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Sample records for late paleozoic sandstones

  1. Late Paleozoic tectonics of the Solonker Zone in the Wuliji area, Inner Mongolia, China: Insights from stratigraphic sequence, chronology, and sandstone geochemistry

    NASA Astrophysics Data System (ADS)

    Shi, Guanzhong; Song, Guangzeng; Wang, Hua; Huang, Chuanyan; Zhang, Lidong; Tang, Jianrong

    2016-09-01

    The geology in the Wuliji area (including the Enger Us and Quagan Qulu areas) is important for understanding the Late Paleozoic tectonics of the Solonker Zone. Ultramafic/mafic rocks in the Enger Us area, previously interpreted as an ophiolitic suture, are actually lava flows and sills in a Permian turbiditic sequence and a small body of fault breccia containing serpentinite. Subduction zone features, such as accretionary complexes, magmatic arc volcanics or LP/HP metamorphism are absent. Early Permian N-MORB mafic rocks and Late Permian radiolarian cherts accompanied by turbidites and tuffeous rocks indicate a deep water setting. In the Quagan Qulu area, outcrops of the Late Carboniferous to Permian Amushan Formation are composed of volcano-sedimenary rocks and guyot-like reef limestone along with a Late Permian volcano-sedimentary unit. A dacite lava in the Late Permian volcano-sedimentary unit yields a zircon U-Pb age of 254 Ma. The gabbros in the Quagan Qulu area are intruded into the Amushan Formation and caused contact metamorphism of country rocks. Sandstones in the Upper Member of the Amushan Formation contain detrital clasts of volcanic fragments and mineral clasts of crystalline basement rocks (i.e. biotite, muscovite and garnet). Geochemical analysis of volcaniclastic sandstones shows a magmatic affinity to both continental island arc (CIA) and active continental margin (ACM) tectonic settings. A Late Permian incipient rift setting is suggested by analyzing the lithostratigraphic sequence and related magmatism in the Wuliji area. The volcano-sedimentary rocks in the Wuliji area experienced a nearly N-S shortening that was probably related to the Early Mesozoic nearly N-S compression well developed in other areas close to the Wuliji area.

  2. Late Paleozoic orogeny in Alaska's Farewell terrane

    USGS Publications Warehouse

    Bradley, D.C.; Dumoulin, J.; Layer, P.; Sunderlin, D.; Roeske, S.; McClelland, B.; Harris, A.G.; Abbott, G.; Bundtzen, T.; Kusky, T.

    2003-01-01

    Evidence is presented for a previously unrecognized late Paleozoic orogeny in two parts of Alaska's Farewell terrane, an event that has not entered into published scenarios for the assembly of Alaska. The Farewell terrane was long regarded as a piece of the early Paleozoic passive margin of western Canada, but is now thought, instead, to have lain between the Siberian and Laurentian (North American) cratons during the early Paleozoic. Evidence for a late Paleozoic orogeny comes from two belts located 100-200 km apart. In the northern belt, metamorphic rocks dated at 284-285 Ma (three 40Ar/39Ar white-mica plateau ages) provide the main evidence for orogeny. The metamorphic rocks are interpreted as part of the hinterland of a late Paleozoic mountain belt, which we name the Browns Fork orogen. In the southern belt, thick accumulations of Pennsylvanian-Permian conglomerate and sandstone provide the main evidence for orogeny. These strata are interpreted as the eroded and deformed remnants of a late Paleozoic foreland basin, which we name the Dall Basin. We suggest that the Browns Fork orogen and Dall Basin comprise a matched pair formed during collision between the Farewell terrane and rocks to the west. The colliding object is largely buried beneath Late Cretaceous flysch to the west of the Farewell terrane, but may have included parts of the so-called Innoko terrane. The late Paleozoic convergent plate boundary represented by the Browns Fork orogen likely connected with other zones of plate convergence now located in Russia, elsewhere in Alaska, and in western Canada. Published by Elsevier B.V.

  3. Modeling late Paleozoic glaciation

    SciTech Connect

    Crowley, T.J.; Baum, S.K. )

    1992-06-01

    Late Paleozoic glaciation on Gondwana is associated with changes in geography, solar luminosity, and estimated CO{sub 2} levels. To assess the relative importance of these boundary conditions, the authors conducted a suite of climate model simulations for the periods before, during, and after peak mid-Carboniferous ({approximately}300 Ma) glaciation (340, 300, and 255 and 225 Ma, respectively). Orbital insolation values favorable for glaciation and interglaciation were used for each time interval. Results indicate that changes in geography cause significant changes in snow area, but the temporal trend is not consistent with the geologic record for glaciation. Combined CO{sub 2}-plus-geography changes yield the best agreement with observations. In addition, interglacial orbital configurations result in almost ice-free conditions for the glacial interval at 300 Ma, at a time of low CO{sub 2}. The large simulated glacial-interglacial snowline fluctuations for Permian-Carboniferous time may explain cyclothem fluctuations at these times. Overall, results support the importance of the CO{sub 2} paradigm, but also indicate that a fuller understanding of past climate change requires consideration of paleogeographic, luminosity, and orbital insolation changes.

  4. Sequence stratigraphic and sedimentologic significance of biogenic structures from a late Paleozoic marginal- to open-marine reservoir, Morrow Sandstone, subsurface of southwest Kansas, USA

    USGS Publications Warehouse

    Buatois, L.A.; Mangano, M.G.; Alissa, A.; Carr, T.R.

    2002-01-01

    high diversity of biogenic structures representing the activity of a benthic fauna developed under normal salinity conditions. Trace fossil and facies analyses allow environmental subdivision of the shoreface-offshore successions and suggest deposition in a weakly storm-affected nearshore area. An onshore-offshore replacement of the Skolithos ichnofacies by the Cruziana ichnofacies is clearly displayed. The lower Morrow fluvio-estuarine valley was incised during a drop of sea level coincident with the Mississippian-Pennsylvanian transition, but was mostly filled during a subsequent transgression. The transgressive nature of the estuarine infill is further indicated by the upward replacement of depauperate brackish-water trace fossil assemblages by the open-marine Cruziana ichnofacies. Additional stratal surfaces of allostratigraphic significance identified within the estuary include the bayline surface, the tidal ravinement surface, the wave ravinement surface, and a basinwide flooding surface recording inundation of the valley interfluves. A younger sequence boundary within the lower Morrow is also recorded in the Gentzler field at the base of a forced regression shoreface, demarcated by the firmground Glossifungites ichnofacies, indicating a rapid basinward facies migration during a sea-level drop. Trace fossil models derived from the analysis of Mesozoic and Cenozoic reservoirs are generally applicable to the study of these late Paleozoic reservoirs. Pennsylvanian brackish-water facies differ ichnologically from their post-Paleozoic counterparts, however, in that they have: (1) lower trace fossil diversity, (2) lower degree of bioturbation, (3) scarcity of crustacean burrows, (4) absence of firmground suites, and (5) absence of ichnotaxa displaying specific architectures designed to protect the tracemaker from salinity fluctuations. Morrow open-marine ichnofaunas closely resemble their post-Paleozoic equivalents. ?? 2002 Elsevier Science B.V. All rights reserved.

  5. Sequence stratigraphic and sedimentologic significance of biogenic structures from a late Paleozoic marginal- to open-marine reservoir, Morrow Sandstone, subsurface of southwest Kansas, USA

    NASA Astrophysics Data System (ADS)

    Buatois, Luis A.; Mángano, M. Gabriela; Alissa, Abdulrahman; Carr, Timothy R.

    2002-09-01

    high diversity of biogenic structures representing the activity of a benthic fauna developed under normal salinity conditions. Trace fossil and facies analyses allow environmental subdivision of the shoreface-offshore successions and suggest deposition in a weakly storm-affected nearshore area. An onshore-offshore replacement of the Skolithos ichnofacies by the Cruziana ichnofacies is clearly displayed. The lower Morrow fluvio-estuarine valley was incised during a drop of sea level coincident with the Mississippian-Pennsylvanian transition, but was mostly filled during a subsequent transgression. The transgressive nature of the estuarine infill is further indicated by the upward replacement of depauperate brackish-water trace fossil assemblages by the open-marine Cruziana ichnofacies. Additional stratal surfaces of allostratigraphic significance identified within the estuary include the bayline surface, the tidal ravinement surface, the wave ravinement surface, and a basinwide flooding surface recording inundation of the valley interfluves. A younger sequence boundary within the lower Morrow is also recorded in the Gentzler field at the base of a forced regression shoreface, demarcated by the firmground Glossifungites ichnofacies, indicating a rapid basinward facies migration during a sea-level drop. Trace fossil models derived from the analysis of Mesozoic and Cenozoic reservoirs are generally applicable to the study of these late Paleozoic reservoirs. Pennsylvanian brackish-water facies differ ichnologically from their post-Paleozoic counterparts, however, in that they have: (1) lower trace fossil diversity, (2) lower degree of bioturbation, (3) scarcity of crustacean burrows, (4) absence of firmground suites, and (5) absence of ichnotaxa displaying specific architectures designed to protect the tracemaker from salinity fluctuations. Morrow open-marine ichnofaunas closely resemble their post-Paleozoic equivalents.

  6. Cycads: fossil evidence of late paleozoic origin.

    PubMed

    Mamay, S H

    1969-04-18

    Plant fossils from Lower Permian strata of the southwestern United States have been interpreted as cycadalean megasporophylls. They are evidently descended from spermopterid elements of the Pennsylvanian Taeniopteris complex; thus the known fossil history of the cycads is extended from the Late Triassic into the late Paleozoic. Possible implications of the Permian fossils toward evolution of the angiosperm carpel are considered.

  7. Cycads: Fossil evidence of late paleozoic origin

    USGS Publications Warehouse

    Mamay, S.H.

    1969-01-01

    Plant fossils from Lower Permian strata of the southwestern United States have been interpreted as cycadalean megasporophylls. They are evidently descended from spermopterid elements of the Pennsylvanian Taeniopteris complex; thus the known fossil history of the cycads is extended from the Late Triassic into the late Paleozoic. Possible implications of the Permian fossils toward evolution of the angiosperm carpel are considered.

  8. Sequential filling of a late paleozoic foreland basin

    USGS Publications Warehouse

    Mars', J. C.; Thomas, W.A.

    1999-01-01

    Through the use of an extensive data base of geophysical well logs, parasequence-scale subdivisions within a late Paleozoic synorogenic clastic wedge resolve cycles of sequential subsidence of a foreland basin, sediment progradation, subsidence of a carbonate shelf edge, diachronously subsiding discrete depositional centers, and basinwide transgression. Although temporal resolution of biostratigraphic markers is less precise in Paleozoic successions than in younger basins, parasequence-scale subdivisions provide more detailed resolution within marker-defined units in Paleozoic strata. As an example, the late Paleozoic Black Warrior basin in the foreland of the Ouachita thrust belt is filled with a synorogenic clastic wedge, the lower part of which intertongues with the fringe of a cratonic carbonate facie??s in the distal part of the basin. The stratal geometry of one tongue of the carbonate facie??s (lower tongue of Bangor Limestone) defines a ramp that grades basinward into a thin black shale. An overlying tongue of the synorogenic clastic wedge (lower tongue of Parkwood Formation) consists of cyclic delta and delta-front deposits, in which parasequences are defined by marine-flooding surfaces above coarsening- and shallow ing-upward successions of mudstone and sandstone. Within the lower Parkwood tongue, two genetic stratigraphie sequences (A and B) are defined by parasequence offlap and downlap patterns and are bounded at the tops by basinwide maximum-flooding surfaces. The distribution of parasequences within sequences A and B indicates two cycles of sequential subsidence (deepening) and progradation, suggesting subsidence during thrust advance and progradation during thrust quiescence. Parasequence stacking in sequences A and B also indicates diachronous differential tectonic subsidence of two discrete depositional centers within the basin. The uppermost sequence (C) includes reworked sandstones and an overlying shallow-marine limestone, a vertical succession

  9. The Paleozoic sandstones in Wadi Feiran - El Tor area, Sinai, Egypt

    NASA Astrophysics Data System (ADS)

    Allam, A.

    The Paleozoic sandstone succession between Wadi Feiran and El-Tor in southwestern Sinai has been subdivided into five distinct lithostratigraphic units: the Lower Cambrian Araba Formation; the Upper Cambrian Naqus Formation; the Lower Carboniferous Abu Durba Formation; the Upper Carboniferous Aheimer Formation and the Permian Qiseib Formation. The present study has also proved that the Paleozoic Earth movements have undergone distinct changes in the sedimentary facies, together with lateral variations in the composition and thickness of strata. The distribution of the sediments and their faunal contents point to the existence of five major phases of sedimentation during the Paleozoic Era.

  10. An exhumed Late Paleozoic canyon in the rocky mountains

    USGS Publications Warehouse

    Soreghan, G.S.; Sweet, D.E.; Marra, K.R.; Eble, C.F.; Soreghan, M.J.; Elmore, R.D.; Kaplan, S.A.; Blum, M.D.

    2007-01-01

    Landscapes are thought to be youthful, particularly those of active orogenic belts. Unaweep Canyon in the Colorado Rocky Mountains, a large gorge drained by two opposite-flowing creeks, is an exception. Its origin has long been enigmatic, but new data indicate that it is an exhumed late Paleozoic landform. Its survival within a region of profound late Paleozoic orogenesis demands a reassessment of tectonic models for the Ancestral Rocky Mountains, and its form and genesis have significant implications for understanding late Paleozoic equatorial climate. This discovery highlights the utility of paleogeomorphology as a tectonic and climatic indicator. ?? 2007 by The University of Chicago. All rights reserved.

  11. Paleozoic fluid history of the Michigan Basin: Evidence from dolomite geochemistry in the Middle Ordovician St. Peter Sandstone

    SciTech Connect

    Winter, B.L.; Johnson, C.M.; Simo, J.A.; Valley, J.W.

    1995-04-03

    The isotope (Sr and O) and elemental (Mg, Ca, Mn, Fe, and Sr) compositions of the various dolomites in the Middle Ordovician St. Peter Sandstone in the Michigan Basin are determined and the variations are modeled in terms of fluid-rock interaction or as mixing relations. These geochemical models, combined with the paragenetic sequence of the dolomites and late anhydrite cement, suggest the existence of at least four distinct diagenetic fluids in the St. Peter Sandstone during the paleozoic. Fluid 1 has a composition consistent with a modified older (pre-Middle Ordovician) seawater origin, which indicates that the flow path for this fluid had a major upward component. This fluid resulted in the first and volumetrically most important burial dolomitization event, producing dolomite in both carbonate and quartz sandstone lithofacies in the St. Peter Sandstone. Fluid 2 has a composition consistent with a modified Middle to early Late Ordovician seawater origin, suggesting a major downward component for fluid flow. Fluid 2 produced dolomite cement in the carbonate lithofacies that postdates Fluid 1 dolomite. The composition of Fluid 3 is best interpreted to reflect a heated, deep basinal brine that had previously interacted with the K-feldspar-rich rocks near the Cambrian-Precambrian unconformity in the Michigan Basin, indicating a major upward component for fluid flow. Fluid 3 produced dolomite cement in quartz sandstone lithofacies that postdates Fluid 1 dolomite. Fluid 4 resulted in precipitation of late anhydrite in fractures. The {sup 87}Sr/{sup 86}Sr ratio of the anhydrite is consistent with Fluid 4 originating as a dilute fluid that interacted extensively with Silurian gypsum in the Michigan Basin; this indicates that the flow path of Fluid 4 had a major downward component.

  12. Late Paleozoic extension in the Great Basin, western United States

    SciTech Connect

    Miller, E.L.; Smith, D.L. )

    1990-08-01

    Geologic mapping in the Toiyabe Range in central Nevada has revealed the existence of normal faults of probable mid-Mississippian to Early Permian age that strike roughly east-west and dip northward. Additional evidence of uplift and erosion followed by mafic volcanism and subsidence suggests that much of the central and southern Toiyabe Range was affected by late Paleozoic extension. Similar patterns of late Paleozoic uplift and subsidence, together with local basaltic volcanism, are widespread in the western United States, suggesting that the continental margin was dominated by extension or transtension in Mississippian to Permian time. This extension was coeval with convergence between North America and South America across the Ouachita and Marathon belts, and the dynamic interaction of these two margins may, by analogy with the Cenozoic tectonics of Asia, has given rise to complex late Paleozoic deformation in the Ancestral Rocky Mountains and adjacent areas of the interior western United States.

  13. Synthesis of late Paleozoic and Mesozoic eolian deposits of the Western Interior of the United States

    USGS Publications Warehouse

    Blakey, R.C.; Peterson, F.; Kocurek, G.

    1988-01-01

    Late Paleozoic and Mesozoic eolian deposits include rock units that were deposited in ergs (eolian sand seas), erg margins and dune fields. They form an important part of Middle Pennsylvanian through Upper Jurassic sedimentary rocks across the Western Interior of the United States. These sedimentary rock units comprise approximately three dozen major eolian-bearing sequences and several smaller ones. Isopach and facies maps and accompanying cross sections indicate that most eolian units display varied geometry and complex facies relations to adjacent non-eolian rocks. Paleozoic erg deposits are widespread from Montana to Arizona and include Pennsylvanian formations (Weber, Tensleep, Casper and Quadrant Sandstones) chiefly in the Northern and Central Rocky Mountains with some deposits (Hermosa and Supai Groups) on the Colorado Plateau. Lower Permian (Wolfcampian) erg deposits (Weber, Tensleep, Casper, Minnelusa, Ingleside, Cedar Mesa, Elephant Canyon, Queantoweap and Esplanade Formations) are more widespread and thicken into the central Colorado Plateau. Middle Permian (Leonardian I) erg deposits (De Chelly and Schnebly Hill Formations) are distributed across the southern Colorado Plateau on the north edge of the Holbrook basin. Leonardian II erg deposits (Coconino and Glorieta Sandstones) are slightly more widespread on the southern Colorado Plateau. Leonardian III erg deposits formed adjacent to the Toroweap-Kaibab sea in Utah and Arizona (Coconino and White Rim Sandstones) and in north-central Colorado (Lyons Sandstone). Recognized Triassic eolian deposits include major erg deposits in the Jelm Formation of central Colorado-Wyoming and smaller eolian deposits in the Rock Point Member of the Wingate Sandstone and upper Dolores Formation, both of the Four Corners region. None of these have as yet received a modern or thorough study. Jurassic deposits of eolian origin extend from the Black Hills to the southern Cordilleran arc terrain. Lower Jurassic intervals

  14. Synthesis of late Paleozoic and Mesozoic eolian deposits of the Western Interior of the United States

    NASA Astrophysics Data System (ADS)

    Blakey, Ronald C.; Peterson, Fred; Kocurek, Gary

    1988-04-01

    Late Paleozoic and Mesozoic eolian deposits include rock units that were deposited in ergs (eolian sand seas), erg margins and dune fields. They form an important part of Middle Pennsylvanian through Upper Jurassic sedimentary rocks across the Western Interior of the United States. These sedimentary rock units comprise approximately three dozen major eolian-bearing sequences and several smaller ones. Isopach and facies maps and accompanying cross sections indicate that most eolian units display varied geometry and complex facies relations to adjacent non-eolian rocks. Paleozoic erg deposits are widespread from Montana to Arizona and include Pennsylvanian formations (Weber, Tensleep, Casper and Quadrant Sandstones) chiefly in the Northern and Central Rocky Mountains with some deposits (Hermosa and Supai Groups) on the Colorado Plateau. Lower Permian (Wolfcampian) erg deposits (Weber, Tensleep, Casper, Minnelusa, Ingleside, Cedar Mesa, Elephant Canyon, Queantoweap and Esplanade Formations) are more widespread and thicken into the central Colorado Plateau. Middle Permian (Leonardian I) erg deposits (De Chelly and Schnebly Hill Formations) are distributed across the southern Colorado Plateau on the north edge of the Holbrook basin. Leonardian II erg deposits (Coconino and Glorieta Sandstones) are slightly more widespread on the southern Colorado Plateau. Leonardian III erg deposits formed adjacent to the Toroweap-Kaibab sea in Utah and Arizona (Coconino and White Rim Sandstones) and in north-central Colorado (Lyons Sandstone). Recognized Triassic eolian deposits include major erg deposits in the Jelm Formation of central Colorado-Wyoming and smaller eolian deposits in the Rock Point Member of the Wingate Sandstone and upper Dolores Formation, both of the Four Corners region. None of these have as yet received a modern or thorough study. Jurassic deposits of eolian origin extend from the Black Hills to the southern Cordilleran arc terrain. Lower Jurassic intervals

  15. Tectonic model for the Late Paleozoic of southeastern New England

    SciTech Connect

    Wintsch, R.P.; Sutter, J.F.

    1986-07-01

    Hornblende and biotite /sup 40/Ar//sup 39/Ar age spectra from rocks in south-central Connecticut help define a Permian-Triassic cooling curve for the area. Together with petrologic and structural information, a time-temperature-pressure-strain path is established. Similar data for the Narragansett basin in Rhode Island and Massachusetts allow correlation of the late Paleozoic histories of the two areas. Together, these data suggest that in the late Paleozoic, south-central New England was part of a fold-thrust belt, and the Narragansett basin was a retroarc foreland basin. NW-SE compression during the final assembly of Pangaea resulted in SE directed thrusting, causing the development of clastic wedges in adjacent Rhode Island and Massachusetts in the Late Carboniferous-Early Permian. A clockwise rotation of this deformation from NW to NNE led to northward underthrusting and concomitant uplift of both eastern Connecticut and Rhode Island in the Permian and Triassic.

  16. Late Paleozoic transpression in Buenos Aires and northeast Patagonia ranges, Argentina

    NASA Astrophysics Data System (ADS)

    Rossello, E. A.; Massabie, A. C.; López-Gamundí, O. R.; Cobbold, P. R.; Gapais, D.

    1997-12-01

    Paleozoic sediments are present in three regions in eastern central Argentina: (1) the Sierras Australes of Buenos Aires, (2) Sierras Septentrionales of Buenos Aires and (3) Northeast Patagonia. All of these deposits share a common deformational imprint imparted by late Paleozoic Gondwanan deformation. Exposures of these rocks are scattered, variably deformed, and isolated by younger sediments deposited in basins related to the Mesozoic through Tertiary opening of the South Atlantic such as the offshore Colorado Basin. The Sierras Australes of Buenos Aires outcrops are the best preserved. They are mostly located along the Sierras Australes foldbelt, with minor outliers distributed in the adjacent Claromec-basin. The Tunas Formation (early-early late? Permian) is the uppermost unit of the Pillahuincó Group (late Carboniferous-Permian) and is crucial to the understanding of the tectono-sedimentary evolution of the region during the late Paleozoic. The underlying units of the Pillahuincó Group (Sauce Grande, Piedra Azul and Bonete Formations) exhibit a depositional and compositional history characterized by glaciomarine sedimentation and postglacial transgression. They are also characterized by rather uniform quartz-rich compositions indicative of a cratonic provenance from the La Plata craton to the NE. In contrast, the sandstone-rich Tunas Formation has low quartz contents, and abundant volcanic and metasedimentary fragments; paleocurrents are consistently from the SW. Glassrich tuffs are interbedded with sandstone in the upper half of the Tunas Formation. The age of the deformation in the Sierras Australes is Permian and early-middle Triassic. This is based on metamorphic events indicated by formation of illite at 282 ± 3 Ma, 273 ± 8 Ma, 265 ± 3 Ma, and 260 ± 3 Ma ( {K}/{Ar} illite) in the Silurian Curamalal Group. Evidence of syntectonic magmatism is provided by a radiometric date of 245 ± 12 Ma ( {K}/{Ar} hornblende) for the López Lecube Granite

  17. Late Paleozoic paleolatitude and paleogeography of the Midland basin, Texas

    SciTech Connect

    Walker, D.A. ); Golonka, J. ); Reid, A.M.; Reid, S.T. )

    1992-04-01

    During the Late Pennsylvanian through Early Permian, the Midland basin was located in the low latitudes. In the Desmoinesian (Strawn), the basin was astride the equator; during the Missourian (Canyon), the center of the basin had migrated northward so it was located at 1-2N latitude. In the Virgilian (Cisco), the basin center was located around 2-4N latitude, and by the Wolfcampian, it was positioned at around 4-6N latitude. From the Desmoinesian (312 Ma) through the Missourian (306 Ma), the relative motion of the basin was 63NE. Later during the Virgilian (298 Ma) to Wolfcampian (280 Ma), the direction of motion was 24NE. This change in motion reflects a major tectonic event, occurring between the Missourian and Virgilian, that greatly modifed the movement of the Laurentian (North American) plate. At that time, Laurentia had collided with Gondwana and become part of the supercontinent Pangea. Throughout the late Paleozoic, Laurentia was rotated so the Midland basin was oriented 43{degree} northeast from its current setting. Late Paleozoic paleogeography and paleolatitude controlled the direction of prevailing winds and ocean currents, thereby influencing the distribution of carbonate facies in the Midland basin. Present prevailing winds and ocean currents have been shown to have a major impact on modern carbonate sedimentation and facies distribution in Belize, the Bahamas and Turks, and Caicos. A clearer understanding of how late Paleozoic latitude and geography affected sedimentation helps explain and predict the distribution of carbonates throughout the Midland basin.

  18. The impact of fire on the Late Paleozoic Earth system.

    PubMed

    Glasspool, Ian J; Scott, Andrew C; Waltham, David; Pronina, Natalia; Shao, Longyi

    2015-01-01

    Analyses of bulk petrographic data indicate that during the Late Paleozoic wildfires were more prevalent than at present. We propose that the development of fire systems through this interval was controlled predominantly by the elevated atmospheric oxygen concentration (p(O2)) that mass balance models predict prevailed. At higher levels of p(O2), increased fire activity would have rendered vegetation with high-moisture contents more susceptible to ignition and would have facilitated continued combustion. We argue that coal petrographic data indicate that p(O2) rather than global temperatures or climate, resulted in the increased levels of wildfire activity observed during the Late Paleozoic and can, therefore, be used to predict it. These findings are based upon analyses of charcoal volumes in multiple coals distributed across the globe and deposited during this time period, and that were then compared with similarly diverse modern peats and Cenozoic lignites and coals. Herein, we examine the environmental and ecological factors that would have impacted fire activity and we conclude that of these factors p(O2) played the largest role in promoting fires in Late Paleozoic peat-forming environments and, by inference, ecosystems generally, when compared with their prevalence in the modern world. PMID:26442069

  19. The impact of fire on the Late Paleozoic Earth system.

    PubMed

    Glasspool, Ian J; Scott, Andrew C; Waltham, David; Pronina, Natalia; Shao, Longyi

    2015-01-01

    Analyses of bulk petrographic data indicate that during the Late Paleozoic wildfires were more prevalent than at present. We propose that the development of fire systems through this interval was controlled predominantly by the elevated atmospheric oxygen concentration (p(O2)) that mass balance models predict prevailed. At higher levels of p(O2), increased fire activity would have rendered vegetation with high-moisture contents more susceptible to ignition and would have facilitated continued combustion. We argue that coal petrographic data indicate that p(O2) rather than global temperatures or climate, resulted in the increased levels of wildfire activity observed during the Late Paleozoic and can, therefore, be used to predict it. These findings are based upon analyses of charcoal volumes in multiple coals distributed across the globe and deposited during this time period, and that were then compared with similarly diverse modern peats and Cenozoic lignites and coals. Herein, we examine the environmental and ecological factors that would have impacted fire activity and we conclude that of these factors p(O2) played the largest role in promoting fires in Late Paleozoic peat-forming environments and, by inference, ecosystems generally, when compared with their prevalence in the modern world.

  20. The impact of fire on the Late Paleozoic Earth system

    PubMed Central

    Glasspool, Ian J.; Scott, Andrew C.; Waltham, David; Pronina, Natalia; Shao, Longyi

    2015-01-01

    Analyses of bulk petrographic data indicate that during the Late Paleozoic wildfires were more prevalent than at present. We propose that the development of fire systems through this interval was controlled predominantly by the elevated atmospheric oxygen concentration (p(O2)) that mass balance models predict prevailed. At higher levels of p(O2), increased fire activity would have rendered vegetation with high-moisture contents more susceptible to ignition and would have facilitated continued combustion. We argue that coal petrographic data indicate that p(O2) rather than global temperatures or climate, resulted in the increased levels of wildfire activity observed during the Late Paleozoic and can, therefore, be used to predict it. These findings are based upon analyses of charcoal volumes in multiple coals distributed across the globe and deposited during this time period, and that were then compared with similarly diverse modern peats and Cenozoic lignites and coals. Herein, we examine the environmental and ecological factors that would have impacted fire activity and we conclude that of these factors p(O2) played the largest role in promoting fires in Late Paleozoic peat-forming environments and, by inference, ecosystems generally, when compared with their prevalence in the modern world. PMID:26442069

  1. Floral responses to the Late Paleozoic deglaciation

    NASA Astrophysics Data System (ADS)

    Looy, C. V.; DiMichele, W. A.

    2011-12-01

    The current human-induced thawing of ice house Earth prompts the careful examination of similar earlier events and their biotic consequences. The most recent full transition from a cool earth to a warm world took place in the Early to Middle Permian. Against a background of global warming, plant communities were affected globally resulting in migrations, extinctions and changed evolutionary patterns as a response to the environmental changes. The collapse of the southern hemisphere ice-sheets resulted in significant changes, not just at higher latitudes, but also in the tropics where the rainfall regime changed from seasonally dry to seasonally wet. In the Early Permian tropics - in areas where net sedimentation facilitates fossilization, to be more specific - vegetation rich in walchian conifers began to replace the spore plants and seed ferns that previously dominated the Late Pennsylvanian wetlands. The replacing drier floras probably lived in the basinal lowlands as well, but episodically at the drier times of climate cycles. New finds within the tropics of latest Early to Middle Permian-age, in particular from north-central Texas, indicate the existence of floras which were adapted to even more extended periods of drought. These were populated by the more derived voltzian conifers and other seed plants, such as cycads. Surprisingly, the clades in these floras were until recently only known from the tens-of-millions-of-years younger Late Permian and Early Mesozoic, where they were the dominant forms. These occurrences demonstrate that even more derived groups were already in existence and well differentiated by the Early Permian, outside the window of preservation. This pattern of change in conifers and their communities from north-central Texas is unique in that it represents the best documented record in the Phanerozoic of terrestrial ecosystem response to a change from a global cool-mode to warm-mode Earth. Conifers serve as "marker plants" for the

  2. Late Paleozoic-early Mesozoic history of the Pacific margin along Antarctica

    SciTech Connect

    Collinson, J.W.; Isbell, J.L. ); Miller, M.F. )

    1990-05-01

    The late Paleozoic-early Mesozoic Pacific margin of Gondwanaland from eastern Australia to Patagonia was characterized by a series of back-arc and foreland basins associated with subduction and volcanism. The Transantarctic basin including the present Transantarctic Mountains and Tasmania evolved from a middle Paleozoic passive continental margin to an Early Permian back-arc basin and a Late Permian-Triassic foreland basin. The earliest evidence of a volcanic arc and subduction is the appearance of abundant volcanic detritus at the base of the Early Permian postglacial marine shale-and-sandstone sequence in the Ellsworth Mountains. Volcaniclastic forearc sediments of Permian( ) to Triassic age are known from the Antarctic Peninsula. The introduction of abundant volcanic detritus to the East Antarctic craton and a 180{degree} paleocurrent reversal in the Late Permian in the Beardmore Glacier area is the earliest evidence of folding along the Antarctic-Pacific margin. By the Early Triassic, folding involved Late Permian sequences in the Ellsworth and Transantarctic (Pensacola) mountains. Thick Upper Permian and Triassic braided-stream deposits of mixed volcanic and cratonic provenance accumulated in this foreland basin. Subsidence ended in the Early Jurassic with uplift and diabase intrusion associated with the breakup of Gondwanaland.

  3. Late Paleozoic magmatic record of Middle Gobi area, South Mongolia and its implications for tectonic evolution: Evidences from zircon U-Pb dating and geochemistry

    NASA Astrophysics Data System (ADS)

    Zhu, Mingshuai; Miao, Laicheng; Baatar, Munkhtsengel; Zhang, Fochin; Anaad, Chimedtseren; Yang, Shunhu; Li, Xingbo

    2016-01-01

    Late Paleozoic subduction-accretion complexes occur widely in Middle Gobi area and provide a good opportunity for unraveling the Paleozoic tectonic evolution of South Mongolia. The magmatic rocks in the Tsavchir hudug district mainly consist of rhyolites and volcaniclastic rocks. The rhyolites show enrichment in LREE and LILE and negative Nb, Ta and Ti anomalies, indicating genesis in the subduction zone. A rhyolite sample from the Tsavchir hudug region yielded a SHRIMP 206Pb/238U zircon age of 315 ± 4 Ma (MSWD = 0.79, n = 15). The andesite overlying the Namdain hundy Early Paleozoic ophiolite shows adakite geochemical features, and the two andesite samples yielded SHRIMP 206Pb/238U zircon ages of 325 ± 3 Ma (MSWD = 1.6, n = 14) and 319 ± 4 Ma (MSWD = 0.56, n = 13), respectively, suggesting that the Carboniferous island arc formed on the basis of Early Paleozoic accretionary complex. The granodiorite sample that intrudes the Early Paleozoic accretion complex with adakite geochemical features yielded a SHRIMP 206Pb/238U zircon age of 333 ± 4 Ma (MSWD = 1.6, n = 16), representing the Late Paleozoic island arc intrusive. The SHRIMP U-Pb analyses for the tuff sandstones that occur associated with Early Paleozic oceanic inliers in Middle Gobi area suggest detrital zircons mainly stem from the Devonian-Carboniferous arc. The age data obtained from the ophiolite (528-509 Ma) and tuff sandstone indicate the accretion in Middle Gobi area lasted from Early Paleozoic to Late Paleozoic for at least ca. 200 Ma, suggesting the ocean of the accretionary complex was the major Paleo-Asain ocean basin. The subduction related magmatic belt in Middle Gobi area includes both Early Paleozoic and Late Paleozoic island arc activities, which is consistent with the accretion duration time obtained from accretionary complex and also attests the argument of major Paleo-Asain ocean basin.

  4. Porosities and permeability of Paleozoic sandstones derived from Nuclear Magnetic Resonance measurements

    NASA Astrophysics Data System (ADS)

    Jorand, Rachel; Koch, Andreas; Mohnke, Oliver; Klitzsch, Norbert; Clauser, Christoph

    2010-05-01

    Paleozoic sandstones. The results show that the used models yield good correlation between gas- and NMR-permeability (R2>0.86 for k>10-19 m2).

  5. Kinematics of late Paleozoic continental collision between Laurentia and Gondwana

    USGS Publications Warehouse

    Sacks, P.E.; Secor, D.T.

    1990-01-01

    In the Appalachians, late Paleozoic Alleghanian orogenesis is widely regarded as resulting from dextral oblique collision between irregular margins of Gondwana and Laurentia. However, this relative plate motion cannot account for coeval convergence in the Ouachitas and Variscides and is incompatible with some tectonic transport indicators in the Appalachians. An alternative kinematic model is proposed in which early sinistral transpression in the Appalachians is followed by counterclockwise rotation of Gondwana and the development of a system of dextral strike-slip faults extending from southern Europe to Alabama.

  6. Chondrites isp. indicating late paleozoic atmospheric anoxia in Eastern Peninsular India.

    PubMed

    Bhattacharya, Biplab; Banerjee, Sudipto

    2014-01-01

    Rhythmic sandstone-mudstone-coal succession of the Barakar Formation (early Permian) manifests a transition from lower braided-fluvial to upper tide-wave influenced, estuarine setting. Monospecific assemblage of marine trace fossil Chondrites isp. in contemporaneous claystone beds in the upper Barakar succession from two Gondwana basins (namely, the Raniganj Basin and the Talchir Basin) in eastern peninsular India signifies predominant marine incursion during end early Permian. Monospecific Chondrites ichnoassemblage in different sedimentary horizons in geographically wide apart (~400 km) areas demarcates multiple short-spanned phases of anoxia in eastern India. Such anoxia is interpreted as intermittent falls in oxygen level in an overall decreasing atmospheric oxygenation within the late Paleozoic global oxygen-carbon dioxide fluctuations. PMID:24616628

  7. Chondrites isp. Indicating Late Paleozoic Atmospheric Anoxia in Eastern Peninsular India

    PubMed Central

    Bhattacharya, Biplab; Banerjee, Sudipto

    2014-01-01

    Rhythmic sandstone-mudstone-coal succession of the Barakar Formation (early Permian) manifests a transition from lower braided-fluvial to upper tide-wave influenced, estuarine setting. Monospecific assemblage of marine trace fossil Chondrites isp. in contemporaneous claystone beds in the upper Barakar succession from two Gondwana basins (namely, the Raniganj Basin and the Talchir Basin) in eastern peninsular India signifies predominant marine incursion during end early Permian. Monospecific Chondrites ichnoassemblage in different sedimentary horizons in geographically wide apart (~400 km) areas demarcates multiple short-spanned phases of anoxia in eastern India. Such anoxia is interpreted as intermittent falls in oxygen level in an overall decreasing atmospheric oxygenation within the late Paleozoic global oxygen-carbon dioxide fluctuations. PMID:24616628

  8. Late paleozoic fusulinoidean gigantism driven by atmospheric hyperoxia.

    PubMed

    Payne, Jonathan L; Groves, John R; Jost, Adam B; Nguyen, Thienan; Moffitt, Sarah E; Hill, Tessa M; Skotheim, Jan M

    2012-09-01

    Atmospheric hyperoxia, with pO(2) in excess of 30%, has long been hypothesized to account for late Paleozoic (360-250 million years ago) gigantism in numerous higher taxa. However, this hypothesis has not been evaluated statistically because comprehensive size data have not been compiled previously at sufficient temporal resolution to permit quantitative analysis. In this study, we test the hyperoxia-gigantism hypothesis by examining the fossil record of fusulinoidean foraminifers, a dramatic example of protistan gigantism with some individuals exceeding 10 cm in length and exceeding their relatives by six orders of magnitude in biovolume. We assembled and examined comprehensive regional and global, species-level datasets containing 270 and 1823 species, respectively. A statistical model of size evolution forced by atmospheric pO(2) is conclusively favored over alternative models based on random walks or a constant tendency toward size increase. Moreover, the ratios of volume to surface area in the largest fusulinoideans are consistent in magnitude and trend with a mathematical model based on oxygen transport limitation. We further validate the hyperoxia-gigantism model through an examination of modern foraminiferal species living along a measured gradient in oxygen concentration. These findings provide the first quantitative confirmation of a direct connection between Paleozoic gigantism and atmospheric hyperoxia.

  9. Late Paleozoic to Cenozoic reconstruction of the Arctic

    SciTech Connect

    Smith, D.G.

    1985-04-01

    The plate tectonic evolution of the Arctic is reassessed in the context of the known histories of the North Atlantic and North Pacific Oceans, and of the tectono-stratigraphic development of the lands around the Arctic Ocean. Computer map-drawing facilities were used to provide geometrical constraints on the reconstructions, which are presented to in the form of eight palinispatic maps. Stratigraphic similarities among presently dispersed continental areas identify fragments of a former Barents plate. Collision of this plate with the Euramerican plate was the cause of the Late Devonian Ellesmerian orogeny. In later Paleozoic time, the Siberian continent also joined Pangea by collision with the combined Barents and Euramerican plates along the Ural-Taymyr suture. The Mesozoic-Cenozoic history of the Arctic is concerned with the fragmentation and dispersal of the former Barents plate, as well as the accretion of new continental fragments from the Pacific.

  10. Late Paleozoic tectonomagmatic evolution of the western southern Tian Shan, Tajikistan

    NASA Astrophysics Data System (ADS)

    Worthington, James R.; Kapp, Paul; Minaev, Vladislav; Chapman, James B.; Oimahmadov, Ilhomjon; Gadoev, Mustafo

    2015-04-01

    -facies metamorphism; crystallization ages are early Paleoproterozoic and Neoproterozoic, suggesting peri-Gondwanan affinity. Metamorphic (consistently low Th/U) rims of zircons from a Garm Bt+Grt quartzofeldspathic gneiss span 324-284 Ma and define a protracted episode of amphibolite-facies metamorphism for the Garm massif that overlaps with both main-stage Gissar and post-collisional magmatism. This overlap favors delamination over post-orogenic extension as a mechanism for producing the 'post-collisional,' juvenile magmatism. The Zerafshan unit (north of the Gissar-Garm unit) comprises a Paleozoic volcano-sedimentary sequence that has been metamorphosed to ~greenschist facies. Chl±Bt schists exhibit zircon U-Pb age spectra similar to those in the Garm massif but with subordinate Paleoproterozoic peaks. Pb-loss discordia are present but weak for Zerafshan zircons, consistent with ~greenschist-facies metamorphism. Detrital-zircon U-Pb age spectra for modern river sands (which drain the Garm massif and Zerafshan unit) and Cretaceous sandstones (which unconformably overlie the Garm massif) reproduce the main and 'post-collisional' stages of magmatism found in the igneous rocks, as well as the Paleoproterozoic and Neoproterozoic ages found in the metasedimentary rocks. A match between a 450 Ma Zerafshan meta-andesite and a peak in a Cretaceous sandstone, taken together with consistency between detrital- and igneous-zircon ɛHf values, suggests that the Cretaceous sandstones were sourced from the Tian Shan rather than age-equivalent terranes in the Pamir. Overall, the igneous and detrital U-Pb and Hf datasets document a late Paleozoic tectonomagmatic evolution of the Gissar arc that is consistent with development of an Andean-style active continental margin followed by ocean closure, continental collision and delamination.

  11. Determining the Provenance of Late Paleozoic Loess Using Radiogenic Isotopes

    NASA Astrophysics Data System (ADS)

    Wiltse, M. R.; Aciego, S.; Soreghan, G. S.; Bailey, A.; Heavens, N. G.; Hinnov, L. A.

    2014-12-01

    Loess deposits in the sedimentary record of the Late Paleozoic tropics are anomalous because Quaternary loess is commonly glaciogenic, and thus confined to mid-high latitudes. The only loess in the tropics today is associated with mountain glaciation. Given the icehouse conditions of the Late Paleozoic, tropical loess could perhaps reflect sourcing from glaciogenic weathering in the Central Pangaean Mountains. Our goals are to constrain spatial and temporal variations in atmospheric "dustiness" and loess/dust provenance. To test the glacial weathering hypothesis and evaluate loess provenance, we collected preliminary data from two intervals (Moscovian or middle Pennsylvanian) of the Copacabana Formation, Madre de Dios Basin (Bolivia). Two 15-m sections representing carbonate inner platform environments were processed to separate the fine-grained silicate mineral fraction (SMF). Given the proximity to arc volcanism, ash fall could complicate the wind-blown weathering signal; initial work is aimed at assessing the volcanic versus continental inputs to the basin. Visual inspection and initial physical - chemical measurements of the dust-loess size fraction indicates discrete differences between the two sections, as well as between ash-rich and ash-poor intervals. The lower section has intervals with up to 72% suspected ash and SMF (non-ash) of 1-7%. The suspected ash layers in the lower section have higher grain sizes (20-40 µm) and distinct 143Nd/144Nd isotopic compositions (ɛNd = -3.5, -3.8) compared to the ash-poor intervals (8 µm, ɛNd = -5.0 to -8.8). The upper section, free of visible ash layers, has high SMF (mean 4-7% up to 41%) with similar size distributions (6-11 µm) and ɛNd (-7.4 to -7.7) to the lower section, but more radiogenic 87Sr/86Sr compositions (0.797 versus 0.71 - 0.75). The distinct physical and isotopic characteristics of the ash and SMF in the sections and sub-intervals suggests that deconvolving ash and loess/dust inputs will be possible

  12. Climate-forcing & Feedbacks of the Late Paleozoic Ice Age

    NASA Astrophysics Data System (ADS)

    Montanez, I. P.; Brand, U.; Poulsen, C. J.; Horton, D. E.

    2011-12-01

    Evaluating climate-forcing and feedbacks during pre-Cenozoic ice ages requires reconstructing marine-terrestrial linkages between atmospheric composition, the regional hydroclimate expression of mean climate change, ice sheets, and sea-level. Here we evaluate the role of different climate parameters and their linkages during the Carboniferous icehouse through integration of a recently developed ID-TIMS U-Pb constrained sea-level history, brachiopod stable isotope time-series from shallow marine regions of paleotropical Pangaea, atmospheric pCO2 inferred from paleosol minerals and fossil leaf stomatal indices, ice sheet variations constrained by the distribution of high-latitude Gondwanan glacial deposits, and paleoclimate simulations. Within chronostratigraphic uncertainty, long-term sea-level lowstands coincide with glacial maxima defined from high-latitude Gondwanan basins, whereas long-term highstands are coeval with glacial minima suggesting a dynamic late Paleozoic icehouse. Superimposed shorter-term sea-level events define a stepwise onset (late Mississippian) and contraction of Carboniferous ice sheets prior to the initiation of Early Permian ice sheets. Sea level fluctuations, at different temporal scales parallel trends defined by brachiopod oxygen and carbon isotope compositions and paleo-atmospheric pCO2 estimates inferred using mineral and biologic proxies. A protracted (~9 my) stepwise sea level rise beginning in the middle Pennsylvanian and culminating in an earliest Gzhelian peak is coincident with overall increasing CO2 levels throughout this interval and substantially decreased effective moisture in paleotropical Pangaea. This possibly CO2-forced period of waning continental ice sheets and sea-level highstand encompassed a large-scale floral turnover across the mid-to-late Pennyslvanian boundary and the onset of the demise of paleotropical rainforests across much of Pangaea. Ocean-atmosphere-ice sheet climate simulations for this period reveal a

  13. Late Paleozoic subulitacea (mollusca:gastropoda), mass extinctions and the replacement of evolutionary faunas

    SciTech Connect

    Erwin, D.H.

    1985-01-01

    Mesogastropod subulitaceans possess characteristics typical of active carnivores and occupied a trophic regime typical of the Mesozoic-Cenozoic evolutionary fauna. Despite occupying a vacant niche, subulitaceans are low in both diversity and abundance in late Paleozoic gastropod faunas. In addition, Paleozoic Archaeogastropoda and Mesogastropoda are taxonomically and functionally distinct from Mesozoic groups and display diversity dynamics typical of the Paleozoic evolutionary fauna, not the Mesozoic-Cenozoic fauna with which they were grouped by Sepkoski. Late Paleozoic gastropods are different from pre-Carboniferous taxa, but there is no preferential expansion of the major Mesozoic taxa, nor is there any pattern of exploitation of a major niche utilized by later groups but under-used by Paleozoic taxa. The high taxonomic level used Sepkoski's factor analysis neglects the finer scale of replacement and diversification. This distinct evolutionary behavior of Paleozoic gastropods may be typical of other taxa as well. It weakens the assertions of Kitchell and Carr and Sepkoksi and Miller that the replacement of evolutionary Fauna II by Fauna III began in the late Paleozoic and would have occurred even without the Guadelupian-Dzulfian mass extinction. Thus for gastropods at last, the Late Permian mass extinction did not merely speed up on ongoing process, but probably determined the evolutionary outcome.

  14. Late Paleozoic-Mesozoic evolution of Arctic North America

    SciTech Connect

    Embry, A.F.

    1987-05-01

    Correlation of the upper Paleozoic to Mesozoic successions of northern Alaska and the Canadian Arctic Islands has revealed close stratigraphic and tectonic links between these two petroliferous areas. Depositional and tectonic trends have been reconstructed for Arctic North America, and such interpretations can assist petroleum assessments of unexplored areas in the region. Five regional unconformities are recognized, and these allow the succession to be divided into four tectonic sequences: Carboniferous-Lower Permian, Lower Permian-lowest Cretaceous, Lower Cretaceous, and Upper Cretaceous. The first sequence, Carboniferous-Lower Permian, developed during a phase of rifting when a series of pull-apart basins formed along the eroded Ellesmerian deformation belt. Fan deltas and shelf carbonates with equivalent basinal shales and evaporites characterize this sequence. An episode of uplift and faulting terminated the first sequence. The second sequence, Lower Permian-lowest Cretaceous, developed under conditions of thermal subsidence over the rifted areas. Clastic sedimentation was dominant with alternating shelf and deltaic deposition. Significant uplift reflecting the initiation of the Amerasian basin by rifting began in earliest Cretaceous. Sequence three, Lower Cretaceous, was deposited during the rifting phase of the Amerasian basin and consists of thick, deltaic, clastic wedges derived from either the craton or the uplifted Brooks Range. The onset of sea-floor spreading in the Amerasian basin in earliest Late Cretaceous resulted in widespread uplift. The fourth sequence, Upper Cretaceous, was deposited coincident with sea-floor spreading in the Amerasian basin. Initial deposits were bituminous shales which were followed by thick clastic wedges that prograded into the ocean basin. This sequence was terminated by uplift in Cretaceous-earliest Tertiary when sea-floor spreading switched to the Eurasian basin.

  15. Late Paleozoic to Jurassic tectonic evolution of the Bogda area (northwest China): Evidence from detrital zircon U-Pb geochronology

    NASA Astrophysics Data System (ADS)

    Tang, Wenhao; Zhang, Zhicheng; Li, Jianfeng; Li, Ke; Chen, Yan; Guo, Zhaojie

    2014-06-01

    Since the Cenozoic, the Tian Shan is rejuvenated by crustal shortening related to the ongoing India-Asia collision. However, the tectonic process prior to the Cenozoic remains ambiguous, especially in the Bogda area of the eastern Tian Shan. The continuous Late Paleozoic-Mesozoic sequences in the Bogda area record abundant information about the basin-mountain interaction. U-Pb (LA-ICP-MS) dating of detrital zircons from seven sandstone samples from Permian to Jurassic was used to investigate the changes of provenance and basin-mountain interaction in the Bogda area. During the Permian, proximal and synchronous pyroclastic materials were the major source. The Late Paleozoic magmatic belt in the North Tian Shan (NTS) had gradually become one of the main sources by the Late Permian, which implies the uplift and exhumation in the NTS area. This is interpreted in terms of near-source sedimentation in basin developing in a post-orogenic extension setting. The large range of U-Pb ages of detrital zircons observed in the Early-Middle Jurassic sediments encompasses most of the available sources implying a wide drainage pattern developing on a rather flat topography. Re-emergence of the Early Permian peak in the spectrum implies that the Bogda Mountains has existed as a gentle positive relief and began to provide materials to the submountain regions. The southern Junggar Basin extended towards to the south and evolved as a passively subsiding basin from the Middle Triassic to the Middle Jurassic. However, the synchronous pyroclastic (tuff) and the exhumed late Paleozoic detrital materials from the uplifted Bogda Mountains were the major component of the Upper Jurassic sediments. Associated to the conglomerate in the Kalaza Formation, the basin-range evolution entered a compression uplift stage. The basin pattern evolution of the Bogda area is consistent with that of the southern Junggar Basin.

  16. Iron cycling in a late Paleozoic dust bowl

    NASA Astrophysics Data System (ADS)

    Owens, J. D.; Soreghan, G. S.; Gerhardt, A.; Sur, S.; Lyons, T. W.

    2009-12-01

    The late Paleozoic glaciation (~300 million years ago) marks the last major, pre-Cenozoic icehouse climate. In addition, emerging research suggests that this was a particularly dusty time, evinced by abundant dust (loessite) deposits throughout western equatorial Pangaea. Delivery of reactive Fe-rich eolian particles to the nutrient-depleted open ocean potentially stimulates primary production during glacial intervals, yet the details remain unclear for recent glaciations and completely unknown for the ancient. Bioavailable Fe is a limiting nutrient in high nitrate, low chlorophyll portions of the open ocean. Because primary abundances of the most labile forms of Fe are not easily assessed in ancient sediments, we use highly reactive Fe (FeHR) (mostly crystalline oxides, some or most of which might have been more soluble precursors at the time of deposition) as determined by a well-calibrated sequential extraction scheme as a proxy for bioavailable Fe. Here we present data from multiple Pennsylvanian-Permian loess and intercalated paleosol (ancient soil) deposits, as well as a modern dust site. We also compare ratios of total Fe (FeT) to Al to ratios of FeHR to FeT to assess whether increased Fe reactivity in dust reflects a net Fe addition or internal mineral repartitioning. We are finding that these paired proxies may provide a unique fingerprint of source relationships. Modern arid Saharan soil dust deposited in the Turks and Caicos Islands has high FeT/Al ratios (0.75 versus ~0.5 for average continental crust), with corresponding FeHR/FeT enrichments (0.48 compared to ~0.38 for typical riverine input). The ancient loessite samples do not show a similar pattern, instead suggesting an antithetic relationship between FeT/Al and FeHR/FeT. Therefore, FeHR was enriched and, by inference, bioavailable despite net Fe loss reflected in sub-crustal FeT/Al ratios. Most work to date has presumed an arid soil source for most bioavailable Fe. However, in light of our work

  17. Late paleozoic tectonic amalgamation of northwestern China. Sedimentary record of the northern Tarim, northwestern Turpan, and southern Junggar basins

    SciTech Connect

    Carroll, A.R.; Graham, S.A.; Hendrix, M.S.; Ying, D.; Zhou, D.

    1995-05-01

    This study focuses on areas adjacent to the Tian Shan (shan is Chinese for mountains) in Xinjiang Uygur Autonomous Region, northwestern China, and provides new field data on Carboniferous and Permian outcrop exposures of sedimentary rocks of the southern Junggar, northwestern Turpan, and northern Tarim basins that bear directly on the history of late Paleozoic tectonic amalgamation. We present here a multifaceted sedimentary basin analysis, including sedimentary facies, paleocurrent, and sandstone provenance analyses, and reconstructions of late Paleozoic basin subsidence. These data provide a unique record not only of the basins themselves, but also of the evolution of the adjacent orogenic belts. This study is based on fieldwork during the summers of 1987, 1988, 1991, and 1992 by workers from Stanford University, the Chinese Academy of Geological Sciences, and the Xinjiang Bureau of Geology and Mineral Resources. Although reconnaissance in nature, the data presented here provide a basis for evaluating alternative hypotheses for the evolution of northwestern China and provide a starting point for more comprehensive future studies. 72 refs., 18 figs., 1 tab.

  18. Late Paleozoic intrusive rocks from the southeastern Lhasa terrane, Tibetan Plateau, and their Late Mesozoic metamorphism and tectonic implications

    NASA Astrophysics Data System (ADS)

    Dong, Xin; Zhang, Zeming; Liu, Feng; He, Zhenyu; Lin, Yanhao

    2014-06-01

    The Lhasa terrane in southern Tibet experienced Late Paleozoic and Mesozoic-Cenozoic composite orogenesis. This work reports a study on the petrology, geochemistry, zircon U-Pb chronology and Hf isotopes of Late Paleozoic and Late Mesozoic intrusive rocks from the southeastern Lhasa terrane. The Late Paleozoic intrusive rocks crystallized in the Late Devonian-Early Carboniferous of 371 to 355 Ma, representing a bimodal igneous association formed in the back-arc extensional setting. The mafic end-member originated from the enriched mantle and experienced contamination of crustal materials, characterized by a slight enrichment of LREE, positive anomalies of U, K and Pb and negative anomalies of Th, Nb, Ta and Ti. The felsic end-member was derived from the partial melting of the ancient continental crust, characterized by metaluminous, positive anomalies of Th, Zr and Hf, negative anomalies of Ba, Sr, Nb, Ta and Ti and negative εHf(t) values of zircon with TDM2 ages from 1.90 to 1.40 Ga. The Late Cretaceous (ca. 107 Ma) mafic intrusions, along with the Late Paleozoic intrusive rocks, underwent nearly syn-intrusion amphibolite-facies metamorphism under P-T conditions of 0.56 to 0.69 GPa and 692 to 735 °C during the Andean-type orogeny correlated with the subduction of the Neo-Tethyan oceanic slab beneath the Lhasa terrane. This study provides a new insight into the pre-Cenozoic tectonic evolution of the Lhasa terrane.

  19. Climatic basis for sluggish macroevolution during the late Paleozoic ice age

    NASA Astrophysics Data System (ADS)

    Powell, Matthew G.

    2005-05-01

    Rates of origination and extinction for marine invertebrates fell at the onset of the late Paleozoic ice age in late Mississippian time and remained low until glaciation ended in middle Permian time. Through the use of a database of stratigraphic and geographic occurrences of brachiopod genera, these macroevolutionary changes are traced to the loss of genera with narrow latitudinal ranges, which had intrinsically high turnover rates, at the onset of glaciation in late Viséan time. When glaciation waned in late Sakmarian time, narrowly distributed genera rebounded abruptly and restored the global fauna to its pre ice-age configuration. Because narrowly distributed brachiopod genera had dominated tropical diversity, the major biotic effects of the late Paleozoic ice age were felt at low latitudes. The climatic regime of this ice age thus altered the marine ecosystem to one characterized by broadly adapted, long-lived genera.

  20. Burning experiments and late Paleozoic high O2 levels

    NASA Astrophysics Data System (ADS)

    Wildman, R.; Essenhigh, R.; Berner, R.; Hickey, L.; Wildman, C.

    2003-04-01

    The Paleozoic rise of land plants brought about increased burial of organic matter and a resulting increase in atmospheric oxygen concentrations. Levels as high as 30-35% O2 may have been reached during the Permo-Carboniferous (Berner and Canfield, 1989; Berner, 2001). However, burning experiments based solely on paper (Watson, 1978) have challenged these results, the claim being that if the oxygen made up more than 25% of the atmosphere, the frequency and intensity of forest fires would increase sufficiently to prevent the continued existence of plant life. Thus, since plants have persisted, it is possible that fires served as a negative feedback against excessive oxygen levels. An initial study of Paleozoic wildfire behavior via thermogravimetric analysis (TGA) was conducted under ambient and enriched oxygen conditions to simulate present and ancient atmospheres. The tests focused on natural fuels, specifically tree leaves and wood, tree fern fibers, and sphagnum peat-moss, simulating Permo-Carboniferous upland and swampland ecosystems, respectively. Three conclusions are: (1) enriched oxygen increases the rate of mass loss during burning; (2) fuel chemistry (cellulose vs. lignin) influences burning patterns; and (3) in geometrically heterogeneous fuels, geometry affects burning rate significantly. Both geometrically and chemically, paper resists fire poorly; thus, we found that it loses its mass at lower temperatures than forest materials and is therefore a poor proxy for Paleozoic ecosystems. Further study of Paleozoic wildfire spread behavior is currently being conducted. Fires are lit using pine dowels, which allow for reproducible fuel density. Steady-state, one-dimensional flame-spread is measured with thermocouples anchored two inches above the fuel bed. Both oxygen concentration of the air supply to the fire and moisture content of the fuels are varied, as we suspect that these are two main controls of wildfire spread. Burning fuels of varying moisture

  1. Lower paleozoic of Baltic Area

    SciTech Connect

    Haselton, T.M.; Surlyk, F.

    1988-01-01

    The Baltic Sea offers a new and exciting petroleum play in northwestern Europe. The Kaliningrad province in the Soviet Union, which borders the Baltic Sea to the east, contains an estimated 3.5 billion bbl of recoverable oil from lower Paleozoic sandstones. To the south, in Poland, oil and gas fields are present along a trend that projects offshore into the Baltic. Two recent Petrobaltic wells in the southern Baltic have tested hydrocarbons from lower Paleozoic sandstone. Minor production comes from Ordovician reefs on the Swedish island of Gotland in the western Baltic. The Baltic synclise, which began subsiding in the late Precambrian, is a depression in the East European platform. Strate dip gently to the south where the Baltic Synclise terminates against a structurally complex border zone. Depth to the metamorphosed Precambrian basement is up to 4,000 m. Overlying basement is 200-300 m of upper Precambrian arkosic sandstone. The Lower Cambrian consists of shallow marine quartzites. During Middle and Late Camnbrian, restricted circulation resulted in anoxic conditions and the deposition of Alum shale. The Lower Ordovician consists of quartzites and shale. The Upper Ordovician includes sandstones and algal reefs. The Silurian contains marginal carbonates and shales. For the last 25 years, exploration in northwest Europe has concentrated on well-known Permian sandstone, Jurassic sandstone, and Cretaceous chalk plays. Extrapolation of trends known and exploited in eastern Europe could open an entirely new oil province in the lower Paleozoic in the Baltic.

  2. Late Devonian glacial deposits from the eastern United States signal an end of the mid-Paleozoic warm period

    USGS Publications Warehouse

    Brezinski, D.K.; Cecil, C.B.; Skema, V.W.; Stamm, R.

    2008-01-01

    A Late Devonian polymictic diamictite extends for more than 400??km from northeastern Pennsylvania across western Maryland and into east-central West Virginia. The matrix-supported, unbedded, locally sheared diamictite contains subangular to rounded clasts up to 2??m in diameter. The mostly rounded clasts are both locally derived and exotic; some exhibit striations, faceting, and polish. The diamictite commonly is overlain by laminated siltstone/mudstone facies associations (laminites). The laminites contain isolated clasts ranging in size from sand and pebbles to boulders, some of which are striated. The diamictite/laminite sequence is capped by massive, coarse-grained, pebbly sandstone that is trough cross-bedded. A stratigraphic change from red, calcic paleo-Vertisols in strata below the diamictite to non-calcic paleo-Spodosols and coal beds at and above the diamictite interval suggests that the climate became much wetter during deposition of the diamictite. The diamictite deposit is contemporaneous with regressive facies that reflect fluvial incision during the Late Devonian of the Appalachian basin. These deposits record a Late Devonian episode of climatic cooling so extreme that it produced glaciation in the Appalachian basin. Evidence for this episode of climatic cooling is preserved as the interpreted glacial deposits of diamictite, overlain by glaciolacustrine varves containing dropstones, and capped by sandstone interpreted as braided stream outwash. The Appalachian glacigenic deposits are contemporaneous with glacial deposits in South America, and suggest that Late Devonian climatic cooling was global. This period of dramatic global cooling may represent the end of the mid-Paleozoic warm interval that began in the Middle Silurian. ?? 2008 Elsevier B.V. All rights reserved.

  3. Late Diagenesis and Mass Transfer in Sandstone Shale Sequences

    NASA Astrophysics Data System (ADS)

    Milliken, K. L.

    2003-12-01

    Between Ca 50 °C and 300 °C, sandstones and mudrocks("shales") undergo massive chemical and textural reorganization. In this temperature interval detrital grains, and the rock textures defined by grains, are lost by reactions with pore fluids. Chemical and physical processes in late diagenesis transform siliciclastic sediments into rocks. Predictive models of porosity evolution with depth depend upon an understanding of these processes. Because the magnitude of the mineralogical changes in late diagenesis is large, these changes also have important implications for understanding rates and mechanisms of element cycling through the crust.Controversy regarding the scale of the elemental mobility that accompanies the mineralogical and textural reorganization has been a defining theme of research in late diagenesis. Conundrums arising from apparent conflicts between petrographic and petrophysical constraints on elemental mobility are well known to students of clastic diagenesis. Interestingly, similar paradoxes have long vexed students of low-grade metamorphism (e.g., Ague, 1991; Rumble, 1994). A related issue in late diagenesis concerns apparent subsurface weathering. Weathering during erosion and transport at the surface fails to remove high-temperature phases from sediments completely, and these detrital components arrive in the realm of late diagenesis with considerable reactive potential. However, after reaching a temperature of 200 °C, these metastable compounds have largely been lost by reaction with pore fluids. Of course, volumetrically significant weathering processes require acid. However, the source(s) of this acid remains disputed. In the context of identifying volumetrically significant sources of acid, other questions arise regarding the extent to which precipitation reactions in late diagenesis should be construed as acid-releasing reverse-weathering reactions.Historically, late diagenesis of siliciclastic rocks was viewed as physical and isochemical

  4. Widespread Late Paleozoic remagnetization of the Great Basin miogeocline: Implications for Basin and Range tectonism

    SciTech Connect

    Geissman, J.W. . Dept. of Earth and Planetary Sciences); Gillett, S.L. . Mackay School of Mines); Bartley, J.M. . Dept. of Geology and Geophysics)

    1992-01-01

    In the eastern and southern Great Basin, heterogeneous, shallow-water miogeocline carbonate rocks give a shallow inclination, south to southeast-directed characteristic magnetization residing in magnetite. The magnetization, found in the Desert Range of southern Nevada, the Egan Range of east-central Nevada, and the House Range of western utah, is interpreted to be secondary. It was acquired after (1) local, soft compaction, because directions of magnetization are not dispersed by macroscopic compaction of stylolites and fine carbonate laminations, of up to 25[degree], wrapping around chert masses, and (2) local karst brecciation, as conglomerate tests are negative. The uniform reversed polarity in addition to the direction of the magnetization is interpreted to suggest a late Paleozoic time of remagnetization, in the Kiaman superchron. The authors interpret the secondary magnetization to be of chemical origin, and speculate that it was acquired in response to cratonward fluid migration initiated by Antler contraction. In the Egan Range, about 4 km of Paleozoic strata have been remagnetized. That this secondary but ancient late Paleozoic magnetization has survived subsequent events is significant for interpreting Mesozoic and Cenozoic processes. First, on a regional scale, the Paleozoic miogeocline never experienced burial temperatures greater than about 300 C during mesozoic contraction. Second, because the secondary magnetization can be referenced to the paleohorizontal, it may prove to be an important passive marker for assessing vertical axis rotation related to, first, Mesozoic thrusting, and, second, Cenozoic extension. This is currently being tested.

  5. Late Paleozoic orogenic episodes, Trans-Pecos Texas

    SciTech Connect

    Muehlberger, W.R. . Dept. of Geological Sciences)

    1993-04-01

    The onset of the Ouachita orogeny is marked by the absence of rock of Early Mississippian age. This is interpreted to be the result of the narrowing of the trans-equatorial seaway between North America and the oncoming South American plate. Foredeep filling (Pulse I) began in Early Meramecian time with northward-prograding Tesnus Fm siliciclastic turbidites. Pulse 2 began in Atokan time with northward-prograding siliciclastic turbidites of the Haymond Fm. The thrust belt to the south had now intersected the edge of the NAm carbonate platform as shown by clasts of Middle Cambrian carbonates, as well as Ouachita facies clasts, and rounded clasts of Precambrian quartzite, metarhyolite, and gneiss of unknown source. During Late Pennsylvanian time deltaic sediments prograded across the Marathon region into the southern Permian Basin (Gaptank Fm). In Early Wolfcampian time (Pulse 3), all these units were translated on the Dugout Creek thrust, then (Pulse 4 ) translated finally on a frontal imbricate before deposition of Upper Wolfcampian units across the eroded toes of the thrust sheets. Permian Basin orogenic phases parallel those outlined above. Transgressive clastics from the south and the subdivision of the earlier broad, shallow Tobosa Basin into the uplifts and basins that characterize the Permian Basin began in the Mississippian and became prominent structural units by Late Mississippian time.

  6. Late Paleozoic paleofjord in the southernmost Parana Basin (Brazil): Geomorphology and sedimentary fill

    NASA Astrophysics Data System (ADS)

    Tedesco, Julia; Cagliari, Joice; Coitinho, Julia dos Reis; da Cunha Lopes, Ricardo; Lavina, Ernesto Luiz Correa

    2016-09-01

    In the southernmost part of the Parana Basin, records of the late Paleozoic glaciation occur in a discontinuous form preserved in paleovalley systems excavated in the crystalline basement. This paper addresses one of these paleovalleys, the Mariana Pimentel, which extends over 60 km with NW-SE valley direction and a constant width of 2.5 km. With the objective of demonstrating that the paleovalley worked as a fjord during the glaciation period, its origin as well as sedimentary fill and morphology were analyzed. The paleovalley morphology was obtained through electrical resistivity (electrical sounding and lateral mapping) and mathematical modeling in four transverse sections. The morphology of the paleovalley documented by the U-shape, steady width, and high depth reaching up to 400 m are typical features of modern glacial valleys. The sedimentary facies that fill the base of the paleovalley, such as rhythmites and dropstones with thickness up to 70 m and diamictites with faceted pebbles (up to 5 m thick) are signs of its glacial origin. During the glaciation period, the paleovalley had a connection to the epicontinental sea located to the northwest, extended toward Namibia, and was excavated by glaciers from the highlands of this region. Thus, the evidence attests that the Mariana Pimentel paleovalley was a fjord during the late Paleozoic glaciation. The duration of the late Paleozoic glaciation (which is longer than the Quaternary glaciation), the apatite fission track that suggests erosion up to 4 km thick in the study area, and the lack of preserved hanging valleys in the Mariana Pimentel indicate that the paleovalley once featured a higher dimension. Furthermore, the existence of paleofjords excavated in the border of the basement corroborates the idea of small ice centers controlled by topography during the late Paleozoic glaciation.

  7. New Paleomagnetic Results From Late Paleozoic and Mesozoic Rocks of Tibet: Implications for the Paleogeography of the Eastern Qiangtang Terrane

    NASA Astrophysics Data System (ADS)

    Lippert, P. C.; Zhao, X.

    2005-12-01

    We present new paleomagnetic, rock magnetic, and geochronologic data from our ongoing study of late Paleozoic and Mesozoic paleomagnetic poles from the Eastern Qiangtang Terrane in Central Tibet. This study consists of four sampling localities of the Eastern Qiangtang Terrane, from south to north: 1) the Kaixingling basalts and andesites, with underlying marls and overlying limestones of late Permian age (11 sites, 81 samples); 2) a basalt flow and overlying quartzose sandstones exposed in the southern TuoTuo He basin, also of suggested late Permian age (4 sites, 41 samples); 3) basalts and andesites from the late Triassic (Norian) Batang Group (7 sites, 55 samples); and a mid-Cretaceous (?) tonolite 15 km south of Wudaoliang (2 sites, 18 samples). These locations have previously been dated by biostratigraphic ages of overlying and underlying strata. Here we present new geochronologic data from the volcanic rocks themselves. High NRM moment values and weak-field susceptibility vs. temperature measurements suggest that magnetite is the dominant magnetic mineral. Resistance to alternating field demagnetization in many samples, in addition to data from magnetic hysteresis measurements, however, indicate a significant amount of hematite exists in these samples as well. All samples were subjected to progressive thermal demagnetization to isolate the characteristic, primary, and secondary magnetizations. Preliminary results show useful paleomagnetic poles may be forthcoming from our collections. Our data may have significant bearing on the geodynamic history of Tibet, including paleogeography of the Eastern Qiangtang Terrane, block rotations, and the nature of the Tertiary low-paleolatitude anomaly in Central Asia.

  8. Tectonic transition associated with Kazakhstan Orocline in the Late Paleozoic: magmatic archives of western Chinese Tianshan

    NASA Astrophysics Data System (ADS)

    Cai, Keda

    2016-04-01

    Kazakhstan accretionary system was a principle component of the Central Asian Orogenic Belt (CAOB) that is one of the largest accretionary orogens on earth. The Kazakhstan composite continent could have been established in the Early Paleozoic by the Kazakhstan accretionary system in the form of progressively amalgamations of diverse tectonic units, such as continental ribbon, accretionary prim, oceanic remnant and arc material. Subsequently, the composite continent was bended to form a spectacular U-shaped architecture that probably occurred in the Late Paleozoic. The western Chinese Tianshan is situated on the south wing of the Kazakhstan Orocline, featured by extensive magmatim, intense deformation and voluminous mineralization. Our new geochronological and geochemical data suggest a noticeable magmatic gap between Late Devonian and Early carboniferous and contrasting magma sources of these magmatic rocks. The significant shifts correspond to the tectonic transition from terrane amalgamation to mountain bending in the Early Paleozoic. This study was financially supported by the Major Basic Research Project of the Ministry of Science and Technology of China (2014CB448000), Xinjiang outstanding youth scientific grant (2013711003) and the Talent Awards to KDC from the China Government under the 1000 Talent Plan.

  9. Late Paleozoic deformation of interior North America: The greater Ancestral Rocky Mountains

    SciTech Connect

    Ye, Hongzhuan |; Royden, L.; Burchfiel, C.; Schuepbach, M.

    1996-09-01

    Late Paleozoic deformation within interior North America has produced a series of north-northwest- to northwest-trending elongate basins that cover much of Oklahoma, Texas, New Mexico, Colorado, and Utah. Each basin thickens asymmetrically toward an adjacent region of coeval basement uplift from which it is separated by synsedimentary faults with great vertical relief. The remarkable coincidence in timing, geometry, and apparent structural style throughout the region of late Paleozoic deformation strongly suggests that these paired regions of basin subsidence and basement uplift form a unified system of regional deformation, the greater Ancestral Rocky Mountains. Over this region, basin subsidence and basement uplift were approximately synchronous, beginning in the Chesterian-Morrowan, continuing through the Pennsylvanian, and ending in the Wolfcampian (although minor post-Wolfcampian deformation occurs locally). The basement uplifts show evidence for folding and faulting in the Pennsylvanian and Early Permian. Reverse faults and thrust faults have been drilled over many of the uplifts, but only in the Anadarko region has thrusting of the basement uplifts over the adjacent basin been clearly documented. Extensive basement-involved thrusting also occurs along the margins of the Delaware and Midland basins, and suggests that the entire greater Ancestral Rocky Mountains region probably formed as the result of northeast-southwest-directed-intraplate shortening. Deformation within the greater Ancestral Rocky Mountains was coeval with late Paleozoic subduction along much of the North American plate margin, and has traditionally been related to emplacement of thrust sheets within the Ouachita-Marathon orogenic belt. The nature, timing, and orientation of events along the Ouachita-Marathon belt make it difficult to drive the deformation of the greater Ancestral Rocky Mountains by emplacement of the Ouachita-Marathon belt along the southern margin of North America.

