas (Souss and Ouarzazate troughs and Boudnib basin); the Essaouria, Doukkala, Tadla, Missour, High Plateau, and Guercif basins; and Meseta and Rif (Rharb and Pre-Rif basins). The targets in the Tindouf basin are Paleozoic, Cambrian, Ordovician (clastics), Devonian (limestones), and Carboniferous reservoirs sourced primarily by Silurian shales. In the remaining basins, excluding the Rharb, the reservoirs are Triassic detritals, limestones atmore » the base of the Lias and Dogger, Malm detritals, and sandy horizons in the Cretaceous. In addition to the Silurian, potential source rocks include the Carboniferous and Permo-Carboniferous shales and clays; Jurassic shales, marls, and carbonates; and Cretaceous clays. In the Rharb basin, the objectives are sand lenses within the Miocene marls. The maturation level of the organic matter generally corresponds to oil and gas. The traps are stratigraphic (lenses and reefs) and structural (horsts and folds). The seals in the pre-Jurassic rocks are shales and evaporites; in the younger rocks, shales and marl. Hydrocarbon accumulations have been found in Paleozoic, Triassic, Liassic, Malm, and Miocene rocks.« less

Geologic map of the Bateman Spring Quadrangle, Lander County, Nevada

USGS Publications Warehouse

Ramelli, Alan R.; Wrucke, Chester T.; House, P. Kyle

2017-01-01

This 1:24,000-scale geologic map of the Bateman Spring 7.5-minute quadrangle in Lander County, Nevada contains descriptions of 24 geologic units and one cross section. Accompanying text includes full unit descriptions and references. This quadrangle includes lower Paleozoic siliciclastic sedimentary rocks of the Roberts Mountain allochthon, Miocene intrusive dikes, alluvial deposits of the northern Shoshone Range piedmont, and riverine deposits of the Reese and Humboldt rivers.Significant findings include: refined age estimates for the Ordovician-Cambrian Valmy Formation and Devonian Slaven Chert, based on new fossil information; and detailed mapping of late Quaternary fault traces along the Shoshone Range fault system.

Stratigraphic setting and mineralogy of the Arctic volcanogenic massive sulfide prospect, Ambler district, Alaska.

USGS Publications Warehouse

Schmidt, J.M.

1986-01-01

The Arctic prospect, south central Brooks Range, is among the 30 largest of 508 volcanic-hosted massive sulphide deposits in the world. The massive sulphide lenses are interlayered with graphitic schist between metamorphosed rhyolite porphyries in Middle Devonian to early Mississippian metamorphosed volcanic, volcaniclastic and sedimentary rocks. Hydrothermal alteration is of three types: chloritic, phyllic s.l., and pyrite-phengite, each type strata-distinctively and respectively below, in, and above the sulphides. Maximum alteration conforms with metal zoning in the sulfides to suggest predominantly northwestward dispersal from a linear vent area in the elongate basin containing the deposit.-G.J.N.

Petroleum geology and resources of the North Ustyurt Basin, Kazakhstan and Uzbekistan

USGS Publications Warehouse

Ulmishek, Gregory F.

2001-01-01

The triangular-shaped North Ustyurt basin is located between the Caspian Sea and the Aral Lake in Kazakhstan and Uzbekistan and extends offshore both on the west and east. Along all its sides, the basin is bounded by the late Paleozoic and Triassic foldbelts that are partially overlain by Jurassic and younger rocks. The basin formed on a cratonic microcontinental block that was accreted northward to the Russian craton in Visean or Early Permian time. Continental collision and deformation along the southern and eastern basin margins occurred in Early Permian time. In Late Triassic time, the basin was subjected to strong compression that resulted in intrabasinal thrusting and faulting. Jurassic-Tertiary, mostly clastic rocks several hundred meters to 5 km thick overlie an older sequence of Devonian?Middle Carboniferous carbonates, Upper Precambrian massifs and deformed Caledonian foldbelts. The Carboniferous?Lower Permian clastics, carbonates, and volca-basement is at depths from 5.5 km on the highest uplifts to 11 nics, and Upper Permian?Triassic continental clastic rocks, pri-km in the deepest depressions. marily red beds. Paleogeographic conditions of sedimentation, Three total petroleum systems are identified in the basin. the distribution of rock types, and the thicknesses of pre-Triassic Combined volumes of discovered hydrocarbons in these sysstratigraphic units are poorly known because the rocks have been tems are nearly 2.4 billion barrels of oil and 2.4 trillion cubic penetrated by only a few wells in the western and eastern basin feet of gas. Almost all of the oil reserves are in the Buzachi Arch areas. The basement probably is heterogeneous; it includes and Surrounding Areas Composite Total Petroleum System in 2 Petroleum Geology, Resources?North Ustyurt Basin, Kazakhstan and Uzbekistan the western part of the basin. Oil pools are in shallow Jurassic and Neocomian sandstone reservoirs, in structural traps. Source rocks are absent in the total petroleum system area; therefore, the oil could have migrated from the adjacent North Caspian basin. The North Ustyurt Jurassic Total Petroleum System encompasses the rest of the basin area and includes Jurassic and younger rocks. Several oil and gas fields have been discovered in this total petroleum system. Oil accumulations are in Jurassic clastic reservoirs, in structural traps at depths of 2.5?3 km. Source rocks for the oil are lacustrine beds and coals in the continental Jurassic sequence. Gas fields are in shallow Eocene sandstones in the northern part of the total petroleum system. The origin of the gas is unknown. The North Ustyurt Paleozoic Total Petroleum System stratigraphically underlies the North Ustyurt Jurassic system and occupies the same geographic area. The total petroleum system is almost unexplored. Two commercial flows of gas and several oil and gas shows have been tested in Carboniferous shelf carbonates in the eastern part of the total petroleum system. Source rocks probably are adjacent Carboniferous deep-water facies interpreted from seismic data. The western extent of the total petroleum system is conjectural. Almost all exploration drilling in the North Ustyurt basin has been limited to Jurassic and younger targets. The underlying Paleozoic-Triassic sequence is poorly known and completely unexplored. No wells have been drilled in offshore parts of the basin. Each of three total petroleum systems was assessed as a single assessment unit. Undiscovered resources of the basin are small to moderate. Most of the undiscovered oil probably will be discovered in Jurassic and Neocomian stratigraphic and structural traps on the Buzachi arch, especially on its undrilled off-shore extension. Most of the gas discoveries are expected to be in Paleozoic carbonate reservoirs in the eastern part of the basin.

Record of the Late Devonian Hangenberg global positive carbon-isotope excursion in an epeiric sea setting: Carbonate production, organic-carbon burial and paleoceanography during the late Famennian

USGS Publications Warehouse

Cramer, Bradley D.; Saltzman, Matthew R.; Day, J.E.; Witzke, B.J.

2008-01-01

Latest Famennian marine carbonates from the mid-continent of North America were examined to investigate the Late Devonian (very late Famennian) Hangenberg positive carbon-isotope (??13 Ccarb) excursion. This global shift in the ?? 13C of marine waters began during the late Famennian Hangenberg Extinction Event that occurred during the Middle Siphonodella praesulcata conodont zone. The post-extinction recovery interval spans the Upper S. praesulcata Zone immediately below the Devonian-Carboniferous boundary. Positive excursions in ?? 13 Ccarb are often attributed to the widespread deposition of organic-rich black shales in epeiric sea settings. The Hangenberg ??13 Ccarb excursion documented in the Louisiana Limestone in this study shows the opposite trend, with peak ??13 Ccarb values corresponding to carbonate production in the U.S. mid-continent during the highstand phase of the very late Famennian post-glacial sea level rise. Our data indicate that the interval of widespread black shale deposition (Hangenberg Black Shale) predates the peak isotope values of the Hangenberg ??13 Ccarb excursion and that peak values of the Hangenberg excursion in Missouri are not coincident with and cannot be accounted for by high Corg burial in epeiric seas. We suggest instead that sequestration and burial of Corg in the deep oceans drove the peak interval of the ??13Ccarb excursion, as a result of a change in the site of deep water formation to low-latitude epeiric seas as the global climate shifted between cold and warm states.

Thermal maturity map of Devonian shale in the Illinois, Michigan, and Appalachian basins of North America

USGS Publications Warehouse

East, Joseph A.; Swezey, Christopher S.; Repetski, John E.; Hayba, Daniel O.

2012-01-01

Much of the oil and gas in the Illinois, Michigan, and Appalachian basins of eastern North America is thought to be derived from Devonian shale that is within these basins (for example, Milici and others, 2003; Swezey, 2002, 2008, 2009; Swezey and others, 2005, 2007). As the Devonian strata were buried by younger sediments, the Devonian shale was subjected to great temperature and pressure, and in some areas the shale crossed a thermal maturity threshold and began to generate oil. With increasing burial (increasing temperature and pressure), some of this oil-generating shale crossed another thermal maturity threshold and began to generate natural gas. Knowledge of the thermal maturity of the Devonian shale is therefore useful for predicting the occurrence and the spatial distribution of oil and gas within these three basins. This publication presents a thermal maturity map of Devonian shale in the Illinois, Michigan, and Appalachian basins. The map shows outlines of the three basins (dashed black lines) and an outline of Devonian shale (solid black lines). The basin outlines are compiled from Thomas and others (1989) and Swezey (2008, 2009). The outline of Devonian shale is a compilation from Freeman (1978), Thomas and others (1989), de Witt and others (1993), Dart (1995), Nicholson and others (2004), Dicken and others (2005a,b), and Stoeser and others (2005).

Earth’s oldest ‘Bobbit worm’ – gigantism in a Devonian eunicidan polychaete

PubMed Central

Eriksson, Mats E.; Parry, Luke A.; Rudkin, David M.

2017-01-01

Whilst the fossil record of polychaete worms extends to the early Cambrian, much data on this group derive from microfossils known as scolecodonts. These are sclerotized jaw elements, which generally range from 0.1–2 mm in size, and which, in contrast to the soft-body anatomy, have good preservation potential and a continuous fossil record. Here we describe a new eunicidan polychaete, Websteroprion armstrongi gen. et sp. nov., based primarily on monospecific bedding plane assemblages from the Lower-Middle Devonian Kwataboahegan Formation of Ontario, Canada. The specimens are preserved mainly as three-dimensional moulds in the calcareous host rock, with only parts of the original sclerotized jaw walls occasionally present. This new taxon has a unique morphology and is characterized by an unexpected combination of features seen in several different Palaeozoic polychaete families. Websteroprion armstrongi was a raptorial feeder and possessed the largest jaws recorded in polychaetes from the fossil record, with maxillae reaching over one centimetre in length. Total body length of the species is estimated to have reached over one metre, which is comparable to that of extant ‘giant eunicid’ species colloquially referred to as ‘Bobbit worms’. This demonstrates that polychaete gigantism was already a phenomenon in the Palaeozoic, some 400 million years ago. PMID:28220886

Tectono-thermal Evolution of the Lower Paleozoic Petroleum Source Rocks in the Southern Lublin Trough: Implications for Shale Gas Exploration from Maturity Modelling

NASA Astrophysics Data System (ADS)

Botor, Dariusz

2018-03-01

The Lower Paleozoic basins of eastern Poland have recently been the focus of intensive exploration for shale gas. In the Lublin Basin potential unconventional play is related to Lower Silurian source rocks. In order to assess petroleum charge history of these shale gas reservoirs, 1-D maturity modeling has been performed. In the Łopiennik IG-1 well, which is the only well that penetrated Lower Paleozoic strata in the study area, the uniform vitrinite reflectance values within the Paleozoic section are interpreted as being mainly the result of higher heat flow in the Late Carboniferous to Early Permian times and 3500 m thick overburden eroded due to the Variscan inversion. Moreover, our model has been supported by zircon helium and apatite fission track dating. The Lower Paleozoic strata in the study area reached maximum temperature in the Late Carboniferous time. Accomplished tectono-thermal model allowed establishing that petroleum generation in the Lower Silurian source rocks developed mainly in the Devonian - Carboniferous period. Whereas, during Mesozoic burial, hydrocarbon generation processes did not develop again. This has negative influence on potential durability of shale gas reservoirs.

The Santa Cruz - Tarija Province of Central South America: Los Monos - Machareti(!) Petroleum System

USGS Publications Warehouse

Lindquist, Sandra J.

1999-01-01

The Los Monos - Machareti(!) total petroleum system is in the Santa Cruz - Tarija Province of Bolivia, Argentina and Paraguay. Province history is that of a Paleozoic, intracratonic, siliciclastic rift basin that evolved into a Miocene (Andean) foreland fold and thrust belt. Existing fields are typified by alternating reservoir and seal rocks in post-Ordovician sandstones and shales on anticlines. Thick Devonian and Silurian shale source rocks, depositionally and erosionally confined to this province, at a minimum have generated 4.1 BBOE known ultimate recoverable reserves (as of 1995, 77% gas, 15% condensate, 8% oil) into dominantly Carboniferous reservoirs with average 20% porosity and 156 md permeability. Major detachment surfaces within the source rocks contributed to the thin-skinned and laterally continuous nature of the deformation. Tertiary foreland burial adequate for significant source maturation coincided with the formation of compressional traps. Further hydrocarbon discovery in the fold and thrust belt is expected. In the foreland basin, higher thermal gradients and variable burial history - combined with the presence of unconformity and onlap wedges - create potential there for stratigraphic traps and pre-Andean, block-fault and forced-fold traps.

Novel reef fabrics from the Devonian Canning Basin, Western Australia

NASA Astrophysics Data System (ADS)

Wood, Rachel

1998-11-01

Large cement-filled cavities (0.2 to 1.5 m wide) are well developed in slope-margin sediments of the spectacular Upper Devonian (Frasnian) reefs of the Canning Basin, Western Australia, where they account for up to 50% of the primary porosity. These are here interpreted as primary reef framework cavities that formed beneath a variety of domal, tabular or laminar stromatoporoid sponges. Of particular note are those created by unusual, very thin (2 to 8 mm), laminar stromatoporoids (mainly Stachyodes australe), that formed arching, hollow domes up to 0.3 m in height and 1.5 m in diameter over the sediment surface to enclose flat-based cavities. The free undersurface of these stromatoporoids often supported a hitherto unrecognised cryptic community, dominated by pendent growth of the putative calcified cyanobacterium Renalcis, with rare intergrown lithistid sponges and spiny atrypid brachiopods. The uneven growth surface of the cryptos imparts an irregular, stromatactis-like texture to the upper surface of the remaining cavity, which is filled by early marine, finely banded, fibrous cements (mainly radiaxial calcite) interbedded with often multiple generations of geopetal sediment containing peloids and ostracod debris. This ecology yields the tabular stromatoporoid- Renalcis fabric described ubiquitously from the Canning Basin reef complex. Such unusual reef fabrics are a consequence of the ecology of shallow marine mid-Palaeozoic reefs which were quite unlike that of modern coral reefs. The frequent preservation of relatively delicate, in situ communities was due to (1) rapid and pervasive early cementation, (2) growth under non-energetic conditions, and (3) the relative insignificance of bioeroders associated with reefs at this time.

Geology and hydrology for environmental planning in Washtenaw County, Michigan

USGS Publications Warehouse

Fleck, William B.

1980-01-01

Washteaw County is underlain by glacial deposits that range in thickness from about 50 feet to about 450 feet. Underlying the glacial deposits are sedimentary rocks of Mississippian and Devonian age. The youngest of these rocks are the sandstones of the Marshall Formation in the western part of the county;  the oldest are the limestones of the Detroit River Group in the southeast corner.Sand and gravel deposits in some places in the county may yield more than 500 gallons per minute of water. Approximately 50 percent of the wells tapping the Marshall Formation, the most reliable bedrock aquifer, can yield as much as 60 gallons per minute.Washtenaw County has sand and gravel deposits that are more than 50 feet thick. The deposits are mined in several areas and are of economic importance. In addition, there may be potential for peat production in the western part of the county and for clay production in the eastern part.

A field trip guidebook to the type localities of Marland Billings' 1935 Paleozoic bedrock stratigraphy near Littleton, New Hampshire

USGS Publications Warehouse

Rankin, Douglas W.; Rankin, Mary B.

2014-01-01

Marland Billings' classic paper published in 1937 in the Geological Society of America Bulletin established a succession of six stratigraphic units in rocks of low metamorphic grade near Littleton, New Hampshire. The two youngest units are fossiliferous in the area, with ages established at the time as “middle” Silurian and Early Devonian. Billings and students mapped the same stratigraphic section in adjacent areas of progressively higher regional metamorphic grade. This work laid the foundation upon which a major part of subsequent work in New England has been directly or indirectly built. This guidebook was written for a field trip held in March 2013 to visit roadcuts that are as close as possible in March to the type localities or areas of Billings’ six-fold stratigraphic succession. Ten stops are in rocks of chlorite grade of Acadian(?) metamorphism; the final stop visits amphibolite of the Ammonoosuc Volcanics. Fieldwork by the authors over the past 20 years confirms Billings’ broad conclusions.

Well-Production Data and Gas-Reservoir Heterogeneity -- Reserve Growth Applications

USGS Publications Warehouse

Dyman, Thaddeus S.; Schmoker, James W.

2003-01-01

Oil and gas well production parameters, including peakmonthly production (PMP), peak-consecutive-twelve month production (PYP), and cumulative production (CP), are tested as tools to quantify and understand the heterogeneity of reservoirs in fields where current monthly production is 10 percent or less of PMP. Variation coefficients, defined as VC= (F5-F95)/F50, where F5, F95, and F50 are the 5th, 95th, and 50th (median) fractiles of a probability distribution, are calculated for peak and cumulative production and examined with respect to internal consistency, type of production parameter, conventional versus unconventional accumulations, and reservoir depth. Well-production data for this study were compiled for 69 oil and gas fields in the Lower Pennsylvanian Morrow Formation of the Anadarko Basin, Oklahoma. Of these, 47 fields represent production from marine clastic facies. The Morrow data were supplemented by data from the Upper Cambrian and Lower Ordovician Arbuckle Group, Middle Ordovician Simpson Group, Middle Pennsylvanian Atoka Formation, and Silurian and Lower Devonian Hunton Group of the Anadarko Basin, one large gas field in Upper Cretaceous reservoirs of north-central Montana (Bowdoin field), and three areas of the Upper Devonian and Lower Mississippian Bakken Formation continuous-type (unconventional) oil accumulation in the Williston Basin, North Dakota and Montana. Production parameters (PMP, PYP, and CP) measure the net result of complex geologic, engineering, and economic processes. Our fundamental hypothesis is that well-production data provide information about subsurface heterogeneity in older fields that would be impossible to obtain using geologic techniques with smaller measurement scales such as petrographic, core, and well-log analysis. Results such as these indicate that quantitative measures of production rates and production volumes of wells, expressed as dimensionless variation coefficients, are potentially valuable tools for documenting reservoir heterogeneity in older fields for field redevelopment and risk analysis.

S-type granite from the Gongpoquan arc in the Beishan Orogenic Collage, southern Altaids: Implications for the tectonic transition

NASA Astrophysics Data System (ADS)

Wang, Xinyu; Yuan, Chao; Zhang, Yunying; Long, Xiaoping; Sun, Min; Wang, Lixing; Soldner, Jeremie; Lin, Zhengfan

2018-03-01

Voluminous Paleozoic intrusions occur in the Beishan Orogenic Collage (BOC) and their genesis and tectonic background are important to reconstruct the accretion-collision processes in the southernmost Altaids. Paleozoic is an important period for arc development in the BOC, where the Gongpoquan and Huaniushan arcs are located. There are two pulses of magmatism in the Huaniushan and Gongpoquan arcs, i.e., the ca. 470-423 Ma I-type and ca. 424-395 Ma S- and A-type granitoids. In this study, we focus on two peraluminous granitic plutons in the Gongpoquan arc, i.e., the Baitoushan muscovite granite and Haergen two-mica granite, aiming at unraveling their petrogenesis and tectonic background. Zircon LA-ICP-MS U-Pb dating yields emplacement ages of ca. 409-395 Ma and ca. 409 Ma for the Baitoushan and Haergen plutons, respectively. Both the granitic plutons are strongly peraluminous with A/CNK ratios of 1.10-1.20, indicative of S-type affinities. The rocks are characterized by high SiO2 and K2O contents with high CaO/Na2O ratios. Moreover, the rocks possess low MgO contents, Rb/Sr and Rb/Ba ratios, together with their relatively high initial 87Sr/86Sr ratios (0.7139-0.7152) and less radiogenic εNd(t) values (-3.15 to -5.17), implying a clay-poor and plagioclase-rich crustal source. Compared with earlier pulse of arc-related magmatism (ca. 470-423 Ma), the latter pulse of magmatism (ca. 424-395 Ma) consists mainly of "normal granite" characterized by higher SiO2 (>66%) and K2O contents, weaker fractionated REE patterns and lower δEu values, and gabbroic to dioritic intrusions are only sporadic. Moreover, the granitoids of the latter pulse show variable but more crust-like Sr-Nd isotopic compositions ((87Sr/86Sr)0 = 0.7038-0.7327; εNd(t) = -6.70 to +0.33) than the earlier ones ((87Sr/86Sr)0 = 0.7024-0.7080; εNd(t) = -2.56 to +8.86), indicating that the Early Devonian (ca. 424-395 Ma) experienced extensive crustal melting with minor involvement of mantle materials. Considering Early Devonian geological evidence, the transition from I- to S- and A-type magmatism probably reflects the Early Devonian amalgamation between the Gongpoquan and Huaniushan arcs, which caused not only regional unconformity and strong deformation-metamorphism, but also extensive melting of the accreted crustal materials in the BOC.

Middle to Late Devonian-Carboniferous collapse basins on the Finnmark Platform and in the southwesternmost Nordkapp basin, SW Barents Sea

NASA Astrophysics Data System (ADS)

Koehl, Jean-Baptiste P.; Bergh, Steffen G.; Henningsen, Tormod; Faleide, Jan Inge

2018-03-01

The SW Barents Sea margin experienced a pulse of extensional deformation in the Middle-Late Devonian through the Carboniferous, after the Caledonian Orogeny terminated. These events marked the initial stages of formation of major offshore basins such as the Hammerfest and Nordkapp basins. We mapped and analyzed three major fault complexes, (i) the Måsøy Fault Complex, (ii) the Rolvsøya fault, and (iii) the Troms-Finnmark Fault Complex. We discuss the formation of the Måsøy Fault Complex as a possible extensional splay of an overall NE-SW-trending, NW-dipping, basement-seated Caledonian shear zone, the Sørøya-Ingøya shear zone, which was partly inverted during the collapse of the Caledonides and accommodated top-NW normal displacement in Middle to Late Devonian-Carboniferous times. The Troms-Finnmark Fault Complex displays a zigzag-shaped pattern of NNE-SSW- and ENE-WSW-trending extensional faults before it terminates to the north as a WNW-ESE-trending, NE-dipping normal fault that separates the southwesternmost Nordkapp basin in the northeast from the western Finnmark Platform and the Gjesvær Low in the southwest. The WNW-ESE-trending, margin-oblique segment of the Troms-Finnmark Fault Complex is considered to represent the offshore prolongation of a major Neoproterozoic fault complex, the Trollfjorden-Komagelva Fault Zone, which is made of WNW-ESE-trending, subvertical faults that crop out on the island of Magerøya in NW Finnmark. Our results suggest that the Trollfjorden-Komagelva Fault Zone dies out to the northwest before reaching the western Finnmark Platform. We propose an alternative model for the origin of the WNW-ESE-trending segment of the Troms-Finnmark Fault Complex as a possible hard-linked, accommodation cross fault that developed along the Sørøy-Ingøya shear zone. This brittle fault decoupled the western Finnmark Platform from the southwesternmost Nordkapp basin and merged with the Måsøy Fault Complex in Carboniferous times. Seismic data over the Gjesvær Low and southwesternmost Nordkapp basin show that the low-gravity anomaly observed in these areas may result from the presence of Middle to Upper Devonian sedimentary units resembling those in Middle Devonian, spoon-shaped, late- to post-orogenic collapse basins in western and mid-Norway. We propose a model for the formation of the southwesternmost Nordkapp basin and its counterpart Devonian basin in the Gjesvær Low by exhumation of narrow, ENE-WSW- to NE-SW-trending basement ridges along a bowed portion of the Sørøya-Ingøya shear zone in the Middle to Late Devonian-early Carboniferous. Exhumation may have involved part of a large-scale metamorphic core complex that potentially included the Lofoten Ridge, the West Troms Basement Complex and the Norsel High. Finally, we argue that the Sørøya-Ingøya shear zone truncated and decapitated the Trollfjorden-Komagelva Fault Zone during the Caledonian Orogeny and that the western continuation of the Trollfjorden-Komagelva Fault Zone was mostly eroded and potentially partly preserved in basement highs in the SW Barents Sea.

Devonian to Carboniferous collision in the Greenland Caledonides: U-Pb zircon and Sm-Nd ages of high-pressure and ultrahigh-pressure metamorphism

NASA Astrophysics Data System (ADS)

Gilotti, Jane A.; Nutman, Allen P.; Brueckner, Hannes K.

2004-10-01

A variety of eclogites from an east-west transect across the North-East Greenland eclogite province have been studied to establish the timing of high pressure (HP) and ultrahigh-pressure (UHP) metamorphism in this northern segment of the Laurentian margin. Garnet + omphacite ± amphibole + whole rock Sm-Nd isochrons from a quartz eclogite, a garnet + omphacite + rutile eclogite and a partially melted zoisite eclogite in the western HP belt are 401±2, 402±9 and 414±18 Ma, respectively. Corresponding sensitive high-resolution ion microprobe (SHRIMP) 206Pb/238U ages of metamorphic zircon in the same samples are 401±7, 414±13, and 393 ±10 Ma. Metamorphic zircon domains were identified using morphology, cathodoluminescence (CL) imaging, U, Th, Th/U and trace element contents. Zircon from the quartz eclogite and the garnet + omphacite + rutile eclogite are typical of eclogite facies zircon with rounded to subhedral shapes, patchy to homogenous CL domains, low U, and very low Th and Th/U. The partially melted eclogite contains euhedral zircons with dark, sector-zoned, higher U, Th and Th/U inherited cores. Three cores give a Paleoproterozoic 207Pb/206Pb age of 1,962±27 Ma, interpreted as the age of the leucogabbroic protolith. CL images of the bright overgrowths show faint oscillatory zoning next to homogenous areas that indicate zircon growth in the presence of a HP melt and later recrystallization. Additional evidence that zircon grew during eclogite facies conditions is the lack of a Eu anomaly in the trace element data for all the samples. These results, combined with additional less precise Sm-Nd ages and our earlier work, point to a Devonian age of HP metamorphism in the western and central portions of the eclogite province. An UHP kyanite eclogite from the eastern part of the transect contains equant metamorphic zircon with homogeneous to patchy zoning in CL and HP inclusions of garnet, omphacite and kyanite. These zircons have slightly higher U, Th and Th/U values than the HP ones, no Eu anomaly, and are thus comparable to UHP zircons in the literature. The 206Pb/238U age of these zircons is 360±5 Ma, much younger than the HP eclogites. The same sample gives a Sm-Nd age of 342±6 Ma. Unlike the HP eclogites, the Sm-Nd age of the UHP rock is ca. 20 Ma younger than the U-Pb zircon age and most likely records slow cooling through the closure temperature, since peak temperatures were in excess of 900°C. Widespread HP metamorphism of both the Laurentian and Baltica continental margins marks the culmination of this continent continent collision in the Devonian. Carboniferous UHP conditions, though localized in the east, suggest a prolonged collisional history rather than a short-lived Scandian orogeny. The traditional Silurian Scandian orogeny should thus be extended through the Devonian.

18 CFR 270.303 - Natural gas produced from Devonian shale.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 18 Conservation of Power and Water Resources 1 2010-04-01 2010-04-01 false Natural gas produced... DETERMINATION PROCEDURES Requirements for Filings With Jurisdictional Agencies § 270.303 Natural gas produced from Devonian shale. A person seeking a determination that natural gas is produced from Devonian shale...

18 CFR 270.303 - Natural gas produced from Devonian shale.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 18 Conservation of Power and Water Resources 1 2011-04-01 2011-04-01 false Natural gas produced... DETERMINATION PROCEDURES Requirements for Filings With Jurisdictional Agencies § 270.303 Natural gas produced from Devonian shale. A person seeking a determination that natural gas is produced from Devonian shale...

U-Pb Geochronology of Devonian Granites in the Meguma Terrane of Nova Scotia, Canada: Evidence for Hotspot Melting of a Neoproterozoic Source.

PubMed

Keppie; Krogh

1999-09-01

U-Pb isotopic analyses of monazite and zircon from six granitic plutons in the Meguma Terrane yield nearly concordant ages of 373+/-3 Ma, interpreted as the time of intrusion. U-Pb analyses of euhedral zircons with thick rims overgrowing cores, which were abraded to remove all or most of the rim, plot on chords between 370+/-3 and 628+/-33 Ma (Larrys River and Halfway Cove plutons), 372+/-3 and approximately 660 Ma (Shelburne pluton), and 373+/-2 and approximately 732 Ma (Barrington Passage pluton). The upper intercepts are interpreted as the age of magma source, correlatives of which are present in the Avalon Composite Terrane to the north. This basement may be either in depositional or tectonic contact with the overlying Cambro-Ordovician Meguma Group. Other zircons in the granites are generally irregular-euhedral with thin rims, and most U-Pb isotopic analyses fall between two chords from 373-2040 and 373-2300 Ma, with a few lying outside this field. These zircons are probably derived from the country rock (Goldenville Formation), which a previous study has shown contains detrital zircons with concordant U-Pb ages of 3000, 2000, and 600 Ma, and numerous intermediate discordant ages. These new ages, along with published data, document a relatively short (5-10 m.yr.) but voluminous period of magmatism. This age is approximately synchronous with intrusion of mafic rocks and lamprophyre dikes and regional low-pressure metamorphism and was followed by rapid denudation of 5-12 km. These observations may be interpreted in terms of shallowly dipping subduction and overriding of a mantle plume that eventually penetrates through the subducting plate to melt the overriding continental plate. Subsequent northward migration of the plume could explain both the approximately 360 Ma magmatism in the Cobequid Highlands (Avalon Composite Terrane) and the mid-Carboniferous plume-related intrusions around the Magdalen Basin.

Fold-structure analysis of paleozoic rocks in the Variscan Harz Mountains (Lautenthal, Central Germany) based on laserscanning and 3D modelling

NASA Astrophysics Data System (ADS)

Wagner, Bianca; Leiss, Bernd; Stöpler, Ralf; Zahnow, Fabian

2017-04-01

Folded paleozoic sedimentary rocks of Upper Devonian to Lower Carboniferous age are very well exposed in the abandoned chert quarry of Lautenthal in the western Harz Mountains. The outcrop represents typical structures of the Rhenohercynian thrust and fold belt of the Variscan orogen and therefore allows quantitative studies for the understanding of e.g. fold mechanisms and the amount of shortening. The sequence is composed of alternating beds of cherts, shales and tuffites, which show varying thicknesses, undulating and thinning out of certain layers. Irregularly occurring lenses of greywackes are interpreted as sedimentary intrusions. The compressive deformation style is expressed by different similar and parallel fold structures at varying scales as well as small-scale reverse faults and triangle structures. An accurate mapping of the outcrop in the classical way is very challenging due to distant and unconnected outcrop parts with differing elevations and orientations. Furthermore, the visibility is limited because of nearby trees, diffuse vegetation cover and no available total view. Therefore, we used a FARO 120 3D laserscanner and Trimble GNSS device to generate a referenced and drawn to scale point cloud of the complete quarry. Based on the point cloud a geometric 3D model of prominent horizons and structural features of various sizes was constructed. Thereafter, we analyzed the structures in matters of orientation and deformation mechanisms. Finally, we applied a retrodeformation algorithm on the model to restore the original sedimentary sequence and to calculate shortening including the amount of pressure solution. Only digital mapping allows such a time-saving, accurate and especially complete 3D survey of this excellent study object. We demonstrated that such 3D-models enable spatial correlations with other complex structures cropping out in the area. Moreover, we confirmed that a structural upscaling to the 100 to 1000 m scale is much easier and much more instructive than it could have been done in the classical way.

Very early Archean crustal-accretion complexes preserved in the North Atlantic craton

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nutman, A.P.; Collerson, K.D.

1991-08-01

The North Atlantic craton contains very early Archean supracrustal rocks, orthogneisses, and massive ultramafic rocks. Most units of supracrustal rocks are dominated by mafic volcanic rocks, layered gabbros, and banded iron formations, bust some also contain abundant felsic volcanic-sedimentary rocks, quartzites, and marbles. Some quartzites contain detrital zircons derived from rocks identical in age to felsic volcanic-sedimentary rocks in these sequences (ca. 3800 Ma) and also from older (ca. 3850 Ma) sources. The presence of the ca. 3850 Ma detrital zircons suggests that the supracrustal units containing them were deposited on, or close to, ca. 3850 Ma sialic crust. Themore » massive ultramafic rocks have chemical affinities to upper mantle rocks. The voluminous suites of tonalitic gneisses are dominated by 3700-3730 Ma bodies that intrude the supracrustal sequences, but they also locally contain components with ages between 3820 and 3920 Ma. The diverse supracrustal units, upper mantle rocks, and {ge} 3820 Ma components in the gneisses were tectonically interleaved in very early Archean convergent plate boundaries, giving rise to accretion complexes. In the period 3700-3730 Ma, voluminous tonalitic magmas produced by partial melting of predominantly mafic rocks in the base of the accretion complexes were emplaced at higher levels, forming juvenile continental crust and leaving behind a refractory lower crustal to upper mantle substrate.« less

A late Frasnian (Late Devonian) radiolarian, sponge spicule, and conodont fauna from the Slaven Chert, northern Shoshone Range, Roberts Mountains allochthon, Nevada

USGS Publications Warehouse

Boundy-Sanders, S. Q.; Sandberg, C.A.; Murchey, B.L.; Harris, A.G.