  10. The Late Paleozoic evolution of the Gondwanaland continental margin in northern Chile

    NASA Astrophysics Data System (ADS)

    Bell, C. M.

    Tectonic activity on the Gondwanaland continental margin in northern Chile and northwestern Argentina has been continuous from the early Paleozoic to the present. Paleozoic accretion resulted from the buildup of accretionary and magmatic arc complexes, and possibly from the addition of exotic terranes. Paleozoic strata between 25°S and 29°S in northern Chile comprise two north-south elongated strips separated by a 100-km-wide graben infilled with younger rocks. The western strip consists of deep-sea turbidites and basic lavas of the Devonian or Early Carboniferous Las Tórtolas Formation. Subduction of these rocks during Carboniferous times produced the Chañaral mélange in the area south of 26°30'S. The mélange probably resulted from intrastratal movements of partly consolidated strata within an accretionary wedge. Further tectonic deformation of both the turbidites and the mélange was produced by northeast directed subduction. The subduction complex is bounded to the east by the Atacama strike-slip fault system. To the east of the graben are relatively undeformed Early Carboniferous lacustrine sedimentary rocks of the Chinches Formation. These were deposited in a deep, elongated basin, possibly of pull-apart type resulting from strike-slip movement parallel to the coastline. Late Carboniferous to Early Permian magmatic activity superimposed on both these sedimentary successions suggests seaward migration of the subduction zone. The development of the Mesozoic and Cenozoic Andean complex, which overlies the Paleozoic rocks with a marked unconformity, was not accompanied by the accretion of a further subduction complex.

  11. Paleolatitudinal changes in vertical facies transitions recording late Paleozoic glaciations: a case study from eastern Australia

    NASA Astrophysics Data System (ADS)

    Fielding, C. R.; Frank, T. D.; Shultis, A. I.

    2011-12-01

    Stratigraphic records of the complex and multi-phase late Paleozoic Ice Age (LPIA) have been examined over a 2000 km paleo-polar to paleo-mid latitude transect from Tasmania to Queensland, eastern Australia. In this presentation, we summarize changes in facies assemblages within glacial and nonglacial epochs and the transitions between them, within the coastal to shallow marine Permian succession. In the earliest Permian P1 glacial interval, facies represent proximal proglacial to locally glacial environments in Tasmania (TAS), and an array of mainly marine proglacial to glacimarine environments in New South Wales (NSW) and Queensland (QLD). A trend of more ice-proximal to less ice-proximal facies assemblages is evident from south to north. The end of P1 is represented both by abrupt flooding trends in some areas and by thicker intervals of more gradually fining-upward facies recording progressive deepening elsewhere. The onset of the Sakmarian/Artinskian P2 glacial interval is best-exposed in southern NSW, where an abrupt change to marine proglacial facies is accompanied by evidence for deepening, suggesting isostatic loading of the sedimentary surface. P2 glacial facies are more proximal in NSW than in QLD. Both P1 and P2 intervals preserve complex internal stratigraphy, in many cases recording multiple glacial-interglacial cycles. The close of P2 is again recorded in a variety of ways, with many sections showing a gradual fining-upward and decrease in indicators of glacial conditions. The Kungurian to Capitanian P3 and P4 glacial intervals are in general represented by less proximal facies than their predecessors, typically intervals of outsize clast-bearing mudrocks and sandstones. These in many areas show diffuse boundaries with the nonglacial facies that enclose them. Furthermore, no significant paleolatitudinal changes in the P3 and P4 facies assemblages are evident from TAS to QLD. The documented patterns support the view that the P1 glacial represents the

  12. Archean inheritance in zircon from late Paleozoic granites from the Avalon zone of southeastern New England: an African connection

    USGS Publications Warehouse

    Zartman, R.E.; Don, Hermes O.

    1987-01-01

    In southeastern New England the Narragansett Pier Granite locally intrudes Carboniferous metasedimentary rocks of the Narragansett basin, and yields a monazite UPb Permian emplacement age of 273 ?? 2 Ma. Zircon from the Narragansett Pier Granite contains a minor but detectable amount of an older, inherited component, and shows modern loss of lead. Zircon from the late-stage, aplitic Westerly Granite exhibits a more pronounced lead inheritance -permitting the inherited component to be identified as Late Archean. Such old relict zircon has not been previously recognized in Proterozoic to Paleozoic igneous rocks in New England, and may be restricted to late Paleozoic rocks of the Avalon zone. We suggest that the Archean crustal component reflects an African connection, in which old Archean crust was underplated to the Avalon zone microplate in the late Paleozoic during collision of Gondwanaland with Avalonia. ?? 1987.

  13. The Late Guadalupian (Permian) event: when everything geologically unusual started for the Paleozoic-Mesozoic transition

    NASA Astrophysics Data System (ADS)

    Isozaki, Y.

    2007-12-01

    The event across the Paleozoic-Mesozoic transition involves the greatest mass extinction in history and other long-term complicated geologic phenomena in various aspects on the Earth, such as Pangean rifting and superanoxia. The Permo-Triassic mid-oceanic sedimentary records documented the double-phased nature of the extinction and relevant environmental changes at the Middle and Upper Permian or Guadalupian-Lopingian boundary (G-LB) and at the Permo-Triassic boundary (P-TB). As all the coeval ocean floors of Panthalassa were lost by subduction, the dataset from the accreted mid-oceanic rocks is particularly important. The deep-sea chert recorded the double-phased remarkable faunal reorganization in radiolarians (major marine plankton in the Paleozoic), i.e., in the Late Guadalupian and at P-TB. It is noteworthy that the superanoxia (ca. 20 million year long deep-sea anoxia) started in the Late Guadalupian culminated at the P-TB. The mid-oceanic paleo-atoll carbonates primarily deposited on seamounts also recorded double-phased extinction in fusulines (a representative Late Paleozoic shallow marine benthos), double-phased negative shift of stable carbon isotope ratio in the Late Guadalupian and at P-TB, and the Phanerozoic minimum in 87Sr/86Sr isotope ratio in the Late Guadalupian. Mid-oceanic deep- and shallow-water sequences indicate that significant changes have occurred in the Permian superocean in a double-phased manner, and that everything geologically unusual started in the Late Guadalupian. These bio- and chemostratigraphical data are concordant with those from the coeval shallow marine shelf sequences around Pangea. The uniquely concentrated occurrence of rhyo-dacitic tuff beds both around G-L B and P-TB suggests that Panthalassa and eastern Tethys (South China) extensively suffered severe volcanic hazards twice almost at the same time as the G-LB and P-TB extinctions. In the framework of the 'Plume Winter' scenario (Isozaki, 2007), the double

  14. Paleoclimate controls on late paleozoic sedimentation and peat formation in the central appalachian basin (U.S.A.)

    USGS Publications Warehouse

    Cecil, C.B.; Stanton, R.W.; Neuzil, S.G.; Dulong, F.T.; Ruppert, L.F.; Pierce, B.S.

    1985-01-01

    In the central Appalachian basin, at least two major climate changes affected sedimentation during the late Paleozoic. Stratigraphically, these two changes are indicated by the distribution of coal beds, the variation in coal quality, and the variation in rock lithologies. In latest Mississippian or earliest Pennsylvanian time, the climate changed from dry-seasonal tropical to ever-wet (equable) tropical. The equable climate prevailed into the Middle Pennsylvanian, influencing the morphology and geochemistry in peat-forming environments. Many of the peat deposits, which formed under the equable climate, were probably domed (raised bogs); low concentrations of dissolved solids in peat formation water resulted in low buffering capacity. Organic acids caused acidic (pH < 4), antiseptic conditions that resulted in intense leaching of mineral matter, minimal degradation of organic matter, and low-ash and low-sulfur peat deposits; the resulting coal beds are also low in ash and sulfur. Associated rocks are noncalcareous and consist of sequences of interbedded shale, siltstone, and sandstone including quartz arenite. Another climate change occurred in late Middle Pennsylvanian time when evapopation periodically exceeded rainfall resulting in an increase of both dissolved solids and pH (4 to ??? 7) in surface and near-surface water. Throughout the remainder of the Pennsylvanian, the surfaces of peat deposits were probably planar (not domed); water in peat-forming and other depositional environments became more nearly neutral. The coal beds derived from these peats are highly variable in both ash and sulfur contents. Drier or more seasonal climates are also indicated by sequences of (1) calcareous sandstone and shale, (2) nonmarine limestone that shows shallow-water and subaerial exposure features, and (3) calcareous paleosols that have caliche characteristics. Our data and observations indicate that physical depositional environment models for the origin of coal do not

  15. The rise and fall of late Paleozoic trilobites of the United States

    USGS Publications Warehouse

    Brezinski, D.K.

    1999-01-01

    Based on range data and generic composition, four stages of evolution are recognized for late Paleozoic trilobites of the contiguous United States. Stage 1 occurs in the Lower Mississippian (Kinderhookian-Osagean) and is characterized by a generically diverse association of short-ranging, stenotopic species that are strongly provincial. Stage 2 species are present in the Upper Mississippian and consist of a single, eurytopic, pandemic genus, Paladin. Species of Stage 2 are much longer-ranging than those of Stage 1, and some species may have persisted for as long as 12 m.y. Stage 3 is present within Pennsylvanian and Lower Permian strata and consists initially of the eurytopic, endemic genera Sevillia and Ameura as well as the pandemic genus Ditomopyge. During the middle Pennsylvanian the very long-ranging species Ameura missouriensis and Ditomopyge scitula survived for more than 20 m.y. During the late Pennsylvanian and early Permian, a number of pandemic genera appear to have immigrated into what is now North America. Stage 4 is restricted to the Upper Permian (late Leonardian-Guadalupian) strata and is characterized by short-ranging, stenotopic, provincial genera. The main causal factor controlling the four-stage evolution of late Paleozoic trilobites of the United States is interpreted to be eustacy. Whereas Stage 1 represents an adaptive radiation developed during the Lower Mississippian inundation of North America by the Kaskaskia Sequence, Stage 2 is present in strata deposited during the regression of the Kaskaskia sea. Stage 3 was formed during the transgression and stillstand of the Absaroka Sequence and, although initially endemic, Stage 3 faunas are strongly pandemic in the end when oceanic circulation patterns were at a maximum. A mid-Leonardian sea-level drop caused the extinction of Stage 3 fauna. Sea-level rise near the end of the Leonardian and into the Guadalupian created an adaptive radiation of stentopic species of Stage 4 that quickly became

  16. Provenance of Late Carboniferous to Jurassic sandstones for southern Taimyr, Arctic Russia: A comparison of heavy mineral analysis by optical and QEMSCAN methods

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaojing; Pease, Victoria; Omma, Jenny; Benedictus, Aukje

    2015-11-01

    Sandstone framework-grain petrography, optical and QEMSCAN (Quantitative Evaluation of Minerals by Scanning Electron Microscopy) heavy mineral analysis carried out on 40 samples collected from east and west southern Taimyr are used to constrain the provenance and tectonic history of Late Carboniferous to Late Jurassic siliciclastic sequences. The tectonic settings of provenance evolved gradually from a mix of volcanic arc and recycled orogen to craton interior. Much of the detritus in the Late Paleozoic to Mesozoic siliciclastic succession came from proximal sources with contributions from multi-type source rocks including acid igneous rocks, basalts, sedimentary rocks and low to medium-grade metamorphic rocks. Carboniferous to Permian sandstones contain low-diversity suites of heavy minerals, including apatite, tourmaline, zircon, rutile, Cr-spinel, monazite and titanite. Cr-spinel indicates probable influx from exposed ophiolitic basement. Abundant euhedral zircon and apatite suggest a volcanic arc source related with Uralian collision. The appearance of garnet in the early Triassic signals the unroofing of a metamorphic source. The abrupt increase of clinopyroxene in Middle to Late Triassic sandstones indicates the influx of detritus from basic rocks related with Siberian Trap magmatism. The decrease of Cr-spinel and an abundance of staurolite in Jurassic samples indicate that unroofing of an ophiolitic source ceased and that stripping of a different thrust sheet containing plenty of staurolite-bearing metamorphic rocks commenced.

  17. The Cottage Grove fault system (Illinois Basin): Late Paleozoic transpression along a Precambrian crustal boundary

    USGS Publications Warehouse

    Duchek, A.B.; McBride, J.H.; Nelson, W.J.; Leetaru, H.E.

    2004-01-01

    The Cottage Grove fault system in southern Illinois has long been interpreted as an intracratonic dextral strike-slip fault system. We investigated its structural geometry and kinematics in detail using (1) outcrop data, (2) extensive exposures in underground coal mines, (3) abundant borehole data, and (4) a network of industry seismic reflection profiles, including data reprocessed by us. Structural contour mapping delineates distinct monoclines, broad anticlines, and synclines that express Paleozoic-age deformation associated with strike slip along the fault system. As shown on seismic reflection profiles, prominent near-vertical faults that cut the entire Paleozoic section and basement-cover contact branch upward into outward-splaying, high-angle reverse faults. The master fault, sinuous along strike, is characterized along its length by an elongate anticline, ???3 km wide, that parallels the southern side of the master fault. These features signify that the overall kinematic regime was transpressional. Due to the absence of suitable piercing points, the amount of slip cannot be measured, but is constrained at less than 300 m near the ground surface. The Cottage Grove fault system apparently follows a Precambrian terrane boundary, as suggested by magnetic intensity data, the distribution of ultramafic igneous intrusions, and patterns of earthquake activity. The fault system was primarily active during the Alleghanian orogeny of Late Pennsylvanian and Early Permian time, when ultramatic igneous magma intruded along en echelon tensional fractures. ?? 2004 Geological Society of America.

  18. The development of floristic provinciality during the Middle and Late Paleozoic

    USGS Publications Warehouse

    Wnuk, C.

    1996-01-01

    Phytogeographic reconstructions have been published for most Paleozoic series since the Pr??i??doli??, but there have been few attempts to synthesize this data into a comprehensive review of the characteristics and causes of the changing phytogeographic patterns for the whole Paleozoic history of the vascular flora. Existing floristic analyses have been compiled in this manuscript and the resulting data are used to reconstruct the evolution of floristic provinces since the Silurian. The earliest plant fossil records indicate that provinciality was characteristic of terrestrial vascular plant distributions right from the beginning of terrestrial colonization by vascular plants. This interpretation differs markedly from the views of many workers who still maintain that pre-Upper Carboniferous floras were uniform and cosmopolitan in distribution. Three of the four major phytogeographic units, i.e. Angara, Euramerica, and Gondwana, can be recognized in the earliest fossil floras. The fourth unit, Cathaysia, differentiated from Euramerica during the late Upper Carboniferous. Phytogeographic differentiation occurs in direct response to climatic gradients and physiographic barriers. As these gradients and barriers change, provincial boundaries expand and contract, fragment, reassemble and reassort. Phytogeographic units are dynamic through time. ?? 1996 Elsevier Science B.V. All rights reserved.

  19. Carboniferous sediment dispersal in the Appalachian-Ouachita juncture: Provenance of selected late Mississippian sandstones in the Black Warrior Basin, Mississippi, United States

    NASA Astrophysics Data System (ADS)

    Xie, Xiangyang; O'Connor, Patrick M.; Alsleben, Helge

    2016-08-01

    The Black Warrior Basin is one of several Carboniferous foreland basins along the Appalachian-Ouachita fold-thrust belt in the southeastern United States. Sediment dispersal within the Black Warrior Basin has been a long-debated topic because of a complex tectonic history and the potential interaction between the Appalachian and Ouachita orogenic belts, as well as far field sediment sources. Three dispersal patterns have been proposed, including dispersal routes from the craton, dispersal via the Appalachian foreland, and dispersal from the arc side of the Ouachita suture, but sediment dispersal in the Black Warrior Basin remains inconclusive. In this study, sandstone modal analysis and U-Pb detrital zircon geochronology are used to document the provenance and potential dispersal patterns for selected Mississippian sandstone units in the Black Warrior Basin, Missouri, USA. Results show that the majority of the Lewis, Evans, Sanders, and Carter sandstones are sublitharenite to mature quartzarenite and fall within the Cratonic Interior field on Q-F-L diagrams. U-Pb detrital zircon analyses of the Lewis, Sanders, and Carter sandstones show that there are four distinctive age clusters, including a prominent Paleozoic age cluster (~ 350-500 Ma), a broad Grenville age cluster (~ 900-1350 Ma), and two minor age clusters of the Granite-Rhyolite (~ 1360-1600 Ma) and the Yavapai-Mazatzal (~ 1600-1800 Ma) provinces. All Mississippian sandstones have similar age distributions except for the Lewis sandstone, which lacks zircon grains from the Superior province (>~2500 Ma). Based on the compositional maturity, similarity of age distributions, and changes of relative abundance among different age groups, we conclude that the Late Mississippian sandstone units analyzed during this study were derived from the Laurussian craton and the northern part of the Appalachian foreland through a major axial drainage that occupied the Mississippi Valley Graben.

  20. A Late Proterozoic Early Paleozoic magmatic cycle in Sierra de la Ventana, Argentina

    NASA Astrophysics Data System (ADS)

    Gregori, D. A.; López, V. L.; Grecco, L. E.

    2005-06-01

    Late Proterozoic-Early Paleozoic intrusive and volcanic rocks of Sierra de la Ventana can be grouped into two magmatic assemblages: the Meyer and Cochenleufú suites. The older (700-570 Ma) is composed of S-type quartz-monzodiorites, synogranites, and monzogranites associated with andesites and rhyolites and related to volcanic-arc and postcollisional settings. The younger (540-470 Ma) corresponds to highly fractionated homogeneous A-type monzogranites, linked to final plutonic events during postorogenic extension in collisional belts. Strong similarities between Sierra de la Ventana magmatic rocks and the S- and A-type granites of the Cape granite suite in South Africa allow positive correlation. In both areas, primitive volcanic arcs or collisional orogens are recognized. Continuous transpressional shearing between the Swartland and Tygerberg terranes in the Saldania belt may have triggered the generation and emplacement of both suites.

  1. Late Paleozoic Orogenies in western Africa and eastern North America: The diachronous closure of Theic Ocean

    NASA Astrophysics Data System (ADS)

    Piqué, Alain; Skehan, James W.

    1992-04-01

    The Carboniferous evolution in western Morocco, southeastern Canada, and New England was dominated by intracontinental processes: the subsidence of pull-apart sedimentary basins, and their subsequent deformation during middle Carboniferous to Early Permian times, with the development of autochthonous structures and mainly low- to medium-grade metamorphism. On the other hand, the structural style of the late Carboniferous deformation in the southern Appalachians, and to a substantial degree also in New England, that is related to a continental collision is characterized by deep-seated northwest-vergent thrusts and medium- to high-grade metamorphism. The Mauritanides structures are symmetrically east-vergent thrusts. This pattern is explained by the diachronous closure of the Theic ocean that separated the Avalon and Carolina microcontinental blocks from paleo-Gondwana. The closure of the Theic ocean occurred during Devonian times between the northern Appalachians and the northwestern edge of paleo-Gondwana (Morocco), whereas it was achieved only at the end of Carboniferous times between the southern Appalachians and western Africa (Mauritania-Senegal). The Late Devonian to early Carboniferous counterclockwise rotation of Gondwana induced the opening of the pull-apart basins of Canada, New England, and Morocco as well as, later, the oblique collision in the southern Appalachians and the generalized late Paleozoic dextral transcurrent faulting along the northern edge of paleo-Gondwana.

  2. Late-Paleozoic emplacement and Meso-Cenozoic reactivation of the southern Kazakhstan granitoid basement

    NASA Astrophysics Data System (ADS)

    De Pelsmaeker, Elien; Glorie, Stijn; Buslov, Mikhail M.; Zhimulev, Fedor I.; Poujol, Marc; Korobkin, Valeriy V.; Vanhaecke, Frank; Vetrov, Evgeny V.; De Grave, Johan

    2015-11-01

    The Ili-Balkhash Basin in southeastern Kazakhstan is located at the junction of the actively deforming mountain ranges of western Junggar and the Tien Shan, and is therefore part of the southwestern Central Asian Orogenic Belt. The basement of the Ili-Balkhash area consists of an assemblage of mainly Precambrian microcontinental fragments, magmatic arcs and accretionary complexes. Eight magmatic basement samples (granitoids and tuffs) from the Ili-Balkhash area were dated with zircon U-Pb LA-ICP-MS and yield Carboniferous to late Permian (~ 350-260 Ma) crystallization ages. These ages are interpreted as reflecting the transition from subduction to (post-) collisional magmatism, related to the closure of the Junggar-Balkhash Ocean during the Carboniferous-early Permian and hence, to the final late Paleozoic accretion history of the ancestral Central Asian Orogenic Belt. Apatite fission track (AFT) dating of 14 basement samples (gneiss, granitoids and volcanic tuffs) mainly provides Cretaceous cooling ages. Thermal history modeling based on the AFT data reveals that several intracontinental tectonic reactivation episodes affected the studied basement during the late Mesozoic and Cenozoic. Late Mesozoic reactivation and associated basement exhumation is interpreted as distant effects of the Cimmerian collisions at the southern Eurasian margin and possibly of the Mongol-Okhotsk Orogeny in SE Siberia during the Jurassic-Cretaceous. Following tectonic stability during the Paleogene, inherited basement structures were reactivated during the Neogene (constrained by Miocene AFT ages of ~ 17-10 Ma). This late Cenozoic reactivation is interpreted as the far-field response of the India-Eurasia collision and reflects the onset of modern mountain building and denudation in southeast Kazakhstan, which seems to be at least partially controlled by the inherited basement architecture.

  3. Climate and vegetational regime shifts in the late Paleozoic ice age earth.

    PubMed

    DiMichele, W A; Montañez, I P; Poulsen, C J; Tabor, N J

    2009-03-01

    The late Paleozoic earth experienced alternation between glacial and non-glacial climates at multiple temporal scales, accompanied by atmospheric CO2 fluctuations and global warming intervals, often attended by significant vegetational changes in equatorial latitudes of Pangaea. We assess the nature of climate-vegetation interaction during two time intervals: middle-late Pennsylvanian transition and Pennsylvanian-Permian transition, each marked by tropical warming and drying. In case study 1, there is a catastrophic intra-biomic reorganization of dominance and diversity in wetland, evergreen vegetation growing under humid climates. This represents a threshold-type change, possibly a regime shift to an alternative stable state. Case study 2 is an inter-biome dominance change in western and central Pangaea from humid wetland and seasonally dry to semi-arid vegetation. Shifts between these vegetation types had been occurring in Euramerican portions of the equatorial region throughout the late middle and late Pennsylvanian, the drier vegetation reaching persistent dominance by Early Permian. The oscillatory transition between humid and seasonally dry vegetation appears to demonstrate a threshold-like behavior but probably not repeated transitions between alternative stable states. Rather, changes in dominance in lowland equatorial regions were driven by long-term, repetitive climatic oscillations, occurring with increasing intensity, within overall shift to seasonal dryness through time. In neither case study are there clear biotic or abiotic warning signs of looming changes in vegetational composition or geographic distribution, nor is it clear that there are specific, absolute values or rates of environmental change in temperature, rainfall distribution and amount, or atmospheric composition, approach to which might indicate proximity to a terrestrial biotic-change threshold.

  4. Subsidence history of the Alabama promontory in response to Late Paleozoic Appalachian-Ouachita thrusting

    SciTech Connect

    Whitting, B.M.; Thomas, W.A. . Dept. of Geological Sciences)

    1994-03-01

    The Alabama promontory of North American continental crust was framed during late Precambrian-Cambrian rifting by the northeast-striking Blue Ridge rift and the northwest-striking alabama-Oklahoma transform fault. A passive margin persisted along the western side of the promontory from Cambrian to Mississippian time, but the eastern side was affected by the Taconic and Acadian orogenies. Prior to initiation of Ouachita and Appalachian (Alleghanian) thrusting, the outline of the rifted margin of continental crust on the Alabama promontory remained intact; and the late paleozoic thrust belt conformed to the shape of the promontory, defining northwest-striking Ouachita thrust faults along the southwest side of the promontory, north-striking Appalachian (Georgia-Tennessee) thrust faults on the east, and northeast-striking Appalachian (Alabama) thrust faults across the corner of the promontory. Subsidence profiles perpendicular to each of the strike domains of the thrust belt have been constructed by calculating total subsidence from decompacted thickness of the synorogenic sedimentary deposits. The profile perpendicular to the Ouachita thrust belt shows increasing subsidence rates through time and toward the thrust front, indicating the classic signature of an orogenic foreland basin. The profile perpendicular to the Georgia-Tennessee Appalachian thrust belt similarly shows increasing subsidence rates through time and toward the orogenic hinterland. These quantitative results support the conclusion that Black Warrior basin subsidence is tectonically rather than sedimentologically driven, and the timing of subsidence events reported here has implications for regional tectonic models.

  5. Late paleozoic base and precious metal deposits, East Tianshan, Xinjiang, China: Characteristics and geodynamic setting

    USGS Publications Warehouse

    Mao, J.; Goldfarb, R.J.; Wang, Y.; Hart, C.J.; Wang, Z.; Yang, J.

    2005-01-01

    The East Tianshan is a remote Gobi area located in eastern Xinjiang, northwestern China. In the past several years, a number of gold, porphyry copper, and Fe(-Cu) and Cu-Ag-Pb-Zn skarn deposits have been discovered there and are attracting exploration interest. The East Tianshan is located between the Junggar block to the north and early Paleozoic terranes of the Middle Tianshan to the south. It is part of a Hercynian orogen with three distinct E-W-trending tectonic belts: the Devonian-Early Carboniferous Tousuquan-Dananhu island arc on the north and the Carboniferous Aqishan - Yamansu rift basin to the south, which are separated by rocks of the Kanggurtag shear zone. The porphyry deposits, dated at 322 Ma, are related to the late evolutionary stages of a subduction-related oceanic or continental margin arc. In contrast, the skarn, gold, and magmatic Ni-Cu deposits are associated with post-collisional tectonics at ca. 290-270 Ma. These Late Carboniferous - Early Permian deposits are associated with large-scale emplacement and eruption of magmas possibly caused by lithosphere delamination and rifting within the East Tianshan.

  6. Gulf of California analogue for origin of Late Paleozoic ocean basins adjacent to western North America

    SciTech Connect

    Murchey, B.L. )

    1993-04-01

    Ocean crust accreted to the western margin of North America following the Late Devonian to earliest Missippian Antler orogeny is not older than Devonian. Therefore, ocean crust all along the margin of western North America may have been very young following the Antler event. This situation can be compared to the present-day margin of North America which lies adjacent to young ocean crust as a result of the subduction of the Farallon plate and arrival of the East Pacific spreading ridge. Syn- and post-Antler rifting that occurred along the North American margin may well be analogous to the formation of the Gulf of California by the propagation of the East Pacific spreading ridge. Black-arc rifting associated with the subduction of very old ocean crust seems a less likely mechanism for the early stages of ocean basin formation along the late Paleozoic margin of western North America because of the apparent absence of old ocean crust to the west of the arc terranes. The eastern Pacific basins were as long-lived as any truly oceanic basins and may have constituted, by the earliest Permian, a single wedge-shaped basin separated from the western Pacific by rifted fragments of North American arc-terranes. In the Permian, the rifted arcs were once again sites of active magmatism and the eastern Pacific basins began to close, from south (Golconda terrane) to north. Final closure of the northernmost eastern Pacific basin (Angayucham in Alaska) did not occur until the Jurassic.

  7. Structural style and timing of Late Paleozoic basement uplifts in southern Oklahoma

    SciTech Connect

    Brown, W.G. . Dept. of Geology)

    1993-04-01

    Proposed theories of deformation in southern Oklahoma presently involve large-scale basement thrusting or large magnitudes of strike slip. As more and better seismic data and well control have become available, a predominant interpretation of the structural style is emerging. This style is characterized by a large basement overhang along the mountain fronts, created by major reverse dip-slip (thrust) faults. Additionally, these reverse faults may have an antithetic back-thrust on the hanging wall. In cross section, this style appears as a wedge-uplift that is often mistakenly interpreted to represent the upper portion of a flower structure created by wrench-faulting. Structural uplifts in southern Oklahoma developed as a result of Late Paleozoic Wichita, Ouachita and Arbuckle orogenies. Emplacement of the thin-skinned Ouachita thrust belt occurred during the Ouachita orogeny (Mississippian through Middle Pennsylvanian). Basement-involved compressional uplifts of the Wichita Mountains and Criner Hills were initially uplifted during the Wichita orogeny (Late Mississippian to Early Pennsylvanian), while the Arbuckle anticline and Tishomingo uplift reached their culmination during the Arbuckle orogeny (Middle to Late Pennsylvanian). Evidence for the timing of these uplifts are the various conglomerates and unconformities preserved in the subsurface, and occasionally exposed at the surface. Age-dating of these unconformities strongly suggests a sequence of deformation in which the culmination of uplift progressed generally from south to north through time. This sequence is also suggested by deformation of the thin-skinned Ouachita thrust belt by basement-involved structures of the Arbuckle orogeny.

  8. High-resolution sequence stratigraphy of lower Paleozoic sheet sandstones in central North America: The role of special conditions of cratonic interiors in development of stratal architecture

    USGS Publications Warehouse

    Runkel, Anthony C.; Miller, J.F.; McKay, R.M.; Palmer, A.R.; Taylor, John F.

    2007-01-01

    continuum of variable stratigraphic packages reflecting variable controls such as subsidence and shelf physiography. Special conditions of exceptionally slow subsidence rate, shallow bathymetry, and nearly flat regional shelf gradient are manifest mostly by the presence of individual systems tracts of relatively long duration that extend for much greater distances across depositional strike than those that characterize successions deposited in more dynamic tectonic and physiographic settings. These results suggest that if other cratonic interior successions are as anomalous as reported, a low sediment supply may have played a primary role in development of their apparently condensed stratal architecture. The results also lead us to suggest that a nonvegetated lower Paleozoic landscape played a relatively insignificant role in the development of what are commonly perceived to be enigmatic stratigraphic features of sheet sandstones, particularly their widespread yet thin geometry, and a scarcity of shale and siltstone. ?? 2007 Geological Society of America.

  9. Paleomagnetism of rocks from Burin Peninsula, Newfoundland: Hypothesis of Late Paleozoic displacement of Acadia criticized

    NASA Astrophysics Data System (ADS)

    Irving, E.; Strong, D. F.

    1985-02-01

    for North America is either entirely Kiaman in age or has been seriously affected by Kiaman overprinting. Consequently, the 30° of southerly displacement which the N magnetization of the St. Lawrence Granite apears to indicate, and the 15° invoked by Kent and Opdyke, we consider to be illusory. Three Late Precambrian rock units (623 to 606 Ma) have scattered declinations but similar inclinations yielding paleolatitudes of about 35°. The scattered declinations presumable were caused by local pre-Carboniferous relative rotations. There is little or no evidence of Kiaman overprinting in Precambrian rocks, indicating that overprinting is comparatively superficial and is probably related to Late Paleozoic groundwater circulation.

  10. A New Paleozoic Symmoriiformes (Chondrichthyes) from the Late Carboniferous of Kansas (USA) and Cladistic Analysis of Early Chondrichthyans

    PubMed Central

    Pradel, Alan; Tafforeau, Paul; Maisey, John G.; Janvier, Philippe

    2011-01-01

    Background The relationships of cartilaginous fishes are discussed in the light of well preserved three-dimensional Paleozoic specimens. There is no consensus to date on the interrelationship of Paleozoic chondrichthyans, although three main phylogenetic hypotheses exist in the current literature: 1. the Paleozoic shark-like chondrichthyans, such as the Symmoriiformes, are grouped along with the modern sharks (neoselachians) into a clade which is sister group of holocephalans; 2. the Symmoriiformes are related to holocephalans, whereas the other Paleozoic shark-like chondrichthyans are related to neoselachians; 3. many Paleozoic shark-like chondrichthyans, such as the Symmoriiformes, are stem chondrichthyans, whereas stem and crown holocephalans are sister group to the stem and crown neoselachians in a crown-chondrichthyan clade. This third hypothesis was proposed recently, based mainly on dental characters. Methodology/Principal Findings On the basis of two well preserved chondrichthyan neurocrania from the Late Carboniferous of Kansas, USA, we describe here a new species of Symmoriiformes, Kawichthys moodiei gen. et sp. nov., which was investigated by means of computerized X-ray synchrotron microtomography. We present a new phylogenetic analysis based on neurocranial characters, which supports the third hypothesis and corroborates the hypothesis that crown-group chondrichthyans (Holocephali+Neoselachii) form a tightly-knit group within the chondrichthyan total group, by providing additional, non dental characters. Conclusions/Significance Our results highlight the importance of new well preserved Paleozoic fossils and new techniques of observation, and suggest that a new look at the synapomorphies of the crown-group chondrichthyans would be worthwhile in terms of understanding the adaptive significance of phylogenetically important characters. PMID:21980367

  11. Preliminary paleomagnetic study on Late Paleozoic to Early Mesozoic rocks in Indochina and its paleogeographic implications

    NASA Astrophysics Data System (ADS)

    Yan, Y.; Huang, B.; Zhao, J.

    2013-12-01

    The Indochina block is one of the main blocks in East Asia and its paleogeographic positions in formation of the Pangea supercontinent are still in debate because of the lack of reliable Late Paleozoic to Early Mesozoic paleomagnetic constraints.Here we present some preliminary Late Paleozoic to Early Mesozoic paleomagnetic results from the Simao block, the northern part of the Indochina block in West Yunnan of China. Following detailed rock magnetic and paleomagnetic experiments on a total of 205 drilled samples in 20 sites, characteristic remanent magnetizations (ChRMs) were isolated from most samples following thermal or integrated thermal and alternating field (AF) demagnetization. Results from 40 samples of the Permian sediments yield a mean paleomagnetic direction of Dg=27.6°, Ig=41.5°, k=82.1, α95=2.7° before and Ds=45.2°, Is=35.8°, k=66.4 ,α95=3.0° after tilt correction. Following magnetic fabric analysis and thin sections analysis with microscope, strong tectonic deformation and medium degree metamorphism were identified in these samples. Results from 65 samples of Middle Triassic limestones yield a mean direction of Dg=46.9°, Ig=38.4°, k=31.8, α95=2.5° before and Ds=52.2°, Is=46.5°, k=35.6°, α95=2.4° after tilt correction. General recrystallization was founded in these samples following thin section analysis with microscope. These two mean directions, with slight change in data grouping after tilt correction, appear to have a secondary origin.However, mean direction of 24 samples obtained from the other Middle Triassic limestones profile is of Dg=45.6°, Ig=70.0°, k=76.4, α95=3.1° before and Ds=82.5°, Is=22.4°, k=68.7°, α95=3.3° after tilt correction, corresponding to a paleopole at 182.7°E,11.3°N with A95=3.3°. We interpret this direction as primary remanence in the light of its significant difference with Cretaceous poles, no significant metamorphism founded on hand-samples and thin sections. Besides, mean direction of 40

  12. Stratigraphic evolution of paleozoic erathem, northern Florida

    SciTech Connect

    Coleman, J.L. Jr.

    1985-02-01

    Unmetamorphosed Paleozoic sedimentary and volcanic rocks have been drilled in numerous wells throughout northern Florida and southern Georgia, in what is today a gently folded and block-faulted relict continental fragment of northwest Africa and northeast South America. Stratigraphic and lithologic equivalents of these North American Paleozoic units are prolific hydrocarbon producers in North Africa. The northern Florida Paleozoic sediments were deposited on Pan-African and Cadoman basement. Widespread continental glaciation from late Precambrian to Early Cambrian introduced a thick sequence of fine-grained marine sandstones (glacial flour), which overlie medium to coarse-grained glaciofluvial sandstones. Basinward of the sand shelf, the accretion of a volcanic island arc complex began during the Ordovician. A fluctuating transgression, accompanying a major glacial minimum, brought open-marine, graptolitic, black shales onto the sand shelf, producing an interbedded shoreface-shelf sand and black shale section during the Middle and Late Ordovician. At the Ordovician-Silurian boundary, renewed continental glaciation lowered sea level, producing a widespread unconformity. A Late Silurian major marine transgression returned black, graptolitic, highly organic shales onto the sand shelf. Devonian deltaic sands from Avalonia(.) to the north and the craton to the south closed the Paleozoic sedimentary record of northern Florida.

  13. Paleomagnetism of Late Paleozoic series in Morocco and Argentina: implications for GAD Hypothesis and Pangea reconstruction

    NASA Astrophysics Data System (ADS)

    Besse, J.; Oufi, O.; Rapalini, A.; Courtillot, V. E.

    2003-12-01

    The configuration of Pangea during the upper Paleozoic is still strongly debated: the APWP for Gondwana and Laurussia should fit in the GAD hypothesis when Pangea is reconstructed using marine data. But they appear to be significantly distinct, by as much as 15° for certain periods. Motion between the two blocks has been proposed (B Pangea of Irving) but is geologically problematic. Erroneous age assignments, magnetic overprints, insufficient demagnetization, problems with the recording of geomagnetic field in sediments (f.i. flattening) and finally non-dipole contributions have all been invoked to reconcile apparently discrepant poles. In this talk, we investigate the geometry of the geomagnetic field during the Late Carboniferous-Early Triassic period (320-240 Ma). As a starting point, we use two recent surveys in Morocco and Argentina, which provide paleomagnetic tests and good age control that were missing in most previous studies and yield respectively paleolatitude data close to the equator and mid/high latitudes. Using a compilation of poles from the GPMDB, we analyze the positions of mean poles for mid-northern and southern, and equatorial latitudes, searching for the distinctive antisymmetrical pattern expected for a dipole with an octupole contribution. We also discuss the main causes of errors, such as the occurrence of lithospheric deformation, which induces important rotations at various scales, particularly in future rift or mountain zones (Colorado, South of France, South American cordilleras, east of Australia, etc.). Even when using only sampling sites close to the Paleo-equator (which minimizes any octupolar effect), the APWP of Gondwana remains offset from that of Laurussia. The plate configuration inferred is a classical A Pangea reconstruction at about 260 Ma, but data do not rule out the possibility of a B Pangea before 270 Ma, which would account for a large number of geological constraints. In contradiction with recently proposed persistent

  14. Late Paleozoic tectonic evolution of the Central Asian Orogenic Belt: Constraints from multiple arc-basin systems in Altai-Junggar area, NW China

    NASA Astrophysics Data System (ADS)

    Li, D.

    2015-12-01

    In this study, we report results from integrated geological, geophysical and geochemical investigations on the Wulungu Depression of the Junggar Basin to understand the Late Paleozoic continental growth of the Junggar area and its amalgamation history with the Altai terrane, within the broad tectonic evolution of the Altai-Junggar area. Based on seismic and borehole data, the Wulungu Depression can be divided into two NW-trending tectonic units by southward thrust faults. The Suosuoquan Sag is composed of gray basaltic andesite, andesite, tuff, tuffaceous sandstone and tuffite, and the overlying Early Carboniferous volcano-sedimentary sequence with lava gushes and marine sediments from a proximal juvenile provenance, compared to the andesite in the Hongyan High. The SIMS Zircon U-Pb ages for andesites from Late Paleozoic strata indicate that these volcanics in Suosuoquan Sag and Hongyan High erupted at 376.3Ma and 313.4Ma, respectively. Most of the intermediate-mafic volcanic rocks exhibit calc-alkaline affinity, low initial 87Sr/86Sr and positive ɛNd(t) and ɛHf(t) values. Furthermore, these rocks have high Th/Yb and low Ce/Pb and La/Yb ratios as well as variable Ba/Th and Ba/La ratios. These features imply that the rocks were derived from partial melting of a mantle wedge metasomatized by subduction-related components in an island arc setting. The basin filling pattern and the distribution of island arc-type volcanics and their zircon Hf model ages with the eruptive time suggest that the Wulungu Depression represents an island arc-basin system with the development of a Carboniferous retro-arc basin. The gravity and magnetic anomaly data suggest that Altai-Junggar area incorporates three arc-basin belts from north to south: the Karamaili-Luliang-Darbut, Yemaquan-Wulungu, and Dulate-Fuhai-Saur. The recognition of the Wulungu arc-basin system demonstrates that the northern Junggar area is built by amalgamation of multiple Paleozoic linear arcs and accretionary

  15. Oxfordian-Kimmeridgian (Late Jurassic) reservoir sandstones in the Witch Ground Graben, U. K. North Sea

    SciTech Connect

    Harker, S.D. Ltd., Aberdeen ); Mantel, K.A. ); Morton, D.J. ); Riley, L.A. )

    1991-03-01

    Oil-bearing Late Jurassic Oxfordian-Kimmeridgian sandstones of the Sgiath and Piper formations are of major economic importance in the Witch Ground Graben. They form the reservoirs in Scott, which in 1993 will be the largest producing North Sea oil field to come on stream for more than a decade. Together with Scott, the Piper, Saltire, Tartan, Highlander, Petronella, Rob Roy, and Ivanhoe fields contained almost 2 Bbbl of recoverable reserves in these formations. The Sgiath and Piper represent two phases of Late Jurassic transgression and regression, initially represented by paralic deposited sand culminating in a wave-dominated delta sequence. The history of the Sgiath and Piper formations is reviewed and lithostratigraphic and biostratigraphic correlations presented to illustrate the distribution of the reservoir sandstones.

  16. New interpretations of Paleozoic stratigraphy and history in the northern Laramie Range and vicinity, Southeast Wyoming

    SciTech Connect

    Sando, W.J.; Sandberg, C.A.

    1987-01-01

    Biostratigraphic and lithostratigraphic studies of the Paleozoic sequence in Southeast Wyoming indicate the need for revision of the ages and nomenclature of Devonian, Mississippian, and Pennsylvanian formations. The Paleozoic sequence begins with a quartzarenite of Devonian age referred to the newly named Fremont Canyon Sandstone, which is overlain by the Englewood Formation of Late Devonian and Early Mississippian age. The Englewood is succeeded by the Madison Limestone of Early and Late Mississippian age, which is overlain disconformably by the Darwin Sandstone Member (Pennsylvanian) of the Casper and Hartville formations. This sequence represents predominantly marine deposition in near-shore environments marginal to the ancient Transcontinental Arch.

  17. Changing Low-Latitude Paleoenvironments During the Onset of the Late Paleozoic Ice Age.

    NASA Astrophysics Data System (ADS)

    Davies, S.

    2007-12-01

    The Carboniferous is one of the critical stepwise transitions in the evolution of the Earth System when rapid changes in climate and atmospheric composition (rise in oxygen/carbon dioxide) coincided with key events in biological evolution (the proliferation of land plants) and increased rates of tectonic plate reorganisation. The paleoequatorial Carboniferous sedimentary successions of Britain and Ireland were deposited in a shallow epicontinental seaway and record high magnitude and high frequency eustatic changes as ice sheets waxed and waned on Gondwana during the onset of the Late Paleozoic ice age. In the Asbian and Brigantian (ca.334-326 Ma) widespread shallow and marginal marine conditions are recorded by mixed carbonate and siliciclastic deposition and carbonate successions on platforms and shelves. In the mid-Brigantian, a marine transgression reduced deposition on the carbonate platforms and connected previously separate sub-basins in central Scotland. Data used to interpret global climate for this time slice are contradictory. A warmer global climate is suggested by the widespread extent of a Gondwanan macrofloral realm that requires frost-free conditions whereas isotope data suggest a cold Asbian followed by a warm, ice-free Brigantian. In the Pendleian to Yeadonian (ca.326-317 Ma), increasingly light oxygen isotope data indicate a return to cold conditions. Well- constrained periods of Gondwanan glacial sedimentation (e.g. in SE Australia), of 1 and 3 Myr duration, coincide with major paleoevironmental changes across Britain and Ireland, including the end of significant carbonate production and the earliest examples of large-scale river paleovalleys (with 20-80 m of erosional relief). Depositional environments (fluvial, deltaic) and basin bathymetry (distinct shelf edges) provided optimal conditions for the effects of sea-level change to be recorded in sedimentary successions of this time slice. These late Mississippian and early Pennsylvanian

  18. Left-lateral intraplate deformation along the ancestral rocky mountains: Implications for late paleozoic plate motions

    NASA Astrophysics Data System (ADS)

    Budnik, Roy T.

    1986-12-01

    North America underwent synchronous orogenic events during the late Paleozoic along its eastern margin (Alleghanian orogeny), southern margin (Ouachita orogeny), and within the southwestern part of the continent (Ancestral Rocky Mountain orogeny). All three orogenies were initiated in the late Mississippian to early Pennsylvanian, reached the greatest intensity in the middle Pennsylvanian, and ended in the early Permian. The Alleghanian and Ouachita orogenies have been related to the closing of the proto-Atlantic and the collision between North America and South America-Africa: it is here proposed that the Ancestral Rocky Mountains were produced by a collision between eastern North America and Africa. The Ancestral Rockies were formed as the result of reactivation of the Wichita megashear, a preexisting zone of weakness that extends from southern Oklahoma to eastern Utah. Previous plate tectonic models have implied that the megashear was a zone of right-lateral strike-slip faulting and north-northwest-directed compression. However, structural and stratigraphic data from Oklahoma and Texas suggest that the Wichita megashear was a major left-lateral fault zone formed under east-northeast-oriented compression. Palinspastic reconstruction of pre-mid-Devonian strata across the megashear in Texas indicates that 120 to 150 km of left slip occurred during the Desmoinesian (middle Pennsylvanian). The proposed plate tectonic model for the Ancestral Rocky Mountain orogeny includes: (1) movement of the North American plate eastward from a spreading center in the proto-Pacific; (2) closing of the proto-Atlantic Ocean; (3) collision of North America-Europe (Laurussia) and South America-Africa (Gondwana) resulting in the Hercynian, Alleghanian, and Ouachita orogenies; (4) differential movement across the Wichita megashear and formation of a left-lateral strike-slip fault zone (Ancestral Rocky Mountain orogeny) as the result of east-west compression within the North American plate

  19. The making of a sandstone colossus: Tectonically and climatically induced flushing of 'Nubian' sands in the Early Paleozoic

    NASA Astrophysics Data System (ADS)

    Luthi, Stefan M.; Hagadorn, James W.; Donselaar, Marinus E.

    2013-04-01

    Massive 'Nubian' sandstones of Cambro-Ordovician age drape most of the Arabian and northern African tectonic plates and preserve a sensitive record of how continental margins evolve under greenhouse conditions. These strata also contain important aquifers, petroleum reservoirs, and archaeological monuments such as Petra, and they were formed by a geologically sudden and long-lasting influx of >500,000 km3 of predominantly quartz sand. The cause and timing of this continent-scale sedimentation event were so far unknown. Here we constrain the depositional history of these strata and hypothesize that poleward migration of the Gondwanan supercontinent out of the horse latitudes caused a five-fold increase in sedimentation rates and buildup of one of the largest epicratonic sand wedges in earth history. Geohistorical sedimentation and subsidence modeling of these sandstones is presented, based on sedimentologic, biostratigraphic, basement paleotopographic, facies, and tectonic dip analyses of a well-preserved paleoslope-axial transect of 542-462 million-year-old strata in Jordan. This region experienced a ~25 m/Ma increase in sedimentation rate over ~30 Ma, concomitant with near-equilibrium plate subsidence response. Sedimentary rocks in the studied sequences exhibit coeval compositional variations that suggest a change in sedimentation style from immature to ultramature clastics. Our results are internally consistent with movement of a continent from an arid subtropical high toward a wet subpolar low, which would have caused widespread flushing of hypermature sands sourced from the interior of the African-Nubian Shield toward the continent margin.

  20. Geodynamics of late Paleozoic magmatism in the Tien Shan and its framework

    NASA Astrophysics Data System (ADS)

    Biske, Yu. S.; Konopelko, D. L.; Seltmann, R.

    2013-07-01

    The Devonian-Permian history of magmatic activity in the Tien Shan and its framework has been considered using new isotopic datings. It has been shown that the intensity of magmatism and composition of igneous rocks are controlled by interaction of the local thermal upper mantle state (plumes) and dynamics of the lithosphere on a broader regional scale (plate motion). The Kazakhstan paleocontinent, which partly included the present-day Tien Shan and Kyzylkum, was formed in the Late Ordovician-Early Silurian as a result of amalgamation of ancient continental masses and island arcs. In the Early Devonian, heating of the mantle resulted in the within-plate basaltic volcanism in the southern framework of the Kazakhstan paleocontinent (Turkestan paleoocean) and development of suprasubduction magmatism over an extensive area at its margin. In the Middle-Late Devonian, the margins of the Turkestan paleoocean were passive; the area of within-plate oceanic magmatism shifted eastward, and the active margin was retained at the junction with the Balkhash-Junggar paleoocean. A new period of active magmatism was induced by an overall shortening of the region under the settings of plate convergence. The process started in the Early Carboniferous at the Junggar-Balkhash margin of the Kazakhstan paleocontinent and the southern (Paleotethian) margin of the Karakum-Tajik paleocontinent. In the Late Carboniferous, magmatism developed along the northern boundary of the Turkestan paleoocean, which was closing between them. The disappearance of deepwater oceanic basins by the end of the Carboniferous was accompanied by collisional granitic magmatism, which inherited the paleolocations of subduction zones. Postcollision magmatism fell in the Early Permian with a peak at 280 Ma ago. In contrast to Late Carboniferous granitic rocks, the localization of Early Permian granitoids is more independent of collision sutures. The magmatism of this time comprises: (1) continuation of the

  1. Quantifying bioavailable iron delivery by dust during the icehouse of the late Paleozoic

    NASA Astrophysics Data System (ADS)

    Owens, J. D.; Lyons, T. W.; Soreghan, G. S.; Soreghan, M. J.; Chappaz, A.; Raiswell, R.

    2011-12-01

    The late Paleozoic glaciation (~300 million years ago) marks the last major, pre-Cenozoic icehouse climate. Delivery of reactive Fe-rich eolian particles to the nutrient-depleted open ocean potentially stimulates primary production during glacial intervals, yet the details remain unclear for recent glaciations and completely unknown for the ancient. Bioavailable Fe is a limiting nutrient in high-nitrate, low-chlorophyll portions of the open ocean. Because primary abundances of the most labile forms of Fe are not easily assessed in ancient sediments, we use highly reactive Fe (FeHR) (mostly crystalline oxides, some or most of which might have been more soluble precursors at the time of deposition) as determined by a well-calibrated sequential extraction scheme, as a rough proxy for bioavailable Fe. Here we present data from multiple Pennsylvanian-Permian loess and intercalated paleosol (ancient soil) deposits, as well as dust (glacial and nonglacial) from modern sites. We also compare ratios of total Fe (FeT) to Al to ratios of FeHR to FeT to assess whether increased Fe reactivity in dust reflects a net Fe addition or internal mineral repartitioning, and we are investigating the reactivity and valence of the reactive Fe using X-ray Absorption Fine Structure spectroscopy (XANES and EXAFS). These paired proxies may provide a unique fingerprint of source relationships. In the modern dust deposits (Chinese loess, Saharan dust from the Turks and Caicos Islands) and glacially derived Alaskan and New Zealand dusts, FeT/Al and FeHR/FeT show a positive correlation. In contrast, these ratios are antithetical in ancient loessite. Therefore, FeHR was enriched when compared to total Fe and, by inference, bioavailable despite net Fe loss reflected in sub-crustal FeT/Al ratios. Most work to date has presumed an arid soil source for the majority of bioavailable Fe. However, in light of our work and recent studies in modern glacial settings, we are exploring other possible ties to

  2. Late-Paleozoic-Mesozoic deformational and deformation related metamorphic structures of Kuznetsk-Altai region

    NASA Astrophysics Data System (ADS)

    Zinoviev, Sergei

    2014-05-01

    Kuznetsk-Altai region is a part of the Central Asian Orogenic Belt. The nature and formation mechanisms of the observed structure of Kuznetsk-Altai region are interpreted by the author as the consequence of convergence of Tuva-Mongolian and Junggar lithospheric block structures and energy of collision interaction between the blocks of crust in Late-Paleozoic-Mesozoic period. Tectonic zoning of Kuznetsk-Altai region is based on the principle of adequate description of geological medium (without methods of 'primary' state recovery). The initial indication of this convergence is the crust thickening in the zone of collision. On the surface the mechanisms of lateral compression form a regional elevation; with this elevation growth the 'mountain roots' start growing. With an approach of blocks an interblock elevation is divided into various fragments, and these fragments interact in the manner of collision. The physical expression of collision mechanisms are periodic pulses of seismic activity. The main tectonic consequence of the block convergence and collision of interblock units is formation of an ensemble of regional structures of the deformation type on the basis of previous 'pre-collision' geological substratum [Chikov et al., 2012]. This ensemble includes: 1) allochthonous and autochthonous blocks of weakly deformed substratum; 2) folded (folded-thrust) systems; 3) dynamic metamorphism zones of regional shears and main faults. Characteristic of the main structures includes: the position of sedimentary, magmatic and PT-metamorphic rocks, the degree of rock dynamometamorphism and variety rock body deformation, as well as the styles and concentrations of mechanic deformations. 1) block terranes have weakly elongated or isometric shape in plane, and they are the systems of block structures of pre-collision substratum separated by the younger zones of interblock deformations. They stand out among the main deformation systems, and the smallest are included into the

  3. Mechanisms of sandstone deposition in a late Proterozoic submarine canyon, Adelaide geosyncline, South Australia

    SciTech Connect

    von der Borch, C.C.; Grady, A.E.

    1984-06-01

    Late Proterozoic submarine canyon fills the Adelaide Supergroup (Flinders Range, South Australia) are asymmetrical in terms of their facies. Coarse breccia units, commonly associated with coarse-grained channelized turbidite sandstone units, generally occur adjacent to north walls of all the east-west-trending canyon incisions. In contrast, fine-grained sandstones and mudstones within the canyon fill are generally associated with south walls. In one canyon (Patsy-Springs canyon), an additional element of asymmetry is associated with the prevalence of northward-climbing sets of climbing ripples (southward-dipping stoss sides) within channelized turbidites, in what are interpreted to be major thalweg channels and their associated levees. Flute casts at the bases of individual turbidite sandstones invariably indicate initial turbidity current flow to the west throughout the vertical sequences of the channel fills. Parallel laminations above the flute casts in each flow pass upward into climbing ripples with south-dipping stoss sides, implying southward lateral accretion across the channel of a levee or bar as each turbidity current decelerated. The asymmetries outlined could be explained by: Coriolis force acting on the turbidity currents, or the existence on a steep slope of a meandering canyon gorge, confining a thalweg channel developed within subsequent canyon fill. In such a situation, roller-coastering turbidity currents would seek outer bends of the meandering primary gorge.

  4. Isotopic and Climate Model Constraints on Paleo-CO2 in the Late Paleozoic

    NASA Astrophysics Data System (ADS)

    Grossman, E. L.; Hyde, W. T.; Pollard, D.; Scotese, C. R.

    2003-12-01

    Atmospheric CO2 is one of the most important drivers controlling ancient climate and one of the hardest to quantify. We have combined three methods for quantifying paleoclimate, a coupled energy balance-ice sheet model (EB/ISM), an atmospheric general circulation model (AGCM), and oxygen isotope analyses of fossils, to constrain late Paleozoic pCO2 levels. Our estimated pCO2 is that which yields the same ice volume determined using two independent approaches, a δ 18O-AGCM method and an EB/ISM. We calculate ice volume from the δ 18O of brachiopod shells and AGCM temperatures (δ 18O-AGCM method). Brachiopod shell δ 18O values depend on two variables, ambient temperature and seawater δ 18O. Using the oxygen isotope paleotemperature equation and ambient temperatures derived from AGCM results, we calculate seawater δ 18O. From this seawater δ 18O we use 18O mass balance to calculate ice volume. We run the AGCM with various values of pCO2, which produce different temperatures and different δ 18O-derived ice volumes. Ice volumes deduced from brachiopod δ 18O increase with pCO2. Ice volumes as a function of pCO2 are also determined from the ice sheet model in the EB/ISM, and those ice volumes decrease with increasing pCO2. Our estimated pCO2 is the intersection of the two ice volume-pCO2 curves. Three different time slices and paleogeographies have been investigated in detail: 360, 320, and 280 Ma. GENESIS 2 AGCM simulations were performed at 1x and 4x modern preindustrial levels (280 ppm) for all time slices, and at 8x pCO2 for 360 Ma. EB/ISM simulations were run with and without topography, with lapse rates of 5 and 7 ° C/km, and with outgoing infrared radiation (OIR) ranging from 187.3 to 205.3 W/m2, equivalent to pCO2 levels of 1x to 16x. EB/ISM simulations yielded ice volumes ranging from 0 to greater than 129 x 106 km3, depending on lapse rate, topography, and outgoing IR radiation. The highest ice volumes were obtained with topography, 7 ° C/km lapse rate

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

    SciTech Connect

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

    1983-09-01

    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 quartz 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.

  6. Late Paleozoic tectonic evolution and concentrated mineralization in Balkhash and West Junggar, western part of the Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Dong, Shuwen; Chen, Xuanhua; Chen, Zhengle

    2016-04-01

    The Central Asia Orogenic Belt (CAOB) is an important area with significant growth of the crust and metallogeny in the Late Paleozoic. The Balkhash-Junggar tectono-metallogenic belt consists of the Balkhash, the West Junggar, and the East Junggar tectono-metallogenic belts in western part of the Central Asian Orogenic Belt (CAOB). According to the structural geological relationship, the East Junggar, the West Junggar, and the Balkhash belts are considered to be once a continuous E-W-trending tectono-metallogenic belt in Late Carboniferous. The West Junggar belt is featured with NE-trending left-lateral strike-slip faulting tectonic system (WJTS), while the left-lateral strike-slip faults are E-W-trending in the Balkhash belt. The WJTS consists of the Darabut, the Mayile, and the Baerluke faults, and the blocks among them. All these left-lateral strike-slip faults are forming due to the transition of tectonic settings from syn-collisional orogeny to post-collisional extension during the closure of the ocean (the Junggar Sea) in Late Carboniferous, with significant intrusion of batholiths and crust growth occurred in this period. These faults are truncated by the right-lateral strike-slip faults, such as the Chingiz-Junggar fault, and the Central Balkhash fault in Mesozoic. The Balkhash-Junggar tectono-metallogenic belt is important for the occurrence of many well-known super-large and large porphyry Cu-Mo deposits (such as the Kounrad, the Aktogai, the Borly, and the Baogutu deposits), large skarn Cu deposits (in the Sayak ore-filed), large rare metal deposits (such as the East Kounrad, the Zhanet, and the Akshatau deposits), and large gold deposits (such as the Hatu deposit). Zircon U-Pb ages, Re-Os isotopic dating of molybdenites, 40Ar/39Ar thermochronology of hornblendes, muscovites, biotites, and K-feldspars, and zircon and apatite fission track (FT) and (U-Th)/He dating and thermal history modeling, provide a multidisciplinary approach to constrain the whole

  7. Groundwater flow, late cementation, and petroleum accumulation the Permian Lyons Sandstone, Denver basin

    SciTech Connect

    Lee, M.K.; Bethke, C.M. )

    1994-02-01

    The gray diagenetic facies of the Permian Lyons Sandstone, associated with all known petroleum accumulations in the formation, formed late in the history of the Denver basin as an alteration product of the formation's red facies. The red facies that makes up most of the sandstone contains iron oxide coating, quartz overgrowths and calcite cements. The gray facies, which occurs locally in the deep basin, is distinguished by pore-filling dolomite and anhydrite cements and by a lack of iron oxide and calcite. The dolomite and anhydrite cements overlie bitumen that was deposited by migrating oil, and hence formed after oil was first generated in the basin, late in the Cretaceous or early in the Tertiary. The isotopic composition of oxygen in the dolomite ranges to such light values that the cement must have formed deep in the basin in the presence of meteoric water. The gray facies likely formed in a regime of groundwater flow resulting from Laramide uplift of the Front Range during the Tertiary. In our model, saline groundwater flowed eastward through the Pennsylvanian Fountain Formation and then upwelled along the basin axis, where is discharged into the Lyons Sandstone. The saline water mixed with more dilute groundwater in the Lyons, driving a reaction that dissolved calcite and, by a common-ion effect, precipitated dolomite and anhydrite. The facies' gray color resulted from reduction of ferric oxide in the presence of migrating oil or the Fountain brine. Underlying source beds by this time had begun to generate petroleum, which migrated by buoyancy into the Lyons. The association of the gray facies with petroleum accumulations can be explained if the Fountain brines discharged across aquitards along the same fractures that transmitted oil. As petroleum accumulated in the Lyons, the newly formed cements prevented continued migration, as is observed in shallower strata, by sealing oil into the reservoirs from which it is produced today. 77 refs., 16 figs., 5 tabs.

  8. Some in situ fossil plants in Late Paleozoic rocks, eastern U. S. A

    SciTech Connect

    Cross, A.T. )

    1991-01-01

    Plants entombed in growth position are generally represented by standing stumps. Rarely, leaves or fronds may also represent plants buried in place. Stemps are most often seen in surface coal mine highwalls and highway cuts. Occasionally they are also found in association with sandstone cliffs. When present in coal-bearing sequences they are most often rooted in the top of the coal and may extend upward through several successive increments of sediments representing point-bar or overbank deposits in deltaic or fluvial depositional environments. Some standing logs in sandstones represent burial by washover fans or transgressive bars. Interpretation of the life environment of the plants and the successive environments in which the sediments that engulfed the plants were deposited demonstrated their paleoenvironment.

  9. Did Patagonia collide against Gondwana in the Late Paleozoic? Some Insights From Magnetic Fabrics of Granitoids in the North Patagonian Massif.

    NASA Astrophysics Data System (ADS)

    Rapalini, A. E.; Lopez de Luchi, M. G.; Tomezzoli, R. N.

    2008-05-01

    The Paleozoic tectonic evolution of Patagonia has been a matter of much debate in the last two decades. There is no consensus on whether the North Patagonian Massif (NPM) was accreted by a frontal collision to Gondwana in the Late Paleozoic or if it shared a similar paleotectonic evolution with other Gondwana blocks during the Paleozoic. Different geologic, geochronologic, geophysical and structural data have been interpreted either as supporting or refuting the collisional model. Paleomagnetic data obtained so far is consistent with an authochtonous evolution since the Devonian, but it does not rule out relative displacements of up to 1500 km between Patagonia and Gondwana.Therefore, a Late Paleozoic frontal collision cannot be definitely ruled out on the basis of paleomagnetic data alone. As part of a muldisciplinary research project a magnetic fabric study, by means of the anisotropy of magnetic susceptibility (AMS), was carried out on Late Paleozoic granitoids exposed in northeastern NPM. Two main composite units were studied, the highly to variably foliated Yaminue Complex, poorly dated as Late Carboniferous and ranging in composition from tonalite to leuco-granite, and the much less deformed granodiorites to monzoganites of the Early Permian (283 Ma) Navarrete complex. While the former is composed of both ferro and paramagnetic units, with a dominance of the latter; the Navarrete plutons are basically ferromagnetic. Directional and scalar AMS results joined with meso and microstructural studies permitted the characterization of the deformational and magmatic fabric of the different units. An evolutionary picture of the succesive intrusive events in NPM emerged which confirms an important NNE-SSW contractional event associated with intrusion of the different units that compose the Yaminue Complex. This event ended before the intrusion of the Navarrete Complex, which is governed by a different stress regime. Our results fit the hypothesis of a collisional event

  10. Controls on deposition of the St. Peter Sandstone (Middle-Late Ordovician), Michigan basin

    SciTech Connect

    Nadon, G.C.; Simo, A.; Byers, C.W.; Dott, R.H, Jr. )

    1991-08-01

    The St. Peter Sandstone (Middle-late Ordovician) of the Michigan basin represents an approximately 10-m.y. interval of clastic deposition in an otherwise carbonate-dominated Ordovician succession. This interval, up to 320 m thick, also coincides with a change in basin configuration from the nearly circular depocenter of the underlying Shakopee Formation to an east-west elongate trough situated west to Saginaw Bay. Interpretation of well logs and core from throughout the basin indicates that the clastics are composed of 20-25 sequences upper shoreface to tidal-flat environments. The sequences are interbedded with heavily bioturbated, shaly, lower shoreface sandstones (1-14 m thick) and, in the central and southeastern parts of the basin, with carbonate shales, stromatolites, and oolitic grain-stones (2-39 m thick). The eastern and southeastern margins of the basin contain the thickest carbonate accumulations. Hydrocarbons fields are located over structural highs formed by reactivation of basement structures. Detailed comparison of well logs within field shows that sedimentary cycles thin over the structures as a result of the local reduction in the formation of accommodation space by syndepositional movements on the faults. The presence of thick carbonates along the southeastern margin of the basin is a result of the combination of distance form the clastic source and the episodic formation of accommodation space by syndepositional normal faulting along the basin margin.

  11. Mineralogy and diagenesis of low-permeability sandstones of Late Cretaceous age, Piceance Creek Basin, northwestern Colorado

    USGS Publications Warehouse

    Hansley, Paula L.; Johnson, Ronald C.

    1980-01-01

    This report presents preliminary results of a mineralogic and diagenetic study of some low-permeability sandstones from measured surface sections and cores obtained from drill holes in the Piceance Creek Basin of northwestern Colorado. A documentation of the mineralogy and diagenetic history will aid in the exploration for natural gas and in the development of recovery technology in these low-permability sandstones. These sandstones are in the nonmarine upper part of the Mesaverde Formation (or Group) of Late Cretaceous age and are separated from overlying lower Tertiary rocks by a major regional unconformity. Attention is focused on the sandstone units of the Ohio Creek Member, which directly underlies the unconformity; however, comparisons between the mineralogy of the Ohio Creek strata and that of the underlying sandstone units are made whenever possible. The Ohio Creek is a member of the Hunter Canyon Formation (Mesaverde Group) in the southwestern part of the basin, and the Mesaverde Formation in the southern and central parts of the basin. The detrital mineralogy is fairly constant throughout all of these nonrnarine Cretaceous sandstone units; however, in the southeastern part of the basin, there is an increase in percentage of feldspar, quartzite, and igneous rock fragments in sandstones of the Ohio Creek Member directly underlying the unconformity. In the southwestern part of the basin, sandstones of the Ohio Creek Member are very weathered and are almost-entirely comprised of quartz, chert, and kaolinite. A complex diagenetic history, partly related to the overlying unconformity, appears to be responsible for transforming these sandstones into potential gas reservoirs. The general diagenetic sequence for the entire Upper Cretaceous interval studied is interpreted to be (early to late): early(?) calcite cement, chlorite, quartz overgrowths, calcite cement, secondary porosity, analcime (surface only), kaolinite and illite, and late carbonate cements

  12. Late Paleozoic to Jurassic chronostratigraphy of coastal southern Peru: Temporal evolution of sedimentation along an active margin

    NASA Astrophysics Data System (ADS)

    Boekhout, F.; Sempere, T.; Spikings, R.; Schaltegger, U.

    2013-11-01

    We present an integrated geochronological and sedimentological study that significantly revises the basin and magmatic history associated with lithospheric thinning in southern coastal Peru (15-18°S) since the onset of subduction at ˜530 Ma. Until now, estimating the age of the sedimentary and volcanic rocks has heavily relied on paleontologic determinations. Our new geochronological data, combined with numerous field observations, provide the first robust constraints on their chronostratigraphy, which is discussed in the light of biostratigraphical attributions. A detailed review of the existing local units simplifies the current stratigraphic nomenclature and clarifies its absolute chronology using zircon U-Pb ages. We observe that the Late Paleozoic to Jurassic stratigraphy of coastal southern Peru consists of two first-order units, namely (1) the Yamayo Group, a sedimentary succession of variable (0-2 km) thickness, with apparently no nearby volcanic lateral equivalent, and (2) the overlying Yura Group, consisting of a lower, 1-6 km-thick volcanic and volcaniclastic unit, the Chocolate Formation, and an upper, 1-2 km-thick sedimentary succession that are in markedly diachronous contact across the coeval arc and back-arc. We date the local base of the Chocolate Formation, and thus of the Yura Group, to 216 Ma, and show that the underlying Yamayo Group spans a >110 Myr-long time interval, from at least the Late Visean to the Late Triassic, and is apparently devoid of significant internal discontinuities. The age of the top of the Chocolate Formation, i.e. of the volcanic arc pile, varies from ˜194 Ma to less than ˜135 Ma across the study area. We suggest that this simplified and updated stratigraphic framework can be reliably used as a reference for future studies.

  13. Provenance study from petrography of the late Permian - Early Triassic sandstones of the Balfour Formation Karoo Supergroup, South Africa

    NASA Astrophysics Data System (ADS)

    Oghenekome, M. E.; Chatterjee, T. K.; Hammond, N. Q.; van Bever Donker, J. M.

    2016-02-01

    Non marine clastic sediments from the Late Permian - Early Triassic Balfour Formation of the Karoo Supergroup were studied to infer the composition, provenance and influence of weathering conditions. Petrographic studies based on quantitative analysis of the detrital minerals reveal that these sediments (mainly sandstones) are mostly composed of quartz, feldspar and sedimentary and metamorphic rock fragments. There is no significant petrographic variation across the sandstone succession of the study. The sandstones are dominantly feldspathic litharenite and ultralithofeldspathic in composition indicating a metamorphic source area. Modal analysis data plot in the dissected and transitional arc block provenance fields of QmFLt (quartz-feldspar-lithic fragments) diagram suggesting an active margin and magmatic arc signature preserving a recycled provenance.

  14. Late Paleozoic fusulinids from Sonora, Mexcio: importance for interpretation of depositional settings, biogeography, and paleotectonics

    USGS Publications Warehouse

    Stevens, Calvin H.; Poole, Forrest G.; Amaya-Martínez, Ricardo

    2014-01-01

    Three sets of fusulinid faunas in Sonora, Mexico, discussed herein, record different depositional and paleotectonic settings along the southwestern margin of Laurentia (North America) during Pennsylvanian and Permian time. The settings include: offshelf continental rise and ocean basin (Rancho Nuevo Formation in the Sonora allochthon), shallow continental shelf (La Cueva Limestone), and foredeep basin on the continental shelf (Mina México Formation). Our data represent 41 fusulinid collections from 23 localities with each locality providing one to eight collections. Reworked fusulinids in the Middle and Upper Pennsylvanian part of the Rancho Nuevo Formation range in age from Desmoinesian into Virgilian (Moscovian-Gzhelian). Indigenous Permian fusulinids in the La Cueva Limestone range in age from middle or late Wolfcampian to middle Leonardian (late Sakmarian-late Artinskian), and reworked Permian fusulinids in the Mina México Formation range in age from early to middle Leonardian (middle-late Artinskian). Conodonts of Guadalupian age occur in some turbidites in the Mina México Formation, indicating the youngest foredeep deposit is at least Middle Permian in age. Our fusulinid collections indicate a hiatus of at least 10 m.y. between the youngest Pennsylvanian (Virgilian) rocks in the Sonora allochthon and the oldest Permian (middle Wolfcampian) rocks in the region. Most fusulinid faunas in Sonora show affinities to those of West Texas, New Mexico, and Arizona; however, some genera and species are similar to those in southeastern California. As most species are similar to those east of the southwest-trending Transcontinental arch in New Mexico and Arizona, this arch may have formed a barrier preventing large-scale migration and mixing of faunas between the southern shelf of Laurentia in northwestern Mexico and the western shelf in the southwestern United States. The Sonora allochthon, consisting of pre-Permian (Lower Ordovician to Upper Pennsylvanian) deep

  15. Detrital Record of the Middle to Late Paleozoic Transition from Subduction to Collision in the Northern Andes: Implications in the Paleogeographic Reconstructions of Pangea

    NASA Astrophysics Data System (ADS)

    Valencia, V.; Cardona, A.

    2014-12-01

    Discriminating between these type of orogens and understanding the transition between subduction and collision in the Northern Andes remains elusive and controversial due to the apparent yuxtaposition of Central and South American terranes within Pangea reconstruction. New U-Pb detrital zircon geochronology from Late Paleozoic sedimentary and meta-sedimentary rocks from the Eastern Cordillera of the Colombian Andes (Santander and Flortesta Massif) were obtained and used to discriminate changes in the relative intensity of magmatic activity and refine the timing of sedimentary accumulation and metamorphism and their relation with tectonic models. The U-Pb LA-ICP-MS results suggest that Early Devonian magmatism is significantly more limited than the former Ordovician to Silurian record and that sedimentation and metamorphism in the Eastern Cordillera of the Colombian Andes is of Late Paleozoic age. We related the major changes in the magmatic input to the Late Paleozoic sedimentary basin as a tracer of the major changes in convergence between Laurentia and Gondwana, that formed an extremely oblique convergent margin between the Devonian and the Carboniferous until the Late Carboniferous metamorphism that end with Pangea agglutination.