1999-01-01

Co-occuring conodonts, radiolarians, and sponge spicules from the type locality of the Slaven Chert, northern Shoshone Range, Nevada, indicate that the radiolarian and sponge spicule assemblage described herein correlates with the Late rhenana conodont Zone (late Frasnian). The moderately well preserved radiolarians are the first Frasnian-age fauna described from the Western Hemisphere. They include spumellarians, Ceratoikiscum, and Paleoscenidium, and a radiolarian which we have assigned to a new genus, Durahelenifore Boundy-Sanders and Murchey, with its type species, Durahelenifore robustum Boundy-Sanders and Murchey. Sponge spicules include umbellate microscleres of the Subclass Amphidiscophora, Order Hemidiscosa, previously documented only in Pennsylvanian and younger rocks.

Origin of the Sudbury Complex by meteoritic impact: Neodymium isotopic evidence

USGS Publications Warehouse

Faggart, B.E.; Basu, A.R.; Tatsumoto, M.

1985-01-01

Samarium-neodymium isotopic data on whole rocks and minerals of the Sudbury Complex in Canada gave an igneous crystallization age of 1840 ?? 21 ?? 106 years. The initial epsilon neodymium values for 15 whole rocks are similar to those for average upper continental crust, falling on the crustal trend of neodymium isotopic evolution as defined by shales. The rare earth element concentration patterns of Sudbury rocks are also similar to upper crustal averages. These data suggest that the Sudbury Complex formed from melts generated in the upper crust and are consistent with a meteoritic impact.

Chronology of paleozoic metamorphism and deformation in the Blue Ridge thrust complex, North Carolina and Tennessee

DOE Office of Scientific and Technical Information (OSTI.GOV)

Goldberg, S.A.; Dallmeyer, R.D.

1997-05-01

The Blue Ridge province in northwestern North Carolina and northeastern Tennessee records a multiphase collisional and accretionary history from the Mesoproterozoic through the Paleozoic. To constrain the tectonothermal evolution in this region, radiometric ages have been determined for 23 regionally metamorphosed amphibolites, granitic gneisses, and pelitic schists and from mylonites along shear zones that bound thrust sheets and within an internal shear zone. The garnet ages from the Pumpkin Patch a thrust sheet (458, 455, and 451 Ma) are similar to those from the structurally overlying Spruce Pine thrust sheet (460, 456, 455, and 450 Ma). Both thrust sheets exhibitmore » similar upper amphibolite-facies conditions. Because of the high closure temperature for garnet, the garnet ages are interpreted to date growth at or near the peak of Taconic metamorphism. Devonian metamorphic ages are recognized in the Spruce Pine thrust sheet, where Sm-Nd and Rb-Sr garnet ages of 386 and 393 Ma and mineral isochron ages of 397 {+-} 14 and 375 {+-} 27 Ma are preserved. Hornblendes record similar {sup 40}Ar/{sup 39}Ar, Sm-Nd, and Rb-Sr ages of 398 to 379 Ma. Devonian {sup 40}Ar/{sup 39}Ar hornblende ages are also recorded in the structurally lower Pumpkin Patch thrust sheet. The Devonian mineral ages are interpreted to date a discrete tectonothermal event, as opposed to uplift and slow cooling from an Ordovician metamorphic event. The Mississippian mylonitization is interpreted to represent thrusting and initial assembly of crystalline sheets associated with the Alleghanian orogeny. The composite thrust stack of the Blue Ridge complex was subsequently thrust northwestward along the Linville Falls fault during middle Alleghanian orogeny (about 300 Ma).« less

Deep resistivity structure of Yucca Flat, Nevada Test Site, Nevada

USGS Publications Warehouse

Asch, Theodore H.; Rodriguez, Brian D.; Sampson, Jay A.; Wallin, Erin L.; Williams, Jackie M.

2006-01-01

The Department of Energy (DOE) and the National Nuclear Security Administration (NNSA) at their Nevada Site Office are addressing groundwater contamination resulting from historical underground nuclear testing through the Environmental Management program and, in particular, the Underground Test Area project. One issue of concern is the nature of the somewhat poorly constrained pre Tertiary geology and its effects on ground-water flow in the area adjacent to a nuclear test. Ground water modelers would like to know more about the hydrostratigraphy and geologic structure to support a hydrostratigraphic framework model that is under development for the Yucca Flat Corrective Action Unit (CAU). During 2003, the U.S. Geological Survey, supported by the DOE and NNSA-NSO, collected and processed data from 51 magnetotelluric (MT) and audio-magnetotelluric (AMT) stations at the Nevada Test Site in and near Yucca Flat to assist in characterizing the pre-Tertiary geology in that area. The primary purpose was to refine the character, thickness, and lateral extent of pre Tertiary confining units. In particular, a major goal has been to define the upper clastic confining unit (late Devonian - Mississippian-age siliciclastic rocks assigned to the Eleana Formation and Chainman Shale) in the Yucca Flat area. The MT and AMT data have been released in separate USGS Open File Reports. The Nevada Test Site magnetotelluric data interpretation presented in this report includes the results of detailed two-dimensional (2 D) resistivity modeling for each profile (including alternative interpretations) and gross inferences on the three dimensional (3 D) character of the geology beneath each station. The character, thickness, and lateral extent of the Chainman Shale and Eleana Formation that comprise the Upper Clastic Confining Unit are generally well determined in the upper 5 km. Inferences can be made regarding the presence of the Lower Clastic Confining Unit at depths below 5 km. Large fault structures such as the CP Thrust fault, the Carpetbag fault, and the Yucca fault that cross Yucca Flat are also discernable as are other smaller faults. The subsurface electrical resistivity distribution and inferred geologic structures determined by this investigation should help constrain the hydrostratigraphic framework model that is under development.

Sedimentology of gas-bearing Devonian shales of the Appalachian Basin

NASA Astrophysics Data System (ADS)

Potter, P. E.; Maynard, J. B.; Pryor, W. A.

1981-01-01

Sedimentology of the Devonian shales and its relationship to gas, oil, and uranium are reported. Information about the gas bearing Devonian shales of the Appalachian Basin is organized in the following sections: paleogeography and basin analysis; lithology and internal stratigraphy; paleontology; mineralogy, petrology, and chemistry; and gas oil, and uranium.

78 FR 79312 - Drawbridge Operation Regulation; Upper Mississippi River, Rock Island, IL

Federal Register 2010, 2011, 2012, 2013, 2014

2013-12-30

...The Coast Guard has issued a temporary deviation from the operating schedule that governs the Rock Island Railroad and Highway Drawbridge across the Upper Mississippi River, mile 482.9, at Rock Island, Illinois. The deviation is necessary to allow the St. Patrick's Day Road Race to cross the bridge. This deviation allows the bridge to be maintained in the closed-to-navigation position for two hours.

Chemostratigraphic and U-Pb geochronologic constraints on carbon cycling across the Silurian-Devonian boundary

NASA Astrophysics Data System (ADS)

Husson, Jon M.; Schoene, Blair; Bluher, Sarah; Maloof, Adam C.

2016-02-01

The Devonian Period hosts extraordinary changes to Earth's biosphere. Land plants began their rise to prominence, with early vascular vegetation beginning its colonization of near-shore environments in the latest Silurian. Across the Silurian-Devonian (Pridoli-Lochkovian) transition, carbon isotope analyses of bulk marine carbonates (δC13carb) from Laurentian and Baltic successions reveal a positive δC13carb shift. Known as the Klonk Event, values reach + 5.8 ‰, making it one of the largest carbon isotope excursions in the Phanerozoic. Assigning rates and durations to these significant events requires a robust, precise Devonian time scale. Here we present 675 micritic matrix and 357 fossil-specific δC13carb analyses from the lower Devonian Helderberg Group of New York and West Virginia that exhibit the very positive δC13carb values observed in other Silurian-Devonian basins. This chemostratigraphic dataset is coupled with 66 ID-TIMS U-Pb dates on single zircons from six ash falls intercalated within Helderberg sediments, including dates on the stratigraphically lowest Devonian ashes yet developed. In this work, we (a) demonstrate that matrix and fossil-specific δC13carb values track one another closely in the Helderberg Group, (b) estimate the Silurian-Devonian boundary age in New York to be 421.3 ± 1.2 Ma (2σ; including decay constant uncertainties), and (c) calculate the time required to evolve from baseline to peak δC13carb values at the onset of the Klonk event to be 1.00 ± 0.25 Myr. Under these constraints, a steady-state perturbation to the global carbon cycle can explain the observed excursion with modern fluxes, as long as DIC concentration in the Devonian ocean remained below ∼2× the modern value. Therefore, potential drivers, such as enhanced burial of organic carbon, need not rely on anomalously high total fluxes of carbon to explain the Klonk Event.

Combined Detrital U/Pb Zircon and 40Ar/39Ar Mica Geoochronology to Test Structural Models for a Devonian Orogenic Collapse Basin in the Norwegian Caledonides

NASA Astrophysics Data System (ADS)

Templeton, J.; Anders, M.; Fossen, H.

2014-12-01

The Hornelen basin is the largest of the Devonian 'Old Red' sandstone basins in Norway, comprising 25 km of alluvial-fluvial deposits which are organized into basin-wide, coarsening-upward megacycles. Hornelen sits with several smaller basins in the hanging wall a major extensional shear zone along which the ultra-high pressure metamorphic core of subducted Baltican crust was rapidly exhumed during the extensional collapse of the Caledonian orogeny. The timing of orogenic collapse corresponds closely to the timing of the basins, which are loosely constrained by sparse trace-fossil assemblages to a mid-Devonian age. Further, the basins are now in brittle fault contact with the underlying mylonitic shear zone and the metamorphic core, implying that they are the upper-crustal expression of large-scale extension and deep-crustal exhumation. Two distinct structural models have been proposed for Hornelen to account for these observations. The strike-slip model juxtaposes different source terranes across the basin-controlling fault and predicts spatially changing provenance within chronostratigraphic units. The supradetachment model links the filling of the basin directly to unroofing of the metamorphic core on a low-angle detachment fault, and predicts basin-wide changes in provenance through time with progressive exhumation of the metamorphic hinterland. We present an extensive new provenance dataset, spanning the Hornelen basin strata through space and time. Detrital zircon U/Pb ages from 18 new samples comprise three distinct populations (1.6, 1.0, and 0.43 Ga) with the Caledonian-aged zircons (ca 0.43 Ga) present mainly along the northern margin of the basin, representing an Upper Allochthon source not found on the southern or eastern margins of the basin. Juxtaposition of different source terranes across the basin supports the strike-slip model. 40Ar/39Ar detrital white mica from the same sample set documents a younging of the dominant age peak from 432 Ma in the oldest sediments to 401 Ma in the youngest units, but does not document any difference between northern and southern mica sources. This trend supports the supradetachment model, but may also be explained by passive, isostatically-driven erosional unroofing of the overthickened orogenic crust.

Cerro de Pasco and other massive sulfide deposits of central Peru

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cheney, E.S.

1985-01-01

The famous Cerro de Pasco Pb-Zn-Ag deposit historically has been considered to be hydrothermally derived from an adjacent Tertiary volcanic vent. However, texturally massive pyrite-chert and pyrite-sphalerite-galena in the deposit have the same strike and cross folds as the adjacent pre-Tertiary strata. Both the deposit and the strata are cut by one of the large Longitudinal Faults. Both dikes and pyrite-enargite veins associated with the vent cut the massive sulfides; fragments of massive pyrite occur in the vent. A few examples of laminated pyrite and chert, banded pyrite and chert, banded pyrite and sphalerite, and banded pyrite, sphalerite, and galenamore » are preserved in the massive sulfide portion of the deposit. The deposit has the composition and zoning patterns typical of shale-hosted massive sulfides. Cerro de Pasco probably in part of the pelitic Devonian Excelsior formation. The Colquijirca deposit 8 km to the south and the San Cristobal district 110 km to the south likewise have been considered to be Tertiary volcanic hydrothermal deposits. Colquijirca consists of stratigraphically controlled mantos of layered pyrite, chert and tuff in the Tertiary Calera formation. The mantos of the San Cristobal district are along the upper contact of the pyritic, Permian, Catalina felsic volcanic rocks; some ore consists of laminated pyrite and sphalerite. Tertiary plutons are conspicuously absent at San Cristobal, and the ores are brecciated by Tertiary folding.« less

Comparative burial and thermal history of lower Upper Cretaceous strata, Powder River basin, Wyoming

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nuccio, V.F.

1989-03-01

Burial histories were reconstructed for three localities in the Powder River basin (PRB), Wyoming. Thermal maturity of lower Upper Cretaceous source rocks was determined by vitrinite reflectance (R/sub m/) and time-temperature index (TTI) modeling, producing independent estimates for timing of the oil window (0.55-1.35% R/sub m/). In the northwestern PRB, lower Upper Cretaceous rocks were buried to about 12,500 ft and achieved a thermal maturity of 0.50% to 0.56% at maximum burial, 10 Ma, based on measured R/sub m/. TTI modeling suggests a slightly higher thermal maturity, with an R/sub m/ equivalent of approximately 0.75%, placing the source rocks atmore » the beginning of the oil window 30 Ma. In the southwestern PRB, lower Upper Cretaceous rocks have been buried to about 15,000 ft and achieved thermal maturities between 0.66% and 0.75% about 10 Ma based on measured R/sub m/; therefore, petroleum generation may have begun slightly earlier. TTI modeling estimates an R/sub m/ equivalent of 1.10%, placing the beginning of the oil window at 45 Ma. In the northeastern PRB, lower Upper Cretaceous rocks have been buried only to approximately 5500 ft. Measured R/sub m/ and TTI modeling indicate a thermal maturity for lower Upper Cretaceous rocks between 0.45% and 0.50% R/sub m/, too low for petroleum generation. The higher R/sub m/ values determined by the TTI models may be due to overestimation of maximum burial depth and/or paleogeothermal gradients. The two independent maturity indicators do, however, constrain fairly narrowly the onset of petroleum generation.« less

Excess europium content in Precambrian sedimentary rocks and continental evolution

NASA Technical Reports Server (NTRS)

Jakes, P.; Taylor, S. R.

1974-01-01

It is proposed that the europium excess in Precambrian sedimentary rocks, relative to those of younger age, is derived from volcanic rocks of ancient island arcs, which were the source materials for the sediments. Precambrian sedimentary rocks and present-day volcanic rocks of island arcs have similar REE patterns, total REE abundances, and excess Eu, relative to the North American shale composite. The present upper crustal REE pattern, as exemplified by that of sediments, is depleted in Eu, relative to chondrites. This depletion is considered to be a consequence of development of a granodioritic upper crust by partial melting in the lower crust, which selectively retains europium.

The giant Carlin gold province: A protracted interplay of orogenic, basinal, and hydrothermal processes above a lithospheric boundary

USGS Publications Warehouse

Emsbo, P.; Groves, D.I.; Hofstra, A.H.; Bierlein, F.P.

2006-01-01

Northern Nevada hosts the only province that contains multiple world-class Carlin-type gold deposits. The first-order control on the uniqueness of this province is its anomalous far back-arc tectonic setting over the rifted North American paleocontinental margin that separates Precambrian from Phanerozoic subcontinental lithospheric mantle. Globally, most other significant gold provinces form in volcanic arcs and accreted terranes proximal to convergent margins. In northern Nevada, periodic reactivation of basement faults along this margin focused and amplified subsequent geological events. Early basement faults localized Devonian synsedimentary extension and normal faulting. These controlled the geometry of the Devonian sedimentary basin architecture and focused the discharge of basinal brines that deposited syngenetic gold along the basin margins. Inversion of these basins and faults during subsequent contraction produced the complex elongate structural culminations that characterize the anomalous mineral deposit "trends." Subsequently, these features localized repeated episodes of shallow magmatic and hydrothermal activity that also deposited some gold. During a pulse of Eocene extension, these faults focused advection of Carlin-type fluids, which had the opportunity to leach gold from gold-enriched sequences and deposit it in reactive miogeoclinal host rocks below the hydrologic seal at the Roberts Mountain thrust contact. Hence, the vast endowment of the Carlin province resulted from the conjunction of spatially superposed events localized by long-lived basement structures in a highly anomalous tectonic setting, rather than by the sole operation of special magmatic or fluid-related processes. An important indicator of the longevity of this basement control is the superposition of different gold deposit types (e.g., Sedex, porphyry, Carlin-type, epithermal, and hot spring deposits) that formed repeatedly between the Devonian and Miocene time along the trends. Interestingly, the large Cretaceous Alaska-Yukon intrusion-related gold deposits (e.g., Fort Knox) are associated with the northern extension of the same lithospheric margin in the Selwyn basin, which experienced an analogous series of geologic events. ?? Springer-Verlag 2006.

Geochemistry and metamorphism of the Paleozoic metasedimentary basement of the Sierra Madre Oriental, NE Mexico. Possible paths from their depositional environment?

NASA Astrophysics Data System (ADS)

Torres Sanchez, Sonia Alejandra; Augustsson, Carita; Alonso Ramirez Fernandez, Juan; Rafael Barboza Gudiño, Jose; Jenchen, Uwe; Abratis, Michael

2013-04-01

We present depositional conditions and possible protholits for Late Paleozoic metasediment in Mexico that were related to the Laurentia-Gondwana collision in Carboniferous time, during Pangea amalgamation. The study aims to reconstruct the depositional and metamorphic evolution of the Granjeno Schist in northeastern Mexico to get a better control on the timing of subduction and collision processes involving the two supercontinents. Remnants of the Mexican Paleozoic continental configuration are present in the Granjeno Schist, the metamorphic basement of the Sierra Madre Oriental in northeastern Mexico. We apply field mapping, petrographic investigations, whole-rock and mineral chemical analysis, as well as U-Pb zircon dating of both metasedimentary and metavolcanic rocks. Field work and petrographic analysis reveal that the Granjeno Schist comprises intercalations of metamorphic rocks with both sedimentary (psammite, pelite, turbidite, conglomerate, black shale) and volcanic (tuff, lava flows, pillow lava and ultramafic bodies) protoliths. The chlorite geothermometer and the presence of phengite in the metasedimentary units as well as U-Pb zircon ages on metapsammite indicate that the Granjeno Schist was metamorphosed under sub-greenschist to greenschist facies with temperatures ranging from 250-345°C during the Carboniferous time (330±30 Ma). The geochemical composition of the metasedimentary rocks is in accordance with iron shale, wacke and quartz arenite protoliths. Some of the variations can be explained by the grain sizes (e. g., 69-74% and 78-96% SiO2 and 10-15% and 3-9% Al2O3 in metapelite and metapsammite, respectively). Our data suggest that the Granjeno Schist metasedimentary units represent a wide variety of clastic sediments derived from mixed felsic basic sources compositions (e. g., Ti/Nb 200-400). Furthermore, the trace element characteristics point to a continental island arc or active continental margin setting due to e. g., Th/Sc and Zr/Sc ratios of 5-8 and 0.3-0.5, respectively, both for metapelite and metapsammite. The metavolcanic rocks are associated with ocean-island basalt (OIB) or mid-ocean ridge basalts (MORB) due to the immobile trace element ratios Zr/Nb and Y/Nb in the ranges 4.91-8.06 and 0.74-1 for the IOB and >9.2 and >1.25 for the MORB, respectively. Detrital zircon ages for three metapsammites reveal that the major sources mainly are Grenvillian (1250-920 Ma) rocks. Such rocks can be found in the ca. 1 Ga Oaxaquia Complex in NE Mexico (Novillo Gneiss). Hence, short transport can be assumed. Maximum depositional ages are Neoproterozoic, Silurian and Devonian. They indicate that the volcanosedimentary deposition probably took place during Devonian time. Based on our results we suggest a plate-tectonic frame for Oaxaquia which is a modification of accepted models. Most models suggest that Oaxaquia was situated between Laurentia and Gondwana during collision in Carboniferous time. The zircon data indicate that the Granjeno Schist was deposited before the collision of Laurentia and Gondwana. The presence of ocean basalt floor, lava flows and serpentinite lenses intercalated with tuff and active continental margin sedimentary rocks necessitates a near-continental environment, such as a back-arc basin. Hence, we present the first evidence of a subduction zone predating the collision of Laurentia and Gondwana.

Marine and Lacustrine Organic-rich Sedimentary Unit Time Markers: Implications from Rhenium-Osmium Geochronology

NASA Astrophysics Data System (ADS)

Selby, D.

2011-12-01

Geochronology is fundamental to understand the age, rates and durations of Earth processes. This concerned Arthur Holmes who, for much of his career, attempted to define a geological time scale. This is a topic still important to Earth Scientists today, specifically the chronostratigraphy of sedimentary rocks. Here I explore the Re-Os geochronology of marine and lacustrine sedimentary rocks and its application to yield absolute time constraints for stratigraphy. The past decade has seen the pioneering research of Re-Os organic-rich sedimentary rock geochronology blossom into a tool that can now to be used to accurately and precisely determine depositional ages of organic-rich rock units that have experienced up to low grade greenschist metamorphism. This direct dating of sedimentary rocks is critical where volcanic horizons are absent. As a result, this tool has been applied to timescale calibration, basin correlation, formation duration and the timing of key Earth events (e.g., Neoproterozoic glaciations). The application of Re-Os chronometer to the Devonian-Mississippian boundary contained within the Exshaw Formation, Canada, determined an age of 361.3 ± 2.4 Ma. This age is in accord with U-Pb dates of interbedded tuff horizons and also U-Pb zircon date for the type Devonian-Mississippian Hasselbachtal section, Germany. The agreement of the biostratigraphic and U-Pb constraints of the Exshaw Formation with the Re-Os date illustrated the potential of the Re-Os chronometer to yield age determinations for sedimentary packages, especially in the absence of interbedd tuff horizons and biozones. A Re-Os date for the proposed type section of the Oxfordian-Kimmeridgian boundary, Staffin Bay, Isle of Skye, U.K., gave an age of 154.1 ± 2.2 Ma. This Re-Os age presents a 45 % (1.8 Ma) improvement in precision for the basal Kimmeridgian. It also demonstrated that the duration of the Kimmeridgian is nominally 3.3 Ma and thus is 1.6 Ma shorter than previously indicated. In addition to these examples, several studies have presented precise dates for Phanerozoic marine organic-rich units that are in excellent agreement with biostratigraphic determinations. A recent Re-Os study of the Woodford Shale (that was deposited throughout the Frasnian and Famennian) has provided important time markers as well as suggesting that the sedimentation rate of the Formation was relatively constant for ~20 Ma. To date only marine organic-rich sedimentary rocks have been utilized for Re-Os geochronology. However, lacustrine sedimentary rocks provide an invaluable archive of continental geological processes responding to tectonic, climatic and magmatic influences. Correlating these rocks to global geological phenomena requires accurate geochronological frameworks. The organic-rich lacustrine sedimentary units of the Eocene Green River Formation are enriched is Re and Os comparable to that of marine units. The Re-Os dates for the Green River Formation from the Uinta basin are 48.5 ± 0.6 Ma and 49.2 ± 1.0 Ma. These dates are in excellent agreement with Ar/Ar and U/Pb dates of interbedded tuffs in the GRF, therefore demonstrating that lacustrine units can be used for Re-Os geochronology in addition to marine organic-rich units.

The impact of precession and obliquity on the Late-Devonian greenhouse climate

NASA Astrophysics Data System (ADS)

De Vleeschouwer, D.; Crucifix, M.; Bounceur, N.; Claeys, P. F.

2012-12-01

To date, only few general circulation model (GCM) have been used to simulate the extremely warm greenhouse climate of the Late-Devonian (~370 Ma). As a consequence, the current knowledge on Devonian climate dynamics comes almost exclusively from geological proxy data. Given the fragmentary nature of these data sources, the understanding of the Devonian climate is rather limited. Nonetheless, the Late-Devonian is a key-period in the evolution of life on Earth: the continents were no longer bare but were invaded by land plants, the first forests appeared, soils were formed, fish evolved to amphibians and 70-80% of all animal species were wiped out during the Late Devonian extinction (~376 Ma). In order to better understand the functioning of the climate system during this highly important period in Earth's history, we applied the HadSM3 climate model to the Devonian period under different astronomical configurations. This approach provides insight into the response of Late-Devonian climate to astronomical forcing due to precession and obliquity. Moreover, the assessment of the sensitivity of the Late-Devonian climate to astronomical forcing, presented here, will allow cyclostratigraphers to make better and more detailed interpretations of recurring patterns often observed in Late-Devonian sections. We simulated Late-Devonian climates by prescribing palaeogeography, vegetation distribution and pCO2 concentration (2180 ppm). Different experiments were carried out under 31 different astronomical configurations: three levels for obliquity (ɛ = 22°; 23.5° and 24.5°) and eccentricity (e = 0; 0.03 and 0.07) were chosen. For precession, 8 levels were considered (longitude of the perihelion= 0°; 45°; 90°; 135°; 180°; 235°; 270°). First results suggest that the intensity of precipitation on the tropical Euramerican continent (also known as Laurussia) is highly dependent on changes in precession: During precession maxima (= maximal insolation in SH during winter solstice), precipitation is up to 300 mm/month higher compared to precession minima during the wet season (September - May). During the dry season (June-July-August), the climate is up to 7°C colder during a precession maxima compared to a precession minima. Obliquity doesn't show a significant influence on the climate of the tropical Euramerican continent. However, the imprint of obliquity on the polar climates is extensive with up to 6°C temperature-differences between obliquity maxima and minima at both poles.

Invasive species and biodiversity crises: testing the link in the late devonian.

PubMed

Stigall, Alycia L

2010-12-29

During the Late Devonian Biodiversity Crisis, the primary driver of biodiversity decline was the dramatic reduction in speciation rates, not elevated extinction rates; however, the causes of speciation decline have been previously unstudied. Speciation, the formation of new species from ancestral populations, occurs by two primary allopatric mechanisms: vicariance, where the ancestral population is passively divided into two large subpopulations that later diverge and form two daughter species, and dispersal, in which a small subset of the ancestral population actively migrates then diverges to form a new species. Studies of modern and fossil clades typically document speciation by vicariance in much higher frequencies than speciation by dispersal. To assess the mechanism behind Late Devonian speciation reduction, speciation rates were calculated within stratigraphically constrained species-level phylogenetic hypotheses for three representative clades and mode of speciation at cladogenetic events was assessed across four clades in three phyla: Arthropoda, Brachiopoda, and Mollusca. In all cases, Devonian taxa exhibited a congruent reduction in speciation rate between the Middle Devonian pre-crisis interval and the Late Devonian crisis interval. Furthermore, speciation via vicariance is almost entirely absent during the crisis interval; most episodes of speciation during this time were due to dispersal. The shutdown of speciation by vicariance during this interval was related to widespread interbasinal species invasions. The lack of Late Devonian vicariance is diametrically opposed to the pattern observed in other geologic intervals, which suggests the loss of vicariant speciation attributable to species invasions during the Late Devonian was a causal factor in the biodiversity crisis. Similarly, modern ecosystems, in which invasive species are rampant, may be expected to exhibit similar shutdown of speciation by vicariance as an outcome of the modern biodiversity crisis.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sari, A.; Geze, Y.

The studied area is a lake basin located in Bolu basin in Turkey. In the basin, from Upper Cretaceous to Upper Miocene 3,000-m thickness sediments were deposited. Upper Miocene Himmetoglu formation consisted of sandstone, claystone, and marl. To the middle level of the formation are located coal, bituminous limestone, and bituminous shales. In the basin, there are two coal beds whose thicknesses range from 1 to 13 m. The coals are easily breakable and black in color. In the coal beds exists some bituminous limestone and bituminous shales, and their thicknesses are between 5 and 45 cm. The amount ofmore » organic matter of the bituminous rocks from the Upper Miocene Himmetoglu formation are between 6.83 and 56.34 wt%, and the amount of organic matter of the bituminous limestone from the formation are between 13.58 and 57.16 wt%. These values indicate that these rocks have very good source potential. According to hydrogen index (HI), S2/S3, HI-T{sub max}, and HI-OI (oxygen index) parameters, kerogen types of the bituminous rocks and coals belonging to Upper Miocene Himmetoglu formation are Type I, Type II, and Type III. In accordance with HI, S2/S3, HI-T{sub max}, and HI-OI parameters, the bituminous rocks and coals from the Upper Miocene Himmetoglu formation are mostly immature.« less

Early Forest Soils and Their Role in Devonian Global Change

PubMed

Retallack

1997-04-25

A paleosol in the Middle Devonian Aztec Siltstone of Victoria Land, Antarctica, is the most ancient known soil of well-drained forest ecosystems. Clay enrichment and chemical weathering of subsurface horizons in this and other Devonian forested paleosols culminate a long-term increase initiated during the Silurian. From Silurian into Devonian time, red clayey calcareous paleosols show a greater volume of roots and a concomitant decline in the density of animal burrows. These trends parallel the decline in atmospheric carbon dioxide determined from isotopic records of pedogenic carbonate in these same paleosols. The drawdown of carbon dioxide began well before the Devonian appearance of coals, large logs, and diverse terrestrial plants and animals, and it did not correlate with temporal variation in volcanic or metamorphic activity. The early Paleozoic greenhouse may have been curbed by the evolution of rhizospheres with an increased ratio of primary to secondary production and by more effective silicate weathering during Silurian time.

Geologic Map of the Clark Peak Quadrangle, Jackson and Larimer Counties, Colorado

USGS Publications Warehouse

Kellogg, Karl S.; Ruleman, Chester A.; Shroba, Ralph R.; Braddock, William A.

2008-01-01

The Clark Peak quadrangle encompasses the southern end of the Medicine Bow Mountains and the northernmost end of the Mummy Range. The Continental Divide traverses the map area and Highway 14 cross the Divide at Cameron Pass, in the southeastern corner of the map. Approximately the eastern half of the map, and a few areas to the west, are underlain by Early Proterozoic plutonic and metamorphic rocks. Most of these basement rocks are part of the ~1,715 Ma Rawah batholith, composed mostly of pinkish, massive to moderately foliated monzogranite and granodiorite intruded by numerous, large pegmatite- aplite bodies. The metamorphic rocks, many of which form large inclusions in the granitic rocks of the Rawah batholith, include biotite-hornblende gneiss, hornblende gneiss, amphibolite, and biotite schist. The crystalline basement rocks are thrust westward along the Medicine Bow thrust over a sequence of sedimentary rocks as old as the Upper Permian Satanka Shale. The Satanka Shale, Middle and Lower Triassic Chugwater group, and a thin sandstone tentatively correlated with the Lower Jurassic and Upper Triassic Jelm Formation are combined as one map unit. This undivided unit is overlain sequentially upward by the Upper Jurassic Sundance Formation, Upper Jurassic Morrison Formation, Lower Cretaceous Dakota Group, Upper and Lower Cretaceous Benton Group, Upper Cretaceous Niobrara Formation, and the Eocene and Paleocene Coalmont Formation. The Late Cretaceous to early Eocene Medicine Bow thrust is folded in places, and several back thrusts produced a complicated thrust pattern in the south part of the map. Early Oligocene magmatism produced rhyolite tuff, dacite and basalt flows, and intermediate dikes and small stocks. A 40Ar/39Ar date on sanidine from one rhyolite tuff is ~28.5 Ma; a similar whole-rock date on a trachybasalt is ~29.6 Ma. A very coarse, unsorted probably pre-Quaternary ridge-top diamicton crops out in the southern part of the quadrangle. Numerous glacial deposits (mostly of Pinedale age), rock glaciers, block-slope deposits, landslide deposits, talus deposits, fan deposits, colluvium, and alluvium comprise the surficial deposits of the map area.

Exotic island arc Paleozoic terranes on the eastern margin of Gondwana: Geochemical whole rock and zircon U-Pb-Hf isotope evidence from Barry Station, New South Wales, Australia

NASA Astrophysics Data System (ADS)

Manton, Ryan J.; Buckman, Solomon; Nutman, Allen P.; Bennett, Vickie C.

2017-08-01

Early Paleozoic intra-oceanic terranes crop out along the Peel-Manning Fault System, in the southern New England Orogen, NSW Australia. These are the Cambrian ophiolitic Weraerai terrane and the Siluro-Devonian island arc Gamilaroi terrane. There has been debate whether these terranes formed at the Gondwana margin or if they are intra-oceanic, and were accreted to Gondwana later in the Paleozoic. Major-trace-REE elemental data indicate Weraerai terrane formed in a supra-subduction environment. Rare zircons extracted from Weraerai terrane gabbro-plagiogranite suites at Barry Station yield a U-Pb zircon date of 504.9 ± 3.5 Ma with initial εHf values of + 11.1 indicating a juvenile source. Amphibole-bearing felsic dykes and net-vein complexes are also found within the gabbro with a U-Pb zircon date of 503.2 ± 5.7 Ma and initial εHf values of + 11.6. These are coeval in age with their host rocks and we propose they represent partial melts of the mafic crust during the circulation of seawater. The Gamilaroi trondhjemites of prehnite-pumpellyite-greenschist metamorphic grade terrane yielded very few zircons with an age of 413 ± 8.7 Ma. Zircon initial εHf values range from + 5.0 to + 2.9, indicating an input from an evolved crustal source, unlike the purely oceanic Weraerai terrane. Gamilaroi terrane trondhjemites are enriched in LREE have low K2O and K2O/Na2O ratios and strong negative Nb anomalies consistent with supra-subduction zone environments. Multiple subduction zones may well have existed within the Panthalassa Ocean during the early-mid Paleozoic with the Weraerai-Gamilaroi being accreted onto the Gondwanan margin during the latest Devonian.

Geology and hydrocarbon potential of the Oued Mya basin, Algeria

DOE Office of Scientific and Technical Information (OSTI.GOV)

Benamrane, O.; Messaoudi, M.; Messelles, H.

1993-09-01

The Oued Mya hydrocarbon system is located in the Sahara basin. It is one of the best producing basins in Algeria, along with the Ghadames and Illizi basins. The stratigraphic section consists of Paleozoic and Mesozoic, and is about 5000 m thick. This intracratonic basin is limited to the north by the Toughourt saddle, and to the west and east it is flanked by regional arches, Allal-Tilghemt and Amguid-Hassi Messaoud, which culminate in the super giant Hassi Messaoud and Hassi R'mel hydrocarbon accumulations, respectively, producing oil from the Cambrian sands and gas from the Trissic sands. The primary source rockmore » in this basin is lower Silurian shale, with an average thickness of 50 m and a total organic carbon of 6% (14% in some cases). Results of maturation modeling indicate that the lower Silurian source is in the oil window. The Ordovician shales are also source rocks, but in a second order. Clastic reservoirs are in the Trissic sequence, which is mainly fluvial deposits with complex alluvial channels, and the main target in the basin. Clastic reservoirs in the lower Devonian section have a good hydrocarbon potential east of the basin through a southwest-northwest orientation. The Late Trissic-Early Jurassic evaporites that overlie the Triassic clastic interval and extend over the entire Oued Mya basin, are considered to be a super-seal evaporite package, which consists predominantly of anhydrite and halite. For paleozoic targets, a large number of potential seals exist within the stratigraphic column. This super seal does not present oil dismigration possibilities. We can infer that a large amount of the oil generated by the Silurian source rock from the beginning of Cretaceous until now still is not discovered and significantly greater volumes could be trapped within structure closures and mixed or stratigraphic traps related to the fluvial Triassic sandstones, marine Devonian sands, and Cambrian-Ordovician reservoirs.« less

Preliminary stratigraphy and facies analysis of the Upper Cretaceous Kaguyak Formation, including a brief summary of newly discovered oil stain, upper Alaska Peninsula

USGS Publications Warehouse

Wartes, Marwan A.; Decker, Paul L.; Stanley, Richard G.; Herriott, Trystan M.; Helmold, Kenneth P.; Gillis, Robert J.

2013-01-01

The Alaska Division of Geological and Geophysical Surveys has an ongoing program aimed at evaluating the Mesozoic forearc stratigraphy, structure, and petroleum systems of lower Cook Inlet. Most of our field studies have focused on the Jurassic component of the petroleum system (this report). However, in late July and early August of 2012, we initiated a study of the stratigraphy and reservoir potential of the Upper Cretaceous Kaguyak Formation. The Kaguyak Formation is locally well exposed on the upper Alaska Peninsula (fig. 25) and was named by Keller and Reiser (1959) for a sequence of interbedded siltstone and sandstone of upper Campanian to Maastrichtian age that they estimated to be 1,450 m thick.Subsequent work by Detterman and Miller (1985) examined 900 m of section and interpreted the unit as the record of a prograding submarine fan.This interpretation of deep-water deposition contrasts with other Upper Cretaceous rocks exposed along the Alaska Peninsula and lower Cook Inlet that are generally described as nonmarine to shallow marine (Detterman and others, 1996; LePain and others, 2012).Based on foraminifera and palynomorphs from the COST No. 1 well, Magoon (1986) concluded that the Upper Cretaceous rocks were deposited in a variety of water depths and environments ranging from upper bathyal to nonmarine. During our recent fieldwork west and south of Fourpeaked Mountain, we similarly encountered markedly varying lithofacies in the Kaguyak Formation (fig. 25), and we also found oil-stained rocks that are consistent with the existence of an active petroleum system in Upper Cretaceous rocks on the upper Alaska Peninsula and in lower Cook Inlet. These field observations are summarized below.

Stratigraphic and structural reconstruction of an Upper Ordovician super-eruption (Catalan Pyrenees)

NASA Astrophysics Data System (ADS)

Marti, Joan; Casas, Josep Maria; Muñoz, Josep A.

2017-04-01

Pre-Variscan basement of the Pyrenees includes evidence of many magmatic episodes represented by different types of granitoids and volcanic rocks, which indicates the complex geodynamic history of this peri-Gondwana terrane during Palaeozoic. One of the most significative magmatic episodes is that of Upper Ordovician (Caradocian) age, which is represented by several granitic and granodioritic bodies and volcanic rocks mostly of pyroclastic nature. In the Catalan Pyrenees this magmatism is well represented in the Ribes de Freser and Nuria area, where the orthogneisses from the Nuria massif and the Ribes granophyre, both with a similar age of 457 Ma, seem to form a calc-alkaline plutonic suite covering terms from deeper to shallower levels. The presence of numerous pyroclastic deposits and lavas interbedded with Caradocian sediments and intruded by and immediately above the Ribes granophyre, suggests that this intrusive episode also generated significant volcanism. The area also hosts an important volume of rhyolitic ignimbrites and andesitic lavas strongly affected by Alpine tectonics and commonly showing tectonised contacts at the base and top of the sequences. These volcanic rocks were previously attributed to the Upper Carboniferous late-Variscan volcanism, extensively represented in the Pyrenees. However, new laser ablation U-Pb zircon geochronology from these rocks has revealed an Upper Ordovician age ( 455 Ma), similar to that of the plutonic rocks of the same area, thus suggesting a probable genetic relation between all them. The palinspatic reconstruction of the Alpine and Variscan tectonic units that affect this area has permitted to infer the geometry, facies distribution, original position, and thickness of these volcanic rocks previously attributed to the late-Variscan volcanism, and reveals how they are spatially (and stratigraphically) associated with the previously identified Late Ordovician volcanic rocks. In particular, the volcanic rocks cropping out at the Ribes de Fresser area correspond to intra-caldera deposits representing a minimum volume of 600 km3, (DRE), which confirm the existence of super-eruptions of Upper Ordovician age in the Pyrenees.

Stage boundary recognition in the Eastern Americas realm based on rugose corals

USGS Publications Warehouse

Oliver, W.A.

2000-01-01

Most Devonian stages contain characteristic coral assemblages but these tend to be geographically and facies limited and may or may not be useful for recognising stage boundaries. Within eastern North America, corals contribute to the recognition of two boundaries: the base of the Lochkovian (Silurian-Devonian boundary) and the base of the Eifelian (Lower-Middle Devonian Series boundary).

Geosites of Lithuania as an environment for dwelling of specific biota: geo- and biodiversity interactions

NASA Astrophysics Data System (ADS)

Skridlaite, Grazina; Motiejunaite, Jurga; Jukoniene, Ilona; Prigodina Lukosiene, Ingrida

2016-04-01

Surface of Lithuania and surrounding countries is sculptured by five glaciations, which left behind morainic tills and melt water deposits, modified by erosion and later used for agriculture or overgrown by wild meadows or forests. The glaciations also left numerous erratic boulders and boulder fields that are declared as natural monuments in Lithuania and surrounding countries. Tens of single boulders and boulder fields are included into the Geosites database at the Lithuanian Geological Survey. Though sparse, but of high scientific value, Devonian, Permian, Triassic and Jurassic outcrops and quarries of Lithuania are variably protected. Quaternary scientists attempted to use single erratic boulders, their fields and abundances in tills to imply glacier dynamics. Some erratics came from known localities in Scandinavia and are called indicator boulders because they show the source and directions of ice sheet movements. Huge single boulders (e.g. 7 m long and 6 m high Puntukas, Anyksciai Regional Park) and wild boulder fields are natural monuments and attractive sites for visitors. Outcrops and quarries of Devonian dolomites and gypsium, Permian limestones and Jurassic sandstones widely used for a scientific research are parts of the protected geo-diversity in the Venta and Birzai regional parks, N and NW Lithuania. On the other hand, a large part of the c. 700 species of lichenized and allied fungi and of c. 500 bryophytes known in Lithuania are confined to natural or semi-natural (quarries) rocky habitats. Eight rock-dwelling lichen and nine bryophyte species are included in the Lithuanian Red Data Book, some of them are known from 1-2 localities or are thought to be extinct now. Besides, the recent investigations of dolomite quarries revealed them to be habitats for 7 bryophyte, 8 lichenized and lichenicolous species, previously unknown for Lithuania. One new lichenicolous species was discovered (Khodosovtsev et al., 2012). Some of the newfinds are rare or absent also in the neighbouring countries. In general, protection of geo-diversity coincides well with protection of narrowly specialized cryptogams, e.g. overgrowing of boulder fields with tall herbs and shrubs also has adversary effect on rock-dwelling lichens. Shading of Devonian outcrops and quarries by trees and shrubs may obscure rocky surfaces and destroy lichens, but favour an establishment of sciophyllous bryophytes. No doubt that cleaning of surfaces of single boulders that are well-known nature monuments prevents an establishment and growth of lichens and bryophytes. However, most of the geological monuments which are subjected to cleaning are situated in localities under strong anthropogenic impact and therefore not suitable for settlement of the rare and protected species. Though conservation conflicts arise even when protecting different species of biota, not to mention conservation of bio- versus geo-diversity, most of the conservation measures for the geoheritage in Lithuania are also suitable for rock-inhabiting lichens and bryophytes. Protection status and measures should be negotiated by bio-and geoscientists, and legislation for bio- and geo-diversity protection should be improved. Khodosovtsev, A., Vondrák, J., Naumovich, A., Kocourková, J., Vondráková, O., Motiejūnaitė, J., 2012. Nova Hedwigia, 95(1-2): 211-220.

High-pressure metamorphism in the southern New England Orogen: Implications for long-lived accretionary orogenesis in eastern Australia

NASA Astrophysics Data System (ADS)

Phillips, G.; Offler, R.; Rubatto, D.; Phillips, D.

2015-09-01

New geochemical, metamorphic, and isotopic data are presented from high-pressure metamorphic rocks in the southern New England Orogen (eastern Australia). Conventional and optimal thermobarometry are augmented by U-Pb zircon and 40Ar/39Ar phengite dating to define pressure-temperature-time (P-T-t) histories for the rocks. The P-T-t histories are compared with competing geodynamic models for the Tasmanides, which can be summarized as (i) a retreating orogen model, the Tasmanides formed above a continuous, west dipping, and eastward retreating subduction zone, and (ii) a punctuated orogen model, the Tasmanides formed by several arc accretion, subduction flip, and/or transference events. Whereas both scenarios are potentially supported by the new data, an overlap between the timing of metamorphic recrystallization and key stages of Tasmanides evolution favors a relationship between a single, long-lived subduction zone and the formation, exhumation, and exposure of the high-pressure rocks. By comparison with the retreating orogen model, the following links with the P-T-t histories emerge: (i) exhumation and underplating of oceanic eclogite during the Delamerian Orogeny, (ii) recrystallization of underplated and exhuming high-pressure rocks at amphibolite facies conditions coeval with a period of rollback, and (iii) selective recrystallization of high-pressure rocks at blueschist facies conditions, reflecting metamorphism in a cooled subduction zone. The retreating orogen model can also account for the anomalous location of the Cambrian-Ordovician high-pressure rocks in the Devonian-Carboniferous New England Orogen, where sequential rollback cycles detached and translated parts of the leading edge of the overriding plate to the next, younger orogenic cycle.

Armorican provenance for the mélange deposits below the Lizard ophiolite (Cornwall, UK): evidence for Devonian obduction of Cadomian and Lower Palaeozoic crust onto the southern margin of Avalonia

NASA Astrophysics Data System (ADS)

Strachan, Rob A.; Linnemann, Ulf; Jeffries, Teresa; Drost, Kerstin; Ulrich, Jens

2014-07-01

Devonian sedimentary rocks of the Meneage Formation within the footwall of the Lizard ophiolite complex in SW England are thought to have been derived from erosion of the over-riding Armorican microplate during collision with Avalonia and the closure of the Rheic Ocean. We further test this hypothesis by comparison of their detrital zircon suites with those of autochthonous Armorican strata. Five samples analysed from SW England (Avalonia) and NW France (Armorica) have a bimodal U-Pb zircon age distribution dominated by late Neoproterozoic to middle Cambrian (c. 710-518 Ma) and Palaeoproterozoic (c. 1,800-2,200 Ma) groupings. Both can be linked with lithologies exposed within the Cadomian belt as well as the West African craton, which is characterized by major tectonothermal events at 2.0-2.4 Ga. The detrital zircon signature of Avalonia is distinct from that of Armorica in that there is a much larger proportion of Mesoproterozoic detritus. The common provenance of the samples is therefore consistent with: (a) derivation of the Meneage Formation mélange deposits from the Armorican plate during Rheic Ocean closure and obduction of the Lizard Complex and (b) previous correlation of quartzite blocks within the Meneage Formation with the Ordovician Grès Armoricain Formation of NW France.

Hydrogeologic framework of the Floridan aquifer system in Florida and in parts of Georgia, South Carolina, and Alabama

USGS Publications Warehouse

Miller, James A.

1986-01-01

The Floridan aquifer system of the Southeastern United States is comprised of a thick sequence of carbonate rocks that are mostly of Paleocene to early Miocene age and that are hydraulically connected in varying degrees. The aquifer system consists of a single vertically continuous permeable unit updip and of two major permeable zones (the Upper and Lower Floridan aquifers) separated by one of seven middle confining units downdip. Neither the boundaries of the aquifer system or of its component high- and low-permeability zones necessarily conform to either formation boundaries or time-stratigraphic breaks. The rocks that make up the Floridan aquifer system, its upper and lower confining units, and a surficial aquifer have been separated into several chronostratigraphic units. The external and internal geometry of these stratigraphic units is presented on a series of structure contour and isopach maps and by a series of geohydrologic cross sections and a fence diagram. Paleocene through middle Eocene units consist of an updip clastic facies and a downdip carbonate bank facies, that extends progressively farther north and east in progressively younger units. Upper Eocene and Oligocene strata are predominantly carbonate rocks throughout the study area. Miocene and younger strata are mostly clastic rocks. Subsurface data show that some modifications in current stratigraphic nomenclature are necessary. First, the middle Eocene Lake City Limestone cannot be distinguished lithologically or faunally from the overlying middle Eocene Avon Park 'Limestone.' Accordingly, it is proposed that the term Lake City be abandoned and the term Avon Park Formation be applied to the entire middle Eocene carbonate section of peninsular Florida and southeastern Georgia. A reference well section in Levy County, Fla., is proposed for the expanded Avon Park Formation. The Avon Park is called a 'formation' more properly than a 'limestone' because the unit contains rock types other than limestone. Second, like the Avon Park, the lower Eocene Oldsmar and Paleocene Cedar Keys 'Limestones' of peninsular Florida practically everywhere contain rock types other than limestone. It is therefore proposed that these units be referred to more accurately as Oldsmar Formation and Cedar Keys Formation. The uppermost hydrologic unit in the study area is a surficial aquifer that can be divided into (1) a fluvial sand-and-gravel aquifer in southwestern Alabama and westernmost panhandle Florida, (2) limestone and sandy limestone of the Biscayne aquifer in southeastern peninsular Florida, and (3) a thin blanket of terrace and fluvial sands elsewhere. The surficial aquifer is underlain by a thick sequence of fine clastic rocks and low-permeability carbonate rocks, most of which are part of the middle Miocene Hawthorn Formation and all of which form the upper confining unit of the Floridan aquifer system. In places, the upper confining unit has been removed by erosion or is breached by sinkholes. Water in the Floridan aquifer system thus occurs under unconfined, semiconfined, or fully confined conditions, depending upon the presence, thickness, and integrity of the upper confining unit. Within the Floridan aquifer system, seven low permeability zones of subregional extent split the aquifer system in most places into an Upper and Lower Floridan aquifer. The Upper Floridan aquifer, which consists of all or parts of rocks of Oligocene age, late Eocene age, and the upper half of rocks of middle Eocene age, is highly permeable. The middle confining units that underlie the Upper Floridan are mostly of middle Eocene age but may be as young as Oligocene or as old as early Eocene. Where no middle confining unit exists, the entire aquifer system is comprised of permeable rocks and for hydrologic discussions is treated as the Upper Floridan aquifer. The Lower Floridan aquifer contains a cavernous high-permeability horizon in the lower part of the early Eocene of south

Reevaluating the age of the Walden Creek Group and the kinematic evolution of the western Blue Ridge, southern Appalachians

USGS Publications Warehouse

Thigpen, J. Ryan; Hatcher, Robert D.; Kah, Linda C.; Repetski, John E.

2016-01-01

An integrated synthesis of existing datasets (detailed geologic mapping, geochronologic, paleontologic, geophysical) with new paleontologic and geochemical investigations of rocks previously interpreted as part of the Neoproterozoic Walden Creek Group in southeastern Tennessee suggest a necessary reevaluation of the kinematics and structural architecture of the Blue Ridge Foothills. The western Blue Ridge of Tennessee, North Carolina, and Georgia is composed of numerous northwest-directed early and late Paleozoic thrust sheets, which record pronounced variation in stratigraphic/structural architecture and timing of metamorphism. The detailed spatial, temporal, and kinematic relationships of these rocks have remained controversial. Two fault blocks that are structurally isolated between the Great Smoky and Miller Cove-Greenbrier thrust sheets, here designated the Maggies Mill and Citico thrust sheets, contain Late Ordovician-Devonian conodonts and stable isotope chemostratigraphic signatures consistent with a mid-Paleozoic age. Geochemical and paleontological analyses of Walden Creek Group rocks northwest and southeast of these two thrust sheets, however, are more consistent with a Late Neoproterozoic (550–545 Ma) depositional age. Consequently, the structural juxtaposition of mid-Paleozoic rocks within a demonstrably Neoproterozoic-Cambrian succession between the Great Smoky and Miller Cove-Greenbrier thrust sheets suggests that a simple foreland-propagating thrust sequence model is not applicable in the Blue Ridge Foothills. We propose that these younger rocks were deposited landward of the Ocoee Supergroup, and were subsequently plucked from the Great Smoky fault footwall as a horse, and breached through the Great Smoky thrust sheet during Alleghanian emplacement of that structure.

delta 15N and non-carbonate delta 13C values for two petroleum source rock reference materials and a marine sediment reference material

USGS Publications Warehouse

Dennen, Kristin O.; Johnson, Craig A.; Otter, Marshall L.; Silva, Steven R.; Wandless, Gregory A.

2006-01-01

Samples of United States Geological Survey (USGS) Certified Reference Materials USGS Devonian Ohio Shale (SDO-1), and USGS Eocene Green River Shale (SGR-1), and National Research Council Canada (NRCC) Certified Marine Sediment Reference Material (PACS-2), were sent for analysis to four separate analytical laboratories as blind controls for organic rich sedimentary rock samples being analyzed from the Red Dog mine area in Alaska. The samples were analyzed for stable isotopes of carbon (delta13Cncc) and nitrogen (delta15N), percent non-carbonate carbon (Wt % Cncc) and percent nitrogen (Wt % N). SDO-1, collected from the Huron Member of the Ohio Shale, near Morehead, Kentucky, and SGR-1, collected from the Mahogany zone of the Green River Formation are petroleum source rocks used as reference materials for chemical analyses of sedimentary rocks. PACS-2 is modern marine sediment collected from the Esquimalt, British Columbia harbor. The results presented in this study are, with the exceptions noted below, the first published for these reference materials. There are published information values for the elemental concentrations of 'organic' carbon (Wt % Corg measured range is 8.98 - 10.4) and nitrogen (Wt % Ntot 0.347 with SD 0.043) only for SDO-1. The suggested values presented here should be considered 'information values' as defined by the NRCC Institute for National Measurement Reference Materials and should be useful for the analysis of 13C, 15N, C and N in organic material in sedimentary rocks.

Mode I Fracture Toughness of Rock - Intrinsic Property or Pressure-Dependent?

NASA Astrophysics Data System (ADS)

Stoeckhert, F.; Brenne, S.; Molenda, M.; Alber, M.

2016-12-01

The mode I fracture toughness of rock is usually regarded as an intrinsic material parameter independent of pressure. However, most fracture toughness laboratory tests are conducted only at ambient pressure. To investigate fracture toughness of rock under elevated pressures, sleeve fracturing laboratory experiments were conducted with various rock types and a new numerical method was developed for the evaluation of these experiments. The sleeve fracturing experiments involve rock cores with central axial boreholes that are placed in a Hoek triaxial pressure cell to apply an isostatic confining pressure. A polymere tube is pressurized inside these hollow rock cylinders until they fail by tensile fracturing. Numerical simulations incorporating fracture mechanical models are used to obtain a relation between tensile fracture propagation and injection pressure. These simulations indicate that the magnitude of the injection pressure at specimen failure is only depending on the fracture toughness of the tested material, the specimen dimensions and the magnitude of external loading. The latter two are known parameters in the experiments. Thus, the fracture toughness can be calculated from the injection pressure recorded at specimen breakdown. All specimens had a borehole diameter to outer diameter ratio of about 1:10 with outer diameters of 40 and 62 mm. The length of the specimens was about two times the diameter. Maximum external loading was 7.5 MPa corresponding to maximum injection pressures at specimen breakdown of about 100 MPa. The sample set tested in this work includes Permian and Carboniferous sandstones, Jurassic limestones, Triassic marble, Permian volcanic rocks and Devonian slate from Central Europe. The fracture toughness values determined from the sleeve fracturing experiments without confinement using the new numerical method were found to be in good agreement with those from Chevron bend testing according to the ISRM suggested methods. At elevated confining pressures, the results indicate a significant positive correlation between fracture toughness and confining pressure for most tested rock types.

Divergent plate motion drives rapid exhumation of (ultra)high pressure rocks

NASA Astrophysics Data System (ADS)

Liao, Jie; Malusà, Marco G.; Zhao, Liang; Baldwin, Suzanne L.; Fitzgerald, Paul G.; Gerya, Taras

2018-06-01

Exhumation of (ultra)high pressure [(U)HP] rocks by upper-plate divergent motion above an unbroken slab, first proposed in the Western Alps, has never been tested by numerical methods. We present 2D thermo-mechanical models incorporating subduction of a thinned continental margin beneath either a continental or oceanic upper plate, followed by upper-plate divergent motion away from the lower plate. Results demonstrate how divergent plate motion may trigger rapid exhumation of large volumes of (U)HP rocks directly to the Earth's surface, without the need for significant overburden removal by erosion. Model exhumation paths are fully consistent with natural examples for a wide range of upper-plate divergence rates. Exhumation rates are systematically higher than the divergent rate imposed to the upper plate, and the modeled size of exhumed (U)HP domes is invariant for different rates of upper-plate divergence. Major variations are instead predicted at depth for differing model scenarios, as larger amounts of divergent motion may allow mantle-wedge exhumation to shallow depth under the exhuming domes. The transient temperature increase, due to ascent of mantle-wedge material in the subduction channel, has a limited effect on exhumed continental (U)HP rocks already at the surface. We test two examples, the Cenozoic (U)HP terranes of the Western Alps (continental upper plate) and eastern Papua New Guinea (oceanic upper plate). The good fit between model predictions and the geologic record in these terranes encourages the application of these models globally to pre-Cenozoic (U)HP terranes where the geologic record of exhumation is only partly preserved.

Upper triassic continental margin strata of the central alaska range: Implications for paleogeographic reconstruction

USGS Publications Warehouse

Till, A.B.; Harris, A.G.; Wardlaw, B.R.; Mullen, M.

2007-01-01

Reexamination of existing conodont collections from the central Alaska Range indicates that Upper Triassic marine slope and basin rocks range in age from at least as old as the late Carnian to the early middle Norian. The conodont assemblages typical of these rocks are generally cosmopolitan and do not define a distinct paleogeographic faunal realm. One collection, however, containsEpigondolella multidentata sensu Orchard 1991c, which appears to be restricted to western North American autochthonous rocks. Although paleogeographic relations cannot be determined with specificity, the present distribution of biofaces within the Upper Triassic sequence could not have been the result of simple accordion-style collapse of the Late Triassic margin.

Multiple fracturing experiments: propellant and borehole considerations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cuderman, J F

1982-01-01

The technology for multiple fracturing of a wellbore, using progressively burning propellants, is being developed to enhance natural gas recovery. Multiple fracturing appears especially attractive for stimulating naturally fractured reservoirs such as Devonian shales where it is expected to effectively intersect existing fractures and connect them to a wellbore. Previous experiments and modeling efforts defined pressure risetimes required for multiple fracturing as a function of borehole diameter, but identified only a weak dependence on peak pressure attained. Typically, from four to eight equally spaced major fractures occur as a function of pressure risetime and in situ stress orientation. The presentmore » experiments address propellant and rock response considerations required to achieve the desired pressure risetimes for reliable multiple fracturing.« less

Geology and undiscovered resource assessment of the potash-bearing Pripyat and Dnieper-Donets Basins, Belarus and Ukraine

USGS Publications Warehouse

Cocker, Mark D.; Orris, Greta J.; Dunlap, Pamela; Lipin, Bruce R.; Ludington, Steve; Ryan, Robert J.; Słowakiewicz, Mirosław; Spanski, Gregory T.; Wynn, Jeff; Yang, Chao

2017-08-03

Undiscovered potash resources in the Pripyat Basin, Belarus, and Dnieper-Donets Basin, Ukraine, were assessed as part of a global mineral resource assessment led by the U.S. Geological Survey (USGS). The Pripyat Basin (in Belarus) and the Dnieper-Donets Basin (in Ukraine and southern Belarus) host stratabound and halokinetic Upper Devonian (Frasnian and Famennian) and Permian (Cisuralian) potash-bearing salt. The evaporite basins formed in the Donbass-Pripyat Rift, a Neoproterozoic continental rift structure that was reactivated during the Late Devonian and was flooded by seawater. Though the rift was divided, in part by volcanic deposits, into the separate Pripyat and Dnieper-Donets Basins, both basins contain similar potash‑bearing evaporite sequences. An Early Permian (Cisuralian) sag basin formed over the rift structure and was also inundated by seawater resulting in another sequence of evaporite deposition. Halokinetic activity initiated by basement faulting during the Devonian continued at least into the Permian and influenced potash salt deposition and structural evolution of potash-bearing salt in both basins.Within these basins, four areas (permissive tracts) that permit the presence of undiscovered potash deposits were defined by using geological criteria. Three tracts are permissive for stratabound potash-bearing deposits and include Famennian (Upper Devonian) salt in the Pripyat Basin, and Famennian and Cisuralian (lower Permian) salt in the Dnieper-Donets Basin. In addition, a tract was delineated for halokinetic potash-bearing Famennian salt in the Dnieper-Donets Basin.The Pripyat Basin is the third largest source of potash in the world, producing 6.4 million metric tons of potassium chloride (KCl) (the equivalent of about 4.0 million metric tons of potassium oxide or K2O) in 2012. Potash production began in 1963 in the Starobin #1 mine, near the town of Starobin, Belarus, in the northwestern corner of the basin. Potash is currently produced from six potash mines in the Starobin area. Published reserves in the Pripyat Basin area are about 7.3 billion metric tons of potash ore (about 1.3 billion metric tons of K2O) mostly from potash-bearing salt horizons in the Starobin and Petrikov mine areas. The 15,160-square-kilometer area of the Pripyat Basin underlain by Famennian potash-bearing salt contains as many as 60 known potash-bearing salt horizons. Rough estimates of the total mineral endowment associated with stratabound Famennian salt horizons in the Pripyat Basin range from 80 to 200 billion metric tons of potash-bearing salt that could contain 15 to 30 billion metric tons of K2O.Parameters (including the number of economic potash horizons, grades, and depths) for these estimates are not published so the estimates are not easily confirmed. Historically, reserves have been estimated above a depth of 1,200 meters (m) (approximately the depths of conventional underground mining). Additional undiscovered K2O resources could be significantly greater in the remainder of the Fammenian salt depending on the extents and grades of the 60 identified potash horizons above the USGS assessment depth of 3,000 m in the remainder of the tract. Increasing ambient temperatures with increasing depths in the eastern parts of the Pripyat Basin may require a solution mining process which is aided by higher temperatures.No resource or reserve data have been published and little is known about stratabound Famennian and Frasnian salt in the Dnieper-Donets Basin. These Upper Devonian salt units dip to the southeast and extend to depths of 15–19 kilometers (km) or greater. The tract of stratabound Famennian salt that lies above a depth of 3 km, the depth above which potash is technically recoverable by solution mining, underlies an area of about 15,600 square kilometers (km2). If Upper Devonian salt units in the Dnieper-Donets Basin contain potash-bearing strata similar to salt of the same age in the Pripyat Basin, then the stratabound Famennian tract in the Dnieper-Donets Basin could contain significant undiscovered potash resources.The Cisuralian evaporite sequence in the Dnieper-Donets Basin consists of 10 evaporite cycles with the upper 3 cycles containing potash-bearing salt (mainly as sylvite and carnallite) in several subbasins and polyhalite in the sulfate bearing parts of the identified tract. The area of the Cisuralian tract is 62,700 km2. Potash-bearing cycles are as much as 40 m thick. One subbasin is reported to contain 794 million metric tons of “raw or crude” potash-bearing salt which could contain 50 to 150 million metric tons of K2O, depending on the grade. Undiscovered potash resources in the remainder of this permissive tract may be significantly greater. Depths to the Permian salt range from less than 100 to about 1,500 m.Undiscovered resources of halokinetic potash-bearing salt in the Dnieper-Donets Basin were assessed quantitatively for this study by using the standard USGS three-part form of mineral resource assessment (Singer, 2007a; Singer and Menzie, 2010). Delineation of the permissive tract was based on distributions of mapped halokinetic salt structures. This tract contains at least 248 diapiric salt structures with a total area of 7,840 km2 that occupies approximately 8 percent of the basin area. The vertical extent of these salt structures is hundreds of meters to several kilometers. This assessment estimated that a total mean of 11 undiscovered deposits contain an arithmetic mean estimate of about 840 million metric tons of K2O in the halokinetic salt structures of the Dnieper-Donets Basin for which the probabilistic estimate was made.

Geologic controls on cave development in Burnsville Cove, Bath and Highland Counties, Virginia

USGS Publications Warehouse

Swezey, Christopher; Haynes, John T.; Lucas, Philip C.; Lambert, Richard A.

2017-01-01

Burnsville Cove in Bath and Highland Counties (Virginia, USA) is a karst region in the Valley and Ridge Province of the Appalachian Mountains. The region contains many caves in Silurian to Devonian limestone, and is well suited for examining geologic controls on cave location and cave passage morphology. In Burnsville Cove, many caves are located preferentially near the axes of synclines and anticlines. For example, Butler Cave is an elongate cave where the trunk channel follows the axis of Sinking Creek syncline and most of the side passages follow joints at right angles to the syncline axis. In contrast, the Water Sinks Subway Cave, Owl Cave, and Helictite Cave have abundant maze patterns, and are located near the axis of Chestnut Ridge anticline. The maze patterns may be related to fact that the anticline axis is the site of the greatest amount of flexure, leading to more joints and (or) greater enlargement of joints. Many of the larger caves of Burnsville Cove (e.g., Breathing Cave, Butler Cave–Sinking Creek Cave System, lower parts of the Water Sinks Cave System) are developed in the Silurian Tonoloway Limestone, the stratigraphic unit with the greatest surface exposure in the area. Other caves are developed in the Silurian to Devonian Keyser Limestone of the Helderberg Group (e.g., Owl Cave, upper parts of the Water Sinks Cave System) and in the Devonian Shriver Chert and (or) Licking Creek Limestone of the Helderberg Group (e.g., Helictite Cave). Within the Tonoloway Limestone, the larger caves are developed in the lower member of the Tonoloway Limestone immediately below a bed of silica-cemented sandstone. In contrast, the larger caves in the Keyser Limestone are located preferentially in limestone beds containing stromatoporoid reefs, and some of the larger caves in the Licking Creek Limestone are located in beds of cherty limestone below the Devonian Oriskany Sandstone. Geologic controls on cave passage morphology include joints, bedding planes, and folds. The influence of joints results in tall and narrow cave passages, whereas the influence of bedding planes results in cave passages with flat ceilings and (or) floors. The influence of folds is less common, but a few cave passages follow fold axes and have distinctive arched ceilings.

Linking Fossil Fish Cyclicity and Paleoenvironmental Proxies in the mid-Devonian

NASA Astrophysics Data System (ADS)

Grogan, D.; Whiteside, J. H.; Trewin, N. H.; Johnson, J. E.

2009-12-01

The significant radiation of fishes throughout the Devonian, combined with the abundance of well-preserved fossil fish assemblages from this period, provides for a high-resolution record of prevalent fish taxa in the Orcadian basin of North Scotland. In addition to their ability to serve as a lake-level and lake-chemistry proxy, the waxing and waning of dominant fish taxa exhibit a pronounced cyclicity, suggesting they respond to broader climate rhythms. Recent studies of mid-Devonian lacustrine sedimentary sequences have quantitatively demonstrated the presence of Milankovitch cyclicity in geochemical and gamma ray proxy records. Spectral analysis of gamma ray data show a strong obliquity peak usually associated with ice-house conditions; this obliquity signal is unexpected as tropical latitudes in the mid-Devonian are traditionally thought to have been in a greenhouse climate. Geochemical data include the measurement of bulk carbon and nitrogen stable isotopes, molecule-specific carbon isotopes of plant biomarkers, and depth ranks from eight sections of the Caithness Flagstone Group of the Orcadian Basin. Evidence for orbital forcing of climate change paired with the fossil fish record provides a unique opportunity to establish an astronomically calibrated timescale for the mid-Devonian, as well as to make a quantitative assessment of the validity of a greenhouse climate existing in the mid-Devonian.