  16. The late Paleozoic palynological diversity in southernmost Paraná (Uruguay), Claromecó and Paganzo basins (Argentina), Western Gondwana

    NASA Astrophysics Data System (ADS)

    Beri, Ángeles; Gutiérrez, Pedro R.; Balarino, M. Lucía

    2015-12-01

    This study explores the changes in palynoflora diversity of the late Paleozoic in boreholes DI.NA.MI.GE. 254 (26 samples) and DI.NA.MI.GE. 221 (14 samples) of the Paraná Basin in Uruguay and in 18 surface samples of the La Deheza Formation (Paganzo Basin) and 10 samples of borehole UTAL.CMM1.La Estrella.x-1 (Claromecó Basin) in Argentina. Possible relationships among biostratigraphic zones, diversity levels, facies and climatic evolution patterns in Western Gondwana are studied. Diversity curves of boreholes 221 and 254 and the La Deheza Formation outcrop exhibit similar diversity evolution patterns, i.e., an increase in lower strata diversity and a decrease in upper strata diversity. The disappearance events are determined to be more prominent in biozones of the Cisuralian to the Guadalupian age and less prominent in biozones of the early Cisuralian age. The number of genera raises from the glaciomarine facies, through the deltaic and the marine facies, up to the shallow marine or lagoon facies, in which the disappearance rates become more prominent. . The diversity of the lower part of the La Estrella borehole is lesser than that of the other sequences These diversity, disappearance and appearance behaviors may reflect post-glacial climatic amelioration patterns and the beginning of an arid phase.

  17. Global deglaciation and the re-appearance of microbial matground-dominated ecosystems in the late Paleozoic of Gondwana.

    PubMed

    Buatois, L A; Netto, R G; Gabriela Mángano, M; Carmona, N B

    2013-07-01

    The extensive matgrounds in Carboniferous-Permian open-marine deposits of western Argentina constitute an anachronistic facies, because with the onset of penetrative bioturbation during the early Paleozoic microbial mats essentially disappeared from these settings. Abundant microbially induced sedimentary structures in the Argentinean deposits are coincident with the disappearance of trace and body fossils in the succession and with a landward facies shift indicative of transgressive conditions. Deposits of the Late Carboniferous-Early Permian glacial event are well developed in adjacent basins in eastern Argentina, Brazil, South Africa and Antarctica, but do not occur in the western Andean basins of Argentina. However, the deglaciation phase is indirectly recorded in the studied region by a rapid rise in sea level referred to as the Stephanian-Asselian transgression. We suggest that an unusual release of meltwater during the final deglaciation episode of the Gondwana Ice Age may have dramatically freshened peri-Gondwanan seas, impacting negatively on coastal and shallow-marine benthic faunas. Suppression of bioturbation was therefore conducive to a brief re-appearance of matground-dominated ecosystems, reminiscent of those in the precambrian. Bioturbation is essential for ecosystem performance and plays a major role in ocean and sediment geochemistry. Accordingly, the decimation of the mixed layer during deglaciation in the Gondwana basins may have altered ecosystem functioning and geochemical cycling. PMID:23621394

  18. The stratigraphy of Oxfordian-Kimmeridgian (Late Jurassic) reservoir sandstones in the Witch Ground Graben, United Kingdom North Sea

    SciTech Connect

    Harker, S.D. ); Mantel, K.A. ); Morton, D.J. ); Riley, L.A. )

    1993-10-01

    Oil-bearing Upper Jurassic Oxfordian-Kimmeridgian sandstones of the Sgiath and Piper formations are of major economic importance in the Witch Ground Gaben, United Kingdom North Sea. They form the reservoirs in 14 fields that originally contained 2 billion bbl of oil reserves, including Scott Field, which in 1993 will be the largest producing United Kingdom North Sea oil field to come on stream in more than a decade. The Sgiath and Piper formations represent Late Jurassic transgressive and regressive phases that began with paralic deposition and culminated in a wave-dominated delta system. These phases preceded the major grabel rifting episode (late Kimmeridgian to early Ryazanian) and deposition of the Kimmeridge Clay Formation, the principal source rock of the Witch Ground Graben oil fields. A threefold subdivision of the middle to upper Oxfordian Sgiath Formation is formally proposed, with Scott field well 15/21a-15 as the designated reference well. The basal Skene Member consists of thinly interbedded paralic carbonaceous shales, coals, and sandstones. This is overlain by transgressive marine shales of the Saltire Member. The upper-most Oxfordian Scott Member consists of shallow marine sandstones that prograded to the southwest. The contact of the Sgiath and Piper formations is a basinwide transgressive marine shale (I shale), which can act as an effective barrier to fluid communication between the Sgiath and Piper reservoir sandstones.

  19. Setting and occurrence of Late Paleozoic radiolarians in the Sylvester allochthon, part of a proto-Pacific ocean floor terrane in the Canadian Cordillera

    USGS Publications Warehouse

    Harms, T.A.; Murchey, B.L.

    1992-01-01

    Late Paleozoic radiolarians have been used to establish th allochthon of the Slide Mountain terrane in British Columbia, and have thereby greatly clarified the geology and tectonic history of the terrane. As the Sylvester radiolarian fauna is limited, age assignments were based on a few distinctive and diagnostic robust forms. Radiolarians occur in cherts from a wide variety of different oceanic sequences that are structurally juxtaposed within the Sylvester allochthon. Like others in a suite of correlative terranes that lie along the length of the Cordillera, the Sylvester allochthon and the radiolarian bearing cherts in it derive from the telescoping together of slices from what was, in the late Paleozoic, a large area of the proto-Pacific ocean. ?? 1992.

  20. Late proterozoic and paleozoic tides, retreat of the moon, and rotation of the earth

    USGS Publications Warehouse

    Sonett, C.P.; Kvale, E.P.; Zakharian, A.; Chan, M.A.; Demko, T.M.

    1996-01-01

    The tidal rhythmites in the Proterozoic Big Cottonwood Formation (Utah, United States), the Neoproterozoic Elatina Formation of the Flinders Range (southern Australia), and the Lower Pennsylvanian Pottsville Formation (Alabama, United States) and Mansfield Formation (Indiana, United States) indicate that the rate of retreat of the lunar orbit is d??/dt k2 sin(2??) (where ?? is the Earth-moon radius vector, k2 is the tidal Love number, and ?? is the tidal lag angle) and that this rate has been approximately constant since the late Precambrian. When the contribution to tidal friction from the sun is taken into account, these data imply that the length of the terrestrial day 900 million years ago was -18 hours.

  1. Late Paleozoic granitoid magmatism in Chukotka and its relation to Ellesmerian orogeny in Arctic Alaska and Canada

    NASA Astrophysics Data System (ADS)

    Luchitskaya, Marina; Sokolov, Sergey; Kotov, Alexander; Katkov, Sergey; Sal'nikova, Elena; Yakovleva, Sonya

    2013-04-01

    Chukotka fold area (Mesozoides) was formed as a result of collision between Chukotka - Arctic Alaska microplate and active margin of Siberian continent [1]. At present the majority of researches distinguish at least three stages of granitoid magmatism of Chukotka Mesozoides: 147-139, 127-100 and 82.4-78.8 Ma [2]. Granites of first two stages intrude metamorphic basement and Paleozoic-Mesozoic fold structures. Formation of Early Cretaceous granitoids are often considered in relation to granite-metamorphic core complexes evolution [3-5]. Intrusion of the third stage granitoid intrusions corresponds to Okhotsk-Chukotka volcanic belt activity. At the same time in several publications there is information of existence of more ancient Paleozoic granitoids. For orthogneisses of East Chukotka there are age estimations 380-320 Ma (U-Pb SHRIMP, [6]). V.V.Akinin [7] showed that protoliths of Velinkenay and Kuekvun plutons have Late Devonian (380-360 Ma) age. Granites of Kibera Peninsula were dated as 439±32 Ma [Rb-Sr method, 8]. Besides basal conglomerates of Carboniferous deposits contain granite pebbles. At the same time on the existing geological maps granites are indicated as Early Cretaceous ones [9]. Thus there are contradictions on the age estimations and scales of Paleozoic and Mesozoic granitoid magmatism manifestation within Chukotka Mesozoides. As a result of this interregional correlations, first of all correlation of Caledonian and Ellesmerian orogenies events in Arctic region, are complicated. So we carried out U-Pb geochronological studies of some reference granitoid plutons of Central Chukotka, located in the cores of antiform structures, composed of Paleozoic deposits, namely granodiorites of Kibera and quartz syenites of Kuekvyun plutons (Kuul and Kuekvyun rises respectively). Granitoids of Kibera pluton (coastal clippings of Kibera Peninsula, coast of East-Siberian Sea) intrude terrigenous Devonian deposits with carbonate units which are overlain with

  2. Origin and development of plains-type folds in the mid-continent (United States) during the late Paleozoic

    USGS Publications Warehouse

    Merriam, D.F.

    2005-01-01

    Plains-type folds are local, subtle anticlines formed in the thin sedimentary package overlying a shallow, crystalline basement on the craton. They are small in areal extent (usually less than 1-3 km 2 [0.4-1.2 mi2]), and their amplitude increases with depth (usually tens of meters), which is mainly the result of differential compaction of sediments (usually clastic units) over tilted, rigid, basement fault blocks. The development of these structural features by continuous but intermittent movement of the basement fault blocks in the late Paleozoic in the United States mid-continent is substantiated by a record of stratigraphic and sedimentological evidence. The recurrent structural movement, which reflects adjustment to external stresses, is expressed by the change in thickness of stratigraphic units over the crest of the fold compared to the flanks. By plotting the change in thickness for different stratigraphic units of anticlines on different fault blocks, it is possible to determine the timing of movement of the blocks that reflect structural adjustment. These readjustments are confirmed by sedimentological evidence, such as convolute, soft-sediment deformation features and small intraformational faults. The stratigraphic interval change in thickness for numerous structures in the Cherokee, Forest City, and Salina basins and on the Nemaha anticline of the mid-continent United States was determined and compared for location and timing of the adjustments. Most of the adjustment occurred during and after time of deposition of the Permian-Pennsylvanian clastic units, which, in turn, reflect tectonic disturbance in adjacent areas, and the largest amount of movement on the plains-type structures occurred on those nearest and semiparallel to major positive features, such as the Nemaha anticline. Depending on the time of origin and development of plains-type folds, they may control the entrapment and occurrence of oil and gas. Copyright ??2005. The American

  3. Magnetic fabric and microstructures of Late Paleozoic granitoids from the North Patagonian Massif: Evidence of a collision between Patagonia and Gondwana?

    NASA Astrophysics Data System (ADS)

    López de Luchi, Mónica G.; Rapalini, Augusto E.; Tomezzoli, Renata N.

    2010-10-01

    Widespread Late Paleozoic magmatism in northern Patagonia is a target to test hypotheses on the long standing question over the origin of Patagonia. In recent years, a dispute over whether it is an accreted crustal block that collided with Gondwana in Paleozoic times or an autochthonous part of South America has taken place. As part of a multidisciplinary study, an integrated microstructural and magnetic fabric study was carried out on the Late Carboniferous Yaminué Complex and the Early Permian Navarrete Plutonic Complex, both exposed in the northeastern corner of the North Patagonian Massif (40.5°S, 67.0°W). Other investigated units are the Late Carboniferous Tardugno Granodiorite, the newly defined Cabeza de Vaca Granite and the Late Permian San Martin pluton. Over 300 oriented cores from 60 sites were collected for anisotropy of magnetic susceptibility (AMS) measurements. A systematic analysis of around 100 petrographic thin sections was performed to characterize the microstructures of the different magmatic units. Microstructures in the Yaminué Complex are indicative of a transition from magmatic to solid-state deformation. Microstructures of the orthogneiss of tonalitic composition suggest an early stage in the emplacement history of this complex. The Cabeza de Vaca Granite, intrusive in Yaminué Complex, is the most evolved unit and records less intense high-temperature solid-state deformation which suggests that the stress field that controlled the emplacement of the Yaminué Complex outlasted it. According to petrologic and structural considerations, the Navarrete Plutonic Complex has been subdivided into three facies, i.e. Robaina, Guanacos and Aranda, respectively. Microstructures of the Navarrete Plutonic Complex are mostly magmatic to submagmatic, versus the solid-state fabric that characterizes the Robaina facies at the contact with the Yaminué Complex. Combined analyses of AMS and microstructural data lead us to suggest that the Yaminué Complex

  4. Petrology and tectonic significance of gabbros, tonalites, shoshonites, and anorthosites in a late Paleozoic arc-root complex in the Wrangellia Terrane, southern Alaska

    SciTech Connect

    Beard, J.S. ); Barker, F. )

    1989-11-01

    Plutonic rocks intrusive into the late Paleozoic Tetelna Formation of southern Alaska are the underpinnings of the late Paleozoic Skolai arc of the Wrangellia Terrane. There are four groups of intrusive rocks within the Skolai arc: (1) Gabbro-diorite plutons that contain gabbroic to anorthositic cumulates along with a differentiated series of gabbros and diorites of basaltic to andesitic composition; (2) Silicic intrusions including tonalite, granodiorite, and granite; (3) Monzonitic to syenitic plutonic rocks of the Ahtell complex and related dikes and sills; (4) Fault-bounded bytownite anorthosite of uncertain age and association. These anorthosites may be related to post-Skolai, Nikolai Greenstone magmatism. The silicic rocks yield discordant U-Pb zircon ages of 290-320 Ma (early to late Pennsylvanian). The monzonitic rocks of the Ahtell complex have shoshonitic chemistry. Similar shoshonitic rocks are widespread in both the Wrangellia terrane and the neighboring Alexander terrane and intrude the contact between the two. In modern oceanic arcs, shoshonitic rocks are typically associated with tectonic instability occurring during the initial stages of subduction or just prior to or during termination or flip of an established subduction zone. The nature of any tectonic instability which may have led to the cessation of subduction in the Skolai arc is unclear. Possibilities include collision of the arc with a ridge, an oceanic plateau, another arc, or a continental fragment. One possibility is that the shoshonitic magmatism marks the late Paleozoic amalgamation of Wrangellia and the Alexander terrane. The scarcity of arc rocks predating the shoshonites in the Alexander terrane supports this possibility, but structural corroboration is lacking.

  5. New gas discoveries in the Ordovician sandstones, Risha area; northeast Jordan

    SciTech Connect

    Sabbah, A.A.; Ramini, H.M.

    1996-12-31

    Over thirty wells for exploration and production purposes were drilled in the Risha Area, northeast Jordan by the Natural Resources Authority since 1986. Commercial gas was discovered in the sandstones of Dubeidib Formation (Late Ordovician age). These sandstones are believed to have been deposited in the form of marine sand bars trending NNE-SSW. During the Early Paleozoic time, Jordan has undergone periods of epirogenic movements ending in Late Ordovician. Two major lineament trends are dominant, one oriented northwest-southeast and the other ENE-WSW. A third trend oriented north-south to NNW-SSE also appears but more discontinuous. Four source rock horizons were developed within the Early Paleozoic times. Oil generation of Lower Paleozoic source horizons took place in the Late Paleozoic. The upper Mudawwara hot shales of Silurian age is believed to have generated liquid hydrocarbons in the Late Cretaceous times, in a second phase of hydrocarbon generation. Dry gas was originated through organic maturation of the Lower Paleozoic source horizons. The Risha Gas Field is producing 30 MMcfgd since it was first discovered in 1987.

  6. New gas discoveries in the Ordovician sandstones, Risha area; northeast Jordan

    SciTech Connect

    Sabbah, A.A.; Ramini, H.M. )

    1996-01-01

    Over thirty wells for exploration and production purposes were drilled in the Risha Area, northeast Jordan by the Natural Resources Authority since 1986. Commercial gas was discovered in the sandstones of Dubeidib Formation (Late Ordovician age). These sandstones are believed to have been deposited in the form of marine sand bars trending NNE-SSW. During the Early Paleozoic time, Jordan has undergone periods of epirogenic movements ending in Late Ordovician. Two major lineament trends are dominant, one oriented northwest-southeast and the other ENE-WSW. A third trend oriented north-south to NNW-SSE also appears but more discontinuous. Four source rock horizons were developed within the Early Paleozoic times. Oil generation of Lower Paleozoic source horizons took place in the Late Paleozoic. The upper Mudawwara hot shales of Silurian age is believed to have generated liquid hydrocarbons in the Late Cretaceous times, in a second phase of hydrocarbon generation. Dry gas was originated through organic maturation of the Lower Paleozoic source horizons. The Risha Gas Field is producing 30 MMcfgd since it was first discovered in 1987.

  7. Late-Proterozoic to Paleozoic history of the peri-Gondwana Calabria-Peloritani Terrane inferred from a review of zircon chronology.

    PubMed

    Fornelli, Annamaria; Micheletti, Francesca; Piccarreta, Giuseppe

    2016-01-01

    U-Pb analyses of zircon from ten samples of augen gneisses, eight mafic and intermediate metaigneous rocks and six metasediments from some tectonic domains along the Calabria-Peloritani Terrane (Southern Italy) contribute to knowledge of peri-Gondwanan evolution from Late-Proterozoic to Paleozoic times. All samples were equilibrated under amphibolite to granulite facies metamorphism during the Variscan orogeny. The zircon grains of all considered samples preserve a Proterozoic memory suggestive of detrital, metamorphic and igneous origin. The available data fit a frame involving: (1) Neoproterozoic detrital input from cratonic areas of Gondwana; (2) Pan-African/Cadomian assemblage of blocks derived from East and West African Craton; (3) metamorphism and bimodal magmatism between 535 and 579 Ma, within an active margin setting; (4) rifting and opening of Ordovician basins fed by detrital input from the assembled Cadomian blocks. The Paleozoic basins evolved through sedimentation, metamorphism and magmatism during the Variscan orogeny involving Palaeozoic and pre-Paleozoic blocks. The Proterozoic zircon records decidedly decrease in the high grade metamorphic rocks affected by Variscan pervasive partial melting. PMID:27026906

  8. Late-Proterozoic to Paleozoic history of the peri-Gondwana Calabria-Peloritani Terrane inferred from a review of zircon chronology.

    PubMed

    Fornelli, Annamaria; Micheletti, Francesca; Piccarreta, Giuseppe

    2016-01-01

    U-Pb analyses of zircon from ten samples of augen gneisses, eight mafic and intermediate metaigneous rocks and six metasediments from some tectonic domains along the Calabria-Peloritani Terrane (Southern Italy) contribute to knowledge of peri-Gondwanan evolution from Late-Proterozoic to Paleozoic times. All samples were equilibrated under amphibolite to granulite facies metamorphism during the Variscan orogeny. The zircon grains of all considered samples preserve a Proterozoic memory suggestive of detrital, metamorphic and igneous origin. The available data fit a frame involving: (1) Neoproterozoic detrital input from cratonic areas of Gondwana; (2) Pan-African/Cadomian assemblage of blocks derived from East and West African Craton; (3) metamorphism and bimodal magmatism between 535 and 579 Ma, within an active margin setting; (4) rifting and opening of Ordovician basins fed by detrital input from the assembled Cadomian blocks. The Paleozoic basins evolved through sedimentation, metamorphism and magmatism during the Variscan orogeny involving Palaeozoic and pre-Paleozoic blocks. The Proterozoic zircon records decidedly decrease in the high grade metamorphic rocks affected by Variscan pervasive partial melting.

  9. Facies and depositional architecture according to a jet efflux model of a late Paleozoic tidewater grounding-line system from the Itararé Group (Paraná Basin), southern Brazil

    NASA Astrophysics Data System (ADS)

    Aquino, Carolina Danielski; Buso, Victoria Valdez; Faccini, Ubiratan Ferrucio; Milana, Juan Pablo; Paim, Paulo Sergio Gomes

    2016-04-01

    During the Late Paleozoic, the Gondwana supercontinent was affected by multiple glacial and deglacial episodes known as "The Late Paleozoic Ice Age" (LPIA). In Brazil, the evidence of this episode is recorded mainly by widespread glacial deposits preserved in the Paraná Basin that contain the most extensive record of glaciation (Itararé Group) in Gondwana. The Pennsylvanian to early Permian glaciogenic deposits of the Itararé Group (Paraná Basin) are widely known and cover an extensive area in southern Brazil. In the Doutor Pedrinho area (Santa Catarina state, southern Brazil), three glacial cycles of glacier advance and retreat were described. The focus of this article is to detail the base of the second glacial episodes or Sequence II. The entire sequence records a deglacial system tract that is represented by a proximal glacial grounding-line system covered by marine mudstones and shales associated with a rapid flooding of the proglacial area. This study deals with the ice proximal grounding-line systems herein interpreted according to lab model named plane-wall jet with jump. Detailed facies analysis allowed the identification of several facies ranging from boulder-rich conglomerates to fine-grained sandstones. No fine-grained deposits such as siltstone or shale were recorded. According to this model, the deposits are a product of a supercritical plane-wall outflow jet that changes to a subcritical jet downflow from a hydraulic jump. The hydraulic jump forms an important energy boundary that is indicated by an abrupt change in grain size and cut-and-fill structures that occur at the middle-fan. The sedimentary facies and facies associations show a downflow trend that can be subdivided into three distinct stages of flow development: (1) a zone of flow establishment (ZFE), (2) a zone of transition (ZFT), and (3) an established zone (ZEF). The proximal discharge is characterized by hyperconcentrated-to-concentrated flow due to the high energy and sediment

  10. Late Paleozoic final closure of the Paleo-Asian Ocean in the eastern part of the Xing-Meng Orogenic Belt: Constrains from Carboniferous-Permian (meta-) sedimentary strata and (meta-) igneous rocks

    NASA Astrophysics Data System (ADS)

    Li, Dapeng; Jin, Ye; Hou, Kejun; Chen, Yuelong; Lu, Zhen

    2015-12-01

    Zircon U-Pb dating and whole-rock geochemical data for Carboniferous-Permian (meta-) sedimentary sequences, igneous rocks, and Precambrian amphibolite in the eastern Xing-Meng Orogenic Belt (XMOB) were used to constrain the final stage evolution and the position of closure of the Paleo-Asian Ocean (PAO). Detrital zircons from Late Paleozoic strata range in age from Archean to Late Paleozoic, with major age groups at ~ 1.0-0.7 Ga and ~ 0.5-0.25 Ga in the northern part and at ~ 2.7-2.5 Ga, ~ 2.1-1.8 Ga, and ~ 0.5-0.25 Ga in the southern part of the XMOB. Striking changes in zircon age distribution patterns indicate inputs to these strata were separated by the Paleo-Asian Ocean (PAO) in the Late Paleozoic. The PAO closed along the Solonker-Linxi suture. The Late Paleozoic formation ages (~ 346 Ma, ~ 303 Ma, and ~ 269 Ma) of the igneous rocks with arc-like geochemical features south to the PAO, together with previously published data on the regional igneous rocks and ophiolites, indicate double-side subduction of the PAO in the Late Paleozoic.

  11. Testing alternative tectonic models of Palaeotethys in the E Mediterranean region: new U-Pb and Lu-Hf isotopic analyses of detrital zircons from Late Carboniferous and Late Triassic sandstones associated with the Anatolide and Tauride blocks (S Turkey)

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    Alternative tectonic models of Palaeotethys during Late Palaeozoic-Early Mesozoic time infer: 1. southward subduction beneath the north margin of Gondwana; 2. northward subduction beneath the south margin of Eurasia, or 3. double subduction (northwards and southwards), at least during Late Carboniferous. U-Pb and Lu-Hf isotopic analysis of detrital zircons, extracted from sandstones, can provide strong indications of age and identity of source terranes. Here, we consider the provenance of both Late Carboniferous and Late Triassic sandstones from both relatively allochthonous and relatively autochthonous units that are all spatially associated with the Anatolide and Tauride continental blocks. The relatively allochthonous units are sandstones (3 samples) from the Late Carboniferous Aladaǧ Nappe (Tauride; in the east), the Konya Complex (Anatolide; central area) and the Karaburun Mélange (Tauride-related; in the west). The relatively autochthonous units are Late Triassic sandstones (4 samples) from the Üzümdere Formation, the Kasımlar Formation (both western Taurides) and the Güvercinlik Formation (Karaburun Peninsula-Tauride related; far west). The Late Carboniferous sandstones from the three relatively allochthonous units are dominated by Precambrian zircon populations, the age distribution of which suggests derivation from two contrasting source regions: First, a NE African-type source (i.e. Saharan craton) for the sandstones of the Konya Mélange and the Aladaǧ Nappe because these sediments have prominent zircon populations dated at 0.5-0.7, 0.8 and 0.9-1.1 Ga. Palaeozoic zircons are minimal in the sandstones of the Aladaǧ Nappe and the Konya Complex (3 and 5% of the whole data, respectively) and are confined to Cambrian to Ordovician. Secondly, a contrasting NW African-type source is inferred for sandstone from the Karaburun Mélange because of the marked absence of Tonian-Stenian zircons and the predominance of ~2 Ga zircons over ~2.5 Ga zircons. In

  12. Early to Late Cenozoic structural inheritance of Paleozoic basement structures in the northern Alpine foreland: examples from eastern France and northern Switzerland

    NASA Astrophysics Data System (ADS)

    Madritsch, Herfried

    2014-05-01

    During his time at the Geological Institute of the University of Basel, Peter Ziegler was the main initiator of the EUCOR-URGENT project, a joint multi-disciplinary research and training programme aiming at a better understanding of seismic hazard, neotectonics and evolution of the Upper Rhine Graben and surrounding areas. Throughout the duration of the programme from 1999 to 2007 the EUCOR-URGENT network embraced more than 40 Ph.D. students, 20 Post-Docs and 18 senior researchers, who were based at one of the 25 involved universities or national organizations. Peter's natural drive, networking capabilities and scientific enthusiasm were without doubt the main reasons for this success story. The Rhine-Bresse Transfer Zone (RBTZ) in eastern France, one of the natural laboratories investigated within the EUCOR-URGENT framework, is a major segment of the European Cenozoic Rift system (Ziegler, 1992) and formed by structural inheritance of the pre-existing Late Paleozoic Burgundy Trough. The Mid-Eocene to Oligocene evolution of the sinistral transtensional RBTZ was kinematically linked to crustal extension across the Upper Rhine and Bresse Grabens (Lacombe et al., 1993). From the Early Miocene onward the RBTZ further evolved under the influence of the far field effects of the Alpine collision involving Late Miocene to Pliocene NW-ward propagation of the thin-skinned Jura Thrust Belt but also thick-skinned reactivation of the Late Paleozoic and Paleogene fault systems in the RBTZ. In fact, shortening throughout the RBTZ appears to be still mildly active, as is indicated by one of the very few clearly oblique-compressive focal mechanisms in the northern Alpine foreland and evidenced by geomorphologic investigations that yielded Late Quaternary folding of fluvial meanders in the area of Besançon (Madritsch et al. 2010). The Late Paleozoic Burgundy Trough as well as the Jura Thrust Belt continue eastward into northern Switzerland. In this area, reprocessed and newly

  13. Evidence for Late-Paleozoic brine migration in Cambrian carbonate rocks of the central and southern Appalachians: Implications for Mississippi Valley-type sulfide mineralization

    USGS Publications Warehouse

    Hearn, P.P.; Sutter, J.F.; Belkin, H.E.

    1987-01-01

    Many Lower Paleozoic limestones and dolostones in the Valley and Ridge province of the central and southern Appalachians contain 10 to 25 weight percent authigenic potassium feldspar. This was considered to be a product of early diagenesis, however, 40Ar 39Ar analyses of overgrowths on detrital K-feldspar in Cambrian carbonate rocks from Pennsylvania, Maryland, Virginia, and Tennessee yield Late Carboniferous-Early Permian ages (278-322 Ma). Simple mass balance calculations suggest that the feldspar could not have formed isochemically, but required the flux of multiple pore volumes of fluid through the rocks, reflecting regional fluid migration events during the Late-Paleozoic Alleghanian orogeny. Microthermometric measurements of fluid inclusions in overgrowths on detrital K-feldspar and quartz grains from unmineralized rocks throughout the study area indicate homogenization temperatures from 100?? to 200??C and freezing point depressions of -14?? to -18.5??C (18-21 wt.% NaCl equiv). The apparent similarity of these fluids to fluid inclusions in ore and gangue minerals of nearby Mississippi Valley-type (MVT) deposits suggests that the regional occurrences of authigenic K-feldspar and MVT mineralization may be genetically related. This hypothesis is supported by the discovery of authigenic K-feldspar intergrown with sphalerite in several mines of the Mascot-Jefferson City District, E. Tennessee. Regional potassic alteration in unmineralized carbonate rocks and localized occurrences of MVT mineralization are both explainable by a gravity-driven flow model, in which deep brines migrate towards the basin margin under a hydraulic gradient established during the Alleghanian orogeny. The authigenic K-feldspar may reflect the loss of K during disequilibrium cooling of the ascending brines. MVT deposits are probably localized manifestations of the same migrating fluids, occurring where the necessary physical and chemical traps are present. ?? 1987.

  14. Evidence for Late-Paleozoic brine migration in Cambrian carbonate rocks of the central and southern Appalachians: Implications for Mississippi Valley-type sulfide mineralization

    NASA Astrophysics Data System (ADS)

    Hearn, Paul P., Jr.; Sutter, John F.; Belkin, Harvey E.

    1987-05-01

    Many Lower Paleozoic limestones and dolostones in the Valley and Ridge province of the central and southern Appalachians contain 10 to 25 weight percent authigenic potassium feldspar. This was considered to be a product of early diagenesis, however, 40Ar /39Ar analyses of overgrowths on detrital K-feldspar in Cambrian carbonate rocks from Pennsylvania, Maryland, Virginia, and Tennessee yield Late Carboniferous-Early Permian ages (278-322 Ma). Simple mass balance calculations suggest that the feldspar could not have formed isochemically, but required the flux of multiple pore volumes of fluid through the rocks, reflecting regional fluid migration events during the Late-Paleozoic Alleghanian orogeny. Microthermometric measurements of fluid inclusions in overgrowths on detrital K-feldspar and quartz grains from unmineralized rocks throughout the study area indicate homogenization temperatures from 100° to 200°C and freezing point depressions of -14° to -18.5°C (18-21 wt.% NaCl equiv). The apparent similarity of these fluids to fluid inclusions in ore and gangue minerals of nearby Mississippi Valley-type (MVT) deposits suggests that the regional occurrences of authigenic K-feldspar and MVT mineralization may be genetically related. This hypothesis is supported by the discovery of authigenic K-feldspar intergrown with sphalerite in several mines of the Mascot-Jefferson City District, E. Tennessee. Regional potassic alteration in unmineralized carbonate rocks and localized occurrences of MVT mineralization are both explainable by a gravity-driven flow model, in which deep brines migrate towards the basin margin under a hydraulic gradient established during the Alleghanian orogeny. The authigenic K-feldspar may reflect the loss of K during disequilibrium cooling of the ascending brines. MVT deposits are probably localized manifestations of the same migrating fluids, occurring where the necessary physical and chemical traps are present.

  15. Late Paleozoic subduction and collision processes during the amalgamation of the Central Asian Orogenic Belt along the South Tianshan suture zone

    NASA Astrophysics Data System (ADS)

    Han, Yigui; Zhao, Guochun; Sun, Min; Eizenhöfer, Paul R.; Hou, Wenzhu; Zhang, Xiaoran; Liu, Qian; Wang, Bo; Liu, Dongxing; Xu, Bing

    2016-03-01

    The provenance of late Paleozoic siliciclastic sedimentary strata on the northern margin of the Tarim Craton and the South Tianshan Orogenic Belt provides important insights into subduction and collision processes during the formation of the southern Central Asian Orogenic Belt. Detrital zircons from Carboniferous and Permian sedimentary rocks in the South Tianshan belt show two predominant age populations of 500-400 and 305-270 Ma, and three subordinate clusters around ~ 2.5 Ga, 2.0-1.7 Ga, and 1.2-0.6 Ma. Such age patterns are similar to major magmatic episodes in the Tarim Craton but are distinct from those in the Central Tianshan-Yili Block, implying that the Carboniferous-Permian strata in the South Tianshan belt were deposited on the northern margin of the Tarim Craton. These data, in combination with Carboniferous passive margin deposition along the South Tianshan and northern Tarim regions and intense arc magmatism in the Central Tianshan area, support the northward subduction of the South Tianshan oceanic crust. The abrupt decrease of zircon εHf(t) values at ~ 310 Ma indicates the tectonic transformation from oceanic subduction to continental collision. However, syn- and post-collisional sediments in the South Tianshan and northern Tarim regions did not contain detritus from the Central Tianshan-Yili Block, as evidenced by the absence/paucity of 380-310 Ma detrital zircons in the late Paleozoic strata and by the stratigraphic record in the regions. Insignificant surface erosion and uplifting during the collision and (ultra-)high-pressure rock exhumation require divergence in the frontal wedge. We propose that the switch from a convergent to a divergent regime was triggered by the arrival of the Tarim mantle plume in the latest Carboniferous, which possibly had profound effects on regional sedimentation and exhumation of (ultra-)high-pressure rocks in the orogenic belt.

  16. Late Paleozoic evolution of the South Tien Shan: Insights from P-T estimates and allanite geochronology on retrogressed eclogites (Chatkal range, Kyrgyzstan)

    NASA Astrophysics Data System (ADS)

    Loury, Chloé; Rolland, Yann; Cenki-Tok, Bénédicte; Lanari, Pierre; Guillot, Stéphane

    2016-05-01

    In the South Tien Shan range (Kyrgyzstan), the Late Paleozoic geodynamic evolution remains debated especially to the west of the Talas-Fergana fault (TFF) fault where suture-related high-pressure (HP) rocks are scarce. We provide new petrological and geochronological data on garnet amphibolites from the Chatkal range, to the west of the TFF, northwest of the South Tien Shan suture. These rocks are retrogressed eclogites. We used a micro-mapping approach combined with forward modeling and empirical thermobarometry to decipher the P-T path of these amphibolitized eclogites. The metamorphic peak conditions culminated at 490 ± 50 °C and 18.5 ± 2 kbar and were followed by higher temperature retrogression (∼560 °C at 11-7 kbar). In order to constrain the age of the HP stage, we dated allanite crystals texturally coeval to the HP mineral assemblage. Allanite grains dated in situ with a U-Pb LA-ICPMS methodology yield an age of 301 ± 15 Ma. Compared with previously published data for the east of the TFF, these P-T constraints allow improving the understanding of the Late Paleozoic geodynamic evolution of the South Tien Shan. To the east of TFF, the Turkestan Ocean closed around 320 Ma with the collision of the Tarim Craton with the Kazakh microcontinent. To the west of TFF, the Turkestan Ocean closed around 300 Ma, when the Alai block collided with the Kazakh microcontinent. This later collision involved nappe-stacking and intense subvertical folding in the western South Tien Shan. This complex folding explains the S-shape of the suture to the west of the TFF that cannot be observed in the eastern part. These new data allow us to propose a distinct tectonic evolution of the two sides of the TFF, which suggests that this fault was a major transform fault before being a strike-slip intra-continental fault.

  17. Geological Setting and Petroleum Potential of the Paleozoic Hudson Platform, Northern Canada

    NASA Astrophysics Data System (ADS)

    Dietrich, J.; Hamblin, T.; Lavoie, D.; Duchesne, M.; Lajeunesse, P.; Zhang, Z.

    2009-05-01

    The Hudson Platform covers an area of 600,000 km2 and represents one of the largest Paleozoic sedimentary basins in Canada. The Hudson Platform contains the large Hudson Bay Basin and smaller Moose River Basin. The Hudson Bay and Moose River basins are surrounded and underlain by Precambrian igneous and metamorphic rocks of the Canadian Shield. The Hudson Platform contains Ordovician to Cretaceous sedimentary strata, with a maximum known thickness of about 2500 m in Hudson Bay. The lower Paleozoic succession includes Late Ordovician to Early Devonian shallow marine carbonates and thin mudstones, deposited during widespread early Paleozoic marine inundation of the Canadian Shield, and Early to Late Devonian marine carbonates, evaporates, and mudstones deposited in saucer-shaped, isolated basin depocentres. There is no record of late Paleozoic sedimentation in the region, perhaps related to cratonic uplift accompanying the Alleghenian Orogeny. Lower Paleozoic strata are unconformably overlain by thin, erosional remnants of Middle Jurassic and Early Cretaceous nonmarine sandstones, mudstones and lignite seams (Moose River Basin) and Early Cretaceous marine sandstones and mudstones (Hudson Bay Basin). The Hudson Platform is currently considered a frontier prospect for hydrocarbon exploration. However, the long- held view that the region is underlain by a thin sedimentary succession with no appreciable hydrocarbon source rocks or reservoir intervals is erroneous. Geological and geophysical data indicate the Hudson Bay Basin contains many prospective petroleum reservoir and trap types, potentially including hydrothermal dolomite. Recent studies indicate Upper Ordovician oil shales are widespread and may have generated hydrocarbons in deeper parts of the Hudson Bay Basin. New high resolution bathymetric surveys in northern Hudson Bay have led to the recognition of circular sea-floor depressions similar to fluid or gas-escape pockmarks. A modern re-evaluation of the

  18. Orogenesis and Basin Development: U-Pb Detrital Zircon Age Constraints on Evolution of the Late Paleozoic St. Marys Basin, Central Mainland Nova Scotia.

    PubMed

    Murphy; Hamilton

    2000-01-01

    The St. Marys Basin, along the southern flank of the composite Late Paleozoic Magdalen Basin in the Canadian Appalachians and along the Avalon-Meguma terrane boundary, contains Late Devonian-Early Carboniferous continental clastic rocks of the Horton Group that were deposited in fluvial and lacustrine environments after the peak of the Acadian orogeny. SHRIMP II (Geological Survey of Canada) data on approximately 100 detrital zircons from three samples of Horton Group rocks from the St. Marys Basin show that most of the zircons have been involved in a multistage history, recycled from clastic rocks in the adjacent Meguma and Avalonian terranes. Although there is a minor contribution from Early Silurian (411 Ma) and Late Devonian suites (ca. 380-370 Ma), Neoproterozoic (ca. 700-550 Ma) and Paleoproterozoic (ca. 2.0-2.2 Ga) zircon populations predominate, with a minor contribution from ca. 1.0-, 1.2-, and 1.8-Ga zircons. Published U-Pb single-zircon analyses on clastic sedimentary rocks indicate that the Meguma and Avalon terranes have different populations of detrital zircons, sourced from discrete portions (Amazonian and West African cratons) of the ancient Gondwanan margin. Both terranes contain Neoproterozoic and Late Archean populations. The SHRIMP data, in conjunction with published sedimentological and geochemical data, indicate that the Horton Group basin-fill sediments are largely the result of rapid uplift and erosion of Meguma terrane metasedimentary and granitoid rocks immediately to the south of the St. Marys Basin during the waning stages of the Acadian orogeny. Regional syntheses indicate that this uplift occurred before and during deposition and was a consequence of dextral ramping of the Meguma terrane over the Avalon terrane along the southern flank of the Magdalen Basin.

  19. New palaeomagnetic results from Late Paleozoic volcanic units along the western Gondwana margin in La Pampa, Argentina

    NASA Astrophysics Data System (ADS)

    Tomezzoli, Renata Nela; Pierre, Teresa Saint; Valenzuela, Claudia

    2009-01-01

    Preliminary palaeomagnetic results from the Paleozoic volcanic units along the Gondwana margin in Argentina are presented. Even though we are still working on the palaeomagnetic data of the sampled section, these data are consistent with data from former studies carried out in the area. More than 90 specimens were measured from the Sierra Chica locality (37°52'S; 65°27'W) computed in 11 sites (Sc1-Sc11). These rocks are carriers of a characteristic remanence magnetization with reverse polarity, acquired during the Early Permian and assigned to the Kiaman Superchron. The resulting palaeomagnetic pole (PP) is Lat.: 64°S; Long.: 017°E, A95 = 15°, K = 12, N = 10. Others interpretations are also possible if the directions of two sites (SC9 and SC10) are considered to have a different magnetic field record. In that case, the PP calculated for sites Sc1-Sc7 is Lat.: 65°S; Long.: 44°E, A95 = 8°, K = 54, N = 7, and the virtual geomagnetic pole (VGP) calculated for sites Sc9 and Sc10 is Lat.: 48.5°S; Long.: 315°E, A 95 = 8°, N = 2. The last possibility to consider Sc9 and Sc10 after structural correction, and the resulting PP position is Lat.: 66.5°S; Long.: 034°E, A 95 = 8°, K = 41, N = 9. This deformation episode could be related to the San Rafaelic orogenic phase, found for the first time in La Pampa province, but previously observed in other neighboring areas during Permian time. However, more detailed palaeomagnetic sampling, rock magnetism studies, and age dating are necessary to complete the palaeomagnetic study of this area.

  20. Multistage Tectonic Block Movements In The Catalan Coastal Ranges (ne Spain) Since Late Paleozoic Assessed By Apatite And Zircon Fission Track, And (u-th)/he Analyses.

    NASA Astrophysics Data System (ADS)

    Juez-Larré, J.; Andriessen, P. A. M.

    The Catalan Coastal Ranges (CCR) are located in the northeastern passive margin of the Iberian Plate and stretch out ~200 km in an ENE-WSW direction subparallel to the coastline. They can be defined as a complex system of asymmetric horsts and grabens. The horst domains are essentially composed of Paleozoic basement and a discordantly overlying Mesozoic cover. All graben domains, however, are infilled by up to 4 km of Miocene and younger sediments. Three major tectonic phases effected the CCR after the Hercynian orogeny: a Late Permian-Late Cretaceous double rift - postrift phase, the Late Cretaceous-Middle Oligocene Pyrenean orogeny, and a Late Oligocene-Middle Miocene rift phase [Salas and Casas, 1993]. Carboniferous metasediments, the oldest lithologies dated by FT, yield apparent AFT and ZFT ages much younger than their sedimentation age pointing to total thermal resetting. The intrusion of important Late Hercynian magmatic bodies is known to have increased the temperature of the adjacent Carboniferous rocks high above the ZFT closure temperature (240+/-50°C) around 290 Ma. The apatites and zircons apparent ages, therefore, would only record the post-Hercynian thermal history. Nonetheless, ZFT ages and AFT thermal models in Paleozoic basement hardly display any thermal history prior to Late Triassic (200 Ma). This suggests the existence of a second event of partial to total thermal resetting around this time. Thermal resetting is correlated to the first Mesozoic rift in which mechanical stretching of the lithosphere was followed by ascent of hot asthenospheric material to shallower crustal depth, initiating volcanism and considerable hydrothermal activity. AFT ages and Mean Track Length (MTL) between 198 and 145 Ma and 12.85 and 11.93 µm, respectively, record the subsequent Jurassic thermal crustal relaxation. New episodes of rift -related thermal activity are once again detected during the second Mesozoic rift phase when substantial fault activity created

  1. Sedimentary evolution of the Paleozoic basin fill, southeast Turkey

    SciTech Connect

    Tunbridge, I.P. )

    1988-08-01

    The Paleozoic succession of southeast Turkey reaches its thickest development in the Hakkari district. Here, well-exposed Paleozoic rocks of Cambrian to Permian age are more than 5 km thick, representing a punctuated accumulation of clastic and carbonate sediments on the northern margin of the Arabian shield. Lower Cambrian rocks (< 1.5 km thick) are recorded in the Sadan Formation. A range of deltaic and fluviatile facies are present here. These developed as large-scale meandering then later braided river systems, which flowed north from the Arabian shield. Peritidal dolomites of the Koruk Formation follow, succeeded by 1 km of Cambrian-Ordovician storm-swept shelf sandstones and mudstones of the Seyisehir Formation. Following a Middle Ordovician break, a thin (25 m) Ashgillian siliciclastic shelf sea succession occurs, known as the Sort Tepe Formation. Silurian sediments are not found, and the Devonian of the Hakkari district is marked by the Upper Devonian Yiginli Formation. This formation records a 380-m regressive-transgressive fluvial-deltaic couplet, with deltaic conditions terminated by an Early Carboniferous eustatic sea-level rise. This event permitted the development of a 250 m-thick black shale facies (Koprulu Formation), which was succeeded by 130 m of carbonate mound facies (Belek Formation). Thick (2,000 m) carbonate sequences of the Habbur Formation (Permian) mark the start of the thick carbonate sequences which persisted from the late Paleozoic through the Mesozoic in the region.

  2. Gold deposits of the northern margin of the North China craton: Multiple late Paleozoic-Mesozoic mineralizing events

    USGS Publications Warehouse

    Hart, C.J.R.; Goldfarb, R.J.; Qiu, Y.; Snee, L.; Miller, L.D.; Miller, M.L.

    2002-01-01

    The northern margin of the North China craton is well-endowed with lode gold deposits hosting a resource of approximately 900 tonnes (t) of gold. The ???1,500-km-long region is characterized by east-trending blocks of metamorphosed Archean and Proterozoic strata that were episodically uplifted during Variscan, Indosinian, and Yanshanian deformational and magmatic events. At least 12 gold deposits from the Daqinshan, Yan-Liao (includes the Zhangjiakou, Yanshan, and Chifeng gold districts), and Changbaishan gold provinces contain resources of 20-100 t Au each. Most deposits are hosted in uplifted blocks of Precambrian metamorphic rocks, although felsic Paleozoic and Mesozoic plutons are typically proximal and host ???30% of the deposits. The lodes are characterized by sulfide-poor quartz veins in brittle structures with low base metal values and high Au:Ag ratios. Although phyllic alteration is most common, intensive alkali feldspar metasomatism characterizes the Wulashan, Dongping, and Zhongshangou deposits, but is apparently coeval with Variscan alkalic magmatism only at Wulashan. Stepwise 40Ar-39Ar geochronology on 16 samples from gangue and alteration phases, combined with unpublished SHRIMP U-Pb dates on associated granitoids, suggest that gold mineralizing events occured during Variscan, Indosinian, and Yanshanian orogenies at circa 350, 250, 200, 180, 150, and 129 Ma. However, widespread Permo-Triassic (???250 Ma) and Early Jurassic (???180 Ma) thermal events caused variable resetting of most of the white mica and K-feldspar argon spectra, as well as previously reported K-Ar determinations. Compiled and new stable isotope and fluid inclusion data show that most ??18O values for ore-stage veins range from 8 to 14???, indicating a fluid in equilibrium with the Precambrian metamorphic basement rocks; ??D values from fluid inclysions range widely from -64 to -154???, which is indicative of a local meteoric component in some veins; and highly variable ??34S data

  3. Paleozoic sedimentary rocks in oaxaca, Mexico.

    PubMed

    Pantoja-Alor, J; Robison, R A

    1967-09-01

    Fossiliferous Cambrian, Ordovician, Mississippian, and Pennsylvanian rocks, never before found in southern Mexico, have been discovered in the Nochixtlán region. Superjacent unfossiliferous sedimentary rocks may be Permian in age. Early Paleozoic and late Paleozoic intervals of marine sedimentation were bounded by intervals of positive tectonism and erosion.

  4. Geochemistry and geochronology of the blueschist in the Heilongjiang Complex and its implications in the late Paleozoic tectonics of eastern NE China

    NASA Astrophysics Data System (ADS)

    Ge, Mao-hui; Zhang, Jin-jiang; Liu, Kai; Ling, Yi-yun; Wang, Meng; Wang, Jia-min

    2016-09-01

    The Paleozoic to early Mesozoic tectonic framework and evolution of Northeast China, especially the Jiamusi block and its related structural belts, are highly debated. In this paper, geochemical, geochronological and isotopic analyses were carried out on the blueschist in the Heilongjiang Complex to address these issues. The Heilongjiang Complex defines the suture belt between the Jiamusi block and the Songliao block in NE China, and the blueschist is a major composition for this complex, coexisting with mafic-ultramafic rocks, greenschist, quartzite and mica schist. The blueschist has a mineral association of sodic amphibole, epidote, chlorite, phengite, albite and quartz with accessory phases of apatite, titanite, zircon and ilmenite. Together with the lithological association, the major and trace element compositions present that the protoliths of the blueschist can be divided into the alkaline and tholeiitic basalts and have OIB affinities, formed in an ocean island setting, indicated by the (La/Yb) N values of 3.57 - 11.54, and the (La/Sm) N values of 0.69 - 3.64. The high and positive εNd (t) values of + 3.7 to + 9.0, and relative enrichment in Nb (vs. Th) and Ta (vs. U) show that both the alkaline and tholeiitic basalts may be derived from the asthenospheric mantle with insignificant crustal contamination. Magmatic zircons from the blueschist in Yilan area yield a 206Pb/238U age of 281 ± 3 Ma, interpreted as its protolithic age. The youngest ages of ~ 200 Ma of the detrital zircons in the associated mica schist from Mudanjiang area place constraints on the timing of metamorphism for the blueschist. These indicate that a big ocean existed between the Jiamusi and Songliao blocks at least since the early Permian, and the blueschist formed since the late Triassic to late Jurassic by the subduction of this ocean. Such an ocean during the Permian - Jurassic is difficult to be interpreted by the tectonic evolution of the Paleo-Asian Ocean.

  5. A Late Paleozoic sill complex and related paleo-topography in the eastern North Sea analyzed using 3D seismic data

    NASA Astrophysics Data System (ADS)

    Clausen, Ole Rønø; Andresen, Katrine Juul; Rasmussen, Jens Andreas

    2016-04-01

    In this paper, we utilize large igneous intrusions as a key to a detailed analysis and understanding of the late Paleozoic evolution of the Ringkøbing-Fyn High, an important structural element in the North West European Craton. The study takes advantage of high-quality 3D seismic data and boreholes to map the geometry and lateral distribution of intrusive sills cross-cutting the sedimentary strata at a low angle (transgressive sills). Our analysis shows that the transgressive sills most likely sourced the vast extrusion of volcanics, which covered most of the Early Permian Northern Basin and which is associated to the Skagerak-Centered Large Igneous Province (SCLIP). Furthermore, a geometrical analysis of the sills demonstrates that the magmatic source for the sills was located SE of the studied area, suggesting a correlation with geophysically inferred lower crust intrusions. Hence, we are in this study able to constrain the full magmatic system from the lower crust intrusions to the surface volcanics. Intrusion of the sills occurred prior to an Early Permian faulting event, which created rotated fault blocks outlining the present Ringkøbing-Fyn High. The sills exposed for erosion at the crest of the footwall in turn controlled the Late Permian paleo-topography and the distribution of the Zechstein evaporites due to the fact that they are harder to erode. Hence, we are able to demonstrate a topography controlled thickness variation of the Zechstein evaporites. The study furthermore emphasizes that an understanding of the deepest parts of the North Sea Basin is crucial when evaluating the potential for yet unrecognized hydrocarbon plays.

  6. Constraints on Phanerozoic paleotemperature and seawater oxygen isotope evolution from the carbonate clumped isotope compositions of Late Paleozoic marine fossils (Invited)

    NASA Astrophysics Data System (ADS)

    Henkes, G. A.; Passey, B. H.; Grossman, E. L.; Pérez-Huerta, A.; Shenton, B.; Yancey, T. E.

    2013-12-01

    A long-standing geoscience controversy has been the interpretation of the observed several per mil increase in the oxygen isotope compositions of marine calcites over the Phanerozoic Eon. Explanations for this trend have included decreasing seawater paleotemperatures, increasing seawater oxygen isotope values, and post-depositional calcite alteration. Carbonate clumped isotope paleothermometry is a useful geochemical tool to test these hypotheses because of its lack of dependence on the bulk isotopic composition of the water from which carbonate precipitated. This technique is increasingly applied to ancient marine invertebrate shells, which can be screened for diagenesis using chemical and microstructural approaches. After several years of clumped isotope analysis of these marine carbonates in a handful of laboratories, a long-term temperature and isotopic trend is emerging, with the results pointing to relatively invariant seawater δ18O and generally decreasing seawater temperatures through the Phanerozoic. Uncertainties remain, however, including the effects of reordering of primary clumped isotope compositions via solid-state diffusion of C and O through the mineral lattice at elevated burial temperatures over hundred million year timescales. To develop a quantitative understanding of such reordering, we present data from laboratory heating experiments of late Paleozoic brachiopod calcite. When combined with kinetic models of the reordering reaction, the results of these experiments suggest that burial temperatures less than ~120 °C allow for preservation of primary brachiopod clumped isotope compositions over geological timescales. Analyses of well-preserved Carboniferous and Permian brachiopods reinforce these results by showing that shells with apparent clumped isotope temperatures of ~150 °C are associated with deep sedimentary burial (>5 km), whereas those with putatively primary paleotemperatures in the 10-30 °C range experienced no more than ~1.5 km

  7. Early Paleozoic (Late Cambrian-Early Ordovician) acritarchs from the metasedimentary Baden-Baden-Gaggenau zone (Schwarzwald, SW Germany).

    PubMed

    Montenari, M; Servais, T

    2000-12-01

    The metasediments of the low-grade metamorphosed Baden-Baden-Gaggenau zone of the northern Schwarzwald (southwestern Germany) have been analyzed palynologically. From 133 samples representing different metasedimentary units, only three samples of the upper part of the Traischbach Serie provide extremely poorly-preserved palynomorphs. The assemblage consists of the galeate acritarch genera Caldariola, Cymatiogaleaand Stelliferidium, as well as specimens of diacromorph and polygonomorph acritarchs. Although determinations are difficult at the generic level and essentially impossible at the specific level, the assemblage can be attributed to an interval between the Late Cambrian and Early Ordovician. This is the first biostratigraphical age assignment for the metasediments of the Baden-Baden-Gaggenau zone, which can possibly be correlated with the Villé Unit of the northern Vosges Mountains (eastern France). PMID:11164213

  8. New late Paleozoic paleopoles from the Donbas Foldbelt (Ukraine): Implications for the Pangea A vs. B controversy

    NASA Astrophysics Data System (ADS)

    Meijers, Maud J. M.; Hamers, Maartje F.; van Hinsbergen, Douwe J. J.; van der Meer, Douwe G.; Kitchka, Alexander; Langereis, Cor G.; Stephenson, Randell A.

    2010-08-01

    The Carboniferous to early Permian apparent polar wander (APW) path for Eurasia is not well constrained, because of the paucity of reliable paleomagnetic poles. This is at least partly responsible for the Pangea A vs. B controversy in the early Permian: is the overlap between the northern and southern continents during the early Permian caused by a lack of reliable paleomagnetic data (Pangea A) or must a large displacement along a mega-shear zone be invoked (Pangea B)? Here, we present results from six paleomagnetic sampling sites ranging in age from the early Carboniferous to the early Permian from sedimentary rocks in the Donbas Foldbelt (Ukraine) to improve the Carboniferous-early Permian APW path for Eurasia and to contribute to solving the Pangea A vs. B controversy. Six time intervals were sampled in the Donbas Foldbelt (eastern Ukraine), which was filled with sediments and volcanic units during the late Devonian to Permian syn- and post-rift subsidence phases. We present results from sediments that were corrected for inclination shallowing with the elongation/inclination ( E/ I) method. We conclude that there is a general northward movement of the Donbas Foldbelt: the resulting paleolatitudes are slightly but generally significantly higher than expected from existing APW paths. The late Carboniferous to early Permian data provide three new reliable paleopoles for Eurasia. The early Permian pole does not necessarily require a Pangea B reconstruction. It results in higher paleolatitudes for Laurussia in the early Permian and removes the overlap between Gondwana and Pangea. We also reconstructed the position of Laurussia based on Carboniferous Laurentian poles recently corrected for inclination shallowing, which clearly favours a Pangea B configuration. It seems that the Pangea A vs. B debate is as lively as before. The three early Carboniferous paleopoles give reliable paleolatitudes, but declinations significantly deviate from the expected directions. We

  9. Petrogenesis of Early-Permian sanukitoids from West Junggar, Northwest China: Implications for Late Paleozoic crustal growth in Central Asia

    NASA Astrophysics Data System (ADS)

    Yin, Jiyuan; Chen, Wen; Xiao, Wenjiao; Yuan, Chao; Sun, Min; Tang, Gongjian; Yu, Shun; Long, Xiaoping; Cai, Keda; Geng, Hongyan; Zhang, Yan; Liu, Xinyu

    2015-11-01

    Sanukitoids and their equivalents are rare subduction-related rock types that have been found in modern arc settings and in Late Archean sequences. The investigation of sanukitoids is of particular importance to a better understanding of crust-forming processes and continental growth. In this paper we report zircon U-Pb and Ar-Ar ages and major element, trace element, and Sr-Nd-Hf isotope data for the Bieluagaxi dioritic pluton and dikes from the southern part of the West Junggar, NW China. These rocks formed in the Early Permian and show a remarkable geochemical affinity with Cenozoic sanukitoids of the Setouchi Volcanic Belt of SW Japan with high Mg# (48-73) values, Cr (54-539 ppm), Ni (21-197 ppm) contents and Th/La (0.15-0.37) ratios and low Sr/Y ratios (16-27) and Sr (263-442 ppm) contents. They may be generated by the partial melting of subducting sediments, and subsequent melt-mantle interaction. Additionally, the sanukitoids are also widespread in the Karamay-Baogutu area of West Junggar accompanied by high Sr (average 713 ppm) contents and Sr/Y (50-130) ratios, and low Y (6.9-12.6 ppm) contents. The difference in petrochemical characteristics between the Baogutu-Karamay and Bieluagaxi sanukitoids can be explained by the difference in depth of initial melting, origin composition and fractional crystallization. The Baogutu-Karamay sanukitoids were probably formed under eclogitic conditions, while the Bieluagaxi sanukitoids were at a shallower depth. Moreover, the compositional similarity between continental-crust forming rocks and the Bieluagaxi sanukitoids suggests that the sanukitoids genesis could be closely related to the process of continental crust formation. The Late Carboniferous-Early Permian sanukitoids in the West Junggar may be an indicator of anomalous thermal activity. Ridge subduction may play a crucial role in the evolution and growth of the continental crust in Central Asia.

  10. Petrogenesis of the Kekesai composite intrusion, western Tianshan, NW China: Implications for tectonic evolution during late Paleozoic time

    NASA Astrophysics Data System (ADS)

    Zhang, Dongyang; Zhang, Zhaochong; Encarnación, John; Xue, Chunji; Duan, Shigang; Zhao, Zhidan; Liu, Junlai

    2012-08-01

    The late Carboniferous to Permian is a critical period for final amalgamation of the Central Asian Orogenic Belt (CAOB), which is characterized by voluminous igneous rocks, particularly granitoids. The Kekesai composite granitoid porphyry intrusion, situated in the Chinese western Tianshan (southwest part of CAOB) includes two intrusive phases, a monzogranite phase, intruded by a granodiorite phase. LA-ICPMS U-Pb zircon analyses suggest that the monzogranitic rocks were formed at 305.5 ± 1.1 Ma, with a wide age range of inherited zircons (358-488 Ma and 1208-1391 Ma), whereas the granodioritic rocks formed at 288.7 ± 1.5 Ma. The monzogranitic and granodioritic phases have similar geochemical features and Sr-Nd-Hf isotopic compositions. They exhibit high and variable SiO2 (66-71 wt.%) and MgO (0.41-2.14 wt.%) contents with some arc-like geochemical characteristics (e.g., enrichment of large ion lithophile elements and negative anomalies of Nb, Ta and Ti) and relatively high initial 87Sr/86Sr ratios (ISr = 0.7055-0.7059), low positive ɛNd(t) (+ 0.84 to + 1.03) as well as a large variation in Hf isotopic compositions with ɛHf(t) between + 3.43 and + 14.8, implying both of them were derived from similar source materials. These geochemical characteristics suggest that they might be mainly derived from the partial melting of arc-derived Mesoproterozoic mafic lower crust with involvement of a mantle-derived component in variable proportions by mantle-derived magma underplating. The presence of late-Ordovician to earliest early Carboniferous inherited zircons and the Hf isotopic compositions in the monzogranitic sample, similar to that of the widespread juvenile arc rocks, indicates some crust contamination during magma emplacement. Our new data, combined with previous studies, imply that extensive post-collisional magmatism due to underplating of mantle-derived magma, could plausibly be explained by slab break-off regime.

  11. Petrogenetic evolution of Late Paleozoic rhyolites of the Harvey Group, southwestern New Brunswick (Canada) hosting uranium mineralization

    NASA Astrophysics Data System (ADS)

    Dostal, J.; van Hengstum, T. R.; Shellnutt, J. G.; Hanley, J. J.

    2016-06-01

    The 360 Ma subaerial felsic volcanic and volcaniclastic rocks of the Harvey Group form a belt about 15 km long and 3 km wide in southwestern New Brunswick (Canada) that has been correlated with parts of the Mount Pleasant caldera complex, the site of a significant polymetallic (tin, tungsten, molybdenum, indium and bismuth) deposit. The Harvey volcanic rocks are highly fractionated peraluminous within-plate F-rich rhyolites, which host uranium mineralization. The rocks were modified by late-magmatic and post-magmatic processes. A comparison of the composition of whole rocks and melt inclusions in the quartz phenocrysts shows that some trace elements, including U, were affected by the post-magmatic processes. Their flat REE patterns accompanied by distinct negative Eu anomalies are typical of highly evolved F-rich leucogranites and rhyolites. Nd isotopic ratios (ɛNd(360) = +0.6 to -1.0) are similar to those of the felsic rocks of the Mount Pleasant complex. The Harvey rhyolites were generated by extensive fractional crystallization of andesites of the Mount Pleasant caldera. The melt evolved at the apex of the magma chamber where volatile elements become concentrated. The Harvey rhyolite (with melt inclusions containing ~20 ppm U) had the potential to develop a significant U mineralization. The erupted glassy rhyolite is a favorable U source rock amendable to leaching by post-magmatic hydrothermal and meteoric water. The high Th/U ratios in the Harvey volcanic rocks compared to the low ratios in the U-rich melt inclusions is indicative of such a process.

  12. New insights into the late Paleozoic evolution of the New England Orogen (eastern Australia) in view of the recent paleomagnetic data

    NASA Astrophysics Data System (ADS)

    Pisarevsky, Sergei; Rosenbaum, Gideon; Shaanan, Uri; Hoy, Derek

    2014-05-01

    The New England orogen is the youngest segment of the eastern Australian Tasmanides. It was developed as an accretionary orogen during the late Paleozoic to early Mesozoic Gondwanide Orogeny (310-230 Ma) that extended along the Pacific margin of the Gondwana supercontinent. The orogen exhibits a doubly vergent oroclinal structure with southern (Manning orocline) and northern (Texas - Coffs Harbour orocline) segments displaying S- and Z-shaped sets of oroclines, respectively. These opposite vergences led to contrasting models of formation. Cawood et al. (2011) proposed an animated model for the paleomagnetically permissive evolution of the orogen. However this model is not unique due to the limited number of reliable paleomagnetic data. In particular, the northern Texas - Coffs Harbour orocline has been strongly underrepresented paleomagnetically. Additionally, the previously published results of paleomagnetic studies in the North Tamworth terrane involved rocks which are c. 20 m.y. younger than the paleomagnetically studied rocks from the southern (Manning) orocline. Recently we collected oriented paleomagnetic samples from the Visean Caroda Formation of the North Tamworth block and from the previously not studied Emu Creek block located at the eastern flank of the Texas orocline. Our new paleomagnetic results from the North Tamworth block are comparable in age with previously published Visean data from the Manning orocline. The comparison of these results suggests that the North Tamworth terrane has been rotated at ~ 90° anticlockwise between 330 and 260 Ma. The new data from the Emu Creek block support the previous model of the movement of the Texas block (Cawood et al., 2011). Here we present the revised animated model of the evolution of the New England Orogen.

  13. Paleozoic paleomagnetism and northward drift of the Alexander Terrane, southeastern Alaska

    NASA Astrophysics Data System (ADS)

    van Der Voo, Rob; Jones, Meridee; Gromme, C. Sherman; Eberlein, G. Donald; Churkin, Michael, Jr.

    1980-10-01

    Paleozoic limestone, graywacke, sandstone, milestone, red beds and volcanic rocks of the Alexander terrane, southeastern Alaska, have yielded six paleomagnetic pole positions after thermal and alternating-field demagnetization. These poles are from sample groups of late Middle Ordovician, Late Ordovician, Devonian, Late Devonian, and early and late Carboniferous age. To test various tectonic models for the structural development of this part of western North America, the paleomagnetic results are compared to those for the North American craton. It is found that the observed inclination and declination values deviate significantly from the values predicted for the present-day position of the Alexander terrane (55.5N, 133.5W). Better matching can be obtained for a paleoposition of the terrane at about 40N, 120W, in the present position of western Nevada and northeastern California. In addition, an in situ 25° clockwise rotation of the terrane is required to restore it to its original position.

  14. Three stages in the Late Paleozoic to Triassic magmatism of southwestern Gondwana, and the relationships with the volcanogenic events in coeval basins

    NASA Astrophysics Data System (ADS)

    Sato, Ana María; Llambías, Eduardo J.; Basei, Miguel A. S.; Castro, Carlos E.

    2015-11-01

    The intermediate to acid Choiyoi Magmatic Province is the most conspicuous feature along the Late Paleozic continental margin of southwestern Gondwana, and is generally regarded as the possible source for the widespread ash fall deposits interlayered with sedimentary sequences in the adjacent Gondwana basins. The Choiyoi magmatism is geologically constrained between the early Permian San Rafael orogenic phase and the Triassic extensional Huarpica phase in the region of Argentine Frontal Cordillera, Precordillera and San Rafael Block. In order to better assess the Choiyoi magmatism in Argentine Frontal Cordillera, we obtained 6 new LA-ICPMS U-Pb ages between 278.8 ± 3.4 Ma and 252.5 ± 1.9 Ma from plutonic rocks of the Colangüil Batholith and an associated volcanic rock. The global analysis of age data compiled from Chilean and Argentine Late Paleozoic to Triassic outcrops allows us to identify three stages of magmatism: (1) pre-Choiyoi orogenic magmatism, (2) Choiyoi magmatism (286-247 Ma), and (3) post-Choiyoi magmatism related to extensional tectonics. In the Choiyoi stage is there an eastward shift and expansion of the magmatism to the southeast, covering an extensive region that defines the Choiyoi magmatic province. On the basis of comparison with the ages from volcanogenic levels identified in the coeval Gondwana basins, we propose: (a) The pre-Choiyoi volcanism from the Paganzo basin (320-296 Ma) probably has a local source in addition to the Frontal Cordillera region. (b) The pre-Choiyoi and Choiyoi events identified in the Paraná basin (304-275 Ma) are likely to have their source in the Chilean Precordillera. (c) The early stage of the Choiyoi magmatism found in the Sauce Grande basin (284-281 Ma) may have come from the adjacent Las Matras to Chadileuvú blocks. (d) The pre-Choiyoi and Choiyoi events in the Karoo basins (302-253 Ma) include the longest Choiyoi interval, and as a whole bear the best resemblance to the age records along the Chilean and

  15. Degradation processes and consolidation of Late Jurassic sandstone dinosaur tracks in museum environment (Museum of Lourinhã, Portugal)

    NASA Astrophysics Data System (ADS)

    Leal, Sofia; mateus, Octavio; Tomas, Carla; Dionisio, Amelia

    2014-05-01

    The current study aims to conciliate conservation and restoration museology diagnosis with paleontological and geological curational needs and has, as subject of study, dinosaur footprints (vertebrates fossils). The footprints have been being exposed since 2004 in the paleontology hall of the Museum of Lourinhã, Portugal, and are part of a important paleontological collection of Late Jurassic vertebrate fossils from Lourinhã Formation. Presently, it is considered a unique heritage in danger of disappearing due to high decay level of disaggregation of its geological structure. The dinosaur footprints, (ML557) found, more precisely, on a coastline cliff in Lourinhã, Porto das Barcas, Lagido do Forno (coordinate 39° 14. 178'N, 9° 20. 397'W), Jurassic period, on the 5th of June 2001, by Jesper Milàn. This cliff of high slope presents sedimentary stratigraphic characteristics of a sandstone/siltstone of gray and red colors, by the '' Munsell scale and Color Chart''. Geological the tracks are Late Jurassic in age, and colected in the Lourinhã Formation, Praia Azul Member, of the Lusitanian Basin. There are three natural infills tridactyl tracks, possibly ascribed to ornithopod, a bipedal herbivore, resultant of a left foot movement, right and left. Footprints have 300-400mm of wide and 330-360mm of height with round fingers, which are elongated due to some degradation/erosion. In 2001, the footprints were collected from the field, cleaned, consolidated and glued in the laboratory of the Museum of Lourinhã before being exhibited in a museum display. Stone matrix was removed and a consolidation product applied, probably a polyvinyl acetate, of the brand Plexigum. The footprint with broken central digit was glued with an epoxy resin, Araldite. Both applied products were confirmed by analysis of µ-FTIR (Fourier Transform Infrared Spectroscopy) and both presented colour change and detachment surface problems. After collecting and storing, in 2004, footprints were

  16. Zircon ages and Hf isotopic compositions of Ordovician and Carboniferous granitoids from central Inner Mongolia and their significance for early and late Paleozoic evolution of the Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Shi, Yuruo; Jian, Ping; Kröner, Alfred; Li, Linlin; Liu, Cui; Zhang, Wei

    2016-03-01

    We present zircon ages and Hf-in-zircon isotopic data for plutonic rocks and review the evolution of central Inner Mongolia, China, in the early and late Paleozoic. Zircons of a granodiorite yielded a 206Pb/238U age of 472 ± 3 Ma that reflects the time of early Paleozoic magmatism. Zircon ages were also obtained for a tonalite (329 ± 3 Ma), quartz-diorite (320 ± 3 Ma), and granite vein (297 ± 2 Ma). Our results, in combination with published zircon ages and geochemical data, document distinct magmatic episodes in central Inner Mongolia. The dated samples are mostly granodiorite, tonalite and quartz-diorite in composition with intermediate to high-silica, high Na2O (3.08-4.26 wt.%), low K2O (0.89-2.86 wt.%), and high Na2O/K2O and Sr/Y ratios. Their chondrite-normalized REE patterns are characterized by LREE enrichment. In mantle-normalized multi-element variation diagrams they show typical negative Nb and Ta anomalies, and all samples display positive εHf(t) and εNd(t) values, and low ISr. The Ordovician rocks, however, show higher Sr/Y and La/Yb ratios than the Carboniferous samples, implying that the older granitoids represent adakitic granitoids, and the Carboniferous granitoids are typical subduction-related arc granitoids but also with adakite-like compositions. The results are compatible with the view that the Central Asian Orogenic Belt (CAOB) in Inner Mongolia evolved through operation of several subduction systems with different polarities: an early-middle Paleozoic subduction and accretion system along the northern margin of the North China Craton and the southern margin of the Mongolian terrane, and late Paleozoic northward subduction along the northern orogen and exhumation of a high-pressure metamorphic terrane on the northern margin of the North China Craton.

  17. Timing, petrogenesis and tectonic setting of the Late Paleozoic gabbro-granodiorite-granite intrusions in the Shalazhashan of northern Alxa: Constraints on the southernmost boundary of the Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Shi, Xingjun; Wang, Tao; Zhang, Lei; Castro, Antonio; Xiao, XuChang; Tong, Ying; Zhang, Jianjun; Guo, Lei; Yang, Qidi

    2014-11-01

    The Late Paleozoic tectonic setting and location of the southernmost boundary of the Central Asian Orogenic Belt (CAOB) with respect to the Alxa Block or Alxa-North China Craton (ANCC) are debated. This paper presents new geochronological, petrological, geochemical and zircon Hf isotopic data of the Late Paleozoic intrusions from the Shalazhashan in northern Alxa and discusses the tectonic setting and boundary between the CAOB and ANCC. Using zircon U-Pb dating, intrusions can be broadly grouped as Late Carboniferous granodiorites (~ 301 Ma), Middle Permian gabbros (~ 264 Ma) and granites (~ 266 Ma) and Late Permian granodiorites, monzogranites and quartz monzodiorites (254-250 Ma). The Late Carboniferous granodiorites are slightly peraluminous and calcic. The remarkably high zircon Hf isotopes (εHf(t) = + 6-+ 10) and characteristics of high silica adakites suggest that these granodiorites were mainly derived from "hot" basaltic slab-melts of the subducted oceanic crust. The Middle Permian gabbros exhibited typical cumulate textures and were derived from the partial melting of depleted mantle. The Middle Permian granites are slightly peraluminous with high-K calc-alkaline and low εHf(t) values from - 0.9 to + 2.9. These granites were most likely derived from juvenile materials mixed with old crustal materials. The Late Permian granodiorites, monzogranites and quartz monzodiorites are characterized as metaluminous to slightly peraluminous, with variable Peacock alkali-lime index values from calc-alkalic to alkali-calcic. These rocks were mainly derived from juvenile crustal materials, as evidenced by their high εHf(t) values (+ 3.3 to + 8.9). The juvenile sources of the above intrusions in the Shalazhashan are similar to those of the granitoids from the CAOB but distinct from the granitoids within the Alxa Block. These findings suggest that the Shalazhashan Zone belongs to the CAOB rather than the Alxa Block and that its boundary with the Alxa block can be

  18. Source-inherited compositional diversity in granite batholiths: The geochemical message of Late Paleozoic intrusive magmatism in central Calabria (southern Italy)

    NASA Astrophysics Data System (ADS)

    Fiannacca, Patrizia; Cirrincione, Rosolino; Bonanno, Fiorenza; Carciotto, Manuele Mario

    2015-11-01

    The Serre Batholith, in central Calabria, is a Late Paleozoic granitoid complex that makes up the middle portion, ca. 13 km thick, of a continuous and nearly complete section of the continental crust. The batholith displays a large compositional variety, with granitoid rocks ranging with continuity from quartz diorite to syenogranite, a distinct group of leucotonalites also occur. The granitoids are on the whole magnesian and calcic to calc-alkalic, with only some of the more evolved rocks showing a ferroan calc-alkalic to alkali-calcic composition. Quartz diorites and tonalites are metaluminous to weakly peraluminous, while granodiorites and granites are weakly to strongly peraluminous, with two-mica porphyritic types being the only population with a genuine strongly peraluminous character. Fe*-number, MALI and ASI features highlight a strong affinity of the Serre Batholith rocks with Cordilleran granitoids, inherited from the compositions of the source rocks rather than reflecting the real tectonic environment of the magmas. Major trace element and existing Sr-Nd data are consistent with an origin of the Serre Batholith from the assembling of several batches of magmas with specific original compositions derived by fluid-absent melting of different crustal sources. Quartz diorites and tonalites originated from a metabasaltic magma source, whereas metagraywackes with various mafic and pelitic contents appear the most likely sources of weakly peraluminous granodiorites and strongly peraluminous granodiorites and granites. Biotite ± amphibole granodiorites could also have been derived from mafic-intermediate metaigneous sources. Two-mica porphyritic leucogranites are the only rock types representing pure crustal melts, resulting from melting of mafic pelitic sources. The other granitoid compositions are too silica-poor and MgO + FeOt rich to represent pure melts, so they need to include other components, such as solid restitic/peritectic material entrained from the

  19. Sandstone reservoirs

    SciTech Connect

    Weimer, R.J.; Tillman, R.W.