Source-rock geochemistry of the San Joaquin Basin Province, California: Chapter 11 in Petroleum systems and geologic assessment of oil and gas in the San Joaquin Basin Province, California

USGS Publications Warehouse

Peters, Kenneth E.; Magoon, Leslie B.; Valin, Zenon C.; Lillis, Paul G.

2007-01-01

Source-rock thickness and organic richness are important input parameters required for numerical modeling of the geohistory of petroleum systems. Present-day depth and thickness maps for the upper Miocene Monterey Formation, Eocene Tumey formation of Atwill (1935), Eocene Kreyenhagen Formation, and Cretaceous-Paleocene Moreno Formation source rocks in the San Joaquin Basin were determined using formation tops data from 266 wells. Rock-Eval pyrolysis and total organic carbon data (Rock-Eval/TOC) were collected for 1,505 rock samples from these source rocks in 70 wells. Averages of these data for each well penetration were used to construct contour plots of original total organic carbon (TOCo) and original hydrogen index (HIo) in the source rock prior to thermal maturation resulting from burial. Sufficient data were available to construct plots of TOCo and HIo for all source-rock units except the Tumey formation of Atwill (1935). Thick, organic-rich, oil-prone shales of the upper Miocene Monterey Formation occur in the Tejon depocenter in the southern part of the basin with somewhat less favorable occurrence in the Southern Buttonwillow depocenter to the north. Shales of the upper Miocene Monterey Formation generated most of the petroleum in the San Joaquin Basin. Thick, organic-rich, oil-prone Kreyenhagen Formation source rock occurs in the Buttonwillow depocenters, but it is thin or absent in the Tejon depocenter. Moreno Formation source rock is absent from the Tejon and Southern Buttonwillow depocenters, but thick, organic-rich, oil-prone Moreno Formation source rock occurs northwest of the Northern Buttonwillow depocenter adjacent to the southern edge of Coalinga field.

Placoderms (Armored Fish): Dominant Vertebrates of the Devonian Period

NASA Astrophysics Data System (ADS)

Young, Gavin C.

2010-05-01

Placoderms, the most diverse group of Devonian fishes, were globally distributed in all habitable freshwater and marine environments, like teleost fishes in the modern fauna. Their known evolutionary history (Early Silurian-Late Devonian) spanned at least 70 million years. Known diversity (335 genera) will increase when diverse assemblages from new areas are described. Placoderms first occur in the Early Silurian of China, but their diversity remained low until their main evolutionary radiation in the Early Devonian, after which they became the dominant vertebrates of Devonian seas. Most current placoderm data are derived from the second half of the group's evolutionary history, and recent claims that they form a paraphyletic group are based on highly derived Late Devonian forms; 16 shared derived characters are proposed here to support placoderm monophyly. Interrelationships of seven placoderm orders are unresolved because Silurian forms from China are still poorly known. The relationship of placoderms to the two major extant groups of jawed fishes—osteichthyans (bony fishes) and chondrichthyans (cartilaginous sharks, rays, and chimaeras)—remains uncertain, but the detailed preservation of placoderm internal braincase structures provides insights into the ancestral gnathostome (jawed vertebrate) condition. Placoderms provide the most complex morphological and biogeographic data set for the Middle Paleozoic; marked discrepancies in stratigraphic occurrence between different continental regions indicate strongly endemic faunas that were probably constrained by marine barriers until changes in paleogeography permitted range enlargement into new areas. Placoderm distributions in time and space indicate major faunal interchange between Gondwana and Laurussia near the Frasnian-Famennian boundary; closure of the Devonian equatorial ocean is a possible explanation.

Geology of Seward Peninsula and Saint Lawrence Island

USGS Publications Warehouse

Till, Alison B.; Dumoulin, Julie A.

1994-01-01

Seward Peninsula (Fig. 1) may be divided into two geologic terranes (Fig. 2) on the basis of stratigraphy, structure, and metamorphic history. The Seward terrane, an area 150 by 150 km in the central and eastern peninsula, is dominated by Precambrian(?) and early Paleozoic blueschist-, greenschist-, and amphibolite-facies schist and marble, and intruded by three suites of granitic rocks. The York terrane, roughly 100 by 75 km, occupies western Seward Peninsula and the Bering Straits region; it is composed of Ordovician, Silurian, Devonian, Mississippian, and possibly older limestone, argillaceous limestone, dolostone, and phyllite, which are cut by a suite of Late Cretaceous tin-bearing granites. The boundary between the Seward and York terranes is poorly exposed but is thought to be a major thrust fault because of its sinuous map trace, a discontinuity in metamorphic grade, and differences in stratigraphy across the boundary (Travis Hudson, oral communication, 1984). The boundary between the Seward terrane and the Yukon-Koyukuk province to the east is complicated by vertical faults (the Kugruk fault Zone of Sainsbury, 1974) and obscured by Cretaceous and Tertiary cover.The Seward Peninsula heretofore was thought to consist largely of rocks of Precambrian age (Sainsbury, 1972, 1974, 1975; Hudson, 1977), Microfossil data, however, indicate that many of the rocks considered to be Precambrian are early Paleozoic in age (Till and others, 1986; Dumoulin and Harris, 1984; Dumoulin and Till, 1985; Till and others, 1983; Wandervoort, 1985). It is likely that Precambrian rocks are a minor part of the stratigraphy of the Seward Peninsula.

Subsurface temperatures and surface heat flow in the Michigan Basin and their relationships to regional subsurface fluid movement

USGS Publications Warehouse

Vugrinovich, R.

1989-01-01

Linear regression of 405 bottomhole temperature (BHT) measurements vs. associated depths from Michigan's Lower Peninsula results in the following equation relating BHT and depth: BHT(??C) = 14.5 + 0.0192 ?? depth(m) Temperature residuals, defined as (BHT measured)-(BHT calculated), were determined for each of the 405 BHT's. Areas of positive temperature residuals correspond to areas of regional groundwater discharge (determined from maps of equipotential surface) while areas of negative temperature residuals correspond to areas of regional groundwater recharge. These relationships are observed in the principal aquifers in rocks of Devonian and Ordovician age and in a portion of the principal aquifer in rocks of Silurian age. There is a similar correspondence between high surface heat flow (determined using the silica geothermometer) and regional groundwater discharge areas and low surface heat flow and regional groundwater recharge areas. Post-Jurassic depositional and tectonic histories suggest that the observed coupling of subsurface temperature and groundwater flow systems may have persisted since Jurassic time. Thus the higher subsurface palaeotemperatures (and palaeogeothermal gradients) indicated by recent studies most likely pre-date the Jurassic. ?? 1989.

Visual classification of very fine-grained sediments: Evaluation through univariate and multivariate statistics

USGS Publications Warehouse

Hohn, M. Ed; Nuhfer, E.B.; Vinopal, R.J.; Klanderman, D.S.

1980-01-01

Classifying very fine-grained rocks through fabric elements provides information about depositional environments, but is subject to the biases of visual taxonomy. To evaluate the statistical significance of an empirical classification of very fine-grained rocks, samples from Devonian shales in four cored wells in West Virginia and Virginia were measured for 15 variables: quartz, illite, pyrite and expandable clays determined by X-ray diffraction; total sulfur, organic content, inorganic carbon, matrix density, bulk density, porosity, silt, as well as density, sonic travel time, resistivity, and ??-ray response measured from well logs. The four lithologic types comprised: (1) sharply banded shale, (2) thinly laminated shale, (3) lenticularly laminated shale, and (4) nonbanded shale. Univariate and multivariate analyses of variance showed that the lithologic classification reflects significant differences for the variables measured, difference that can be detected independently of stratigraphic effects. Little-known statistical methods found useful in this work included: the multivariate analysis of variance with more than one effect, simultaneous plotting of samples and variables on canonical variates, and the use of parametric ANOVA and MANOVA on ranked data. ?? 1980 Plenum Publishing Corporation.

Petroleum potential of the Reggane Basin, Algeria

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boudjema, A.; Hamel, M.; Mohamedi, A.

1990-05-01

The intracratonic Reggane basin is located on the Saharan platform, southwest of Algeria. The basin covers an area of approximately 140,000 km{sup 2}, extending between the Eglab shield in the south and the Ougarta ranges in the north. Although exploration started in the early 1950s, only a few wells were drilled in this basin. Gas was discovered with a number of oil shows. The sedimentary fill, mainly Paleozoic shales and sandstones, has a thickness exceeding 5,000 m in the central part of the basin. The reservoirs are Cambrian-Ordovician, Siegenian, Emsian, Tournaisian, and Visean sandstones with prospective petrophysical characteristics. Silurian Uppermore » Devonian and, to a lesser extent Carboniferous shales are the main source rocks. An integrated study was done to assess the hydrocarbon potential of this basin. Tectonic evolution source rocks and reservoirs distribution maturation analyses followed by kinetic modeling, and hydrogeological conditions were studied. Results indicate that gas accumulations could be expected in the central and deeper part of the basin, and oil reservoirs could be discovered on the basin edge.« less

Hydrogeologic framework of the Wood River Valley aquifer system, south-central Idaho

USGS Publications Warehouse

Bartolino, James R.; Adkins, Candice B.

2012-01-01

The Wood River Valley contains most of the population of Blaine County and the cities of Sun Valley, Ketchum, Hailey, and Bellevue. This mountain valley is underlain by the alluvial Wood River Valley aquifer system, which consists primarily of a single unconfined aquifer that underlies the entire valley, an underlying confined aquifer that is present only in the southernmost valley, and the confining unit that separates them. The entire population of the area depends on groundwater for domestic supply, either from domestic or municipal-supply wells, and rapid population growth since the 1970s has caused concern about the long-term sustainability of the groundwater resource. As part of an ongoing U.S. Geological Survey effort to characterize the groundwater resources of the Wood River Valley, this report describes the hydrogeologic framework of the Wood River Valley aquifer system. Although most of the Wood River Valley aquifer system is composed of Quaternary-age sediments and basalts of the Wood River Valley and its tributaries, older igneous, sedimentary, or metamorphic rocks that underlie these Quaternary deposits also are used for water supply. It is unclear to what extent these rocks are hydraulically connected to the main part of Wood River Valley aquifer system and thus whether they constitute separate aquifers. Paleozoic sedimentary rocks in and near the study area that produce water to wells and springs are the Phi Kappa and Trail Creek Formations (Ordovician and Silurian), the Milligen Formation (Devonian), and the Sun Valley Group including the Wood River Formation (Pennsylvanian-Permian) and the Dollarhide Formation (Permian). These sedimentary rocks are intruded by granitic rocks of the Late Cretaceous Idaho batholith. Eocene Challis Volcanic Group rocks overlie all of the older rocks (except where removed by erosion). Miocene Idavada Volcanics are found in the southern part of the study area. Most of these rocks have been folded, faulted, and metamorphosed to some degree, thus rock types and their relationships vary over distance. Quaternary-age sediment and basalt compose the primary source of groundwater in the Wood River Valley aquifer system. These Quaternary deposits can be divided into three units: a coarse-grained sand and gravel unit, a fine-grained silt and clay unit, and a single basalt unit. The fine- and coarse-grained units were primarily deposited as alluvium derived from glaciation in the surrounding mountains and upper reaches of tributary canyons. The basalt unit is found in the southeastern Bellevue fan area and is composed of two flows of different ages. Most of the groundwater produced from the Wood River Valley aquifer system is from the coarse-grained deposits. The altitude of the pre-Quaternary bedrock surface in the Wood River Valley was compiled from about 1,000 well-driller reports for boreholes drilled to bedrock and about 70 Horizontal-to-Vertical Spectral Ratio (HVSR) ambient-noise measurements. The bedrock surface generally mimics the land surface by decreasing down tributary canyons and the main valley from north to south; it ranges from more than 6,700 feet in Baker Creek to less than 4,600 feet in the central Bellevue fan. Most of the south-central portion of the Bellevue fan is underlain by an apparent topographically closed area on the bedrock surface that appears to drain to the southwest towards Stanton Crossing. Quaternary sediment thickness ranges from less than a foot on main and tributary valley margins to about 350 feet in the central Bellevue fan. Hydraulic conductivity for 81 wells in the study area was estimated from well-performance tests reported on well-driller reports. Estimated hydraulic conductivity for 79 wells completed in alluvium ranges from 1,900 feet per day (ft/d) along Warm Springs Creek to less than 1 ft/d in upper Croy Canyon. A well completed in bedrock had an estimated hydraulic conductivity value of 10 ft/d, one well completed in basalt had a value of 50 ft/d, and three wells completed in the confined system had values ranging from 32 to 52 ft/d. Subsurface outflow of groundwater from the Wood River Valley aquifer system into the eastern Snake River Plain aquifer was estimated to be 4,000 acre-feet per year. Groundwater outflow beneath Stanton Crossing to the Camas Prairie was estimated to be 300 acre-feet per year.

Detrital zircon ages in Korean mid-Paleozoic meta-sandstones (Imjingang Belt and Taean Formation): Constraints on tectonic and depositional setting, source regions and possible affinity with Chinese terranes

NASA Astrophysics Data System (ADS)

Han, Seokyoung; de Jong, Koen; Yi, Keewook

2017-08-01

Sensitive High-Resolution Ion Microprobe (SHRIMP) U-Th-Pb isotopic data of detrital zircons from mature, quartz-rich meta-sandstones are used to constrain possible tectonic affinities and source regions of the rhythmically layered and graded-bedded series in the Yeoncheon Complex (Imjingang Belt) and the correlative Taean Formation. These metamorphic marine turbidite sequences presently occur along the Paleoproterozoic (1.93-1.83 Ga) Gyeonggi Massif, central Korea's main high-grade metamorphic gneiss terrane. Yet, detrital zircons yielded highly similar multimodal age spectra with peaks that do not match the age repartition in these basement rocks, as late (1.9-1.8 Ga) and earliest (∼ 2.5 Ga) Paleoproterozoic detrital modes are subordinate but, in contrast, Paleozoic (440-425 Ma) and Neoproterozoic (980-920 Ma) spikes are prominent, yet the basement essentially lacks lithologies with such ages. The youngest concordant zircon ages in each sample are: 378, 394 and 423 Ma. The maturity of the meta-sandstones and the general roundness of zircons of magmatic signature, irrespective of their age, suggest that sediments underwent considerable transport from source to sink, and possibly important weathering and recycling, which may have filtered out irradiation-weakened metamorphic zircon grains. In combination with these isotopic data, presence of a low-angle ductile fault contact between the Yeoncheon Complex and the Taean Formation and the underlying mylonitized Precambrian basement implies that they are in tectonic contact and do not have a stratigraphic relationship, as often assumed. Consequently, in all likelihood, both meta-sedimentary formations: (1) are at least of early Late Devonian age, (2) received much of their detritus from distant (reworked) Silurian-Devonian and Early Neoproterozoic magmatic sources, not present in the Gyeonggi Massif, (3) and not from Paleoproterozoic crystalline rocks of this massif, or other Korean Precambrian basement terranes, and (4) should be viewed as independent tectonic units that had sources not exposed in Korea. A thorough literature review reveals that the Yeoncheon Complex and the Taean Formation were potentially sourced from the Liuling, Nanwan and Foziling groups in the Qinling-Dabie Belt, which all show very similar detrital zircon age spectra. These immature middle-late Devonian sandstones were deposited in a pro-foreland basin formed as a result of the aborted subduction of the South Qinling Terrane below the North Qinling Terrane, which was uplifted and eroded during post-collision isostatic rebound. The submarine fans where the mature distal turbiditic Yeoncheon and Taean sandstones were deposited may have constituted the eastern terminal part of a routing system originating in the uplifted and eroded middle Paleozoic Qinling Belt and adjacent part of the foreland basin.

DOE Office of Scientific and Technical Information (OSTI.GOV)

McCollum, L.B.; Buchanan, J.P.; McCollum, M.B.

The Antler orogeny is a textbook example of a Paleozoic mountain building and crustal shortening event in western North America. A relatively complex geologic history of the type Antler at Battle Mountain, Nevada, is interpreted as distinct thrust plates of Lower Cambrian Scott Canyon Formation, Upper Cambrian Harmony Sandstone, and Ordovician Valmy Formation, overlain unconformably by the Middle Pennsylvanian Battle Formation. Mississippian crustal deformation and emplacement of the Roberts Mountain thrust have previously been thought to characterize the Antler orogen. Detailed sedimentology studies of the Scott Canyon and Harmony, and the relationship with the overlying Battle Formation at the typemore » section of the Antler orogeny, cast doubt on the previously accepted geologic history. The Scott Canyon is an interbedded sequence of pillow basalts, Late Devonian radiolarian cherts, and mudstone debris flows with numerous limestone olistoliths, many containing undescribed archaeocyathid fauna. The contact of the Harmony with the Battle Formation appears channeled, but otherwise conformable, and the Battle has been interpreted as an alluvial fan facies. The paleoenvironmental interpretation of these sediments is that the Scott Canyon was deposited upon a Late Devonian active continental margin setting, with prograding fan deposits of the Harmony Sandstone, overlain by Middle Pennsylvanian fanglomerates of the Battle Formation. This conformable sequence appears to preclude any major uplift within the type Antler orogen.« less

Structure of the crust and upper mantle in the western United States

USGS Publications Warehouse

Pakiser, L.C.

1963-01-01

Seismic waves generated by underground nuclear and chemical explosions have been recorded in a network of nearly 2,000 stations in the western conterminous United States as a part of the VELA UNIFORM program. The network extends from eastern Colorado to the California coastline and from central Idaho to the border of the United States and Mexico. The speed of compressional waves in the upper-mantle rocks ranges from 7.7 km/sec in the southern part of the Basin and Range province to 8.2 km/sec in the Great Plains province. In general, the speed of compressional waves in the upper-mantle rocks tends to be nearly the same over large areas within individual geologic provinces. Measured crustal thickness ranges from less than 20 km in the Central Valley of California to 50 km in the Great Plains province. Changes in crustal thickness across provincial boundaries are not controlled by regional altitude above sea level unless the properties of the upper mantle are the same across those boundaries. The crust tends to be thick in regions where the speed of compressional waves in the upper-mantle rocks (and presumably the density) is high, and tends to be relatively thin where the speed of compressional waves in the upper-mantle rocks (and density) is lower. With in the Basin and Range province, crustal thickness seems to vary directly with regional altitude above sea level. Evidence that a layer of intermediate compressional-wave speed exists in the lower part of the crust has been accumulated from seismic waves that have traveled least-time paths, as well as secondary arrivals (particularly reflections). On a scale that includes many geologic provinces, isostatic compensation is related largely to variations in the density of the upper- mantle rocks. Within geologic provinces or adjacent provinces, isostatic compensation may be related to variations in the thickness of crustal layers. Regions of thick crust and dense upper mantle have been relatively stable in Cenozoic time. Regions of thinner crust and low-density upper mantle have had a Cenozoic history of intense diastrophism and silicic volcanism.

Deformation associated to exhumation by detachment faulting of upper mantle rocks in a fossil Ocean Continent Transition: The example of the Totalp unit in SE Switzerland

NASA Astrophysics Data System (ADS)

Picazo, S.; Manatschal, G.; Cannat, M.

2013-12-01

The exhumation of upper mantle rocks along detachment faults is widespread at Mid-Ocean Ridges and at the Ocean-Continent Transition (OCT) of rifted continental margins. Thermo-mechanical models indicate that significant strain softening of the fault rocks in the footwall is required in order to produce such large fault offsets. Our work focuses on deformation textures, and the associated mineralogy in ultramafic rocks sampled in the upper levels of the footwall next to the exhumation fault. We present two OCT examples, the Totalp relict of a paleo-Tethys OCT exposed in SE Switzerland, and the Iberian distal margin (ODP Leg 173 Site 1070). We built a new geological map and a section of the Totalp unit near Davos (SE Switzerland) and interpreted this area as a local exposure of a paleo-seafloor that is formed by an exhumed detachment surface and serpentinized peridotites. The top of the exhumed mantle rocks is made of ophicalcites that resulted from the carbonation of serpentine under static conditions at the seafloor. The ophicalcites preserve depositional contacts with Upper Jurassic to Lower Cretaceous pelagic sediments. These sequences did not exceed prehnite-pumpellyite metamorphic facies conditions, and locally escaped Alpine deformation. Thin mylonitic shear zones as well as foliated amphibole-bearing ultramafic rocks have been mapped. The age of these rocks and the link with the final exhumation history are yet unknown but since amphibole-bearing ultramafic rocks can be found as clasts in cataclasites related to the detachment fault, they pre-date detachment faulting. Our petrostructural study of the exhumed serpentinized rocks also reveals a deformation gradient from cataclasis to gouge formation within 150m in the footwall of the proposed paleo-detachment fault. This deformation postdates serpentinization. It involves a component of plastic deformation of serpentine in the most highly strained intervals that has suffered pronounced grain-size reduction and a polyphase cataclastic overprint.

Paleogeographic implications of an erosional remnant of Paleogene rocks southwest of the Sur-Nacimiento Fault Zone, southern Coast Ranges, California

USGS Publications Warehouse

Vedder, J.G.; McLean, H.; Stanley, R.G.; Wiley, T.J.

1991-01-01

A small tract of heretofore-unrecognized Paleogene rocks lies about 30 km northeast of Santa Maria and 1 km southwest of the Sur-Nacimiento fault zone near upper Pine Creek. This poorly exposed assemblage of rocks is less than 50 m thick, lies unconformably on regionally distributed Upper Cretaceous submarine-fan deposits, and consists of three units: fossiliferous lower Eocene mudstone, Oligocene(?) conglomerate, and basaltic andesite that has a radiometric age of 26.6 ?? 0.5 Ma. Both the sedimentary and igneous constituents in the Paleogene sequence are unlike those of known sequences on either side of the Sur-Nacimiento fault zone. The Paleogene sedimentary rocks near upper Pine Creek presumably are remnants of formerly widespread early Eocene bathyal deposits and locally distributed Oligocene(?) fluvial deposits southwest of the fault zone. The 26.6 Ma basaltic andesite, however, may not have extended much beyond its present outcrops. An episode of Oligocene(?) displacement is required by the contrast in thicknesses, depositional patterns, and paleobathymetry of the juxtaposed rock sequences. -from Authors

The Jurassic section along McElmo Canyon in southwestern Colorado

USGS Publications Warehouse

O'Sullivan, Robert B.

1997-01-01

In McElmo Canyon, Jurassic rocks are 1500-1600 ft thick. Lower Jurassic rocks of the Glen Canyon Group include (in ascending order) Wingate Sandstone, Kayenta Formation and Navajo Sandstone. Middle Jurassic rocks are represented by the San Rafael Group, which includes the Entrada Sandstone and overlying Wanakah Formation. Upper Jurassic rocks comprise the Junction Creek Sandstone overlain by the Morrison Formation. The Burro Canyon Formation, generally considered to be Lower Cretaceous, may be Late Jurassic in the McElmo Canyon area and is discussed with the Jurassic. The Upper Triassic Chinle Formation in the subsurface underlies, and the Upper Cretaceous Dakota Sandstone overlies, the Jurassic section. An unconformity is present at the base of the Glen Canyon Group (J-0), at the base of the San Rafael Group (J-2), and at the base of the Junction Creek Sandstone (J-5). Another unconformity of Cretaceous age is at the base of the Dakota Sandstone. Most of the Jurassic rocks consist of fluviatile, lacustrine and eolian deposits. The basal part of the Entrada Sandstone and the Wanakah Formation may be of marginal marine origin.

Interpretation of 40Ar/39Ar Age-spectra in Low-grade Polymetamorphic Rocks: The Importance of Petrologic constraints

NASA Astrophysics Data System (ADS)

Kunk, M. J.

2007-12-01

40Ar/39Ar age-spectra of white micas from low-grade polymetamorphic terranes can be difficult to interpret, because these low-grade rocks frequently have multiple generations of cleavage-forming white mica that grew at temperatures below their closure for diffusion of argon (~350°C). Under such conditions, each generation of cleavage-forming white mica will retain its original growth age. In addition, rocks from metamorphic terranes can also contain populations of detrital and diagenetic white micas which also have distinct ages associated with them. A final complication, frequently found in these low-grade polymetamorphic samples is the presence of inseparable, intergrown chlorite and the problems with associated 39Ar recoil during irradiation of the samples, prior to sample analysis. The shapes of 40Ar/39Ar age spectra of white micas separated from such samples are frequently complex and are quite variable in shape. Some age spectra show a steady increase in age with increase in the temperature of release, while others have sigmoidal or saddle-shaped patterns. The age of most of the steps in such age spectra are mixtures of the various age populations of white mica in the sample, and as such are geologically meaningless. Nonetheless, useful constraints on the ages of at least some events recorded in these complex low-grade polymetamorphic rocks can be discerned with the help of petrographic observations, and by placing the results in a spatial context to test for reproducibility and/or the occurrence of meaningful patterns. If no chlorite is present and the sample contains no detrital white mica, an estimate of the maximum age of the youngest component and the minimum age of the oldest cleavage forming white mica populations can frequently be discerned. If the sample contains detrital white mica, a minimum age for its cooling or crystallization can be estimated. The presence of a small amount of intimately intergrown chlorite masks the age of the youngest white mica population, but the minimum age of the oldest generation of white mica may still be estimated. Samples from the Blue Ridge anticlinorium in northern VA indicate cleavage formation during both the Devonian and the Pennsylvanian. Similar, but somewhat more complex samples from the Potomac terrane in the eastern Piedmont of northern VA and MD indicate discrete tectonothermal events in the Ordovician, Silurian, and Pennsylvanian, while samples from the Westminster terrane in the westerm Piedmont of MD suggest cleavage formation in the middle Silurian, the Devonian and the Pennsylvanian. While the results are not of high precision, they are very useful at the orogenic level.

Correlation of the Klamath Mountains and Sierra Nevada

USGS Publications Warehouse

Irwin, William P.

2003-01-01

This report graphically portrays the broadly parallel tectonic development of the Klamath Mountains and Sierra Nevada from early Paleozoic to Early Cretaceous time. It is dedicated to J.S. Diller of the U.S. Geological Survey who, during his pioneer field studies a century ago, recognized significant similarities between these two important provinces. The report is based mainly on the numerous published reports of the field and laboratory studies by various geologists and students during the last century, and to a lesser extent on my own field work which has been substantial in the Klamath Mountains but minimal in the Sierra Nevada. For brevity, required by the format of this report, little of the extensive literature pertaining to these two provinces is referenced. This report is preliminary in nature and was prepared as an aid to further study of the tectonic relations between the Klamath Mountains and Sierra Nevada. This report consists of two sheets: Sheet 1, Map showing accreted terranes and plutons of the Klamath Mountains and Sierra Nevada, and Sheet 2, Successive accretionary episodes of the Klamath mountains and northern part of Sierra Nevada, showing related plutonic, volcanic, and metamorphic events. The map on Sheet 1 was compiled and modified from two Open-File maps (Irwin and Wooden, 1999 and 2001) which had been compiled and modified mainly from Jennings (1977), Harwood (1992), Irwin (1994), Jayko (1988), Graymer and Jones (1994), Edelman and Sharp (1989), Schweickert and others (1999), Saucedo and Wagner(1992), Saleeby and Sharp (1980), Wagner and others (1981), and various other sources. For detailed lists of the sources for the isotopic age data used in Sheets 1 and 2, see Irwin and Wooden (1999 and 2001). On Sheet 2, the accretionary episodes are shown sequentially from left to right in two tiers of figures. Episodes for the Klamath Mountains are in the upper tier; correlative episodes of the Sierra Nevada are directly below in the lower tier. The sequence shown for the Klamath Mountains is modified from Irwin and Mankinen (1998) and Irwin and Wooden (1999). The episodes are named for the accreting terranes of the Klamath Mountains, but those names may not be suitable for reference to the correlative episodes of the Sierra Nevada. In the figure for each episode, a heavy black line represents the active suture that separated oceanic crustal rocks on the left from the earlier accreted terranes on the right. Plutons are particularly useful for timing the accretionary episodes. The preaccretionary plutons, which commonly represent the roots of oceanic volcanic arcs, are shown in the accreting oceanic crustal rocks to the left of the heavy black line. The accretionary plutons consist of rock that has been subducted and remobilized as magma during the accretionary process and injected into an overlying earlier accreted terrane on the right of the heavy black line. Thus, isotopic dating of the accretionary plutons (preferably U/Pb dates measured on zircon extracted from the plutonic rock) provides a useful basis for assigning ages to the accretionary episodes. Many plutons are rootless at depth, as they tend to be truncated by the subduction zone sutures of younger accreting terranes. Volcanic deposits resulting from accretionary episodes apparently are uncommon except for those deposited on the backstop terranes. In the Klamath Mountains, the Eastern Klamath terrane, which consists of the Yreka, Trinity and Redding subterranes, was the backstop for the Central Metamorphic and younger accretionary episodes, and displays a remarkable record of sedimentation, volcanism and plutonism from Silurian-Devonian to Jurassic time. In the Sierra Nevada, the correlative backstop was the Northern Sierra terrane which shows a similar long record of volcanism in the Taylorsville, Permian, and Jurassic volcanic arc sequences. During some accretionary episodes the subducting oceanic rocks were dynamically metamorphosed to schist along the suture zone beneath the overriding accreted terranes. Examples of this in the Klamath Mountains are the Devonian Salmon and Abrams Schists of the Central Metamorphic terrane, the Triassic(?) schist of the Fort Jones terrane , and the Early Cretaceous South Fork Mountain Schist that structurally underlies Klamath Mountains terranes along much of the western edge of the province. The Fort Jones terrane and South Fork Mountains Schist were metamorphosed under blueschist-facies conditions. In the Sierra Nevada, schist that is correlative with the Central Metamorphic terrane is present in patches along the Feather River terrane (see Hacker and Peacock, 1990); the Triassic(?) Red Ant Schist is correlative with the Fort Jones terrane; but a correlative of the South Fork Mountain Schist is not present. In addition to the similarities in the sequences of accretion, plutonism, volcanism, and metamorphism, strong ties between the two provinces are also provided by paleontologic data. The Permian McCloud fusulinid fauna of the Redding subterrane also is present in the Northern Sierra terrane. Rare Tethyan fusulinids are found in Permian limestone of the Eastern Hayfork terrane of the Klamath Mountains and also in limestone blocks in the Central Belt of the Sierra Nevada. Ichthyosaur fossils have been collected from the Triassic of both the Redding subterrane and Northern Sierra terrane. Jurassic ammonites and the pelecypod Buchia concentrica occur in both the Galice Formation of the western Klamath Mountains and the Mariposa Formation of the western Sierra Nevada. Events that preceded the Central Metamorphic episode prior to Silurian-Devonian time are not clearly understood and are not shown in the succession of diagrams on Sheet 2. The oldest rocks of the Klamath Mountains are Neoproterozic and they predate the Central Metamorphic episode by possibly a hundred million years or more. They include ophiolitic rocks of the Trinity subterrane and the Antelope Mountain Quartzite of the Yreka subterrane (see Mankinen and others, 2002). In the Sierra Nevada, correlatives of the ancient ophiolitic rocks may be part of the Feather River terrane. Although Neoproterozoic fossils have not yet been found in the Sierra Nevada, petrologic study shows the quartzite of the Lang sequence is closely similar to the Antelope Mountain Quartzite (see Bond and Devay, 1980). Correlation of the two quartzite formations is also suggested by the similarity of their positions in the accretionary sequence.

Sojourner Sits Near "Rock Garden"

NASA Image and Video Library

2003-02-01

The Mars Pathfinder Rover Sojourner images by the Imager for Mars Pathfinder as it nears the rock "Wedge." Part of the Rock Garden is visible in the upper right of the image. http://photojournal.jpl.nasa.gov/catalog/PIA04318

From success to persistence: Identifying an evolutionary regime shift in the diverse Paleozoic aquatic arthropod group Eurypterida, driven by the Devonian biotic crisis.

PubMed

Lamsdell, James C; Selden, Paul A

2017-01-01

Mass extinctions have altered the trajectory of evolution a number of times over the Phanerozoic. During these periods of biotic upheaval a different selective regime appears to operate, although it is still unclear whether consistent survivorship rules apply across different extinction events. We compare variations in diversity and disparity across the evolutionary history of a major Paleozoic arthropod group, the Eurypterida. Using these data, we explore the group's transition from a successful, dynamic clade to a stagnant persistent lineage, pinpointing the Devonian as the period during which this evolutionary regime shift occurred. The late Devonian biotic crisis is potentially unique among the "Big Five" mass extinctions in exhibiting a drop in speciation rates rather than an increase in extinction. Our study reveals eurypterids show depressed speciation rates throughout the Devonian but no abnormal peaks in extinction. Loss of morphospace occupation is random across all Paleozoic extinction events; however, differential origination during the Devonian results in a migration and subsequent stagnation of occupied morphospace. This shift appears linked to an ecological transition from euryhaline taxa to freshwater species with low morphological diversity alongside a decrease in endemism. These results demonstrate the importance of the Devonian biotic crisis in reshaping Paleozoic ecosystems. © 2016 The Author(s). Evolution © 2016 The Society for the Study of Evolution.

Study of hydrocarbon production from the Devonian shale in Letcher, Knott, Floyd, Martin, and Pike Counties, eastern Kentucky annual technical report, July 1, 1984-June 30, 1985

DOE Office of Scientific and Technical Information (OSTI.GOV)

Frankie, W.T.

The Kentucky Geological Survey (KGS) at the University of Kentucky is conducting a 2-year research project funded by the Gas Research Institute (GRI) to study hydrocarbon production from the Devonian shale in eastern Kentucky. Objectives are to develop an understanding of relationships between stratigraphy and hydrocarbon production, create a data base, and prepare geologic reports for each county in the study area. Data were compiled from the KGS, GRI Eastern Gas Data System (EGDS), U. S. Department of Energy (DOE), and industry. Research for Letcher County was completed and 270 Devonian wells were entered into the KGS computer data base.more » Devonian black-shale units were correlated using gamma-ray logs. Structure and isopach maps, and stratigraphic cross sections have been constructed. An isopotential map defining areas of equal initial gas production has been prepared. Statistics for Letcher County have been run on the data base using Datatrieve software package. Statistical analyses focused on different types of formation treatments and the resulting production. Temperature logs were used to detect gas-producing intervals within the Mississippian-Devonian black-shale sequence. The results of the research provide the petroleum industry with a valuable tool for gas exploration in the Devonian shales.« less

An Exceptionally Preserved Transitional Lungfish from the Lower Permian of Nebraska, USA, and the Origin of Modern Lungfishes

PubMed Central

Pardo, Jason D.; Huttenlocker, Adam K.; Small, Bryan J.

2014-01-01

Complete, exceptionally-preserved skulls of the Permian lungfish Persephonichthys chthonica gen. et sp. nov. are described. Persephonichthys chthonica is unique among post-Devonian lungfishes in preserving portions of the neurocranium, permitting description of the braincase of a stem-ceratodontiform for the first time. The completeness of P. chthonica permits robust phylogenetic analysis of the relationships of the extant lungfish lineage within the Devonian lungfish diversification for the first time. New analyses of the relationships of this new species within two published matrices using both maximum parsimony and Bayesian inference robustly place P. chthonica and modern lungfishes within dipterid-grade dipnoans rather than within a clade containing Late Devonian ‘phaneropleurids’ and common Late Paleozoic lungfishes such as Sagenodus. Monophyly of post-Devonian lungfishes is not supported and the Carboniferous-Permian taxon Sagenodus is found to be incidental to the origins of modern lungfishes, suggesting widespread convergence in Late Paleozoic lungfishes. Morphology of the skull, hyoid arch, and pectoral girdle suggests a deviation in feeding mechanics from that of Devonian lungfishes towards the more dynamic gape cycle and more effective buccal pumping seen in modern lungfishes. Similar anatomy observed previously in ‘Rhinodipterus’ kimberyensis likely represents an intermediate state between the strict durophagy observed in most Devonian lungfishes and the more dynamic buccal pump seen in Persephonichthys and modern lungfishes, rather than adaptation to air-breathing exclusively. PMID:25265394

Widespread effects of middle Mississippian deformation in the Great Basin of western North America

USGS Publications Warehouse

Trexler, J.H.; Cashman, P.H.; Cole, J.C.; Snyder, W.S.; Tosdal, R.M.; Davydov, V.I.

2003-01-01

Stratigraphic analyses in central and eastern Nevada reveal the importance of a deformation event in middle Mississippian time that caused widespread deformation, uplift, and erosion. It occurred between middle Osagean and late Meramecian time and resulted in deposition of both synorogenic and postorogenic sediments. The deformation resulted in east-west shortening, expressed as east-vergent folding and east-directed thrusting; it involved sedimentary rocks of the Antler foredeep as well as strata associated with the Roberts Mountains allochthon. A latest Meramecian to early Chesterian unconformity, with correlative conformable lithofacies changes, postdates this deformation and occurs throughout Nevada. A tectonic highland-created in the middle Mississippian and lasting into the Pennsylvanian and centered in the area west and southwest of Carlin, Nevada- shed sediments eastward across the Antler foreland, burying the unconformity. Postorogenic strata are late Meramecian to early Chesterian at the base and are widespread throughout the Great Basin. The tectonism therefore occurred 20 to 30 m.y. after inception of the Late Devonian Antler orogeny, significantly extending the time span of this orogeny or representing a generally unrecognized orogenic event in the Paleozoic evolution of western North America. We propose a revised stratigraphic nomenclature for Mississippian strata in Nevada, based on detailed age control and the recognition of unconformities. This approach resolves the ambiguity of some stratigraphic names and emphasizes genetic relationships within the upper Paleozoic section. We take advantage of better stratigraphic understanding to propose two new stratigraphic units for southern and eastern Nevada: the middle Mississippian Gap Wash and Late Mississippian Captain Jack Formations.

Hydrocarbon source rock potential of the Karoo in Zimbabwe

NASA Astrophysics Data System (ADS)

Hiller, K.; Shoko, U.

1996-07-01

The hydrocarbon potential of Zimbabwe is tied to the Karoo rifts which fringe the Zimbabwe Craton, i.e. the Mid-Zambezi basin/rift and the Mana Pools basin in the northwest, the Cabora Bassa basin in the north and the Tuli-Bubye and Sabi-Runde basins in the south. Based on the geochemical investigation of almost one thousand samples of fine clastic Karoo sediments, a concise source rock inventory has been established showing the following features. No marine source rocks have been identified. In the Mid-Zambezi area and Cabora Bassa basin, the source rocks are gas-prone, carbonaceous to coaly mudstones and coal of Lower Karoo age. In the Cabora Bassa basin, similar gas-prone source rocks occur in the Upper Karoo (Angwa Alternations Member). These kerogen type III source rocks are widespread and predominantly immature to moderately mature. In the southern basins, the Lower Karoo source rocks are gas-prone; in addition some have a small condensate potential. Most of the samples are, however, overmature due to numerous dolerite intrusions. Samples with a mixed gas, condensate and oil potential (mainly kerogen types II and III) were identified in the Lower Karoo (Coal Measure and Lower Madumabisa Mudstone Formations) of the Mid-Zambezi basin, and in the Louver Karoo (Mkanga Formation) and Upper Karoo (Upper Angwa Alternations Member Formation) of the Cabora Bassa basin. The source rocks, with a liquid potential, are also immature to moderately mature and were deposited in swamp, paludal and lacustrine environments of limited extent.

Reconnaissance of ground-water resources in the Eastern Coal Field Region, Kentucky

USGS Publications Warehouse

Price, William E.; Mull, D.S.; Kilburn, Chabot

1962-01-01

In the Eastern Coal Field region of Kentucky, water is obtained from consolidated sedimentary rocks ranging in age from Devonian to Pennsylvanian and from unconsolidated sediments of Quaternary age. About 95 percent of the area is underlain by shale, sandstone, and coal of Pennsylvanian age. Principal factors governing the availability of water in the region are depth, topographic location, and the lithology of the aquifer penetrated. In general, the yield of the well increases as the depth increases. Wells drilled in topographic lows, such as valleys, are likely to yield more water than wells drilled on topographic highs, such as hills. Sand and gravel, present in thick beds in the alluvium along the Ohio River, form the most productive aquifer in the Eastern Coal Field. Of the consolidated rocks in the region sandstone strata are the best aquifers chiefly because joints, openings along bedding planes, and intergranular pore spaces are best developed in them. Shale also supplies water to many wells in the region, chiefly from joints and openings along bedding planes. Coal constitutes a very small part of the sedimentary section, but it yields water from fractures to many wells. Limestone yields water readily from solution cavities developed along joint and bedding-plane openings. The availability of water in different parts of the region was determined chiefly by analyzing well data collected during the reconnaissance. The resulting water-availability maps, published as hydrologic investigations atlases (Price and others, 1961 a, b; Kilburn and others, 1961) were designed to be used in conjunction with this report. The maps were constructed by dividing the region into 5 physiographic areas, into 10 subareas based chiefly on lithologic facies, and, in the case of the Kanawha section, into 2 quality-of-water areas. The 5 physiographic areas are the Knobs, Mississippian Plateau, Cumberland Plateau section, Kanawha section, and Cumberland Mountain section. The 10 subareas are as follows: 1. The Chattanooga shale. This black shale yields only enough water for a minimum domestic supply-100 to 500 gpd (gallons per day). 2. Mississippian-Devonian rocks exposed along Pine Mountain. These rocks consist of shale, limestone, and sandstone. The limestone yields water to springs, and faulted limestone and sandstone lying below drainage may yield several hundred gallons per minute to wells. 3. Mississippian rocks exposed along the western margin of the region. These rocks consist of thick limestone underlain by shale. The limestone yields enough water for a modern domestic supply (more than 500 gpd) , and discharges as much as 100 gpm (gallons per minute) to springs. The shale yields only enough water for a minimum domestic supply. 4. Subarea 1 of the Lee formation of Pennsylvanian age. The thin shaly rocks of this subarea generally yield only enough water for a minimum domestic supply. 5. Subarea 2 of the Lee formation of Pennsylvanian age. This subarea is predominantly underlain by massive sandstones; it generally yields enough water for a modern domestic supply, and in some places, enough water for small public and industrial supplies. 6. Subarea 1 of the Breathitt and Conemaugh formations of Pennsylvanian age. Rocks in this subarea contain more shale than sandstone. Wells in this subarea range from adequate for a minimum domestic supply to adequate for a modern domestic supply. 7. Subarea 2 of the Breathitt formation of Pennsylvanian age and undifferentiated post-Lee Pennsylvanian rocks. Wells in this subarea yield enough water for a modern domestic supply, and in many places, enough water for small public and industrial supplies. 8. Alluvium along the Ohio River. Mostly composed of glacial outwash sand and gravel, the alluvium is reported to yield as much as 360 gpm to wells. 9. Alluvium along the Big Sandy River and lower reaches of its Tug and Levisa Forks. Where consisting mostly of sand,

500 Myr of thermal history elucidated by multi-method detrital thermochronology of North Gondwana Cambrian sandstone (Eilat area, Israel)

NASA Astrophysics Data System (ADS)

Vermeesch, P.; Avigad, D.

2009-04-01

Following the Neoproterozoic Pan-African orogeny, the Arabian-Nubian Shield (ANS) of North Africa and Arabia was eroded and then covered by Cambrian sandstones that record the onset of platform sedimentation. We applied K-feldspar 40Ar/39Ar, zircon and apatite fission track and apatite (U-Th)/He thermochronology to detritus from Cambrian sandstones of southern Israel deposited at about 500 Ma. U-Pb detrital zircon ages from these sandstones predate deposition and record the earlier Neoproterozoic crustal evolution of the Pan-African orogens. 40Ar/39Ar ages from 50 single grains of K-feldspar yield a Cambrian mean of approximately 535 Ma. The 40Ar/39Ar age spectrum of a multi-grain K-feldspar aliquot displays diffusion behaviour compatible with >560 Ma cooling later affected by a heating event. Assuming that the high temperature domains of the K-feldspars have not been affected by subsequent (hydro)thermal events, and taking previously published K-Ar and Rb-Sr ages from other parts of the East African Orogen at face value, these ages apparently record Pan-African thermal resetting below a thick volcano-sedimentary pile similar to the Saramuj conglomerate in Jordan and/or the Hammamat in Egypt. Detrital zircon fission track (ZFT) ages cluster around 380 Ma, consistent with previous ZFT results from Neoproterozoic basement and sediments of the region, revealing that the Cambrian platform sequence experienced a middle Devonian thermal event and low-grade metamorphism. Regional correlation indicates that during Devonian time the sedimentary cover atop the Cambrian in Israel was never in excess of 2.5 km, requiring an abnormally steep geothermal gradient to explain the complete ZFT annealing. A basal Carboniferous unconformity can be traced from Syria to southern Saudi Arabia, suggesting that the observed Devonian ZFT ages represent a regional tectonothermal event. Similar Devonian ZFT ages were reported from ANS basement outcrops in the Eastern Desert, 500 km south of Eilat. The detrital apatites we studied all have extremely rounded cores suggestive of a distant provenance, but some grains also feature distinct euhedral U-rich apatite overgrowth rims. Authigenic apatite may have grown during the late Devonian thermal event we dated by ZFT, coinciding with existing Rb-Sr ages from authigenic clays in the same deposits and leading to the conclusion that the Devonian event was probably hydrothermal. Like the ZFT ages, the detrital apatite fission track (AFT) ages were also completely reset after deposition. Sixty single grain detrital apatite fission track (AFT) ages group at ~270 Ma with significant dispersion. Inverse modeling of the AFT data indicate extended and/or repeated residence in the AFT partial annealing zone, in turn suggesting an episodic burial-erosion history during the Mesozoic caused by low-amplitude vertical motions. Seven detrital apatite (U-Th)/He ages scatter between 33 and 77 Ma, possibly resulting from extreme compositional zonation associated with the authigenic U-rich overgrowths. The ~70 Ma (U-Th)/He ages are more likely to be accurate, setting 1-2 km as an upper limit (depending on the geothermal gradient) on the post-Cretaceous exhumation of the Cambrian sandstone and showing no evidence for substantial denudation related to Tertiary rifting of the Red Sea.

Precise U/Pb zircons dates of bentonites in Upper Ordovician and Lower Silurian reference sections in North America and Britain.

NASA Astrophysics Data System (ADS)

Suarez, S. E.; Brookfield, M. E.; Catlos, E. J.; Stockli, D. F.; Batchelor, R. A.

2016-12-01

The end of the Ordovician marks one of the greatest of the Earth's mass extinctions. One hypothesis explains this mass extinction as the result of a short-lived, major glaciation preceded by episodes of increased volcanism brought on by the Taconic orogeny. K-bentonites, weathered volcanic ash, provide evidence for increased volcanism. However, there is a lack of modern precise U-Pb dating of these ashes and some confusion in the biostratigraphy. The aim of this study is to obtain more precise U-Pb zircon ages from biostratigraphically constrained bentonites which will lead to better correlation of the Upper Ordovician and Lower Silurian relative time scales, as well as time the pulses of eruption. Zircon grains were extracted from the samples by heavy mineral separation and U-Pb dated using the Laser Ablation-Inductively Coupled Plasma-Mass Spectrometer at the University of Texas-Austin. We report here 3 precise U-Pb zircon ages from the Trenton Group, Ontario, Canada, and Dob's Linn, Scotland. The youngest age from the top of the Kirkfield Formation in Ontario is 448.0 +/- 18 Ma, which fits with existing late Ordovician stratigraphic ages. At Dob's Linn, Scotland, the site of the Ordovician/Silurian Global Boundary Stratigraphic Section and Point (GSSP), the youngest age for DL7, a bentonite 5 meters below the GSSP is 402.0 +/- 12.0 Ma, and for DL24L, a bentonite 8 meters above the GSSP is 358.2 +/- 7.9 Ma. These are Devonian ages in current timescales - the current age for the GSSP is 443.8 +/- 1.8 Ma, based on an U/Pb dates from a bentonite 1.6 meters above the GSSP at Dob's Linn. We are confident that our techniques rule out contamination and the most likely explanation is that the small zircons we analyzed either suffered Pb loss, or grew overgrowths during low grade hydrothermal metamorphism of the sediments during the intrusion of the Southern Upland Devonian granites during the Caledonian orogeny. These Devonian ages suggest that the 443.8 +/- 1.8 Ma age may also be suspect. The Dob's Linn site is therefore unsuitable for calibrating the biostratigraphic horizons. Work in progress will provide more U-Pb dating of bentonites from around the Ordovician-Silurian boundary in Canada, United States, Britain and Scandinavia with the aim of calibrating the local series and stages in order to help in International correlations.

Phosphorus losses from an irrigated watershed in the Northwestern U.S.: Case study of the Upper Snake Rock Watershed

USDA-ARS?s Scientific Manuscript database

Watersheds utilizing surface water for irrigation often return a portion of the water to a water body. This irrigation return flow often includes sediment and nutrients that reduce the quality of the receiving water body. Research in the 82,000 ha Upper Snake Rock (USR) watershed from 2005 to 2008 s...

"Rock Garden"

NASA Image and Video Library

1997-10-14

This false color composite image of the Rock Garden shows the rocks "Shark" and "Half Dome" at upper left and middle, respectively. Between these two large rocks is a smaller rock (about 0.20 m wide, 0.10 m high, and 6.33 m from the Lander) that was observed close-up with the Sojourner rover (see PIA00989). http://photojournal.jpl.nasa.gov/catalog/PIA00987

Dismembered Archaean ophiolite in the southeastern Wind River Mountains, Wyoming: Remains of Archaean oceanic crust

NASA Technical Reports Server (NTRS)

Harper, G. D.

1986-01-01

Archean mafic and ultramafic rocks occur in the southeastern Wind River Mountains near Atlantic City, Wyoming and are interpreted to represent a dismembered ophiolite suite. The ophiolitic rocks occur in a thin belt intruded by the 2.6 Ga Louis Lake Batholith on the northwest. On the southeast they are in fault contact with the Miners Delight Formation comprised primarily of metagraywackes with minor calc-alkaline volcanics. The ophiolitic and associated metasedimentry rocks (Goldman Meadows Formation) have been multiply deformed and metamorphosed. The most prominant structures are a pronounced steeply plunging stretching lineation and steeply dipping foliation. These structural data indicate that the ophiolitic and associated metasedimentary rocks have been deformed by simple shear. The ophiolitic rocks are interpreted as the remains of Archean oceanic crust, probably formed at either a mid-ocean ridge or back-arc basin. All the units of a complete ophiolite are present except for upper mantle periodotities. The absence of upper mantle rocks may be the result of detactment within the crust, rather than within the upper mantle, during emplacement. This could have been the result of a steeper geothermal gradient in the Archean oceanic lithosphere, or may have resulted from a thicker oceanic crust in the Archean.

Geomorphology and forest ecology of a mountain region in the central Appalachians

USGS Publications Warehouse

Hack, John Tilton; Goodlett, John C.

1960-01-01

The area studied, mostly in the headwaters of the Shenandoah River, Augusta and Rockingham Counties, Va., includes about 55 square miles of densely forested mountain land and has an average relief of about 1,500 feet. It is part of an area that in June 1949 was subjected to a violent cloudburst which damaged large tracts on slopes and bottom lands. Most of the area is underlain by flaggy arkosic sandstone and interbedded reddish shale of the Hampshire formation of Devonian age. The highest ridges are capped by massive sandstone of the Pocono formation of Mississippian age. In most of the area the rocks dip gently to the southeast but in the northwestern and southeastern parts they are folded into synclines that localize northeastward-trending ridges.

Foreland-forearc collisional granitoid and mafic magmatism caused by lower-plate lithospheric slab breakoff: The Acadian of Maine, and other orogens

USGS Publications Warehouse

Schoonmaker, A.; Kidd, W.S.F.; Bradley, D.C.

2005-01-01

During collisional convergence, failure in extension of the lithosphere of the lower plate due to slab pull will reduce the thickness or completely remove lower-plate lithosphere and cause decompression melting of the asthenospheric mantle; magmas from this source may subsequently provide enough heat for substantial partial melting of crustal rocks under or beyond the toe of the collisional accretionary system. In central Maine, United States, this type of magmatism is first apparent in the Early Devonian West Branch Volcanics and equivalent mafic volcanics, in the slightly younger voluminous mafic/silicic magmatic event of the Moxie Gabbro-Katahdin batholith and related ignimbrite volcanism, and in other Early Devonian granitic plutons. Similar lower-plate collisional sequences with mafic and related silicic magmatism probably caused by slab breakoff are seen in the Miocene-Holocene Papuan orogen, and the Hercynian-Alleghenian belt. Magmatism of this type is significant because it gives evidence in those examples of whole-lithosphere extension. We infer that normal fault systems in outer trench slopes of collisional orogens in general, and possibly those of oceanic subduction zones, may not be primarily due to flexural bending, but are also driven by whole-lithosphere extension due to slab pull. The Maine Acadian example suggests that slab failure and this type of magmatism may be promoted by pre-existing large margin-parallel faults in the lower plate. ?? 2005 Geological Society of America.

The volcanic-sedimentary sequence of the Lousal deposit, Iberian Pyrite Belt (Portugal)

NASA Astrophysics Data System (ADS)

Rosa, Carlos; Rosa, Diogo; Matos, Joao; Relvas, Jorge

2010-05-01

The Iberian Pyrite Belt (IPB) is a massive sulfide province that is located in the south of Portugal and Spain, and hosts more than 90 massive sulfide deposits that amount to more than 1850 million metric tonnes of sulfide ore (Tornos, 2006). The ore deposits size, vary from ~1Mt to >100Mt (e.g. Neves Corvo and Aljustrel in Portugal, and Rio Tinto and Tharsis in Spain). The ore deposits are hosted by a submarine sedimentary and volcanic, felsic dominated, succession that constitutes the Upper Devonian to Lower Carboniferous Volcanic and Sedimentary Complex (VSC). The VSC ranges in thickness from approximately 600 to 1300 m (Tornos 2006). The VSC overlies the Phyllite-Quartzite Group (PQ) (Upper Devonian, base unknown) and is overlain by the Baixo Alentejo Flysch Group (Lower to Upper Carboniferous). The Lousal massive sulfide deposit is located in the western part of the IPB and occurs mostly interbedded with black mudstone. The VSC sequence at Lousal mine consists of a mudstone and quartzite sequence (PQ Group) in the lower part of the succession, over which a thick sequence of rhyolitic lavas (>300 m) occurs. Above the rhyolitic lavas there is a thick sequence of black and grey mudstone that hosts the massive sulfide ore bodies, and a rhyolitic sill. The upper part of the VSC sequence consists of a thick mudstone interval that hosts two thick basaltic units, locally with pillows. The rhyolites have small coherent cores, locally with flow bands, that grade to surrounding massive clastic intervals, with large lateral extent. The clasts show jigsaw-fit arrangement in many places and have planar or curviplanar margins and locally are perlitic at the margin. The top contact of these units is in most locations not exposed, which makes difficult to interpret the mode of emplacement. However, the thick clastic intervals, above described, are in accordance with quenching of volcanic glass with abundant water and therefore indicate that quenching of the rhyolites was the dominant fragmentation mechanism. Unlike many locations of the IPB, fiamme-rich pyroclastic units were not identified at Lousal. The ore deposits occur in close proximity with this volcanic centre that may have driven hydrothermal circulation that led to ore formation. The volcanic rocks show intense chloritic alteration, indicating that the mineralizing event occurred after most of the rhyolitic units have emplaced. The massive sulfides show abundant sedimentary structures which is not typical in the massive sulfide deposits of the IPB. The Lousal 50 Mt massive sulfide deposit consists of at least 11 ore bodies and was exploited until 1988 mainly for pyrite. The ores mined averaged 0.7% Cu, 0.8%Pb e 1.4%Zn (Strauss, 1971). These relatively low base metal grades led to an evaluation of the contents and distribution of high-tech element in the ore bodies, which would improve the economic viability of mining the deposit. This evaluation is currently focusing on the distribution and mineralogy of selenium, as ores mined in the past were known to be rich in this element. This work benefits from research projects INCA (PTDC/CTE-GIN/67027/2006; Characterization of crucial mineral resources for the development of renewable energy technologies: The Iberian Pyrite Belt ores as a source of indium and other high-technology elements) and project ARCHYMEDES II (POCTI/CTA/45873/2002), both funded by the Fundação para a Ciência e Tecnologia. REFERENCES Strauss, G.K., 1970. Sobre la geologia de la provincia piritifera del Suroeste de la Peninsula Iberica y sus yacimientos, en especial sobre la mina de pirita de Lousal (Portugal): Memoria del IGME 77, 1-266. Tornos, F., 2006. Environment of formation and styles of volcanogenic massive sulfides: The Iberian Pyrite Belt. Ore Geology Reviews 28, 259-307.

Sedimentology of the Pennsylvanian and Permian Strathearn Formation, Northern Carlin Trend, Nevada; with a section on microfossil controls on the age of the Strathearn Formation

USGS Publications Warehouse

Berger, Vladimir I.; Singer, Donald A.; Theodore, Ted G.; Harris, Anita G.; Stevens, Calvin H.

2001-01-01

Two framework-supported, poorly bedded conglomerate units of the middle Upper Pennsylvanian and middle Lower Permian Strathearn Formation belonging to the overlap assemblage of the Antler orogen are prominent in the northern Carlin trend. These horizons stratigraphically and temporally bracket thrust emplacement of a major allochthonous thrust plate of mainly quartzarenite of the Ordovician Vinini Formation. Lithologic and shape-ratio data from approximately 4,200 pebbles and cobbles at 17 sites as well as biostratigraphic data in the Strathearn, and their geologic implications, are included in this report. Conodont biofacies throughout the Strathearn Formation are normal marine and suggest middle shelf or deeper depositional environments. The conglomerate units roughly are similar in that they contain only chert and quartzarenite pebbles, but they differ in compositional proportions of the two lithologies. The relative proportion of quartzarenite pebbles increases sixfold in the middle Lower Permian upper conglomerate unit versus its content in the middle Upper Pennsylvanian lower unit, whereas chert pebbles predominate in both units. Various roundness categories of chert pebbles in both conglomerate units of the Strathearn show that the equant pebble class (B/A) = 1 clearly is represented strongly even in the subangular category, the lowest roundness categories for the pebbles. Thus, development of equant pebbles cannot be ascribed totally to a rounding process during predeposition transport. The equant character of many pebbles might, in part, be an original feature inherited from pre-erosion rock fractures and (or) bedding that control overall form of the fragments prior to their release to the transport environment. The allochthon of the Coyote thrust has been thrust above the lower conglomerate unit of the Strathearn during a regionally extensive contractional event in the late Paleozoic. The middle Lower Permian upper conglomerate unit, highest unit recognized in the Strathearn Formation, as well as similarly-aged dolomitic siltstone, onlap directly onto quartzarenite that comprises the allochthon of the Coyote thrust. The conglomerate units thus represent submarine fanglomerates whose quartz grains and quartzarenite fragments of variable roundness and shape were derived from a sedimentologically restored largely southeastward advancing late Paleozoic allochthonous lobe of mostly quartzarenite of the Ordovician Vinini Formation. Chert fragments in the conglomerates probably were derived mostly from Devonian Slaven Chert, including a widespread thick melange unit of the Slaven in the footwall of the Coyote thrust. Some chert pebbles may have been derived from the Ordovician Vinini Formation.

Evaluation of ground-water quality data from Kentucky

USGS Publications Warehouse

Sprinkle, C.L.; Davis, R.W.; Mull, D.S.

1983-01-01

The report reviews and summarizes 10,578 chemical analyses, from 2,362 wells and springs in Kentucky. These water-quality data were collected prior to September 30, 1981, and are available in computer files of the U.S. Geological Survey. The principal water-bearing rocks in Kentucky were combined into 10 major groups to aid in data summary preparation and general description of the ground-water quality of the State. Ground water in Kentucky is generally fresh near the outcrop of the rocks comprising the aquifer. Slightly saline to briny water occurs at variable depths beneath the freshwater. Preparation of quadrilinear diagrams revealed three principal geochemical processes in the aquifers of Kentucky: (1) mixing of freshwater and saline water in an interface zone; (2) dedolomitization of the Devonian and Silurian and Lower Mississippian carbonate rocks; (3) sodium for calcium exchange in the freshwater sections of many of the sandstone-shale aquifers. A number of errors and deficiencies were found in the data base. The principal deficiencies were: (1) very few complete analyses which included important field measurements; (2) inadequate definition of the chemistry of the freshwater-saline water interface zone throughout much of the State; (3) no analyses of stable isotopes and dissolved gases; (4) fewer than 10 analyses of most trace metals, radionuclides, and man-made organic chemicals; and (5) no data on bacteria in ground water from any aquifer in the State. (USGS)

Carbon isotope geochemistry of graphite vein deposits from New Hampshire, U.S.A.

NASA Astrophysics Data System (ADS)

Rumble, Douglas, III; Hoering, Thomas C.

1986-06-01

Graphite veins of hydrothermal origin occur throughout central New Hampshire. Veins truncate sillimanite-grade, metasedimentary rocks of Early Devonian-Silurian age and range in size from microscopic to meters in thickness. In addition to graphite, veins may contain quartz, tourmaline, ilmenite, rutile, sillimanite, muscovite or chlorite. Vein mineralogy is generally compatible with wall rock mineral assemblages. Mineralization structures include wall-rock alteration zones, coxcomb graphite crystals on vein walls, and botryoidal, concentrically layered graphite-silicate nodules. The δ13C values of graphite in 14 deposits studied range from - 28%. (PDB) to - 9%. Veins whose textures give evidence of a single stage of mineralization have a narrow range of δ13C values (± 0.2%.). Other veins record successive episodes of graphite precipitation and have ranges of 3-6%. In one sample, adjacent layers of graphite differ by 3%. The wide range of δ13C may be explained by mixing carbon from two crustal reservoirs: biogenic, reduced carbon and carbonate. Precipitation of graphite results from mixing two or more aqueous fluids with different CO 2/CH 4 ratios. Parental fluids are produced by devolatilization during metamorphism. Water-rich fluids with CH4 > CO2 and low δ13C are derived from pelites that contained organic matter; whereas fluids with CO2 > CH4 and high δ13C come from siliceous carbonates.

Lower permian reef-bank bodies’ characterization in the pre-caspian basin

NASA Astrophysics Data System (ADS)

Wang, Zhen; Wang, Yankun; Yin, Jiquan; Luo, Man; Liang, Shuang

2018-02-01

Reef-bank reservoir is one of the targets for exploration of marine carbonate rocks in the Pre-Caspian Basin. Within this basin, the reef-bank bodies were primarily developed in the subsalt Devonian-Lower Permian formations, and are dominated by carbonate platform interior and margin reef-banks. The Lower Permian reef-bank present in the eastern part of the basin is considered prospective. This article provides a sequence and sedimentary facies study utilizing drilling and other data, as well as an analysis and identification of the Lower Permian reef-bank features along the eastern margin of the Pre-Caspian Basin using sub-volume coherence and seismic inversion techniques. The results indicate that the sub-volume coherence technique gives a better reflection of lateral distribution of reefs, and the seismic inversion impedance enables the identification of reef bodies’ development phases in the vertical direction, since AI (impedance) is petrophysically considered a tool for distinguishing the reef limestone and the clastic rocks within the formation (limestone exhibits a relatively high impedance than clastic rock). With this method, the existence of multiple phases of the Lower Permian reef-bank bodies along the eastern margin of the Pre-Caspian Basin has been confirmed. These reef-bank bodies are considered good subsalt exploration targets due to their lateral connectivity from south to north, large distribution range and large scale.

Palaeomagnetic results from the Palaeozoic of Istanbul: A hypothesis for Remagnetization

NASA Astrophysics Data System (ADS)

Lom, Nalan; Domeier, Mathew; Ülgen, Semih Can; İşseven, Turgay; Celal Şengör, Ali Mehmet

2016-04-01

The Istanbul Zone in northwestern Turkey is a part of a larger continental fragment called the Rhodope-Pontide Fragment. The Istanbul Zone differs from its surroundings by its continuous, well-developed sedimentary sequence extending from the early-medial Ordovician to the early Carboniferous. The İstanbul Zone has a complicated deformation history related to the Hercynide (or Scythide), Cimmeride and Alpide orogenies. Although the region of Istanbul shows essentially no metamorphism and only a weak cleavage development, constraining the entire history of the deformation in the İstanbul Zone marginal fold and thrust belt is a difficult task, primarily due to the multiple deformation phases. But yet it is not impossible. The Palaeozoic sequence is cut by late Cretaceous plutonics together with dacitic and andesitic dykes. This arc magmatism is ascribed to the north-dipping subduction of the Neo-Tethyan ocean along the İzmir-Ankara-Erzincan suture. The Palaeozoic sequence is unconformably overlain by Permian and younger sedimentary strata. In this study a total of 523 samples were obtained from 48 sites around İstanbul and Kocaeli. 465 samples collected from Palaeozoic sedimentary rocks and 58 samples belong to the dykes that cut these sediments. Specimens were demagnetized in the laboratory by using both AF and thermal treatments depending on their effectiveness. After demagnetization treatments, 290 specimens showed stable demagnetization patterns and majority of these samples have a characteristic remanent magnetization component close to the present day geomagnetic field. Demagnetization studies demonstrate variable degrees of overprinting in a large number of samples. After the application of the tilt correction, %70 of the specimens failed the fold test at site level (early Ordovician siltstones; late Silurian-early Devonian limestones; late Devonian limestones; early Carboniferous turbidites). Rest of them clearly got scattered with increasing α95 and decreasing k values (mid Ordovician conglomerates; mid-late Devonian shales; late Ordovician-early Silurian sandstone and siltstones). This secondary magnetization, acquired during or after the folding event, constitutes evidence of pervasive remagnetization that can be caused by regional re-heating related to the Cretaceous arc magmatism. This suggestion contradicts the previous palaeomagnetic studies and requires further and detailed investigation on Palaeozoic sequence.

Geology and undiscovered oil and gas resources in the Madison Group, Williston Basin, North Dakota and Montana

USGS Publications Warehouse

Gaswirth, Stephanie B.; Lillis, Paul G.; Pollastro, Richard M.; Anna, Lawrence O.