    1982-01-01

    The Rocky Mountain province of the United States contains structural and stratigraphic traps from which petroleum is produced from all types of sandstone reservoirs ranging in age from Cambrian to the Eocene. Three large typical stratigraphic traps in this province, where reservoirs are of Cretaceous age, are described. The Cut Bank Field, Montana produces from aluvial point bar sandstones; Patrick Draw field, Wyoming produces from marine shoreline sandstones; and, Hartzog Draw field, Wyoming produces from marine shelf sandstone. 10 refs.

  20. Sandstone provenance and diagenesis in relation to Late Cretaceous regional depositional systems and paleogeography, Sacramento Basin, CA

    SciTech Connect

    Mertz, K.A. Jr. ); Nilsen, T.H. )

    1990-05-01

    Petrographic modal analyses of sandstone samples from the Upper Cretaceous Guinda, Forbes, Kone, Marsh Creek, Chico, Starky, Winters, and Mokelumne River formations of the Sacramento basin reveal that samples are dominated by plutoniclastic and volcaniclastic detritus, have intermediate plagioclase-to-total=feldspar ratios (0.48-0.65), and have high but variable L{sub v}/L ratios (0.51-0.80). Forbes/Kione sandstones, in comparison to Starkey/Winters samples, have higher proportions of volcaniclastic (plagioclase) to plutoniclastic (Q{sub m}, K) detritus and higher W{sub p}/total Q and L{sub m}/L{sub v} ratios. The Chico Formation, like the Starkey/Winters, is dominated by plutoniclastic material; in comparison to Forbes/Kione samples, the Chico has higher total lithic values (L{sub t}), especially in the L{sub m} fraction. These data strongly support derivation of the sands from the Cordilleran magmatic arc system to the north and east. Sandstones from the Chico, Starkey, Winters, and Mokelumne River formations were derived primarily from the dissected Sierran magmatic arc complex to the east, with a minor but significant secondary source in foothill belt metamorphic complexes. Forbes and Kione sandstones, in contrast, appear to have been derived from the Idaho Batholith and Blue Mountain regions of Idaho/Oregon to the north and northeast. When corrections are applied to account for significant diagenetic dissolution of plagioclase and compactional alteration of lithic fragments (especially L{sub v}), the dissected or transitional arc provenance for most samples is strengthened. Modal data and paleogeographic reconstructions suggest that during the early and middle Campanian, most detritus in the Sacramento basin was derived from the north/northeast (erosion of the Idaho batholith arc system), reflecting southward progradation of the Kion/Forbes delta-submarine fan system into the longitudinal forearc basin.

  1. Late Paleozoic-Mesozoic tectonic evolution of SW Japan: A review - Reappraisal of the accretionary orogeny and revalidation of the collisional model

    NASA Astrophysics Data System (ADS)

    Charvet, Jacques

    2013-08-01

    This paper makes a review of the interpretations of the tectonic evolution of SW Japan during the last three decades. In the late 1970s, the dominant model was the so-called "Pacific-type orogeny", emphasizing the purported absence of nappes and the contrast with the alpine chains, and interpreting the evolution as due to a steady oceanic subduction since the Paleozoic time. In the 80s, the discovery of the actual structure made of a pile of large thrust sheets led authors to propose collisional models, involving the intermittent underthrusting of buoyant blocks like micro-continents. At the same time, the use of high-resolution biostratigraphy allowed several authors to recognize ancient accretionary wedges, with a reconstructed ocean plate stratigraphy of individual accreted units, especially in the Tanba and Shimanto zones. Also, precise radiometric dating permitted the distinction of metamorphosed units, especially in Sanbagawa and Shimanto belts. As a result of these new data, since the 1990s, the plate tectonic interpretation of the history of the Japanese Islands was revised by Japanese scientists and presented again in terms of accretionary processes linked to a steadily oceanic subduction, with an episodic ridge subduction: the so-called "Miyashiro-type orogeny". The review of different data leads to the following conclusions. The structure of SW Japan is made of a pile of sub-horizontal nappes, polydeformed, with a geometry similar to the one encountered in collisional orogens. The geodynamic mechanisms advocated for the tectonic building within the accretionary orogeny concept (Miyashiro-type orogeny) are inappropriate. A permanent oceanic subduction with the intermittent "collision" (actually subduction) of an active ridge or seamount chain is unable to build such structures, as this process induces in fact an acceleration of the tectonic erosion and collapse of the upper plate; the underthrusting of a micro-continent or mature arc is likely needed. The

  2. 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

  3. Late Paleozoic closure of the Ob-Zaisan Ocean along the Irtysh/Chara shear zone and implications for arc amalgamation and oroclinal bending in the western Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Li, Pengfei; Sun, Min; Rosenbaum, Gideon

    2016-04-01

    The Irtysh/Chara Shear Zone is one of the largest strike-slip systems in the Central Asian Orogenic Belt (CAOB). It records collisional processes of the peri-Siberian orogenic system with the West Junggar-Kazakhstan-Tianshan orogenic system following the closure of the Ob-Zaisan Ocean, but the exact timing of these events remains enigmatic. We conducted detailed structural analysis along the Irtysh Shear Zone (NW China), which together with new geochronological data allows us to reconstruct the tectonic evolution during the final closure of the Ob-Zaisan Ocean. Our results showed that subduction-accretion processes lasted at least until the Late Carboniferous in the Chinese Altai and the East/West Junggar. The subsequent arc amalgamation is characterized by a cycle of crustal thickening, orogenic collapse and transpressional thickening. On a larger scale, the West Junggar- Kazakhstan -Tianshan orogenic system defines a U-shape oroclinal structure (e.g. Xiao et al., 2010). A major phase of oroclinal bending that involved ~110° rotation may have occurred during the Late Devonian to Early Carboniferous (Levashova et al., 2012). Previous authors have linked oroclinal bending with the late Paleozoic amalgamation of the western CAOB, and proposed that a quasi-linear West Junggar- Kazakhstan -Tianshan orogenic system was buckled during the convergence of the Siberian and Tarim cratons following the closure of the Ob-Zaisan Ocean (in the north) and the South Tianshan Ocean (in the south) (e.g. Abrajevitch et al., 2008). This model, however, is not supported by our new data that constrain the closure of the Ob-Zaisan Ocean to the Late Carboniferous. Alternatively, we propose that oroclinal bending may have involved two phases of bending, with the ~110° rotation in the Late Devonian to Early Carboniferous possibly associated with trench retreat. Further tightening may have occurred in response to the convergence of the Siberian and Tarim cratons during the Late

  4. Evolution of the late Paleozoic accretionary complex and overlying forearc-magmatic arc, south central Chile (38°-41°S): Constraints for the tectonic setting along the southwestern margin of Gondwana

    NASA Astrophysics Data System (ADS)

    Martin, Mark W.; Kato, Terence T.; Rodriguez, Carolina; Godoy, Estanislao; Duhart, Paul; McDonough, Michael; Campos, Alberto

    1999-08-01

    Stratigraphic, structural, metamorphic, and geochronologic studies of basement rocks in the Andean foothills and Coast Ranges of south central Chile (39°-41°S) suggest a protracted late Paleozoic to middle Mesozoic deformational and metamorphic history that imposes important constraints on the tectonic development of the southwestern Gondwana margin. In the study area the late Paleozoic paired metamorphic belt, coeval magmatic arc, and overlying Triassic sedimentary units preserve a record of Late Carboniferous to Early Permian subduction and arc magmatism, subsequent deep exhumation of the Western Series subduction complex, and diminished uplift and erosion of the Eastern Series arc-forearc region by the Late Triassic. Late Paleozoic structural elements and metamorphic assemblages formed during early subduction and arc magmatism, collectively referred to as Dl, are largely erased in the Western Series by the dominant D2 schistosity and lower greenschist grade metamorphism. D1 structural features, as well as original sedimentary textures, are relatively well preserved in the less penetratively deformed Eastern Series. The regional distribution of late Paleozoic arc magmatism suggests that the late Paleozoic convergent margin deviated from a N-S trend north of this area to a NW-SE trend near this latitude and faced an open marine environment to the southwest. A transition from F2 isoclinal folding to more open, larger-scale F3 folds, interpreted as change in ductility during differential uplift of the Western Series, is not apparent in the Eastern Series. Despite a lesser degree of uplift during the main exhumational D2 event, delineation of unconformities and U-Pb dating of detrital zircons and intrusions into the Eastern Series allow tighter constraints to be placed on timing of uplift and denudation of the Eastern Series than on that in the Western Series. A regional unconformity exposed in the Lake District that separates more highly deformed Eastern Series

  5. Detrital zircon U-Pb ages and Hf isotopes of Permo-Carboniferous sandstones in central Inner Mongolia, China: Implications for provenance and tectonic evolution of the southeastern Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Chen, Yan; Zhang, Zhicheng; Li, Ke; Yu, Haifei; Wu, Tairan

    2016-03-01

    The tectonic setting of the southeastern Central Asian Orogenic Belt (CAOB) during the Late Paleozoic has been debated for many years. Provenance analysis of Permo-Carboniferous sedimentary rocks can effectively address this issue. In this study, eight sandstone samples were collected for zircon U-Pb and Lu-Hf isotopic analyses combined with petrographic analysis. Framework petrography and zircon morphology suggest that the samples were from recycled orogen of an igneous origin. Carboniferous rocks, with a significant age peak at 432 Ma and εHf (t) values of - 9.0 to 13.6, were mainly derived from Early to Mid-Paleozoic magmatic rocks and deposited in a piedmont zone, namely, the margin of an inland sea. Permian rocks, mostly with age peaks at 445 Ma and/or 280 Ma and εHf (t) values of - 25.2 to 11.4, dominantly originated from a pre-existing Early to Mid-Paleozoic magmatic arc and Late Paleozoic igneous rocks. These rocks formed in restricted basins of the piedmont and intermountain zones. Based on zircon spectral discrimination, sedimentary environmental analysis, and previous studies, this study supports the interpretation that the southeastern CAOB entered stages of extension and rifting during the Late Paleozoic. In the end, this study proposes a tectonic-paleogeographic reconstruction to explain the tectonic evolution of the southeastern CAOB and the exhumation-transportation-deposition processes between the basins and ranges developed in this orogen.

  6. Detrital modes of the Pyeongan Supergroup (Late Carboniferous Early Triassic) sandstones in the Samcheog coalfield, Korea: implications for provenance and tectonic setting

    NASA Astrophysics Data System (ADS)

    Lee, Yong Il; Sheen, Dong-Hee

    1998-08-01

    Medium to coarse sandstones of the Carboniferous to Early Triassic Pyeongan Supergroup in the Samcheog coalfield, Korea, were studied to infer the provenance and tectonic settings of the source areas. Sandstone detrital modes change upwards stratigraphically. Sandstone types from the Manhang to Dosagog formations low to middle in the sequence are quartzarenite, and sublitharenite to litharenite, whereas sandstones of the Gohan and Donggo formations high in the sequence are feldspathic litharenite and arkose, respectively. Using various ternary diagrams, the provenance of the Manhang to Gohan formations is suggested to be a recycled orogen setting. Some Gohan Formation sandstones plot within the arc-related setting field, and the Donggo Formation sandstones plot within both continental block and recycled orogen fields. Results of quartz grain petrography are consistent with those of detrital modes. Quartz in sandstones of all units except the Donggo Formation indicates derivation from low-rank metamorphic sources. Quartz in Donggo sandstones was derived from medium- to high-rank metamorphic and plutonic source rocks. Considering the sandstone composition and palaeocurrent data, the Pyeongan Supergroup probably was deposited in a molasse foreland basin and was derived from a synbasinal orogenic belt, probably the Akiyoshi orogen located in southwest Japan.

  7. First results of U-Pb dating of detrital zircons from the Upper Ordovician sandstones of the Bashkir uplift (Southern Urals)

    NASA Astrophysics Data System (ADS)

    Kuznetsov, N. B.; Belousova, E. A.; Degtyarev, K. E.; Pyzhova, E. S.; Maslov, A. V.; Gorozhanin, V. M.; Gorozhanina, E. N.; Romanyuk, T. V.

    2016-04-01

    The first results of U-Pb dating of detrital zircons from Upper Ordovician sandstones of the Bashkir uplift in the Southern Urals and U-Pb isotopic ages available for detrital zircons from six stratigraphic levels of the Riphean-Paleozoic section of this region are discussed. It is established that the long (approximately 1.5 Ga) depositional history of sedimentary sequences of the Bashkir uplift includes a peculiar period lasting from the Late Vendian to the Emsian Age of the Early Devonian (0.55-0.41 Ga). This period is characterized by the following features: (1) prevalence of material from eroded Mesoproterozoic and Early Neoproterozoic crystalline complexes among clastics with ages atypical of the Volga-Urals segment of the East European Platform basement; (2) similarity of age spectra obtained for detrital zircons from different rocks of the period: Upper Vendian-Lower Cambrian lithic sandstones and Middle Ordovician substantially quartzose sandstones.

  8. 40Ar/39Ar dating of basaltic dykes swarm in Western Cameroon: Evidence of Late Paleozoic and Mesozoic magmatism in the corridor of the Cameroon Line

    NASA Astrophysics Data System (ADS)

    Tchouankoue, Jean Pierre; Simeni Wambo, Nicole Armelle; Kagou Dongmo, Armand; Li, Xian-Hua

    2014-05-01

    40Ar/39Ar ages of three basalt dykes that intrude the Precambrian basement in the southern continental part of the Cretaceous Cameroon Line are presented. Specimen were sampled at Dschang, Maham and Kendem (Cameroon). The ages obtained are 421.3 ± 3.5 Ma (Dschang), 404.22 ± 3.51 Ma (Maham), and 192.10 ± 7.45 Ma (Kendem). The Dschang and Maham samples yield a relatively undisturbed spectrum while the Kendem sample shows an excess of argon but with plateau ages in the frame of the Mesozoic. Plateau ages at Dschang, Maham and Kendem represent more than 80% of the total 39Ar released and are interpreted as emplacement ages. 40Ar/39Ar dating results confirm Devonian and Jurassic K/Ar ages obtained from similar dykes of the same region. Geochemically, the basalt dykes are subalkaline in composition with 45-50 wt.% SiO2. Incompatible trace elements and rare earth elements are lower than that of the Cameroon Line basalts. Overall geochemical characteristics of the basalt dykes much more closely resemble those of tholeiites of the Benue Through in Nigeria that are interpreted as related to the opening of the Atlantic Ocean. The combination of 40Ar/39Ar ages, major, trace and rare earth elements geochemistry data demonstrate a magmatic phase that is significantly older and different of that of the Cretaceous Cameroon Line and younger than the dominantly granitic Neoproterozoic to early Paleozoic magmatism in the region. These findings offer new clues for a better understanding of the tectonic history of the region, particularly the origin of the Cameroon Line and Africa-South America pre-drift reconstitutions.

  9. Provenance of Gebel El-Zeit sandstones, gulf of Suez, Egypt

    NASA Astrophysics Data System (ADS)

    Abdel-Wahab, Antar A.

    1992-01-01

    The Paleozoic elastic succession at Gebel Zeit chiefly consists of fine- to medium-grained quartz arenite, locally containing well-rounded quartz pebbles. The marine Araba Formation (Early Cambrian) was deposited during transgression over a Precambrian granite. The overlying Naqus Formation (Late Cambrian) is fluvial, except for the uppermost few meters. Paleocurrent data for the Araba and Naqus formations indicate derivation from the north-northeast and south-southwest respectively. Quartz typology, other morphologic features of quartz, and mineral inclusions in quartz, as well as the study of heavy minerals were used to determine the provenance of the sandstones. Quartz typology successfully identified a granitic source for the Araba Formation. A combination of parameters indicates that the Naqus Formation was derived chiefly from a metamorphic terrain. Two ratios, polycrystalline/monocrystalline quartz and undulose/non-undulose quartz, successfully distinguish sandstones of the Araba Formation from those of the Naqus Formation. These values are 0.14 and 0.25 for Araba sandstones and 0.26 and 0.46 for Naqus sandstones, respectively. These differences either reflect different source rocks, or have resulted from selective abrasion loss of polycrystalline quartz in the rigorous surf zone during the marine transgression that deposited the Araba Formation.

  10. Permian tectonism in Rocky Mountain foreland and its importance in Exploration for Minnelusa and Lyons sandstones

    SciTech Connect

    Moore, W.R.

    1985-05-01

    Permian sandstones are important producers of oil in the Powder River and Denver basins of the Rocky Mountain foreland region. In the Powder River basin, Wolfcampian Minnelusa Sandstone produces oil from structural and stratigraphic traps on both sides of the basin axis, whereas in Denver basin, the Leonardian Lyons Sandstone produces oil mainly from structural traps on the west flank of the basin. Two fields, North Fork-Cellars Ranch in the Powder River basin, and Black Hollow in the Denver basin, are examples of Permian growth of structural features. At North Fork-Cellars Ranch, a period of Permian structural growth and resultant differential sedimentation is documented by structure and isopach maps of the Minnelusa and overlying Goose Egg Formation. Structural growth began at the end of Minnelusa deposition and resulted in deposition of a much thicker Goose Egg section on the west flank of the field. At Black Hollow, mapping indicates structural growth was initiated before deposition of the Lyons Sandstone and continued throughout Leonardian time. In both fields growth abruptly ceased in the Late Permian. Both North Fork-Cellars Ranch and Black Hollow are located on structural highs, or arches, which trend east-west across the Powder River and Denver basins. These arches were present during the pre-Laramide migration of Paleozoic-sourced hydrocarbons into the basins and acted as pathways for migration. Exploration for Permian reservoirs in the two basins should be concentrated on the arches, as the early formed traps were present when migration began.

  11. The Paleozoic world: Continental flooding, hypsometry, and sea level

    SciTech Connect

    Algeo, T.J. . Dept. of Geology); Seslavinsky, K.B. ); Wilkinson, B.H. . Dept. of Geological Sciences)

    1992-01-01

    Absolute amplitudes of Paleozoic sea-level fluctuations are poorly known: two major curves show eustatic maxima of +300 m (Vail et al. 1977) and +600 m (Hallam 1984). Based on analysis of the flooding records of thirteen Paleozoic landmasses, the authors estimate that sea-level elevations were substantially lower than previously thought, ca. 50--220 m for most of the Paleozoic. The analysis also shows that: (1) small continents are inherently more floodable than large continents, (2) there is no difference in mean flooding of continents of a given size between the Early and Late Paleozoic, and (3) reduced global flooding during the Late Paleozoic is primarily attributable to the existence of a few large continents, rather than many small ones as during the Early Paleozoic. Global sea-level trends reflect the division of the Paleozoic into two geotectonic subcycles comprising the Cambro-Silurian (terminated by the Taconic/Caledonian Orogeny). Deviations of individual continents from the mean global curve are due to changes in hypsometry associated with tectonic/epeirogenic events. For example, a major Early Silurian regression on Laurentia resulted from the Taconic Orogeny, while large Early Ordovician and Middle-Late Devonian regressions on Gondwana are associated with rifting of the North China and South China/Indochina blocks.

  12. Paleozoic Hydrocarbon-Seep Limestones

    NASA Astrophysics Data System (ADS)

    Peckmann, J.

    2007-12-01

    To date, five Paleozoic hydrocarbon-seep limestones have been recognized based on carbonate fabrics, associated fauna, and stable carbon isotopes. These are the Middle Devonian Hollard Mound from the Antiatlas of Morocco [1], Late Devonian limestone lenses with the dimerelloid brachiopod Dzieduszyckia from the Western Meseta of Morocco [2], Middle Mississippian limestones with the dimerelloid brachiopod Ibergirhynchia from the Harz Mountains of Germany [3], Early Pennsylvanian limestones from the Tantes Mound in the High Pyrenees of France [4], and Late Pennsylvanian limestone lenses from the Ganigobis Shale Member of southern Namibia [5]. Among these examples, the composition of seepage fluids varied substantially as inferred from delta C-13 values of early diagenetic carbonate phases. Delta C-13 values as low as -50 per mil from the Tantes Mound and -51 per mil from the Ganigobis limestones reveal seepage of biogenic methane, whereas values of -12 per mil from limestones with Dzieduszyckia associated with abundant pyrobitumen agree with oil seepage. Intermediate delta C-13 values of carbonate cements from the Hollard Mound and Ibergirhynchia deposits probably reflect seepage of thermogenic methane. It is presently very difficult to assess the faunal evolution at seeps in the Paleozoic based on the limited number of examples. Two of the known seeps were typified by extremely abundant rhynchonellide brachiopods of the superfamily Dimerelloidea. Bivalve mollusks and tubeworms were abundant at two of the known Paleozoic seep sites; one was dominated by bivalve mollusks (Hollard Mound, Middle Devonian), another was dominated by tubeworms (Ganigobis Shale Member, Late Pennsylvanian). The tubeworms from these two deposits are interpreted to represent vestimentiferan worms, based on studies of the taphonomy of modern vestimentiferans. However, this interpretation is in conflict with the estimated evolutionary age of vestimentiferans based on molecular clock methods

  13. Sedimentology and petroleum occurrence, Schoolhouse Tongue of Weber Sandstone (lower Permian), Northwest Colorado

    SciTech Connect

    Johnson, S.Y.; Schenk, C.J.; Anders, D.E.; Tuttle, M.L.

    1988-01-01

    The Schoolhouse Tongue of the Weber Sandstone, an extensive paleo-petroleum reservoir in northwest Colorado, consists mainly of bleached or oil-stained sandstone of inferred eolian sand-sheet origin. Low-angle to parallel-bedded, very fine to fine-grained sandstone is the dominant facies. Low-angle deflationary surfaces and deflation lags are common. Cross-bedded dune deposits are a less common sand-sheet facies. Interbedded fluvial deposits are present in most sections. The sand-sheet deposits of the Schoolhouse Tongue are sedimentologically similar to those in the gradationally underlying red beds of the Middle Pennsylvanian to Lower Permian Maroon Formation, and the Schoolhouse Tongue is best constructed as the uppermost sand sheet in the Maroon sequence. At Rifle Creek, the site of a late Paleozoic-early Mesozoic structural high, the Schoolhouse Tongue is 66 m thick and oil staining extends several hundred meters down into the underlying Maroon Formation. Away from Rifle Creek, the Schoolhouse Tongue thins to the north and pinches out to the southeast and east (within 40-65 km), and oil staining in the Maroon is minimal. The distribution of oil-stained rock suggests that hydrocarbons were introduced at a point source, possibly related to faults on the margins of the paleohigh. Oil in the Schoolhouse Tongue mainly occurs in secondary pore space resulting from the dissolution of carbonate cement by migrating organic acids. Oil was trapped below overlying red siltstones. Geochemical typing of the hydrocarbons is consistent with a late Paleozoic source rock.

  14. A review of the geological characteristics and geodynamic setting of Late Paleozoic porphyry copper deposits in the Junggar region, Xinjiang Uygur Autonomous Region, Northwest China

    NASA Astrophysics Data System (ADS)

    Yang, Fuquan; Mao, Jingwen; Pirajno, Franco; Yan, Shenghao; Liu, Guoren; Zhou, Gang; Zhang, Zhixin; Liu, Feng; Geng, Xinxia; Guo, Chunli

    2012-04-01

    In this review, we describe the geological characteristics of porphyry copper deposits in Junggar region, Xinjiang, and place these into their metallogenic-tectonic context. These porphyry copper deposits are mainly found in four metallogenic belts: (1) a Late Silurian to Early Devonian Cu-Mo metallogenic belt in the Qiongheba area; (2) the Late Devonian Kalaxiange'er Cu metallogenic belt; (3) the Early Carboniferous Xilekuduke-Suoerkuduke porphyry-skarn Cu-Mo metallogenic belt; and (4) the Late Carboniferous Baogutu porphyry Cu metallogenic belt. The ages of mineralization can be divided into three broad intervals: <427-409 Ma, 378-374 Ma and 327-310 Ma. Homogenization temperatures of fluid inclusions in the porphyry copper deposits range mainly from 300 to 180 °C. Salinity ranges from 0.5 to 21.7 wt.% NaCl equiv and 28.9 to 66.76 wt.% NaCl equiv. Ore-forming fluids in the Baogutu and Yunyingshan deposits in the Baogutu and Qiongheba belts, were mainly derived from magmatic fluids, whereas those in the Halasu, Yulekenhalasu and Xilekuduke deposits in the Kalaxiange'er and Xilekuduke-Suoerkuduke belts were mainly derived from magmatic fluids, with some contributions from meteoric water. Sulfur isotope compositions of some porphyry copper deposits cluster around 0‰, indicating that the sulfur was probably derived from mantle-related magmas. The ore-forming processes in all porphyry copper deposits are closely related to the emplacement of intermediate, intermediate-felsic and felsic porphyry intrusions. Porphyry copper deposits in Junggar region developed in a range of tectonic regimes including continental arc, ocean island arc and post collisional settings.

  15. Reservoir quality and diagenetic evolution of Upper Mississippian rocks in the Illinois Basin; influence of a regional hydrothermal fluid-flow event during late diagenesis

    USGS Publications Warehouse

    Pitman, Janet K.; Henry, Mitchell E.; Seyler, Beverly

    1998-01-01

    Conventional reservoir quality data for more than 300 wells provided by the Illinois and Indiana State Geological Surveys were analyzed to determine the factors governing porosity and permeability in the Upper Mississippian Bethel Sandstone and Cypress Sandstone, two of the principal producing units in the Illinois Basin. In addition, approximately 150 samples of the Bethel Sandstone-Cypress Sandstone interval from about 80 wells in the Illinois Basin were collected for mineralogical and geochemical analysis to reconstruct the burial and diagenetic history and to establish the timing of diagenesis relative to the entrapment of hydrocarbons. One aspect of the study involved linking inorganic and organic diagenesis to late Paleozoic tectonism and hydrothermal fluid-flow events in the region.

  16. Geochronology and geochemistry of late Paleozoic magmatic rocks in the Yinwaxia area, Beishan: Implications for rift magmatism in the southern Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Zheng, Rongguo; Wu, Tairan; Zhang, Wen; Meng, Qingpeng; Zhang, Zhaoyu

    2014-09-01

    since Early Devonian, and then changed into a continental rift stage around late Carboniferous-early Permian.

  17. Structural and kinematic evolution of the Yukon-Tanana upland tectonites, east-central Alaska: A record of late Paleozoic to Mesozoic crustal assembly

    USGS Publications Warehouse

    Hansen, V.L.; Dusel-Bacon, C.

    1998-01-01

    The Yukon-Tanana terrane, the largest tectonostratigraphic terrane in the northern North American Cordillera, is polygenetic and not a single terrane. Lineated and foliated (L-S) tectonites, which characterize the Yukon-Tanana terrane, record multiple deformations and formed at different times. We document the polyphase history recorded by L-S tectonites within the Yukon-Tanana upland, east-central Alaska. These upland tectonites compose a heterogeneous assemblage of deformed igneous and metamorphic rocks that form the Alaskan part of what has been called the Yukon-Tanana composite terrane. We build on previous kinematic data and establish the three-dimensional architecture of the upland tectonites through kinematic and structural analysis of more than 250 oriented samples, including quartz c-axis fabric analysis of 39 samples. Through this study we distinguish allochthonous tectonites from parautochthonous tectonites within the Yukon-Tanana upland. The upland tectonites define a regionally coherent stacking order: from bottom to top, they are lower plate North American parautochthonous attenuated continental margin; continentally derived marginal-basin strata; and upper plate ocean-basin and island-arc rocks, including some continental basement rocks. We delineate three major deformation events in time, space, and structural level across the upland from the United States-Canada border to Fairbanks, Alaska: (1) pre-Early Jurassic (>212 Ma) northeast-directed, apparent margin-normal contraction that affected oceanic rocks; (2) late Early to early Middle Jurassic (>188-185 Ma) northwest-directed, apparent margin-parallel contraction and imbrication that resulted in juxtaposition of the allochthonous tectonites with parautochthonous continental rocks; and (3) Early Cretaceous (135-110 Ma) southeast-directed crustal extension that resulted in exposure of the structurally deepest, parautochthonous continental rocks. The oldest event represents deformation within a west

  18. Eolian Signal of the Onset of the Late Paleozoic Ice Age in North America Re-Deposited and Preserved As Paleo-Cave Sediments, Southwestern Colorado, U.S.a.

    NASA Astrophysics Data System (ADS)

    Evans, J. E.; Soreghan, M. J.

    2014-12-01

    The Molas Formation is a loessite consisting of reddish silt of Early Pennsylvanian (Bashkirian) age. U-Pb age spectra of accessory zircons indicate long-distance (>2000 km) transport from the Grenville province in northeastern North America plus sources from the peri-Gondwanan terranes in southeastern North America and local sources in the Ancestral Rocky Mountains uplift. These eolian sediments formed a blanket deposit <30 m thick above a paleokarst landscape in southwestern Colorado, infilling solution valleys and burying karst towers developed on the underlying Mississippian (Tournaisian-Visean) Leadville Limestone. The loessite is an eolian signal for the probable onset of glaciation at multiple locations in tectonically uplifted mountainous areas in North America. However, the loessite is easily eroded and has low preservation potential. Prior to lithification, significant amounts of the loess were remobilized and transported into the underlying karst system. As paleo-cave deposits, encased in limestone and dolostone, the silt-rich deposits have a higher preservation potential, and the eolian signal of the onset of the Late Paleozoic Ice Age in North America is still recognizable. However, the following signal modification processes need to be understood: (1) source area weathering and pedogenesis; (2) land-atmosphere transfer processes; (3) deposition effects of paleotopography, vegetation and moisture conditions, and infiltration into open fractures and/or the matrix of colluvium; (4) remobilization by surface runoff into open fractures and/or groundwater piping/sapping processes in loess soils; (5) transport into vadose and phreatic karst passageways by episodic ("streamflood") hydrologic events, forming event deposits (debrites, inundites, and jointites); (6) breakout dome collapse (forming interbedded cave sediments, karst breccias, and speleothems); (7) lithification and diagenesis; (8) post-lithification modification including pervasive hydrothermal

  19. Jurassic sandstone from the tropical atlantic.

    PubMed

    Fox, P J; Heezen, B C; Johnson, G L

    1970-12-25

    The oldest sediment yet sampled from the abyssal margins of South America, late Jurassic (or possibly very early Cretaceous) shallow-water, coarse-grained, calcareous sandstone containing palynomorphs and mollusk prisms, was recovered from a depth of 4400 meters on the seaward scarp of the Demerara Plateau. The sandstone was deposited in a shallow, late Jurassic epicontinental sea after the initial stages of rifting when the newly created Atlantic began to founder.

  20. Morrow fluvial and deltaic sandstones of Anadarko basin in southeastern and east-central Colorado

    SciTech Connect

    Patterson, E.; Cruthis, W.

    1985-05-01

    Paleozoic sediments in southeastern and east-central Colorado were deposited in the northwest portion of the Anadarko basin. The primary hydrocarbon reservoirs are fluvial and/or deltaic sandstones that represent late regressive cycles of Morrowan sedimentation in the Anadarko basin. The associated transgressive cycles resulted in deposition of marine shales above and below the sandstones. These shales are the source rock in which oil was generated. Morrowan point bars, bar fingers, and the Keyes Formation are productive in the study area along with 11 other formations, both younger and older. Deeper objectives, such as the Arbuckle Limestone and Misner Sandstone, have had limited penetrations and were mostly off-structure tests. The primary objectives of earlier wells in the area were the Mississippian reservoirs. Many of these wells were located on seismic highs or randomly drilled along the Las Animas arch. One reason that better oil production from Morrowan point bars was not found in earlier tests was a lack of understanding of the depositional history of the region. The primary objectives of current wells being drilled in the area are the numerous Morrowan point bars, which are located by stratigraphic seismic methods along with a thorough understanding of the geologic framework in the study area. The point bars have excellent reservoir qualities, with porosities ranging from 18 to 22% and permeabilities as high as 5500 md being reported. Point bars have been defined that cover over 3000 ac and can be penetrated above 6500 ft (1981 m).

  1. Shelf sandstones of Twowells tongue, Dakota sandstone, northwestern New Mexico

    SciTech Connect

    Wolter, N.R.; Nummedal, D.

    1988-02-01

    The Dakota Sandstone of northwestern New Mexico is composed of basal continental strata and three marine sandstone tongues, which intertongue with the Mancos Shale. The late Cenomanian Twowells tongue was the last tongue deposited in the Dakota transgressive systems tract. This tongue is most commonly gradationally underlain by the Whitewater Arroyo shale tongue and abruptly overlain by the Rio Salado tongue of the Mancos Shale. Data collected from 85 outcrop sections and 180 electric well logs, from the San Juan, Acoma, and Zuni basins, indicates that the Twowells tongue represents three phases of marine deposition.

  2. The Paleozoic petroleum geology of central Arabia

    SciTech Connect

    McGillivray, J.G.; Husseini, M.I. )

    1991-08-01

    Recent exploratory drilling in central Saudi Arabia indicates that all the geological elements of a major petroleum basin are present in this province. Several Paleozoic siliciclastic sequences which were deposited along the stable Arabian margin of Gondwanaland constitute excellent reservoirs. The identified reservoir targets include the Cambrian-Ordovician Saq Formation, Upper Ordovician-Lower Silurian glaciogenic clastics of the Sarah and Zarqa formations, and both fluvial and shallow marine sandstones of the Permian-Carboniferous Unayzah Formation. The source rock is a widespread organic-rich shale which was deposited during the regional deglaciation in the earliest Silurian. Migration occurred vertically along faults and/or updip from the regional Qusaiba shale subcrop through the reservoirs. Interbedded upper Permian shales and evaporites form the basal sequence of a major carbonate transgression and provide a capping seal. The traps are broad, low-relief, fault-generated structures which developed primarily during the Triassic.

  3. A paleozoic pangaea.

    PubMed

    Boucot, A J; Gray, J

    1983-11-11

    Paleozoic paleogeographies should be consistent with all available, reliable data. However, comparison of three different Devonian paleogeographies that are based largely or wholly on the data of remanent magnetism show them to be inconsistent in many regards. When these three paleogeographies are provided with possible ocean surface current circulation patterns, and have added to them lithofacies and biogeographic data, they also are shown to be inconsistent with such data. A pangaeic reconstruction positioned in the Southern Hemisphere permits the lithofacies and biogeographical data to be reconciled in a plausible manner.

  4. Late Paleozoic structural evolution of Permian basin

    SciTech Connect

    Ewing, T.E.

    1984-04-01

    The southern Permian basin is underlain by the NNW-trending Central Basin disturbed belt of Wolfcamp age (Lower Permian), the deep Delaware basin to its west, and the shallower Midland basin to its eat. The disturbed belt is highly segmented with zones of left-lateral offset. Major segments from south to north are: the Puckett-Grey Ranch zone; the Fort Stockton uplift; the Monahans transverse zone; the Andector ridges and the Eunice ridge; the Hobbs transverse zone; and the Tatum ridges, which abut the broad Roosevelt uplift to the north. The disturbed belt may have originated along rift zones of either Precambrian or Cambrian age. The extent of Lower and Middle Pennsylvanian deformation is unclear; much of the Val Verde basin-Ozona arch structure may have formed then. The main Wolfcamp deformation over thrust the West Texas crustal block against the Delaware block, with local denudation of the uplifted edge and eastward-directed backthrusting into the Midland basin. Latter in the Permian, the area was the center of a subcontinental bowl of subsidence - the Permian basin proper. The disturbed belt formed a pedestal for the carbonate accumulations which created the Central Basin platform. The major pre-Permian reservoirs of the Permian basin lie in large structural and unconformity-bounded traps on uplift ridges and domes. Further work on the regional structural style may help to predict fracture trends, to assess the timing of oil migration, and to evaluate intrareservoir variations in the overlying Permian giant oil fields.

  5. Ordovician and Late Paleozoic Early Mesozoic tectonothermal history of the La Noria area, northern Acatlán Complex, southern Mexico: Record of convergence in the Rheic and paleo-Pacific Oceans

    NASA Astrophysics Data System (ADS)

    Hinojosa-Prieto, H. R.; Nance, R. D.; Keppie, J. D.; Dostal, J. V.; Ortega-Rivera, A.; Lee, J. K. W.

    2008-12-01

    muscovite plateau ages probably closely post-date the D 2 event. D 1 may be correlated with early Carboniferous deformation elsewhere in the Acatlán Complex. On the other hand, the initial 40Ar/ 39Ar steps at ca. 300, 220 and 172 Ma probably indicate thermal disturbances below 300 °C during the Permo-Carboniferous, Triassic and Jurassic, respectively. Whereas the Ordovician history of the plutons and volcano-sedimentary units coincides with the lifespan of both the Iapetus and Rheic oceans, the Late Paleozoic-Early Mesozoic deformation better reflects closure of the Rheic Ocean and convergence tectonics on the paleo-Pacific margin following the amalgamation of Pangea.

  6. Petrology and stratigraphy of Paleogene nonmarine sandstones, Cascade Range, Washington

    USGS Publications Warehouse

    Frizzell, Virgil A.

    1979-01-01

    The Cascade Range of Washington north of 47? latitude is composed of probable Paleozoic and Mesozoic metamorphic rocks and Mesozoic and Tertiary plutonic rocks. Several Paleogene nonmarine arkosic sandstone units fringe and in part occur within the complex crystalline core. The early to middle Eocene Chuckanut Formation is present on the west side of the crystalline core in the western foothills of the Cascades. The early to middle Eocene Swauk Formation partially encircles the Mt. Stuart massif of the central Cascades. In the western foothills of the Cascades, between the main body of Chuckanut Formation near Bellingham and the main outcrop area of the Swauk Formation south of Mt. Stuart, many smaller bodies of arkosic sandstone have variously been referred to either the Swauk or Chuckanut Formations. The early Eocene Manastash Formation occurs locally in an area south of the Yakima River. The middle to late Eocene Chumstick Formation is mostly confined to the Chiwaukum graben within the crystalline core and is separated from the Swauk Formation on the southwest by the Leavenworth Fault. The Oligocene Wenatchee Formation unconformably over lies the Chumstick Formation near Wenatchee. The middle to late Eocene Roslyn Formation crops out north of the Yakima River and is underlain by the Teanaway Basalt which separates the Roslyn from the older Swauk Formation. The middle Eocene to early Oligocene Naches Formation forms a north-trending body that crosses the Yakima River and is in fault contact with both the Swauk and Manastash Formations. The middle to late Eocene Puget Group underlies the Quaternary deposits of the Puget Lowland southeast of Seattle on the western flank of the Cascades. The various formations are all composed predominantly of fine- to medium-grained sandstones with lesser amounts of interbedded shale, conglomerate and coal. Compositionally, the units are predominantly either feldspathic or litho-feldspathic subquartzose sandstones. Volcanic rocks

  7. Late Paleozoic tectono-metamorphic evolution of the Altai segment of the Central Asian Orogenic Belt: Constraints from metamorphic P-T pseudosection and zircon U-Pb dating of ultra-high-temperature granulite

    NASA Astrophysics Data System (ADS)

    Li, Zilong; Yang, Xiaoqiang; Li, Yinqi; Santosh, M.; Chen, Hanlin; Xiao, Wenjiao

    2014-09-01

    Ultra-high-temperature (UHT) granulite-facies rocks offer important constraints on crustal evolution processes and tectonic history of orogens. UHT granulites are generally rare in Phanerozoic orogens. In this study, we investigate the late Paleozoic pelitic UHT granulites from Altai in the western segment of the Central Asian Orogenic Belt (CAOB). The diagnostic minerals in these rocks include high alumina orthopyroxene (Al2O3 up to 9.76 wt.%, and y(opx) = AlVI in orthopyroxene up to 0.21) coexisting with sillimanite and quartz, and low Zn spinel (ZnO = 1.85-2.50 wt.%) overgrowth with quartz. Cordierite corona separates sillimanite from orthopyroxene. The high alumina orthopyroxene is replaced by symplectites of low-alumina orthopyroxene (~ 5.80 wt.% Al2O3) and cordierite. These textural observations are consistent with a significant decompression following the peak UHT metamorphism. Phase equilibrium modeling using pseudosections and the y(opx) isopleths indicate an anti-clockwise P-T path for the exhumation of the Altai orogenic belt. The pre-peak assemblage of spinel + quartz in garnet is stable at high- to ultra-high-temperature and low-pressure conditions (P < 5.8 kbar at T ~ 900 °C). The peak P-T values recorded by high aluminium orthopyroxene is > 940 °C and 7.8 to 10 kbar. Subsequent near-isothermal decompression occurred at 890 to 940 °C and 5 to 6 kbar. The final-stage cooling is recorded at 750 and 800 °C and 4 to 5 kbar accompanied by a decrease in the y(opx) values (0.11-0.12). In the UHT granulite, zircon grains are commonly enclosed within cordierite. The overgrowth rims of the zircon grains yield a weighted mean 206Pb/238U age of 277 ± 2 Ma using LA-ICP-MS zircon dating, which is interpreted to mark the timing of decompression and cooling. We propose that the anti-clockwise P-T path of the UHT granulite in the Altai orogenic belt could be related to an extensional event related to the sinistral strike-slip along the Irtish tectonic belt after

  8. Paleozoic paleogeographic and depositional developments on the central proto-Pacific margin of Gondwana: Their importance to hydrocarbon accumulation

    NASA Astrophysics Data System (ADS)

    Gohrbandt, K. H. A.

    1992-11-01

    During the Paleozoic Era, the western portion of the Gondwana continent between the equator and latitude 27°S of present-day South America bordered the proto-Pacific Ocean as a predominantly convergent margin. Following the Middle Cambrian accretion of the Arequipa-Belen-Antofalla Terrane, an epicontinental sea with communication to the proto-Pacific Ocean established itself along the length of the western margin of Gondwana during Late Cambrian and Early Ordovician time. The emergence of a proto-Cordillera led to significant separation of the epicontinental sea from the proto-Pacific Ocean during Silurian and Devonian times. Gradual erosion of that proto-Cordillera during Carboniferous and Early Permian time once again facilitated widespread transgression of the proto-Pacific Ocean into the epicontinental domain. At the end of the Early Permian, the sea retreated from Gondwana and a proto-Cordillera was re-established. The proto-Cordillera and the craton of Gondwana controlled sediment type and distribution in the epicontinental sea. Deposition occurred in five tectono-sedimentary cycles, which were separated by orogenic pulses that resulted in regional erosion of the previously deposited section. Oil and gas have been produced from the Paleozoic epicontinental sediments of Argentina, Bolivia, Peru, and Brazil, in an area in which exploration efforts are ongoing. Sandstone reservoirs and argillaceous source rocks of commercial importance formed during the episodes of sedimentation, but carbonates do not contribute to commercial hydrocarbon generation and accumulation. Cap rocks are provided by shales or evaporites.

  9. Paleozoic unconformities favorable for uranium concentration in northern Appalachian basin

    SciTech Connect

    Dennison, J.M.

    1986-05-01

    Unconformities can redistribute uranium from protore rock as ground water moves through poorly consolidated strata beneath the erosion surface, or later moves along the unconformity. Groundwater could migrate farther than in present-day lithified Paleozoic strata in the Appalachian basin, now locally deformed by the Taconic and Allegheny orogenies. Several paleoaquifer systems could have developed uranium geochemical cells. Sandstone mineralogy, occurrences of fluvial strata, and reduzate facies are important factors. Other possibilities include silcrete developed during desert exposure, and uranium concentrated in paleokarst. Thirteen unconformities are evaluated to determine favorable areas for uranium concentration. Cambrian Potsdam sandstone (New York) contains arkoses and possible silcretes just above crystalline basement. Unconformities involving beveled sandstones and possible fluvial strata include Cambrian Hardyston sandstone (New Jersey), Cambrian Potsdam Sandstone (New York), Ordovician Oswego and Juniata formations (Pennsylvania and New York), Silurian Medina Group (New York), and Silurian Vernon, High Falls, and Longwood formations (New York and New Jersey). Devonian Catskill Formation is beveled by Pennsylvanian strata (New York and Pennsylvania). The pre-Pennsylvanian unconformity also bevels Lower Mississippian Pocono, Knapp, and Waverly strata (Pennsylvania, New York, and Ohio), truncates Upper Mississippian Mauch Chunk Formation (Pennsylvania), and forms paleokarst on Mississippian Loyalhanna Limestone (Pennsylvania) and Maxville Limestone (Ohio). Strata associated with these unconformities contain several reports of uranium. Unconformities unfavorable for uranium concentration occur beneath the Middle Ordovician (New York), Middle Devonian (Ohio and New York), and Upper Devonian (Ohio and New York); these involve marine strata overlying marine strata and probably much submarine erosion.

  10. Origin of the Nubian and similar sandstones

    USGS Publications Warehouse

    McKee, E.D.

    1963-01-01

    The Nubian Sandstone and similar sandstone bodies exposed across much of northern Africa and adjoining parts of Asia are characteristically formed of clean sand that is conspicuously cross stratified throughout. Such sandstone, here called Nubian-type sandstone, ranges from Cambrian through Cretaceous in age and its genesis has been interpreted in many ways. Studies of its primary structures, and of the direction of sand transport, based on statistical measurements of foreset dip directions, have contributed new data on its genesis. By far the most common structure in Nubian-type sandstone is a medium-scale planar-type cross stratification in which sets of evenly dipping cross beds are bounded by essentially flat-lying top and bottom surfaces to form tabular bodies. Other less numerous but typical structures are large-scale, truncated-wedge cross strata, trough-type cross strata, intraformational recumbent folds, small-scale ripple laminae, and dipping sets of tabular-planar cross beds. An analysis of these structures suggests that in the typical Nubian Sandstone of Cretaceous age eolian deposits are not represented and normal marine types probably also are lacking; flood plain, pond or lagoon, and other continental and marginal environments are indicated. In the Carboniferous rocks of Sinai Peninsula some beach sandstone and possibly some eolian, in addition to the types described, form part of the sequence. Direction of sand transport, as determined from cross-bed dips, was northerly in the Cretaceous Nubian of Libya, Sudan, and Egypt; easterly in the Jurassic Adigrat of Ethiopia; westerly in the Carboniferous of Sinai; northwesterly in the early Paleozoic of Jordan. ?? 1963 Ferdinand Enke Verlag Stuttgart.

  11. Detrital zircon geochronology and Nd isotope geochemistry of an early Paleozoic succession in Korea:

    NASA Astrophysics Data System (ADS)

    Lee, Yong Il; Choi, Taejin; Lim, Hyoun Soo; Orihashi, Yuji

    2015-04-01

    This study reports the results of an analysis of U-Pb ages of detrital zircons and Nd isotope compositions from the well-established lower Paleozoic platform succession developed on the Precambrian gneiss and metasedimentary rocks in South Korea. The three stratigraphic units in the basal part of the succession are the Jangsan, Myeonsan, and Myobong Formations. The unfossiliferous Jangsan (white­to­pink quartz sandstone) and Myeonsan (dark-gray ilmenite-rich sandstone/shale) Formations are in fault contact and are generally considered to be coeval (Early Cambrian). Both formations are also generally considered to be conformably overlain by the dark­ gray, fossiliferous, fine-grained Myobong Formation (late Early-early Middle Cambrian). We here report U-Pb ages of detrital zircons and Nd isotopic data from the Jangsan, Myeonsan, and Myobong Formations. The Jangsan and Myeonsan Formations provide Archean-Paleoproterozoic U-Pb ages, but the former is characterized by Archean Sm-Nd model ages and the latter by late Paleoproterozoic Sm-Nd model ages, which is indicative of a significant change in provenance. This suggests that the Jangsan Formation predates the Myeonsan Formation. The Myobong Formation provides dominantly Meso- to Neoproterozoic U-Pb ages and Sm-Nd model ages that are slightly younger than those of the Myeonsan Formation. Contrary to the conventional wisdom, the combined evidence of unconformable contact and marked changes in zircon U-Pb ages and Nd isotopic compositions suggests that the Myobong Formation overlies the Jangsan and Myeonsan Formations unconformably. Considering the metamorphic age of the immediately underlying Precambrian basement metasediments (0.8 to 0.9 Ga), this stratigraphic relationship strongly suggests that the Jangsan Formation may be Neoproterozoic in age and that the Myeonsan Formation may be latest Neoproterozoic to Early Cambrian and calls for reevaluation of Precambrian-Paleozoic history of the Korean Peninsula. The

  12. Paleozoic lithofacies in southwestern Sinai and their depositional environments

    SciTech Connect

    Bhattacharyya, D.P.; Peck, N.R.; Mansour, S.E.

    1983-03-01

    Major breaks in sedimentation, accompanied by well-developed paleosols, have been successfully used to subdivide the 600 m (1968 ft) of Paleozoic sandstone and shale sequence of southwestern Sinai, Egypt, into five smaller facies association units (i.e., formations). The lowest unit (the Araba Formation) is dominated by 1 to 10 m (3 to 32 ft) thick coarsening-up sequences of parallel-bedded, varicolored, fine-grained arkosic sandstone and muddy sandstone. This is the deposit of a low-energy prograding sandy coastal plain complex that grades upward into a thin, fining-up channel-overbank deposits with poorly developed paleosols. The overlying Naqus Formation scours deep into the Araba, and is characterized by lenticular, coarse to medium-grained, cross-bedded quartz sandstone with only a few clayey intervals. Cross-beds are common. The Naqus is interpreted as alluvial fanbraided stream deposits. A 15 to 20 m (40 to 66 ft) thick, conspicuous dark brown, ferruginous shale, ochre-yellow dolomitic sandstone and fossiliferous gray siltstone sequence, persistent all along the Qabeliat valley, overlies the Naqus and represents lagoonal deposits laterally equivalent to the shallow marine shale-dolomite sequence of the Um Bogma Formation farther north. Basal fluvial channel sands of the succeeding Ataqa Formation cut into the Um Bogma paleosol, and grade upward into the fossiliferous green-red marine shales and subordinate sandstones in shoaling-upward sequences. Southward in the Qabeliat valley, a parallel-bedded sequence of thick green shales and thin brown sandstones, both nonfossiliferous, intervenes in the middle of the Budra Formation and represents ephemeral lake deposits related to the fluvial system.

  13. Integrated provenance analysis of Zakeen (Devonian) and Faraghan (early Permian) sandstones in the Zagros belt, SW Iran

    NASA Astrophysics Data System (ADS)

    Zoleikhaei, Yousef; Amini, Abdolhossein; Zamanzadeh, S. Mohammad

    2015-01-01

    Successions of a controversial period of time in the Zagros and Arabian Plate stratigraphic column, including Zakeen (Devonian) and Faraghan (early Permian) formations are investigated for their provenance characteristics. Nearly similar depositional environments of the formations, regardless of 70-80 My hiatus between them, is the main motivation for this study. Evidence from various methods are put together to reconstruct a comprehensive image of their provenance. Results from petrographic and detrital mode analysis indicate a continental block provenance for of the sandstones of both formations. In addition, evidence of recycling is evident from some rock fragments in the conglomeratic facies. Heavy mineral diversities are limited to the ultra-stable species which represent consistent morphological characteristics in both formations. However, the values of rutile: zircon index (RZi) showed intermittent changes from low RZi to high RZi intervals in both formations. Detrital zircon age data in previous studies represented the same source for these two formations, which also remained unchanged from Neo-Proterozoic to late Paleozoic successions. Zircon grains' morphology, however, showed remarkable difference between the Zakeen and Faraghan formations on the one hand and successions deposited in the basin prior to the tectonic movements of mid-Paleozoic time on the other. Outcomes of this study show that, although each single technique may shed light on a particular aspect of the greater provenance problem, by integration of all the data, important evidence of recycled nature of these successions could be confirmed. Changes in the thickness of the Paleozoic units, the nature of their stratal surfaces, along with the information from magmatic events in the area provide a tectono-stratigraphic framework for northern margin of Gondwana in which the recycled nature of these successions is justifiable. The recycled nature of the studied formations on the one hand, and

  14. The early Paleozoic sedimentary-tectonic evolution of the circum-Mangar areas, Tarim block, NW China: Constraints from integrated detrital records

    NASA Astrophysics Data System (ADS)

    Dong, Shunli; Li, Zhong; Jiang, Lei

    2016-07-01

    The Mangar depression, located in the eastern part of the Tarim basin, had deposited extremely-thick lower Paleozoic sediments, which yields great scientific value and hydrocarbon resource potential. Due to the lack of enough outcrop and core studies, many issues, e.g., early Paleozoic geographical evolution, basin nature and tectonic affinity, are still poorly understood. In this study, we selected circum-Mangar areas (i.e., the South Quruqtagh, Tabei and Tazhong areas), and carried out comprehensive detrital provenance analysis including detrital modal analysis, heavy mineral and trace element analysis, and detrital zircon U-Pb dating on the Middle-Upper Ordovician and Silurian sandstones. The results show that Upper Ordovician-Lower Silurian detrital provenances of the South Quruqtagh and Tabei areas were primarily derived from the intracontinental uplifts in Tarim. Meanwhile, Upper Silurian detrital provenances of the above two areas were mainly derived from the mix of intracontinental uplifts and continental-margin arcs. Dramatic Late Silurian provenance-change suggests the evident tectonic transition of the northern Tarim margin, which is the opening of the South Tianshan back-arc oceanic basin. Combining the previous studies, an integral redefinition model for the Mangar depression has been made. The evolution process of the Mangar depression could be divided into four stages: graben stage (late Neoproterozoic), transitional stage (Cambrian to Middle Ordovician), downwarp stage (Late Ordovician to Early Silurian) and extinction stage (Late Silurian). Hence, the Mangar depression evolved as an aulacogen. Significantly, the evolutional scenario of the Mangar aulacogen was consistent with that of the North Altyn Tagh and the North Qilian, suggesting that the Mangar aulacogen was involved mainly in the Proto-Tethys tectonic realm south to the Tarim block. However, the Late Silurian tectonic activity in the northern Tarim margin did produce massive detrital

  15. From Back-arc Drifting to Arc Accretion: the Late Jurassic-Early Cretaceous Evolution of the Guerrero Terrane Recorded by a Major Provenance Change in Sandstones from the Sierra de los Cuarzos, Central Mexico

    NASA Astrophysics Data System (ADS)

    Palacios Garcia, N. B.; Martini, M.

    2014-12-01

    The Guerrero terrane composed of Middle Jurassic-Early Cretaceous arc assemblages, were drifted from the North American continental mainland during lower Early Cretaceous spreading in the Arperos back arc basin, and subsequently accreted back to the continental margin in the late Aptian. Although the accretion of the Guerrero terrane represents one of the major tectonic processes that shaped the southern North American Pacific margin, the stratigraphic record related to such a regional event was not yet recognized in central Mexico. Due to the Sierra de los Cuarzos is located just 50 km east of the Guerrero terrane suture belt, its stratigraphic record should be highly sensitive to first order tectonic changes and would record a syn-tectonic deposits related to this major event. In that study area, were identified two main Upper Jurassic-Lower Cretaceous clastic units. The Sierra de los Cuarzos formation represents the lowermost exposed stratigraphic record. Sedimentary structures, sandstones composition, and U-Pb detrital zircon ages document that the Sierra de los Cuarzos formation reflects a vigorous mass wasting along the margin of the North American continental mainland, representing the eastern side of the Arperos back arc basin. Sandstones of the Sierra de los Cuarzos formation are free from detrital contributions related to the Guerrero terrane juvenile sources, indicating that the Arperos Basin acted like an efficient sedimentological barrier that inhibited the influence of the arc massifs on the continental mainland deposits. The Sierra de los Cuarzos formation is overlain by submarine slope deposits of the Pelones formation, which mark a sudden change in the depositional conditions. Provenance analysis documents that sandstones from the Pelones formation were fed by the mafic to intermediate arc assemblages of the Guerrero terrane, as well as by quartz-rich sources of the continental mainland, suggesting that, by the time of deposition of the Pelones

  16. Provenance of sandstones in the Golconda terrane, north central Nevada

    SciTech Connect

    Jones, E.A. )

    1991-02-01

    The upper Paleozoic Golconda terrane of north-central Nevada is a composite of several structurally bounded subterranes made of clastic, volcanic, and carbonate rocks. The clastic rocks provide important clues for the interpretation of the provenance and paleogeographic settings of the different lithologic assemblages found in these subterranes. Two petrographically distinct sandstones are identified in the Golconda terrane in the Osgood Mountains and the Hot springs Range of north-central Nevada. The sandstone of the Mississippian Farrel Canyon Formation, part of the Dry Hills subterrane, is characterized by quartzose and sedimentary and lithic-rich clasts with a small feldspar component. in contrast, the sandstone of the Permian Poverty Peak (II) subterrane is a silty quartzarenite with no lithic component, and a very limited feldspar component. The sandstone of the Farrel Canyon Formation is similar to nonvolcanic sandstones reported from elsewhere in the Golconda terrane. Modal data reflect a provenance of a recycled orogen and permit the interpretation that it could have been derived from the antler orogen as has been proposed for other sandstones of the golconda terrane. The sandstone of the Poverty Peak (II) subterrane is more mature than any of the other sandstones in either the Golconda terrane, the Antler overlap sequence, or the Antler foreland basin sequence. Modal data put the Poverty Peak (II) sandstone in the continental block provenance category. The distinct extrabasinal provenances represented in these different sandstones support the idea that the Golconda basin was made up of complex paleogeographic settings, which included multiple sources of extrabasinal sediment.

  17. Late Paleozoic onset of subduction and exhumation at the western margin of Gondwana (Chilenia Terrane): Counterclockwise P-T paths and timing of metamorphism of deep-seated garnet-mica schist and amphibolite of Punta Sirena, Coastal Accretionary Complex, central Chile (34° S)

    NASA Astrophysics Data System (ADS)

    Hyppolito, T.; García-Casco, A.; Juliani, C.; Meira, V. T.; Hall, C.

    2014-10-01

    by the non-coaxial exhumation-related foliation S2. During exhumation and retrograde D2 deformation, the garnet-mica schist and amphibolite were tectonically mingled at a depth of ca. 30 km at ca. 315 Ma. We propose that the Punta Sirena unit comprises a “pseudo”-coherent sequence formed by heterogeneous lithologies that followed non-chaotic exhumation mingling, now representing the remnants of the fossil subduction channel developed at the onset of the Late Paleozoic subduction at central Chile.

  18. Ophiolites of Iran: Keys to understanding the tectonic evolution of SW Asia: (I) Paleozoic ophiolites

    NASA Astrophysics Data System (ADS)

    Shafaii Moghadam, Hadi; Stern, Robert J.

    2014-09-01

    Iran is a mosaic of Ediacaran-Cambrian (Cadomian; 520-600 Ma) blocks, stitched together by Paleozoic and Mesozoic ophiolites. In this paper we summarize the Paleozoic ophiolites of Iran for the international geoscientific audience including field, chemical and geochronological data from the literature and our own unpublished data. We focus on the five best known examples of Middle to Late Paleozoic ophiolites which are remnants of Paleotethys, aligned in two main zones in northern Iran: Aghdarband, Mashhad and Rasht in the north and Jandagh-Anarak and Takab ophiolites to the south. Paleozoic ophiolites were emplaced when N-directed subduction resulted in collision of Gondwana fragment “Cimmeria” with Eurasia in Permo-Triassic time. Paleozoic ophiolites show both SSZ- and MORB-type mineralogical and geochemical signatures, perhaps reflecting formation in a marginal basin. Paleozoic ophiolites of Iran suggest a progression from oceanic crust formation above a subduction zone in Devonian time to accretionary convergence in Permian time. The Iranian Paleozoic ophiolites along with those of the Caucausus and Turkey in the west and Afghanistan, Turkmenistan and Tibet to the east, define a series of diachronous subduction-related marginal basins active from at least Early Devonian to Late Permian time.

  19. Ecological Controls on the Evolutionary Recovery of Post-Paleozoic Crinoids

    PubMed

    Foote

    1996-11-29

    Analysis of morphological characters of a global sample of post-Paleozoic crinoid echinoderms shows that this group underwent a rapid diversification after the extinction at the end of the Permian to reach maximal morphological disparity by the Late Triassic, which is essentially the same evolutionary pattern seen during the group's early Paleozoic radiation. The accelerated morphological diversification of a single class implies that, even if clades surviving from the Paleozoic represented ecological incumbents that hindered the origin of new higher taxa, species within individual higher taxa rapidly exploited available ecological opportunities in the Mesozoic. PMID:8929402

  20. 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

  1. Petrography, diagenesis and reservoir characteristics of the Pre-Cenomanian sandstone, Sheikh Attia area, East Central Sinai, Egypt

    NASA Astrophysics Data System (ADS)

    Kassab, Mohamed A.; Hassanain, Ibrahim M.; Salem, Alaa M.

    2014-08-01

    The diagenetic influence on reservoir characteristics was investigated for the Pre-Cenomanian (Early Paleozoic and Early Cretaceous) sandstone sequence in the Sheikh Attia area, East Central Sinai. This sequence can be distinguished into four formations: Sarabit El-Khadim Formation (Cambrian) at the base, Abu Hamata Formation (Cambro-Ordovician), Adedia Formation (Ordovician-Silurian) and Malha Formation (Early Cretaceous) on the top. The sandstones of Pre-Cenomanian sequence in the Sheikh Attia area are dominantly quartz arenites and subarkoses, where the quartz grains constitute about 82.3-98.4% of the framework composition with an average value of approximately 94% of the framework composition. Feldspars range in abundance from 0% to14.2%, with an average value of about 3% of the framework composition. The rock fragments constitute up to 9.8% of volume percent of framework grains, with an average of about 2.7%. Diagenetic events identified in these sandstones include compaction, cementation by calcite, quartz, clay minerals and iron oxides, dissolution and alteration of unstable clastic grains, and tectonically induced grain fracturing. Unstable clastic grains like feldspars suffered considerable alteration to kaolinite. The Pre-Cenomanian (Early Paleozoic and Early Cretaceous) sandstones possess good reservoir characteristics because they retain sufficient porosity and permeability in some intervals. These sandstones are characterized by porosity ranges between 3.80% and 27.60%, and have a permeability range from k ⩽ 0.03 mD, for tight sandstones to k ⩾ 50 mD, for the more permeable parts. The Pre-Cenomanian sandstones can be classified into four petrophysical flow units (megaport, macroport, mesoport and microport) with varying reservoir performances and are distinguished by comparable ranges of R35. Petrographic observations showed that the Early Paleozoic sandstones are texturally immature owing to the abundance of angular grains, non-uniformity of grain

  2. "Sydney sandstone": Heritage Stone from Australia

    NASA Astrophysics Data System (ADS)

    Cooper, Barry; Kramar, Sabina

    2014-05-01

    Sydney is Australia's oldest city being founded in 1788. The city was fortunate to be established on an extensive and a relatively undeformed layer of lithified quartz sandstone of Triassic age that has proved to be an ideal building stone. The stone has been long identified by geologists as the Hawkesbury Sandstone. On the other hand the term "Sydney sandstone" has also been widely used over a long period, even to the extent of being utilised as the title of published books, so its formal designation as a heritage stone will immediately formalise this term. The oldest international usage is believed to be its use in the construction of the Stone Store at Kerikeri, New Zealand (1832-1836). In the late 19th century, public buildings such as hospitals, court houses as well as the prominent Sydney Town Hall, Sydney General Post Office, Art Gallery of New South Wales, State Library of New South Wales as well as numerous schools, churches, office building buildings, University, hotels, houses, retaining walls were all constructed using Sydney sandstone. Innumerable sculptures utilising the gold-coloured stone also embellished the city ranging from decorative friezes and capitals on building to significant monuments. Also in the late 19th and early 20th century, Sydney sandstone was used for major construction in most other major Australian cities especially Melbourne, Adelaide and Brisbane to the extent that complaints were expressed that suitable local stone materials were being neglected. Quarrying of Sydney sandstone continues today. In 2000 it was recorded noted that there were 33 significant operating Sydney sandstone quarries including aggregate and dimension stone operations. In addition sandstone continues to be sourced today from construction sites across the city area. Today major dimension stone producers (eg Gosford Quarries) sell Sydney sandstone not only into the Sydney market but also on national and international markets as cladding and paving products

  3. Delayed onset sandstone pneumoconiosis: a case report

    SciTech Connect

    Symanski, H.

    1981-01-01

    An unusual case of silicosis is described in a worker who inhaled the dust of pure silica while working in a sandstone quarry. The exposure lasted only eight years. In 1980, 45 years after exposure ceased, severe clinical manifestations of silicosis appeared for the first time. The chest X-ray showed a pneumoconiosis A 2mn/A2 Mn Cor, em, hilus, based on the International Classification of Geneva, 1958. A diagnosis of sandstone pneumoconiosis was made. The case is one further example of late-occurring disease appearing after a latency of several decades.

  4. Delayed onset sandstone pneumoconiosis: a case report.

    PubMed

    Symanski, H

    1981-01-01

    An unusual case of silicosis is described in a worker who inhaled the dust of pure silica while working in a sandstone quarry. The exposure lasted only eight years. In 1980, 45 years after exposure ceased, severe clinical manifestations of silicosis appeared for the first time. The chest X-ray showed a pneumoconiosis A 2mn/A2 Mn Cor, em, hilus, based on the International Classification of Geneva, 1958. A diagnosis of sandstone pneumoconiosis was made. The case is one further example of late-occurring disease appearing after a latency of several decades.

  5. Paleozoic tectonics of the Ouachita Orogen through Nd isotopes

    SciTech Connect

    Gleason, J.D.; Patchett, P.J.; Dickinson, W.R.; Ruiz, J. . Dept. of Geosciences)

    1992-01-01

    A combined isotopic and trace-element study of the Late Paleozoic Ouachita Orogenic belt has the following goals: (1) define changing provenance of Ouachita sedimentary systems throughout the Paleozoic; (2) constrain sources feeding into the Ouachita flysch trough during the Late Paleozoic; (3) isolate the geochemical signature of proposed colliding terranes to the south; (4) build a data base to compare with possible Ouachita System equivalents in Mexico. The ultimate aim is to constrain the tectonic setting of the southern margin of North America during the Paleozoic, with particular emphasis on collisional events leading to the final suturing of Pangea. Nd isotopic data identify 3 distinct groups: (1) Ordovician passive margin sequence; (2) Carboniferous proto-flysch (Stanley Fm.), main flysch (Jackfork and Atoka Fms.) and molasse (foreland Atoka Fm.); (3) Mississippian ash-flow tuffs. The authors interpret the Ordovician signature to be essentially all craton-derived, whereas the Carboniferous signature reflects mixed sources from the craton plus orogenic sources to the east and possibly the south, including the evolving Appalachian Orogen. The proposed southern source is revealed by the tuffs to be too old and evolved to be a juvenile island arc terrane. They interpret the tuffs to have been erupted in a continental margin arc-type setting. Surprisingly, the foreland molasse sequence is indistinguishable from the main trough flysch sequence, suggesting the Ouachita trough and the craton were both inundated with sediment of a single homogenized isotopic signature during the Late Carboniferous. The possibility that Carboniferous-type sedimentary dispersal patterns began as early as the Silurian has important implications for the tectonics and paleogeography of the evolving Appalachian-Ouachita Orogenic System.

  6. Paleozoic orogens in New England, USA

    USGS Publications Warehouse

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

    1998-01-01

    Stratigraphy and isotope geochronology in the crystalline core of the Appalachians suggest revised interpretations of the extent, nature and timing of Paleozoic orogens in New England. Five major episodes of magmatism, deformation, and high-grade regional metamorphism are recognized: Taconian (455-442 Ma), Acadian (423-385 Ma), Neo-Acadian (366-350 Ma), Late Pennsylvanian (300-290 Ma) and Alleghanian (280-260 Ma). In the Taconian, the passive margin of Laurentia was subducted below a complex magmatic arc lasting from 480 to 442 Ma, founded in part on continental crust of a Medial New England terrane with possible affinities with Amazonia. Questions about Medial New England involve its coherence as a single plate, and the nature of its underlying crust. The Acadian began in Late Silurian as a collision between the amalgamated Laurentia-Medial New England and outer belts of Composite Avalon along a cryptic suture in coastal Maine, and progressed northwestward to the Connecticut Valley basin by mid-Devonian. Tonalitic-granitic magmatism and up to granulite-facies metamorphism culminated in Early Devonian, possibly tied to lithospheric detachment below the subducting northwestern plate and consequent asthenosphere upwelling. Newly discovered Neo-Acadian Late Devonian to Early Mississippian tonalitic-granitic magmatism, up to granulite-facies metamorphism, and severe deformation in central Massachusetts took place in a plate context poorly understood. Late Pennsylvanian effects include magmatism, metamorphism, and deformation near south New England gneiss domes and the Sebago batholith, and development of the right-lateral Norumbega fault system. Permian Alleghanian effects include penetrative deformation, granitic intrusions and up to sillimanite-grade metamorphism of Pennsylvanian beds in southeastern New England. These last two episodes relate to the arrival of Africa.

  7. North American Paleozoic land snails with a summary of other Paleozoic nonmarine snails

    USGS Publications Warehouse

    Solem, Alan; Yochelson, Ellis Leon

    1979-01-01

    family placement of Anthracopupa, growth forms of modern pupillid and tornatellinid snails have been distinguished. The apertural barriers in Anthracopupa are identical in placement and growth pattern with those of living Tornatellinidae and independently confirm the family placement derived from study of the general form. One new species, A. sturgeoni, has been named. Anthracopupa is found most commonly in thin limestones interpreted as having been deposited in pools into which the small shells floated. Dendropupa is most commonly found in erect tree stumps that were covered by rapid sedimentation. Both environments are similar to those in which the shells of allied living species may be found today, and the fossils support environmental interpretations made entirely from lithology. A survey of the few European occurrences of Paleozoic land snails indicates that both Anthracopupa and Dendropupa occur in Lower Permian strata; Anthracopupa is known from beds as old as Westphalian B. These genera cannot be used for determining the Carboniferous-Permian boundary. Both the long local stratigraphic range of A. brittanica and D. vetusta reported in the literature and the moderately long range and great variability of A. ohioensis suggest that the land snails have little stratigraphic utility. On the other hand, the occurrence of these land snails in the late Paleozoic of the Northern Hemisphere provides further fossil evidence suggestive of a closed Atlantic Ocean at that time. A comparison of the Paleozoic and the present distributions of land -snail families on both sides of the Atlantic provides some interesting data on geographic shifts of organisms. Finally, the assignment of the earliest land snails to extant taxa at the family level indicates that the subclass Pulmonata has been very conservative in its evolution after initial radiation. A few notes on Paleozoic freshwater snails complete this survey.

  8. Paleozoic diamictites in the Peruvian Altiplano: evidence and tectonic implications

    NASA Astrophysics Data System (ADS)

    Díaz-Martínez, Enrique; Acosta, Harmuth; Cardenas, José; Carlotto, Víctor; Rodríguez, Rildo

    2001-11-01

    Striated and faceted clasts found within the diamictites of the San Gabán Formation immediately north of Ayaviri (southeast Peru) are interpreted as evidence for the late Ashgill-Llandovery glaciations in the Peruvian Altiplano, an area where this unit was previously considered not to be deposited. The Lower Paleozoic stratigraphic sequence cropping out in the area includes the Sandia, San Gabán, and Ananea Formations, and thus belongs to the Eastern Cordillera tectonostratigraphic domain, but within the Altiplano morphotectonic region. The marked difference between the Lower Paleozoic sequences of the Altiplano and Eastern Cordillera tectonostratigraphic domains suggests important tectonic shortening along the boundary fault zone during Andean Cenozoic deformation.

  9. 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.

  10. Shelf sandstones of Twowells tongue, Dakota Sandstone, northwestern New Mexico

    SciTech Connect

    Wolter, N.R.; Nummedal, D.

    1988-01-01

    The Dakota Sandstone of northwestern New Mexico is composed of basal continental strata and three marine sandstone tongues, which intertongue was the Mancos Shale. The late Cenomanian Twowells tongue was the last tongue deposited in the Dakota transgressive systems tract. This tongue is most commonly gradationallly underlain by the Whitewater Arroyo shale tongue and abruptly overlain by the Rio Salado tongue of the Mancos Shale. Data collected from 85 outcrop sections and 180 electric well logs, from the San Juan, Acoma, and Zuni Basins, indicates that the Twowells tongue represents three phases of marine deposition. The White-water Arroyo shale tongue, the muddy burrowed facies, and the horizontally bedded facies of the Twowells tongue represent a shoaling-upward sequence (regressive phase) of shelf and shoreface deposition. The regressive phase is sharply overlain by an inferred transgressive cross-bedded facies. Erosional scour and an extensive pebble lag mark the contact between the regressive and the transgressive facies. In the Acoma basin, the transgressive cross-bedded facies describes a north-south oriented shelf-sand ridge 32 km long, 18 km wide, and 32 m thick.

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

    SciTech Connect

    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 and Lemhi Range. Late Devonian (Frasnian) carbonates of the Jefferson formation show buildup development on deep ramp sediments.

  12. Stochastic reconstruction of sandstones

    PubMed

    Manwart; Torquato; Hilfer

    2000-07-01

    A simulated annealing algorithm is employed to generate a stochastic model for a Berea sandstone and a Fontainebleau sandstone, with each a prescribed two-point probability function, lineal-path function, and "pore size" distribution function, respectively. We find that the temperature decrease of the annealing has to be rather quick to yield isotropic and percolating configurations. A comparison of simple morphological quantities indicates good agreement between the reconstructions and the original sandstones. Also, the mean survival time of a random walker in the pore space is reproduced with good accuracy. However, a more detailed investigation by means of local porosity theory shows that there may be significant differences of the geometrical connectivity between the reconstructed and the experimental samples.

  13. Exploration potential of Paleozoic rocks of Morocco

    SciTech Connect

    Ehrlich, R.; Onarept, H.J.

    1985-02-01

    Paleozoic rocks of Morocco have some similarities with the producing Paleozoic sequences in Algeria. In Morocco, there is a basic division between the cratonal sequences of the Tidouf basin and contiguous areas and the Paleozoic megabasin to the north and possibly to the west under the present continental shelf areas. The Paleozoic of the northern megabasin has the following positive exploration elements. (1) Both wrench and normal extensional tectonics have produced significant structures that may have been reactivated during 2 later orogenic events. (2) Reservoir quality, although poor in outcrop, can be significantly improved in the subsurface. Wells from the Bojad region of the Tadla basin encountered porosities up to 30% in Devonian clastic sequences. (3) No area can be condemned on the basis of present published geochemical evidence. Burial depths are sufficient for mature hydrocarbons, and rocks with organic material are present in sediment ranging in age from Cambrian to Carboniferous. Paleozoic oil shows have been encountered and may actually serve as the source of hydrocarbon in the Essouira basin in a downfaulted Triassic red-bed sequence. (4) Quality of seismic data is good, even where Paleozoic rocks are onlapped by Mesozoic and Cenozoic sediments. Drilling for Paleozoic targets has been sparse, hence, few data are available to test both source and reservoir potential. Paleozoic rocks still need to be tested by industry and must be considered a frontier area.

  14. Paleozoic oil in Uzbekistan and adjacent territories

    SciTech Connect

    Ryzhkov, O.A.; Khaimov, R.N.; Vitchinkin, M.M.; Zuev, Yu.N.

    1983-01-01

    Direct evidence of the presence of oil in the region is characteristically widespread within a broad stratigraphic span as well as territorially. This Paleozoic oil is of the naphthene aromatic type, in contrast with the Mesozoic and Tertiary oils of Uzbekistan, suggesting a justifiable hypothesis of an independent Paleozoic cycle of oleogenesis involving accumulation of hydrocarbons.

  15. Paleozoic plate-tectonic evolution of the Tarim and western Tianshan regions, western China

    SciTech Connect

    Yangshen, S.; Huafu, L.; Dong, J.

    1994-11-01

    The plate-tectonic evolution of the Tarim basin and nearby western Tianshan region during Paleozoic time is reconstructed in an effort to further constrain the tectonic evolution of Central Asia, providing insights into the formation and distribution of oil and gas resources. The Tarim plate developed from continental rifting that progressed during early Paleozoic time into a passive continental margin. The Yili terrane (central Tianshan) broke away from the present eastern part of Tarim and became a microcontinent located somewhere between the Junggar ocean and the southern Tianshan ocean. The southern Tianshan ocean, between the Tarim craton and the Yili terrane, was subducting beneath the Yili terrane from Silurian to Devonian time. During the Late Devonian-Early Carboniferous, the Tarim plate collided with the Yili terrane by sinistral accretional docking that resulted in a late Paleozoic deformational episode. Intracontinental shortening (A-type subduction) continued through the Permian with the creation of a magmatic belt. 21 refs., 7 figs., 1 tab.

  16. Status of Early Paleozoic biostratigraphy of the Tethyan Himalayan successions

    NASA Astrophysics Data System (ADS)

    Parcha, Suraj Kumar; Pandey, Shivani

    2015-04-01

    The early Paleozoic successions of the Tethys Himalaya is exposed in the Spiti- Zanskar, Kashmir, Kumaun and in Garhwal regions. The most complete sequence described from the Tethys Himalayan region is exposed in the Spiti- Zanskar basin. The sedimentary succession of Spiti-Zanskar basin has a thick sequence of early Paleozoic age. The early Paleozoic rocks of these basins rest over the crystalline rock. The contact between underlying crystallines with the Paleozoic rocks has been interpreted unconformable/conformable and gradual/faulted by various workers. There is no definite record of faunal elements from the Neoproterozoic metasedimentary rocks of both the basins. Above the metasedimentary rocks of Neoproterozoic the fossiliferous Cambrian rock rests. The fossiliferous Cambrian sequence of Spiti- Zanskar basins are corresponding to one another as far as the distribution of fauna is concerned. The early Cambrian successions in both the basins have more or less identical ichnogenera. Whereas, the Middle Cambrian of Zanskar Basin is dominated by agnostid trilobites along with polymerid trilobites on the other hand in the Spiti Basin Pagetides along with polymerid trilobites dominates during this period with few agnostid. In the Kashmir Basin the early Cambrian is equally dominated by Ichnofossils and the Middle Cambrian is controlled similarly by trilobite fauna like that of Spiti- Zanskar basins. In the Kumaun-Garhwal region so far no detailed studies have been carried out however earlier studies and in recent years ichnofossils of early Cambrian age has been reported along with some fragmentary report of trilobites. But from the Ordovician and Silurian successions of Garhwal basin brachiopods have been reported. The Ordovician succession of Spiti basin indicates shallow water depositional cycle, whereas the Zanskar basin indicates the sub aerial fluvial and deltaic depositional environment. A gradational contact has been observed between the Ordovician and

  17. First North American occurrence of Anacoracid selachian Squalicorax yangaensis, Upper Cretaceous Dalton sandstone, near Crownpoint, New Mexico

    SciTech Connect

    Wolberg, D.L.; Bellis, D. )

    1989-09-01

    This report documents the first North American occurrence of Squalicorax yangaensis in the Upper Cretaceous Dalton sandstone, Borrego Pass area, southeast of Crownpoint, New Mexico. The Dalton sandstone has been interpreted to be a regressive coastal barrier sandstone deposited parallel to the southeast-trending shoreline of the Late Cretaceous epeiric seaway.

  18. Sand and sandstone

    SciTech Connect

    Pettijohn, F.J.; Potter, P.E.; Siever, R.

    1987-01-01

    Here is a new, second edition of a classical textbook in sedimentology, petrology, and petrography of sand and sandstones. It has been extensively revised and updated, including: new techniques and their utility; new literature; new illustrations; new, explicitly stated problems for the student; and a wider scope.

  19. Paleozoic-involving thrust array in the central Sierras Interiores (South Pyrenean Zone, Central Pyrenees): regional implications

    NASA Astrophysics Data System (ADS)

    Rodriguez, L.; Cuevas, J.; Tubía, J. M.

    2012-04-01

    This work deals with the structural evolution of the Sierras Interiores between the Tena and Aragon valleys. The Sierras Interiores is a WNW-trending mountain range that bounds the South Pyrenean Zone to the north and that is characterized by a thrust-fold system with a strong lithological control that places preferably decollements in Triassic evaporites. In the studied area of the Sierras Interiores Cenomanian limestones cover discordantly the Paleozoic rocks of the Axial Zone because there is a stratigraphic lacuna developed from Triassic to Late Cretaceous times. A simple lithostratigraphy of the study area is made up of Late Cenomanian to Early Campanian limestones with grey colour and massive aspect in landscape (170 m, Lower calcareous section), Campanian to Maastrichtian brown coloured sandstones (400-600 m, Marboré sandstones) and, finally, Paleocene light-coloured massive limestones (130-230 m), that often generate the higher topographic levels of the Sierras Interiores due to their greater resistance to erosion. Above the sedimentary sequence of the Sierras Interiores, the Jaca Basin flysch succession crops out discordantly. Based on a detailed mapping of the studied area of the Sierras Interiores, together with well and structural data of the Jaca Basin (Lanaja, 1987; Rodríguez and Cuevas, 2008) we have constructed a 12 km long NS cross section, approximately parallel to the movement direction deduced for this region (Rodríguez et al., 2011). The main structure is a thrust array made up of at least four Paleozoic-involving thrusts (the deeper thrust system) of similar thickness in a probably piggyback sequence, some of which are blind thrusts that generate fold-propagation-folds in upper levels. The higher thrust of the thrust array crops out duplicating the lower calcareous section all over the Sierras Interiores. The emplacement of the deeper thrust system generated the tightness of previous structures: south directed piggyback duplexes (the upper

  20. U-Pb geochronology and petrology of the late Paleozoic Gil Marquez pluton: magmatism in the Variscan suture zone, southern Iberia, during continental collision and the amalgamation of Pangea

    NASA Astrophysics Data System (ADS)

    Gladney, Evan R.; Braid, James A.; Murphy, J. Brendan; Quesada, Cecilio; McFarlane, Christopher R. M.

    2014-07-01

    The origin of plutonic complexes that stitch suture zones developed during collision is not well understood. In southern Iberia, the Pulo du Lobo suture zone (PDLZ) is intruded by the syn- to postcollisional Gil Marquez pluton (GMP), thought to be part of the Sierra Norte Batholith. U-Pb (LA-ICPMS, zircon) data on various phases of the GMP yield from oldest to youngest: (1) a 354.4 ± 7.6 Ma unfoliated gabbro; (2) a 345.6 ± 2.5 Ma foliated intermediate phase; (3) a 346.5 ± 5.4 Ma unfoliated porphyritic granite; (4) a 335.1 ± 2.8 Ma unfoliated biotite granite. This sequence is consistent with cross-cutting relationships observed in the field. The range in ages is consistent with interpretations that the GMP is part of the composite (ca. 350-308 Ma) SNB. Inherited ages preserved in the GMP intermediate and felsic phases indicate that its magmas traversed through South Portuguese Zone and PDLZ crust during emplacement. The ca. 345 Ma emplacement of the late kinematic foliated intermediate phase constrains the age of late-stage strike slip deformation within the PDLZ, and the lack of a foliation in the older gabbro indicates that is was not proximal to a shear zone neither at the time of emplacement, nor during its subsequent history. The unfoliated porphyritic granite and unfoliated biotite granite cut the foliation of the intermediate phase indicating emplacement during the waning stages of collision, while the ca. 335 Ma biotite granite intrudes the Santa Ira Flysch, thereby providing a tight constraint for the latest stage of deformation in the PDLZ.

  1. The potential of paleozoic nonmarine trace fossils for paleoecological interpretations

    USGS Publications Warehouse

    Maples, C.G.; Archer, A.W.

    1989-01-01

    Many Late Paleozoic environments have been interpreted as marine because of the co-occurrence of supposedly exclusively marine trace fossils. Beginning in the Late Ordovician, however, nonmarine trace-fossil diversity increased throughout the Paleozoic. This diversification of nonmarine organisms and nonmarine trace fossils was especially prevalent in Devonian and later times. Diversification of freshwater organisms is indicated by the large number of freshwater fish, arthropods, annelids and molluscs that had developed by the Carboniferous. In addition to diverse freshwater assemblages, entirely terrestrial vertebrate and invertebrate ecosystems had developed by the Devonian. This rapid diversification of freshwater and terrestrial organisms is inherently linked to development and diversification of land plants and subsequent shedding of large quantities of organic detritus in nonmarine and marginal-marine areas. Nearshore marine organisms and their larvae that are able to tolerate relatively short periods of lowered salinities will follow salt-water wedges inland during times of reduced freshwater discharge. Similarly, amphidromous marine organisms will migrate periodically inland into nonmarine environments. Undoubtedly, both of these processes were active in the Paleozoic. However, both processes are restricted to stream/distributary channels, interdistributary bays, or estuaries. Therefore, the presence of diverse trace-fossil assemblages in association with floodplain deposits is interpreted to reflect true nonmarine adaptation and diversity. Conversely, diverse trace-fossil assemblages in association with stream/distributary channel deposits, interdistributary-bay deposits, or estuarine deposits may reflect migration of salt-water wedges inland, or migration of marine organisms into freshwater environments (amphidromy), or both. ?? 1989.

  2. The first find of cuprous gold in the Lower Paleozoic psephites of the Northern Urals

    NASA Astrophysics Data System (ADS)

    Nikulova, N. Yu.; Filippov, V. N.; Shvetsova, I. V.

    2014-06-01

    The results of study of the composition of gold from conglobreccias in the basement of the Lower Paleozoic terrigenous sequence of the Polar Urals (Malaya Kara River) are presented. Three gold types distinct in chemical composition were identified. A significant part of the gold contains a high (up to 23 wt %) amount of copper, the distribution of which (increase from center to rim) in the grains is opposite to that in gold from the terrigenous Lower Paleozoic rocks of the northern Urals. It is suggested that cuprous gold is a result of destruction of the Late Cambrian serpentinites and subsequent hydrothermal reworking of Au-bearing terrigenous sequences.

  3. 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

  4. Solonker ophiolite in Inner Mongolia, China: A late Permian continental margin-type ophiolite

    NASA Astrophysics Data System (ADS)

    Luo, Zhi-wen; Xu, Bei; Shi, Guan-zhong; Zhao, Pan; Faure, M.; Chen, Yan

    2016-09-01

    The Solonker ophiolite is exposed along the border between Mongolia and China within the Solonker zone, the southeastern Central Asian Orogenic Belt (CAOB), and it is composed dominantly of serpentinized peridotite with subordinate gabbro, basaltic lava, radiolarian-bearing siliceous rocks, and minor plagiogranite. Meanwhile, layered mafic-ultramafic cumulates are not ubiquitous. In this study, zircon grains from two gabbros and a plagiogranite yield 206Pb/238U ages of 259 ± 6 Ma, 257 ± 3 Ma and 263 ± 1 Ma. These data were interpreted to represent the formation age of the Solonker ophiolite. The studied gabbros and basalts have a tholeiitic composition, showing a MORB affinity. They are also characterized by enrichment of Pb and depletion of Nb relative to La and Th. Furthermore, the studied gabbros contain inherited zircon grains and display a large range of zircon Hf isotopes (εHf(t) = - 5.27 to + 10.19). These features imply that crustal contamination played an important role in the generation of these mafic rocks. Major elements derived from the radiolarian-bearing siliceous rocks suggest a continental margin setting. This is confirmed by rock association. Terrigenous rocks (sandstones and siltstones) interstratified with siliceous rocks. U-Pb dating of detrital zircon grains in sandstones from both the northern and southern sides of the Solonker ophiolite belt, along with published data, reveals that the Late Carboniferous-Early Permian strata in fault contact with the Solonker ophiolite was deposited above Early Paleozoic orogens. The lines of petrological, geochemical, geochronological, and isotopic evidence led us to propose that the Solonker ophiolite is a Late Permian continental margin-type body formed during the early stages of opening of an ocean basin, following rifting and break-up of the Early Paleozoic orogens. Accordingly, the Permian Solonker zone is characterized by an intra-continental extensional setting.

  5. Paleozoic CO2 and the Permo-Carboniferous Glaciation

    NASA Astrophysics Data System (ADS)

    Berner, R. A.

    2006-12-01

    Models (GEOCARB and GEOCARBSULF) of the long-term, or multimillion year, carbon cycle have been constructed which include quantitative treatment of:(1) uptake of atmospheric CO2 by the weathering of silicate and carbonate rocks on the continents and the deposition of carbonate minerals and organic matter in oceanic sediments and (2) the release of CO2 to the atmosphere via the weathering of kerogen in sedimentary rocks and degassing resulting from the volcanic/metamorphic/diagenetic breakdown of carbonates and organic matter at depth . Sensitivity analysis indicates that an important factor affecting CO2 was the rise of vascular plants in the Paleozoic. A large Devonian drop in CO2 was brought about primarily by the acceleration of silicate rock weathering by the development of deeply rooted plants in well-drained upland soils. The quantitative effect of this accelerated weathering has been estimated by present-day field studies where all factors affecting weathering, other than the presence or absence of vascular plants, have been held relatively constant. An important additional factor, bringing about further CO2 drop into the Carboniferous and Permian, was enhanced burial of organic matter in sediments due to the production of microbially resistant plant remains, such as lignin . Paleozoic levels of atmospheric CO2 calculated from the GEOCARB and GEOCARBULF models generally agree with independent estimates based on measurements of the carbon isotopic composition of paleosols and the stomatal index for fossil plants, The mid-to-late Paleozoic drop in CO2 preceded and contributed to the Permo-Carboniferous continental glaciation, the longest and most extensive glaciation of the entire Phanerozoic. ..

  6. (U-Th)/He Ages of Detrital Zircons From Paleozoic Strata of the Severnaya Zemlya Archipelago (Russian High Arctic): implication for testing the different tectonic models

    NASA Astrophysics Data System (ADS)

    Ershova, Victoria; Anfinson, Owen; Prokopiev, Andrei; Khudoley, Andrei; Stockli, Daniel; Faleide, Jan Inge; Gaina, Carmen; Malyshev, Nikolay

    2016-04-01

    The Severnaya Zemlya archipelago comprises four main islands (Pioneer, October Revolution, Komsomolets and Bol'shevik), along with numerous other small islands, islets and island groups. It contains rocks varying in age from Late Cambrian to Permian and is a key area for understanding the tectonic evolution of the North Kara and Laptev Sea basins. Various models have been proposed for the Paleozoic history of the Kara Terrane: 1) Kara terrane inferred as a part of a larger continent block called Arctida (Zonenshain et al, 1990). 2) Lorenz et al. (2008a, 2008b) described the Kara terrane as a marginal part of Baltica. 3) The Kara Terrane existed as a separate terrane or microcontinent during the Paleozoic (Bogdanov et al., 1998; Gramberg & Ushakov, 2000; Metelkin et al., 2000, 2005) Here we present (U-Th)/He ages of detrital zircons collected from Ordovician - Devonian strata of Pioneer and October Revolution islands) along with Sedov Islands. All detrital zircon (U-Th)/He ages are older than age of host rocks indicating the samples were not buried deep enough (less than ~6-8 km) to reset the (U-Th)/He isotopic system. Thus, (U-Th)/He ages indicate the exhumational history of the clastic source region. The (U-Th)/He detrital zircon ages from Ordovician- Silurian strata, with a peak age of ca. 465 Ma, suggest the primary source region was located within the Caledonian Orogen, which is unknown in the modern vicinity of Severnaya Zemlya. The abundance of Caledonian (U-Th)/He zircon ages in the studied samples suggests a continuation of Caledonides northeastward across Barents shelf as previously inferred from pre-Permo-Carboniferous rifting restoration and illustrated by geophysical data. In contrast to older clastic rocks, (U-Th)/He detrital zircon ages from the Devonian deposits show a mixture of Ellesmerian and Caledonian ages with age peaks at ca. 365 Ma and 465 Ma and the youngest grains nearing the depositional age of the strata. The ages suggest the clastic

  7. Petroleum prospectivity in Precambrian and Early Paleozoic basins, Australia

    SciTech Connect

    Goldstein, B.A. )

    1991-03-01

    Proterozoic to Devonian age strata with some potential for petroleum accumulations are known from sedimentary basins covering {approximately}1,870,000 km{sup 2} onshore Australia. Portions of these very old basins have not sustained the deleterious effects of deep burial. Explorers with vision continue to target these very old rocks in the MacArthur/South Nicholson, Amadeus, Canning, Adavale, and Bonaparte basins. Approximately 429,000 km{sup 2} of these basins remain under license for petroleum exploration. The oldest known oil in Australia is reservoired within and sourced from the mid-Proterozoic in the McArthur basin. The Early Ordovician Pacoota Sandstone of the Amadeus basin is the oldest formation commercially exploited for oil and gas in Australia. Significant discoveries awaiting development include Dingo, Pictor, and Gilmore. The Tern gas field trap in the Bonaparte basin is related to a salt diapir; the salt probably being Silurian-Devonian in age. Salt probably of the same age has formed diapirs in the Canning basin, too. Cambrian and Proterozoic salt-bearing strata are likewise the cause and core of some anticlinal and diapiric structures in the Amadeus basin. Minor oil shows have been reported from the Cambrian of the Officer basin. The Warburton, Pedirka, Arrowie, Ord, Wiso, Georgina, and Ngalia basins contain Proterozoic and early Paleozoic sedimentary rocks but are ascribed only limited petroleum prospectivity at this time.

  8. Preliminary delineation and description of the regional aquifers of Tennessee : basal sandstone west of the Valley and Ridge Province

    USGS Publications Warehouse

    Brahana, J.V.; Bradley, Michael W.; Macy, Jo Ann; Mulderink, Dolores

    1986-01-01

    The basal sandstone is a poorly sorted, well indurated sandstone, which lies below the Conasauga Group and above the Precambrian crystalline rocks. It is an unknown resource defined by limited data, with only 14 data points (wells) for the entire State of Tennessee. The basal sandstone is thought to occur throughout most of the State west of the Valley and Ridge province at depths of generally more than 5,500 feet below land surface. The basal sandstone probably does not receive significant vertical recharge because the sandstone is overlain by such a thick sequence of flat-lying, low-porosity lower Paleozoic carbonates and shales. Data from two sites indicate that the rocks of the basal sandstone have relatively low porosity and permeability. The concentrations of dissolved solids in water from the basal sandstone range from less than 40,000 milligrams per liter to more than 200,000 milligrams per liter. The basal sandstone is not being used as a source of drinking water because of its great depth, the presence of shallower sources of drinking water, and possible concentrations of more than 10,000 milligrams per liter dissolved solids throughout its area of occurrence.

  9. Tidal-bundle sequences in the Jordan Sandstone (Upper Cambrian), southeastern Minnesota, U.S.A.: Evidence for tides along inboard shorelines of the Sauk Epicontinental Sea

    USGS Publications Warehouse

    Tape, C.H.; Cowan, Clinton A.; Runkel, Anthony C.

    2003-01-01

    This study documents for the first time tidal bundling in a lower Paleozoic sheet sandstone from the cratonic interior of North America, providing insights into the hydrodynamics of ancient epicontinental seas. The Jordan Sandstone (Upper Cambrian) in the Upper Mississippi Valley contains large-scale planar tabular cross-sets with tidal-bundle sequences, which were analyzed in detail at an exceptional exposure. Tidal-bundle sequences (neap-spring-neap cycles) were delineated by foreset thickening-thinning patterns and composite shale drapes, the latter of which represent accumulations of mud during the neap tides of neap-spring-neap tidal cycles. Fourier analysis of the bundle thickness data from the 26 measurable bundle sequences revealed cycles ranging from 15 to 34 bundles per sequence, which suggests a semidiurnal or mixed tidal system along this part of the Late Cambrian shoreline. We extend the tidal interpretation to widespread occurrences of the same facies in outcrops of lesser quality, where the facies is recognizable but too few bundles are exposed for tidal cycles to be measured. By doing so, this study shows that tidally generated deposits have a significant geographic and temporal extent in Upper Cambrian strata of central mid-continent North America. The deposition and preservation of tidal facies was related to the intermittent development of shoreline embayments during transgressions. The tidally dominated deposits filled ravined topographies that were repeatedly developed on the updip parts of the shoreface. Resulting coastal geomorphologies, accompanied perhaps by larger-scale changes in basinal conditions and/or configuration, led to changes in depositional conditions from wave-dominated to tide-dominated. Outcrops of the Jordan Sandstone tidal facies in the Upper Mississippi Valley represent the farthest inboard recorded transmission of ocean-generated tides in the Laurentian epicontinental seas, demonstrating that tidal currents were

  10. Similarities in the Paleozoic successions of north Africa and Arabia and implications for petroleum exploration

    SciTech Connect

    Clark-Lowes, D.D. )

    1988-08-01

    From field studies in southwest Libya and northwest Saudi Arabia, the facies of the Paleozoic succession of the north African/Arabian stable cratonic margin of Gondwanaland are interpreted as fluvial, estuarine, deltaic, shallow marine, and glacial deposits. The facies of the Saq and Tabuk Formations of Saudi Arabia bear witness to a sedimentary history that is very similar to that of north Africa, the Saq Formation (Cambrian-Arenig) being equivalent to the Hassaouna Formation of Libya and the Tabuk Formation being subdivided and correlated using well-dated shale members to the following formations: Haouaz (Llanvirn-Llandeilo), Melez-Chograne (Caradoc), Memouniat (Ashgill), Tanezzuft/Acacus (Llandovery-Ludlow), and Tadrart (Gedinnian -Emsian). The Cambrian-Ordovician succession comprises Nubian-type fluvial and estuarine sandstones which pass up to regressive deltaic/shallow marine sequences overlain by Upper Ordovician glacial deposits that lie in deeply incised paleovalleys recorded from Saudi Arabia and north Africa. The Silurian succession comprises the deposits of a postglacial marine transgression of vast lateral extent and a subsequent regression, the sandstones of which are markedly diachronous. The Lower Devonian succession comprises fining-upward retrogradational deltaic (transgressive) sequences of Nubian-type sandstones (fluvial to shallow marine) which form widespread blanket sandstone bodies. The prospectivity of these strata is well known from Algeria in the west to Jordan in the east, the Llandoverian oil-prone source rocks providing the key to Cambrian-Ordovician and Lower Devonian plays. The significance of underlying paleovalley-fill fluvioglacial sandstones as linear reservoir targets has yet to be fully appreciated.

  11. Assessment of Appalachian basin oil and gas resources: Utica-Lower Paleozoic Total Petroleum System: Chapter G.10 in Coal and petroleum resources in the Appalachian basin: distribution, geologic framework, and geochemical character

    USGS Publications Warehouse

    Ryder, Robert T.; Ruppert, Leslie F.; Ryder, Robert T.

    2014-01-01

    Both conventional oil and gas resources and continuous (unconventional) gas resources are present in the UticaLower Paleozoic TPS. Conventional oil and gas resources in the Utica-Lower Paleozoic TPS were assessed by the U.S. Geological Survey (USGS) in 2002 in the following assessment units (AU): (1) the Lower Paleozoic Carbonates in Thrust Belt AU, (2) the Knox Unconformity AU, (3) the Black River-Trenton Hydrothermal Dolomite AU, and (4) the Lockport Dolomite AU. The total estimated undiscovered oil and gas resources for these four AUs, at a mean value, was about 46 million barrels of oil (MMBO) and about 3 trillion cubic feet of gas (TCFG), respectively. In contrast, continuous (unconventional) gas resources in the TPS were assessed by the USGS in 2002 in four AUs associated with the “Clinton” sandstone, Medina sandstone, Medina Group sandstones, Tuscarora Sandstone, and sandstones in the Queenston Shale. The total estimated undiscovered gas for these four AUs, at a mean value, was about 26.8 TCFG. A hypothetical Utica Shale AU for oil(?) and continuous gas is identified in this report. In 2012, the Utica Shale was recognized by the USGS as a continuous AU and was assessed by Kirschbaum and others (2012).

  12. Thermochronological Constraints on Detrital Sediments of the Late Permian Karoo Basin: Insights Into Uplift History of the Cape Fold Belt

    NASA Astrophysics Data System (ADS)

    Tohver, E.; Arosio, R.; Schmieder, M.; Jourdan, F.; Wilson, A.; Flint, S.

    2012-12-01

    The Karoo Basin and its equivalents cover most of southern Africa, with correlative basins found also in South America. The vast geographic expanse of these basins indicates a common history of deposition along the active Panthalassan margin of southern Gondwana. The early Paleozoic history of the Karoo Basin is marked by early glacio-marine to later shallow marine-deltaic sedimentation with a final shift to a continental setting by the late Permian. In South Africa, this transition to a fluvial environment is defined by the deposition of the Beaufort Group, a ca. 5 km thick sequence of meandering river channel sandstones and muddy overbank deposits. We have identified an 800 m thick sequence of the lowermost Beaufort Group where magnetostratigraphy and U-Pb dating of zircon in volcanic tuffs establish a depositional age of 264-268 Ma. Detrital zircon from sandstone samples were dated by U-Pb SHRIMP, revealing age populations typical of the cratonic/metamorphic provinces of the Kalahari craton (Kaapval and Namaqua-Natal provinces) as well as late Paleozoic magmatic zircons probably from southern South America. Populations of detrital muscovite dated using the 40Ar/39Ar step-heating technique are dominated by a tight cluster of ca. 272 Ma cooling ages, indicating rapid exhumation of the tectonically active Cape Fold belt and short lag times (4-8 Ma) for detritus deposited into the Karoo foreland basin, similar to rates observed for modern sediments of Himalayan-draining rivers. Ongoing work will reveal whether the Cape Belt is the source for the sediments of the Karoo foreland basin.

  13. Geology of 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 geology of the Paleozoic rocks in the Upper Colorado River Basin in Arizona, Colorado, New Mexico, Utah, and Wyoming, was studied as part of the U.S. Geological Survey's Regional Aquifer-System Analysis Program to provide support for hydrogeological interpretations. The study area is segmented by numerous uplifts and basins caused by folding and faulting that have recurred repeatedly from Precambrian to Cenozoic time. Paleozoic rocks in the study area are 0-18,000 feet thick. They are underlain by Precambrian igneous, metamorphic, and sedimentary rocks and are overlain in most of the area by Triassic formations composed mostly of shale. The overlying Mesozoic and Tertiary rocks are 0-27,000 feet thick. All Paleozoic systems except the Silurian are represented in the region. The Paleozoic rocks are divisible into 11 hydrogeologic units. The basal hydrogeologic unit consisting of Paleozoic rocks, the Flathead aquifer, predominantly is composed of Lower to Upper Cambrian sandstone and quartzite. The aquifer is 0-800 feet thick and is overlain gradationally to unconformably by formations of Cambrian to Mississippian age. The Gros Ventre confining unit consists of Middle to Upper Cambrian shale with subordinate carbonate rocks and sandstone. The confining unit is 0-1,100 feet thick and is overlain gradationally to unconformably by formations of Cambrian to Mississippian age. The Bighom aquifer consists of Middle Cambrian to Upper Ordovician limestone and dolomite with subordinate shale and sandstone. The aquifer is 0-3,000 feet thick and is overlain unconformably by Devonian and Mississipplan rocks. The Elbert-Parting confining unit consists of Lower Devonian to Lower Mississippian limestone, dolomite, sandstone, quartzite, shale, and anhydrite. It is 0-700 feet thick and is overlain conformably to unconformably by Upper Devonian and Mississippian rocks. The Madison aquifer consists of two zones of distinctly different lithology. The lower (Redwall-Leadville) zone

  14. Petrology, diagnosis, and sedimentology of oil reservoirs in Upper Cretaceous Shannon Sandstone Beds, Powder River basin, Wyoming

    SciTech Connect

    Hansley, P.L.; Whitney, C.G.

    1990-01-01

    This paper reports on a study of the petrology of the Shannon Sandstone Member that indicates diagenetic alterations of outcrop and near-surface sandstones cannot be used to predict the diagenesis of deeply buried sandstones. Textural relations show that oil migrated to reservoirs late in the postdepositional history of the Shannon. Petrologic and sedimentologic data suggest that an alternative depositional model (for example, a nearshore rather than mid-shelf setting) should be considered for the Shannon.

  15. Factors controlling reservoir quality in tertiary sandstones and their significance to geopressured geothermal production. Annual report, May 1, 1979-May 31, 1980

    SciTech Connect

    Loucks, R.G.; Richmann, D.L.; Milliken, K.L.

    1980-07-01

    Differing extents of diagenetic modification is the factor primarily responsible for contrasting regional reservoir quality of Tertiary sandstones from the Upper and Lower Texas Gulf Coast. Detailed comparison of Frio sandstones from the Chocolate Bayou/Danbury Dome area, Brazoria County, and Vicksburg sandstones from the McAllen Ranch Field area, Hidalgo County, reveals that extent of diagenetic modification is most strongly influenced by (1) detrital mineralogy and (2) regional geothermal gradients. Vicksburg sandstones from the McAllen Ranch Field area are less stable, chemically and mechanically, than Frio sandstones from the Chocolate Bayou/Danbury dome area. Vicksburg sandstones are mineralogically immature and contain greater proportions of feldspars and rock fragments than do Frio sandstones. Thr reactive detrital assemblage of Vicksubrg sandstones is highly susceptible to diagenetic modification. Susceptibility is enhanced by higher than normal geothermal gradients in the McAllen Ranch Field area. Thus, consolidation of Vicksburg sandstones began at shallower depth of burial and precipitation of authigenic phases (especially calcite) was more pervasive than in Frio sandstones. Moreover, the late-stage episode of ferroan calcite precipitation that occluded most secondary porosity in Vicksburg sandstones did not occur significantly in Frio sandstones. Therefore, regional reservoir quality of Frio sandstones from Brazoria County is far better than that characterizing Vicksburg sandstones from Hidalgo County, especially at depths suitable for geopressured geothermal energy production.

  16. (Vitrinites of Mesozoic, Cenozoic, and Paleozoic coals)

    SciTech Connect

    Faizullina, E.M.; Lapo, A.V.

    1982-01-01

    In the reported experiment, the vitrinites of the coalification stages from B to A have been studied by IR spectrometry. A comparison of the intensities of the absorption bands of equally coalified vitrinites of different ages has shown that they differ mainly in their content of stretching vibrations of aliphatic CH and CH/sub 2/ groups (absorption bands at 2930 and 2860 cm/sup -1/) and the stretching vibrations of C.0 groups (band close to 1700 cm/sup -1/). A high absorption in the vitrinites of Mesozoic and Cenozoic coals due to aliphatic CH and CH/sub 2/ groups as compared with the vitrinities of Paleozoic coals has been found. The laws established previously in the coalification series for the vitrinites of Paleozoic coals have also been confirmed for the vitrinites of Meso-Cenozoic coals. 13 refs.

  17. Isotopic age constraints on middle Paleozoic deformation in the northern Sierra Nevada, California

    SciTech Connect

    Saleeby, J.; Hannah, J.L.; Varga, R.J.

    1987-08-01

    Allochthons of the lower Paleozoic Shoo Fly Complex in the northern Sierra Nevada were assembled and internally deformed prior to formation of a Devonian-Permian island-arc sequence. U/Pb data on zircons indicate ages of 423 +5/-15 Ma for a submarine tuff within the uppermost thrust slice of the Shoo Fly Complex and 378 +5/-10 Ma for a granitic intrusion that may be cogenetic with the lower part of the arc sequence. These data indicate late Early Silurian Shoo Fly deposition and proximity to active volcanism, as well as late Middle Devonian initiation of arc-related magmatism.

  18. The Geochemical Figure Print of an Early Paleozoic OAE

    NASA Astrophysics Data System (ADS)

    Gill, B.; Young, S.; Kump, L.; Saltzman, M.; Lyons, T.

    2007-12-01

    The Paleozoic Era contains many large, commonly globally expressed positive carbon isotope excursions recorded in carbonate rocks. In younger Mesozoic rocks, similar excursions are often easily linked to organic-rich deposits formed from enhanced carbon burial under ocean-scale anoxia -i.e., oceanic anoxic events (OAEs). These events are important since voluminous organic carbon and pyrite burial in anoxic settings can be a central player in modulating the amount of oxygen and carbon dioxide in the atmosphere, and many of Earth's major extinctions are coeval with ocean-scale anoxia. In contrast, physical records of organic carbon burial tied to the carbon isotope record are scarce in the Paleozoic; leading to ambiguity in the interpretation of the isotope data. These data become less cryptic when viewed in light of coeval seawater sulfur isotope trends. For the globally expressed, Late Cambrian (SPICE) carbon isotope excursion, carbonate-C and sulfate-S records reveal parallel, positive isotope shifts suggesting enhanced organic C and pyrite S burial. Additionally, both organic carbon and pyrite sulfur isotope data from the Alum Shale of Sweden record the SPICE Event, putting to rest questions of the primary nature of the carbonate records. Comparison of the SPICE to similar isotope data from the Toarcian OAE and results from geochemical box modeling of both events lead us to conclude that the SPICE Event is a prime candidate for an early Paleozoic OAE. Additional evidence for increased ocean anoxia coincident with the SPICE also comes from the Alum Shale. Molybdenum concentrations show muted enrichment during the extent of the SPICE, despite data that show the basin was persistently euxinic before, during and after the event. Significant increases in molybdenum concentration occur only immediately after the event; suggesting a depleted seawater Mo inventory associated with a greatly expanded global anoxic Mo sink during the SPICE. An interesting result from

  19. From source-to-sink: The Late Permian SW Gondwana paleogeography and sedimentary dispersion unraveled by a multi-proxy analysis

    NASA Astrophysics Data System (ADS)

    Alessandretti, Luciano; Machado, Rômulo; Warren, Lucas Veríssimo; Assine, Mario Luis; Lana, Cristiano

    2016-10-01

    The Late Permian sedimentary succession of the Paraná Basin, southern Brazil, provide a valuable source of information about sediment provenance, tectonic processes and, consequently, the paleogeography of the southwestern Gondwana supercontinent. In order to understand the patterns of sedimentary dispersal and reconstruct the Late Permian source-to-sink dynamic, we report a complete series of U-Pb ages and Hf isotopic compositions of detrital zircons from the Rio do Rasto Formation sandstones allied with detailed paleocurrent and sedimentologic data. Our integrated provenance study reveals a consistent sediment transport from the south to the north and northwest. According to the evaluation of zircon ages and Hf isotopes, it was possible to determine four distinct source areas: (i) a distant Late Paleozoic active magmatic arc located in the southwestern Gondwana margin (i.e. Gondwanides Orogen), corresponding to the North Patagonian Massif; (ii) recycling of orthoquartzites from the uplifted Paleozoic Ventania Fold Belt and immature sandstones from the Claromecó Foreland Basin in central-eastern Argentina and the Silurian-Devonian successions of the southern Paraná Basin (central-northern Uruguay) and North Patagonian Massif; (iii) exhumed areas of the Archean-Paleoproterozoic basement and Neoproterozoic to Early Paleozoic mobile belts of the Damara in southwestern Africa and Ribeira Fold Belt in Uruguay and southern Brazil; and (iv) southeastward provenance of Grenvillian (1.2-1.0 Ga) zircons coming from the mafic to intermediate Mesoproterozoic igneous units of the Namaqua-Natal Belt in South Africa and Namibia. These data allow us to argue that sediments deposited in the Paraná Basin during the Late Permian come from both short- and long-distance source areas. In this context, an important population of Permian detrital zircons comes from the Gondwanides Orogen in the south, probably carried by transcontinental alluvial systems. Close to the source area

  20. The Madong Early Paleozoic fold-thrust belt in southern Tarim Basin

    NASA Astrophysics Data System (ADS)

    Li, Yue-Jun; Wen, Lei; Li, Hui-Li; Peng, Geng-Xin; Qiu, Bin; Zheng, Duo-Ming; Luo, Jun-Cheng; Zhang, Qiang; Jia, Tie-Gan

    2016-01-01

    The Madong fold-thrust belt, which strikes NE-SW and thrusts southeastward, locates in the southern Tarim Basin. It is a part of the Kunlun Early Paleozoic foreland fold-thrust belt, and so is the Tangnan fold-thrust belt on the southeast of Madong. The Madong and Tangnan fold-thrust belts developed in Cambrian-Ordovician strata, and the Middle Cambrian gypsum-salt layer serves as the main décollement surface. The Middle Silurian and above strata unconformably overlie Madong while the upper Lower Silurian unconformably overlie Tangnan. On the basis of the facts that: (1) the Upper Ordovician is the youngest strata involved in the fold-thrust deformation, (2) the upper-Lower to Middle Silurian is the oldest strata unconformably overlying the foreland fold-thrust belt (including Madong and Tangnan), and growth strata exist in the upper part of the Upper Ordovician, we infer that the deformation time of the Kunlun Early Paleozoic foreland fold-thrust belt (including Madong and Tangnan) was during the Late Ordovician-Early Silurian. Tangnan is the residual of the major part of the foreland fold-thrust belt. Its northwestward thrust direction represents the main thrust direction of the foreland fold-thrust belt. Madong is the front belt of the foreland fold-thrust belt. It mainly thrusts southeastward and serves as the back-thrust belt of the Kunlun Early Paleozoic foreland fold-thrust belt. It is a triangle zone between Madong and Tangnan. The Madong fold-thrust belt is the best-preserved section of the Kunlun Early Paleozoic collisional orogenic belt, and thus is an important geological record of the Kunlun Early Paleozoic orogeny.

  1. Paleozoic terranes of eastern Australia and the drift history of Gondwana

    NASA Astrophysics Data System (ADS)

    McElhinny, Michael W.; Powell, Chris McA.; Pisarevsky, Sergei A.

    2003-02-01

    Critical assessment of Paleozoic paleomagnetic results from Australia shows that paleopoles from locations on the main craton and in the various terranes of the Tasman Fold Belt of eastern Australia follow the same path since 400 Ma for the Lachlan and Thomson superterranes, but not until 250 Ma or younger for the New England superterrane. Most of the paleopoles from the Tasman Fold Belt are derived from the Lolworth-Ravenswood terrane of the Thomson superterrane and the Molong-Monaro terrane of the Lachlan superterrane. Consideration of the paleomagnetic data and geological constraints suggests that these terranes were amalgamated with cratonic Australia by the late Early Devonian. The Lolworth-Ravenswood terrane is interpreted to have undergone a 90° clockwise rotation between 425 and 380 Ma. Although the Tamworth terrane of the western New England superterrane is thought to have amalgamated with the Lachlan superterrane by the Late Carboniferous, geological syntheses suggest that movements between these regions may have persisted until the Middle Triassic. This view is supported by the available paleomagnetic data. With these constraints, an apparent polar wander path for Gondwana during the Paleozoic has been constructed after review of the Gondwana paleomagnetic data. The drift history of Gondwana with respect to Laurentia and Baltica during the Paleozoic is shown in a series of paleogeographic maps.

  2. Paleozoic large igneous provinces of Northern Eurasia: Correlation with mass extinction events

    NASA Astrophysics Data System (ADS)

    Kravchinsky, Vadim A.

    2012-04-01

    This paper assesses data from recently described major Paleozoic large igneous provinces (LIPs), mostly in Northern Eurasia. The 10 LIPs reviewed form a unimodal distribution in terms of volume. Eight LIPs have an initial modal volume greater than 0.1 × 106 km3. The rift associated basalts of 2 LIPs from the end of the Late Cambrian Period and the end of the Late Ordovician Period do not occupy a large volume. Some of the provinces were discovered or rediscovered relatively recently and dating is still approximate, but most provinces fit a simple model in which volcanism persisted on the order of 10-20 Myr, often resulting in continental break-up. Correlation between LIP ages and the ages of geological events in the Paleozoic Era that reflect mass extinctions and oceanic anoxia agrees with correlations suggested by Courtillot (1994) and Courtillot and Renne (2003) for the Cenozoic and Mesozoic eras, considering that the absolute dating of some Paleozoic LIPs needs to be strengthened in the future.

  3. Paleozoic and mesozoic evolution of East-Central California

    USGS Publications Warehouse

    Stevens, C.H.; Stone, P.; Dunne, G.C.; Greene, D.C.; Walker, J.D.; Swanson, B.J.

    1997-01-01

    East-central California, which encompasses an area located on the westernmost part of sialic North America, contains a well-preserved record of Paleozoic and Mesozoic tectonic events that reflect the evolving nature of the Cordilleran plate margin to the west. After the plate margin was formed by continental rifting in the Neoproterozoic, sediments comprising the Cordilleran miogeocline began to accumulate on the subsiding passive margin. In east-central California, sedimentation did not keep pace with subsidence, resulting in backstepping of a series of successive carbonate platforms throughout the early and middle Paleozoic. This phase of miogeoclinal development was brought to a close by the Late Devonian-Early Mississippian Antler orogeny, during the final phase of which oceanic rocks were emplaced onto the continental margin. Subsequent Late Mississippian-Pennsylvanian faulting and apparent reorientation of the carbonate platform margin are interpreted to have been associated with truncation of the continental plate on a sinistral transform fault zone. In the Early Permian, contractional deformation in east-central California led to the development of a narrow, uplifted thrust belt flanked by marine basins in which thick sequences of deep-water strata accumulated. A second episode of contractional deformation in late Early Permian to earliest Triassic time widened and further uplifted the thrust belt and produced the recently identified Inyo Crest thrust, which here is correlated with the regionally significant Last Chance thrust. In the Late Permian, about the time of the second contractional episode, extensional faulting created shallow sedimentary basins in the southern Inyo Mountains. In the El Paso Mountains to the south, deformation and plutonism record the onset of subduction and arc magmatism in late Early Permian to earliest Triassic time along this part of the margin. Tectonism had ceased in most of east-central California by middle to late Early

  4. Mid-Paleozoic latitudinal predation gradient: Distribution of brachiopod ornamentation reflects shifting Carboniferous climate

    NASA Astrophysics Data System (ADS)

    Dietl, Gregory P.; Kelley, Patricia H.

    2001-02-01

    Shell ornamentation in modern oceans increases toward the tropics in conjunction with an equatorward increase in shell-breaking predation. Latitudinal gradients in antipredatory ornamentation were previously documented for Devonian brachiopods. We examined the latitudinal distribution of shell ornamentation in Tournaisian, Visean, and Namurian articulate brachiopods to test the hypothesis that the latitudinal gradient in antipredatory ornamentation was present in the Carboniferous. We found a statistically significant latitudinal ornamentation gradient, which was most pronounced in the Tournaisian, when the latitudinal temperature gradient was most steep. These results support the hypothesis that a latitudinal gradient in defensive morphology occurred as a result of the mid-Paleozoic increase in predation. Although the mid-Paleozoic and late Mesozoic intervals of predator-prey escalation may have differed in dynamics and intensity, both episodes produced adaptations in prey morphology that varied along a latitudinal gradient.

  5. Extending the western North American Proterozoic and Paleozoic continental crust through the Mojave Desert

    SciTech Connect

    Martin, M.W.; Walker, J.D. )

    1992-08-01

    Data supporting the existence of Proterozoic basement in the central and western Mojave Desert include U-Pb zircon geochronology and Nd, Sr, and Pb isotopic values of quartzofeldspathic gneisses, detrital zircon provenance ages, and the presence of basement clasts in Paleozoic and Mesozoic conglomerates. These data corroborate existing isotopic data from Mesozoic and Tertiary intrusive rocks that suggest involvement of Proterozoic crust in their genesis. Exposures of Proterozoic basement and Late Proterozoic and Paleozoic transitional miogeoclinal-cratonal facies trends in the central and western Mojave Desert consistently imply that cratonal North America continues westward uninterrupted through this region to the San Andreas fault. These data place geographic limits on the position of several pre-Tertiary tectonic elements speculated to exist in the Mojave Desert.

  6. New isotopic evidence for the origin of groundwater from the Nubian Sandstone Aquifer in the Negev, Israel

    USGS Publications Warehouse

    Vengosh, A.; Hening, S.; Ganor, J.; Mayer, B.; Weyhenmeyer, C.E.; Bullen, T.D.; Paytan, A.

    2007-01-01

    SO4-rich groundwater from the underlying Jurassic aquifer contributes significantly to the salt budget of the Nubian Sandstone aquifer. The unique chemical and isotopic composition of the Jurassic groundwater (??34SSO4 ??? +14???; ??18OSO4 ??? 14???; 87Sr/86Sr ???0.70764) is interpreted as reflecting dissolution of Late Triassic marine gypsum deposits. In the southern Arava Valley the authors postulate that SO4-rich groundwater with distinctively high Br/Cl (3 ?? 10-3) low 87Sr/86Sr (0.70734), and high ??34SSO4 values (+15???) is derived from mixing with underlying brines from the Paleozoic units. The radiocarbon measurements reveal low 14C activities (0.2-5.8 pmc) in both the northeastern Negev and southern Arava Valley. Taking into account dissolution of carbonate rocks and bacterial SO4 reduction in the unconfined area, estimated mean residence times of groundwater in the confined zone in the northeastern Negev are on the order of 21-38 ka, which suggests recharge predominantly during the last glacial period. The 14C signal in groundwater from the southern Arava Valley is equally low but due to evidence for mixing with external water sources the residence time estimates are questionable. ?? 2007 Elsevier Ltd. All rights reserved.

  7. Petroleum potential of lower and middle Paleozoic rocks in Nebraska portion of Mid-Continent

    SciTech Connect

    Carlson, M.P. )

    1989-08-01

    Central North America during the Paleozoic was characterized by northern (Williston) and southern (Anadarko) depositional regimes separated by a stable Transcontinental arch. Nebraska lies on the southern flank of this arch and contains the northern zero edges of the lower and middle Paleozoic rocks of the southern regime. Most of these rocks are secondary dolomites with zones of excellent intercrystalline porosity. The Reagan-LaMotte Sandstones and the overlying Arbuckle dolomites are overlapped by Middle Ordovician rocks toward the Transcontinental arch. Rocks equivalent to the Simpson consist of a basal sand (St. Peter) and overlying interbedded gray-green shales and dolomitic limestones. An uppermost shale facies is present in the Upper Ordovician (Viola-Maquoketa) eastward and southward across Nebraska. The dolomite facies extends northward into the Williston basin. The Silurian dolomites, originally more widely deposited, are overlapped by Devonian dolomites in southeastern Nebraska. Upper Devonian rocks exhibit a regional facies change from carbonate to green-gray shale to black shale southeastward across the Mid-Continent. Mississippian carbonates overlap the Devonian westward and northward across the Transcontinental arch. Pennsylvanian uplift and erosion were widespread, producing numerous stratigraphic traps. Sands related to the basal Pennsylvanian unconformity produce along the Cambridge arch. Arbuckle, Simpson, Viola, and Hunton production is present in the Forest City basin and along the Central Kansas uplift. Although source rocks are scarce and the maturation is marginal, current theories of long-distance oil migration encourage exploration in the extensive lower and middle Paleozoic reservoirs in this portion of the Mid-Continent.

  8. Middle-Late Mesozoic sedimentary provenances of the Luxi and Jiaolai areas: Implications for tectonic evolution of the North China Block

    NASA Astrophysics Data System (ADS)

    Xu, Jianqiang; Li, Zhong

    2015-11-01

    Provenances of sedimentary rocks may provide important constraints on the tectonic evolution of the North China Block (NCB). Previous studies have demonstrated that the northern NCB (NNCB) and the Xing-Meng orogenic belt (XMOB) supplied massive detritus southward into the hinterland of the NCB during the Jurassic. In order to study the evolution of sedimentary provenance during the Middle-Late Mesozoic, U-Pb geochronology and Hf isotopic geochemistry of detrital zircon grains and chemical compositions of detrital garnets from sandstones in the Luxi and Jiaolai areas, eastern NCB, were analyzed in combination with published data on the Jurassic sandstones. The Late Paleozoic-Mesozoic (367-139 Ma) zircons in the lowermost Cretaceous Mengyin Formation samples from the Luxi area show εHf(t) values of -15.3 to -3.2 and +1.3 to +10.0, which are very similar to the results of analyses of the Jurassic formations. Further, the increased amount of Mesozoic zircons and granulite-derived garnets in the Mengyin Formation samples, compared to those in the Jurassic samples, indicates there was more detritus supply from the NNCB than from the XMOB. In the overlying Qingshan Formation samples, zircon grains do not exhibit Paleozoic ages, but most of them have Early Cretaceous ages and negative εHf(t) values, which are similar to the zircon grains extracted from the widespread Early Cretaceous igneous rocks in the NCB. This suggests that the provenance might have changed to a locally derived source. In contrast, the zircon population of the Early Cretaceous sandstones from the Jiaolai basin is dominated by grains of mid-Neoproterozoic age (700-900 Ma) which signifies contribution from the Sulu orogen. Moreover, the detrital garnet assemblages of sandstones in the Luxi area are not consistent with those from representative metamorphic rocks in the Sulu orogen. The above results seem to confirm that the Mesozoic sedimentary provenance of the Luxi area had no evident connection with

  9. Evolution of Complexity in Paleozoic Ammonoid Sutures.

    PubMed

    Saunders; Work; Nikolaeva

    1999-10-22

    The septal sutures of 588 genera of Paleozoic ammonoids showed a 1600 percent increase in mean complexity over 140 million years. Within 475 ancestor/descendant pairs, descendants were more than twice as likely to be more complex than their ancestors. Twelve subclades (373 genera) averaged 34 percent increased complexity. These patterns are compatible with an active or driven system of long-term bias for increased complexity. Mass extinctions acted in opposition to this long-term trend, tending to eliminate more-complex forms and resetting the trend with each extinction event.

  10. Environmental trends in extinction during the Paleozoic

    NASA Technical Reports Server (NTRS)

    Sepkoski, J. John, Jr.

    1987-01-01

    Extinction intensities calculated from 505 Paleozoic marine assemblages divided among six environmental zones and 40 stratigraphic intervals indicate that whole communities exhibit increasing extinction offshore but that genera within individual taxonomic classes tend to have their highest extinction onshore. The offshore trend at the community level results from a concentration of genera in classes with low characteristic extinction rates in nearshore environments. This finding is consistent with the ecologic expectation that organisms inhabiting unpredictably fluctuating environments should suffer more extinction than counterparts living under more predictably equitable conditions.

  11. Operation Sandstone: 1948. Technical report

    SciTech Connect

    Berkhouse, L.H.; Hallowell, J.H.; McMullan, F.W.; Davis, S.E.; Jones, C.B.

    1983-12-19

    SANDSTONE was a three-detonation atmospheric nuclear weapon test series conducted during the spring of 1948 at Enewetak Atoll in the Marshall Islands. Report emphasis is on the radiological safety of the personnel. Available records on personnel exposure are summarized.

  12. A New Classification of Sandstone.

    ERIC Educational Resources Information Center

    Brewer, Roger Clay; And Others

    1990-01-01

    Introduced is a sandstone classification scheme intended for use with thin-sections and hand specimens. Detailed is a step-by-step classification scheme. A graphic presentation of the scheme is presented. This method is compared with other existing schemes. (CW)

  13. Artesian pressures and water quality in Paleozoic aquifers in the Ten Sleep area of the Bighorn Basin, north-central Wyoming

    USGS Publications Warehouse

    Cooley, Maurice E.

    1986-01-01

    The major Paleozoic artesian aquifers, the aquifers most favorable for continued development, in the Ten Sleep area of the Bighorn Basin of Wyoming are the Tensleep Sandstone, the Madison Limestone and Bighorn Dolomite (Madison-Bighorn aquifer), and the Flathead Sandstone. The minor aquifers include the Goose Egg and Park City Formations (considered in the Ten Sleep area to be the lateral equivalent of the Phosphoria Formation) and the Amsden Formation. Most wells completed in the major and minor aquifers flow at the land surface. Wellhead pressures generally are less than 50 pounds per square inch for the Tensleep Sandstone, 150-250 pounds per square inch for the Madison-Bighorn aquifer, and more than 400 pounds per square inch for the Flathead Sandstone. Flowing wells completed in the Madison-Bighorn aquifer and the Flathead Sandstone yield more than 1,000 gallons per minute. The initial test of one well completed in the Madison-Bighorn aquifer indicated a flow rate of 14,000 gallons per minute. Transmissivities range from 500 to 1,900 feet squared per day for the Madison-Bighorn aquifer and from about 90 to 325 feet squared per day for the Tensleep and Flathead Sandstones. Significant secondary permeability from fracturing in the Paleozoic aquifers allows local upward interformational movement of water, and this affects the altitude of the potentiometric surfaces of the Tensleep Sandstone and the Madison-Bighorn aquifer. Water moves upward from the Tensleep and other formations, through the Goose Egg Formation, to discharge at the land surface as springs. Much of the spring flow is diverted for irrigation or is used for rearing fish. Decreases from original well pressures were not apparent in wells completed in the Tensleep Sandstone or in the Madison-Bighorn aquifer in the study area except for a few wells in or near the town of Ten Sleep. Most wells completed in the Flathead Sandstone, which also are open to the Madison-Bighorn aquifer, show a decrease of

  14. Fragments of the Vendian-Paleozoic oceanic crust of the Paleo-Asian Ocean in foldbelts (Altai-Sayan, Central Asia)

    NASA Astrophysics Data System (ADS)

    Safonova, I.; Buslov, M.

    2003-04-01

    Four main accretion-collision stages of the evolution of the Paleo-Asian ocean have been recognized in Altai-Sayan: 1) Early-Middle Cambrian, 2) Late Cambrian-Early Ordovician, 3) Devonian-Early Carboniferous and 4) Late Paleozoic. The 1st and 2nd stages characterize evolution of the Kuznetsk-Altai island-arc system, which was accreted to the Siberian continent. The third stage refers to two collisional events during the closing of the Paleo-Asian Ocean: the Gondwana-derived Altai-Mongolian terrane collided with the Siberian continent (D3), and the latter collided with the Kazakhstan continent (C2). Each stage was recorded in folded rock units. Paleooceanic crust fragments occur within accretionary wedges and suture zone. Their geological identification was supported by geochemical data. The better studied areas are Kurai and Katun accretionary wedges, Charysh-Terekta shear zone, and Chara ophiolitic suture zone. Identification of the Vendian-Early Carboniferous oceanic crust extended our knowledge about the Paleo-Asian Ocean evolution. The Kurai and Katun accretionary wedges recorded the Vendian-Cambrian stage of the Kuznetsk-Altai island arc evolution. The Charysh-Terekta zone resulted from the Late Devonian collision of the Altai-Mongolian terrane and the Siberian continent. The Chara ophiolitic suture was formed after the Late Carboniferous-Permian collision of the Siberian and Kazakhstan continents. The Kurai accretionary wedge is composed of the tectonic sheets of the Baratal paleoisland and Chagan-Uzun ophiolites. The Katun accretionary wedge involves paleo-oceanic island rock units: limestones, dolomites, siliceous shales, and basaltic flows. The Charysh-Terekta zone is composed of several tectonic lenses (e.g. Zasurin Formation) comprising sandstones, cherts, pillow-basalts, volcanoclastics, and gabbro-diabase sills and dikes. The Chara ophiolitic belt consists of several melange zones with high-pressure metamorphic rocks (metabasaltic rocks) metamorphosed

  15. Grebull sandstone pool (Lower Cretaceous) on Elk Basin thrust-fold complex, Wyoming and Montana

    SciTech Connect

    Stone, D.S.

    1984-07-01

    The Elk Basin field in the northern Bighorn basin is a giant structural trap with cumulative production surpassing 500 million bbl, principally from a Paleozoic common pool. Abundant well data and seismic information have been used in a stratigraphic and structural study focusing on the Greybull (Lower Cretaceous) gas pool and on deeper formations along this structural complex. These data support an interpretation of the Elk Basin field as a thrust-fold complex, underlain by a listric thrust fault zone which probably emanates from Precambrian basement at an angle of 45/sup 0/ or less. The fault steepens upward and dies out in steeply dipping Mesozoic clastics that are attenuated and cut by extensional faults at the surface. The little known Greybull Sandstone pool at Elk Basin field, which is now used for gas storage, was discovered in 1920, and contained estimated primary recoverable reserves of 54 bcf of gas at an average depth of about 2500 ft (760 m). The Greybull lies stratigraphically between the Dakota and Morrison Formations, and is composed of two distinct sandstone units, called A and B at the North Clark's Fork field in southern Montana. The lower B unit at Elk Basin is a fluvial river-channel deposit which ranges up to 150 ft (45 m) in thickness and nearly 2 mi (3 km) in width. The upper A unit is a series of shoreline sandstone deposits oriented northwest-southeast. Individual, porous A sandstone bodies range from a few feet to more than 20 ft (6 m) in thickness at Elk Basin. These two Greybull Sandstone units are part of a common gas pool covering about 2000 acres (800 ha.) of the crestal closure of the Elk Basin anticline. Seismic modeling indicates that Greybull Sandstone channels over 60 ft (18 m) thick may be detected by reflection character changes in CDP seismic data.

  16. Diagenetic history of fluvial and lacustrine sandstones of the Hartford Basin (Triassic Jurassic), Newark Supergroup, USA

    NASA Astrophysics Data System (ADS)

    Wolela, A. M.; Gierlowski-Kordesch, E. H.

    2007-04-01

    The early introduction of clays into continental sandstones has been attributed to mechanical infiltration by percolation of clay-rich surface waters into grain framework or cutans formed from pedogenic processes. The discovery of pedogenic mud aggregates as traction-load mud in ancient fluvial deposits suggests that permeability and porosity of terrigenous sandstones can be influenced at deposition and control early diagenetic patterns. This study compares diagenesis in fluvial (subaerially exposed) sandstones with lacustrine (subaqueous) sandstones in a Triassic-Jurassic continental rift basin (Hartford Basin, Newark Supergroup). Diversity of diagenetic minerals and sequence of diagenetic alteration can be directly related to depositional environment. The fluvial sandstones in the New Haven Arkose, East Berlin Formation, and Shuttle Meadow Formation of the Hartford Basin are dominated by concretionary calcite and early calcite cement, infiltrated clays (illite-smectite), pedogenic mud aggregates (smectite and illite-smectite), grain coating clays (illite/hematite, illite-chlorite/hematite), quartz overgrowths, late stage carbonate cements (calcite, ferroan calcite), pore-filling clays (illite, kaolinite with minor amounts of smectite, smectite-chlorite, illite-smectite) and hematite. However, pedogenic processes in these fluvial sandstones retarded the development of quartz and feldspar overgrowths, and carbonate authigenesis, as well as the quality of diagenetically enhanced porosity. Dark gray-black lacustrine (subaqueous) sandstones and mudrocks in the East Berlin and Shuttle Meadow Formations are dominated by pyrite, concretionary dolomite and early dolomite cement, radial grain coating clays (smectite-chlorite, illite-smectite), late stage carbonate cements (dolomite, ferroan dolomite, ankerite), albite and pore-filling clays (smectite-chlorite, illite-smectite, illite-chlorite). Clay minerals exist as detrital, mechanically infiltrated, and neoformed clay

  17. Paleoenvironmental setting of Paleozoic mud mounds

    SciTech Connect

    Wanless, H.R. . Dept. Geological Sciences); Tedesco, L.P. )

    1992-01-01

    Paleozoic carbonate mud mounds formed above storm wave base, which in many settings was in moderate to extremely shallow water. This is concluded by a comparative analysis of sedimentary structures, fabrics and small scale sequences occurring in Mississippian and Pennsylvanian mounds and in modern mud mounds and Halimeda bioherms. Most small mounds studied contain a shallowing sequence that represents shallowing into the zone of daily agitation. The bulk of each mound sequence is detrital deposition of layered mudstones to wackestones in the mound core and packstones to grainstones on the flanks and shoal cap. If macroskeletal fauna and flora are present, an autochthonous skeletal packstone may occur in the upper portion of the shallowing sequence beneath the detrital grainstone cap. Burrow excavations and grainy tubular tempestite infillings partially to completely modify the primary depositional fabric of all of these facies. Larger mounds studied are a composite of several to numerous smaller mound depositional sequences. High vertical relief of some larger mounds may be more the result of continued accommodation space provided by subsidence/downfaulting than be deposition in extremely deep water. Although the biotic components of carbonate mounds vary greatly through the Paleozoic, the contained sedimentary structures, fabrics and fundamental depositional sequences remain very similar. This suggests a general similarity in the mechanism and depositional setting of mound formation.

  18. Assessment of Appalachian Basin Oil and Gas Resources: Utica-Lower Paleozoic Total Petroleum System

    USGS Publications Warehouse

    Ryder, Robert T.

    2008-01-01

    The Utica-Lower Paleozoic Total Petroleum System (TPS) is an important TPS identified in the 2002 U.S. Geological Survey (USGS) assessment of undiscovered, technically recoverable oil and gas resources in the Appalachian basin province (Milici and others, 2003). The TPS is named for the Upper Ordovician Utica Shale, which is the primary source rock, and for multiple lower Paleozoic sandstone and carbonate units that are the important reservoirs. Upper Cambrian through Upper Silurian petroleum-bearing strata that constitute the Utica-Lower Paleozoic TPS thicken eastward from about 2,700 ft at the western margin of the Appalachian basin to about 12,000 ft at the thrust-faulted eastern margin of the Appalachian basin. The Utica-Lower Paleozoic TPS covers approximately 170,000 mi2 of the Appalachian basin from northeastern Tennessee to southeastern New York and from central Ohio to eastern West Virginia. The boundary of the TPS is defined by the following geologic features: (1) the northern boundary (from central Ontario to northeastern New York) extends along the outcrop limit of the Utica Shale-Trenton Limestone; (2) the northeastern boundary (from southeastern New York, through southeastern Pennsylvania-western Maryland-easternmost West Virginia, to northern Virginia) extends along the eastern limit of the Utica Shale-Trenton Limestone in the thrust-faulted eastern margin of the Appalachian basin; (3) the southeastern boundary (from west-central and southwestern Virginia to eastern Tennessee) extends along the eastern limit of the Trenton Limestone in the thrust-faulted eastern margin of the Appalachian basin; (4) the southwestern boundary (from eastern Tennessee, through eastern Kentucky, to southwestern Ohio) extends along the approximate facies change from the Trenton Limestone with thin black shale interbeds (on the east) to the equivalent Lexington Limestone without black shale interbeds (on the west); (5) the northern part of the boundary in southwestern Ohio

  19. Lithofacies in Twowells tongue of Dakota sandstone, southern San Juan basin, New Mexico

    SciTech Connect

    Dillinger, J.K. )

    1989-09-01

    The Upper Cretaceous Twowells Tongue forms the uppermost part of the Dakota Sandstone in the southern San Juan basin and represents the last minor regressive pulse in the regional Cenomanian transgression of the Late Cretaceous seaway. This widespread marine sandstone ranges in thickness from less than 15 to 98 ft in the study area between Gallup and Laguna, New Mexico. In outcrop, four major lithofacies are distinguished on the basis of sedimentologic structures and ichnofossils: (1) very silty, (2) horizontally bedded, (3) bioturbated structureless, and (4) cross-bedded sandstone. The distribution of these lithofacies suggests that depositional environments varied significantly from west to east. The very silty sandstone facies is the lowest unit in the coarsening-upward sequence of the Twowells. To the east, this facies also occurs in the middle of the tongue, indicating fluctuating depositional conditions. The horizontally bedded sandstone and bioturbated structureless sandstone facies usually occur above the very silty sandstone but randomly alternate with each other. These two facies are thinner to the east and are replaced by the cross-bedded sandstone and very silty sandstone facies. The cross-bedded sandstone facies occurs at the top of the sequence. It is scarce in the west because of erosion or non-deposition. To the east, it occurs within, and at the top of, the tongue; at one locality it composes the entire tongue. These four lithofacies formed under a wide range of energy conditions, show similarities to deposits in both shoreface and offshore marine environments, and indicate a complex depositional history for the Twowells Tongue.

  20. The diversification of Paleozoic fire systems and fluctuations in atmospheric oxygen concentration.

    PubMed

    Scott, Andrew C; Glasspool, Ian J

    2006-07-18

    By comparing Silurian through end Permian [approximately 250 million years (Myr)] charcoal abundance with contemporaneous macroecological changes in vegetation and climate we aim to demonstrate that long-term variations in fire occurrence and fire system diversification are related to fluctuations in Late Paleozoic atmospheric oxygen concentration. Charcoal, a proxy for fire, occurs in the fossil record from the Late Silurian (approximately 420 Myr) to the present. Its presence at any interval in the fossil record is already taken to constrain atmospheric oxygen within the range of 13% to 35% (the "fire window"). Herein, we observe that, as predicted, atmospheric oxygen levels rise from approximately 13% in the Late Devonian to approximately 30% in the Late Permian so, too, fires progressively occur in an increasing diversity of ecosystems. Sequentially, data of note include: the occurrence of charcoal in the Late Silurian/Early Devonian, indicating the burning of a diminutive, dominantly rhyniophytoid vegetation; an apparent paucity of charcoal in the Middle to Late Devonian that coincides with a predicted atmospheric oxygen low; and the subsequent diversification of fire systems throughout the remainder of the Late Paleozoic. First, fires become widespread during the Early Mississippian, they then become commonplace in mire systems in the Middle Mississippian; in the Pennsylvanian they are first recorded in upland settings and finally, based on coal petrology, become extremely important in many Permian mire settings. These trends conform well to changes in atmospheric oxygen concentration, as predicted by modeling, and indicate oxygen levels are a significant control on long-term fire occurrence.

  1. Basin analysis studies of lower Paleozoic rocks, Powder River basin, Wyoming and Montana

    SciTech Connect

    Macke, D.L.

    1988-07-01

    The lower Paleozoic (Cambrian through Mississippian) sedimentary rocks of the Powder River basin represent nearly half of Phanerozoic time, yet they remain virtually unexplored in the subsurface. Rocks of the same age in the Big Horn and Williston basins and in the Central Montana trough have produced much oil and gas, as have the overlying Pennsylvanian strata of the Powder River basin. A synthesis of published stratigraphic information, together with a regional analysis of sedimentary sequences, has been undertaken to evaluate the economic potential of the lower Paleozoic formations. The lack of an economic impetus to study these rocks has hampered the development of precise depositional models for these sequences. Furthermore, the depths of prospective beds, as well as long-standing misconceptions about the regional stratigraphy, have also served to restrain exploration. Stratigraphic studies have documented a succession of marine transgressions and regressions on the flanks of a highland in southeastern Wyoming. The highland persisted as a subdued geographic feature through most of early Paleozoic time, until it rose at the end of the Mississippian. Erosion during the Late Silurian and Devonian removed much of the depositional record in the area, but onlap can be demonstrated with relative certainty for Ordovician and Mississippian rocks. The repetition of sedimentologic features indicates persistent geologic controls in the region and suggests that these paleoenvironments might provide good targets for exploration.

  2. The Timan-Pechora Basin province of northwest Arctic Russia; Domanik, Paleozoic total petroleum system

    USGS Publications Warehouse

    Lindquist, Sandra J.

    1999-01-01

    The Domanik-Paleozoic oil-prone total petroleum system covers most of the Timan-Pechora Basin Province of northwestern Arctic Russia. It contains nearly 20 BBOE ultimate recoverable reserves (66% oil). West of the province is the early Precambrian Eastern European craton margin. The province itself was the site of periodic Paleozoic tectonic events, culminating with the Hercynian Uralian orogeny along its eastern border. The stratigraphic record is dominated by Paleozoic platform and shelf-edge carbonates succeeded by Upper Permian to Triassic molasse siliciclastics that are locally present in depressions. Upper Devonian (Frasnian), deep marine shale and limestone source rocks ? with typically 5 wt % total organic carbon ? by middle Mesozoic time had generated hydrocarbons that migrated into reservoirs ranging in age from Ordovician to Triassic but most focused in Devonian and Permian rocks. Carboniferous structural inversions of old aulacogen borders, and Hercynian (Permian) to Early Cimmerian (Late Triassic to Early Jurassic) orogenic compression not only impacted depositional patterns, but also created and subsequently modified numerous structural traps within the province.