2010-01-01

Two of the total petroleum systems (TPS) defined as part of the U.S. Geological Survey (USGS) assessment of the Williston Basin contain Mississippian Madison Group strata: 1) the Bakken-Lodgepole TPS, which includes the Lodgepole Formation; and 2) the Madison TPS, which includes the Mission Canyon, Charles, and Spearfish formations. The Bakken-Lodgepole TPS is defined as the area in which oil generated from the upper and lower shales of the Upper Devonian-Lower Mississippian Bakken Formation has accumulated in reservoirs in the Three Forks, Bakken, and Lodgepole formations. Two conventional assessment units (AU) have been identified within the Bakken-Lodgepole TPS, including one in the Bakken Formation and another in the Waulsortian mound reservoirs of the lower Lodgepole Formation. Lodgepole Formation Waulsortian mound oil production has been restricted to a small part of Stark County, North Dakota. Reservoirs are sealed by middle and upper Lodgepole Formation tight argillaceous limestones. Several nonproductive mounds and mound-like structures have also been identified in the Lodgepole Formation. Productivity correlates closely with the oil window of the Bakken Formation shales, and also indicates the likelihood of limited lateral migration of Bakken Formation oil into Lodgepole Formation reservoirs in North Dakota and Montana. Such considerations limit the estimated mean of undiscovered, technically recoverable resources to 8 million barrels of oil (MMBO) for the Lodgepole Formation conventional reservoirs. The Madison TPS is defined as the area where oil generated from Mission Canyon and Charles formation source rocks has accumulated in reservoirs of the Mission Canyon and Charles formations and in reservoirs within the Triassic Spearfish Formation. One continuous reservoir AU, the Mission Canyon-Charles AU, was defined within the Madison TPS; its boundary coincides with the TPS boundary. There is extensive conventional production throughout the AU on major structures and in stratigraphic-structural traps. The largest fields are on the Little Knife, Billings Nose, and Nesson anticlines. Recent studies show that Madison Group oils were generated from organic-rich Mission Canyon Formation and Ratcliffe Interval carbonates adjacent to the reservoirs. Seals were formed by overlying or lateral evaporites or tight carbonates. Based on available geologic and production data, the undiscovered oil resources for conventional reservoirs in the Mission Canyon-Charles AU were estimated to have a mean of 45 MMBO.

Tectonic stresses in the lithosphere: constraints provided by the experimental deformation of rocks.

USGS Publications Warehouse

Kirby, S.H.

1980-01-01

The strengths of rocks clearly place an upper limit on the stress that can be sustained by the upper half of the lithosphere. Laboratory data on rock rheology are generally lacking at intermediate temperatures and pressures on the important rock types expected in the lithosphere, so a definitive accounting of the strength distribution with depth in the upper lithosphere is presently unattainable. Analogies are drawn between the fragmentary strength data on slicates at intermediate temperature and the more extensive experimental data on marble and limestone, and several tentative conclusions are drawn: First, brittle processes, such as faulting and cataclasis, are expected to control rock strength at low pressures and temperatures. The strengths associated with these brittle mechanisms increase rapidly with increasing effective pressure and are relatively insensitive to temperature and strain rate. Second, the transitions between brittle and ductile processes occur at critical values of the least principal stress sigma3. I suggest that the concept of the deformation mechanism map of Ashby (1972) be extended to brittle-ductile transitions by normalizing the applied differential stress sigma by sigma3, i.e., the transitions occur at critical values of sigma/sigma3. -from Author

Isotopic composition of ice cores and meltwater from upper fremont glacier and Galena Creek rock glacier, Wyoming

USGS Publications Warehouse

DeWayne, Cecil L.; Green, J.R.; Vogt, S.; Michel, R.; Cottrell, G.

1998-01-01

Meltwater runoff from glaciers can result from various sources, including recent precipitation and melted glacial ice. Determining the origin of the meltwater from glaciers through isotopic analysis can provide information about such things as the character and distribution of ablation on glaciers. A 9.4 m ice core and meltwater were collected in 1995 and 1996 at the glacigenic Galena Creek rock glacier in Wyoming's Absaroka Mountains. Measurements of chlorine-36 (36Cl), tritium (3H), sulphur-35 (35S), and delta oxygen-18 (??18O) were compared to similar measurements from an ice core taken from the Upper Fremont Glacier in the Wind River Range of Wyoming collected in 1991-95. Meltwater samples from three sites on the rock glacier yielded 36Cl concentrations that ranged from 2.1 ?? 1.0 X 106 to 5.8??0.3 X 106 atoms/l. The ice-core 36Cl concentrations from Galena Creek ranged from 3.4??0.3 X 105 to 1.0??0.1 X 106 atoms/l. Analysis of an ice core from the Upper Fremont Glacier yielded 36Cl concentrations of 1.2??0.2 X 106 and 5.2??0.2 X 106 atoms/l for pre- 1940 ice and between 2 X 106 and 3 X 106 atoms/l for post-1980 ice. Purdue's PRIME Lab analyzed the ice from the Upper Fremont Glacier. The highest concentration of 36Cl in the ice was 77 ?? 2 X 106 atoms/l and was deposited during the peak of atmospheric nuclear weapons testing in the late 1950s. This is an order of magnitude greater than the largest measured concentration from both the Upper Fremont Glacier ice core that was not affected by weapons testing fallout and the ice core collected from the Galena Creek rock glacier. Tritium concentrations from the rock glacier ranged from 9.2??0.6 to 13.2??0.8 tritium units (TU) in the meltwater to -1.3??1.3 TU in the ice core. Concentrations of 3H in the Upper Fremont Glacier ice core ranged from 0 TU in the ice older than 50 years to 6-12 TU in the ice deposited in the last 10 years. The maximum 3H concentration in ice from the Upper Fremont Glacier deposited in the early 1960s during peak weapons testing fallout for this isotope was 360 TU. One meltwater sample from the rock glacier was analyzed for 35S with a measured concentration of 5.4??1.0 millibecquerel per liter (mBeq/l). Modern precipitation in the Rocky Mountains contains 35S from 10 to 40 mBeq/L. The ??18O results in meltwater from the Galena Creek rock glacier (-17.40??0.1 to -17.98??0.1 per mil) are similar to results for modern precipitation in the Rocky Mountains. Comparison of these isotopic concentrations from the two glaciers suggest that the meltwater at the Galena Creek site is composed mostly of melted snow and rain that percolates through the rock debris that covers the glacier. Additionally, this water from the rock debris is much younger (less than two years) than the reported age of about 2000 years for the subsurface ice at the mid-glacier coring site. Thus the meltwater from the Galena Creek rock glacier is composed primarily of melted surface snow and rain water rather than melted glacier ice, supporting previous estimates of slow ablation rates beneath the surface debris of the rock glacier.

GP Section selects Best Student Paper

NASA Astrophysics Data System (ADS)

The AGU Geomagnetism and Paleomagnetism (GP) Section has announced its selection of a paper entitled “Multicomponent Magnetization of the Upper Silurian-Lower Devonian Ringerike Sandstone, Adjacent Dikes, and Permian Lavas, Oslo, Norway” as the best GP student paper presented at the 1986 AGU Spring Meeting. The primary author, Dartmouth College Ph.D. candidate David Douglass, was assisted on the paper by a colleague from Lamont-Doherty Geological Observatory. Douglass received his B.S. in geology from the University of California, Los Angeles, in 1980, and in 1984, he received his M.S. in earth sciences at Dartmouth. His current studies examine the paleomagnetism, structure, and sedimentation of several North Atlantic old red sandstone basins.

Constraints on the Amount of deeply subducted Water from numerical Models in comparison with natural Samples

NASA Astrophysics Data System (ADS)

Konrad-Schmolke, M.; Halama, R.

2014-12-01

The subduction of hydrated slab mantle to beyond-arc depths is the most important and yet weakly constrained factor in the quantification of the Earth's deep geologic water cycle. During subduction of hydrated oceanic lithosphere, dehydration reactions in the downgoing plate lead to a partitioning of water between upper and lower plate. Water retained in the slab is recycled into the mantle where it controls its rheology and thus plate tectonic velocities. Hence, quantification of the water partitioning in subduction zones is crucial for the understanding of mass transfer between the Earth's surface and the mantle. Combined thermomechanical and thermodynamic models yield quantitative constraints on the water cycle in subduction zones, but unless model results can be linked to natural observations, the reliability of such models remains speculative. We present combined thermomechanical, thermodynamic and geochemical models of active and paleo-subduction zones, whose results can be tested with independent geochemical features in natural rocks. In active subduction zones, evidence for the validity of our model comes from the agreement between modeled and observed across-arc trends of boron concentrations and isotopic compositions in arc volcanic rocks. In the Kamchatkan subduction zone, for example, the model successfully predicts complex geochemical patterns and the spatial distribution of arc volcanoes. In paleo-subduction zones (e.g. Western Gneiss Region and Western Alps), constraints on the water budget and dehydration behavior of the subducting slab come from trace element zoning patterns in ultra-high pressure (UHP) garnets. Distinct enrichments of Cr, Ni and REE in the UHP zones of the garnets can be reconciled by our models that predict intense rehydration and trace element re-enrichment of the eclogites at UHP conditions by fluids released from the underlying slab mantle. Models of present-day subduction zones indicate the presence of 2.5-6 wt.% of water within the uppermost 15 km of the subducted slab mantle. Depending on hydration depth, between 25 and 90% of this water is recycled into the deeper mantle. The Lower Devonian example from the Western Gneiss Region indicates that subduction of water into the Earth's deeper mantle is an active process at least since the middle Paleozoic.

Devonian magmatism in the Timan Range, Arctic Russia - subduction, post-orogenic extension, or rifting?

NASA Astrophysics Data System (ADS)

Pease, V.; Scarrow, J. H.; Silva, I. G. Nobre; Cambeses, A.

2016-11-01

Devonian mafic magmatism of the northern East European Craton (EEC) has been variously linked to Uralian subduction, post-orogenic extension associated with Caledonian collision, and rifting. New elemental and isotopic analyses of Devonian basalts from the Timan Range and Kanin Peninsula, Russia, in the northern EEC constrain magma genesis, mantle source(s) and the tectonic process(es) associated with this Devonian volcanism to a rift-related context. Two compositional groups of low-K2O tholeiitic basalts are recognized. On the basis of Th concentrations, LREE concentrations, and (LREE/HREE)N, the data suggest two distinct magma batches. Incompatible trace elements ratios (e.g., Th/Yb, Nb/Th, Nb/La) together with Nd and Pb isotopes indicate involvement of an NMORB to EMORB 'transitional' mantle component mixed with variable amounts of a continental component. The magmas were derived from a source that developed high (U,Th)/Pb, U/Th and Sm/Nd over time. The geochemistry of Timan-Kanin basalts supports the hypothesis that the genesis of Devonian basaltic magmatism in the region resulted from local melting of transitional mantle and lower crust during rifting of a mainly non-volcanic continental rifted margin.

Observations on the geology and petroleum potential of the Cold Bay-False Pass area, Alaska Peninsula

USGS Publications Warehouse

McLean, Hugh James

1979-01-01

Upper Jurassic strata in the Black Hills area consist mainly of fossiliferous, tightly cemented, gently folded sandstone deposited in a shallow marine environment. Upper Cretaceous strata on Sanak Island are strongly deformed and show structural features of broken formations similar to those observed in the Franciscan assemblage of California. Rocks exposed on Sanak Island do not crop out on the peninsular mainland or on Unimak Island, and probably make up the acoustic and economic basement of nearby Sanak basin. Tertiary sedimentary rocks on the outermost part of the Alaska Peninsula consist of Oligocene, Miocene, and lower Pliocene volcaniclastic sandstone, siltstone, and conglomerate deposited in nonmarine and very shallow marine environments. Interbedded airfall and ash-flow tuff deposits indicate active volcanism during Oligocene time. Locally, Oligocene strata are intruded by quartz diorite plutons of probable Miocene age. Reservoir properties of Mesozoic and Tertiary rocks are generally poor due to alteration of chemically unstable volcanic rock fragments. Igneous intrusions have further reduced porosity and permeability by silicification of sandstone. Organic-rich source rocks for petroleum generation are not abundant in Neogene strata. Upper Jurassic rocks in the Black Hills area have total organic carbon contents of less than 0.5 percent. Deep sediment-filled basins on the Shumagin Shelf probably contain more source rocks than onshore correlatives, but reservoir quality is not likely to be better than in onshore outcrops. The absence of well-developed folds in most Tertiary rocks, both onshore and in nearby offshore basins, reduces the possibility of hydrocarbon entrapment in anticlines.

Basis for paleoenvironmental interpretation of magnetic properties of sediment from Upper Klamath Lake (Oregon): Effects of weathering and mineralogical sorting

USGS Publications Warehouse

Rosenbaum, J.G.; Reynolds, R.L.

2004-01-01

Studies of magnetic properties enable reconstruction of environmental conditions that affected magnetic minerals incorporated in sediments from Upper Klamath Lake. Analyses of stream sediment samples from throughout the catchment of Upper Klamath Lake show that alteration of Fe-oxide minerals during subaerial chemical weathering of basic volcanic rocks has significantly changed magnetic properties of surficial deposits. Titanomagnetite, which is abundant both as phenocrysts and as microcrystals in fresh volcanic rocks, is progressively destroyed during weathering. Because fine-grained magnetite is readily altered due to large surface-to-volume ratios, weathering causes an increase in average magnetic grain size as well as reduction in the quantity of titanomagnetite both absolutely and relative to hematite. Hydrodynamic mineralogical sorting also produces differences in magnetic properties among rock and mineral grains of differing sizes. Importantly, removal of coarse silicate and Fe-oxide grains by sorting concentrated extremely fine-grained magnetite in the resulting sediment. The effects of weathering and sorting of minerals cannot be completely separated. These processes combine to produce the magnetic properties of a non-glacial lithic component of Upper Klamath Lake sediments, which is characterized by relatively low magnetite content and coarse magnetic grain size. Hydrodynamic sorting alone causes significant differences between the magnetic properties of glacial flour in lake sediments and of fresh volcanic rocks in the catchment. In comparison to source volcanic rocks, glacial flour in the lake sediment is highly enriched in extremely fine-grained magnetite.

Timing of crust formation and recycling in accretionary orogens: Insights learned from the western margin of South America

NASA Astrophysics Data System (ADS)

Bahlburg, Heinrich; Vervoort, Jeffrey D.; Du Frane, S. Andrew; Bock, Barbara; Augustsson, Carita; Reimann, Cornelia

2009-12-01

Accretionary orogens are considered major sites of formation of juvenile continental crust. In the central and southern Andes this is contradicted by two observations: siliciclastic fills of Paleozoic basins in the central Andean segment of the accretionary Terra Australis Orogen consist almost exclusively of shales and mature sandstones; and magmatic rocks connected to the Famatinian (Ordovician) and Late Paleozoic magmatic arcs are predominantly felsic and characterized by significant crustal contamination and strongly unradiogenic Nd isotope compositions. Evidence of juvenile crustal additions is scarce. We present laser ablation (LA)-ICPMS U-Pb ages and LA-MC-ICPMS Hf isotope data of detrital zircons from seven Devonian to Permian turbidite sandstones incorporated into a Late Paleozoic accretionary wedge at the western margin of Gondwana in northern Chile. The combination with Nd whole-rock isotope data permits us to trace the evolution of the South American continental crust through several Proterozoic and Paleozoic orogenic cycles. The analyzed detrital zircon spectra reflect all Proterozoic orogenic cycles representing the step-wise evolution of the accretionary SW Amazonia Orogenic System between 2.0 and 0.9 Ga, followed by the Terra Australis Orogen between 0.9 and 0.25 Ga. The zircon populations are characterized by two prominent maxima reflecting input from Sunsas (Grenville) age magmatic rocks (1.2-0.9 Ga) and from the Ordovician to Silurian Famatinian magmatic arc (0.52-0.42 Ga). Grains of Devonian age are scarce or absent from the analyzed zircon populations. The Hf isotopic compositions of selected dated zircons at the time of their crystallization ( ɛHf ( T) ; T = 3.3-0.25 Ga) vary between - 18 and + 11. All sandstones have a significant juvenile component; between 20 and 50% of the zircons from each sedimentary rock have positive ɛHf ( T) and can be considered juvenile. The majority of the juvenile grains have Hf-depleted mantle model ages (Hf TDM) between 1.55 and 0.8 Ga, the time of the Rondonia-San Ignacio and Sunsas orogenic events on the Amazonia craton. The corresponding whole-rock ɛNd ( T) values fot these same rocks are between - 8 and - 3 indicating a mixture of older evolved and juvenile sources. Nd-depleted mantle model ages (Nd TDM*) are between 1.5 and 1.2 Ga and coincide broadly with the zircon Hf model ages. Our data indicate that the Paleo- and Mesoproterozoic SW Amazonia Orogenic System, and the subsequent Neoproterozoic and Paleozoic Terra Australis Orogen in the region of the central and southern Andes, developed following two markedly different patterns of accretionary orogenic crustal evolution. The SW Amazonia Orogenic System developed by southwestward growth over approximately 1.1 Ga through a combination of accretion of juvenile material and crustal recycling typical of the extensional or retreating mode of accretionary orogens. In contrast, the central Andean segment of the Terra Australis Orogen evolved from 0.9 to 0.25 Ga in the compressional or advancing mode in a relatively fixed position without the accretion of oceanic crustal units or large scale input of juvenile material to the orogenic crust. Here, recycling mainly of Mesoproterozoic continental crust has been the dominant process of crustal evolution.

Origin and geodynamic significance of the early Mesozoic Weiya LP and HT granulites from the Chinese Eastern Tianshan

NASA Astrophysics Data System (ADS)

Mao, Ling-Juan; He, Zhen-Yu; Zhang, Ze-Ming; Klemd, Reiner; Xiang, Hua; Tian, Zuo-Lin; Zong, Ke-Qing

2015-12-01

The Chinese Tianshan in the southwestern part of the Central Asian Orogenic Belt (CAOB) is characterized by a variety of high-grade metamorphic rocks, which provide critical constraints for understanding the geodynamic evolution of the CAOB. In this paper, we present detailed petrological and zircon U-Pb geochronological studies of the Weiya low-pressure and high-temperature (LP-HT) granulites of the Chinese Eastern Tianshan. These granulites were previously considered to be a product of a regional metamorphic orogenic event. Due to different bulk-rock chemistries the Weiya granulites, which occur as lenses within the contact metamorphic aureole of the Weiya granitic ring complex, have a variety of felsic-pelitic and mafic granulites with different textural equilibrium mineral assemblages including garnet-cordierite-sillimanite-bearing granulites, cordierite-sillimanite-bearing granulites, cordierite-orthopyroxene-bearing granulites, and orthopyroxene-clinopyroxene-bearing granulites. Average P-T thermobarometric calculations and conventional geothermobarometry indicates that the Weiya granulites underwent early prograde metamorphism under conditions of 600-650 °C at 3.2-4.2 kbar and peak metamorphism of 750-840 °C at 2.9-6.3 kbar, indicating a rather high geothermal gradient of ca. 60 °C/km. Zircon U-Pb LA-ICP-MS dating revealed metamorphic ages between 244 ± 1 to 237 ± 3 Ma, which are in accordance with the crystallization age of the Weiya granitic ring complex. We suggest that the formation of the Weiya granulites was related to contemporaneous granitic magmatism instead of a regional metamorphic orogenic event. In addition, a Late Devonian metamorphic age of ca. 380 Ma was recorded in zircon mantle domains from two pelitic samples which is consistent with the metamorphic age of the Xingxingxia metamorphic complex in the Chinese Eastern Tianshan. This suggests that the mantle domains of the zircon grains of the Weiya granulites probably formed during the Late Devonian regional metamorphism and were overprinted by the Early Triassic contact metamorphism. Therefore, Early Triassic geodynamic models for the southwestern part of the CAOB, which are based on a previously suggested regional metamorphic orogenic event of the Weiya granulites, need to be viewed with caution.

87Sr/86Sr Across the Devonian-Carboniferous Transition Within the Pho Han Formation, Cat Ba Island, Vietnam: New Data Outside of an Old Orogeny

NASA Astrophysics Data System (ADS)

Paschall, O. C.; Carmichael, S. K.; Dombrowski, A. D.; Batchelor, C. J.; Coleman, D. S.; Waters, J. A.; Königshof, P.

2017-12-01

The Devonian-Carboniferous (D-C) transition is a period of mass extinction and rapid global faunal changes that affected both marine and terrestrial ecosystems. Although the paleontology and carbon and oxygen isotopes across of the D-C boundary have been studied in detail, there is very little continuous 87Sr/86Sr isotope data for this time iteration due to unconformities and/or diagenetic alteration in many sections. Conodont biostratigraphy indicates that the D-C boundary is present within the Pho Han Formation on Cat Ba Island in northeastern Vietnam. This unit represents a starved basinal facies on the South China carbonate platform, and has continuous sedimentation across the D-C boundary. Whole rock geochemical results indicate increased clastic input at the D-C transition, potentially due to the regression observed in many Hangenberg Event localities around the world, but the isolated nature of the basin could instead indicate complete shutdown of the carbonate factory. New 87Sr/86Sr measurements of carbonate across the D-C boundary in the Pho Han Formation indicate oscillating fluctuations from 0.708052 to 0.708672. Many of these values are within the McArthur et al. (2012) LOWESS fit for seawater, with excursions towards higher values tentatively identified at the boundary between the Palmatolepis expansa and lower Siphonodella praesulcata conodont zones, and within the Siphonodella duplicata zone. There is a lack of correlation between 87Sr/86Sr values with whole rock geochemistry and δ18O isotope values across the section, suggesting that these 87Sr/86Sr values are not due to clastic contamination and that the samples have not experienced major diagenetic alteration. The continuous sedimentation in this section and its location in an area far from the Variscan orogeny make this unit a valuable site in which to compare 87Sr/86Sr ratios to existing studies in Europe and North America which experienced substantial sediment shedding from the Appalachian Mountains. McArthur et al. (2012) The Geologic Time Scale, 1: 127-144.

The problem of the age and structural position of the Blyb metamorphic complex (Fore Range zone, Great Caucasus) granitoids.

NASA Astrophysics Data System (ADS)

Kamzolkin, Vladimir; Latyshev, Anton; Ivanov, Stanislav

2016-04-01

The Blyb metamorphic complex (BMC) of the Fore Range zone is one of the most high-grade metamorphosed element of the Great Caucasus fold belt. Determination of the timing and the mechanism of formation of the Fore Range fold-thrust structures are not possible without investigation of the BMC located at the basement of its section. At the same time, the conceptions about its structure and age are outdated and need revision. Somin (2011) determined the age of the protolith and metamorphism of the Blyb complex as the Late Devonian - Early Carboniferous. We have recently shown that the BMC has not the dome, as previously thought, but nappe structure (Vidjapin, Kamzolkin, 2015), and is metamorphically coherent with the peak metamorphism pressures up to 22 kbar (Kamzolkin et al., 2015; Konilov et al., 2013). Considering the age and structure of the Blyb complex it is necessary to revise the age of granitoid intrusions and their relations with gneisses and schists, which constitute the main part of the section of the complex. Most authors (Gamkrelidze, Shengelia, 2007; Lavrischev, 2002; Baranov, 1967) adheres to Early Paleozoic age of intrusives, which is doubtful, considering the younger age of metamorphic rocks. We suppose, that the intrusive bodies broke through a BMC nappe structure during the exhumation of the complex (Perchuk, 1991) at the Devonian - Carboniferous boundary. Seemingly, the massive monzodiorites body (Lavrischev, 2002), intruding garnet-muscovite schists and amphibolite gneisses of the Blyb complex and cut by the Main Caucasian fault (MCF), are younger. Given the timing of termination of the MCF movement activity as the Middle Jurassic (Greater Caucasus..., 2005), their age should be in the Early Carboniferous - Middle Jurassic interval. At the same time, on the modern geological map (Lavrischev, 2002) monzodiorites body is assigned to the Middle Paleozoic. The study of the BMC granitoids and monzodiorites will help in determining of the mechanism and age of exhumation of the Blyb metamorphic complex high-pressure rocks. The reported study was partially supported by RFBR, research projects No. 16-35-00571mol_a; 16-05-01012a

Geochronology and geochemistry of the Borohoro pluton in the northern Yili Block, NW China: Implication for the tectonic evolution of the northern West Tianshan orogen

NASA Astrophysics Data System (ADS)

Wang, Meng; Zhang, Jinjiang; Zhang, Bo; Liu, Kai; Chen, Youxin; Zheng, Yanrong

2018-03-01

The closure of the North Tianshan Ocean between the Junggar Terrane and the Yili Block is a longtime debated issue in literature, because of the different understanding of the Carboniferous volcanic rocks in the northern margin of the Yili Block. This study presents new geochronological and whole-rock geochemical data for the granitic rocks from the Borohoro pluton to provide constraints on the tectonic regime for the northern West Tianshan during the Carboniferous. LA-ICP-MS U-Pb dating results reveal two magmatic phases for the Borohoro pluton. The former magmatic activity in the Early Carboniferous formed the fine-grained granodiorite (332 Ma). The later magmatic activity occurred during the Late Carboniferous (305-300 Ma), forming a diversity of granitic rocks, involving quartz diorite, granodiorite and granite. Geochemical and mineralogical studies reveal that the studied granitic rocks from the Borohoro pluton all belong to metaluminous to weakly peraluminous, calc-alkaline I-type granites. They are characterized by enrichment in LILEs relative to HFSEs, and depletion of Nb, Ti and P, typical of continental arc-type granites. The intermediate SiO2, high Al2O3, and relatively low Fe2O3T, MgO and TiO2 contents reflect that these granitic rocks are mainly crust-derived. But the high Mg# values for most samples and the occurrence of microgranular mafic enclaves indicate that their magma sources were mixed by mantle-derived components. Especially, the Late Carboniferous rocks define an elegant mixing trend in both the Rb-Rb/V and the 1/V-Rb/V diagrams, consistent with mixing between magmas from subcontinental lithospheric mantle and mafic lower crust. Taking into consideration of the facts that all the Devonian to Carboniferous granitoids belong to calc-alkaline I-type granites, and granitoids of A-type didn't appear until the Early Permian, we suggest that the subduction of the North Tianshan Ocean continued to the Late Carboniferous, generating the granitic rocks of the Borohoro pluton.

Origin of high-grade gold ore, source of ore fluid components, and genesis of the Meikle and neighboring Carlin-type deposits, Northern Carlin Trend, Nevada

USGS Publications Warehouse

Emsbo, P.; Hofstra, A.H.; Lauha, E.A.; Griffin, G.L.; Hutchinson, R.W.

2003-01-01

The Meikle mine exploits one of the world's highest grade Carlin-type gold deposits with reserves of ca. 220 t gold at an average grade of 24.7 g/t. Locally, gold grades exceed 400 g/t. Several geologic events converged at Meikle to create these spectacular gold grades. Prior to mineralization, a Devonian hydrothermal system altered the Bootstrap limestone to Fe-rich dolomite. Subsequently the rocks were brecciated by faulting and Late Jurassic intrusive activity. The resulting permeability focused flow of late Eocene Carlin-type ore fluids and allowed them to react with the Fe-rich dolomite. Fluid inclusion data and mineral assemblages indicate that these fluids were hot (ca. 220??C),of moderate salinity (400 g/t. Petrographic observations, geochemical data, and stable isotope results from the Meikle mine and other deposits at the Goldstrike mine place important constraints on genetic models for Meikle and other Carlin-type gold deposits on the northern Carlin trend. The ore fluids were meteoric water (??D = -135???, ??18O = -5???) that interacted with sedimentary rocks at a water/rock ratio of ca. 1 and temperatures of ca. 220??C. The absence of significant silicification suggests that there was little cooling of the ore fluids during mineralization. These two observations strongly suggest that ore fluids were not derived from deep sources but instead flowed parallel to isotherms. The gold was transported by H2S (??34S = 9???), which was derived from Paleozoic sedimentary rocks. The presence of auriferous sedimentary exhalative mineralization in the local stratigraphic sequence raises the possibility that preexisting concentrations of gold contributed to the Carlin-type deposits. Taken together our observations suggest that meteoric water evolved to become an ore fluid by shallow circulation through previously gold- and sulfur-enriched rocks. Carlin-type gold deposits formed where these fluids encountered permeable, reactive Fe-rich rocks.

No geochemical evidence for an asteroidal impact at late Devonian mass extinction horizon

NASA Astrophysics Data System (ADS)

McGhee, G. R., Jr.; Gilmore, J. S.; Orth, C. J.; Olsen, E.

1984-04-01

Three sedimentary sequences in New York State (Dunkirk Beach, Walnut Creek Gorge, and Mills Mills) and one sedimentary sequence in Belgium (Sinsin), that cross the Devonian Frasnian-Famennian boundary, were examined for an iridium (Ir) anomaly to determine whether the biotic extinctions at the end of the Cretaceous could have been caused by an asteroidal impact. The sampling at three of the four areas was on 2-cm center points, and 15 to 20 g of sample were collected. The instrumental neutron activation method required 5 g samples, and consequently the distance between samples was less than 1 cm. Though the Devonian samples studied had a high probability of locating an Ir anomaly, none was found. The highest Ir values were between 0.2 and 2 percent of those reported for the marine and terrestrial Ir analyses at the Cretaceous-Tertiary boundary, and Devonian pyrite-rich sediments did not exhibit high Ir concentrations.

Cambrian to Devonian evolution of alluvial systems: The sedimentological impact of the earliest land plants

NASA Astrophysics Data System (ADS)

Davies, Neil S.; Gibling, Martin R.

2010-02-01

In present-day alluvial environments, the impact of vegetation on sedimentological processes and deposits is well known. A vegetated catchment may decrease sediment yield, sediment erodibility, Hortonian overland flow, aeolian winnowing of fines, the proportion of sediment transported as bedload, and may increase bank stability, infiltration into substrates, and bed roughness. Vegetation also promotes the production of chemically-weathered clays and soils and the adoption of a meandering style. It is generally understood that, prior to the evolution of terrestrial vegetation during the Early Palaeozoic, ancient alluvial systems were markedly different from modern systems, with many systems adopting a "sheet-braided" style. This understanding has previously informed the interpretations of many Precambrian pre-vegetation alluvial successions, but there has been relatively little work regarding Early Palaeozoic alluvial successions laid down prior to and during the initial colonization of the Earth's surface by plants. A comprehensive review of 144 Cambrian to Devonian alluvial successions documented in published literature was combined with original field data from 34 alluvial successions across Europe and North America. The study was designed to identify changes in alluvial style during the period that vegetation was evolving and first colonizing alluvial environments. An increase in mudrock proportion and sandstone maturity is apparent, along with a decrease in overall sand grain size through the Early Palaeozoic. These trends suggest that primitive vegetation cover promoted the production and preservation of muds from the mid Ordovician onwards and increased the residence time of sand-grade sediment in alluvial systems. The compilation also enables the first stratigraphic occurrence of certain vegetation-dependent sedimentary features to be pinpointed and related to the evolution of specific palaeobotanical adaptations. The first markedly heterolithic alluvial sequences appeared at about the same time as the most primitive terrestrial vegetation in the Ordovician, and prolific pedogenic calcite, charcoal and bioturbated floodplain fines first appeared in the rock record at about the same time as vascular-plant macrofossils became abundant in the late Silurian. Lateral accretion sets in channel deposits appeared near the Silurian-Devonian boundary, at or shortly before the appearance of underground rooting systems, and become progressively more abundant in the record during the Devonian, implying a major expansion of meandering rivers as rooted plants stabilized river banks. Coals become abundant after the development of plant arborescence. The analysis suggests that the evolution of embryophytes had a profound effect on fluvial processes and deposits, and this period of landscape evolution must be considered amongst the most significant environmental and geomorphological changes in Earth history, with profound consequences for all aspects of the Earth system.

Geology of the southern Elkhorn Mountains, Jefferson and Broadwater Counties, Montana

USGS Publications Warehouse

Klepper, M.R.; Weeks, R.A.; Ruppel, E.T.