  3. The fossil record, function, and possible origins of shell color patterns in Paleozoic marine invertebrates

    SciTech Connect

    Kobluk, D.R. ); Mapes, R.H. )

    1989-02-01

    Fossil invertebrate shells and carapaces displaying preserved original color patterns are among the rarest fossils. The fossil record of color patterns extends into the Middle Cambrian where the trilobite Anomocare displays a fan-like array of stripes on the pygidium. About 180 Paleozic genera are known with patterns, including trilobites, cephalopods, gastropods, brachiopods, bivalves, crinoids, and crustaceans. Based upon an analysis of these taxa, it appears that patterns and pigments in middle and late Paleozoic invertebrates may have served several functions such as warning displays, light screening, camouflage, or waste disposal. However, the presence of color patterns in fossil invertebrates in the early Paleozoic may have developed prior to the evolution of vision sufficiently sophisticated to see them. This suggests that camouflage and warning displays were not the original functions of color patterns, and that in the earliest Paleozoic they may not have been functional. The authors propose a hypothesis that involves three developmental phases in the evolution of invertebrate color patterns: (1) the incorporation of metabolic by-products, perhaps some pigmented and some not pigmented, into shells and carapaces as a means of disposal of dietary or metabolic wastes, (2) use of these pigments and patterns as an environmental adaptation, such as light screening, and (3) display during and following the evolution of vision in predators sufficiently sophisticated to see the patterns.

  4. Diagenetic framework for chemical remanence acquisition in lower Paleozoic carbonate rocks from W. Newfoundland

    SciTech Connect

    Beaubouef, R.T.; Rush, P.F. )

    1991-03-01

    The Lower Ordovician (Tremadocian) St. George Group on Port au Port Peninsula forms part of the Cambro-Ordovician autochthonous carbonate sequences of W. Newfoundland. The geology and stratigraphy of the St. George Group indicates that these rocks have been subjected to distinct uplift and exposure events and their petrographic characteristics suggest a complex diagenetic history. Paleomagnetic, petrographic, geochemical, and geological evidence will be presented that indicates both Paleozoic components record chemical remanent magnetizations associated with subaerial exposures of the ancient continental shelf during at least two distinct times in the Paleozoic. Given the observed range of petrographic and magnetic variability, it appears that during the (Early-Middle ) Ordovician, the lower St. George rocks underwent relatively rapid diagenesis, including lithification, calcite cementation, sulfide precipitation, dolomitization, dedolomitization, and hematite authigenesis. The Late Paleozoic component appears to represent a remagnetization component also associated with dedolomitization and hematite authigenesis and cementation. Perhaps more important, rock samples bearing hematite as the major remanence phase can be petrographically identical to one another, yet carry distinct directional components acquired at different times in geologic history.

  5. Tidal influence within Pennsylvanian sandstones

    SciTech Connect

    Archer, A.W. )

    1991-08-01

    Within Pennsylvanian-age strata of the Illinois basin, large-scale linear sand bodies have been previously interpreted as fluvial and deltaic in origin. Nonetheless, analyses of fine-scale sedimentology and bed forms within such sandstones and the associated shales indicate that tidal processes greatly influenced the depositional environments within such lithofacies. Recent work on Mid-Continent Pennsylvanian-age sandstones indicates the occurrence of similar depositional environments. Based upon the pervasive tidal influence observed within such strata, environmental analogs other than fluvial and deltaic bear consideration. In general, tidally influenced estuarine models seem particularly appropriate. Within such settings, the changeover from a fluvially dominated deposystem to tidally influenced estuary occurs during transgressive phases. Despite the tidal influence that can be interpreted from the sedimentology, the strata contain few, if any, marine indicators because of the low salinities that occurred during deposition. Ongoing work in the Mid-Continent indicates that Morrowan, Atokan, Desmoinesian, Missourian, and Virgilian sands share a number of similarities with the tidally influenced environments delineated in the Illinois basin studies. Thus a tidal/estuarine interpretation might be a generalizable model for many Pennsylvanian sandstones. In addition, enhanced understanding of the siliciclastic parts of Mid-Continent cyclothems provides a more useful framework for documentation of carbonate/siliciclastic interrelationships. Oscillations of carbonate/siliciclastic environments may be more readily explainable by climatic cycles rather than by traditionally popular depth-related facies models.

  6. New concepts in exploring subsalt Paleozoic hydrocarbon systems in mature and near producing areas of Morocco

    SciTech Connect

    Jabour, H.; Deminati, A.; Hcaine, M.; El Alji, M.

    1996-12-31

    The subsalt Paleozoic hydrocarbon systems are one of the areally largest and paradoxally the least drilled in Morocco. Although, worldwide, these systems contain the largest potential gas reserves and contain one of the largest emerging oil plays and better still the few wells drilled to test the system in Essaouira Basin are producing commercial wet gas, these systems have never been tested in the Interatlasic and Prerif Basins. Impediments to exploration in these areas focused on the inability to map beneath the {open_quotes}geophysical basement{close_quotes}, to seismically image sub-salt, pre-Jurassic block faulted structures and the perceived lack of adequate source rock. Recent integrated study combining newly acquired deep targeted seismic, gravity, magnetic, geochemical data and basin modelling techniques, has permitted to decipher the pre-salt structures, interpret basin evolution and assess source rock potential. The sub-salt Paleozoic hydrocarbon system evolved in basically five stages: (1) simultaneous sediment accumulation and structural formation during the Paleozoic; (2) major tectonism and erosion in Late Paleozoic (Hercynian); (3) Triassic-Lower Jurassic deposition of a regional seal (salt and evaporate); (4) Mesozoic charging primarily from Silurian to Carboniferous sources; and (5) re-initiation of generation from Silurian source in uplifted blocks following atlasic (Neogene) compression. Large structures and prospective stratigraphic features exhibiting many similarities to the prolific Triassic objectives of neighboring Algeria are now defined and await to be drilled. Furthermore, the Maghreb-Europe gas pipeline will shortly cross both the Interatlasic and the Prerif areas providing additional positive attribute that makes these exploration areas more attractive.

  7. New concepts in exploring subsalt Paleozoic hydrocarbon systems in mature and near producing areas of Morocco

    SciTech Connect

    Jabour, H.; Deminati, A.; Hcaine, M.; El Alji, M. )

    1996-01-01

    The subsalt Paleozoic hydrocarbon systems are one of the areally largest and paradoxally the least drilled in Morocco. Although, worldwide, these systems contain the largest potential gas reserves and contain one of the largest emerging oil plays and better still the few wells drilled to test the system in Essaouira Basin are producing commercial wet gas, these systems have never been tested in the Interatlasic and Prerif Basins. Impediments to exploration in these areas focused on the inability to map beneath the [open quotes]geophysical basement[close quotes], to seismically image sub-salt, pre-Jurassic block faulted structures and the perceived lack of adequate source rock. Recent integrated study combining newly acquired deep targeted seismic, gravity, magnetic, geochemical data and basin modelling techniques, has permitted to decipher the pre-salt structures, interpret basin evolution and assess source rock potential. The sub-salt Paleozoic hydrocarbon system evolved in basically five stages: (1) simultaneous sediment accumulation and structural formation during the Paleozoic; (2) major tectonism and erosion in Late Paleozoic (Hercynian); (3) Triassic-Lower Jurassic deposition of a regional seal (salt and evaporate); (4) Mesozoic charging primarily from Silurian to Carboniferous sources; and (5) re-initiation of generation from Silurian source in uplifted blocks following atlasic (Neogene) compression. Large structures and prospective stratigraphic features exhibiting many similarities to the prolific Triassic objectives of neighboring Algeria are now defined and await to be drilled. Furthermore, the Maghreb-Europe gas pipeline will shortly cross both the Interatlasic and the Prerif areas providing additional positive attribute that makes these exploration areas more attractive.

  8. Buried structural traps in upper paleozoic strata of the Orenburg region and their petroleum prospects. [USSR

    SciTech Connect

    Orel, A.V.

    1982-07-01

    Analysis of drilling data within the Orenburg sector of the northern marginal zone of the Caspian Basin and the Sol'-Ilets rise has shown that horizons of the Moscovian Stage of Late Carboniferous and Early Permian age rest on an eroded surface of Bashkirian deposits in a transgressive succession.Changes in thicknesses in the upper Paleozoic stratigraphic complexes indicate a significant discordance between the structural plans of the Artinskian and Bashkirian deposits and the possibility of discovering buried traps here, promising in the search for oil and gas.

  9. A direct comparison of the ages of detrital monazite versus detrital zircon in Appalachian foreland basin sandstones: Searching for the record of Phanerozoic orogenic events

    NASA Astrophysics Data System (ADS)

    Hietpas, Jack; Samson, Scott; Moecher, David

    2011-10-01

    The provenance potential of detrital monazite was investigated by in situ measurement of 232Th- 208Pb dates of grains isolated from six Middle Carboniferous-Permian sandstones from the Appalachian foreland basin. Provenance assessment of these units was previously investigated by measuring U-Pb crystallization ages of detrital zircon (Thomas et al., 2004; Becker et al., 2005, 2006). Approximately 90% of the detrital zircon ages record Mesoproterozoic or older ages, with only 10% recording the three major pulses of tectonism (Taconian, Acadian and Alleghanian) that are the hallmark of the Appalachian Orogen. 232Th- 208Pb ages of detrital monazite, however, strongly record the complex phases of Paleozoic orogenesis. Nearly 65% of the ages record Paleozoic events, while 35% record Neoproterozoic or older ages. In several of the analyzed sandstones, detrital monazite ages record Paleozoic orogenic events that are completely missed by detrital zircon ages, demonstrating that monazite ages more accurately reflect the character of the sediment source rocks. The inferred maximum age of sediment deposition, as determined by the youngest monazite grains, is ~ 550 Ma younger for two of the analyzed sandstones compared to depositional constraints based on the youngest detrital zircon. The different physical properties and petrogenesis of zircon and monazite are interpreted to be factors for the dramatic differences in sediment provenance information provided by each mineral. The results from this study have important implications for determining sediment provenance, constraining maximum age of sediment deposition, and developing robust regional tectonic models.

  10. Lower Paleozoic and Proterozoic rocks of Southern Brooks Range, Alaska

    SciTech Connect

    Dillion, J.T.

    1985-04-01

    Lower Paleozoic or Proterozoic basement rocks occur in windows and thrust plates in several areas of the Brooks Range. Uranium-lead radiometric analyses of highly metamorphosed rocks from the Baird Mountains and Ernie Lake area have yielded Proterozoic ages. Structural, stratigraphic, petrologic, and isotopic evidence exists for Proterozoic(.) rocks in the schist belt; around the Chandalar, Arrigetch,and Igikpak plutons; and in the Cosmos Hills window. Fossiliferous, Lower Paleozoic, low-grade metasedimentary rocks occur in the Romanzof Mountains, Doonerak window, and Baird Mountains, and may also surround the Chandalar plutons. Locally, the Lower Paleozoic rocks are unconformably overlain by Devonian to Mississippian metasediments and may stratigraphically overlie older, higher grade metamorphic rocks. Similarities in the stratigraphic settings and lithologies and in fossil ages and affinities allow correlation of the Lower Paleozoic rocks in the southern Brooks Range. Correlation of Lower Paleozoic rocks exposed beneath the Endicott allochthon at the Doonerak fenster with coeval rocks in an overlying thrust plate to the south at Snowsden Mountain is especially significant. A west-trending thrust fault, which is rooted in Lower Paleozoic basement, along the north side of Snowsden Mountain is postulated to account for these relationships. Apparently, the Endicott allochthon roots beneath the Snowsden Mountain thrust fault. Evidence form conodont samples currently being studied by A. Harris may bear on the extent of the Lower Paleozoic rocks in the upper plate of the Snowsden Mountain thrust and in the Chandalar area.

  11. Biostratigraphic refinements of paleozoics of Great Basin using palynology

    SciTech Connect

    Hutter, T.J.

    1987-08-01

    Examining material from numerous wells and extensive collections of Paleozoic sediments from throughout the Great Basin shows large morphic diversity of the acritarchs, chitinozoans, and spores. Quantitative analysis of these palynomorphs provides data on biostratigraphy, paleoenvironments, and organic thermal maturation throughout the Paleozoic stratigraphic units. Biostratigraphic boundaries and associated lithostratigraphic units can be recognized by using the acritarch, chitinozoan, and spore assemblages. The Paleozoic microflora and microfauna from the Great Basin show remarkable affinities to assemblage records from western Australia. Comparisons with established graptolite and conondont zone are also established.

  12. Allochthonous deep-water basin deposits of the western US: Implications for Paleozoic paleogeography and plate margin tectonics

    SciTech Connect

    Miller, E.L. . Geology Dept.)

    1993-04-01

    The stratigraphy and sedimentology of the lower Paleozoic Roberts Mts. and upper Paleozoic Golconda allochthons can be used to reconstruct their general paleogeographic setting in the Paleozoic. Basalt pillow lavas and radiolarian chert, were once considered straightforward evidence that the allochthons represented imbricated ocean crust formed at sites far removed from continental influences. Better stratigraphic definition, provenance studies and geochemistry of lavas now indicate that clastic components were derived from the continental shelf or interior and basalts in the Roberts Mountains allochthon were erupted in an intraplate setting through thinned continental crust (Madrid, 1987). Both in the earliest Mississippian and in the Late Permian, the Antler Basin (Roberts Mts.) and the Havallah Basin (Golconda) received proximal detritus from island arc sources to the west, immediately prior to closure of the basins by thrust-faulting. These data suggest that both systems of basins formed as marginal basins by rifting on the continental shelf (Antler Basin) and along the continental margin (Havallah Basin) and were flanked to the west by active island arcs at least during part of their history. As such, their stratigraphy provides a great deal of insight regarding tectonism along the western plate margin of North America during the Paleozoic.

  13. Paleogeography of the upper Paleozoic basins of southern South America: An overview

    NASA Astrophysics Data System (ADS)

    Limarino, Carlos O.; Spalletti, Luis A.

    2006-12-01

    The paleogeographic evolution of Late Paleozoic basins located in southern South America is addressed. Three major types of basins are recognized: infracratonic or intraplate, arc-related, and retroarc. Intraplate basins (i.e., Paraná, Chaco-Paraná, Sauce Grande-Colorado, and La Golondrina) are floored by continental or quasi-continental crust, with low or moderate subsidence rates and limited magmatic and tectonic activity. Arc-related basins (northern and central Chile, Navidad-Arizaro, Río Blanco, and Calingasta-Uspallata basins and depocenters along Chilean Patagonia) show a very complex tectonic history, widespread magmatic activity, high subsidence rates, and in some cases metamorphism of Late Paleozoic sediments. An intermediate situation corresponds to the retroarc basins (eastern Madre de Dios, Tarija, Paganzo, and Tepuel-Genoa), which lack extensive magmatism and metamorphism but in which coeval tectonism and sedimentation rates were likely more important than those in the intraplate region. According to the stratigraphic distribution of Late Paleozoic sediments, regional-scale discontinuities, and sedimentation pattern changes, five major paleogeographic stages are proposed. The lowermost is restricted to the proto-Pacific and retroarc basins, corresponds to the Mississippian (stage 1), and is characterized by shallow marine and transitional siliciclastic sediments. During stage 2 (Early Pennsylvanian), glacial-postglacial sequences dominated the infracratonic (or intraplate) and retroarc basins, and terrigenous shallow marine sediments prevailed in arc-related basins. Stage 3 (Late Pennsylvanian-Early Cisuralian) shows the maximum extension of glacial-postglacial sediments in the Paraná and Sauce Grande-Colorado basins (intraplate region), whereas fluvial deposits interfingering with thin intervals of shallow marine sediments prevailed in the retroarc basins. To the west, arc-related basins were dominated by coastal to deep marine conditions

  14. Pore-throat sizes in sandstones, tight sandstones, and shales

    USGS Publications Warehouse

    Nelson, Philip H.

    2009-01-01

    Pore-throat sizes in silidclastic rocks form a continuum from the submillimeter to the nanometer scale. That continuum is documented in this article using previously published data on the pore and pore-throat sizes of conventional reservoir rocks, tight-gas sandstones, and shales. For measures of central tendency (mean, mode, median), pore-throat sizes (diameters) are generally greater than 2 μm in conventional reservoir rocks, range from about 2 to 0.03 μm in tight-gas sandstones, and range from 0.1 to 0.005 μm in shales. Hydrocarbon molecules, asphaltenes, ring structures, paraffins, and methane, form another continuum, ranging from 100 Å (0.01 μm for asphaltenes to 3.8 A (0.00038 μm) for methane. The pore-throat size continuum provides a useful perspective for considering (1) the emplacement of petroleum in consolidated siliciclastics and (2) fluid flow through fine-grained source rocks now being exploited as reservoirs.

  15. On Restoring Sedimentary Basins for Post-Depositional Deformation - Paleozoic Basins of the Central Andes

    NASA Astrophysics Data System (ADS)

    Bahlburg, H.

    2015-12-01

    The reconstruction and interpretation of sedimentary basins incorporated into folded and thrusted mountain belts is strongly limited by the style and intensity of shortening. This problem is exacerbated if deformation is polyphasic as is the case for the Paleozoic basins in the central Andes. Some of these have been deformed by folding and thrusting during at least 3 events in the Late Ordovician, the Late Paleozoic and Cenozoic. A realistic reconstruction of the original basin dimensions and geometries from outcrops and maps appears to be almost impossible. We present results of a stepwise reconstruction of the Paleozoic basins of the central Andes by restoring basin areas and fills accounting for crustal shortening. The structurally most prominent feature of the central Andes is the Bolivian Orocline which accomodated shortening in the last 45 Ma on the order of between 300 and 500 km. In a first step basins were restored by accounting for Cenozoic rotation and shortening by deconvolving the basins using an enhanced version of the oroclinal bending model of Ariagada et al. (2008). Results were then restored stepwise for older deformation. Constraints on these subsequent steps are significantly poorer as values of shortening can be derived only from folds and thusts apparent in outcrops. The amount of shortening accomodated on unexposed and therefore unknown thrusts can not be quantified and is a significant source of error very likely leading to an underestimation of the amount of shortening. Accepting these limitations, basin restoration results in an increase in basin area by ≥100%. The volumes of stratigraphically controlled basin fills can now be redistributed over the wider, restored area, translating into smaller rates of accumulation and hence required subsidence. The restored rates conform to those of equivalent modern basin settings and permit a more realistic and actualistic analysis of subsidence drivers and the respective tectonic framework.

  16. Provenance and depositional conditions of Cretaceous-Paleogene boundary sandstones from northeastern Mexico

    NASA Astrophysics Data System (ADS)

    Rehrmann, Stephanie; Augustsson, Carita; Izaguirre Valdez, Rocio Nereyda; Jenchen, Uwe; Schulte, Peter

    2012-12-01

    We compare Late Maastrichtian siliciclastic sandstone in northeastern Mexico with those representing the Cretaceous-Paleogene (K-Pg) boundary to reveal differences in provenance and depositional conditions between background sedimentation and K-Pg sand. Lithology and compositional variations are presented for the deep-water Burgos Basin and the shallow-water La Popa Basin. The Late Maastrichtian sandstones in the Burgos Basin have sharp lower contacts, contain abundant trace fossils and are separated by meter-thick marl layers. They represent sporadic mass flows from coastal areas separated by long phases of hemipelagic sedimentation. The K-Pg sandstone layers are amalgamated, contain thin marl intercalations only in the uppermost part and trace fossils are present in the top sandstone layer only. Also this succession represents mass-flow deposits, but the sand may have been deposited during a very short period. The La Popa Basin sandstones represent deltaic sedimentation interrupted by submarine channel deposition during the K-Pg boundary transition with abundant rip-up clasts and bioclasts at the base. The sandstones of the Burgos Basin are quartz to akosic wacke dominated by quartz (> 90%) and some feldspar (< 10%) in calcite cement and matrix. Lithic fragments are rare and dominated by chert and bioclasts. Ultra-stable heavy minerals (ZTR = 50-80) and plutonic quartz grains (ca. 40% of the total quartz population) are particularly common in the K-Pg sandstones. In the Maastrichtian sandstones, metamorphic heavy minerals, particularly chlorite, clinozoisite, and tourmaline (20-50% of the heavy mineral population), and metamorphic quartz (80% of the quartz population) have higher abundances. The La Popa sandstones are subarkose to arkose and arkosic wacke and have a high abundance of feldspar (15-30%) and lithic fragments (5-20%), mainly of siltstone and carbonate. The sandstones from both basins have chemical compositions typical for recycling (Zr/Sc = 12-27 and

  17. North American Paleozoic Oceanography: Overview of Progress Toward a Modern Synthesis

    NASA Astrophysics Data System (ADS)

    Johnson, Markes E.

    1987-04-01

    Three fundamental questions have confronted paleoceanographers from the beginning of their North American explorations. What was the size and timing of ancient epicontinental seas: large and long-lasting or small and brief? What characterized the distribution of biotas and sediments at any one point in time: a multitude of complex facies patterns or a more spacially homogeneous cover? What promoted continental foundering: eustatic changes in sea level or relative changes in sea level brought about by regional tectonics? These questions have been debated by North Americans since the middle 1800s in response to various new insights, usually coming from abroad but often elaborated into substantial contributions of equal standing. Contemporary facies zones in Mediterranean biota found by the Englishman E. Forbes attracted the notice of geologists as early as 1844. C. Whittlesey was among the first to apply the bathymetric scheme of Forbes to the interpretation of American Paleozoic strata in 1851. The outstanding "native" innovation of the period was J. Hall's geosyncline concept, which is reflected in the earliest map of Paleozoic North America made by T. C. Chamberlin in 1881. Another wave of influence spread from the late 19th century work on stratigraphic facies patterns by the German J. Walther. A. W. Grabau is best remembered as Walther's foremost American champion against the formidable layer-caker E. O. Ulrich in the first decades of the 20th century, but he also made pioneering contributions of his own on Paleozoic sea level studies and global paleogeographic reconstructions. Charles Schuchert was the consummate paleogeographer of this period. Meanwhile, the term "cyclothem" was coined by J. Marvin Weller in 1930 for recurrent Carboniferous strata in Illinois. Controversy fast erupted over a glacial as opposed to tectonic mode of origin for these cycles. In 1964, A. B. Shaw restimulated interest in Paleozoic oceanography through his reformulation of Walther

  18. Post-paleozoic structural styles in northern Sierra de Palomas: Chihuahua, Mexico

    SciTech Connect

    Sivils, D.J.

    1988-01-01

    Sierra de Palomas is the largest and most northerly range of the Boca Grande trend in northwestern Chihuahua, Mexico. Sierra de Palomas is composed of more than 1.5 km of late Paleozoic shelf carbonates and clastics. Detailed mapping the northern 150 km/sup 2/ of the range (at a scale of 1:12,500) has shown that four post-Paleozoic tectonic events have affected the range. The Laramide orogeny, two separate periods of basin and range extension, and recent (Rio Grande rift.) extension have left very distinct structures in the range. Laramide structures are predominantly vergent to the northeast, and are manifested as folds and thrusts. Folds are asymmetric and northwest trending, with amplitudes on the order of 10-50 m. Major thrusts in the range have minimum displacements on the order of a few kilometers. Basin and range structures include two distinct sets of high-angle faults; an early northeast-trending set is truncated by a late northwest-trending set. Recent Rio Grande rift(.) extension in the area is evident in fault scarps that offset alluvial fan deposits and in steeply eastward-tilted alluvial deposits.

  19. Prospects for hydrocarbon exploration in the Mesozoic and Paleozoic sections of the Pannonian basin in Hungary

    SciTech Connect

    Mattick, R. ); Koncz, I.; Bardocz, B.; Szalay, A.; Szent-Gyoergyi, K. ); Csaszar, G.; Juhasz, E. )

    1993-09-01

    To date, exploration in the Pannonian basin of Hungary has concentrated on oil and gas believed to be derived from source rocks of the Cenozoic. In this sense, the basin is a mature hydrocarbon province. However, exploration of the Mesozoic and Paleozoic sections has just begun. These section may contain significant quantities of hydrocarbons derived from source rocks of the Mesozoic. Much of the buried basement consists of a complex system of stacked nappes composed of Mesozoic and older rocks. Basement structures from three areas are shown: (1) southwestern Hungary, where oil and gas produced from fracture zones in the crest of nappes; (2) southeastern Hungary, where thrusting occurred subsequent to Upper Cretaceous deposition; and (3) western Hungary, where thrusting occurred prior to Upper Cretaceous deposition. In general, Paleozoic-Middle Triassic rocks are overmature; however, Upper Triassic-Cretaceous rocks entered the oil-generation window during the Neogene. The heavy oils of the Zala basin were generated from organic-rich marls of the Late Triassic. In the Mecsek area, Toarcian shales are likely a good source for oil. Upper Cretaceous rocks, because of their terrestrial character, are inferred to be gas prone. Reservoir properties of Triassic and older rocks are expected to be poor, except where fracture porosity occurs. In the Nagylengyel field, rudist limestones of Late Cretaceous contain prolific reservoirs with primary solution and fracture porosity. Although the average porosities of these reservoir rocks are relatively low (2-4%), permeabilities are >1-2 d as a result of paleokarst development.

  20. The emplacement time of the Hegenshan ophiolite: Constraints from the unconformably overlying Paleozoic strata

    NASA Astrophysics Data System (ADS)

    Zhou, Jian-Bo; Han, Jie; Zhao, Guo-Chun; Zhang, Xing-Zhou; Cao, Jia-Lin; Wang, Bin; Pei, Sheng-Hui

    2015-11-01

    Controversy has long surrounded the emplacement time of the Hegenshan ophiolite that is considered to mark a suture zone, called the Hegenshan-Heihe suture, resulting from the closure of a back-arc basin in the Paleo-Asian Ocean. The Hegenshan ophiolite in the Xiaobaliang area is unconformably overlain by a sequence of Paleozoic strata, called the Zhesi Formation that consists of conglomerate, sandstone, siltstone and limestone, some of which contain Permian marine fossils of Brachiopods. Therefore, the ages of these Paleozoic strata can be used to constrain the emplacement time of the Hegenshan ophiolite. Four samples of the Zhesi Formation collected in the Xiaobaliang area yield the detrital zircon U-Pb ages of 285-272 Ma (with the peak at 279 Ma), 315-288 Ma (with a peak at 300 Ma), 320-358 Ma (with a peak at 336 Ma), and 406 ± 3 Ma, of which the ~ 280 and ~ 300 Ma age groups are remarkably similar to the ages of latest Carboniferous-Early Permian Gegenaobao/Dashizai Formation, or A-type granites, which formed under a post-collisional setting. However, the age groups of 320 to 358 Ma with a peak at 336 Ma, show the features of mafic-ultramafic zircons in CL image, most likely derived from local mafic-ultramafic rocks of the Hegenshan ophiolite in the Xiaobaliang area, which is supported by the fact of the ophiolite unconformably overlain by the Middle Permian Zhesi Formation. Therefore, we propose that the emplacement time of the Hegenshan ophiolite must have happened at some time before the Middle Permian (~ 280 Ma), most likely between 300 and 335 Ma, not in the Silurian, Devonian or Mesozoic as previously considered.

  1. Paleozoic structural controls on shortening transfer in the Subandean foreland thrust system, Ene and southern Ucayali basins, Peru

    NASA Astrophysics Data System (ADS)

    Espurt, Nicolas; Brusset, StéPhane; Baby, Patrice; Hermoza, Wilber; BolañOs, Rolando; Uyen, Dennys; DéRamond, Joachim

    2008-06-01

    The Neogene evolution of the Ene and southern Ucayali basins of the Subandes has been controlled by two stacked thrust wedges that differ in terms of tectonic styles. The lower thrust wedge is formed by deep-seated décollements within the basement related to thick-skinned foreland structures inherited from an Early Carboniferous thrust system. Seismic reflection data show that this Paleozoic compressional system has been eroded and unconformably covered by Late Carboniferous clastic sediments. It generated an irregular Paleozoic sedimentary architecture controlling the Neogene thrust propagation. The upper thin-skinned thrust wedge developed within this Paleozoic sedimentary series and constitutes the Subandean zone. Cross-section balancing shows an along-strike homogenous horizontal shortening of ˜56 km (˜30%) across the Ene-southern Ucayali thrust system. This amount of shortening was vertically partitioned onto the two stacked thrust wedges. The N-S thickness variations of the Paleozoic sedimentary prism controlled the eastward propagation of the upper thrust wedge. The southern thickening of the Paleozoic series generated major décollements and the shortening excess is of 7 km (16%) in comparison to the north. Consequently, the northern lack of shortening onto the upper thrust wedge was transferred to the Early Carboniferous compressional structures of the lower thrust wedge. We suggest that this vertical partitioning of the shortening was accommodated by a regional oblique ramp: the Tambo transfer zone. This geometrical analysis of the Ene-southern Ucayali thrust system provides new perspectives for future hydrocarbon exploration in this region.

  2. Provenance characterization of Appalachian clastic wedges from sandstone petrography and clast compositions

    SciTech Connect

    Eriksson, K.A. . Dept. of Geological Science); Simpson, E.L. . Dept. of Physical Science); Krogstad, E.J. . Dept. of Geology); McLennan, S.M. . Dept. of Earth and Space Science); Norman, M. )

    1994-03-01

    Sandstones in the Taconic, Acadian and Alleghanian clastic wedges in the Appalachian Orogenic Belt provide evidence for changing provenances during the late Ordovician through pennsylvanian, Neoproterozoic-Early Cambrian, synrift sandstones are predominantly feldspathic arenites, whereas quartz arenites typify sandstones in the Cambrian passive-margin prism. In contrast, sandstones in the overlying foreland-basin clastic wedges typically are lithic arenites and occupy the quartzose to lithic recycled fields on QmFLt diagrams. Mid-Ordovician lithic arenites (Knobs, Bays Fms.) are dominated by a variety of sedimentary rock fragments including feldspathic and quartz arenites, limestone, dolomite and chert. Conglomerates in the Bays Formation similarly are dominated by recycled sedimentary clasts; gneiss clasts are only rarely observed. Above a regional unconformity in the middle Tuscarora formation, a succession of quartz arenites (upper Tuscarora, Rose Hill and Eagle Rock Fms.) developed in response to prolonged reworking. Overlying lithic arenites (Middle Devonian-Pennsylvanian) contain a variety of metamorphic rock fragments including quartz-mica schist, strained and polycrystalline quartz, and detrital mica. Sandstone petrography and clast compositions thus indicate that the Taconic orogeny involved uplift of the older passive-margin prism in a fold-and-thrust belt or accretionary prism. Coarse-grained sedimentary rocks provide no evidence of an arc to the east. Mature Silurian sandstones record an inter-orogenic, quiescent phase of the Appalachian Orogeny.

  3. Multidisciplinary studies on ancient sandstone quarries of Western Sardinia (Italy).

    NASA Astrophysics Data System (ADS)

    Grillo, Silvana Maria; Del Vais, Carla; Naitza, Stefano

    2013-04-01

    The ancient coastal quarries of Mediterranean are increasingly considered geosites of multidisciplinary relevance. They are sites of historical-archaeological interest that show ancient techniques of stone extraction; they are significant for cultural heritage conservation and restoration, as sources of the stones used in ancient buildings and monuments; they are sites of geological relevance, as often retain important stratigraphic sections; they are also useful markers of secular changes in the sea level. A multisciplinary study is in progress on the ancient quarries of the Sinis region (western Sardinia island), integrating archaeological, geological, minero-petrographical data. In Sardinia, coastal quarries have been established from Punic and Roman times. Many of them exploited Quaternary sediments along the southern and western coasts of the island. They consist of middle-late Pleistocene marine conglomerates and carbonate sandstones, and of coastal (aeolian) carbonate sandstones. Sandstone blocks of different sizes have been widely used in ancient cities for buildings, defensive works, harbours, etc. Three main areas of stone extraction (San Giovanni di Sinis, Punta Maimoni, Is Arutas) have been so far recognized in the Sinis. GIS-supported mapping and documentation of the sites includes their geology and stratigraphy, the extension and layout of the quarries, and an evaluation of volumes of extracted rocks. Documented archaeological evidences include ancient extraction fronts, spoil heaps, working areas, working traces in the old fronts, transport routes of blocks, and traces of loading facilities. The study is aimed at reconstructing the relationships of the quarries with the urban areas of Sinis, as the ancient Punic-Roman city of Tharros. Consequently, a minero-petrographical characterization (optical microscopy, XRD) is performed on sandstones sampled in each quarry, and in historical buildings in Tharros and other centres of the region (Cabras

  4. Origin of a classic cratonic sheet sandstone: Stratigraphy across the Sauk II-Sauk III boundary in the Upper Mississippi Valley

    USGS Publications Warehouse

    Runkel, Anthony C.; McKay, R.M.; Palmer, A.R.

    1998-01-01

    The origin of cratonic sheet sandstones of Proterozoic and early Paleozoic age has been a long-standing problem for sedimentologists. Lower Paleozoic strata in the Upper Mississippi Valley are best known for several such sandstone bodies, the regional depositional histories of which are poorly understood. We have combined outcrop and subsurface data from six states to place the Upper Cambrian Wonewoc (Ironton and Galesville) Sandstone in a well-constrained stratigraphic framework across thousands of square kilometers. This framework makes it possible for the first time to construct a regional-scale depositional model that explains the origin of this and other cratonic sheet sandstones. The Wonewoc Sandstone, although mapped as a single contiguous sheet, is a stratigraphically complex unit that was deposited during three distinct conditions of relative sea level that span parts of four trilobite zones. During a relative highstand of sea level in Crepicephalus Zone time, quartzose sandstone lithofacies aggraded more or less vertically in nearshore-marine and terrestrial environments across much of the present-day out-crop belt around the Wisconsin arch. At the same time, finer grained, feldspathic sandstone, siltstone, and shale aggraded in deeper water immediately seaward of the quartzose sand, and shale and carbonate sediment accumulated in the most distal areas. During Aphelaspis and Dunderbergia Zones time a relative fall in sea level led to the dispersal of quartzose sand into a basinward-tapering, sheet-like body across much of the Upper Mississippi Valley. During early Elvinia Zone time a major transgression led to deposition of a second sheet sandstone that is generally similar to the underlying regressive sheet. The results of this investigation also demonstrate how subtle sequence-bounding unconformities may be recognized in mature, cratonic siliciclastics. We place the Sauk II-Sauk III subsequence boundary at the base of the coarsest bed in the Wonewoc

  5. Laurentian and Baltican components of Terranes in NW Washington: Implications for Displacement of Paleozoic Terranes

    NASA Astrophysics Data System (ADS)

    Schermer, E. R.; Brown, N.; Gehrels, G. E.

    2015-12-01

    New field, U-Pb, and Lu-Hf data constrain the geologic history, age, and origin of the Yellow Aster Complex (YAC) in NW Washington, and suggest that this Paleozoic arc terrane originated along the paleo-Arctic margin of NE Laurentia. Field work shows the oldest YAC consists of quartzo-feldspathic paragneiss (meta-arkosic sandstone + conglomerate) and quartzose calc-silicate gneiss (meta-calcareous siltstone) in gradational contact. Paragneisses are cut by syn- and post-tectonic intrusions, and faulted against granitic orthogneiss. U-Pb results show that 1) maximum depositional ages of paragneisses are Silurian to early Devonian (399 to 434 Ma); 2) quartzose calc-silicate gneisses show a broad age peak from 1000-1900 Ma, while quartzofeldspathic gneisses contain several distinct Precambrian age peaks, including at 1.8-2.0 Ga and 2.4-2.5 Ga; 3) Both gneisses contain early Paleozoic grains with peaks at ~400-420 and ~450-460 Ma; 4) pre-tectonic orthogneiss and syn- and post-tectonic dikes range from 410 to 398 Ma; 4) All intrusive rocks contain apparently xenocrystic ~450 Ma grains. Lu-Hf data show that nearly all Paleozoic grains have negative epsilon Hf values, and zircons in the meta-arkose samples are more highly evolved than those in the calc-silicate. Several meta-arkose samples yield epsilon Hf values of -40 to -50, which is rare in the North American Cordillera, and requires the involvement of Early Archean crustal components. The most likely source region is Greenland, which implies derivation from the paleo-Arctic margin of northeastern Laurentia or Baltica. The chemistry and petrology of the igneous rocks suggest the terrane was in a continental arc setting during or very shortly after deposition of the sedimentary rocks. The data suggest that sedimentation, deformation, metamorphism, and magmatism all occurred within a brief (~15 m.y.) period in the early Devonian. These relationships suggest a Caledonian origin for YAC prior to translation to the

  6. Co-evolution of Eukaryotes and Ocean and Atmosphere Oxygenation in the Neoproterozoic and Paleozoic Eras

    NASA Astrophysics Data System (ADS)

    Lenton, T. M.; Daines, S. J.; Mills, B.; Boyle, R. A.

    2014-12-01

    The nature, timing and cause(s) of the Earth's second oxygenation event are widely debated. It has been argued that there was a single pronounced rise in atmospheric oxygen toward present levels in the Late Neoproterozoic, which in turn triggered the evolution of animals. Here we suggest a more complex co-evolutionary scenario, with fluctuations in ocean and atmosphere oxygenation in the Late Neoproterozoic and Early Paleozoic caused partly by the evolution of animals, followed by a pronounced rise of atmospheric oxygen to present levels later in the Paleozoic caused by the rise of land plants. Current geochemical evidence suggests some parts of the deep oceans became oxygenated during the Ediacaran, but there was subsequent de-oxygenation of the ocean during the Cambrian that may have persisted into the Ordovician. Only later in the Paleozoic is there evidence for widespread oxygenation of the deep ocean, together with charcoal indicating atmospheric oxygen had approached present levels. The limited Neoproterozoic oxygenation of the ocean could be explained by the evolution of filter-feeding sponges removing oxygen demand from the water column and encouraging a shift from cyanobacteria to faster-sinking eukaryotic algae, which transferred oxygen demand to greater depths and into sediments. The resulting oxygenation of shelf bottom waters would have increased phosphorus removal from the ocean thus lowering global productivity and oxygen demand in a positive feedback loop encouraging ocean oxygenation [1]. The subsequent Cambrian de-oxygenation of the ocean could be explained by the evolution of bioturbating animals oxygenating the sediments and thus lowering the C/P burial ratio of organic matter, reducing organic carbon burial and lowering atmospheric oxygen [2]. The later rise of land plants, selectively weathering phosphorus from continental rocks and producing recalcitrant high C/P biomass, increased organic carbon burial and atmospheric oxygen, finally

  7. Discovery of a Late Devonian magmatic arc in the southern Lancangjiang zone, western Yunnan: Geochemical and zircon U-Pb geochronological constraints on the evolution of Tethyan ocean basins in SW China

    NASA Astrophysics Data System (ADS)

    Nie, Xiaomei; Feng, Qinglai; Metcalfe, Ian; Baxter, Alan T.; Liu, Guichun

    2016-03-01

    The Tibetan Plateau and western Yunnan are known to have formed by the amalgamation of Gondwana-derived continental blocks and arc terranes as a result of Tethyan subduction followed by continental collisions during the Paleozoic, Mesozoic and Cenozoic. The Devonian and the southern Lancangjiang zone, western Yunnan is a critical period and key region for studying the transformation between the "Proto-Tethyan" and Paleo-Tethyan oceanic systems. New geochemical data and LA-ICPMS U-Pb zircon ages of the Late Devonian volcanogenic sediments from the southern Lancangjiang zone in western Yunnan, SW China, are presented. The studied sedimentary rocks of the Nanguang Formation are volcaniclastic rocks with high volcanic lithic content (55-65%, mostly andesite, dacite, with some rhyolite and tuffs). Whole rock geochemistry, zircon trace elements and detrital modal analyses indicate derivation from a subduction-related magmatic arc. Three tuff samples yield Late Devonian weighted mean 206Pb/238U ages of 378 ± 4 Ma, 366 ± 5 Ma and 382 ± 8 Ma, suggesting a Late Devonian depositional age. 104 zircon U-Pb analyses on 104 zircon grains from two sandstone samples present extremely tight age clusters, mostly ranging from 380 Ma to 360 Ma. This indicates a single Late Devonian igneous source. A short transport distance and a high rate of denudation and deposition within an arc-related basin are considered likely for the tuffs and volcaniclastic rocks in this study. This implies the presence of an as yet unidentified Late Devonian magmatic arc in the southern Lancangjiang zone. The cryptic Late Devonian arc is likely to represent either a continuation of Late Ordovician-Late Silurian "Proto-Tethyan" subduction or the initial stage of the Paleo-Tethyan Lincang Arc and indicates that subduction of the Changning-Menglian ocean beneath the Simao/Indochina Block occurred in the Late Devonian.

  8. Geological investigations of pre-late Jurassic terranes in the southernmost Andes

    NASA Astrophysics Data System (ADS)

    Forsythe, R. D.

    Pre-Late Jurassic terranes of the Patagonian Archipelago were investigated. Their regional stratigraphic and structural characteristics were surveyed. Their significance in the late Paleozoic to early Mesozoic evolution of South America were determined. Pre-Late Jurassic rocks within the archipelago are distributed in two belts. Within the outer belt the Madre de Dios Archipielago was studied in detail. Pre-Late Jurassic rocks of this area are divisible into three mappable units. These three units are interpreted to be part of a late Paleozoic to early Mesozoic accretionary prism that was located along the ancestral Pacific margin of the South American sector of Gondwana. Within the inner belt, the region of Peninsula Staines was studied in detail. In this region greenschist facies metamorphism and pervasive deformation fabrics prevent stratigraphic subdivision of the terrane. However the lithologies present are correlative with the outer belt suggesting that they also were part of the late Paleozoic to early Mesozoic accretionary prism.

  9. Hydrogeology of the Leadville limestone and other paleozoic rocks in northwestern Colorado, with results of aquifer tests at Glenwood Springs

    USGS Publications Warehouse

    Geldon, Arthur L.

    1989-01-01

    Paleozoic rocks in northwestern Colorado were investigated during the U.S. Geological Survey 's Regional Aquifer Systems Analysis of the Upper Colorado River Basin. Paleozoic rocks in the study area are grouped into 11 hydrostratigraphic units on the basis of lithologic and hydrologic properties. Devonian and Mississippian carbonate rocks and Pennsylvanian and Permian sandstone are regional aquifers, with natural discharges commonly ranging from 50 to 1,000 gal/min. Other hydrostratigraphic units in the area are either local aquifers or confining layers, with discharges rarely exceeding 50 gal/min. Aquifer tests at Glenwood Springs indicate that the Devonian and Mississippian carbonate rocks unit locally has a transmissivity of 47,000 sq ft/day, a storage coefficient of 0.0005, and a hydraulic conductivity of more than 100 ft/day. Hydraulic conductivities in most hydrostratigraphic units decrease with distance away from structural uplifts. Water in the Devonian and Mississippian carbonate rocks unit flows from structural uplifts to structural and fluvial basins. This hydrostratigraphic unit supplies water to streams that drain the White River Plateau, hot springs at Glenwood Springs, and artesian wells in the Burns basin. (USGS)

  10. Habitat of petroleum in the Paleozoic basins of Brazil: A look back, a comparison, a look forward

    SciTech Connect

    Meister, E.M.; Campos, J.N.P.; Filho, C.B.; Brazil, I.R.; Neves, C.A.O.; Goes, A.M.O.; Milani, E.J. )

    1991-03-01

    It took almost a century of intermittent petroleum exploration in Brazil's vast Paleozoic basins before continuous production of about 5000 bbl per day of light oil, together with gas, could be established in one of them. Proved volumes of oil equivalent in place so far discovered in Paleozoic reservoirs amount to only 0.6% of the domestic total, but hopes of substantial new finds are great. In the Rio Urucu field of Solimoes basin (Upper Amazon), hydrocarbons are being produced from Early Carboniferous Monte Alegre formation sandstones roofed by evaporites and carbonates of the Carboniferous Itaituba formation which were intruded by thick Juro-Triassic igneous sills and folded during a Cretaceous reactivation event into the present-day shape of gentle anticlinal trends controlled by reverse faulting. The widespread occurrence of igneous intrusions and extrusions in the Solimoes, Amazonas, Parnaiba, and Parana basins is a major problem met by explorationists throughout the years but can be faced with presently available technology, seismic and other. Further investigations in these four basins are needed in order to better define details of basin architecture, configuration of basement, location of the oil kitchens, main carrier beds, windows in the dyke walls through which hydrocarbons could find their way to the traps, etc. Examples from the various basins, along with a comparison to some successful exploration cases in the USA, suggest that the habitat of other commercial oil and gas in the Paleozoic basins of Brazil may be localized in the deeper basinal positions - like in the Rio Urucu trend - but also in the shallow flank areas, where igneous rocks tend to be scarcer and exploration baroquely started.

  11. Sandstone units of the Lee Formation and related strata in eastern Kentucky

    USGS Publications Warehouse

    Rice, Charles L.

    1984-01-01

    Most of the Cumberland Plateau region of southeastern Kentucky is underlain by thick sequences of quartzose sandstone which are assigned for the most part to the Lee Formation. Much new information has been gathered about the Lee and related strata as a result of the cooperative mapping program of the U. S. Geological Survey and the Kentucky Geological Survey between 1960 and 1978. This report summarizes the age, lithology, distribution, sedimentary structures, and stratigraphic relations of the sandstone units of the Lee within and between each of three major outcrop belts in Kentucky: Cumberland Mountain, Pine Mountain, and the Pottsville Escarpment area. The Lee Formation generally has been regarded as Early Pennsylvanian in age and separated from Mississippian strata in Kentucky by an unconformity. However, lithostratigraphic units included in the formation as presently defined are broadly time-transgressive and range in age from Late Mississippian in parts of the Cumberland Mountain outcrop belt to Middle Pennsylvanian in the Pottsville Escarpment area. Members of the Lee intertongue with and grade into the underlying Pennington Formation and overlying Breathitt Formation. Sandstone and conglomeratic sandstone members of the Lee of Mississippian age found only in parts of the Cumberland overthrust sheet are closely associated with marine rocks; Pennsylvanian members are mostly associated with continental coal-bearing strata. Sandstone members of the Lee are mostly quartz rich and range from more than 90 percent to more than 99 percent quartz. They are relatively coarse grained, commonly pebbly, and in places conglomeratic. The units are southwest-trending linear or broadly lobate bodies. The Lee Formation is as much as 1,500 ft thick in the type area in Cumberland Mountain where it has been divided into eight members. The Pinnacle Overlook, Chadwell, White Rocks Sandstone, Middlesboro, Bee Rock Sandstone, and Naese Sandstone Members are mostly quartzose

  12. Isotopic age constraints on provenance of exotic terranes, latest Permian collision and fast Late Triassic post-collisional cooling and tectonic exhumation of the Korean collision belt

    NASA Astrophysics Data System (ADS)

    de Jong, Koenraad; Han, Seokyoung; Ruffet, Gilles; Yi, Keewook

    2016-04-01

    The Korean peninsula is located in the eastern margin of the Eurasian continent where major late Palaeozoic to early Mesozoic continental collision zones, like the Central Asian Orogenic Belt and the Central China Orogen, merge with circum-Pacific subduction-accretion systems. We present an integrated view of the Korean collision belt using recent Ar/Ar laser-probe step-heating single grain ages from the uppermost Gyeonggi Massif, central Korea's Palaeoproterozoic high-grade granite-gneiss terrane affected by Permo-Triassic metamorphism, the bordering Hongseong zone and the overlying Imjingang belt and the correlative Taean Formation, as well as SHRIMP isotopic ages of detrital zircons from meta-sandstones from the latter metamorphic marine turbidite sequences. We show that early Paleozoic isolated exotic terranes form part of the collision belt and were reworked in Permo-Triassic time. Age spectra of zircons from mature meta-sandstones in the Misan Formation (Imjingang Belt) and Taean Formation do not match the age distribution of the Gyeonggi Massif, to which both are usually assigned, as they show only subordinate 1.9-1.8 Ga and ~2.5 Ga age modes but dominant 441-426 Ma and 978-919 Ma peaks. Much of the sediment appears to have been derived from distant, exotic middle Paleozoic and Early Neoproterozoic magmatic sources, not present in Gyeonggi or other Korean basement massifs. The youngest concordant zircon ages are: 394, 398 and 402 Ma, showing that both formations are at least of Early Devonian age. Terranes with a substratum with Early Neoproterozoic and Silurian-Devonian granitoids are present in the South Chinese Cathaysia Terrane and in the Qinling Terrane (Central China Orogen). Both formations may, hence, represent the submarine fan part of a routing system and a delta-shelf system originally situated in China. The Taean Formation and Imjingang Belt are thus exotic Paleozoic terranes tectonically emplaced in the Korean collision belt. Muscovite, biotite

  13. Reservoir sandstone bodies in lower Silurian Clinton sandstone interval, eastern Ohio

    SciTech Connect

    Coogan, A.H.

    1987-09-01

    The stratigraphic relationships of the sandstones, shales, limestones, dolomites, and related beds of the Lower Silurian Clinton sandstone interval in Ohio have been examined using several thousand well logs from Medina County to Coshocton County in eastern Ohio. This north-south band of counties lies semiparallel to the north-northeast-trending depositional edge of the Clinton lower deltaic and coastal plain. Continuous and discontinuous bar sandstones with patterns similar to barrier island deposits are found at the edge of the deltaic plain. The thicker sandstone reservoirs in these deposits have been prolific oil and gas pools. The discontinuous bar sands are more common, however, and where drilling is sparse or where only the cleaner sandstones are mapped, these bar sands appear as isolated, thick, porous sandstone bodies. Examples exist in Holmes and Wayne Counties, Ohio. Elongate, nearly straight, narrow sandstone bodies occur on the lower deltaic plain, and were deposited in channels that were fluvial or partly estuarine. The channel sandstones are less than 1000 ft wide, extend for distances up to 10 mi and can be seen in Coshocton, Summit, and Medina Counties. The reservoirs in these sandstones are prolific oil and gas producers, but they are not easy to locate. At the seaward end of the elongate channel, sandstones are thick, localized sand bodies that fit in the sedimentological picture as river mouth bars. An example from Medina County illustrates this reservoir geometry at the site of excellent oil production from the Clinton interval.

  14. A comparative study of diversification events: the early Paleozoic versus the Mesozoic

    NASA Technical Reports Server (NTRS)

    Erwin, D. H.; Valentine, J. W.; Sepkoski, J. J. Jr; Sepkoski JJ, J. r. (Principal Investigator)

    1987-01-01

    We compare two major long-term diversifications of marine animal families that began during periods of low diversity but produced strikingly different numbers of phyla, classes, and orders. The first is the early-Paleozoic diversification (late Vendian-Ordovician; 182 MY duration) and the other the Mesozoic phase of the post-Paleozoic diversification (183 MY duration). The earlier diversification was associated with a great burst of morphological invention producing many phyla, classes, and orders and displaying high per taxon rates of family origination. The later diversification lacked novel morphologies recognized as phyla and classes, produced fewer orders, and displayed lower per taxon rates of family appearances. The chief difference between the diversifications appears to be that the earlier one proceeded from relatively narrow portions of adaptive space, whereas the latter proceeded from species widely scattered among adaptive zones and representing a variety of body plans. This difference is believed to explain the major differences in the products of these great radiations. Our data support those models that hold that evolutionary opportunity is a major factor in the outcome of evolutionary processes.

  15. Early Paleozoic paleogeography of the northern Gondwana margin: new evidence for Ordovician-Silurian glaciation

    NASA Astrophysics Data System (ADS)

    Semtner, A.-K.; Klitzsch, E.

    1994-12-01

    During the Early Paleozoic, transgressions and the distribution of sedimentary facies on the northern Gondwana margin were controlled by a regional NNW-SSE to almost north-south striking structural relief. In Early Silurian times, a eustatic highstand enabled the sea to reach its maximum southward extent. The counterclockwise rotation of Gondwana during the Cambrian and Early Ordovician caused the northern Gondwana margin to shift from intertropical to southern polar latitudes in Ordovician times. Glacial and periglacial deposits are reported from many localities in Morocco, Algeria, Niger, Libya, Chad, Sudan, Jordan and Saudi Arabia. The Late Ordovician glaciation phase was followed by a period of a major glacioeustatic sea-level rise in the Early Silurian due to the retreat of the ice-cap. As a consequence of the decreasing water circulation in the basin centers (Central Arabia, Murzuk- and Ghadames basins), highly bituminous euxinic shales were deposited. These shales are considered to be the main source rock of Paleozoic oil and gas deposits in parts of Saudi Arabia, Libya and Algeria. The following regression in the southern parts of the Early Silurian sea was probably caused by a second glacial advance, which was mainly restricted to areas in Chad, Sudan and Niger. Evidence for glacial activity and fluvioglacial sedimentation is available from rocks overlying the basal Silurian shale in north-east Chad and north-west Sudan. The Early Silurian ice advance is considered to be responsible for the termination of euxinic shale deposition in the basin centers.

  16. Post-Paleozoic crinoid radiation in response to benthic predation preceded the Mesozoic marine revolution

    PubMed Central

    Baumiller, Tomasz K.; Salamon, Mariusz A.; Gorzelak, Przemysław; Mooi, Rich; Messing, Charles G.; Gahn, Forest J.

    2010-01-01

    It has been argued that increases in predation over geological time should result in increases in defensive adaptations in prey taxa. Recent in situ and laboratory observations indicate that cidaroid sea urchins feed on live stalked crinoids, leaving distinct bite marks on their skeletal elements. Similar bite marks on fossil crinoids from Poland strongly suggest that these animals have been subject to echinoid predation since the Triassic. Following their near-demise during the end-Permian extinction, crinoids underwent a major evolutionary radiation during the Middle–Late Triassic that produced distinct morphological and behavioral novelties, particularly motile taxa that contrasted strongly with the predominantly sessile Paleozoic crinoid faunas. We suggest that the appearance and subsequent evolutionary success of motile crinoids were related to benthic predation by post-Paleozoic echinoids with their stronger and more active feeding apparatus and that, in the case of crinoids, the predation-driven Mesozoic marine revolution started earlier than in other groups, perhaps soon after the end-Permian extinction. PMID:20231453

  17. Post-Paleozoic crinoid radiation in response to benthic predation preceded the Mesozoic marine revolution.

    PubMed

    Baumiller, Tomasz K; Salamon, Mariusz A; Gorzelak, Przemyslaw; Mooi, Rich; Messing, Charles G; Gahn, Forest J

    2010-03-30

    It has been argued that increases in predation over geological time should result in increases in defensive adaptations in prey taxa. Recent in situ and laboratory observations indicate that cidaroid sea urchins feed on live stalked crinoids, leaving distinct bite marks on their skeletal elements. Similar bite marks on fossil crinoids from Poland strongly suggest that these animals have been subject to echinoid predation since the Triassic. Following their near-demise during the end-Permian extinction, crinoids underwent a major evolutionary radiation during the Middle-Late Triassic that produced distinct morphological and behavioral novelties, particularly motile taxa that contrasted strongly with the predominantly sessile Paleozoic crinoid faunas. We suggest that the appearance and subsequent evolutionary success of motile crinoids were related to benthic predation by post-Paleozoic echinoids with their stronger and more active feeding apparatus and that, in the case of crinoids, the predation-driven Mesozoic marine revolution started earlier than in other groups, perhaps soon after the end-Permian extinction. PMID:20231453

  18. Detrital zircon U-Pb ages of Paleozoic sedimentary rocks from the eastern Hexi Corridor Belt (NW China): Provenance and geodynamic implications

    NASA Astrophysics Data System (ADS)

    Zhao, Xiaochen; Liu, Chiyang; Wang, Jianqiang; Zhao, Yan; Wang, Lei; Zhang, Qihang

    2016-06-01

    The Paleozoic tectonic framework of the eastern Hexi Corridor Belt is ambiguous. However, thick Paleozoic sediments from the eastern Hexi Corridor Belt can provide clues to this problem. In this paper, we deal with the detrital zircon provenance of Middle Ordovician to Late Devonian strata using LA-ICP-MS U-Pb dating, documenting the temporal and spatial changes of provenance. Detrital zircon U-Pb ages indicate that the primary provenance was the Qilian Orogenic Belt and the Alxa Block. However, two samples from Late Devonian strata show different provenance characteristics, from the North Qilian Orogenic Belt, and the Alxa Block and the North China Block, respectively. Different age distributions through time reflect provenance changes due to continuous convergence of the Central Qilian Block and the Alxa Block from the Middle Ordovician to Late Devonian. A significant age cluster ranging from 2000 to 1800 Ma, which is a detrital zircon signature of the North China Block, appeared in the Late Devonian Zhongning Formation. Our preferred interpretation is that the amalgamation of the Alxa Block and the North China Block likely occurred at that time. Moreover, similar Paleozoic fossils, paleolatitudes and detrital zircon distribution indicate that the Hexi Corridor Belt has an affinity to eastern Gondwana.

  19. Salamanca sandstone: a good GHSR not suitable for all construction purposes.

    NASA Astrophysics Data System (ADS)

    Pereira, Dolores; Blanco, Jose Antonio; Nespereira, Jose

    2016-04-01

    Salamanca sandstone, which in fact is an opal-cemented formation of sandstones and conglomerates, was used in the construction of many historical buildings of Salamanca old city, as well as other places nearby. Salamanca is recognized as World Heritage site since 1988, precisely because the homogeneous architecture and the use of local natural resources, as the Salamanca sandstone, the Villamayor sandstone and some local granites. The reason for using the sedimentary stone was the easy access of the resource, as the city is built on top of the Salamanca sandstone Formation, a late Cretaceous-early Palaeocene deposit. This formation consists of siliciclastic successions that were deposited in braided fluvial systems. These materials are derived from a deeply weathered Variscan basement showing ferruginous alteration that adds an aesthetic value to the global view of the natural stone. However, after several centuries, the stone has started to show serious problems due to water absorption, mainly in those places where it was used as basement of the buildings. Restoration of historical buildings should consider the use of the same original material when replacement is requested. But when this original material has been demonstrated to be not appropriate for long-term constructions, a matching and preferable natural stone should be used for replacement. There is such possibility in Salamanca and this has not have to mean the disregard of the Salamanca sandstone for other uses. The natural stone has been used for interior use and for sculpture with quality results. We present the Salamanca sandstone as a possible candidate to be taken into account as GHSR, supported by complete characterization and use recommendation.

  20. GREYBULL SANDSTONE PETROLEUM POTENTIAL ON THE CROW INDIAN RESERVATION, SOUTH-CENTRAL MONTANA

    SciTech Connect

    David A. Lopez

    2000-12-14

    Evaluation of the Lower Cretaceous Greybull Sandstone on the Crow Indian Reservation for potential stratigraphic traps in the valley-fill sandstone was the focus of this project. The Crow Reservation area, located in south-central Montana, is part of the Rocky Mountain Foreland structural province, which is characterized by Laramide uplifts and intervening structural basins. The Pryor and Bighorn mountains, like other foreland uplifts, are characterized by asymmetrical folds associated with basement-involved reverse faults. The reservation area east of the mountains is on the northwestern flank of the Powder River Basin. Therefore, regional dips are eastward and southeastward; however, several prominent structural features interrupt these regional dips. The nearly 4,000 mi{sup 2} reservation is under explored but has strong potential for increased oil and gas development. Oil and gas production is well established in the Powder River Basin of Wyoming to the south as well as in the areas north and west of the reservation. However, only limited petroleum production has been established within the reservation. Geologic relations and trends indicate strong potential for oil and gas accumulations, but drilling has been insufficient for their discovery. The Greybull Sandstone, which is part of the transgressive systems tract that includes the overlying Fall River Sandstone, was deposited on a major regional unconformity. The erosional surface at the base of the Greybull Sandstone is the +100 Ma, late Aptian-Early Albian regional unconformity of Weimer (1984). This lowstand erosional surface was controlled by a basin-wide drop in sea level. In areas where incised Greybull channels are absent, the lowstand erosional unconformity is at the base of the Fall River Sandstone and equivalent formations. During the pre-Greybull lowstand, sediment bypassed this region. In the subsequent marine transgression, streams began to aggrade and deposit sand of the lower Greybull Sandstone

  1. Provenance of Norphlet sandstone, northern Gulf Coast

    SciTech Connect

    Ryan, W.P.; Ward, W.C.; Kuglar, R.L.

    1987-09-01

    The Upper Jurassic Norphlet sandstone of the northern Gulf Coast is predominantly subarkose, with some arkose in the eastern area and sublitharenite and quartzarenite in the western area. Despite great depths of burial and despite feldspar and rock-fragment constituents, diagenesis has not appreciably altered the composition of Norphlet sandstone. Therefore, reconstruction of original composition of Norphlet sandstone presented little difficulty. Variation in detrital modes of the Norphlet suggests compositionally distinct source terranes. Samples from Florida, Alabama, and Mississippi reflect the influence of metamorphic and plutonic rocks of the Appalachian Piedmont Province and of Triassic-Jurassic volcanic rocks. Sandstones in east Texas, northern Louisiana, and southern Arkansas were derived from sedimentary and metasedimentary rocks of the Ouachita system. The Arbuckle Mountains and Llano uplift may have supplied trace amounts of quartzo-feldspathic and volcanic-rock fragments to the extreme western part of the study area. Norphlet sandstones represent a mixture of collision-orogen-derived sediment from the Appalachian and/or Ouachita system and continental-block-derived sediment from paleohighs and uplifts within the Gulf basin. However, Norphlet sandstones plot in the craton-interior and transitional-continental fields on Q-F-L and QM-F-Lt tectonic-provenance diagrams, because of mineralogically mature source rocks, elimination of unstable grains by abrasion and sorting during deposition, and/or sediment mixing from different source terranes.

  2. Porosity prediction in sandstones using erosional unconformities

    SciTech Connect

    Shanmugam, G.

    1989-03-01

    Erosional unconformities of subaerial origin are created by tectonic uplifts and eustatic sea level fall. Most erosional unconformities developed on sandstones are planes of increased porosity because uplifted sandstones are exposed to undersaturated CO/sub 2/-charged meteoric waters that result in dissolution of unstable framework grains and cements. The chemical weathering of sandstones is intensified in humid regions by the heavy rainfall, soil zones, lush vegetation, and accompanying voluminous production of organic and inorganic acids. Erosional unconformities are considered hydrologically open systems because of abundant supply of fresh meteoric water and relatively unrestricted transport of dissolved constituents away from the site of dissolution, causing a net gain in porosity near unconformities. Thus, porosity in sandstones tends to increase toward overlying unconformities. Such porosity trends have been observed in hydrocarbon-bearing sandstone reservoirs in Alaska, Algeria, Australia, China, Libya, Netherlands, Norwegian North Sea, Norwegian Sea, and Texas. A common attribute of these reservoirs is that they were all subaerially exposed under heavy rainfall conditions. An empirical model has been developed for the Triassic and Jurassic sandstone reservoirs in the Norwegian North Sea on the basis of the observed relationship that shows an increase in porosity in these reservoirs with increasing proximity to the overlying base of Cretaceous unconformity. An important practical attribute of this model is that it allows for the prediction of porosity in the neighboring undrilled areas by recognizing the base of Cretaceous unconformity in seismic reflection profiles and by constructing subcrop maps.

  3. Quartz cement in sandstones: a review

    NASA Astrophysics Data System (ADS)

    McBride, Earle F.

    Quartz cement as syntaxial overgrowths is one of the two most abundant cements in sandstones. The main factors that control the amount of quartz cement in sandstones are: framework composition; residence time in the "silica mobility window"; and fluid composition, flow volume and pathways. Thus, the type of sedimentary basin in which a sand was deposited strongly controls the cementation process. Sandstones of rift basins (arkoses) and collision-margin basins (litharenites) generally have only a few percent quartz cement; quartzarenites and other quartzose sandstones of intracratonic, foreland and passive-margin basins have the most quartz cement. Clay and other mineral coatings on detrital quartz grains and entrapment of hydrocarbons in pores retard or prevent cementation by quartz, whereas extremely permeable sands that serve as major fluid conduits tend to sequester the greatest amounts of quartz cement. In rapidly subsiding basins, like the Gulf Coast and North Sea basins, most quartz cement is precipitated by cooling, ascending formation water at burial depths of several kilometers where temperatures range from 60° to 100° C. Cementation proceeds over millions of years, often under changing fluid compositions and temperatures. Sandstones with more than 10% imported quartz cement pose special problems of fluid flux and silica transport. If silica is transported entirely as H 4SiO 4, convective recycling of formation water seems to be essential to explain the volume of cement present in most sandstones. Precipitation from single-cycle, upward-migrating formation water is adequate to provide the volume of cement only if significant volumes of silica are transported in unidentified complexes. Modeling suggests that quartz cementation of sandstones in intracratonic basins is effected by advecting meteoric water, although independent petrographic, isotopic or fluid inclusion data are lacking. Silica for quartz cement comes from both shale and sandstone beds within

  4. Petrography and diagenesis of Eagle Mills sandstones, subsurface - Northeast Texas and southwest Arkansas

    SciTech Connect

    Dawson, W.C.; Callender, C.A. )

    1991-03-01

    The Eagle Mills Formation (Triassic-Jurassic) has been penetrated by several deep wells (12,000 to 18,000 ft) in northeast Texas and southwest Arkansas. It consists of green, red, and pink conglomeratic lithic arenites and fine- to coarse-grained feldspathic arenites, interbedded with red and greenish gray shales and siltstones. Lithic arenites contain basalt, chert, quartzite, and dolomite rock fragments; plagioclase is the predominant feldspar. All Eagle Mills sandstones have low textural and mineralogic maturities. Eagle Mills red beds and associated intrusive igneous rocks (diabase and basalt dikes and sills) represent the fillings of grabens or rift basins that actively subsided during deposition (in alluvial, fluvial-deltaic, and lacustrine paleoenvironments). Eagle Mills lithic and feldspathic sandstones have undergone a complex diagenetic history, including chlorite cementation (pore linings and pore fillings), compaction, quartz and feldspar overgrowths, dolomite cementation, chloritization and albitization of detrital feldspars, local dissolution of framework grains (igneous lithics and feldspars), precipitation of kaolinite, late Fe-calcite cementation, and saddle dolomite formation. Cement mineralogies are strongly correlative with lithofacies. Lithic sandstones contain the highest frequency of chlorite cements, whereas feldspathic sandstones are preferentially cemented with carbonates and anhydrite; quartz and feldspar overgrowths are ubiquitous. The suite of authigenic minerals in Eagle Mills sandstones records progressive burial into a deep, high-temperature (120-150C), semiclosed, diagenetic regime.

  5. Comparative development of the Western United States and southern Kazakhstan, Soviet Union - Two early Paleozoic carbonate passive margins

    SciTech Connect

    Cooke, H.E. ); Taylor, M.E. ); Zhemchuzhnikov, S.V.; Apollonov, M.K.; Ergaliev, G. Kh.; Sargaskaev, Z.S. ); Dubinina, S.V. )

    1991-02-01

    Early Paleozoic passive continental margins of the Western united States and southern Kazakhstan evolved at low latitudes on rifted Precambrian continental crust adjacent to the proto-Pacific Ocean. In the Western United States, early Paleozoic carbonate submarine fans and slides formed on continental slopes in central Nevada. Coeval shoal-water carbonate sediments occurred to the east, in Utah, where they interfingered with siliciclastic sediments and onlapped the craton. In contrast, early Paleozoic carbonate sediments of the Malyi Karatau, southern Kazakhstan, were deposited on isolated microcontinental blocks that developed during Late Proterozoic rifting of the continental crust. Comparison of stratigraphic sections from Nevada and Malyi Karatau indicate a similar upward-shallowing and seaward-prograding evolution. The Hot Creek Range section in Nevada consists of the Upper Cambrian Swarbrick Formation and Tybo Shale, and Upper Cambrian and lowest Ordovician Hales Limestone. These depositional facies include basin plain (about 500 m), carbonate submarine fan and slides (200 m), upperslope (150 m), and platform margin (150 m). The Kyrshabakty and Batyrbay sections in the Malyi Karatau consist of Cambrian and lowest Ordovician rocks of the Shabakty Suite. Stratigraphic sections in both the Western United States and Malyi Karatau record three coeval episodes of sea level lowstands. These lowstands, which the authors interpret to be eustatic, are recognized by times of seaward collapse of large segments of the platform margins and deeper water slopes and by solution breccias and faunal discontinuities in shoal-water platform-interior sites.

  6. Structural styles of Paleozoic intracratonic fault reactivation: A case study of the Grays Point fault zone in southeastern Missouri, USA

    USGS Publications Warehouse

    Clendenin, C.W.; Diehl, S.F.

    1999-01-01

    A pronounced, subparallel set of northeast-striking faults occurs in southeastern Missouri, but little is known about these faults because of poor exposure. The Commerce fault system is the southernmost exposed fault system in this set and has an ancestry related to Reelfoot rift extension. Recent published work indicates that this fault system has a long history of reactivation. The northeast-striking Grays Point fault zone is a segment of the Commerce fault system and is well exposed along the southeast rim of an inactive quarry. Our mapping shows that the Grays Point fault zone also has a complex history of polyphase reactivation, involving three periods of Paleozoic reactivation that occurred in Late Ordovician, Devonian, and post-Mississippian. Each period is characterized by divergent, right-lateral oblique-slip faulting. Petrographic examination of sidwall rip-out clasts in calcite-filled faults associated with the Grays Point fault zone supports a minimum of three periods of right-lateral oblique-slip. The reported observations imply that a genetic link exists between intracratonic fault reactivation and strain produced by Paleozoic orogenies affecting the eastern margin of Laurentia (North America). Interpretation of this link indicate that right-lateral oblique-slip has occurred on all of the northeast-striking faults in southeastern Missouri as a result of strain influenced by the convergence directions of the different Paleozoic orogenies.

  7. Volcanic Debris Flows of the Latest Paleozoic Arbasay Formation: Geomorphological Characters and Paleoenvironment Reconstruction of Northern Tian Shan, NW China

    NASA Astrophysics Data System (ADS)

    Yang, W.; Liu, D.; Guo, Z.

    2015-12-01

    Texturally well-preserved volcanic debris flows (also called lahars) are exposed in the Latest Paleozoic Arbasay Formation, Northern Tian Shan. LA-ICP-MS zircon dating of the intercalated fallout tuff sample provided an age of 314.4±3.4 Ma (MSWD=1.6), suggesting they were deposited at Latest Carboniferous. The lahars consist primarily of two lithofacies: massive, poorly lithified diamictites and stratified, moderately lithified gravelly sandstones. The diamictites can be generally divided into two subfacies, i.e., the matrix-supported and the clast-supported diamictites. Most diamictites are structureless and nongraded. They are thick in beds and contain large clasts up to 3 m in dimension. The gravelly sandstones display much finer particle size and have wedge or lenticular geometries. Large clasts are absent within them and the sorting characters are much better than the diamictites. Despite the different size grading, the matrix and the clasts of the two lithofacies appear to be homogeneous. The matrix is generally sandy mudstone. The clasts comprise rhyolites, dacites, andesites, andesitic basalts and basalts, same to the co-existing volcanic rocks, suggesting they originate from the cognate volcanics. The disorganized diamictites are supposed to deposit from a turbulent flood or pyroclastic surge. The gravelly sandstone lithofacies are interpreted as sand-rich flood flows or hyperconcentrated flood flows during the waning stage of a mass-flow event. The overall characteristics of the deposits suggest a mass-flow dominated alluvial fan environment. It's noteable that several syn- sedimentary normal faults occurred within these lahar deposits, indicating that the Southern Junggar Basin was in an extensional regime during the lahars' deposition. Structure is dominated by normal faulting, allowing the existence of relatively small, highly compartmentalized depocenters. This is also supported by geochemistry and detrital zircon studies.

  8. Artesian pressures and water quality in Paleozoic aquifers in the Ten Sleep area of the Bighorn Basin, north-central Wyoming

    USGS Publications Warehouse

    Cooley, M.E.

    1985-01-01

    Major Paleozoic artesian aquifers in the southeastern Bighorn Basin of Wyoming area, in descending order, the Tensleep Sandstone; the Madison Limestone and Bighorn Dolomite, which together form the Madison-Bighorn aquifer; and the Flathead Sandstone. Operating yields commonly are more than 1,000 gallons per minute from flowing wells completed in the Madison-Bighorn aquifer. The initial test of one well indicated a flow of 14,000 gallons per minute. Wellhead pressures range from less than 50 to more than 400 pounds per square inch. Transmissivities are 500-1,900 feet squared per day for the Madison-Bighorn aquifer and 90-325 feet squared per day for the Tensleep and Flathead Sandstones. Despite extensive development for irrigation there have been few decreases in pressure. Some decreases in pressure have occurred in wells completed in the Flathead Sandstone. Fractures along linear structural features result in significant secondary permeability and allow upward interformational movement of water that affects the altitude of the potentiometric surfaces in the Tensleep Sandstone and Madison-Bighorn aquifer. Upward-moving water from the Tensleep and other formations discharges at the land surface as springs along or near these lineations. Water from the aquifers generally contains minimal concentrations of dissolved solids and individual constituents but has excessive hardness. The water is satisfactory for irrigation and other purposes when hardness is not a detrimental factor. Wellhead temperatures range from 11 degrees to 27.5 degrees C, giving a geothermal gradient of about 0.44 degrees C per 100 feet. (USGS)

  9. Quantitative petrographic analysis of Cretaceous sandstones from southwest Montana

    SciTech Connect

    Dyman, T.S. Krystinik, K.B.; Takahashi, K.I.

    1986-05-01

    The Albian Blackleaf Formation and the Cenomanian lower Frontier Formation in southwest Montana lie within or east of the fold and thrust belt in the Cretaceous foreland basin complex. Petrography of these strata record a complex interaction between source-area tectonism, basin subsidence, and sedimentation patterns associated with a cyclic sequence of transgressions and regressions. Because the petrographic data set was large (127 thin sections) and difficult to interpret subjectively, statistical techniques were used to establish sample and variable relationships. Theta-mode cluster and correspondence analysis were used to determine the contributing effect (total variance) of key framework grains. Monocrystalline quartz, plagioclase, potassium feldspar, and sandstone-, limestone-, and volcanic-lithic grain content contribute most to the variation in the framework-grain population. Theta-mode cluster and correspondence analysis were used to identify six petrofacies. Lower Blackleaf petrofacies (I-III) contain abundant monocrystalline quartz (55-90%) and sedimentary lithic grains (10-50%), which are distributed throughout the study area. Petrofacies I-III are differentiated by variable monocrystalline quartz and sedimentary lithic grain content. Upper Blackleaf and lower Frontier petrofacies (IV-VI) exhibit highly variable, sedimentary and volcanic lithic ratios, and contain less monocrystalline quartz (20-50%) than lower Blackleaf petrofacies. Information from quantitative analyses combined with available paleocurrent data indicates that Blackleaf and lower Frontier detritus was derived from variable source areas through time. Lower Blackleaf detritus was derived from Precambrian through Paleozoic sedimentary terranes to the west, north, and east; whereas, upper Blackleaf and lower Frontier detritus was derived from both sedimentary and volcanic terranes to the south.

  10. Geochronology, geochemistry and origins of the Paleozoic-Triassic plutons in the Langshan area, western Inner Mongolia, China

    NASA Astrophysics Data System (ADS)

    Wang, Zeng-Zhen; Han, Bao-Fu; Feng, Li-Xia; Liu, Bo

    2015-01-01

    The Langshan area is the northeastern part of the Alxa block and adjacent to the Inner Mongolia-Da Hinggan Orogenic Belt (IMDOB) to the north, and geochronological and geochemical studies of the Langshan plutons would be helpful for unraveling the relationship of the magmatism in the Langshan area with that in the IMDOB. Based on zircon U-Pb ages presented in this study and in published papers, five magmatic stages are recognized in Langshan area: Late Silurian (∼418 Ma), Carboniferous (328-304 Ma), Early Permian (294-272 Ma), Late Permian (260-254 Ma) and Middle-Late Triassic (245-227 Ma). The Late Silurian two-mica granite is peraluminous and has a source from ancient continental crust, indicating a collision event. The late Early Carboniferous mafic plutons are subalkaline, show appinitic affinities, and may originate from the subduction-modified continental lithospheric mantle. The late Early Permian granodiorite is weakly peraluminous and high-K calc-alkaline and may be derived from ancient continental crust, while the late Early Permian alkaline gabbro-diorite displays EM I-like Sr-Nd isotopic signatures, indicating an enriched subcontinental lithospheric mantle source. The Late Permian granodiorite is calc-alkaline and peraluminous and may result from the partial melting of ancient lower continental crust, whereas the Late Permian leuconorite belongs to low-K tholeiitic series and has a cumulate origin from an enriched mantle source with the input of juvenile mantle materials. The Paleozoic-Triassic magmatic stages in the Langshan area are consistent with the main magmatic periods in the northern NCC, which are the Late Silurian to Middle Devonian (∼418-386 Ma) and Early Carboniferous to Late Triassic (∼342-211 Ma, with three magmatic stages of Carboniferous, Permian and Triassic). Especially, the Carboniferous to Late Triassic magmatic period in the northern NCC are closely comparable with that in the IMDOB, indicating the two domains might be

  11. Microstructure of deformed graywacke sandstones

    SciTech Connect

    Dengler, L.A.

    1980-03-05

    Microsctures in low-permeability graywacke sandstones were studied by optical and scanning electron microscopy (SEM). SEM specimens were prepared by ion-bombardment of thick polished samples. The undeformed rock contains grains in a matrix composed primarily of authigenic chlorite and kaolinite. Chlorite platelets are randomly arranged in face-to-edge relation to one another. Kaolinite occurs as pseudohexagonal crystals stacked face-to-face in pore filling books. Uniaxial-stress experiments covered a range of confining pressures from .1 to 600 MPa. Below 50 MPa confining pressure, intergranular fracturing occurs within the fault zone and near the sample's cylindrical surface. Between 100 and 300 MPa confining pressure, fault zones contain highly fractured grains, gauge and slickensides on grain surfaces. At 600 MPa, the sample contains a diffuse shear zone of highly fractured grains and no well-defined fault. In all samples, the distribution of microcracks is heterogeneous. Different clay minerals exhibit different modes of deformation. Chlorite structure responds to applied stress by compaction, reducing both pore size and volume. Chlorite platelets are plastically deformed in even the least strained samples. Kaolinite does not deform plastically in any of the samples examined. Deformation of kaolinite is restricted to toppling of the book structure. Dilatant crack growth was studied in two samples unloaded prior to failure. Uniaxially-strained samples deform primarily along grain boundaries, producing intergranular cracks and realignment of chlorite platelets. Intragranular crack density is linearly related to axial-strain, although grains are less fractured than in uniaxially-stressed samples tested at equivalent mean pressures. Cracks are rarely longer than a grain diameter. Nuclear-explosively deformed samples were recovered after the Rio Blanco gas stimulation experiment. (JGB)

  12. Magnetotelluric imaging of a fossil paleozoic intraoceanic subduction zone in western Junggar, NW China

    NASA Astrophysics Data System (ADS)

    Xu, Yixian; Yang, Bo; Zhang, Sheng; Liu, Ying; Zhu, Lupei; Huang, Rong; Chen, Chao; Li, Yongtao; Luo, Yinhe

    2016-06-01

    The fate of subducted oceanic slabs can provide important clues to plate reconstruction through Earth history. Since oceanic slabs in continental collision zones are typically not well preserved, ancient subduction zones have rarely been imaged by geophysical techniques. Here we present an exception from the Darbut belt in the Junggar accretionary collage in the southern Altaids of Asia. We deployed a 182 km long magnetotelluric (MT) profile including 60 broadband sounding sites across the belt. Quality off-diagonal impedances were inverted by a three-dimensional scheme to image resistivities beneath the profile. The resistivity model along with MT impedance phase ellipses and induction vectors were tested and interpreted in detail. Combining geological and geophysical observations, mineral physical experiment, and geodynamic modeling results, the MT transect suggests a fossil intraoceanic subduction zone during the Late Paleozoic in the western Junggar that has been well preserved due to lack of significant subsequent tecto-thermal events.

  13. A Double Mass Extinction at the End of the Paleozoic Era

    NASA Astrophysics Data System (ADS)

    Stanley, S. M.; Yang, X.

    1994-11-01

    Three tests based on fossil data indicate that high rates of extinction recorded in the penultimate (Guadalupian) stage of the Paleozoic era are not artifacts of a poor fossil record. Instead, they represent an abrupt mass extinction that was one of the largest to occur in the past half billion years. The final mass extinction of the era, which took place about 5 million years after the Guadalupian event, remains the most severe biotic crisis of all time. Taxonomic losses in the Late Permian were partitioned among the two crises and the intervening interval, however, and the terminal Permian crisis eliminated only about 80 percent of marine species, not 95 or 96 percent as earlier estimates have suggested.

  14. Paleozoic-early Mesozoic gold deposits of the Xinjiang Autonomous Region, northwestern China

    USGS Publications Warehouse

    Rui, Z.; Goldfarb, R.J.; Qiu, Y.; Zhou, T.; Chen, R.; Pirajno, F.; Yun, G.

    2002-01-01

    The late Paleozoic-early Mesozoic tectonic evolution of Xinjiang Autonomous Region, northwestern China provided a favorable geological setting for the formation of lode gold deposits along the sutures between a number of the major Eastern Asia cratonic blocks. These sutures are now represented by the Altay Shan, Tian Shan, and Kunlun Shan ranges, with the former two separated by the Junggar basin and the latter two by the immense Tarim basin. In northernmost Xinjiang, final growth of the Altaid orogen, southward from the Angara craton, is now recorded in the remote mid- to late Paleozoic Altay Shan. Accreted Early to Middle Devonian oceanic rock sequences contain typically small, precious-metal bearing Fe-Cu-Zn VMS deposits (e.g. Ashele). Orogenic gold deposits are widespread along the major Irtysh (e.g. Duyolanasayi, Saidi, Taerde, Kabenbulake, Akexike, Shaerbulake) and Tuergen-Hongshanzui (e.g. Hongshanzui) fault systems, as well as in structurally displaced terrane slivers of the western Junggar (e.g. Hatu) and eastern Junggar areas. Geological and geochronological constraints indicate a generally Late Carboniferous to Early Permian episode of gold deposition, which was coeval with the final stages of Altaid magmatism and large-scale, right-lateral translation along older terrane-bounding faults. The Tian Shan, an exceptionally gold-rich mountain range to the west in the Central Asian republics, is only beginning to be recognized for its gold potential in Xinjiang. In this easternmost part to the range, northerly- and southerly-directed subduction/accretion of early to mid-Paleozoic and mid- to late Paleozoic oceanic terranes, respectively, to the Precambrian Yili block (central Tian Shan) was associated with 400 to 250 Ma arc magmatism and Carboniferous through Early Permian gold-forming hydrothermal events. The more significant resulting deposits in the terranes of the southern Tian Shan include the Sawayaerdun orogenic deposit along the Kyrgyzstan border and

  15. Paleozoic vertical movements in Um Bogma area, southwestern Sinai

    SciTech Connect

    Beyth, M.

    1981-01-01

    The Wadi Khaboba-Gebel Nukhul high, in the Um Bogma area of southwestern Sinai, underwent a small-scale uplift-subsidence cycle during the Paleozoic. The trend of this structure is close to and almost parallel with the Suez rift, indicating that the young rift is related to older structures.

  16. Sediment and weathering control on the distribution of Paleozoic magmatic tin-tungsten mineralization

    NASA Astrophysics Data System (ADS)

    Romer, Rolf L.; Kroner, Uwe

    2015-03-01

    The formation of major granite-hosted Sn and/or W deposits and lithium-cesium-tantalum (LCT) type pegmatites in the Acadian, Variscan, and Alleghanian orogenic belts of Europe and Atlantic Northern America involves weathering-related Sn and W enrichment in the sedimentary debris of the Cadomian magmatic arc and melting of these sedimentary source rocks during later tectonic events, followed by magmatic Sn and W enrichment. We suggest that within this, more than 3,000-km long late Paleozoic belt, large Sn and/or W deposits are only found in regions where later redeposition of the Sn-W-enriched weathered sediments, followed by tectonic accumulation, created large volumes of Sn-W-enriched sedimentary rocks. Melting of these packages occurred both during the formation of Pangea, when continental collision subjected these source rocks to high-grade metamorphism and anatexis, and during post-orogenic crustal extension and mantle upwelling. The uncoupling of source enrichment and source melting explains (i) the diachronous occurrence of tin granites and LCT pegmatites in this late Paleozoic orogenic belt, (ii) the occurrence of Sn and/or W mineralizations and LCT pegmatites on both sides of the Rheic suture, and (iii) the contrasting tectonic setting of Sn and/or W mineralizations within this belt. Source enrichment, sedimentary and tectonic accumulation of the source rocks, and heat input to mobilize metals from the source rocks are three unrelated requirements for the formation of Sn and/or W granites. They are the controlling features on the large scale. Whether a particular granite eventually generates a Sn and/or W deposit depends on local conditions related to source melting, melt extraction, and fractionation processes.

  17. Ouachita-Appalachian juncture: A paleozoic transpressional zone in the Southeastern USA

    SciTech Connect

    Hale-Erlich, W.S.; Coleman, J.L. Jr. )

    1993-04-01

    The northern margin of Gondwana collided with the southern margin of the North American craton in the late Paleozoic (330-265 Ma.). Near-normal compressional stresses, generated where the trend of the North American margin was nearly perpendicular to Gondwana's plate-motion vector (closure direction), caused extensive crustal shortening and decollement thrusting within the sedimentary section. The application and Ouachita fold belts are the erosional remnants of this collision on the North American margin. Transecting the ouachita fold belt are several zones of late Palezoic transcurrent faulting: the Val Verde, Ardmore-Anadarko, and Reelfoot zones. They occur where the precollision margin of the North American craton was oriented oblique of parallel to the closure direction with Gondwana. Stresses generated within these zones during the collision were transpressional rather than simply compressional, and gave rise to high-angle faulting, high-amplitude vertical displacements, and the emplacement of positive flower structures. In the Val Verde and Ardmore-Anadarko basins, these features have proven to be major structural traps for oil and gas. On the basis of seismic and well data, this study identifies a zone of complex structures, including positive flower structures, in the subsurface Paleozoic section of Kemper County in east-central Mississippi. The region is considered to be another transpressional zone analogous to the Val Verde, Armore-Anadarko, and Reelfoot zones. The Kemper County zone separates and truncates the Appalachian Valley and Ridge fold belt to the west and is, therefore, also identified as the juncture between the Ouachita and Appalachian fold-belt systems in the southeastern U.S.A. 81 refs., 13 figs., 1 tab.

  18. /sup 40/Ar//sup 39/Ar age of detrital muscovite within Lower Ordovician sandstone in the coastal plain basement of Florida: implications for west African terrane linkages

    SciTech Connect

    Dallmeyer, R.D.

    1987-11-01

    Detrital muscovite was concentrated from a core of Lower Ordovician sandstone recovered from 1282 m in the Sun Oil Company, H.T. Parker No.1 well, Marion County, Florida. The concentrate records a /sup 40/Ar//sup 39/Ar plateau age of 504.1 +/- 2.1 Ma. The Paleozoic sedimentary section penetrated in this well is part of an extensive subsurface Lower Ordovician-Middle Devonian sedimentary succession characterized by Gondwanan paleontological affinities. The succession has been correlated with sequences of similar age in the Bove Basin of west Africa which unconformably overlie metamorphic units of the Bassaride and Rokelide orogens in Senegal and Guinea. Muscovite within these metamorphic rocks records ca. 500-510 Ma postmetamorphic /sup 40/Ar//sup 39/Ar cooling ages and was likely a proximal source for the lower Paleozoic clastic detritus represented in the pre-Mesozoic sedimentary sequences beneath the southeastern US coastal plain.

  19. Sea level and paleotectonic controls on distribution of reservoir sandstone of Lower Cretaceous Muddy Sandstone, Hilight Field, Powder River basin, Wyoming

    SciTech Connect

    Wheeler, D.M.; Gustason, E.R.

    1987-05-01

    To date, over 74 million bbl of oil have been produced from stratigraphic traps at Hilight field. Production is primarily from thin but stratigraphically complex fluvial and shallow marine sandstone of the Lower Cretaceous Muddy Sandstone. The deposition and preservation of these reservoirs were controlled by the interplay between sea level and tectonics. The Muddy Sandstone in Hilight field was deposited during a late Albian sea level rise. It onlaps an erosional surface, developed during the preceding sea level drop, including a dendritic valley system cut deeply into the underlying Skull Creek Shale. In this area, the Muddy consists of four members that are bounded by transgressive disconformities. These members were deposited during stillstands in the overall rise of sea level. The lower two members consist of fluvial and fluvial-estuarine deposits which fill the valley system; the upper two members consist of fluvial-deltaic and barrier island deposits. Three northeast-trending lineaments transect Hilight field. These lineaments are interpreted to represent basement faults that experienced recurrent movement during Muddy deposition. Relative structural downdrop controlled the orientation of drainages that cut the Hilight valley system. Recurrent movement provided structural and topographic lows within which relatively thick fluvial-deltaic and barrier island sandstones were deposited and preserved. Thinner sequences were deposited and subsequently eroded on adjacent structural and topographic highs.

  20. Paleozoic tectonic history of the Arctic basin north of Alaska

    USGS Publications Warehouse

    Churkin, M.

    1969-01-01

    The geology of the margin of the Canada Basin, together with geophysical data, leads me to reject the continental subsidence theory for the origin of the deep Canada Basin. Instead, the Canada Basin is, I believe, a true and probably very ancient ocean basin floored by oceanic crust and rimmed by an early Paleozoic geosynclinal belt. In the Upper Devonian, uplifts in this circumarctic geosyncline, accompanied by granitic intrusion, produced a wedge of coarse clastic sediments (exogeosyncline) that spread southward onto adjoining areas of Alaska, Canada, and Siberia. In both northern Alaska and the Canadian Arctic Islands, thick sequences of upper Paleozoic and younger strata were deposited unconformably on the rocks of the early Paleozoic geosyncline, showing a similarity in tectonic history between the areas. The Paleozoic history of the southern rim of the Canada Basin resembles that of other mobile belts bordering North America. The movement of the floor of the Arctic Ocean against the continental crust of North America (sea-floor spreading) would provide a mechanism to account for the long history of orogenic activity along the basin margin. The sharp bend in the structural elements of southern Alaska (the Alaska orocline) has been cited as evidence of clockwise rotation of the Arctic Islands of Canada from Alaska and the Soviet Arctic to their present position during the Mesozoic. However, the geologic and geophysical evidence available indicates that the Arctic basin has a longer history, extending into the Paleozoic, and that this bend in Alaskan structures may have been largely caused by spreading of the Pacific sea floor against the continental margin in the Gulf of Alaska.

  1. Interpreting Fracture Patterns in Sandstones Interbedded with Ductile Strata at the Salt Valley Anticline, Arches National Park, Utah

    SciTech Connect

    LORENZ, JOHN C.; COOPER, SCOTT P.

    2001-12-01

    Sandstones that overlie or that are interbedded with evaporitic or other ductile strata commonly contain numerous localized domains of fractures, each covering an area of a few square miles. Fractures within the Entrada Sandstone at the Salt Valley Anticline are associated with salt mobility within the underlying Paradox Formation. The fracture relationships observed at Salt Valley (along with examples from Paleozoic strata at the southern edge of the Holbrook basin in northeastern Arizona, and sandstones of the Frontier Formation along the western edge of the Green River basin in southwestern Wyoming), show that although each fracture domain may contain consistently oriented fractures, the orientations and patterns of the fractures vary considerably from domain to domain. Most of the fracture patterns in the brittle sandstones are related to local stresses created by subtle, irregular flexures resulting from mobility of the associated, interbedded ductile strata (halite or shale). Sequential episodes of evaporite dissolution and/or mobility in different directions can result in multiple, superimposed fracture sets in the associated sandstones. Multiple sets of superimposed fractures create reservoir-quality fracture interconnectivity within restricted localities of a formation. However, it is difficult to predict the orientations and characteristics of this type of fracturing in the subsurface. This is primarily because the orientations and characteristics of these fractures typically have little relationship to the regional tectonic stresses that might be used to predict fracture characteristics prior to drilling. Nevertheless, the high probability of numerous, intersecting fractures in such settings attests to the importance of determining fracture orientations in these types of fractured reservoirs.

  2. Evidence of multi-stage faulting by clay mineral analysis: Example in a normal fault zone affecting arkosic sandstones (Annot sandstones)

    NASA Astrophysics Data System (ADS)

    Buatier, Martine D.; Cavailhes, Thibault; Charpentier, Delphine; Lerat, Jérémy; Sizun, Jean Pierre; Labaume, Pierre; Gout, Claude

    2015-06-01

    Fault affecting silicoclastic sediments are commonly enriched in clay minerals. Clays are sensitive to fluid-rock interactions and deformation mechanisms; in this paper, they are used as proxy for fault activity and behavior. The present study focuses on clay mineral assemblages from the Point Vert normal fault zone located in the Annot sandstones, a Priabonian-Rupelian turbidite succession of the Alpine foredeep in SE France. In this area, the Annot sandstones were buried around 6-8 km below the front of Alpine nappes soon after their deposition and exhumed during the middle-late Miocene. The fault affects arkosic sandstone beds alternating with pelitic layers, and displays throw of about thirty meters. The fault core zone comprises intensely foliated sandstones bounding a corridor of gouge about 20 cm thick. The foliated sandstones display clay concentration along S-C structures characterized by dissolution of K-feldspar and their replacement by mica, associated with quartz pressure solution, intense microfracturation and quartz vein precipitation. The gouge is formed by a clayey matrix containing fragments of foliated sandstones and pelites. However, a detailed petrographical investigation suggests complex polyphase deformation processes. Optical and SEM observations show that the clay minerals fraction of all studied rocks (pelites and sandstones from the damage and core zones of the fault) is dominated by white micas and chlorite. These minerals have two different origins: detrital and newly-formed. Detrital micas are identified by their larger shape and their chemical composition with a lower Fe-Mg content than the newly-formed white micas. In the foliated sandstones, newly-formed white micas are concentrated along S-C structures or replace K-feldspar. Both types of newly formed micas display the same chemical composition confirmed microstructural observations suggesting that they formed in the same conditions. They have the following structural formulas: Na0

  3. New Perspectives on the Old Red Sandstone

    NASA Astrophysics Data System (ADS)

    Miall, Andrew D.

    The Old Red Sandstone is amongst the most distinctive and well-known stratigraphic units in the British Isles. It is mainly of Devonian age; in fact, its lower boundary was used to define the base of the Devonian until relatively recently and it was called "Old" back in the nineteenth century to distinguish it from a superficially similar succession of Triassic age named the New Red Sandstone. The Old Red Sandstone has long been known to be a non-marine syntectonic to post-tectonic deposit associated with the Caledonian Orogeny One of the most famous outcrops of the red sandstone is at Siccar Point in northeast England at one of several outcrops named "Hutton's unconformity" where it lies, with marked angularity on Silurian lithic sandstones and shales. It was at these outcrops, toward the end of the eigthteenth century that James Hutton first came to understand the meaning of angular unconformities as structures representing vast amounts of missing time during which major upheavals of the Earth's crust occurred.

  4. Facies patterns and conodont biogeography in Arctic Alaska and the Canadian Arctic Islands: Evidence against juxtaposition of these areas during early Paleozoic time

    USGS Publications Warehouse

    Dumoulin, J.A.; Harris, A.G.; Bradley, D.C.; De Freitas, T. A.

    2000-01-01

    Differences in lithofacies and biofacies suggest that lower Paleozoic rocks now exposed in Arctic Alaska and the Canadian Arctic Islands did not form as part of a single depositional system. Lithologic contrasts are noted in shallow- and deep-water strata and are especially marked in Ordovician and Silurian rocks. A widespread intraplatform basin of Early and Middle Ordovician age in northern Alaska has no counterpart in the Canadian Arctic, and the regional drowning and backstepping of the Silurian shelf margin in Canada has no known parallel in northern Alaska. Lower Paleozoic basinal facies in northern Alaska are chiefly siliciclastic, whereas resedimented carbonates are volumetrically important in Canada. Micro- and macrofossil assemblages from northern Alaska contain elements typical of both Siberian and Laurentian biotic provinces; coeval Canadian Arctic assemblages contain Laurentian forms but lack Siberian species. Siberian affinities in northern Alaskan biotas persist from at least Middle Cambrian through Mississippian time and appear to decrease in intensity from present-day west to east. Our lithologic and biogeographic data are most compatible with the hypothesis that northern Alaska-Chukotka formed a discrete tectonic block situated between Siberia and Laurentia in early Paleozoic time. If Arctic Alaska was juxtaposed with the Canadian Arctic prior to opening of the Canada basin, biotic constraints suggest that such juxtaposition took place no earlier than late Paleozoic time.

  5. Geochemistry of dolomites in the St. Peter Sandstone of the Michigan Basin

    SciTech Connect

    Winter, B.L.; Johnson, C.M.; Valley, J.W. . Dept. of Geology and Geophysics)

    1992-01-01

    Quartz sandstone units in mid-continent sedimentary basins are considered to be major migration pathways for fluids throughout the history of such basins, possibly including connate and meteoric water, hydrocarbons, evaporite and basinal brines, and MVT ore-forming fluids. To gain an understanding of the fluid history of the Michigan Basin, the authors are investigating the dolomites in the St. Peter Sandstone. Based on petrography and lithofacies occurrence, they categorize the dolomites as: dolomite cement in quartz sandstone (DCS), replacive dolomite in carbonate-dominated intervals (RD), and fracture fill dolomite (FFD) associated with RD. RD and FFD display a linear covariation of mole %FeCO[sub 3] and Mn with Fe/Mn ratios increasing from 6 for bright orange luminescent RD to 11 for non-luminescent FFD. DCS display the highest %FeCO[sub 3] and no Fe-Mn correlation. DCS have higher ratios and SR concentrations than RD and FFD. Data for RD and FFD define two different, linear positive-sloping, Sr-87/Sr-86-%FeCO[sub 3] covariation trends. Samples with higher ratios and %FeCO[sub 3] have systematically lower [delta] O-18 values. Dolomites with Sr < 130ppm (mostly RD and FFD) follow the Sr-%MgCO[sub 3] trend defined by modern seawater dolomites; most of the DCS plot above this seawater dolomite trend. These data suggest that the RD and FFD precipitated from mid-Paleozoic seawater that progressively evolved in a basinal setting or mixed with an evolved basinal brine. DCS precipitated from a basinal brine that had interacted with rocks containing a significant amount of K-feldspar. The different correlation trends suggest heterogeneous water-rock interaction and isolated flow paths.

  6. Sandstone geometry, porosity and permeability distribution, and fluid migration in eolian system reservoirs

    USGS Publications Warehouse

    Lupe, Robert; Ahlbrandt, Thomas S.

    1975-01-01

    Upper Paleozoic to Mesozoic eolian blanket sandstones of the Colorado Plateau and the Rocky Mountains of Colorado and southern Wyoming are texturally complex. As petroleum reservoirs they commonly have poor performance histories. They contain the sediments of a depositional system comprised of three closely associated depositional subenvironments: dune, interdune, and extradune. Sediments of each subenvironment have different textural properties which resulted from different depositional processes. Dune sediments are usually more porous and permeable than interdune or extradune sediments and may be better quality reservoirs than interdune or extradune sediments. Interdune sediments are here restricted to those nondune sediments deposited in the relatively flat areas between dunes. Extradune sediments (a new term) include all deposits adjacent to a dune field and are mainly subaqueous deposits. Dune sediments may be enveloped by extradune sediments as the depositional system evolves resulting in a texturally inhomogeneous reservoir having poor fluid migration properties. This model of textural inhomogeneity in eolian blanket sandstones. was applied to the Weber (Tensleep) Sandstone in Brady, Wertz, and Lost Soldier fields, Sweetwater County, Wyoming. Data were obtained from both outcrop and subsurface and included environmental interpretation, textural analysis, and plotting of the distribution of depositional subenvironments. As predicted from the model, the texture of dune sediments in Brady field differed markedly from interdune and extradune sediments. The predicted geometric distribution of subenvironments was confirmed in Lost Soldier and Wertz fields. However, secondary cementation and fracturing there has obscured the original porosity and permeability contrasts. The porosity and permeability distribution, a characteristic depending partly on depositional processes, could impede fluid migration in the reservoir and significantly reduce recovery of

  7. Origin of northern Gondwana Cambrian sandstone revealed by detrital zircon SHRIMP dating

    USGS Publications Warehouse

    Avigad, D.; Kolodner, K.; McWilliams, M.; Persing, H.; Weissbrod, T.

    2003-01-01

    Voluminous Paleozoic sandstone sequences were deposited in northern Africa and Arabia following an extended Neoproterozoic orogenic cycle that culminated in the assembly of Gondwana. We measured sensitive high-resolution ion microprobe (SHRIMP) U-Pb ages of detrital zircons separated from several Cambrian units in the Elat area of southern Israel in order to unravel their provenance. This sandstone forms the base of the widespread siliciclastic section now exposed on the periphery of the Arabian-Nubian shield in northeastern Africa and Arabia. Most of the detrital zircons we analyzed yielded Neoproterozoic concordant ages with a marked concentration at 0.55–0.65 Ga. The most likely provenance of the Neoproterozoic detritus is the Arabian-Nubian shield; 0.55–0.65 Ga was a time of posttectonic igneous activity, rift-related volcanism, and strike-slip faulting there. Of the zircons, 30% yielded pre-Neoproterozoic ages grouped at 0.9–1.1 Ga (Kibaran), 1.65–1.85 Ga, and 2.45–2.7 Ga. The majority of the pre-Neoproterozoic zircons underwent Pb loss, possibly as a consequence of the Pan-African orogeny resetting their provenance. Rocks of the Saharan metacraton and the southern Afif terrane in Saudi Arabia (∼1000 km south of Elat) are plausible sources of these zircons. Kibaran basement rocks are currently exposed more than 3000 km south of Elat (flanking the Mozambique belt), but the shape of the detrital zircons of that age and the presence of feldspar in the host sandstone are not fully consistent with such a long-distance transport. Reworking of Neoproteorozoic glacial detritus may explain the presence of Kibaran detrital zircons in the Cambrian of Elat, but the possibility that the Arabian-Nubian shield contains Kibaran rocks (hitherto not recognized) should also be explored.

  8. Late Jurassic paleogeographic evolution of the Andean back-arc basin: New constrains from the Lagunillas Formation, northern Chile (27°30ʹ-28°30ʹS)

    NASA Astrophysics Data System (ADS)

    Oliveros, Verónica; Labbé, Mariana; Rossel, Pablo; Charrier, Reynaldo; Encinas, Alfonso

    2012-08-01

    The Late Jurassic Lagunillas Formation exposed between 27°30ʹ and 28°30ʹS in the northern Chilean Andes comprises two members: a lower sedimentary member, and an upper volcanic member. This unit was deposited during a significant palaeogeographic change related to a major relative sea-level fall that took place in the Andean back-arc basin between 18° and 44°S. The sedimentary member of the Lagunillas Formation consists of a prograding succession in which distal sheetflood alluvial deposits interbedded with aeolian sandstones predominate in the lower part whereas channelized conglomerates, characteristic of more proximal alluvial fan deposition, become progressively more abundant to the top. U-Pb geochronology on detrital zircons indicate maximum depositional ages for the Lagunillas Formation at the Kimmerigdian/Tithonian boundary (150.8 ± 4.0 Ma). These results constitute the first age data for this or correlative units in Chile and indicate correlation of the Lagunillas Formation with the continental Tordillo Formation in the Neuquén basin. Provenance studies by clast count analyses and U-Pb ages in detrital zircons suggest a temporal variation in the sources of the clastic material. At the beginning of the deposition, fine-grained detritus would have been supplied mainly from the Mesozoic magmatic arc located to the west of the basin, but also from Late Paleozoic units probably located to the east. As deposition proceeded, most of the material was being supplied by Paleozoic to Neoproterozoic ("Grenvillian") units. Mesoproterozoic cratonic units, likely located further east, were exposed and eroded at the end of the deposition, prior to the onset of volcanism in the back-arc.

  9. Middle Micoene sandstone reservoirs of the Penal/Barrackpore field

    SciTech Connect

    Dyer, B.L. )

    1991-03-01

    The Penal/Barrackpore field was discovered in 1938 and is located in the southern subbasin of onshore Trinidad. The accumulation is one of a series of northeast-southwest trending en echelon middle Miocene anticlinal structures that was later accentuated by late Pliocene transpressional folding. Relative movement of the South American and Caribbean plates climaxed in the middle Miocene compressive tectonic event and produced an imbricate pattern of southward-facing basement-involved thrusts. Further compressive interaction between the plates in the late Pliocene produced a transpressive tectonic episode forming northwest-southeast oriented transcurrent faults, tear faults, basement thrust faults, lystric normal faults, and detached simple folds with infrequent diapiric cores. The middle Miocene Herrera and Karamat turbiditic sandstones are the primary reservoir rock in the subsurface anticline of the Penal/Barrackpore field. These turbidites were sourced from the north and deposited within the marls and clays of the Cipero Formation. Miocene and Pliocene deltaics and turbidites succeed the Cipero Formation vertically, lapping into preexisting Miocene highs. The late Pliocene transpression also coincides with the onset of oil migration along faults, diapirs, and unconformities from the Cretaceous Naparima Hill source. The Lengua Formation and the upper Forest clays are considered effective seals. Hydrocarbon trapping is structurally and stratigraphically controlled, with structure being the dominant trapping mechanism. Ultimate recoverable reserves for the field are estimated at 127.9 MMBo and 628.8 bcf. The field is presently owned and operated by the Trinidad and Tobago Oil Company Limited (TRINTOC).

  10. A NMR characterisation of a banded sandstone.

    PubMed

    Bolam, A C; Packer, K J

    1998-01-01

    1H-nuclear magnetic resonance (NMR) measurements have been carried out on a banded sandstone to investigate the effects of structural inhomogeneities on the fluid dynamics of the sample as a whole. The results obtained from average propagator measurements (the probability of a displacement z in a time delta or P delta (z)) using pulsed-field-gradient techniques have been compared to those obtained from a study of a homogeneous sandstone. Relaxation has been used to derive the pore sizes for the differing bands and have been found to correlate with flow velocities within the bands.

  11. Diagenesis and reservoir quality of Paleocoene sandstones in the Kupe South field, Taranaki Basin, New Zealand

    SciTech Connect

    Martin, K.R. ); Baker, J.C. ); Hamilton, P.J. ); Thrasher, G.P. )

    1994-04-01

    The Kupe South field, Taranaki basin, New Zealand is a gas condensate and oil field offshore in the southern Taranaki basin. Its Paleocene reservoir sandstones contain a diagenetic mineral assemblage that records major shifts in pore-water composition during the burial history of the basin. Early calcite formed a shallow burial largely from meteoric depositional pore waters, whereas later chlorite/smectic records the downward passage of marine pore waters into the sandstones from overlying, marine mudrocks prior to significant sandstone compaction during the late Miocene. Late calcite and ferroan carbonates may record the presence of connate meteoric water expelled upward from nonmarine sedimentary rocks of the underyling Cretaceous sequence, whereas later kaolinite and secondary porosity formation are related to localized meteoric influx resulting from late Miocene to early Pliocene uplift and erosion of the reservoir section. Hydrocarbon entrapment occurred during further Pliocene to Holocene sediment accumulation. Labile-grain alteration has been less severe in the lower part of the hydrocarbon-bearing section than in the upper sands with the result that the lower sands contain mainly chlorite/smectite and the upper sands contain mainly ferroan carbonates and kaolinite formed by extensive alteration of labile grains and earlier formed chlorite/smectite. Reservoir quality in the lower sands is controlled mostly by grain size and the presence of chlorite/smectite, but in the upper sands, the presence of kaolinite is the single most important cause of poor reservoir quality. 36 refs., 13 figs., 3 tabs.

  12. Isotopic tracers of gold deposition in Paleozoic limestones, Southern Nevada

    SciTech Connect

    Peterman, Z.E.; Widmann, B.L.; Marshall, B.D.; Aleinikoff, J.N.; Futa, K.; Mahan, S.A.

    1994-12-31

    Strontium isotopic analyses of barren and mineralized Paleozoic carbonate rocks show that hydrothermal fluids added radiogenic strontium ({sup 87}Sr) to the mineralized zones. At Bare Mountain, samples collected from mineralized areas have {delta}{sup 87}Sr{sub t} values ranging from +3.0 to +23.0, whereas unmineralized carbonate rocks have {delta}{sup 87}Sr, values of {minus}0.6 to +2.9. In other ranges, {delta}{sup 87}Sr, values of the unmineralized carbonate rocks are even lower and virtually indistinguishable from primary marine values. This correlation of elevated {delta}{sup 87}Sr{sub t} values with mineralized zones provides a useful technique for assessing the mineral potential of the Paleozoic basement beneath Yucca Mountain, and may find broader use in mineral exploration in the Basin and Range province as a whole.

  13. Isotopic tracers of gold deposition in Paleozoic limestones, southern Nevada

    USGS Publications Warehouse

    Peterman, Z.E.; Widmann, B.L.; Marshall, B.D.; Aleinikoff, J.N.; Futa, K.; Mahan, S.A.

    1994-01-01

    Strontium isotopic analyses of barren and mineralized Paleozoic carbonate rocks show that hydrothermal fluids added radiogenic strontium (87Sr) to the mineralized zones. At Bare Mountain, samples collected from mineralized areas have ??87Srt values (per mil deviation from primary marine values) ranging from +3.0 to +23.0 (mean of this log-normal distribution is +7.0), whereas unmineralized carbonate rocks have ??87Srt values of -0.6 to +2.9 (mean of +1.07??1.03). In other ranges (Striped Hills, Spring Mountains, and ranges in the vicinity of Indian Springs Valley), ??87Srt values of the unmineralized carbonate rocks are even lower and virtually indistinguishable from primary marine values. This correlation of elevated ??87Srt values with mineralized zones provided a useful technique for assessing the mineral potential of the Paleozoic basement beneath Yucca Mountain, and may find broader use in mineral exploration in the Basin and Range province as a whole.

  14. Ontogenetic evidence for the Paleozoic ancestry of salamanders.

    PubMed

    Schoch, Rainer R; Carroll, Robert L

    2003-01-01

    The phylogenetic positions of frogs, salamanders, and caecilians have been difficult to establish. Data matrices based primarily on Paleozoic taxa support a monophyletic origin of all Lissamphibia but have resulted in widely divergent hypotheses of the nature of their common ancestor. Analysis that concentrates on the character states of the stem taxa of the extant orders, in contrast, suggests a polyphyletic origin from divergent Paleozoic clades. Comparison of patterns of larval development in Paleozoic and modern amphibians provides a means to test previous phylogenies based primarily on adult characteristics. This proves to be highly informative in the case of the origin of salamanders. Putative ancestors of salamanders are recognized from the Permo-Carboniferous boundary of Germany on the basis of ontogenetic changes observed in fossil remains of larval growth series. The entire developmental sequence from hatching to metamorphosis is revealed in an assemblage of over 600 specimens from a single locality, all belonging to the genus Apateon. Apateon forms the most speciose genus of the neotenic temnospondyl family Branchiosauridae. The sequence of ossification of individual bones and the changing configuration of the skull closely parallel those observed in the development of primitive living salamanders. These fossils provide a model of how derived features of the salamander skull may have evolved in the context of feeding specializations that appeared in early larval stages of members of the Branchiosauridae. Larvae of Apateon share many unique derived characters with salamanders of the families Hynobiidae, Salamandridae, and Ambystomatidae, which have not been recognized in any other group of Paleozoic amphibians. PMID:12752770

  15. Impact Metamorphism of Sandstones at Amguid Crater, Algeria

    NASA Astrophysics Data System (ADS)

    Sahoui, R.; Belhai, D.

    2016-08-01

    Amguid is a 450 m diameter sample crater; it is emplaced in Lower Devonian sandstones.We have carried out a petrographic study in order to investigate shock effects recorded in these sandstones and define shock stages in Amguid.

  16. Trace fossils and sedimentary facies from a Late Cambrian-Early Ordovician tide-dominated shelf (Santa Rosita Formation, northwest Argentina): Implications for ichnofacies models of shallow marine successions

    USGS Publications Warehouse

    Mangano, M.G.; Buatois, L.A.; Acenolaza, G.F.

    1996-01-01

    The Santa Rosita Formation is one the most widely distributed lower Paleozoic units of northwest Argentina. At the Quebrada del Salto Alto section, east of Purmamarca, Jujuy Province, it is represented by four sedimentary facies: thick-bedded planar cross-stratified quartzose sandstones (A), thin-bedded planar cross-stratified quartzose sandstones and mudstones (B), wave-rippled sandstones and bioturbated mudstones (C), and black and greenish gray shales (D). Paleocurrent data, sandstone architecture, and sedimentary structures from facies A and B indicate bipolar/bimodal paleoflows, suggesting the action of tidal currents. The succession is interpreted as that of a tide-dominated shelf, with only secondary influence of wave processes. Trace fossils are restricted to facies B and C. The Cruziana ichnocoenosis is preserved on the soles of thin-bedded planar cross-stratified quartzose sandstones (facies B). This ichnocoenosis consists of Conostichus isp., Cruziana omanica, C. semiplicata, C. cf. tortworthi, Cruziana isp. Helminthopsis abeli, Monomorphichnus bilinearis, M. multilineatus, Palaeophycus tubularis, Rusophycus carbonarius, R. latus, and R. isp. The occurrence of Cruziana semiplicata, C. omanica, C. cf. tortworthi, and Rusophycus latus supports a Late Cambrian-Tremadoc age. Slabbing of Cruziana shows complex interactions between biologic and sedimentologic processes, and suggests a predominance of exhumed traces, washed out and recast by tractive sand deposition. Sandstone soles are densely packed with biogenic structures and exhibit distinctive clusters of Rusophycus isp. that most likely represent trilobite nesting burrows. The Cruziana ichnocoenosis records the resident fauna of a protected, lower intertidal to subtidal interbar setting. The Skolithos ichnocoenosis is represented by high to low density vertical burrows of Skolithos linearis, which extend downwards to the quartzose sandstone soles of facies B and cross the Cruziana ichnocoenosis. The

  17. Upper Paleozoic stratigraphic sequences in the Western Interior, USA

    SciTech Connect

    Maughan, E.K.; Macke, D.L.

    1993-04-01

    Major depositional sequences in the upper Paleozoic (Mississippian through Permian) of the Western Interior reflect either tectonism, eustatic sea-level change, or both. The stratigraphic sequences approximate (1) the Lower Mississippian Lodgepole Limestone of the Madison Group, (2) the Lower and Upper Mississippian Mission Canyon Limestone in the Madison Group, (3) the Upper Mississippian Big Snowy Group, (4) the Lower and Middle Pennsylvanian Amsden Group, (5) the Middle Pennsylvanian and Lower Permian Minnelusa Group, and (6) the Middle and Upper Permian Park City Group. These upper Paleozoic sequences in the Western Interior seem to be intricately related to similar, third-order transgressive-regressive cycles in the Cordilleran region, but precise relationships of some sequence boundaries remain to be determined. Parasequence sets evidence minor eustatic oscillations within these six major Western Interior sequences. The widespread paraconformable contact between Permian and overlying Triassic strata on the Wyoming shelf indicates that this sequence boundary resulted primarily from eustatic marine regression. Overall, the upper Paleozoic sequences of the Western Interior were deposited in a stable epeirogenic framework that succeeded Devonian tectonism but were diastrophically affected again during the Pennsylvanian. The timing of these diastrophic events in the Western Interior seem to coincide with plate collision events along the eastern and southern margins of North America, but eustatic changes may be related to other causes.

  18. New insights into Paleozoic charophyte morphology and phylogeny.

    PubMed

    Feist, Monique; Liu, Junying; Tafforeau, Paul

    2005-07-01

    Examination of Paleozoic charophyte fructifications using microscopy and high-resolution x-ray synchrotron microtomography has revealed that most of them have a utricle that forms a supplementary calcified cover around the gyrogonite. All Paleozoic families with utricles have been assigned to the Sycidiales. We consider the Moellerinaceae to occupy a central position in the phylogeny of the Charophyta. From these, one group of descendants constitutes the gyrogonites inside the utricles of the Sycidiales; a second descendant goup is thought to be the utricle-free ancestors of the Charales prior to inversion of spiralization and reduction in cell number. The Sycidiales have a multilayered wall and an internal vesicle, but their families are distinguished by diversity in orientation of external cells, complexity of the utricle wall, and in presence or absence of antheridia. The solidly packed structure of the utricle is believed to be an organ protecting the zygote against dessication. We interpret the morphological similarities between Paleozoic Sycidiales and Mesozoic Clavatoraceae, both with a utricle, as homoplasous rather than expressing a true phylogenetic relationship. We confirm that some umbellids might correspond to utricles of charophytes.

  19. Origin of natural gases in the Paleozoic-Mesozoic basement of the Polish Carpathian Foredeep

    NASA Astrophysics Data System (ADS)

    Kotarba, Maciej

    2012-08-01

    Hydrocarbon gases from Upper Devonian and Lower Carboniferous reservoirs in the Paleozoic basement of the Polish Carpathian Foredeep were generated mainly during low-temperature thermogenic processes ("oil window"). They contain only insignificant amounts of microbial methane and ethane. These gaseous hydrocarbons were generated from Lower Carboniferous and/or Middle Jurassic mixed Type III/II kerogen and from Ordovician-Silurian Type II kerogen, respectively. Methane, ethane and carbon dioxide of natural gas from the Middle Devonian reservoir contain a significant microbial component whereas their small thermogenic component is most probably genetically related to Ordovician-Silurian Type II kerogen. The gaseous hydrocarbons from the Upper Jurassic and the Upper Cretaceous reservoirs of the Mesozoic basement were generated both by microbial carbon dioxide reduction and thermogenic processes. The presence of microbial methane generated by carbon dioxide reduction suggests that in some deposits the traps had already been formed and sealed during the migration of microbial methane, presumably in the immature source rock environment. The traps were successively supplied with thermogenic methane and higher hydrocarbons generated at successively higher maturation stages of kerogen. The higher hydrocarbons of the majority of deposits were generated from mixed Type III/II kerogen deposited in the Middle Jurassic, Lower Carboniferous and/or Devonian strata. Type II or mixed Type II/III kerogen could be the source for hydrocarbons in both the Tarnów and Brzezówka deposits. In the Cenomanian sandstone reservoir of the Brzezowiec deposit and one Upper Jurassic carbonate block of the Lubaczów deposit microbial methane prevails. It migrated from the autochthonous Miocene strata.

  20. Setting and Paleozoic age of the HP-complexes in the South Carpathians

    NASA Astrophysics Data System (ADS)

    Sàbàu, G.; Massonne, H.

    2007-12-01

    -accretion complex (479.1±6.5 Ma). In all three HP complexes magmatic ages reflect juvenile igneous suites (arc, back-arc basins) Late Precambrian to Early Paleozoic in age, as well as reworked crustal inheritance (by anatexis/crustal contamination) covering a wide spectrum of ages. Dominant West-African inherited age spectra and subordinate Avalonian ones attest complex (micro)plate-margin interactions of Gondwana-derived terrains during the Early Paleozoic.

  1. Paleozoic oil/gas shale reservoirs in southern Tunisia: An overview

    NASA Astrophysics Data System (ADS)

    Soua, Mohamed

    2014-12-01

    During these last years, considerable attention has been given to unconventional oil and gas shale in northern Africa where the most productive Paleozoic basins are located (e.g. Berkine, Illizi, Kufra, Murzuk, Tindouf, Ahnet, Oued Mya, Mouydir, etc.). In most petroleum systems, which characterize these basins, the Silurian played the main role in hydrocarbon generation with two main 'hot' shale levels distributed in different locations (basins) and their deposition was restricted to the Rhuddanian (Lllandovery: early Silurian) and the Ludlow-Pridoli (late Silurian). A third major hot shale level had been identified in the Frasnian (Upper Devonian). Southern Tunisia is characterized by three main Paleozoic sedimentary basins, which are from North to South, the southern Chotts, Jeffara and Berkine Basin. They are separated by a major roughly E-W trending lower Paleozoic structural high, which encompass the Mehrez-Oued Hamous uplift to the West (Algeria) and the Nefusa uplift to the East (Libya), passing by the Touggourt-Talemzane-PGA-Bou Namcha (TTPB) structure close to southern Tunisia. The forementioned major source rocks in southern Tunisia are defined by hot shales with elevated Gamma ray values often exceeding 1400 API (in Hayatt-1 well), deposited in deep water environments during short lived (c. 2 Ma) periods of anoxia. In the course of this review, thickness, distribution and maturity maps have been established for each hot shale level using data for more than 70 wells located in both Tunisia and Algeria. Mineralogical modeling was achieved using Spectral Gamma Ray data (U, Th, K), SopectroLith logs (to acquire data for Fe, Si and Ti) and Elemental Capture Spectroscopy (ECS). The latter technique provided data for quartz, pyrite, carbonate, clay and Sulfur. In addition to this, the Gamma Ray (GR), Neutron Porosity (ΦN), deep Resistivity (Rt) and Bulk Density (ρb) logs were used to model bulk mineralogy and lithology. Biostratigraphic and complete

  2. Illitization and paleothermal regimes in the Middle Ordovician St. Peter Sandstone, Central Michigan Basin: K-Ar, Oxygen Isotope, and fluid inclusion data

    SciTech Connect

    Girard, J.P.; Barnes, D.A.

    1995-01-01

    Hydrocarbon reservoirs occur in the Middle Ordovician St. Peter Sandstone in the central Michigan basin at depths of 1.5-3.5 km and are diagenetically altered. Latest diagenetic cements include saddle dolomite, pervasive microcrystalline illite and chlorite, and quartz. A K-Ar and {sup 18}O/{sup 16}O study of the fine-grained authigenic illite in 25 samples from 16 wells covering a large area within the basin yields K-Ar ages ranging from 367 to 322 Ma and {delta}{sup 18}O values between 12.7 and 16.9% SMOW. The {delta}{sup 18}O values of diagenetic quartz overgrowths range from 15.2 to 18.9%. Fluid inclusion temperatures in the quartz cement range from 70 to 170{degrees}C, reflecting multiple generations of diagenetic quartz and/or precipitation over most of the diagenetic history. Reequilibrated fluid inclusions in the saddle dolomite cement yield temperatures ranging from 90 to 150{degrees}C. A regionally significant episode of illitization occurred during the Late Devonian-Mississipian. Temperatures of illite formation are indirectly estimated to be in the range of 125-170{degrees}C and most paleodepths of illitization are between 2.8 and 3.2 km. These results imply that (1) illite formed from {sup 18}O-rich fluids, and (2) elevated geothermal gradients, i.e., greater than 34% C/km, existed in the Michigan basin in the late Paleozoic. The K-Ar ages and the {delta}{sup 18}O values are not correlated to present depths of the samples or paleodepths of illitization. Illites with young ages and low {delta}{sup 18}O values tend to be geographically distributed along the north-south branch of the buried Precambrian rift. The {delta}{sup 18}O values of the diagenetic quartz follow a similar trend. The spread of illite K-Ar ages and {delta}{sup 19}O values, and their geographic distribution, are best explained as reflecting abnormally high thermal regimes in the part of the basin located above the presumably highly fractured basement along the rift.

  3. Fractures and stresses in Bone Spring sandstones

    SciTech Connect

    Lorenz, J.C.; Warpinski, N.R.; Sattler, A.R.; Northrop, D.A.

    1990-09-01

    This project is a collaboration between Sandia National Laboratories and Harvey E. Yates Company being conducted under the auspices of the Oil Recovery Technology Partnership. The project seeks to apply perspectives related to the effects of natural fractures, stress, and sedimentology to the simulation and production of low-permeability gas reservoirs to low-permeability oil reservoirs as typified by the Bone Spring sandstones of the Permian Basin, southeast New Mexico. This report presents the results and analysis obtained in 1989 from 233 ft of oriented core, comprehensive suite of logs, various in situ stress measurements, and detailed well tests conducted in conjunction with the drilling of two development wells. Natural fractures were observed in core and logs in the interbed carbonates, but there was no direct evidence of fractures in the sandstones. However, production tests of the sandstones indicated permeabilities and behavior typical of a dual porosity reservoir. A general northeast trend for the maximum principal horizontal stress was observed in an elastic strain recovery measurements and in strikes of drilling-induced fractures; this direction is subparallel to the principal fracture trend observed in the interbed carbonates. Many of the results presented are believed to be new information for the Bone Spring sandstones. 57 figs., 18 tabs.

  4. Geochemistry of brachiopods: Oxygen and carbon isotopic records of Paleozoic oceans

    NASA Astrophysics Data System (ADS)

    Veizer, Ján; Fritz, Peter; Jones, Brian

    1986-08-01

    Combined trace element and isotope studies of 319 brachiopods, covering the Ordovician to Permian time span, show that δ 13C and δ 18O in well preserved specimens varied during the Paleozoic. The overall δ 13C secular trend is in accord with the previously published observations, but its details are obscured by vital isotopic fractionation effects at generic level. Nonetheless, the results suggest that the negative correlation between marine δ 13C carbonate and δ 34S sulphate deteriorates at time scales of ⩽ 10 6 years, due to the long residence time, and thus slow response, of SO 42- in the ocean. For oxygen isotopes, all Devonian and older specimens have δ 18O of ⩽ -4%, while the well preserved Permian samples have near-present day δ 18O of about -1% (PDB). This isotopic dichotomy is probably not due to post-depositional phenomena, salinity, or biogenic fractionation effects. This leaves open the perennial arguments for a change in 18O /16O of sea water versus warmer ancient oceans. The present data are difficult to explain solely by the temperature alternative. The coincidence of the proposed shift in δ 18O with the large Late Paleozoic changes in marine 87Sr /86Sr , 13C /12C , 34S /32S , and "sea level stands" argues for a tectonic cause and for a change in 18O /16O of sea water, although such explanation is difficult to reconcile with global balance considerations and with isotopic patterns observed in alteration products of ancient basalts and ophiolites. Whatever the precise cause, or combination of causes, the implications for tectonism and/or paleoclimatology are of first order significance.

  5. Emplacement of sandstone intrusions during contractional tectonics

    NASA Astrophysics Data System (ADS)

    Palladino, Giuseppe; Grippa, Antonio; Bureau, Denis; Alsop, G. Ian; Hurst, Andrew

    2016-08-01

    Sandstone injections are created by the forceful emplacement of remobilized sand in response to increases in overpressure. However, the contribution provided by horizontal compressive stress to the build-up in overpressure, and the resulting emplacement of sand injection complexes, is still to be substantiated by robust field observations. An opportunity to address this issue occurs in Central California where a large volume of sandstone intrusions record regionally-persistent supra-lithostatic pore-pressure. Detailed fieldwork allows sandstone-filled thrusts to be recognized and, for the first time, permits us to demonstrate that some sandstone intrusions are linked to contractional deformation affecting the western border of the Great Valley Basin. Fluidized sand was extensively injected along thrust surfaces, and also fills local dilatant cavities linked to thrusting. The main aims of this paper are to provide detailed descriptions of the newly recognized syn-tectonic injections, and describe detailed cross-cutting relationships with earlier sandstone injection complexes in the study area. Finally, an evolutionary model consisting of three phases of sand injection is provided. In this model, sand injection is linked to contractional tectonic episodes affecting the western side of the Great Valley Basin during the Early-Middle Cenozoic. This study demonstrates that sand injections, driven by fluid overpressure, may inject along thrusts and folds and thereby overcome stresses associated with regional contractional deformation. It is shown that different generations of sand injection can develop in the same area under the control of different stress regimes, linked to the evolving mountain chain.

  6. Re-evaluating origins of Paleozoic orbital-scale and My-scale stratigraphic cyclicity using oxygen isotopes of marine apatite

    NASA Astrophysics Data System (ADS)

    Elrick, M.; Theiling, B. P.; Wallace, Z. A.; Reardon, D.; Labor, W.; Martin, J.

    2012-12-01

    High-frequency (104-105 yr) sedimentary cycles and My-scale depositional sequences in Paleozoic marine strata have been studied for over a century and though debated, their origins are most commonly attributed to sea-level changes. Early studies focused mainly on repetitive shallowing and deepening facies changes, subaerial exposure features, and widespread correlations to argue for eustatic drivers. Subsequent studies utilized 1D and 2D computer models and statistical and time series analysis to argue for eustasy and for Milankovitch-scale periodicities. With increasing high-resolution numeric age control provided by newly discovered ash beds, the durations of many Paleozoic cycles and sequences are found to lie within the Milankovitch-frequency band. Recently the origins of Paleozoic cycles and sequences have been evaluated using oxygen isotopes from marine apatite (conodonts) to specifically test for glacio-eustatic origins. Isotopic trends from well studied Ordovician, Silurian, Devonian, Mississippian, and Pennsylvanian marine successions support the hypothesis that the cycles and sequences were generated by glacio-eustasy with decreasing and low isotopic values occurring within deepening and deepest water facies and increasing and high values occurring in shallowing and shallowest water facies. Of particular interest is that the magnitudes of isotopic change and by inference, the magnitude of climatic change, observed across cycles and sequences developed in Paleozoic greenhouse time intervals (Silurian, Devonian) are as large as those observed in icehouse (Neogene, Pennsylvanian) and transitional (Late Ordovician, Early Mississippian) climatic intervals. These oxygen isotope results combined with earlier stratigraphic, modeling, and statistical studies suggest that short- and long-period Milankovitch-forced glacio-eustasy controlled cycle and sequence development throughout the Paleozoic.

  7. Provenance and diagenesis of Oligocene sandstones, southern San Joaquin basin, California

    SciTech Connect

    Hayes, M.J.

    1988-03-01

    Oligocene Vedder sandstones and correlatives from the southern San Joaquin basin provide an opportunity to compare diagenesis resulting from variable provenance, depositional environment, and burial or tectonic history. Sandstones were examined from 15 cores in this basin-wide petrographic survey. Oligocene sandstones typically are fine to medium grained, moderately sorted, subangular, and quartzofeldspathic, although sandstones from the western and east-central basin are enriched in potassium feldspar and intermediate volcanic rock fragments, respectively. Detrital compositions are transitional between uplifted continental block and undissected to dissected magmatic arc on provenance diagrams. Sediment provenance included the granodioritic Sierra Nevada-Tehachapi Mountain magmatic arc complex and perhaps granitic terranes to the west. Volcanic detritus was shed from southern and eastern sources. Diagenesis varies within the basin, partly reflecting local pore-fluid evolution and detrital composition. The effects of variable geothermal gradients, sedimentation rate, and tectonism on diagenesis await evaluation. In the composite basin-wide paragenetic sequence, calcite, dolomite, siderite, and chlorite-smectite are earliest authigenic phases. Variable cement and compaction relationships indicate nonuniform depth and timing of cementation. Early cements inhibited subsequent diagenesis and compaction. With deeper burial, plagioclase, potassium feldspar, and carbonates dissolved, pore-filling kaolinite precipitated, plagioclase was albitized and zeolitized, and late-stage carbonates crystallized. Further geochemical analyses will better define composition and origin of authigenic phases and document reaction progress. Cement zones and sources may be identified and spatially and temporally linked in an attempt to constrain scales and rates of mass transfer of calcium basin wide.

  8. Paleozoic accretionary and collisional tectonics of the eastern Chinese Tianshan: implications for crustal growth of central Asia

    NASA Astrophysics Data System (ADS)

    Xiao, W. J.; Qin, K. Z.; Sun, S.; Li, J. L.

    2003-04-01

    The Paleozoic tectonics of Chinese Tianshan was complicated in the east by jointing of the NWW-trending Junggar and the E-W-trending East Tianshan belts. From South to North, this orogenic collage is subdivided into several tectonics terranes, which have recorded the Middle to Late Paleozoic geological history in framework of a complicated collision between two archipelago system lying along the northern Tarim and the southern Siberian margins, respectively. The southern archipelago system, constructed followed collapse of the northern passive margin of the Tarim, was mainly active in the Silurian to Early Carboniferous time, and was characterized by suturing of a Neoproterozoic to Late Devonian passive margin, the Tarim, in the south and a Silurian-Mid-Devonian arc terrane, the Kawabulak-Central Tianshan arc, in the north with squeezed intervening Late Devonian to Early Carboniferous backarc basins. The northern archipelago system was a Devonian-Carboniferous composite arc, which comprises the Carboniferous the Yamansu arc, the Early- to Mid-Carboniferous Kanguer accretionary forearc basin, the Devonian-Carboniferous Dananhu arc, the Xiaopu intra-arc basin, the Harlik arc, and the Kelameili composite arc system. These two archipelagos collided softly leaving a cryptic suture zone represented by the Late Carboniferous to Permian Mishigou-Weiya accretionary complex including ophiolitic fragments. Predominant northward subduction during final formation of the suture gave rise to a large-scale, post-collisional, south-directed thrust-and-fold belt in the Early Triassic. By deciphering the various tectonic terranes, this paper presents a new model for the evolution of this portion of Central Asia.

  9. True triaxial testing of Castlegate sandstone.

    SciTech Connect

    Ingraham, M. D.; Holcomb, David Joseph; Issen, Kathleen A.

    2010-03-01

    Deformation bands in high porosity sandstone are an important geological feature for geologists and petroleum engineers; however, their formation is not fully understood. Axisymmetric compression, the common test for this material, is not sufficient to fully evaluate localization criteria. This study seeks to investigate the influence of the second principal stress on the failure and the formation of deformation bands in Castlegate sandstone. Experimental results from tests run in the axisymmetric compression stress state, as well as a stress state between axisymmetric compression and pure shear will be presented. Samples are tested using a custom triaxial testing rig at Sandia National Laboratories capable of applying stresses up to 400 MPa. Acoustic emissions are used to locate deformation bands should they not be visible on the specimen exterior. It is suspected that the second invariant of stress has a strong contribution to the failure mode and band formation. These results could have significant bearing on petroleum extraction as well as carbon dioxide sequestration.

  10. Fractures and stresses in Bone Spring sandstones

    SciTech Connect

    Warpinski, N.R.; Sattler, A.R.; Lorenz, J.C.; Northrop, D.A.

    1992-06-01

    This project was a collaboration between Sandia National Laboratories and the Harvey E. Yates Company (Heyco), Roswell, NM, conducted under the auspices of Department of Energy's Oil Recovery Technology Partnership. The project applied Sandia perspectives on the effects of natural fractures, stress, and sedimentology for the stimulation and production of low permeability gas reservoirs to low permeability oil reservoirs, such as those typified by the Bone Spring sandstones of the Delaware Basin, southeast New Mexico. This report details the results and analyses obtained in 1990 from core, logs, stress, and other data taken from three additional development wells. An overall summary gives results from all five wells studied in this project in 1989--1990. Most of the results presented are believed to be new information for the Bone Spring sandstones.

  11. Preserving Native American petroglyphs on porous sandstone

    USGS Publications Warehouse

    Grisafe, D.A.

    1996-01-01

    A new method of chemical treatment is proposed to improve the durability of soft, porous sandstones onto which Native American petroglyphs have been carved. Cores of Dakota Sandstone from the Faris Cave site, located along the Smoky Hill River in Ellsworth County, Kansas, were treated with ethyl silicate dissolved in a lightweight ketone carrier, and some cores were subsequently treated with a combination of ethyl silicate and silane using the same solvent. Measurement of the resulting physical properties, when compared to untreated cores, indicate the treatments substantially increased the compressive strength and freeze-thaw resistance of the stone without discoloring the stone or completely sealing the pore system. The treatment increases the durability of the stone and provides a method for preserving the petroglyphs at the site. After treating test panels at the site, the petroglyphs were treated in like manner.

  12. Radionuclide transport in sandstones with WIPP brine

    SciTech Connect

    Weed, H.C.; Bazan, F.; Fontanilla, J.; Garrison, J.; Rego, J.; Winslow, A.M.

    1981-02-01

    Retardation factors (R) have been measured for the transport of /sup 3/H, /sup 95m/Tc, and /sup 85/Sr in WIPP brine using St. Peter, Berea, Kayenta, and San Felipe sandstone cores. If tritium is assumed to have R=1, /sup 95m/Tc has R=1.0 to 1.3 and therefore is essentially not retarded. Strontium-85 has R = 1.0 to 1.3 on St. Peter, Berea, and Kayenta, but R=3 on San Felipe. This is attributed to sorption on the matrix material of San Felipe, which has 45 volume % matrix compared with 1 to 10 volume % for the others. Retardation factors (R/sub s/) for /sup 85/Sr calculated from static sorption measurements are unity for all the sandstones. Therefore, the static and transport results for /sup 85/Sr disagree in the case of San Felipe, but agree for St. Peter, Berea, and Kayenta.

  13. Paleomagnetism of Paleozoic sedimentary rocks from the Karatau Range, Southern Kazakhstan: Multiple remagnetization events correlate with phases of deformation

    NASA Astrophysics Data System (ADS)

    Kirscher, U.; Zwing, A.; Alexeiev, D. V.; Echtler, H. P.; Bachtadse, V.

    2013-08-01

    The paleogeography of the Altaids and its kinematic and tectonic evolution during the final collision and amalgamation of Eurasia is still poorly known. Addressing this problem, a paleomagnetic study has been undertaken on Paleozoic sedimentary rocks from the Karatau, Southern Kazakhstan. Stepwise thermal demagnetization reveals the presence of a high-temperature component of magnetization in most samples. Fold tests indicate a syn-folding age of magnetic remanence acquisition at three of the five areas studied. Directional data of Devonian and Permian rocks yield a positive fold test, implying a primary magnetization. Resulting prefolding paleolatitudes for Permian and Devonian rocks show the proximity of the Karatau to Baltica during those times. Syn- and post-folding magnetizations result in paleolatitudes for Karatau, which intersect the paleolatitude curve based on the Baltica apparent polar wander path (APWP), at times, which can be correlated to major deformational events at ~280 Ma, ~260 Ma, and ~230 Ma, respectively. We interpret this with complicated pattern of remagnetization events accompanying deformation, which can include syn-folding remagnetization events and areas of primary magnetic signals. Additionally, the differences between reference declinations based on the APWP for Baltica and observed declinations suggest successive counterclockwise rotational reorganization of the Karatau during the late Paleozoic to Early Mesozoic, with maximal rotation values of ~65° with respect to Baltica. The remagnetization events are correlated with latest intracontinental stages of orogenic evolution in the Ural mountains and thus the Paleozoic amalgamation of the Eurasian continent and suggest synchronous and coherent tectonic evolution in the Urals and Karatau mountains.

  14. Disentangling Middle Paleozoic sea level and tectonic events in cratonic margins and cratonic basins of North America

    NASA Astrophysics Data System (ADS)

    Bond, Gerard C.; Kominz, Michelle A.

    1991-04-01

    The cratonic margins and basins of North America contain evidence of distinct changes in relative sea level, one of the most intriguing of which occurred in middle Paleozoic time. The change in relative sea level began in Frasnian time (Late Devonian) and continued through Visean time (Middle Mississippian) in the Cordilleran miogeocline, in the Southern Oklahoma Aulacogen, in the Appalachian miogeocline and in the Michigan, Illinois, and Williston basins. The synchroneity and wide geographic distribution of this event are striking and would seem to argue for an eustatic mechanism. An estimate of the middle Paleozoic sea level rise relative to the stable craton in Iowa suggests that while a large sea level rise occurred, it is smaller than the magnitude of subsidence in the cratonic basins and margins. Flexural foreland basin models do not appear to account for the all of the events in the cratonic margins, and thermal subsidence mechanisms do not seem appropriate for the subsidence in the cratonic basins. The middle Paleozoic stratigraphic record from the North American craton and its margins, therefore, poses a basic problem of identifying a mechanism for producing a large-amplitude rise in sea level relative to the stable craton at the same time as a synchronous onset of tectonic subsidence in widespread basinal and marginal settings of diverse tectonic origin. One plausible mechanism for the tectonic subsidence in the basins and margins is a pulse of intraplate compressive stress. The origin of the large sea level rise relative to the stable craton could reflect an unusually large eustatic sea level change, but we cannot eliminate the possibility of a small component of subsidence or change in dynamic topography of the North American craton. The synchroneity of the sea level rise relative to the craton with the subsidence of basins and margins may be fortuitous, but it is also predicted by recent mantle convection models for the early stages of accretion of

  15. Early Paleozoic accretionary orogenesis along northern margin of Gondwana constrained by high-Mg metaigneous rocks, SW Yunnan

    NASA Astrophysics Data System (ADS)

    Xing, Xiaowan; Wang, Yuejun; Cawood, Peter A.; Zhang, Yuzhi

    2015-12-01

    SW Yunnan of China constituted part of the northern margin of Gondwana facing the proto-Tethys ocean in the early Paleozoic. However, the evolution of the region and its relationship with the accretionary orogenism have been poorly established. This paper reports a set of new zircon U-Pb age data and whole-rock major oxides, elemental and Sr-Nd isotopic data for early Paleozoic metavolcanic rocks from the previously defined Lancang Group and reveals the development of an Ordovician suprasubduction zone in SW Yunnan. Zircon U-Pb ages of 462 ± 6 and 454 ± 27 Ma for two representative samples indicate eruption of the volcanic rocks in the Late Ordovician. Geochemical data for the metavolcanic rocks together with other available data indicate a calc-alkaline affinity with high Al2O3 (13.04-18.77 wt%) and low TiO2 (0.64-1.00 wt%). They have Mg-numbers ranging from 62 to 50 with SiO2 of 53.57-69.10 wt%, compositionally corresponding to the high-Mg andesitic rocks. They display enrichments in LREEs and LILEs with significant Eu negative anomalies (δEu = 0.20-0.33), and depletions in HFSEs, similar to arc volcanic rocks. Their initial 87Sr/86Sr ratios range from 0.721356 to 0.722521 and ɛNd(t) values from -7.63 to -7.62 with Nd model ages of 2.06-2.10 Ga. Integration of ages and geochemical data with available geological observations, we propose the presence of Ordovician magmatism related to proto-Tethyan evolution in SW Yunnan and the metaigneous rocks formed in an island-arc setting. They were part of a regional accretionary orogen that extended along the northern margin of Gondwana during Neoproterozoic to early Paleozoic period.

  16. Paleogeographic and tectonic implications of the first paleomagnetic results from the Middle Late Cambrian Mesón Group: NW Argentina

    NASA Astrophysics Data System (ADS)

    Spagnuolo, Cecilia M.; Rapalini, Augusto E.; Astini, Ricardo A.

    2008-02-01

    The first paleomagnetic data from autochthonous Cambrian rocks in NW Argentina is reported to constrain the apparent polar wander path (APWP) of Gondwana during the Early Paleozoic. The paleomagnetic pole (Lat 4.5°S; Long 359.0°E; dp = 5.5; dm = 8.8; n = 26) was obtained from the red to purple sandstones of the Campanario Formation. These rocks present a characteristic remanence carried by fine-grained hematite. The pole indicates that during the Late Cambrian, rocks now exposed in the Eastern Cordillera of NW Argentina were deposited at relatively low latitudes (≈26°S), consistent with intense chemical alteration during wet and warm climates, as indicated from petrography of apparent first-cycle quarzites of the Mesón Group. However, the pole position is anomalous with respect to the most accepted apparent polar wander paths for Gondwana, suggesting that the study area (22°50'S, 65°00'W) underwent clockwise rotation of 38° ± 8°, likely related to the Cenozoic central Andes rotation pattern characteristic of the region.

  17. Isotopic fractionation of uranium in sandstone

    USGS Publications Warehouse

    Rosholt, J.N.; Shields, W.R.; Garner, E.L.

    1963-01-01

    Relatively unoxidized black uranium ores from sandstone deposits in the western United States show deviations in the uranium-235 to uranium-234 ratio throughout a range from 40 percent excess uranium-234 to 40 percent deficient uranium-234 with respect to a reference uranium-235 to uranium-234 ratio. The deficient uranium-234 is leached preferentially to uranium-238 and the excess uranium-234 is believed to result from deposition of uranium-234 enriched in solutions from leached deposits.

  18. Wettability changes in trichloroethylene-contaminated sandstone.

    PubMed

    Harrold, G; Gooddy, D C; Lerner, D N; Leharne, S A

    2001-04-01

    It is usually assumed that chlorinated solvent nonaqueous-phase liquids (NAPLs) are nonwetting with respect to water-saturated porous media. The focus of this work was to examine whether this supposition is appropriate for used trichloroethylene (TCE) samples. In this work, the term "used" indicates that the sample has been employed industrially and therefore contains solutes and breakdown products related to its previous use. The data obtained in this study indicate that exposure of initially water wet quartz slides to industrially used solvents can cause a contact angle change, measured through the aqueous phase, of 100 degrees with a maximum stable contact angle of 170 degrees (indicative of strong NAPL wetting characteristics) being recorded. The work on quartz slides was complemented by the use of sandstone cores. Wettability was measured using the Amott test. Used TCE again proved able to alter the wetting properties of sandstone to neutral wetting. The complexity of the industrially used samples precluded any realistic attempt to examine the agents causing these wetting changes. The data captured in these experiments were compared with laboratory grade TCE, and some attempts were made to synthesize known mixtures in order to replicate wetting changes. These experiments resulted in contact angle changes but did not alter the overall wettability of the quartz slides or sandstone cores. Finally the work reported here also demonstrates that increasing the duration of exposure to solvent has an important impact upon measured contact angle.

  19. Reservoir quality and heterogeneity of tidal inlet sandstones, Halfway Formation, northeastern British Columbia, Canada

    SciTech Connect

    Munroe, H.D. ); Moslow, T.F. )

    1991-03-01

    A subsurface investigation of the mid-to-late Triassic Halfway Formation in northeastern British Columbia has identified a series of wave-dominated tidal inlet sandstones associated with transgressive and prograding barrier island shoreline trends. Depositional models and facies reconstructions were based on sedimentologic analysis approximately 60 cored sequences and 1200 well logs within the Halfway. Tidal inlet sequences are very fine to coarse-grained quartzose sandstone ranging from 4.0 to 10.0 m in thickness. Facies with greatest reservoir quality are contained within the lower half of the sequence. Fine- to medium-grained stacked fining-upward units with scoured lower contacts and planar to trough cross-bedding characterize this facies. Molluscan shell molds and casts can comprise up to 60% of an inlet sequence. Porosity values as high as 25% are associated with these coquinas.

  20. Paleocurrent, petrography and provenance analyses of the Ajali Sandstone (Upper Cretaceous), southeastern Benue Trough, Nigeria

    NASA Astrophysics Data System (ADS)

    Amajor, L. C.