1957-01-01

The geology of an area of about 270 square miles in the southern Elkhorn Mountains, west of Townsend in west-central Montana, is described. The mountains in the southern part of the area comprise northward-trending alternating ridges and valleys underlain principally by folded sedimentary rocks. They merge northward into the higher and more rugged main mass of the mountains, which is underlain principally by upper Cretaceous volcanic rocks. The mountaintops are 1,000 to 4,500 feet above the major valleys. The sedimentary rocks range in age from Precambrian to Tertiary and the igneous rocks from late Cretaceous to probably middle Tertiary. The oldest rocks are varicolored mudstone, shale, and sandstone of the Belt series of late Precambrian age. They are overlain with slight unconformity by a moderately thick but incomplete section of Paleozoic rocks. The basal Paleozoic formation is the Flathead quartzite of Middle Cambrian age, which is overlain by alternating units of shale and carbonate rock : the Wolsey shale, the Meagher limestone, the Park shale, the Pilgrim dolomite, and the Red Lion formation, all of Cambrian age. A slight erosional unconformity between the Red Lion formation and the Maywood formation of late Devonian age marks a long interval of crustal stability in the area. The Maywood is overlain by the Jefferson dolomite and the Three Forks shale of Late Devonian and Mississippian age, and these in turn are conformably overlain by the Lodgepole and Mission Canyon limestones, a thick carbonate sequence of Mississippian age. A slight erosional unconformity separates the Mission Canyon limestone from the Amsden formation, which probably includes beds of both Mississippian and Pennsylvanian age. The Amsden is composed of a heterogeneous assemblage of arenaceous, argillaceous, dolomitic, and calcareous rocks and grades upward into the Quadrant formation of Pennsylvanian age, an alternation of quartzitic sandstone and dolomite. At the top of the Paleozoic section is the Phosphoria formation of Permian age, a thin unit of chert and quartzitic sandstone that contains a few thin phosphate beds. The basal Mesozoic unit is the Swift formation of late Jurassic age, a thin calcareous marine sandstone that overlies the Phosphoria with slight erosional unconformity. It is overlain by nonmarine shale and sandstone of the Morrison formation of late Jurassic age and the Kootenai formation of Early Cretaceous age. The Kootenai is overlain, possibly with slight erosional unconformity, by the Colorado formation an assemblage of marine dark shale and siliceous mudstone and nonmarine quartz-chert sandstone. The Colorado formation as here used includes beds of both Early and Late Cretaceous age. The Colorado in places grades upwards into a sequence of feldspathic sandstone and tuff beds here named the Slim Sam formation. Elsewhere within the area, the Slim Sam formation is absent, probably in part owing to erosion and in part nondeposition. Where present, the Slim Sam grades upward into a thick sequence of andesitic and quartz latitic volcanic rocks, comprising tuffs, lapilli tuffs, breccias, welded tuffs and flows, that are here named the Elkhorn Mountains volclinics and are probably entirely of Cretaceous age. Where the Slim Sam formation is absent, the Elkhorn Mountains volcanics rest with angular unconformity on beds as old as the Morrison. The pre-Tertiary layered rocks, aggregating more than 15,000 feet in thickness, were folded and intruded by igneous rocks of several types, and the area was uplifted and eroded to a terrain of mature relief, similar to that of the present. During the Oligocene epoch, volcanic sediments with interbreds of nonvolcanic gravel accumulated. These beds were in turn moderately eroded, and gravel of Miocene ( ?) age was deposited in channels within them. Subsequently, probably during the Pliocene epoch, the Tertiary beds were weakly deformed locally, and a pediment was cut across the Tertiary and older rocks in the southern part of the area. Fan gravel, in part of Recent origin and in part older, blankets parts of the pediment. Glacial deposits of at least two stages of Pleistocene glaciation are present in the higher mountains in the northern part of the area. The intrusive igneous rocks, except for a few felsite dikes of uncertain age, are divisible into two groups, primarily on the basis of structural relations and secondarily on the basis of composition and fabric. The older group of dioritic and andesitic rocks were intruded in part, if not wholly, prior to the main folding and are similar in chemical and mineralogical composition to the Elkhorn Mountains volcanics. They were probably emplaced throughout the period of volcanism that commenced in late Niobrara time and continued until late Cretaceous time. The younger group consists chiefly of quartzbearing phanerites but includes rocks ranging from gabbro to alaskitic granite and aplite. These rocks were emplaced after the main episode of folding and faulting. The Boulder batholith, composed dominantly of quartz monzonite, is the principal body of this younger group. The older igneous rocks metamorphosed the invaded rocks only slightly. In contrast, the younger intrusive bodies, and especially the batholith, altered and recrystallized the country rock in moderately broad belts, changing them to various types of hornfels, calcsilicate rock, marble, and vitreous quartzite. Concomitantly magnetite, garnet, axinite, and other high-temperature replacement minerals formed locally as products of additive metamorphism. The pre-Tertiary layered rocks of the southern Elkhorn Mountains are folded into northward-trending folds and are cut by many faults. The sedimentary rocks tend to be more tightly folded than the Elkhorn Mountains volcanics, although both were involved in the major folding. The principal folds of the area from east to west are : a major dome, a complex syncline with several second-order folds, and a remnant of a northward-plunging anticline, the major part of which was engulfed by the batholith. The folded rocks are cut by many faults of small to moderate displacement and by two faults of large displacement. Most of the faults were probably formed by the same forces that produced the folds. The origin of the two major faults, however, is uncertain, and may be related to igneous activity. The batholith crosscuts the folded structure and is in turn cut by small faults. Some parts of the area were elevated along steep normal faults in late Tertiary time. The southern part of the Elkhorn Mountains has been mountainous at least since early Oligocene time, and probably began to take form during the Cretaceous. As a consequence of long continued erosion, the modern topography reflects the structure and lithologic character of the underlying rocks except in a few areas blanketed by poorly consolidated Tertiary rocks and in the higher mountains where glaciation has been prominent. Silver, lead, zinc, and gold have been produced, either singly or, more typically, as a combination of metals from a number of types of ore deposits. Replacement deposits in carbonate rocks are the most common type, but veins, contact metamorphic deposits, and pipelike bodies of breccia cemented by ore and gangue minerals also are present. The Elkhorn mining district has the largest number of mines and the greatest variety of types of deposits. In the Tizer Basin several narrow goldbearing veins cut andesitic volcanic rocks, and in the southern part of the area sporadic small veins and replacement deposits occur in carbonate rocks. The mines and prospects of the area are described, and some suggestions for future prospecting are outlined. The application of geochemical prospecting techniques may prove of value, judging from the results of reconnaissance soil sampling in the vicinity of the Elkhorn mine.

Geochemical and multi-isotopic ( 87Sr/ 86Sr, 143Nd/ 144Nd, 238U/ 235U) perspectives of sediment sources, depositional conditions, and diagenesis of the Marcellus Shale, Appalachian Basin, USA

DOE PAGES

Phan, Thai T.; Gardiner, James B.; Capo, Rosemary C.; ...

2017-10-25

Here, we investigate sediment sources, depositional conditions and diagenetic processes affecting the Middle Devonian Marcellus Shale in the Appalachian Basin, eastern USA, a major target of natural gas exploration. Multiple proxies, including trace metal contents, rare earth elements (REE), the Sm-Nd and Rb-Sr isotope systems, and U isotopes were applied to whole rock digestions and sequentially extracted fractions of the Marcellus shale and adjacent units from two locations in the Appalachian Basin. The narrow range of εNd values (from –7.8 to –6.4 at 390 Ma) is consistent with derivation of the clastic sedimentary component of the Marcellus Shale from amore » well-mixed source of fluvial and eolian material of the Grenville orogenic belt, and indicate minimal post-depositional alteration of the Sm-Nd system. While silicate minerals host >80% of the REE in the shale, data from sequentially extracted fractions reflect post-depositional modifications at the mineralogical scale, which is not observed in whole rock REE patterns.« less

U-Pb ages and metamorphic evolution of the La Pampa Gneisses: Implications for the evolution of the Chilenia Terrane and Permo-Triassic tectonics of north Central Chile

NASA Astrophysics Data System (ADS)

Álvarez, Javier; Mpodozis, Constantino; Blanco-Quintero, Idael; García-Casco, Antonio; Arriagada, César; Morata, Diego

2013-11-01

The La Pampa Gneisses are an enclave of orthogneisses emplaced within late Paleozoic to Triassic granitoids of the Chollay Batholith, in the Cordillera Frontal, to the east of Vallenar. Previous geochronological data (a Rb/Sr “errorchron” of 415 ± 4 Ma) allowed to some authors to suggest that these rocks were part of the Chilenia Terrane accreted to Gondwana during the Middle Devonian (ca. 390 Ma). New petrographic, chemical and geothermobarometric studies, together with U-Pb geochronological data show that the protolith of the La Pampa Gneisses derives from peraluminous tonalites emplaced during the Pennsylvanian at 306.5 ± 1.8 Ma, ruling out the hypothesis considering these rocks as remnant of the pre-collisional Chilenia basement. The tonalites were metamorphosed between 5.06 and 5.58 kbar and 709-779 °C during the middle Permian (267.6 ± 2.1 Ma), possibly in conjunction with the San Rafael tectonic event and the emplacement of the oldest granitoids of the Chollay Batholith. A new intrusive episode occurred at ca. 240 Ma, followed by exhumation and cooling during a regional Triassic extensional episode.

The deep layers of a Paleozoic arc: geochemistry of the Copley-Balaklala series, northern California

NASA Astrophysics Data System (ADS)

Brouxel, Marc; Lapierre, Henriette; Michard, Annie; Albarède, Francis

1987-10-01

REE, Zr, Nb concentrations and Sr, Nd isotope compositions have been measured in Copley basalts and andesites, Balaklala rhyolites, and Mule Mountain trondhjemites (northern California) which represent the deep layers of a well preserved intra-oceanic island arc of Siluro-Devonian age. 87Sr/ 86Sr is shifted towards high values (up to 0.707) whereas Ce is preferentially removed from rhyolites. A large proportion of the analyzed samples including some acidic rocks shows a pronounced depletion in light REE. The ɛ Nd(T) values of most Copley, Balaklala, and Mule Mountain rocks fall in the range +6 to +8 which suggests that they originated from a normal MORB-type source ( ɛ Nd(T) ≈ +9 ) contaminated with either sediments or an OIB-type component. In modern island arcs, only the shallow levels are accessible: comparison with the Copley-Balaklala-Mule Mountain Series suggests that, at depth, an immature island arc is likely to comprise thick layers of LILE-depleted tholeiites and rhyolites intensely altered by pervasive circulation of seawater. Least-square solutions of trace element models suggest that rhyolites and trondhjemites represent remelting of mafic volcanics from the arc basement rather than residual melts of basalt-andesite differentiation.

Geochemical and multi-isotopic ( 87Sr/ 86Sr, 143Nd/ 144Nd, 238U/ 235U) perspectives of sediment sources, depositional conditions, and diagenesis of the Marcellus Shale, Appalachian Basin, USA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Phan, Thai T.; Gardiner, James B.; Capo, Rosemary C.

Here, we investigate sediment sources, depositional conditions and diagenetic processes affecting the Middle Devonian Marcellus Shale in the Appalachian Basin, eastern USA, a major target of natural gas exploration. Multiple proxies, including trace metal contents, rare earth elements (REE), the Sm-Nd and Rb-Sr isotope systems, and U isotopes were applied to whole rock digestions and sequentially extracted fractions of the Marcellus shale and adjacent units from two locations in the Appalachian Basin. The narrow range of εNd values (from –7.8 to –6.4 at 390 Ma) is consistent with derivation of the clastic sedimentary component of the Marcellus Shale from amore » well-mixed source of fluvial and eolian material of the Grenville orogenic belt, and indicate minimal post-depositional alteration of the Sm-Nd system. While silicate minerals host >80% of the REE in the shale, data from sequentially extracted fractions reflect post-depositional modifications at the mineralogical scale, which is not observed in whole rock REE patterns.« less

Bedded Barite Deposits from Sonora (nw Mexico): a Paleozoic Analog for Modern Cold Seeps

NASA Astrophysics Data System (ADS)

Canet, C.; Anadón, P.; González-Partida, E.; Alfonso, P.; Rajabi, A.; Pérez-Segura, E.; Alba-Aldave, L. A.

2013-05-01

The Mazatán barite deposits represent an outstanding example of Paleozoic bedded barite, a poorly understood type of mineral deposit of major economic interest. The largest barite bodies of Mazatán are hosted within an Upper Carboniferous flysch succession, which formed part of an accretionary wedge related to the subduction of the Rheic Ocean beneath Gondwana. As well, a few barite occurrences are hosted in Upper Devonian, pre-orogenic turbidites. A variety of mineralized structures is displayed by barite, including: septaria nodules, enterolitic structures, rosettes and debris-flow conglomerates. Barite is accompanied by chalcedony, pyrite (framboids) and berthierine. Gas-rich fluid inclusions in barite were analyzed by Raman spectroscopy and methane was identified, suggesting the occurrence of light hydrocarbons in the environment within which barite precipitated. 13C-depleted carbonates (δ13C: -24.3 to -18.8‰) were found in the barite deposits; they formed through anaerobic oxidation of methane coupled to sulfate reduction, and yield negative δ18O values (-11.9 to -5.2‰) reflecting the isotopic composition of Devonian-Carboniferous seawater. Methane-derived carbonates occur in modern hydrocarbon seeps and have been reported from Mesozoic and Cenozoic seep sediments, but they have never before been described in Paleozoic bedded barite deposits. δ34S of barite varies from +17.6 to +64.1‰, with the lowest values overlapping the range for coeval seawater sulfate; this distribution indicates a process of sulfate reduction. Barite precipitation can be explained by mixing of methane- and barium-rich fluids with pore-water (seawater) containing sulfate residual from microbial reduction. Two analyses from barite gave an 87Sr/86Sr within and slightly above the range for seawater at the time of deposition, with 0.708130 and 0.708588, which would preclude the involvement of hydrothermal fluids in the mineralization process.

Tectonic setting and metallogenesis of volcanogenic massive sulfide deposits in the Bonnifield Mining District, Northern Alaska Range: Chapter B in Recent U.S. Geological Survey studies in the Tintina Gold Province, Alaska, United States, and Yukon, Canada--results of a 5-year project

USGS Publications Warehouse

Dusel-Bacon, Cynthia; Aleinikoff, John N.; Premo, Wayne R.; Paradis, Suzanne; Lohr-Schmidt, Ilana; Gough, Larry P.; Day, Warren C.

2007-01-01

This paper summarizes the results of field and laboratory investigations, including whole-rock geochemistry and radiogenic isotopes, of outcrop and drill core samples from volcanogenic massive sulfide (VMS) deposits and associated metaigneous rocks in the Wood River area of the Bonnifield mining district, northern Alaska Range (see fig. 1 of Editors’ Preface and Overview). U-Pb zircon igneous crystallization ages from felsic rocks indicate a prolonged period of Late Devonian to Early Mississippian (373±3 to 357±4 million years before present, or Ma) magmatism. This magmatism occurred in a basinal setting along the ancient Pacific margin of North America. The siliceous and carbonaceous compositions of metasedimentary rocks, Precambrian model ages based on U-Pb dating of zircon and neodymium ages, and for some units, radiogenic neodymium isotopic compositions and whole-rock trace-element ratios similar to those of continental crust are evidence for this setting. Red Mountain (also known as Dry Creek) and WTF, two of the largest VMS deposits, are hosted in peralkaline metarhyolite of the Mystic Creek Member of the Totatlanika Schist. The Mystic Creek Member is distinctive in having high concentrations of high-field-strength elements (HFSE) and rare-earth elements (REE), indicative of formation in a within-plate (extensional) setting. Mystic Creek metarhyolite is associated with alkalic, within-plate basalt of the Chute Creek Member; neodymium isotopic data indicate an enriched mantle component for both members of this bimodal (rhyolite-basalt) suite. Anderson Mountain, the other significant VMS deposit, is hosted by the Wood River assemblage. Metaigneous rocks in the Wood River assemblage span a wide compositional range, including andesitic rocks, which are characteristic of arc volcanism. Our data suggest that the Mystic Creek Member likely formed in an extensional, back-arc basin that was associated with an outboard continental-margin volcanic arc that included rocks of the Wood River assemblage. We suggest that elevated HFSE and REE trace-element contents of metavolcanic rocks, whose major-element composition may have been altered, are an important prospecting tool for rocks of VMS deposit potential in east-central Alaska.

Clay alteration and gold deposition in the genesis and blue star deposits, Eureka County, Nevada

USGS Publications Warehouse

Drews-Armitage, S. P.; Romberger, S.B.; Whitney, C.G.

1996-01-01

The Genesis and Blue Star sedimentary rock-hosted gold deposits occur within the 40-mile-long Carlin trend and are located in Eureka County, Nevada. The deposits are hosted within the Devonian calcareous Popovich Formation, the siliciclastic Rodeo Creek unit and the siliciclastic Vinini Formation. The host rocks have undergone contact metamorphism, decalcification, silicification, argillization, and supergene oxidation. Detailed characterization of the alteration patterns, mineralogy, modes of occurrence, and associated geochemistry of clay minerals resulted in the following classifications: least altered rocks, found distal to the orebody, consisting of both metamorphosed and unmetamorphosed host rock that has not been completely decalcified; and altered rocks, found proximal to the orebody that have been decalcified. Altered rocks are classified further into the following groups based on clay mineral content: silicic, 1 to 10 percent clay; silicicargillic, 10 to 35 percent clay; and argillic, 35 to 80 percent clay. Clay species identified are 1M illite, 2M1 illite, kaolinite, halloysite, and dioctahedral smectite. An early hydrothermal event resulted in the precipitation of euhedral kaolinite and at least one generation of silica. This event occurred contemporaneously with decalcification which increased rock permeability and porosity. A second clay alteration event resulted in the precipitation of hydrothermal 1M illite which replaced hydrothermal kaolinite and is associated with gold deposition. Silver and silica deposition is also associated with this phase of hydrothermal alteration. Hydrothermal alteration was followed by supergene alteration which resulted in the formation of supergene kaolinite, halloysite, and smectite as well as the oxidation of iron-bearing minerals. Supergene clays are concentrated along faults, dike margins, and within rocks containing carbonate. Gold mineralization is not associated with supergene clay minerals within the Genesis and Blue Star deposits. Rocks classified as silicic-argillic in the Popovich Formation represent the most significant gold host. Silicicargillic rocks commonly exhibit bedding-parallel alteration zones. This pattern of alteration indicates that stratigraphy as well as northwest-trending structures played a significant role in the migration of gold-bearing fluids. Based on K-Ar age determinations of hydrothermal 1M illite associated with gold, the main event of mineralization in the Genesis and Blue Star deposits occurred between 93 and 100 Ma, during mid-Cretaceous time.

Geology and Ore Deposits of the Uncompahgre (Ouray) Mining District, Southwestern Colorado

USGS Publications Warehouse

Burbank, Wilbur Swett; Luedke, Robert G.

2008-01-01

The Uncompahgre mining district, part of the Ouray mining district, includes an area of about 15 square miles (mi2) on the northwestern flank of the San Juan Mountains in southwestern Colorado from which ores of gold, silver, copper, lead, and zinc have had a gross value of $14 to 15 million. Bedrock within the district ranges in age from Proterozoic to Cenozoic. The oldest or basement rocks, the Uncompahgre Formation of Proterozoic age, consist of metamorphic quartzite and slate and are exposed in a small erosional window in the southern part of the district. Overlying those rocks with a profound angular unconformity are Paleozoic marine sedimentary rocks consisting mostly of limestones and dolomites and some shale and sandstone that are assigned to the Elbert Formation and Ouray Limestone, both of Devonian age, and the Leadville Limestone of Mississippian age. These units are, in turn, overlain by rocks of marine transitional to continental origin that are assigned to the Molas and Hermosa Formations of Pennsylvanian age and the Cutler Formation of Permian age; these three formations are composed predominantly of conglomerates, sandstones, and shales that contain interbedded fossiliferous limestones within the lower two-thirds of the sequence. The overlying Mesozoic strata rest also on a pronounced angular unconformity upon the Paleozoic section. This thick Mesozoic section, of which much of the upper part was eroded before the region was covered by rocks of Tertiary age, consists of the Dolores Formation of Triassic age, the Entrada Sandstone, Wanakah Formation, and Morrison Formation all of Jurassic age, and the Dakota Sandstone and Mancos Shale of Cretaceous age. These strata dominantly consist of shales, mudstones, and sandstones and minor limestones, breccias, and conglomerates. In early Tertiary time the region was beveled by erosion and then covered by a thick deposit of volcanic rocks of mid-Tertiary age. These volcanic rocks, assigned to the San Juan Formation, are chiefly tuff breccias of intermediate composition, which were deposited as extensive volcaniclastic aprons around volcanic centers to the east and south of the area. The Ouray area, in general, exhibits the typical effects of a minimum of three major uplifts of the ancestral San Juan Mountains. The earliest of these uplifts, with accompanying deformation and erosion, occurred within the Proterozoic, and the other two occurred at the close, respectively, of the Paleozoic and Mesozoic. The last event, known as the Laramide orogeny, locally was accompanied by extensive intrusion of igneous rocks of dominantly intermediate composition. Domal uplifts of the ancestral mountains resulted in peripheral monoclinal folds, plunging anticlines radial to the central core of the mountain mass, faults, and minor folds. The principal ore deposits of the Uncompahgre district were associated with crosscutting and laccolithic intrusions of porphyritic granodiorite formed during the Laramide (Late Cretaceous to early Tertiary) orogeny. The ores were deposited chiefly in the Paleozoic and Mesozoic sedimentary strata having an aggregate thickness of about 4,500 feet (ft) and occur beneath the early Tertiary unconformity, which in places truncated some of the uppermost deposits. A few ore deposits of late Tertiary age occur also in the sedimentary rocks near the southern margin of the district, but are restricted mostly to the overlying volcanic rocks. Ore deposits in the Uncompahgre district range from low-grade, contact-metamorphic through pyritic base-metal bodies containing silver and gold tellurides and native gold to silver-bearing lead-zinc deposits, and are zoned about the center of intrusive activity, a stock in an area referred to as The Blowout. Ore deposition within the Uncompahgre district was largely controlled by structural trends and axes of uplift established mainly in the late Paleozoic phase of deformation, but also in part by structural lin

Basin-mountain structures and hydrocarbon exploration potential of west Junggar orogen in China

NASA Astrophysics Data System (ADS)

Wu, Xiaozhi; He, Dengfa; Qi, Xuefeng

2016-04-01

Situated in northern Xinjiang, China, in NE-SW trend, West Junggar Orogen is adjacent to Altai fold belt on the north with the Ertix Fault as the boundary, North Tianshan fold belt on the south with the Ebinur Lake Strike-slip Fault as the boundary, and the Junggar Basin on the southeast with Zaire-Genghis Khan-Hala'alat fold belt as the boundary. Covering an area of about 10×104 km2 in China, there are medium and small intermontane basins, Burqin-Fuhai, Tacheng, Hefeng and Hoxtolgay, distributing inside the orogen. Tectonically West Junggar Orogen lies in the middle section of the Palaeo-Asian tectonic domain where the Siberia, Kazakhstan and Tarim Plates converge, and is the only orogen trending NE-SW in the Palaeo-Asian tectonic domain. Since the Paleozoic, the orogen experienced pre-Permian plate tectonic evolution and post-Permian intra-plate basin evolution. Complex tectonic evolution and multi-stage structural superimposition not only give rise to long term controversial over the basin basement property but also complex basin-mountain coupling relations, structures and basin superimposition modes. According to analysis of several kinds of geological and geophysical data, the orogen was dominated by compressive folding and thrust napping from the Siberia plate in the north since the Late Paleozoic. Compressive stress weakened from north to south, corresponding to subdued vertical movement and enhanced horizontal movement of crustal surface from north to south, and finally faded in the overthrust-nappe belt at the northwest margin of the Junggar Basin. The variation in compressive stress is consistent with the surface relief of the orogen, which is high in the north and low in the south. There are two kinds of basin-mountain coupling relationships, i.e. high angle thrusting and overthrusting and napping, and two kinds of basin superimposition modes, i.e. inherited and progressive, and migrating and convulsionary modes. West Junggar orogen has rich oil and gas shows, and oil and gas fields have also been discovered in the Zaysan Basin in adjacent Kazakhstan and in adjacent Junggar, Tuha and Santanghu Basins. Drilling data, geochemical analysis of outcrop data, and the disection of ancient Bulongguoer oil reservoir at the south margin of the Hefeng Basin show there developed two sets of good transitional source rocks, the lower Hujierste Formation in the Middle Devonian (D2h1) and the Hebukehe Formation in the Upper Devonian and Lower Carboniferous (D3-C1h) in this area, which, 10 to 300 m thick, mainly distribute in the shoal water zone along Tacheng-Ertai Late Paleozoic island arc belt. Reservoirs were mainly formed in the Jurassic and then adjusted in two periods, one from the end of the Jurassic to middle Cretaceous and the other in early Paleogene. Those early oil reservoirs might be destroyed in areas such as Bulongguoer with poor preservation conditions, but in an area with good geologic and preserving conditions, oil and gas might accumulate again to form new reservoirs. Therefore, a potential Middle Devonian-Lower Carboniferous petroleum system may exist in Tacheng-Ertai island arc belt, which may become a new domain for exploration, north faulted fold belt in the Heshituoluogai basin, and Hongyan fault bench zone in north Ulungur Depression in the Junggar Basin are promising areas for hydrocarbon exploration.

What was the Paleogene latitude of the Lhasa terrane? A reassessment of the geochronology and paleomagnetism of Linzizong volcanic rocks (Linzhou basin, Tibet)

NASA Astrophysics Data System (ADS)

Huang, Wentao; Dupont-Nivet, Guillaume; Lippert, Peter C.; van Hinsbergen, Douwe J. J.; Dekkers, Mark J.; Waldrip, Ross; Ganerød, Morgan; Li, Xiaochun; Guo, Zhaojie; Kapp, Paul

2015-03-01

The Paleogene latitude of the Lhasa terrane (southern Tibet) can constrain the age of the onset of the India-Asia collision. Estimates for this latitude, however, vary from 5°N to 30°N, and thus, here, we reassess the geochronology and paleomagnetism of Paleogene volcanic rocks from the Linzizong Group in the Linzhou basin. The lower and upper parts of the section previously yielded particularly conflicting ages and paleolatitudes. We report consistent 40Ar/39Ar and U-Pb zircon dates of 52 Ma for the upper Linzizong, and 40Ar/39Ar dates ( 51 Ma) from the lower Linzizong are significantly younger than U-Pb zircon dates (64-63 Ma), suggesting that the lower Linzizong was thermally and/or chemically reset. Paleomagnetic results from 24 sites in lower Linzizong confirm a low apparent paleolatitude of 5°N, compared to the upper part ( 20°N) and to underlying Cretaceous strata ( 20°N). Detailed rock magnetic analyses, end-member modeling of magnetic components, and petrography from the lower and upper Linzizong indicate widespread secondary hematite in the lower Linzizong, whereas hematite is rare in upper Linzizong. Volcanic rocks of the lower Linzizong have been hydrothermally chemically remagnetized, whereas the upper Linzizong retains a primary remanence. We suggest that remagnetization was induced by acquisition of chemical and thermoviscous remanent magnetizations such that the shallow inclinations are an artifact of a tilt correction applied to a secondary remanence in lower Linzizong. We estimate that the Paleogene latitude of Lhasa terrane was 20 ± 4°N, consistent with previous results suggesting that India-Asia collision likely took place by 52 Ma at 20°N.

A Classroom Simulation of Water-Rock Interaction for Upper-Level Geochemistry Courses.

ERIC Educational Resources Information Center

Cercone, Karen Rose

1988-01-01

Describes a simple hands-on model of water-rock interaction that can be constructed in the classroom using styrofoam bowls and foil-wrapped candies. This interactive simulation allows students to vary the factors which control water-rock interaction and to obtain immediate results. (Author/CW)

Experimental investigation of flow-induced fabrics in rocks at upper-mantle pressures: Application to understanding mantle dynamics and seismic anisotropy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kohlstedt, David L.

2016-04-26

The goal of this collaborative research effort between W.B. Durham at the Massachusetts Institute of Technology (MIT) and D.L. Kohlstedt and S. Mei at the University of Minnesota (UMN) was to exploit a newly developed technology for high-pressure, high-temperature deformation experimentation, namely, the deformation DIA (D-DIA) to determine the deformation behavior of a number of important upper mantle rock types including olivine, garnet, enstatite, and periclase. Experiments were carried out under both hydrous and anhydrous conditions and at both lithospheric and asthenospheric stress and temperature conditions. The result was a group of flow laws for Earth’s upper mantle that quantitativelymore » describe the viscosity of mantle rocks from shallow depths (the lithosphere) to great depths (the asthenosphere). These flow laws are fundamental for modeling the geodynamic behavior and heat transport from depth to Earth’s surface.« less

Experimental investigation of flow-induced fabrics in rocks at upper-mantle pressures. Application to understanding mantle dynamics and seismic anisotropy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Durham, William B.

2016-05-02

The goal of this collaborative research effort between W.B. Durham at the Massachusetts Institute of Technology (MIT) and D.L. Kohlstedt and S. Mei at the University of Minnesota (UMN) was to exploit a newly developed technology for high-pressure, high-temperature deformation experimentation, namely, the deformation DIA (D-DIA), to determine the deformation behavior of a number of important upper mantle rock types including olivine, garnet, enstatite, and periclase. Experiments were carried out under both hydrous and anhydrous conditions and at both lithospheric and asthenospheric stress and temperature conditions. The result was a group of flow laws for Earth’s upper mantle that quantitativelymore » describe the viscosity of mantle rocks from shallow depths (the lithosphere) to great depths (the asthenosphere). These flow laws are fundamental for modeling the geodynamic behavior and heat transport from depth to Earth’s surface.-« less

Archean upper crust transition from mafic to felsic marks the onset of plate tectonics.

PubMed

Tang, Ming; Chen, Kang; Rudnick, Roberta L

2016-01-22

The Archean Eon witnessed the production of early continental crust, the emergence of life, and fundamental changes to the atmosphere. The nature of the first continental crust, which was the interface between the surface and deep Earth, has been obscured by the weathering, erosion, and tectonism that followed its formation. We used Ni/Co and Cr/Zn ratios in Archean terrigenous sedimentary rocks and Archean igneous/metaigneous rocks to track the bulk MgO composition of the Archean upper continental crust. This crust evolved from a highly mafic bulk composition before 3.0 billion years ago to a felsic bulk composition by 2.5 billion years ago. This compositional change was attended by a fivefold increase in the mass of the upper continental crust due to addition of granitic rocks, suggesting the onset of global plate tectonics at ~3.0 billion years ago. Copyright © 2016, American Association for the Advancement of Science.

Geometry of an outcrop-scale duplex in Devonian flysch, Maine

USGS Publications Warehouse

Bradley, D.C.; Bradley, L.M.

1994-01-01

We describe an outcrop-scale duplex consisting of 211 exposed repetitions of a single bed. The duplex marks an early Acadian (Middle Devonian) oblique thrust zone in the Lower Devonian flysch of northern Maine. Detailed mapping at a scale of 1:8 has enabled us to measure accurately parameters such as horse length and thickness, ramp angles and displacements; we compare these and derivative values with those of published descriptions of duplexes, and with theoretical models. Shortening estimates based on line balancing are consistently smaller than two methods of area balancing, suggesting that layer-parallel shortening preceded thrusting. ?? 1994.

Development of multiple unconformities during the Devonian-Carboniferous transition on parts of Laurussia

USGS Publications Warehouse

Ettensohn, F.R.; Pashin, J.C.

1997-01-01

The Devonian-Carboniferous transition on Laurussia was a time of diverse geologic activity associated with the assembly of Pangea, including episodes of Late Devonian glacial-eustatic lowstand and active orogeny on four margins. Six widespread unconformities are present in the Devonian-Carboniferous (Mississippian) interval on southern parts of Laurussia. We suggest that attention to the timing and plan of the unconformities may provide ways of discerning tectonic and climatic controls on their respective origins. Indeed, unconformities generated by pure eustasy are ideally of interregional extent, whereas unconformities generated by tectonism reflect more local factors associated with the evolution of sedimentary basins. Each of the six unconformities analyzed provides evidence for concurrent eustasy and tectonism. Glaciation was apparently the dominant factor driving the development of unconformities during the latest Devonian. During the Early Carboniferous, however, the volume of glacial ice available to drive eustasy was limited and, at times, tectonism may have been the source of a subordinate eustatic signal. Development of unconformities in southern Laurussia appear to be local manifestations of tectonic and climatic processes associated with supercontinent assembly. Thus, the time may be at hand for construction of a new global stratigraphic paradigm that is based on the plate tectonic supercycle affecting continentality and climate.

Air-breathing adaptation in a marine Devonian lungfish.

PubMed

Clement, Alice M; Long, John A

2010-08-23

Recent discoveries of tetrapod trackways in 395 Myr old tidal zone deposits of Poland (Niedźwiedzki et al. 2010 Nature 463, 43-48 (doi:10.1038/nature.08623)) indicate that vertebrates had already ventured out of the water and might already have developed some air-breathing capacity by the Middle Devonian. Air-breathing in lungfishes is not considered to be a shared specialization with tetrapods, but evolved independently. Air-breathing in lungfishes has been postulated as starting in Middle Devonian times (ca 385 Ma) in freshwater habitats, based on a set of skeletal characters involved in air-breathing in extant lungfishes. New discoveries described herein of the lungfish Rhinodipterus from marine limestones of Australia identifies the node in dipnoan phylogeny where air-breathing begins, and confirms that lungfishes living in marine habitats had also developed specializations to breathe air by the start of the Late Devonian (ca 375 Ma). While invasion of freshwater habitats from the marine realm was previously suggested to be the prime cause of aerial respiration developing in lungfishes, we believe that global decline in oxygen levels during the Middle Devonian combined with higher metabolic costs is a more likely driver of air-breathing ability, which developed in both marine and freshwater lungfishes and tetrapodomorph fishes such as Gogonasus.

Air-breathing adaptation in a marine Devonian lungfish

PubMed Central

Clement, Alice M.; Long, John A.

2010-01-01

Recent discoveries of tetrapod trackways in 395 Myr old tidal zone deposits of Poland (Niedźwiedzki et al. 2010 Nature 463, 43–48 (doi:10.1038/nature.08623)) indicate that vertebrates had already ventured out of the water and might already have developed some air-breathing capacity by the Middle Devonian. Air-breathing in lungfishes is not considered to be a shared specialization with tetrapods, but evolved independently. Air-breathing in lungfishes has been postulated as starting in Middle Devonian times (ca 385 Ma) in freshwater habitats, based on a set of skeletal characters involved in air-breathing in extant lungfishes. New discoveries described herein of the lungfish Rhinodipterus from marine limestones of Australia identifies the node in dipnoan phylogeny where air-breathing begins, and confirms that lungfishes living in marine habitats had also developed specializations to breathe air by the start of the Late Devonian (ca 375 Ma). While invasion of freshwater habitats from the marine realm was previously suggested to be the prime cause of aerial respiration developing in lungfishes, we believe that global decline in oxygen levels during the Middle Devonian combined with higher metabolic costs is a more likely driver of air-breathing ability, which developed in both marine and freshwater lungfishes and tetrapodomorph fishes such as Gogonasus. PMID:20147310

Reconnaissance for uranium in the southeastern states, 1953

USGS Publications Warehouse

Johnson, Henry S.

1953-01-01

During the last quarter of 1952 and most of 1953 the U.S. Geological Survey carried on a program of reconnaissance for radioactive material in the southeastern states on behalf to the Atomic Energy Commission. In the course of the study 111 localities were examined and 43 samples were taken for radioactivity measurements at the Survey's Trace Elements laboratory in Denver, Colo. No economic deposits of uranium were found as a result of this work, but weak radioactivity was noted at the Tungsten Mining Coperation property near Townsville, N. C.; the Comolli granite quarry near Elberton, Ga.; in the Beech and Cranberry granite near Roan Mountain, Tenn.; and in several shales in the Valley and Ridge and Appalachian Plateau provinces. Devonian through Pennsylvanian rocks in these two provinces probably constitute the most favorable ground for new discoveries of uranium in the Southeast.

Exploration limited since '70s in Libya's Sirte basin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thomas, D.

1995-03-13

Esso Standard made the first Libyan oil discovery in the western Ghadames basin in 1957. The Atshan-2 well tested oil from Devonian sandstones, and the play was a continuation of the Paleozoic trend found productive in the neighboring Edjeleh region of eastern Algeria. Exploration in the Sirte basin began in earnest in 1958. Within the next 10 years, 16 major oil fields had been discovered, each with recoverable reserves greater than 500 million bbl of oil. Libya currently produces under OPEC quota approximately 1.4 million b/d of oil, with discovered in-place reserves of 130 billion bbl of oil. The papermore » describes the structural framework, sedimentary basins of Libya, the Sirte basin, petroleum geology, play types, source rocks, generation and migration of hydrocarbons, oil reserves, potential, and acreage availability.« less

Interpretation of Gravimetric and Aeromagnetic Data of the Tecoripa Chart in Southeast Sonora, Mexico.

NASA Astrophysics Data System (ADS)

Martínez-Retama, S.; Montaño-Del Cid, M. A.

2015-12-01

The Tecoripa chart H12-D64 is located southeast of the state of Sonora, México, south of Arizona. The geology is represented by sedimentary rocks of the Ordovician and Triassic, volcanic rocks of the Upper Cretaceous and Tertiary, intrusive rocks from the Upper Cretaceous- Tertiary and sedimentary rocks of the Cenozoic. In this paper a gravimetric study was conducted to determine the configuration and depth of the basement and to develop a structural model of the subsurface. For this purpose a consistent gravimetric survey in 3 profiles was conducted. To complement this study, gravimetric data obtained by INEGI (96 gravimetric stations spaced every 4000 m) that correspond to a regional survey was also used. The two sets of data were corrected and processed with the WinGLink software. The profiles were then modeled using the Talwani method. 4 Profiles corresponding to the gravimetric survey and 5 data profiles from INEGI were modeled. Aeromagnetic data from the total field of Tecoripa chart were also processed. The digital information was integrated and processed by generating a data grid. Processes applied to data consisted of reduction to the pole, regional-residual separation and upward continuations. In general, the obtained structural models show intrusive bodies associated with well-defined high gravimetric and magnetic and low gravimetric and magnetic are associated with basins and sedimentary rocks. The obtained geological models show the basement represented by volcanic rocks of the Tarahumara Formation from the Upper Cretaceous which are in contact with sedimentary rocks from the Barranca Group from Upper Cretaceous and limestones from the Middle Ordovician. Both volcanic and sedimentary rocks are intruded by granodiorite- granite with ages of the Tertiary-Oligocene. Based on the superficial geology as well as in the configuration of the basement and the obtained structural model the existence of faults with NW-SE orientation that originate Horst and Graben type structures can be inferred. The basins have depths of 2,000 to 4,000m with sedimentary fillings from the Báucarit Formation and Quaternary sediments.

7. Photographic copy of the original construction drawing, dated June ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

7. Photographic copy of the original construction drawing, dated June 1934, from the linens in possession of U.S. Army Engineers, Rock Island District, Clock Tower Building, Arsenal Island, Rock Island, Illinois. MISSISSIPPI RIVER, LOCK AND DAM NO. 15, LOCK OPERATOR'S SHELTER HOUSE, ELEVATIONS AND PLANS - Locks & Dam No. 15, Locks Operator's Shelter House, Arsenal Island, Upper Mississippi River, Rock Island, Rock Island County, IL

8. Photographic copy of the original construction drawing dated June ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

8. Photographic copy of the original construction drawing dated June 1934, from the linens in possession of U.S. Army Engineers, Rock Island District, Clock Tower Building, Arsenal Island, Rock Island, Illinois. MISSISSIPPI RIVER, LOCK AND DAM NO. 15, LOCK OPERATOR'S SHELTER HOUSE, SECTIONS AND DETAILS - Locks & Dam No. 15, Locks Operator's Shelter House, Arsenal Island, Upper Mississippi River, Rock Island, Rock Island County, IL

Land plants, weathering, and Paleozoic climatic evolution

NASA Astrophysics Data System (ADS)

Goddéris, Yves; Maffre, Pierre; Donnadieu, Yannick; Carretier, Sébastien

2017-04-01

At the end of the Paleozoic, the Earth plunged into the longest and most severe glaciation of the Phanerozoic eon (Montanez et al., 2013). The triggers for this event (called the Late Paleozoic Ice Age, LPIA) are still debated. Based on field observations and laboratory experiments showing that CO2 consumption by rock weathering is enhanced by the presence of plants, the onset of the LPIA has been related to the colonization of the continents by vascular plants in the latest Devonian. By releasing organic acids, concentrating respired CO2 in the soil, and by mechanically breaking rocks with their roots, land plants may have increased the weatherability of the continental surfaces. The "greening" of the continents may also have contributed to an enhanced burial of organic carbon in continental sedimentary basins, assuming that lignin decomposers have not yet evolved (Berner, 2004). As a consequence, CO2 went down, setting the conditions for the onset of the LPIA. This scenario is now widely accepted in the scientific community, and reinforces the feeling that biotic evolutionary steps are main drivers of the long-term climatic evolution. Although appealing, this scenario suffers from some weaknesses. The timing of the continent colonization by vascular plants was achieved in the late Devonian, several tens of million years before the onset of the LPIA (Davies and Gibling, 2013). Second, lignin decomposer fungi were present at the beginning of the Carboniferous, 360 million years ago while the LPIA started around 340-330 Ma (Nelsen et al., 2016). Land plants have also decreased the continental albedo, warming the Earth surface and promoting runoff. Weathering was thus facilitated and CO2 went down. Yet, temperature may have stayed constant, the albedo change compensating for the CO2 fall (Le Hir et al., 2010). From a modelling point of view, the effect of land plants on CO2 consumption by rock weathering is accounted for by forcing the weatherability of the continents to rise by a factor of 6 (Berner, 2004). This factor has been inferred from studies of the weathering rate of rocks in young environments, such as recent lava flows colonized by the vegetation (e.g. Moulton et al., 2001). Nevertheless, present-day continental areas displaying a dense vegetal cover (equatorial forests) are characterized by low weathering rates (West, 2012). Indeed, the development of thick and depleted weathering profiles has shifted those systems into a supply-limited regime. The arising questions are thus: is the land plant effect on CO2 consumption by weathering only transient, and if yes, how long does it last? Thousand, million, or tens of million years? Is a world fully vegetated weathering faster than a naked world? Those questions will be investigated through a modelling study simulating the colonization of the continents by land plants in the late Paleozoic using a simple cellular automata algorithm, coupled to a weathering model accounting for the role of the regolith thickness on the weathering regime.

Establishing the Relationship between Fracture-Related Dolomite and Primary Rock Fabric on the Distribution of Reservoirs in the Michigan Basin

DOE Office of Scientific and Technical Information (OSTI.GOV)

G. Michael Grammer

2006-09-30

This topical report covers the year 2 of the subject 3-year grant, evaluating the relationship between fracture-related dolomite and dolomite constrained by primary rock fabric in the 3 most prolific reservoir intervals in the Michigan Basin (Ordovician Trenton-Black River Formations; Silurian Niagara Group; and the Devonian Dundee Formation). The characterization of select dolomite reservoirs has been the major focus of our efforts in Phase II/Year 2. Fields have been prioritized based upon the availability of rock data for interpretation of depositional environments, fracture density and distribution as well as thin section, geochemical, and petrophysical analyses. Structural mapping and log analysismore » in the Dundee (Devonian) and Trenton/Black River (Ordovician) suggest a close spatial relationship among gross dolomite distribution and regional-scale, wrench fault related NW-SE and NE-SW structural trends. A high temperature origin for much of the dolomite in the 3 studied intervals (based upon initial fluid inclusion homogenization temperatures and stable isotopic analyses,) coupled with persistent association of this dolomite in reservoirs coincident with wrench fault-related features, is strong evidence for these reservoirs being influenced by hydrothermal dolomitization. For the Niagaran (Silurian), a comprehensive high resolution sequence stratigraphic framework has been developed for a pinnacle reef in the northern reef trend where we had 100% core coverage throughout the reef section. Major findings to date are that facies types, when analyzed at a detailed level, have direct links to reservoir porosity and permeability in these dolomites. This pattern is consistent with our original hypothesis of primary facies control on dolomitization and resulting reservoir quality at some level. The identification of distinct and predictable vertical stacking patterns within a hierarchical sequence and cycle framework provides a high degree of confidence at this point that results will be exportable throughout the basin. Ten petrophysically significant facies have been described in the northern reef trend, providing significantly more resolution than the standard 4-6 that are used most often in the basin (e.g. Gill, 1977). Initial petrophysical characterization (sonic velocity analysis under confining pressures) shows a clear pattern that is dependent upon facies and resulting pore architecture. Primary facies is a key factor in the ultimate diagenetic modification of the rock and the resulting pore architecture. Facies with good porosity and permeability clearly show relatively slow velocity values as would be expected, and low porosity and permeability samples exhibit fast sonic velocity values, again as expected. What is significant is that some facies that have high porosity values, either measured directly or from wireline logs, also have very fast sonic velocity values. This is due to these facies having a pore architecture characterized by more localized pores (vugs, molds or fractures) that are not in communication.« less

The Frasnian-Famennian boundary (Upper Devonian) within the Hanover-Dunkirk transition, northern Appalachian basin, western New York state

DOE Office of Scientific and Technical Information (OSTI.GOV)

Over, D.J.

In western New York State interbedded pyritic silty green and dark grey shales and siltstone of the Hanover Member, Java Formation, West Falls Group, are overlain by thick pyritic dark grey-black shale of the Dunkirk Member of the Canadaway formation. The dark shales in the upper Hanover and Dunkirk contain a diverse and well preserved conodont fauna which allows precise placement of the Frasnian-Famennian boundary at several described sections. At Pt. Gratiot, in far western New York State, the contact between the Hanover and Dunkirk is disconformable. The Frasnian-Famennian boundary is marked by a pyritic lag deposit at the basemore » of the Dunkirk which contains Palmatolepis triangularis and Pa. subperlobata. The underlying upper Hanover is characterized by Pa. bogartensis , Pa. cf. Pa. rhenana, Pa. winchelli, and Ancyrognathus (asymmetricus/calvini) Eastward, in the direction of the paleo-source area, the Frasnian-Famennian boundary is within the upper Hanover Member. At Irish Gulf the boundary is recognized within a 10 cm thick laminated pyritic dark grey shale bed 3.0 m below the base of the Dunkirk. Palmatolepis triangularis and Pa. subperlobata occur below a conodont-rich lag layer in the upper 2 cm of the bed. Palmatolepis bogartensis , Pa. cf. Pa. rhenana, Ancyrodella curvata, and Icriodus alternatus occur in the underlying 8 cm. Palmatolepis triangularis and Pa. winchelli occur in an underlying dark shale bed separated from the boundary bed by a hummocky cross-bedded siltstone layer.« less

Crustal structure in the Elko-Carlin Region, Nevada, during Eocene gold mineralization: Ruby-East Humboldt metamorphic core complex as a guide to the deep crust

USGS Publications Warehouse

Howard, K.A.

2003-01-01

The deep crustal rocks exposed in the Ruby-East Humboldt metamorphic core complex, northeastern Nevada, provide a guide for reconstructing Eocene crustal structure ~50 km to the west near the Carlin trend of gold deposits. The deep crustal rocks, in the footwall of a west-dipping normal-sense shear system, may have underlain the Pinon and Adobe Ranges about 50 km to the west before Tertiary extension, close to or under part of the Carlin trend. Eocene lakes formed on the hanging wall of the fault system during an early phase of extension and may have been linked to a fluid reservoir for hydrothermal circulation. The magnitude and timing of Paleogene extension remain indistinct, but dikes and tilt axes in the upper crust indicate that spreading was east-west to northwest-southeast, perpendicular to a Paleozoic and Mesozoic orogen that the spreading overprinted. High geothermal gradients associated with Eocene or older crustal thinning may have contributed to hydrothermal circulation in the upper crust. Late Eocene eruptions, upper crustal dike intrusion, and gold mineralization approximately coincided temporally with deep intrusion of Eocene sills of granite and quartz diorite and shallower intrusion of the Harrison Pass pluton into the core-complex rocks. Stacked Mesozoic nappes of metamorphosed Paleozoic and Precambrian rocks in the core complex lay at least 13 to 20 km deep in Eocene time, on the basis of geobarometry studies. In the northern part of the complex, the presently exposed rocks had been even deeper in the late Mesozoic, to >30 km depths, before losing part of their cover by Eocene time. Nappes in the core plunge northward beneath the originally thicker Mesozoic tectonic cover in the north part of the core complex. Mesozoic nappes and tectonic wedging likely occupied the thickened midlevel crustal section between the deep crustal core-complex intrusions and nappes and the overlying upper crust. These structures, as well as the subsequent large-displacement Cenozoic extensional faulting and flow in the deep crust, would be expected to blur the expression of any regional structural roots that could correlate with mineral belts. Structural mismatch of the mineralized upper crust and the tectonically complex middle crust suggests that the Carlin trend relates not to subjacent deeply penetrating rooted structures but to favorable upper crustal host rocks aligned within a relatively coherent regional block of upper crust.

12. Photograph of a photograph in possession of Rock Island ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

12. Photograph of a photograph in possession of Rock Island Arsenal Historical Office. BIRD'S-EYE RENDERING; LOOKING SW. TNT BUILDING (SEE HAER NO. IL-20V) IS SHOWN AT THE UPPER LEFT, ATTACHED BY OVERHEAD PASSAGEWAYS TO THE BUILDING'S SOUTH ELEVATION. RENDERING PREPARED BY WESTINGHOUSE-CHURCH-KERR COMPANY OF NEW YORK. DATED APRIL 18, 1917. - Rock Island Arsenal, Building No. 250, Gillespie Avenue between Ramsey Street & South Avenue, Rock Island, Rock Island County, IL

Ichnology applied to sequence stratigraphic analysis of Siluro-Devonian mud-dominated shelf deposits, Paraná Basin, Brazil

NASA Astrophysics Data System (ADS)

Sedorko, Daniel; Netto, Renata G.; Savrda, Charles E.

2018-04-01

Previous studies of the Paraná Supersequence (Furnas and Ponta Grossa formations) of the Paraná Basin in southern Brazil have yielded disparate sequence stratigraphic interpretations. An integrated sedimentological, paleontological, and ichnological model was created to establish a refined sequence stratigraphic framework for this succession, focusing on the Ponta Grossa Formation. Twenty-nine ichnotaxa are recognized in the Ponta Grossa Formation, recurring assemblages of which define five trace fossil suites that represent various expressions of the Skolithos, Glossifungites and Cruziana ichnofacies. Physical sedimentologic characteristics and associated softground ichnofacies provide the basis for recognizing seven facies that reflect a passive relationship to bathymetric gradients from shallow marine (shoreface) to offshore deposition. The vertical distribution of facies provides the basis for dividing the Ponta Grossa Formation into three major (3rd-order) depositional sequences- Siluro-Devonian and Devonian I and II-each containing a record of three to seven higher-order relative sea-level cycles. Major sequence boundaries, commonly coinciding with hiatuses recognized from previously published biostratigraphic data, are locally marked by firmground Glossifungites Ichnofacies associated with submarine erosion. Maximum transgressive horizons are prominently marked by unbioturbated or weakly bioturbated black shales. By integrating observations of the Ponta Grossa Formation with those recently made on the underlying marginal- to shallow-marine Furnas Formation, the entire Paraná Supersequence can be divided into four disconformity-bound sequences: a Lower Silurian (Llandovery-Wenlock) sequence, corresponding to lower and middle units of the Furnas; a Siluro-Devonian sequence (?Pridoli-Early Emsian), and Devonian sequences I (Late Emsian-Late Eifelian) and II (Late Eifelian-Early Givetian). Stratigraphic positions of sequence boundaries generally coincide with regressive phases on established global sea-level curves for the Silurian-Devonian.

Assessing Distribution and Origin of Methane in Shallow Groundwater in Horizontal Oil and Gas Play Areas, Eastern Kentucky

NASA Astrophysics Data System (ADS)

Zhu, J.; Parris, T. M.; Taylor, C. J.; Webb, S. E.; Davidson, B.; Smath, R.; Richardson, S. D.; Molofsky, L.; Kromann, J. S.

2016-12-01

Rapid implementation of horizontal drilling and hydraulic fracturing technology to produce oil and gas from tight rock formations across the country has increased public concern about possible impact on the environment, especially on shallow drinking-water aquifers. In eastern Kentucky, horizontal drilling and hydraulic fracturing have been used to develop the Upper Devonian Berea Sandstone in recent years. Although production in the Berea Sandstone is at a relatively small scale, the Rogersville Shale, a deeper, thicker, and more spatially extensive organic-rich shale, is projected to become a major shale play in eastern Kentucky. This has necessitated a better understanding of groundwater quality, especially the occurrence of dissolved methane, in aquifers overlying the Berea and Rogersville plays to help address the public's environmental concerns and protect groundwater resources. To assess baseline groundwater chemistry and evaluate distribution and origin of methane detected in the groundwater, 51 water wells in Greenup, Carter, Boyd, Lawrence, Johnson, and Elliott Counties were sampled and analyzed for major cations and anions, metals, and dissolved light hydrocarbon gases including methane. Twenty-six wells were identified as having methane concentrations greater than 1 mg/L and were further analyzed for carbon and hydrogen isotopes. The results indicate that methane is a relatively common constituent in shallow groundwater in eastern Kentucky. Correlation of methane distribution with water chemistry data shows that elevated methane concentrations were more common in sodium bicarbonate type water and in low-nitrate, low-sulfate redox conditions. Carbon and hydrogen isotope analysis suggests that the methane detected in groundwater is derived primarily from bacterial sources from the CO2 reduction pathway.

Influence of mid-crustal rheology on the deformation behavior of continental crust in the continental subduction zone

NASA Astrophysics Data System (ADS)

Li, Fucheng; Sun, Zhen; Zhang, Jiangyang

2018-06-01

Although the presence of low-viscosity middle crustal layer in the continental crust has been detected by both geophysical and geochemical studies, its influence on the deformation behavior of continental crust during subduction remains poorly investigated. To illustrate the crustal deformation associated with layered crust during continental subduction, we conducted a suite of 2-D thermo-mechanical numerical studies with visco-brittle/plastic rheology based on finite-differences and marker-in-cell techniques. In the experiments, we established a three-layer crustal model with a quartz-rich middle crustal layer embedded between the upper and lower continental crust. Results show that the middle crustal layer determines the amount of the accreted upper crust, maximum subduction depth, and exhumation path of the subducted upper crust. By varying the initial effective viscosity and thickness of the middle crustal layer, the further effects can be summarized as: (1) a rheologically weaker and/or thicker middle crustal layer results in a larger percentage of the upper crust detaching from the underlying slab and accreting at the trench zone, thereby leading to more serious crustal deformation. The rest of the upper crust only subducts into the depths of high pressure (HP) conditions, causing the absence of ultra-high pressure (UHP) metamorphic rocks; (2) a rheologically stronger and/or thinner middle crustal layer favors the stable subduction of the continental crust, dragging the upper crust to a maximum depth of ∼100 km and forming UHP rocks; (3) the middle crustal layer flows in a ductile way and acts as an exhumation channel for the HP-UHP rocks in both situations. In addition, the higher convergence velocity decreases the amount of subducted upper crust. A detailed comparison of our modeling results with the Himalayan collisional belt are conducted. Our work suggests that the presence of low-viscosity middle crustal layer may be another possible mechanism for absence of UHP rocks in the southern Tibet.

Paleotopography and substrate lithology as controls on initiation of Waulsortian Reef Growth: examples from Sacramento Mountains, New Mexico

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahr, W.M.; Blount, W.M.; George, P.G.

1986-05-01

Frameless mud mounds, usually called Waulsortian reefs, are common in Osagean and Kinderhookian rocks of North America and western Europe. Spectacular Waulsortian reefs crop out in the Sacramento Mountains of New Mexico along 10 mi of continuous exposure, where detailed petrographic studies and field measurements of the strata between the top of the Devonian and the base of the reefs reveal: (1) down-to-the-southwest paleoslope on an uneven, gently dipping ramp; (2) widespread deposition of skeletal packstones and siliciclastics to the northeast; (3) patchy, local thicks of skeletal packstones surrounded by shaly wackestones to the southwest; (4) relict highs on themore » Devonian surface beneath the skeletal packstone pods; (5) clusters of sheetlike reefs weakly associated with paleotopography in the northern outcrops; and (6) large, dome-like individual reefs strongly associated with depositional topography and skeletal packstone/grainstone substrates in the southern outcrops. The pre-reef strata do not exhibit abrupt changes in thickness or lithology to indicate a break in regional slope, and the reefs are not aligned with patterns in thickness of facies that would distinguish shelf-edge environments from lagoonal environments. Like their European counterparts, the Osagean reefs in the Sacramento Mountains grew on a ramp where the nonreef facies were grainy updip and muddy downdip, and reef anatomy varied from sheetlike updip to dome-like downdip. The association between paleotopography, substrate lithology, and the initiation of Waulsortian reef growth provides new information about regional depositional patterns in the Early Mississippian.« less

Productivity Contribution of Paleozoic Woodlands to the Formation of Shale-Hosted Massive Sulfide Deposits in the Iberian Pyrite Belt (Tharsis, Spain)

NASA Astrophysics Data System (ADS)

Fernández-Remolar, David C.; Harir, Mourad; Carrizo, Daniel; Schmitt-Kopplin, Philippe; Amils, Ricardo

2018-03-01

The geological materials produced during catastrophic and destructive events are an essential source of paleobiological knowledge. The paleobiological information recorded by such events can be rich in information on the size, diversity, and structure of paleocommunities. In this regard, the geobiological study of late Devonian organic matter sampled in Tharsis (Iberian Pyrite Belt) provided some new insights into a Paleozoic woodland community, which was recorded as massive sulfides and black shale deposits affected by a catastrophic event. Sample analysis using TOF-SIMS (Time of Flight Secondary Ion Mass Spectrometer), and complemented by GC/MS (Gas Chromatrograph/Mass Spectrometer) identified organic compounds showing a very distinct distribution in the rock. While phytochemical compounds occur homogeneously in the sample matrix that is composed of black shale, the microbial-derived organics are more abundant in the sulfide nodules. The cooccurrence of sulfur bacteria compounds and the overwhelming presence of phytochemicals provide support for the hypothesis that the formation of the massive sulfides resulted from a high rate of vegetal debris production and its oxidation through sulfate reduction under suboxic to anoxic conditions. A continuous supply of iron from hydrothermal activity coupled with microbial activity was strictly necessary to produce this massive orebody. A rough estimate of the woodland biomass was made possible by accounting for the microbial sulfur production activity recorded in the metallic sulfide. As a result, the biomass size of the late Devonian woodland community was comparable to modern woodlands like the Amazon or Congo rainforests.

Karst connections between unconfined aquifers and the Upper Floridan aquifer in south Georgia: geophysical evidence and hydrogeological models

NASA Astrophysics Data System (ADS)

Thieme, D. M.; Denizman, C.

2011-12-01

Buried karst features in sedimentary rocks of the south Georgia Coastal Plain present a challenge for hydrogeological models of recharge and confined flow within the underlying Upper Floridan aquifer. The Withlacoochee River, the trunk stream for the area, frequently disappears into subsurface caverns as it makes its way south to join the Suwannee River in northern Florida. The Withlacoochee also receives inputs from small ponds and bays which in turn receive spring and seep groundwater inputs. We have mapped karst topography at the "top of rock" using ground-penetrating radar (GPR). Up to seven meters of relief is indicated for the paleotopography on Miocene to Pliocene rocks, contrasting with the more subdued relief of the modern landscape. Current stratigraphic and hydrogeological reconstructions do not incorporate this amount of relief or lateral variation in the confining beds. One "pipe" which is approximately four meters in diameter is being mapped in detail. We have field evidence at this location for rapid movement of surficial pond and river water with a meteoric signature through several separate strata of sedimentary rock into an aquifer in the Hawthorn formation. We use our geophysical and hydrological field evidence to constrain quantitative hydrogeological models for the flow rates into and out of both this upper aquifer and the underlying Upper Floridan aquifer, which is generally considered to be confined by the clays of the Hawthorn.

Provenance analysis on detrital zircons from the back-arc Arivechi basin: Implications for the Upper Cretaceous tectonic evolution of northern Sonora and southern Arizona

NASA Astrophysics Data System (ADS)

Rodríguez-Castañeda, José Luis; Ortega-Rivera, Amabel; Roldán-Quintana, Jaime; Espinoza-Maldonado, Inocente Guadalupe

2018-07-01

In the Arivechi region of eastern Sonora, northwestern Mexico, mountainous exposures of Upper Cretaceous rocks that contain monoliths within coarse sedimentary debris are enigmatic, in a province of largely Late Cretaceous continental-margin arc rocks. The rocks sequence in the study area are grouped in two Upper Cretaceous units: the lower Cañada de Tarachi and the younger El Potrero Grande. Detrital zircons collected from three samples of the Cañada de Tarachi and El Potrero Grande units have been analyzed for U-Pb ages to constrain their provenance. These ages constrain the age of the exposed rocks and provide new insights into the geological evolution of eastern Sonora Cretaceous rocks. The detrital zircon age populations determined for the Cañada de Tarachi and El Potrero Grande units contain distinctive Precambrian, Paleozoic, and Mesozoic zircon ages that provide probable source areas which are discussed in detail constraining the tectonic evolution of the region. Comparison of these knew ages with published data suggests that the source terranes, that supplied zircons to the Arivechi basin, correlate with Proterozoic, Paleozoic and Mesozoic domains in southern California and Baja California, northern Sonora, southern Arizona and eastern Chihuahua. The provenance variation is vital to constrain the source of the Cretaceous rocks in eastern Sonora and support a better understanding of the Permo-Triassic Cordilleran Magmatic Arc in the southwestern North America.

Rockbolt and installer wand

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lane, W.L.; Lewis, D.L.

1987-04-07

A rockbolt is described for installation in a bore in the roof of an underground excavation to support the roof, the rockbolt comprising: a sleeve insertable into the bore and having an upper and a lower end; at least one port in the sleeve near the upper end; means inside the sleeve near the upper end for engaging a device for supplying hardenable binder material inserted into the sleeve, the engaging means having at least one passage therein communicating with the port to allow binder material to pass from the device through the engaging means and out the port, tomore » encase the sleeve in binder material; means for engaging the sleeve, near the lower end, to the roof face; means for engaging the sleeve near the upper end to the rock surrounding the bore and means for tensioning the rockbolt to compress the rock between the upper and lower ends.« less

Folded fabric tunes rock deformation and failure mode in the upper crust.

PubMed

Agliardi, F; Dobbs, M R; Zanchetta, S; Vinciguerra, S

2017-11-10

The micro-mechanisms of brittle failure affect the bulk mechanical behaviour and permeability of crustal rocks. In low-porosity crystalline rocks, these mechanisms are related to mineralogy and fabric anisotropy, while confining pressure, temperature and strain rates regulate the transition from brittle to ductile behaviour. However, the effects of folded anisotropic fabrics, widespread in orogenic settings, on the mechanical behaviour of crustal rocks are largely unknown. Here we explore the deformation and failure behaviour of a representative folded gneiss, by combining the results of triaxial deformation experiments carried out while monitoring microseismicity with microstructural and damage proxies analyses. We show that folded crystalline rocks in upper crustal conditions exhibit dramatic strength heterogeneity and contrasting failure modes at identical confining pressure and room temperature, depending on the geometrical relationships between stress and two different anisotropies associated to the folded rock fabric. These anisotropies modulate the competition among quartz- and mica-dominated microscopic damage processes, resulting in transitional brittle to semi-brittle modes under P and T much lower than expected. This has significant implications on scales relevant to seismicity, energy resources, engineering applications and geohazards.

Causes of the great mass extinction of marine organisms in the Late Devonian

NASA Astrophysics Data System (ADS)

Barash, M. S.

2016-11-01

The second of the five great mass extinctions of the Phanerozoic occurred in the Late Devonian. The number of species decreased by 70-82%. Major crises occurred at the Frasnian-Famennian and Devonian-Carboniferous boundary. The lithological and geochemical compositions of sediments, volcanic deposits, impactites, carbon and oxygen isotope ratios, evidence of climate variability, and sea level changes reflect the processes that led the critical conditions. Critical intervals are marked by layers of black shales, which were deposited in euxinic or anoxic environments. These conditions were the main direct causes of the extinctions. The Late Devonian mass extinction was determined by a combination of impact events and extensive volcanism. They produced similar effects: emissions of harmful chemical compounds and aerosols to cause greenhouse warming; darkening of the atmosphere, which prevented photosynthesis; and stagnation of oceans and development of anoxia. Food chains collapsed and biological productivity decreased. As a result, all vital processes were disturbed and a large portion of the biota became extinct.

Timing and petroleum sources for the Lower Cretaceous Mannville Group oil sands of northern Alberta based on 4-D modeling

USGS Publications Warehouse

Higley, D.K.; Lewan, M.D.; Roberts, L.N.R.; Henry, M.

2009-01-01

The Lower Cretaceous Mannville Group oil sands of northern Alberta have an estimated 270.3 billion m3 (BCM) (1700 billion bbl) of in-place heavy oil and tar. Our study area includes oil sand accumulations and downdip areas that partially extend into the deformation zone in western Alberta. The oil sands are composed of highly biodegraded oil and tar, collectively referred to as bitumen, whose source remains controversial. This is addressed in our study with a four-dimensional (4-D) petroleum system model. The modeled primary trap for generated and migrated oil is subtle structures. A probable seal for the oil sands was a gradual updip removal of the lighter hydrocarbon fractions as migrated oil was progressively biodegraded. This is hypothetical because the modeling software did not include seals resulting from the biodegradation of oil. Although the 4-D model shows that source rocks ranging from the Devonian-Mississippian Exshaw Formation to the Lower Cretaceous Mannville Group coals and Ostracode-zone-contributed oil to Mannville Group reservoirs, source rocks in the Jurassic Fernie Group (Gordondale Member and Poker Chip A shale) were the initial and major contributors. Kinetics associated with the type IIS kerogen in Fernie Group source rocks resulted in the early generation and expulsion of oil, as early as 85 Ma and prior to the generation from the type II kerogen of deeper and older source rocks. The modeled 50% peak transformation to oil was reached about 75 Ma for the Gordondale Member and Poker Chip A shale near the west margin of the study area, and prior to onset about 65 Ma from other source rocks. This early petroleum generation from the Fernie Group source rocks resulted in large volumes of generated oil, and prior to the Laramide uplift and onset of erosion (???58 Ma), which curtailed oil generation from all source rocks. Oil generation from all source rocks ended by 40 Ma. Although the modeled study area did not include possible western contributions of generated oil to the oil sands, the amount generated by the Jurassic source rocks within the study area was 475 BCM (2990 billion bbl). Copyright ?? 2009. The American Association of Petroleum Geologists. All rights reserved.

The Northeast Kingdom batholith, Vermont: magmatic evolution and geochemical constraints on the origin of Acadian granitic rocks

USGS Publications Warehouse

Ayuso, R.A.; Arth, Joseph G.

1992-01-01

Five Devonian plutons (West Charleston, Echo Pond, Nulhegan, Derby, and Willoughby) that constitute the Northeast Kingdom batholith in Vermont show wide ranges in elemental abundances and ratios consistent with major crustal contributions during their evolution. The batholith consists of metaluminous quartz gabbro, diorite and quartz monzodiorite, peraluminous granodiorite and granite, and strongly peraluminous leucogranite. Contents of major elements vary systematically with increasingSiO40) and have small negative Eu anomalies. The strongly peraluminous Willoughby leucogranite has unique trace-element abundances and ratios relative to the rest of the batholith, including low contents of Hf, Zr, Sr, and Ba, low values of K/Rb (80-164), Th/Ta (<9), Rb/Cs (7-40), K/Cs (0.1-0.5), Ce/Pb (0.5-4), high values of Rb/Sr (1-18) low to moderate REE contents and light-REE enriched patterns (with small negative Eu anomalies). Flat REE patterns (with large negative Eu anomalies) are found in a small, hydrothermally-altered area characterized by high abundances of Sn (up to 26 ppm), Rb (up to 670 ppm), Li (up to 310 ppm), Ta (up to 13.1 ppm), and U (up to 10 ppm). There is no single mixing trend, fractional crystallization assemblage, or assimilationscheme that accounts for all trace elementvariations from quartz gabbro to granite in the Northeast Kingdom batholith. The plutons originated by mixing mantle-derived components and crustal melts generated at different levels in the heterogeneous lithosphere in a continental collisional environment. Hybrid rocks in the batholith evolved by fractional crystallization and assimilation of country rocks (<50% by mass), and some of the leucogranitic rocks were subsequently disturbed by a mild hydrothermal event that resulted in the deposition of small amounts of sulfide minerals. ?? 1992 Springer-Verlag.