    1987-09-01

    Paleocurrent, petrographic and heavy-mineral analyses of the Ajali Sandstone (Late Cretaceous) in southeastern Nigeria show that the sedimentary rocks on the Santonian Okigwe-Abakaliki anticlinorium provided the major detritus, whereas minor contributions of the eastern Precambrian basement block (Oban massif) are confined along a narrow belt southeast of Alayi in the Afikpo Basin. The sandstones derived from the major sedimentary source are quartz arenites characterized by a zircon-tourmaline heavy-mineral assemblage and a radial paleocurrent pattern which parallels the paleoslope of the provenance. On the other hand, those sands generated from the eastern basement block are arkose and sub-arkose dominated by a garnet-apatite-rutile heavy-mineral assemblage and southwesterly directed paleocurrent modes. The results of this study support the previous hypothesis that most ancient quartz arenites are multicycle in origin.

  1. Petrography and geochemistry of the Cambro-Ordovician Wajid Sandstone, southwest Saudi Arabia: Implications for provenance and tectonic setting

    NASA Astrophysics Data System (ADS)

    Wanas, H. A.; Abdel-Maguid, N. M.

    2006-09-01

    The Wajid Sandstone, of probable Cambro-Ordovician age, rests unconformably on peneplained Precambrian crystalline rocks on the southeastern margin of the Arabian Shield. The sandstone is composed of varicolored siliciclastic rocks, mainly coarse-to fine-grained sandstones with granule conglomerate and siltstone interbeds, displaying diverse sedimentary primary structures such as planar- and trough-cross bedding, and flat bedding. They form repeated fining-upward cycles, typical of deposition from braided streams. Current indicators indicate that flow was from SW to NNE. Petrographically, all samples of the Wajid Sandstone are of quartz arenite type, highly enriched in quartz, but poor in heavy minerals, feldspar and lithic fragments. The provenance and tectonic setting of the Wajid Sandstone have been assessed using integrated petrographic and geochemical studies. Petrographic analysis reveals that mono-and poly-crystalline quartz grains and heavy minerals from metamorphic and igneous rocks of a craton interior setting were the dominant sources. Chemically, major and trace element concentrations in the rocks of the Wajid Sandstone indicate deposition in a passive continental margin setting. Petrographic and geochemical data suggest that the sediments were derived from metamorphic and igneous rocks forming the adjacent Precambrian basement rocks of the Arabian Shield, and were deposited on a passive continental margin. Deposition took place after stabilization of the Arabian Shield following the Late Precambrian Pan-African Orogeny. The Wajid Sandstone can be correlated with similar deposits elsewhere in Arabia and North Africa which were deposited on a low-lying landmass forming the stable continental margin of the Arabian-Nubian Shield, flanking the southern margin of the Paleo-Tethys Ocean.

  2. Paleomagnetism of the Newcastle Range, northern Queensland: Eastern Gondwana in the Late Paleozoic

    NASA Astrophysics Data System (ADS)

    Anderson, Kari L.; Lackie, Mark A.; Clark, David A.; Schmidt, Phil W.

    2003-06-01

    The Newcastle Range is an extensive (2500 km2) and well-exposed caldera system erupted on the trailing edge of Eastern Gondwana between 325 and 295 Ma. Paleomagnetic samples were collected from ignimbrites and associated microgranitoid intrusions from the central, northern and southern calderas from which three components of magnetization are recognized. Component 1 is considered to be a viscous magnetization acquired during the Brunhes Chron. A presumed Permian component, C2, is found in seven paleomagnetic sites with a mean pole at 30.9°S, 139.7°E (K = 13.9, A95 = 16.8°, ASD = 21.7°), agreeing with previously reported Permian data from Australia. Carboniferous units have a well-defined characteristic component, C3, distinguished by dual polarity (predominantly reversed) and moderate to steep inclination directions. Paleomagnetic polarities in the Newcastle Range Volcanics are formation dependent and new constraints on the timing of Carboniferous volcanism (˜325-317 Ma) are consistent with recent reanalysis of the base of the Permo-Carboniferous Reversed Superchron (PCRS). A mean paleomagnetic pole, calculated from 15 VGPs, lies at 63.4°S, 125°E (K = 26.22, A95 = 7.6°, ASD = 15.8°), suggesting that Australia remained at midlatitudes into the Middle Carboniferous. This paleomagnetic pole is consistent with similarly aged poles from Western Gondwana, the conformity of which indicates contributions from nondipole components of the Earth's paleofield were probably not significant in the time immediately preceding the PCRS.

  3. Burning of forest materials under late Paleozoic high atmospheric oxygen levels

    NASA Astrophysics Data System (ADS)

    Wildman, Richard A., Jr.; Hickey, Leo J.; Dickinson, Matthew B.; Berner, Robert A.; Robinson, Jennifer M.; Dietrich, Michael; Essenhigh, Robert H.; Wildman, Craig B.

    2004-05-01

    Theoretical models suggest that atmospheric oxygen reached concentrations as high as 35% O2 during the past 550 m.y. Previous burning experiments using strips of paper have challenged this idea, concluding that ancient wildfires would have decimated plant life if O2 significantly exceeded its present level of 21%. New thermochemistry and flame-spread experiments using natural fuels contradict these results and indicate that sustained burning of forest fuels at moisture contents common to living plants does not occur between 21% and 35% O2. Therefore, the fires under atmospheres with high oxygen concentrations would not have prevented the persistence of plant communities. Times of high O2 also agree with observations of concurrent fire-resistant plant morphology, large insects, and high concentrations of fossil charcoal.

  4. Mississippian fossils from southern appalachian metamorphic rocks and their implications for late paleozoic tectonic evolution.

    PubMed

    Gastaldo, R A; Guthrie, G M; Steltenpohl, M G; Gastaldo, R A; Steltenpohl, M G

    1993-10-29

    Fossils of Periastron reticulatum Unger emended. Beck recovered from the Erin Slate of the Talladega slate belt of Alabama establish that these rocks have a Mississippian (Kinderhookian-Tournaisian) age. The Talladega slate belt, the southwestern extension of the western Blue Ridge belt, was interpreted to have been affected by regional dynamothermal metamorphism and coeval deformation as a result of the Acadian orogeny. This fossil find indicates that metamorphism and deformation of the Talladega belt occurred after the Early Carboniferous (Alleghanian), requiring a reevaluation of tectonic interpretations of the southernmost Appalachians.

  5. The Boundary of Tectonic Units of the South China Continent in the Meso-Neoproterozoic - Early Paleozoic: Insights from Integrated Geophysical Study

    NASA Astrophysics Data System (ADS)

    Guo, L.; Gao, R.; Meng, X.; Zhang, J.; Wang, H.; Liu, Y.

    2013-12-01

    The South China continent (SCC), located in the transition zone of the Eurasia, India and Pacific plates, formed in the Meso-Neoproterozoic by collision of the Yangtze block and the Cathaysia block. However, the boundaries of the two blocks before the late Paleozoic (from Meso-Neoproterozoic to early Paleozoic) remain debated in the literature due to strong and complex tectonic and magmatic activities since then. The south of Jiangnan archicontinent is covered mostly by the thick strata since the late Paleozoic, the surface of which is widely covered by the vegetation. And the regional tectonic deformation is extremely complicated with few basal outcrops. For decades, a variety of geophysical detections have been performed in the SCC for understanding the deep structure and tectonic evolution, including deep seismic sounding (DSS) profiles, magnetotelluric sounding (MT) profiles, gravity and magnetic surveys and a small amount of deep seismic reflection profiles. However, due to the limitations of resolution and accuracy of the observed geophysical data in the past, especially short of the deep seismic reflection profiles to reveal fine lithosphere structure, different scientists presented various views on the division of tectonic units in the SCC. In quite recent years, the SinoProbe-02 project launched a long profile of geophysical detections across the two blocks in the SCC, including deep seismic reflection, DSS, MT, and broadband seismic observation, the resolution and accuracy of which had been improved greatly. These newly data will benefit better understanding the deep structure and tectonic evolution of the SCC. Here, we assembled high-resolution Bouguer gravity anomalies and aeromagnetic anomalies data in the SCC. The magnetic data were reduced to the pole by used a varying magnetic inclinations algorithm. We then performed anomaly separation and multi-scales lineation structure analysis on the gravity and RTP magnetic data, and then did 3D fusion

  6. Hydrofacies In Sandstones. Evidence For Feedback Between Sandstone Lithofacies and Permeability Development

    NASA Astrophysics Data System (ADS)

    Bloomfield, J. P.; Newell, A.; Moreau, M.

    In order to enhance our ability to develop effective numerical models of flow and con- taminant transport in the Permo-Triassic sandstone aquifer of the UK, relationships between lithofacies, rock mass characteristics (such as porosity and pore-throat size distribution), and permeability have been investigated through a series of case studies. Flow in the Permo-Triassic sandstones is primarily through the matrix. Permeability distribution is principally a function of the pore-throat size distribution and there is a relatively weak correlation with primary sedimentary lithofacies. It is observed that matrix permeability data broadly fall into two, discontinuous, sub-populations above and below about 1 mD. It is proposed that modification of primary sedimentary litho- facies by circulation of groundwater is the main control on the development of these two permeability sub-populations or hydrofacies. Identification of these two hydrofa- cies has significant implications for numerical modelling of the sandstones.

  7. Paleozoic oolitic ironstones of the Algerian Sahara: a review

    NASA Astrophysics Data System (ADS)

    Guerrak, Salah

    The Paleozoic sediments are present over the greatest part of the SaharanPlatform, from the border of Morocco, Rio de Oro and Mauritania in the W, to the Libyan frontier in the E. They outcrop in the Ougarta chains, the Gourara and the Touat, the Northern border of the Reguibat Shield and constitute a sedimentary girdle around the Touareg Shield, namely the Azzel Matti, the Ahnet, the Mouydir, the Ajjers Tassilis, the Tafassasset Tassilis and the Ouan Ahaggar Tassilis. In all these formations, numerous oolitic ironstones occur, particularly in Ordovician, Devonian and Lower Carboniferous rocks. We can distinguish essentially two types of oolitic ironstones (OIS): OIS with constant thin beds and horizontal extension: they will be named EXID type (Extensive Iron Deposition), and OIS of local extension and irregular thickness: they will be named LOID type (Local Iron Deposition). The EXID type is located in the Ordovician, the Middle Devonian and in the very Lower Carboniferous (Tournaisian) sedimentary rocks. The LOID type occurs in the Lower and Upper Devonian rocks and appears as the economically interesting type. From the Zemmour to the Fezzan, a real Paleozoic oolitic iron belt appears 3000 km long, determining a N Gondwanian oolitic iron province, formed during cold to temperate climates.

  8. Age of the Bedford Shale, Berea Sandstone, and Sunbury Shale in the Appalachian and Michigan basins, Pennsylvania, Ohio, and Michigan

    USGS Publications Warehouse

    De Witt, Wallace

    1970-01-01

    The suggestion by Sanford (1967, p. 994) that the Bedford Shale, Berea Sandstone, and Sunbury Shale of the Michigan basin are of Late Devonian age because these strata contain Hymenozonotriletes lepidophytus Kedo is invalid for these formations in the Appalachian basin, the area of their type localities. Endosporites lacunosus Winslow, a synonym of Hymenozonotriletes lepidophytus Kedo, occurs in upper Chautauqua (Upper Devonian) rocks through much of the Kinderhook (Lower Mississippian) strata in Ohio. The Sunbury Shale, the Sunbury Member of the Orangeville Shale in part of northern Ohio, contains a Siplionodella fauna which clearly demonstrates the Kinderhook age of the unit. The basal strata of the Bedford Shale contain Spathoffnathodus anteposlcornis which suggests a very Late Devonian or very Early Mississippian age for this part of the Bedford. Except for the basal fossil zone, most of the Bedford Shale and the younger Berea Sandstone overlie the Murrysville sand, which along the Allegheny Front in central Pennsylvania contains an Adiantites flora of Early Mississippian (Kinderhook) age. The presence of Adiantites in the Murrysville sand indicates that most of the Bedford Shale and all the Berea Sandstone are of Early Mississippian age. Lithostratigraphic evidence suggests that the Berea Sandstone of Ohio may be a temporal equivalent of the basal Beckville Member of the Pocono Formation of the Anthracite region of Pennsylvania. The clearly demonstrable Kinderhook age of the Sunbury, Berea, and most of the Bedford in the Appalachian basin strongly indicates a similar age for the same units in the Michigan basin.

  9. Magnetic polarity stratigraphy of the Permian and Carboniferous: The extension of the magnetic reversal record into the Paleozoic

    SciTech Connect

    Opdyke, N.D. )

    1991-03-01

    Magnetic polarity stratigraphy has revolutionized stratigraphic studies in Jurassic to Pleistocene sediments. These studies have been greatly facilitated by the reversal record that is recorded in rocks of the ocean floor. For times prior to the Jurassic, the reversal history of the magnetic field must be determined and eventually related through the type section concept. The magnetic reversal history of the late Paleozoic is dominated by the Permo-Carboniferous reversed superchron (PCRS), which extends from the late Permian to the Carboniferous (Westphalian). Recent studies by the author and his students in Middle Carboniferous sediments of eastern Canada, Pennsylvania, Arizona, and Nevada reveal that the magnetic field has reversed frequently in late Mississippian and early Pennsylvanian times (Meramecian through late Morrowan). The polarity of the magnetic field over this interval is approximately 50% normal and 50% reversed. The frequency of reversal appears to be about one reversal per m.y. The possibility, therefore, exists that this pattern may be used for continental and intercontinental correlation. Attempts are currently underway to correlate this magnetic stratigraphy to fossiliferous marine sections. The base of the PCRS is probably of Atokan age.

  10. Early Paleozoic oceanic inliers and reconstruction of accretionary tectonics in the Middle Gobi region, Mongolia: Evidence from SHRIMP zircon U-Pb dating and geochemistry

    NASA Astrophysics Data System (ADS)

    Zhu, Mingshuai; Miao, Laicheng; Baatar, Munkhtsengel; Zhang, Fochin; Anaad, Chimedtseren; Yang, Shunhu; Li, Xingbo

    2016-09-01

    The ophiolites that occur as inliers among the Late Paleozoic formations in the Middle Gobi area are crucial for understanding the tectonic evolution of South Mongolia. In this paper, we conducted detailed studies on the Namdain hundy ophiolite to provide some constraints on the Early Paleozoic evolution of the Middle Gobi region in Mongolia. The ophiolite mainly consists of ultramafic rocks (carbonatation), plagiogranite, metagabbro, basalt and chert. The metagabbro and plagiogranite from Namdain hundy ophiolite yielded SHRIMP zircon U-Pb ages of 528 ± 7 Ma and 519 ± 5 Ma, respectively. Though most of the volcanic rocks of this ophiolite show supra-subduction zone (SSZ) affinity, samples with OIB and N-MORB geochemical features were also identified, indicating genesis in a forearc setting. The granodiorite intruding into the Namdain hundy ophiolite yielded a SHRIMP zircon U-Pb age of 491 ± 3 Ma, which constrained the upper age limit of ophiolite emplacement. This granodiorite shows adakitic geochemical affinity, attesting to the existence of Cambrian paleo - subduction in South Mongolia. Based on the available data so far, we suggest the Middle Gobi area comprises of the Manlay accretion complex, the island arc and the Biluutiin ovoo back-arc basin. The spatial configuration of these three tectonic belts suggests that the polarity of the paleo-ocean subduction was from south to north in the Early Paleozoic, forming a trench-arc-basin system south of the Central Mongolia microcontinent.

  11. New Early Paleozoic Paleomagnetic Poles From NW Argentina: a Reappraisal of Tectonic Models

    NASA Astrophysics Data System (ADS)

    Spagnuolo, C. M.; Rapalini, A. E.; Astini, R. A.

    2007-05-01

    A paleomagnetic study carried out on Early Ordovician volcanic units in the Famatina Ranges of NW Argentina yielded a pre-tectonic paleomagnetic pole at 32.7°S, 4.3°E, (5.6°/ 8.6°, N=14 sites) that is consistent with four previous Early Ordovician poles from the Famatina - Eastern Puna Eruptive Belt of NW Argentina. However, these five poles are rotated around 50° clockwise respect to the coeval reference pole of Gondwana. Our new results seem to confirm previous models of this belt as a paraauthocthonous rotated terrane on the southwestern margin of Gondwana. However, a recent paleomagnetic pole from the Late Cambrian Mesón Group, at the Eastern Cordillera of NW Argentina, corresponding to the Gondwana foreland (4.5°S, 359.0°E, dp=5.5°, dm=8.8°, n=26 samples) and preliminary paleopoles obtained from the same unit and the latest Cambrian - Early Ordovician Santa Victoria Group at other three localities in the same region, also indicate an anomalous pole position rotated some 40° clockwise respect to the reference pole for Gondwana. These results suggest that the postulated model of a rotated terrane for the Famatina-Eastern Puna belt must be reconsidered. Different alternative scenarios including the possibility of an Early Paleozoic displacement of the whole basement of the Eastern Sierras Pampeanas of Argentina ("Pampia") will be explored.

  12. Pripyat basin, U. S. S. R: An oil productive Middle Paleozoic rift

    SciTech Connect

    Ulmishek, G.F. )

    1991-03-01

    The Pripyat basin occupies the extreme northwestern part of the Pripyat-Donets middle Paleozoic rift, which separates the Ukrainian shield from the rest of the Russian craton. The basement structure is typical of rifts and consists of a series of east-west-trending tilted fault blocks. The prerift sequence is chiefly composed of Middle Devonian clastic and carbonate rocks. The rift sequence is of Late Devonian age and is composed of two thick salt formations separated by lower Famennian carbonate rocks. The upper salt formation is significantly deformed by salt flowage; the lower one is only locally affected. The postrift sequence includes uppermost Devonian and Carboniferous strata. Principal source rocks are black-shale facies in the synrift intersalt carbonate formation. This same formation contains about two-thirds of the hydrocarbon reserves. The rest of the reserves is in prerift carbonate and clastic rocks beneath the lower salt. Faulted structural traps control all fields. Stratigraphic traps and lower Famennian (intersalt) reefs are potential exploration targets.

  13. Mass extinction of ocean organisms at the Paleozoic-Mesozoic boundary: Effects and causes

    NASA Astrophysics Data System (ADS)

    Barash, M. S.

    2012-04-01

    At the end of the Permian, at the boundary between the Paleozoic and Mesozoic (251.0 ± 0.4 Ma), the largest mass extinction of organisms on the Earth occurred. Up to 96% of the species of marine invertebrates and ˜70% of the terrestrial vertebrates died off. A lot of factors were suggested and substantiated to explain this mass mortality, such as the disappearance of environmental niches in the course of the amalgamation of the continental plates into Pangea, sea level fluctuations, anoxia, an elevated CO2 content, H2S intoxication, volcanism, methane discharge from gas-hydrates, climate changes, impact events (collisions with large asteroids), or combinations of many of these reasons. Some of these factors are in subordination to others, while others are independent. Almost all of these factors developed relatively slowly and could not cause the sudden mass mortality of organisms globally. It could have happened when large asteroids, whose craters have been discovered lately, fell to the Earth. It is suggested that the impact events "finished off" the already suppressed biota. A simultaneous change in many of the factors responsible for the biodiversity, including those not connected in a cause-and-effect relationship, proves the existence of a common extrater-restrial cause that affected both the changes in the internal and external geospheres and the activation of asteroid attacks (the Sun's transit of spiral arms of our galaxy, the Sun's oscillations perpendicularly to the galactic plane, etc).

  14. CO2-Driven Convection Produced the Vertical Distribution of Sandstone Colors and Iron Concretions in Navajo Sandstone at Zion National Park, Utah (USA)

    NASA Astrophysics Data System (ADS)

    Kettler, R. M.; Loope, D. B.

    2011-12-01

    Along cliff faces exposed in Zion National Park (SW Utah), the porous and permeable Navajo Sandstone (Jurassic) is 700 m thick, and is capped by impermeable mudrocks and evaporites of the Carmel Formation. Previous workers have documented an areally extensive color pattern that is easily visible across much of southwestern and south-central Utah: the uppermost Navajo Sandstone is nearly white, the middle third of the formation is pink, and the lowermost fraction is reddish brown. To the northwest of the park, however, the formation is uniformly red (likely its primary color; G.B. Nielsen et al., 2009). Spheroidal concretions with dense, iron-oxide-cemented rinds and iron-poor cores are abundant in the pink and brown sandstones. Rhomb-shaped clots of iron oxide cement that are pseudomorphous after siderite are present in the cores of the largest concretions. The color variations are evidence that iron was transported from the upper portion of the Navajo SS to the lower portion. The pseudomorphs are evidence that the concretions are the oxidized remains of siderite-cemented precursors. The vertical iron transport and the precipitation of siderite require similar vertical transport of reducing, CO2-rich formation waters through the Navajo Sandstone. We argue that this circulation was driven in part by groundwater convection beneath a CO2 accumulation that was trapped below the Navajo-Carmel contact. This circulation caused aqueous iron and aqueous carbonate to be displaced downward and to accumulate (in the form of siderite) in the lower Navajo Sandstone. There are numerous CO2 reservoirs in the Colorado Plateau region; the gas was derived mainly from mantle sources. We hypothesize that, in the late Tertiary, the Carmel Formation capped a broad, structurally high accumulation of CO2 and CH4 in the Navajo Sandstone. The CH4 bleached the upper portion of the sandstone, releasing Fe2+ into the formation water. CO2 dissolved in the water, thereby increasing its density

  15. On the tectonic position of the Baoshan region during the Late Palaeozoic

    NASA Astrophysics Data System (ADS)

    Xunlian, Wang; Makoto, Kato; Hongzhen, Wang

    The aim of this study is to discuss the tectonic position of Baoshan in Yunnan Province, China, during the Late Paleozoic by comparison of the sedimentary facies, fauna and palaeomagnetic data from the Baoshan region with those from the Yangtze region and southern Tibet. The sedimentary facies change suggests that in the Late Palaeozoic the Baoshan region underwent a similar geological history to southern Tibet, but different from that of the Yangtze region. The rugose corals and brachiopods as well as vertebrates of Baoshan are different from those of the Yangtze region during the Late Palaeozoic. An evident segregation seems to exist between them. The Late Paleozoic fauna of Baoshan shows certain similarities to southern Tibet. The Devonian and Late Carboniferous faunas, especially, are very similar to those in southern Tibet. This indicates that there was no evident segregation between them in the Late Palaeozoic. The palaeomagnetic data reveal that in the Late Palaeozoic the Yangtze region was close to the equator, while the Baoshan region and southern Tibet were situated in the middle latitudes. On the basis of the palaeontological, sedimentological and palaeomagnetic data, it is inferred that Baoshan and southern Tibet were situated in the same continental margin, and both regions were far from the Yangtze region during the Late Paleozoic. The Baoshan region may be considered as a massif within the Gondwana tectonic domain which includes southern Tibet, while the Yangtze region was located in another tectonic domain—the South Asian domain, with a wide ocean, the Tethys between them.

  16. Little known mid-Paleozoic salts of northwestern North Dakota

    SciTech Connect

    Fischer, D.W.; Anderson, S.B.

    1984-07-01

    Four Paleozoic formations that contain bedded salts previously undescribed in North Dakota have been identified and mapped. They are the Silurian Interlake, and Devonian Ashern, Souris River, and Duperow Formations. A series of stratigraphically and areally discontinuous, thin, bedded salts has been identified in the Silurian Interlake Formation. As many as five, thin, bedded salts are present in the upper gray member of the Devonian Ashern Formation. Where found, these salts are stratigraphically correlatable but laterally discontinuous. A thin, bedded salt is present in both the Souris River and Duperow. These salts are laterally continuous with salts previously described in Saskatchewan. Although the occurrences of the salts discussed commonly are discontinuous, knowledge of their presence can be helpful in designing a drilling and testing program for wells in areas where they occur. Furthermore, a knowledge of the presence of these salts is helpful in understanding the overall tectonic and depositional history of the Williston basin.

  17. Paleozoic oil and gas complexes of the Baltic syneclise

    SciTech Connect

    Geodekyan, A.A.; Dubovskoy, I.T.; Kleshchev, K.A.; Mazur, V.B.; Ostrovskiy, M.I.; Sakalavskas, K.A.

    1981-10-01

    Principal directions for exploration of new commercial accumulations of oil and gas in the main Paleozoic prospective complexes in the Baltic syneclise, including its sea portion, have been based on an analysis of the lithologic-facies composition, structural features, attitude of the rocks, and the distribution of the reservoir horizons and possible different types of traps. The promise of the deep parts of the southeastern Baltic Sea region, where a large number of local uplifts have been identified, and traps of nonanticlinal and combined types have been recorded, is emphasized where the principal focus for the generation of oil hydrocarbons inthe Baltic syneclise is located. As compared with the land area, it is suggested that there is an increase in the supply stock and the capacity parameters of the traps and an improvement in the conditions of preservation of petroleum accumulations here.

  18. Early Paleozoic magmatic history of central Inner Mongolia, China: implications for the tectonic evolution of the Southeast Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Wu, Chen; Liu, Changfeng; Zhu, Yan; Zhou, Zhiguang; Jiang, Tian; Liu, Wencan; Li, Hongying; Wu, Chu; Ye, Baoying

    2016-07-01

    To provide insights into the Early Paleozoic tectonic evolution of the southern portion of the long-lived Central Asian Orogenic Belt, we have conducted major and trace element analyses and zircon U-Pb dating of granitoid samples from central Inner Mongolia. Our study area covers three pre-Mesozoic tectonic units from north to south: the Wenduermiao subduction-accretionary complex, the Bainaimiao magmatic belt, and the northern margin of the North China craton. Our new geochronological and geochemical data show the temporal and genetic relationships between the three tectonic units. Accordingly, we suggest that the Wenduermiao subduction-accretionary complex developed in the Middle Cambrian-Late Silurian (509-421 Ma), comprising of coeval oceanic crust, arc magmatism, and forearc deposits. The Bainaimiao continental arc was developed during the Late Cambrian to Early Silurian (501-437 Ma), which superposed on the basement with the affinity of the North China craton. The back-arc basin opened prior to Early Silurian and lasted to the Late Silurian, which is slightly younger than Bainaimiao island arc. The Wenduermiao Ocean, between the Wenduermiao subduction-accretionary complex and the Bainaimiao continental arc, existed in Early Paleozoic.

  19. The Neoproterozoic and Paleozoic tectonostratigraphic evolution of Southwestern Mongolia and implications for crustal growth in Asia

    NASA Astrophysics Data System (ADS)

    Macdonald, F. A.; Bold, U.; Buchwaldt, R.; Smith, E. F.

    2013-12-01

    much of the Cryogenian and Ediacaran periods. During the early Cambrian exotic Ediacaran to early Cambrian arcs and Proterozoic continental fragments accreted onto the western and southern margins of the Zavkhan Terrane, resulting in foreland deposition and a larger hybrid ribbon continent, defined by an active fringing arc. In the latest Devonian, the composite ribbon continent began to obliquely collide with Siberia, and oroclinally buckled through the late Paleozoic, culminating in extensive Permian plutonism.

  20. The Origin of a Layer of Subcircular Mudflakes in the Ross Sandstone Formation of County Clare, Ireland

    NASA Astrophysics Data System (ADS)

    Robinson, K. H.; Kackstaetter, U. R.

    2015-12-01

    The west coast of Ireland in County Clare is famous for its Paleozoic stratigraphy containing spectacular exposures of deposits from carbonate shelf, deep marine, slope and deltaic environments, exposed at several distinctive and well-known locations including the Burren, Cliffs of Moher, and Bridges of Ross. Underlying the silty sandstones of the Gull Island Formation and overlying the Clare Shale, the Carboniferous Ross Sandstone Formation comprises a series of fine-grained sandstone and mudstone deep water turbidite deposits. Approximately a half-kilometer northeast of the Bridges of Ross and about 15 meters below the upper boundary of the Ross Formation is a particular stratum exhibiting an assemblage of unique circular to ovoid impressions. These features densely cover an exposed horizontal surface of approximately 100 square meters, positioned about 5 meters above and adjacent to a cluster of sand volcanoes. The impressions frequently overlap and completely cover the exposed surface of the rock unit and continue along the same plane of the buried portion of the stratum. Diameters of the impressions range between 2 and 20 centimeters, and many contain clasts of pale grey shale or claystone material. Samples were collected from the layer of interest as well as from subjacent and superjacent strata, spanning a total thickness of just over 1 meter. Thin sections were created and analyzed to determine both composition and estimated porosity of the rock in a continuous vertical cross-section through the series of strata surrounding the impressions. Characteristics of each stratum were examined to explore possible depositional relationships of each layer to the others and to indicate likely diagenetic processes of the subcircular features. Two broad possible origins are discussed: a primary sedimentary origin, i.e. turbidite channel mudflake conglomerate; or a post-depositional soft sediment deformation origin due to either (i) sediment loading and dewatering, (ii

  1. Late Ordovician (Ashgillian) glacial deposits in southern Jordan

    NASA Astrophysics Data System (ADS)

    Turner, Brian R.; Makhlouf, Issa M.; Armstrong, Howard A.

    2005-11-01

    The Late Ordovician (Ashgillian) glacial deposits in southern Jordan, comprise a lower and upper glacially incised palaeovalley system, occupying reactivated basement and Pan-African fault-controlled depressions. The lower palaeovalley, incised into shoreface sandstones of the pre-glacial Tubeiliyat Formation, is filled with thin glaciofluvial sandstones at the base, overlain by up to 50 m of shoreface sandstone. A prominent glaciated surface near the top of this palaeovalley-fill contains intersecting glacial striations aligned E-W and NW-SE. The upper palaeovalley-fill comprises glaciofluvial and marine sandstones, incised into the lower palaeovalley or, where this is absent, into the Tubeiliyat Formation. Southern Jordan lay close to the margin of a Late Ordovician terrestrial ice sheet in Northwest Saudi Arabia, characterised by two major ice advances. These are correlated with the lower and upper palaeovalleys in southern Jordan, interrupted by two subsidiary glacial advances during late stage filling of the lower palaeovalley when ice advanced from the west and northwest. Thus, four ice advances are now recorded from the Late Ordovician glacial record of southern Jordan. Disturbed and deformed green sandstones beneath the upper palaeovalley-fill in the Jebel Ammar area, are confined to the margins of the Hutayya graben, and have been interpreted as structureless glacial loessite or glacial rock flour. Petrographic and textural analyses of the deformed sandstones, their mapped lateral transition into undeformed Tubeiliyat marine sandstones away from the fault zone, and the presence of similar sedimentary structures to those in the pre-glacial marine Tubeiliyat Formation suggest that they are a locally deformed facies equivalent of the Tubeiliyat, not part of the younger glacial deposits. Deformation is attributed to glacially induced crustal stresses and seismic reactivation of pre-existing faults, previously weakened by epeirogenesis, triggering sediment

  2. Depositional environments, diagenesis, and porosity of upper cretaceous volcanic-rich Tokio sandstone reservoirs, Haynesville Field, Clairborne Parish, Louisiana

    SciTech Connect

    Clark, W.J.

    1995-10-01

    Tokio Formation sandstones produce oil from volcanic-rich to quartzose lithic sandstones in the Haynesville Field. The Tokio interval is approximately 210 feet thick and has been divided into four sandstone zones separated by shales or scoured contacts. In ascending order, the four zones are the RA, S3, S2, and S1. The RA is composed of quartzose sublitharenites inferred to have been deposited in delta front bars and distributary channels. The upper three zones are composed of sublitharenite and feldspathic litharenite to quartzose litharenite. The upper sands are interpreted to have been deposited in littoral environments including storm influenced shelf, tidal flats and channels, and barrier island/strand plain. The diagenesis of these sands is strongly related to composition: greater percentages of cements and secondary porosity occur in lithic-rich sandstones. Diagenetic cements in quartzose sandstones are mainly quartz overgrowths with minor early K-spar overgrowths on plagioclase, early chlorite-rims, and late patchy calcite, pyrite, and rare dolomite and siderite. Diagenesis in lithic-rich sands includes greater amounts of chlorite rim and pore-filling kaolinite cements and less quartz-overgrowth and other cements. The effect of the original mineralogy and diagenetic minerals on wireline logs includes: (1) reduction of SP due to cements, (2) increase in GR response due to K-spar and volcanic detritus, (3) higher resistivity due to carbonate minerals, and (4) increase in irreducible water saturation due to pore-lining and pore-filling clay. Thus, potential reservoir zones with lithic-rich sandstones like the Tokio could be overlooked in many areas around the world.

  3. Mechanical stratigraphy of deep-water sandstones: insights from a multisciplinary field and laboratory study

    NASA Astrophysics Data System (ADS)

    Agosta, Fabrizio; di Celma, Claudio; Tondi, Emanuele; Corradetti, Amerigo; Cantalamessa, Gino

    2010-05-01

    -perpendicular joint spacing/bed thickness (S/T) relationships on sandstone bodies that experienced similar diagenetic and tectonic histories. The field area is located in the Periadriatic foreland basin, eastern central Italy, which show late Pliocene slope turbidites in excellent 3d views. The Periadriatic foreland basin is an elongated, roughly N-S oriented trough located immediately east of the Apennines fold-thrust belt. The basin fill mostly consists of deepwater Plio-Pleistocene sediments partially incorporated into the frontal part of the orogenic wedge. During the late Pliocene, gravel and sand originated from the uplifting Apennines were abundantly supplied to the deep-water basin through a series of erosional conduits that, in the rock record, appear as a series of N-S oriented slope submarine canyon systems deeply incised into the hemipelagic mudstones of the adjacent slope. The studied exposure allows direct observation of spatial and temporal relationships among the various depositional elements comprising the canyon system and related lithofacies, as well as the bed-perpendicular joint density within each lithofacies. We performed a multidisciplinary work involving the following tasks: (i) 3D stratigraphic model of the depositional architecture of the Castignano and Ascensione canyon systems (Marche region, Italy); (ii) 2D scanline survey of several outcrops displaying bed-perpendicular joints; (iii) digital image analysis of selected thin-section obtained from oriented hand samples to characterize the 3D intergranualr porosity; (iv) Stiffness analysis of representative sandstone bodies by mean of Schmidt hammer tests. The first results of this ongoing study on the mechanical stratigraphy of the two Late Pliocene canyon systems are consistent with the joint density being effected by both geometrical (i.e., bed thickness) and mechanical properties. This data set will help field and experimental geologists to better define common strategies to assess the controlling

  4. Lower Paleozoic Continuity of the East Gondwanan Margin and Implications for Interpretation of Tectonostratigraphic Zones of the Himalaya

    NASA Astrophysics Data System (ADS)

    Myrow, P.; Hughes, N.; Fanning, C. M.; Banerjee, D.; Dipietro, J. A.

    2009-12-01

    .7-0.54 Ga, and ~ 0.5 Ga peaks. New detrital zircon age data are presented for three Cambrian deposits: (1) the Tethyan Cambrian Tanawal Formation from the Peshwar Basin, Pakistan, north of the P-K Fault (=MCT), (2) cratonic Indian strata of the Tunklian Sandstone of Rajasthan, and (3) the Quartzite Formation of the Pele La Group of the Black Mountains of Bhutan. The detrital age spectra of these samples match those from Cambrian deposits across the central Himalaya. Thus, these new detrital spectra, in combination with stratigraphic data, demonstrate the continuity of lowermost Paleozoic strata along and across the Himalaya. Such continuity requires similar stratigraphic architecture in the LH, TH, and Greater Himalaya prior to Cenezoic deformation, and requires considerable removal of Neoproterozoic through Cambrian strata from the Lesser Himalaya during Himalayan uplift.

  5. Diagenesis of the Almond sandstone in the Washakie Basin

    SciTech Connect

    Yin, Peigui; Liu, Jie; Surdam, C.R. . Dept. of Geology and Geophysics)

    1992-01-01

    The marginal marine and nonmarine Almond sandstones are mostly sublitharenite, litharenite, and lithic arkose. The sandstones are fine-to very-fine-grained, and are well-sorted. The framework composition, authigenic minerals, and porosity and permeability distributions in the Almond sandstones are different below and above 8,000 feet, resulting in a variation in hydrocarbon reservoir types. The shallow conventional reservoirs are permeable, producing both liquid oil and gas, whereas the deep gas-bearing sandstones are very tight and overpressured. Porosity of the shallow Almond sandstones have been significantly enhanced by dissolution of the feldspar grains and lithic fragments. Quartz overgrowth cement and authigenic clay rims have occluded most of the intergranular pores, as well as the previously leached pores. The Almond sandstones have been buried deeper than their present depths. The sandstones in each part of the Washakie Basin have experienced different uplift and subsidence. Reconstruction of the burial history and diagenetic modeling are essential steps for understanding the diagenetic evolution of the Almond sandstones.

  6. A sequence stratigraphic study of the Tangaroa Sandstone, Taranaki Basin, New Zealand

    SciTech Connect

    Gresko, M.D.; Jordan, D.W.; Thompson, P.R. )

    1990-05-01

    Seismic sequence interpretation of the Tangaroa Sandstone, combined with detailed biostratigraphic analysis, well log interpretation, and core descriptions, confirm the Tangaroa as a late Eocene-early Oligocene, sand-rich, submarine fan complex within the Taranaki basin of northwest New Zealand. The Tangaroa Sandstone is underlain by deep-water shales (Eocene Kaiata Formation) and overlain by a thick deep-water limestone (Oligocene Te Kuiti Formation), and typically consists of two, 25-150-m-thick vertically stacked sandstones, separated by a thin (8 m) limestone. Seismic isochron thickness maps of the Tangaroa interval display a fan-shaped geometry. Internal seismic facies are dominated by erosional channels and progradational wedges. The erosional channels, to 1-5 km wide and approximately 70-150 m thick, are interpreted as upper to mid-fan feeder channels. Thin progradational wedges are located basinward of the channels. Paleobathymetic data, based on micropaleontology, indicate a shelf-to-deep-water genesis of the Tangaroa. Conventional core data suggest that the Tangaroa comprises fine- to coarse-grained clastics that were deposited by debris flows, liquefied flows, and turbidites. Using seismic sequence techniques, verified by biostratigraphic control, the Tangaroa Sandstone is subdivided into two sequences: the Lower Tangaroa sequence and the Upper Tangaroa sequence, which formed during two distinct relative lowstands in sea level. The intervening limestone and the overlying Te Kuiti Limestone, apparently were deposited during periods of relative highstands in sea level. The Eocene Oligocene boundary is located in the thin limestone of the Lower Tangaroa sequence.

  7. SHRIMP zircon U-Pb dating of the Paleozoic granitoids in the Khovd province, western Mongolia

    NASA Astrophysics Data System (ADS)

    Oyungerel, S.; Lee, I.; Munkhbat, N.

    2013-12-01

    The different composition magmatic rocks are widely distributed on the territory of Mongolia and they have been formed during a long period since the Proterozoic until the Cenozoic magmatic activities. Especially, Paleozoic magmatism manifested in the west, northwestern, north, center, south, southeastern part of Mongolia, as the different shapes intrusive bodies. Five samples were collected from two complexes in the Khovd province which is located in the western part of Mongolia. Zircons for the SHRIMP geochronology were separated from one granodiorite (115) sample of the Togtokh's shil and four different phases' granite samples (1, 039, 068, and 085) of the Khovd intrusive complexes. Zircons from all samples are colorless, transparent to untransparent, and subhedral to euhedral, stubby or equant and prismatic to elongate in shape. Most of the zircon Th/U ratios are mostly bigger than 0.3, indicating it is of magmatic origin. SHRIMP U-Pb dating of magmatic zircons from a granodiorite (115) has yielded a concordant 206Pb/238U age of 488.5×4.1Ma which is corresponding to the Late (Furongian) Cambrian. Zircons from the Khovd complex intrusions indicate different SHRIMP U-Pb ages: The best estimate of the crystallization age of sample 1, based on the weighted mean 206Pb/238U ratio is 465.5×4.6Ma. It's corresponding to the Middle Ordovician. Two zircons from the sample 1 indicate largely different SHRIMP U-Pb ages: 204×3 Ma and 218×2Ma (Late Triassic). It will indicate that the sample is contaminated or small dyke series and pegmatite veins included here. The majority of zircons in sample 1 have dark CL images. The reason of this darkness related to REEs. Dy3+ is considered to be the principal elemental factor, although other constituents such as Sm3+, Eu2+ and Tb3+ may also be CL emitters in zircon. A total of 15 spot analyses were made on twelve zircons of sample 039 and one of them was rejected and yields a weighted mean 206Pb/238U age of 398.8×2.8Ma which

  8. Brittle and compaction creep in porous sandstone

    NASA Astrophysics Data System (ADS)

    Heap, Michael; Brantut, Nicolas; Baud, Patrick; Meredith, Philip

    2015-04-01

    Strain localisation in the Earth's crust occurs at all scales, from the fracture of grains at the microscale to crustal-scale faulting. Over the last fifty years, laboratory rock deformation studies have exposed the variety of deformation mechanisms and failure modes of rock. Broadly speaking, rock failure can be described as either dilatant (brittle) or compactive. While dilatant failure in porous sandstones is manifest as shear fracturing, their failure in the compactant regime can be characterised by either distributed cataclastic flow or the formation of localised compaction bands. To better understand the time-dependency of strain localisation (shear fracturing and compaction band growth), we performed triaxial deformation experiments on water-saturated Bleurswiller sandstone (porosity = 24%) under a constant stress (creep) in the dilatant and compactive regimes, with particular focus on time-dependent compaction band formation in the compactive regime. Our experiments show that inelastic strain accumulates at a constant stress in the brittle and compactive regimes leading to the development of shear fractures and compaction bands, respectively. While creep in the dilatant regime is characterised by an increase in porosity and, ultimately, an acceleration in axial strain to shear failure (as observed in previous studies), compaction creep is characterised by a reduction in porosity and a gradual deceleration in axial strain. The overall deceleration in axial strain, AE activity, and porosity change during creep compaction is punctuated by excursions interpreted as the formation of compaction bands. The growth rate of compaction bands formed during creep is lower as the applied differential stress, and hence background creep strain rate, is decreased, although the inelastic strain required for a compaction band remains constant over strain rates spanning several orders of magnitude. We find that, despite the large differences in strain rate and growth rate

  9. Autocyclic progradation and allocyclic ravinement of a shoreface: Sedimentology and sequence stratigraphy of the Panther Sandstone Tongue (Upper Cretaceous, Campanian), Wasatch plateau, Utah, U. S. A

    SciTech Connect

    Krause, F.F.; Aitken, S.A.; Braunberger, W.F.; Chung, P.; Macrae, A.; Meyer, R.O.; Nunez-Betelu, L.; Williams, C.A.; Hol, H.M. )

    1993-04-01

    The Panther Sandstone Tongue of the Star Point Formation exposed in the vicinity of Helper, Utah reflects a coarse-grained, clastic wedge that penetrated the Mancos Shale basin in Early Campanian (Late Cretaceous) time. Panther Sandstone rocks may be grouped into six lithofacies: (1) thin-bedded, bioturbated and rippled, mudstone and very fine-grained sandstone; (2) thin- to medium-bedded, bioturbated, rippled and parallel laminated, mudstone and very fine-grained sandstone; (3) thick- to very thick-bedded HCS and parallel-laminated, mudstone and fine- to medium-grained sandstone; (4) medium- to thick-bedded, Ophiomorpha bioturbated, medium- to coarse-grained sandstone; (5) medium- to very-thick bedded, current bedded and hydroplasticly deformed sandstone, and (6) medium- to thick-bedded, trough cross-stratified and bundle-laminated, fine grained sandstone. Lithofacies are arranged in definable vertical and lateral successions. L. 1, 2 and 3 are upward coarsening and shoaling and are common in the Helper area. L. 5 and 6 are common to the west. L. 4 is a transgressive and ravinement lag that rests on all other lithofacies. Interpreted environments reflect a storm modified, microtidal, strandplain system. Rocks, except L. 4, are contained in a parasequence system that built into the basin during relative sea-level fall. This system prograded episodically suggesting varying sediment supply and event-controlled sediment reworking -- responses associated with autocyclic forcing. In contrast, ravinement decapitated the parasequence intersecting progressively shallower lithofacies. These responses suggest that ravinement was driven by allocyclic forcing, perhaps in response to tectonism in the foreland.

  10. Dilatant hardening of fluid-saturated sandstone

    NASA Astrophysics Data System (ADS)

    Makhnenko, Roman Y.; Labuz, Joseph F.

    2015-02-01

    The presence of pore fluid in rock affects both the elastic and inelastic deformation processes, yet laboratory testing is typically performed on dry material even though in situ the rock is often saturated. Techniques were developed for testing fluid-saturated porous rock under the limiting conditions of drained, undrained, and unjacketed response. Confined compression experiments, both conventional triaxial and plane strain, were performed on water-saturated Berea sandstone to investigate poroelastic and inelastic behavior. Measured drained response was used to calibrate an elasto-plastic constitutive model that predicts undrained inelastic deformation. The experimental data show good agreement with the model: dilatant hardening in undrained triaxial and plane strain compression tests under constant mean stress was predicted and observed.

  11. The Paleozoic Dust Bowl: Dust Deposition in Tropical Western Pangaea (Midcontinent U.S.) at the Terminus of the Late Paleozoic Ice Age

    NASA Astrophysics Data System (ADS)

    Soreghan, G. S.; Heavens, N. G.; Benison, K. C.; Soreghan, M. J.; Mahowald, N. M.; Foster, T.; Zambito, J.; Sweet, A.; Kane, M.

    2012-12-01

    Atmospheric dust is well recognized and studied as both an archive and agent of climate change in Earth's relatively recent past. Archives of past dust include loess deposits and dust recovered from ocean- and ice-cores. Dust remains poorly known in Earth's past prior to the Cenozoic, but is increasingly recognized in the form of paleo-loess deposits, and (epeiric) marine strata that accumulated isolated from fluvio-deltaic influx. Here, we report on the growing recognition of voluminous dust deposits preserved in the Permian record of the U.S. Midcontinent (western tropical Pangaea). Fine-grained redbeds predominate in Permian strata throughout the U.S. Midcontinent, but notably in a swath extending from Oklahoma through South Dakota. These units consist predominantly of red mudstone and siltstone in commonly massive units, but sedimentary structures and bedding that signal aqueous processes (e.g. laminations, ripples) have led most to infer deltaic or tidal deposition. The absence of channel systems to deliver the sediment, as well as the predominantly massive and laterally continuous character and the uniform fine grain size signal wind transport, implying that these units record sustained dust deposition overprinted at times by sub-aqueous deposition in lakes, including ephemeral saline and acid lakes that led to evaporite cementation. Detrital zircon geochronology indicates that much of the dust originated in the relatively distant Appalachian-Ouachita orogenic systems, which formed part of the central Pangaean mountains (CPM), the collisional zone that sutured the supercontinent. Within the Anadarko basin of Oklahoma, Permian redbeds record >2 km of predominantly dust deposition, some of the thickest dust deposits yet documented in Earth's record. Yet the tropical setting is remarkably non-uniformitarian, as much Quaternary loess occurs in mid- to high-latitude regions, commonly linked to glacial genesis. We are currently investigating with both data and modeling possible causes and consequences of this massive dust record, which may include (1) partial glacial genesis in the CPM, (2) the action of the Pangaean mega-monsoon, and (3) particularly effective dust traps in the Midcontinent region. Modeling constrains the erosivity (the effect of winds and soil moisture effects) of a range of possible climate states on dust mobilization and underscores the relative difficulty of sourcing dust directly from the Appalachian-Ouachita orogenic system under most circumstances. Combining data and modeling helps constrain the erodibility (sediment availability, coherence, etc.) of dust sources. Reconstructions of marine dust deposition to the south and the west of the Anadarko basin suggest glacial-interglacial timescale erodibility changes were similar to those seen in the Midcontinent in the last 20,000 years, when it was at a much higher latitude.

  12. U-Pb zircon geochronology of Paleozoic units in Western and Central Guatemala: insights into the tectonic evolution of Middle America

    NASA Astrophysics Data System (ADS)

    Solari, L. A.; Ortega-Gutierrez, F.; Elias-Herrera, M.; Schaaf, P.; Norman, M.; Torres de Leon, R.; Ortega-Obregon, C.; Moran Ical, S.; Chiquin, M.

    2007-05-01

    Precambrian and Paleozoic basements are present in southern Mexico and Central America, where several crustal blocks are recognized by their different geologic record, and juxtaposed along lateral faults. Some of those crustal blocks are currently located between southernmost north America (the Maya block) and Central America (Chortis block).To better understand the geology of these crustal blocks, and to establish comparisons between their geologic history, U-Pb ages of both igneous and metasedimentary key units cropping out in central and western Guatemala are presented here. In the Altos Cuchumatanes (Maya block) granites yield both Permian (269 +/- 29 Ma) and Early Devonian (391 +/- 7.4 Ma) U-Pb ages. LA-ICPMS detrital zircon ages from rocks of the San Gabriel sequence, interpreted as the oldest metasedimentary unit of the Maya block, and overlain by the Late Paleozoic Upper Santa Rosa Group, yield Precambrian detrital zircons bracketed between 920 Ma and 1,000 Ma. The presence of these metasedimentary units, as well as Early Devonian to Silurian granites in the Mayan continental margin, from west (Altos Cuchumatanes), to east (Maya Mountains of Belize) indicate a more or less continuous belt of Lower Paleozoic igneous activity, also suggesting that the continental margin of the Maya block can be extended south of the Polochic fault, up to the Baja Verapaz shear zone. A metasedimentary sample belonging to the Chuacus Complex yielded detrital zircons with ages between 440 Ma and 1,325 Ma. The younger ages are similar to the igneous ages reported from the entire southern Maya continental margin, and show proximity of the Complex in the Middle-Late Palaeozoic. The S. Diego Phyllite, which overlies high-grade basement units of the Chortis block, contains zircons that are Lower Cambrian (538 Ma), Mesoproterozoic (980 to 1,150 Ma) and even Paleoproterozoic (1,820 Ma). Absence of younger igneous zircons in the San Diego Phyllite indicates that either its sedimentation

  13. Attenuation of Landfill Leachate In Unsaturated Sandstone

    NASA Astrophysics Data System (ADS)

    Butler, A. P.; Brook, C.; Godley, A.; Lewin, K.; Young, C. P.

    Landfill leachate emanating from old "dilute and disperse" sites represents a potential (and in many cases actual) threat to the integrity of groundwater. Indeed, this concern has been included in EU legislation (80/86/EEC), where key contaminants (e.g. ammonia, various toxic organic compounds and heavy metals) are explicitly highlighted in terms of their impact on groundwater. In the UK, whilst there are a substantial number of unlined landfills sited on major aquifers, many of these are in locations where there is a substantial unsaturated zone. Thus, there exists the opportunity for the modification and attenuation of contaminants prior to it encountering the water table. An understanding of likely changes in leachate content and concentrations at such sites will enable a more comprehensive assessment of the potential risks and liabilities posed by such sites to be evaluated. The Burntstump landfill, situated 8 km north of Nottingham (UK), is sited on an outcrop of Sherwood sandstone. The fine friable sand has been quarried since the 1960s and the excavated volume used to store municipal waste. Filling at the site commenced in the mid 1970s and originally was unlined. In 1978 the first of what was to become a series of boreholes was installed within an area of roughly 5 m radius over one of the original waste cells. Cores of the waste and underlying sandstone were extracted and analysed for a range of physical and chemical parameters. The most recent set of analyses were obtained in 2000. The series of investigations therefore provide an important record of leachate migration and modification through the unsaturated zone for over twenty years. The progression of the leachate front is clearly delineated by the chloride concentration profile with an average velocity of around 1.6 m.yr-1. Combining this value with an average (and reasonably uniform) measured moisture content of about 7% gives a mean inter-granular specific discharge of 110 mm.yr-1. An interesting

  14. Early-Middle Paleozoic subduction-collision history of the south-eastern Central Asian Orogenic Belt: Evidence from igneous and metasedimentary rocks of central Jilin Province, NE China

    NASA Astrophysics Data System (ADS)

    Pei, Fu-Ping; Zhang, Ying; Wang, Zhi-Wei; Cao, Hua-Hua; Xu, Wen-Liang; Wang, Zi-Jin; Wang, Feng; Yang, Chuan

    2016-09-01

    To constrain the Early-Middle Paleozoic tectonic evolution of the south-eastern segment of the Central Asian Orogenic Belt (CAOB), we undertook zircon U-Pb dating and analyzed major and trace elements and zircon Hf isotope compositions of Late Cambrian to Middle Devonian igneous and metasedimentary rocks in central Jilin Province, NE China. LA-ICP-MS zircon U-Pb dating indicates that the Early-Middle Paleozoic magmatism in central Jilin Province can be divided into four episodes: Late Cambrian (ca. 493 Ma), Middle Ordovician (ca. 467 Ma), Late Ordovician-Early Silurian (ca. 443 Ma), and Late Silurian-Middle Devonian (425-396 Ma). The progression from subduction initiation to maturity is recorded by Late Cambrian low-K tholeiitic meta-diabase, Middle Ordovician medium-K calc-alkaline pyroxene andesite, and Late Ordovician to Early Silurian low-K tonalite, which all have subduction-related characteristics and formed in an evolving supra-subduction zone setting. Late Silurian to Middle Devonian calc-alkaline igneous rocks, with the lithological association of granodiorite, monzogranite, rhyolite, dacite, and trachydacite, show progressively increasing K2O contents from medium K to shoshonite series. Furthermore, the Early-Middle Devonian monzogranites are characterized by high K2O, Sr/Y, and [La/Yb]N values, indicating they were generated by the melting of thickened lower crust. These results suggest a transition from subduction to post-orogenic setting during the Late Silurian-Middle Devonian. Our interpretation is supported by the maximum age of molasse deposition in the Zhangjiatun member of the Xibiehe Formation. Overall, we suggest that Late Cambrian tholeiitic meta-diabase, Middle Ordovician pyroxene andesite, and Late Ordovician-Early Silurian tonalite formed above the northward-subducting and simultaneously seaward-retreating of Paleo-Asian Ocean plate. Subsequently, the northern arc collided with the North China Craton and post-orogenic extension occurred

  15. From Gondwana to Europe: the journey of Elba Island (Italy) as recorded by U-Pb detrital zircon ages of Paleozoic metasedimentary rocks

    NASA Astrophysics Data System (ADS)

    Jacobs, Joachim; Sirevaag, Hallgeir; Ksienzyk, Anna K.; Rocchi, Sergio; Paoli, Gabriele

    2016-04-01

    The configuration of the northern Gondwana margin throughout the Paleozoic is difficult to reconstruct owing to the complex geodynamic setting of the Mediterranean region in Mesozoic to Cenozoic times. Detrital zircons in early Paleozoic to early Mesozoic metasedimentary rocks on Elba and mainland Tuscany record the Gondwana provenance of Adria and its rifting from the northern Gondwana margin. A large new LA-ICP-MS and SIMS U-Pb zircon data set allows us to trace this history. Three main stratigraphic units have been investigated on Elba Island. The oldest Porto Azzurro Unit was deposited in the early Cambrian and has zircon age distributions indicating a typical northern African provenance, most likely sourced from the Saharan Metacraton. The Ortano Unit has a simple, mostly unimodal Ordovician age distribution that is entirely dominated by metavolcanic rocks and their erosional products; a sample of the metavolcanic Ortano Porphyroids provided a SIMS U-Pb zircon age of 460 ± 3 Ma. This phase of intense volcanism is related to the subduction of the Rheic Ocean beneath Gondwana, terminating with initial rifting and subsequent opening of the Paleotethys. This also marks the onset of the separation of a range of European terranes, including Adria and future Elba Island, from Gondwana. The Permo-Triassic Monticiano-Roccastrada Unit is the first to show a European provenance with the appearance of large amounts of Variscan and late to post-Variscan detritus. The presence of Variscan detrital zircons in the Permo-Triassic sediments is unexpected, since a Variscan age signature is so far not well recorded in the Adria Plate. This dataset is the most comprehensive detrital zircon data set so far available for the Adria Plate and documents Adria's close affinity to Africa in the Lower Paleozoic, as well as its initial rifting within an active continental margin setting during the Ordovician and its final separation and independent evolution since late Palaeozoic times.

  16. The E-MORB like geochemical features of the Early Paleozoic mafic-ultramafic belt of the Cuyania terrane, western Argentina

    NASA Astrophysics Data System (ADS)

    Boedo, F. L.; Vujovich, G. I.; Kay, S. M.; Ariza, J. P.; Pérez Luján, S. B.

    2013-12-01

    The Argentine Precordillera is located in the central western region of Argentina, within the Central Andes. Throughout its westernmost sector, mafic and ultramafic bodies including serpentinites, mafic granulites, basaltic dikes/sills and pillow lavas are associated with metasedimentary rocks deposited in a deep marine and slope environment. These magmatic units, which are known as the Precordillera ultramafic-mafic belt, are considered to have a range of Early Paleozoic age based on published U-Pb zircon ages and fossil fauna. The entire sequence shows the effects of complex polyphase Paleozoic deformation and was subjected to a low grade metamorphism considered to be of middle-late Devonian age. The chemistry of the Peñasco and Cortaderas mafic dikes and sills in the southern part of this belt, which are largely plagioclase + clinopyroxene-bearing tholeiitic basalts, is the focus of this study. These volcanic rocks all have E-MORB-like major and trace element and ɛNd (+6.0 to +9.3) signatures with similarities to those previously reported throughout the belt. The new descriptions and major and trace-element analyses presented here confirm the similarity of the E-MORB-like chemistry of the Early Paleozoic mafic rocks along the entire belt, which spans some 500 km in length. There is a general consensus that these units are exposed as a consequence of the collision of the Chilenia terrane against the Gondwana margin during the middle to late Devonian, but the details of timing, the origins of the continental blocks and the nature of the collision are still debated. The results presented support the western Precordillera basaltic dikes/sills as having formed in the early stages of oceanic rifting along the Gondwana (Precordillera) continental margin with their E-MORB-like character reflecting mixing of depleted and enriched mantle and continental lithospheric sources.

  17. Assessment of Paleozoic shale gas resources in the Sichuan Basin of China, 2015

    USGS Publications Warehouse

    Potter, Christopher J.; Schenk, Christopher J.; Charpentier, Ronald R.; Gaswirth, Stephanie B.; Klett, Timothy R.; Leathers, Heidi M.; Brownfield, Michael E.; Mercier, Tracey J.; Tennyson, Marilyn E.; Pitman, Janet K.

    2015-10-14

    Using a geology-based assessment methodology, the U.S. Geological Survey estimated a mean of 23.9 trillion cubic feet of technically recoverable shale gas resources in Paleozoic formations in the Sichuan Basin of China.

  18. Assessment of Paleozoic shale gas resources in the Sichuan Basin of China, 2015

    USGS Publications Warehouse

    Potter, Christopher J.; Schenk, Christopher J.; Charpentier, Ronald R.; Gaswirth, Stephanie B.; Klett, Timothy R.; Leathers, Heidi M.; Brownfield, Michael E.; Mercier, Tracey J.; Tennyson, Marilyn E.; Pitman, Janet K.

    2015-01-01

    Using a geology-based assessment methodology, the U.S. Geological Survey estimated a mean of 23.9 trillion cubic feet of technically recoverable shale gas resources in Paleozoic formations in the Sichuan Basin of China.

  19. Lithology, hydraulic properties, and water quality of the Sandstone Aquifer in the northwestern part of the Bad River Indian Reservation, Wisconsin, 1998-1999

    USGS Publications Warehouse

    Dunning, Charles P.

    2005-01-01

    The Precambrian sandstone aquifer in the northwestern part of the Bad River Band of Lake Superior Tribe of Chippewa Indians Reservation, Ashland County, Wisconsin, provides much of the drinking water to area residents. A study was undertaken in cooperation with the Bad River Tribe to provide specific information about the lithology, hydraulic properties, and water quality of the sandstone aquifer. During 1998 and 1999, the U.S. Geological Survey installed three monitoring wells, collected and analyzed lithologic and water samples, and conducted geophysical logging and aquifer tests to characterize the sandstone aquifer. The two monitoring wells in the southeastern part of the study area, the Diaperville Monitoring Well #1 (Diaperville MW #1) and the Tolman Monitoring Well #1 (Tolman MW #1) , are believed to have encountered older Middle Proterozoic Oronto Group sandstones. The sandstone encountered in the Ackley Monitoring Well #1 (Ackley MW #1) is believed to be Chequamegon Sandstone of the Late Proterozoic Bayfield Group. This interpretation is based on previous studies, as well as thin- section analysis of sandstone core recovered from the Ackley Monitoring Well #1. Results of aquifer tests conducted in the Diaperville Monitoring Well #1 and the Tolman Monitoring Well #1 provide ranges for hydraulic param - eter values in the sandstone aquifer: transmissivity ranges from 83 to 509 square feet per day; hydraulic conductivity ranges from 1.6 to 4.5 feet per day; storativity ranges from 0.00019 to 0.00046; and specific capacity ranges from 0.22 to 0.67 gallons per minute per foot. Though high- and low-angle fractures are present in Ackley Monitoring Well #1 core, the hydraulic properties of the bedrock appear to be due largely to the matrix porosity measured in thin section (16–21 percent) and permeability of the sandstone. The aquifer test for the Diaperville Monitoring Well #1 resulted in observed drawdown in nearby glacial wells, evidence of a hydraulic

  20. Regional diagenetic patterns in the St. Peter Sandstone; implications for brine migration in the Illinois Basin

    USGS Publications Warehouse

    Pitman, Janet K.; Goldhaber, Martin B.; Spoetl, Christoph

    1997-01-01

    Diagenetic minerals and alteration patterns in the Ordovician St. Peter Sandstone, Illinois Basin, record varied hydrologic and chemical conditions during the basin?s long and complex geologic history. Major diagenetic events modifying the St. Peter Sandstone include (1) mechanical compaction, (2) early K-feldspar overgrowth and dolospar precipitation, (3) burial quartz, dolospar, anhydrite, and calcite cementation, and (4) carbonate-cement and K-feldspar grain dissolution. Radiometric age dates of authigenic K-feldspar and illite in combination with the reconstructed burial history of the St. Peter reveal that early-diagenetic K-feldspar and dolospar precipitated at shallow to moderate depths in the Devonian, whereas late-diagenetic quartz, dolospar, anhydrite, and calcite formed during deep burial in the Late Pennsylvanian to Early Permian. Stable-isotope geochemistry and fluid-inclusion paleothermometry suggest that burial cements precipitated from saline fluids over a wide temperature range. In the southern part of the basin, burial cements preserve a record of diagenetic effects that were in part controlled by fractures and hydrothermal-fluid circulation. Baroque dolospar cementation is the most significant of these effects.

  1. 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.

    2016-01-01

    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.

  2. Sodium-hydroxide solution treatment on sandstone cores

    SciTech Connect

    Lee, S.J.

    1984-01-01

    This research was performed to study the effect of sodium hydroxide solution on the sandstone core samples and to develop a method whereby the permeability of the samples could be increased by the injection of sodium hydroxide solution. This work should provide the first step in developing a technique that can be used in the stimulation of oil and gas wells. A series of tests was conducted in which sodium hydroxide solution with concentrations ranging from 0.25 N to 2.00 N was injected into a number of Berea sandstone cores. The tests were conducted at room temperature and at 180{degree}F. In some cases the core sample were damaged by the injection of fresh water which resulted in a marked reduction in the permeability of the cores prior to the injection of sodium hydroxide solution. Based on laboratory testing with measurements of uniaxial compressive strength, SEM examination and X-ray analysis, it was found that sodium hydroxide interacted with sandstone to promote (1) partial dissolution of the sandstone minerals; (2) sandstone weight loss; (3) increased porosity; (4) weakening of the sandstone cores; and (5) changes in permeability. The interaction increased with increasing temperature and increasing sodium hydroxide concentration. However, at concentrations higher than 1.00 N, the degree of increase in permeability was not as large even though the sandstone weight loss and the increase in porosity did increase.

  3. Paleogeographic significance of Clavohamulus hintzei Miller (Conodonta) and other Ibexian conodonts in an early Paleozoic carbonate platform facies of the Argentine Precordillera

    USGS Publications Warehouse

    Lehnert, O.; Miller, J.F.; Repetski, J.E.

    1997-01-01

    Pre-Tremadocian conodonts and trilobites and Tremadocian conodonts are reported from the Cambrian and Ordovician La Silla Formation in the Cerro La Silla section in east-southeast Ja??chal, San Juan Province, Argentina. A shallow marine conodont fauna contains elements of Clavohamulus hintzei Miller, a common species in North America, but reported for the first time from the early Paleozoic platform carbonates of the western Argentine Precordillera. The presence of this species suggests a correlation with the Clavohamulus hintzei conodont subbiozone of the Cordylodus intermedius conodont biozone in North America, considered Early Ordovician (Skullrockian Stage, Ibexian Series) in North America, but by South American and European standards, this biozone would be of latest Cambrian age. C. hintzei and associated conodonts of the La Silla Formation are typical of the tropical faunas of the North American Midcontinent Faunal Province; Late Cambrian trilobites from lower in the formation also are typical North American taxa. The presence of these faunas in the platform carbonates is consistent with plate reconstructions suggesting that the Precordillera was in a tropical or subtropical position close to Laurentia during the late Precambrian and early Paleozoic. These new paleontological data provide one more argument for recent models of the Precordillera as a displaced terrane derived from the Ouachita Embayment at the southern margin of Laurentia.

  4. Competitive displacement among post-Paleozoic cyclostome and cheilostome bryozoans

    NASA Technical Reports Server (NTRS)

    Sepkoski, J. J. Jr; McKinney, F. K.; Lidgard, S.; Sepkoski JJ, J. r. (Principal Investigator)

    2000-01-01

    Encrusting bryozoans provide one of the few systems in the fossil record in which ecological competition can be observed directly at local scales. The macroevolutionary history of diversity of cyclostome and cheilostome bryozoans is consistent with a coupled-logistic model of clade displacement predicated on species within clades interacting competitively. The model matches observed diversity history if the model is perturbed by a mass extinction with a position and magnitude analogous to the Cretaceous/Tertiary boundary event, Although it is difficult to measure all parameters in the model from fossil data, critical factors are intrinsic rates of extinction, which can be measured. Cyclostomes maintained a rather low rate of extinction, and the model solutions predict that they would lose diversity only slowly as competitively superior species of cheilostomes diversified into their environment. Thus, the microecological record of preserved competitive interactions between cyclostome and cheilostome bryozoans and the macroevolutionary record of global diversity are consistent in regard to competition as a significant influence on diversity histories of post-Paleozoic bryozoans.

  5. Paleozoic origin of insect large dsDNA viruses.

    PubMed

    Thézé, Julien; Bézier, Annie; Periquet, Georges; Drezen, Jean-Michel; Herniou, Elisabeth A

    2011-09-20

    To understand how extant viruses interact with their hosts, we need a historical framework of their evolutionary association. Akin to retrovirus or hepadnavirus viral fossils present in eukaryotic genomes, bracoviruses are integrated in braconid wasp genomes and are transmitted by Mendelian inheritance. However, unlike viral genomic fossils, they have retained functional machineries homologous to those of large dsDNA viruses pathogenic to arthropods. Using a phylogenomic approach, we resolved the relationships between bracoviruses and their closest free relatives: baculoviruses and nudiviruses. The phylogeny showed that bracoviruses are nested within the nudivirus clade. Bracoviruses establish a bridge between the virus and animal worlds. Their inclusion in a virus phylogeny allowed us to relate free viruses to fossils. The ages of the wasps were used to calibrate the virus phylogeny. Bayesian analyses revealed that insect dsDNA viruses first evolved at ∼310 Mya in the Paleozoic Era during the Carboniferous Period with the first insects. Furthermore the virus diversification time frame during the Mesozoic Era appears linked to the diversification of insect orders; baculoviruses that infect larvae evolved at the same period as holometabolous insects. These results imply ancient coevolution by resource tracking between several insect dsDNA virus families and their hosts, dating back to 310 Mya.

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

    SciTech Connect

    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 large 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.

  7. Provenance discrimination of Paleozoic mudstones within a contact metamorphic aureole determined by REE, Th, and Sc analyses, Sierra Nevada, California

    SciTech Connect

    Yoshinobu, A.S.; Hanson, A.D.; Girty, G.H. . Dept. of Geological Sciences); Knaack, C.; Johnson, D. . Dept. of Geology)

    1993-04-01

    REE, Th, and Sc analyses of samples collected from the Lower Paleozoic Shoo Fly Complex (SFC), northern Sierra terrane, support the hypothesis that the structurally lowest portion of the SFC (i.e., the Lang, Black Oak Spring, and Zion Hill sequences) is primarily composed of continentally derived detritus. Fifteen samples collected from mudstones in and adjacent to the contact aureole of the Middle Jurassic Emigrant Gap composite pluton vary in metamorphic grade from chlorite [+-] white mica slaty argillites outside of the aureole to K-feldspar [+-] sillimanite phyllitic schists adjacent to the pluton. On chondrite-normalized REE distribution diagrams, the samples exhibit (1) no systematic change as a result of increasing contact metamorphic grade, (2) LREE enrichment trends, and (3) Eu anomalies ranging from 0.46 to 0.93, and averaging 0.66. These REE characteristics are like those documented for passive margin turbidites and Post Archean Average Shale (PAAS), and suggest that contact metamorphism did not significantly alter REE distribution. On a La-Th-Sc ternary diagram the authors data cluster in the fields of passive continental margin and PAAS. The average Th/U ratio is 8.8 which strongly implies a recycled and/or weathered source. These new data, coupled with the quartz-rich nature of interbedded sandstones, the absence of volcanic material, and previously determined Precambrian detrital zircon ages suggest that clastic detritus within the Lang, Black Oak Spring, and Zion Hill sequences was derived form a cratonal source which may have been the North American continent.

  8. An alternative hypothesis for the mid-Paleozoic Antler orogeny in Nevada

    USGS Publications Warehouse

    Ketner, Keith B.

    2012-01-01

    A great volume of Mississippian orogenic deposits supports the concept of a mid-Paleozoic orogeny in Nevada, and the existence and timing of that event are not questioned here. The nature of the orogeny is problematic, however, and new ideas are called for. The cause of the Antler orogeny, long ascribed to plate convergence, is here attributed to left-lateral north-south strike-slip faulting in northwestern Nevada. The stratigraphic evidence originally provided in support of an associated regional thrust fault, the Roberts Mountains thrust, is now known to be invalid, and abundant, detailed map evidence testifies to post-Antler ages of virtually all large folds and thrust faults in the region. The Antler orogeny was not characterized by obduction of the Roberts Mountains allochthon; rocks composing the "allochthon" essentially were deposited in situ. Instead, the orogeny was characterized by appearance of an elongate north-northeast-trending uplift through central Nevada and by two parallel flanking depressions. The eastern depression was the Antler foreland trough, into which sediments flowed from both east and west in the Mississippian. The western depression was the Antler hinterland trough into which sediments also flowed from both east and west during the Mississippian. West of the hinterland trough, across a left-lateral strike-slip fault, an exotic landmass originally attached to the northwestern part of the North American continent was moved southward 1700 km along a strike-slip fault. An array of isolated blocks of shelf carbonate rocks, long thought to be autochthonous exposures in windows of the Roberts Mountains allochthon, is proposed here as an array of gravity-driven slide blocks dislodged from the shelf, probably initiated by the Late Devonian Alamo impact event.

  9. A two scale analysis of tight sandstones

    NASA Astrophysics Data System (ADS)

    Adler, P. M.; Davy, C. A.; Song, Y.; Troadec, D.; Hauss, G.; Skoczylas, F.

    2015-12-01

    Tight sandstones have a low porosity and a very small permeability K. Available models for K do not compare well with measurements. These sandstones are made of SiO_2 grains, with a typical size of several hundreds of micron. These grains are separated by a network of micro-cracks, with sizes ranging between microns down to tens of nm. Therefore, the structure can be schematized by Voronoi polyhedra separated by plane and permeable polygonal micro-cracks. Our goal is to estimate K based on a two scale analysis and to compare the results to measurements. For a particular sample [2], local measurements on several scales include FIB/SEM [3], CMT and 2D SEM. FIB/SEM is selected because the peak pore size given by Mercury Intrusion Porosimetry is of 350nm. FIB/SEM imaging (with 50 nm voxel size) identifies an individual crack of 180nm average opening, whereas CMT provides a connected porosity (individual crack) for 60 nm voxel size, of 4 micron average opening. Numerical modelling is performed by combining the micro-crack network scale (given by 2D SEM) and the 3D micro-crack scale (given by either FIB/SEM or CMT). Estimates of the micro-crack density are derived from 2D SEM trace maps by counting the intersections with scanlines, the surface density of traces, and the number of fracture intersections. K is deduced by using a semi empirical formula valid for identical, isotropic and uniformly distributed fractures [1]. This value is proportional to the micro-crack transmissivity sigma. Sigma is determined by solving the Stokes equation in the micro-cracks measured by FIB/SEM or CMT. K is obtained by combining the two previous results. Good correlation with measured values on centimetric plugs is found when using sigma from CMT data. The results are discussed and further research is proposed. [1] Adler et al, Fractured porous media, Oxford Univ. Press, 2012. [2] Duan et al, Int. J. Rock Mech. Mining Sci., 65, p75, 2014. [3] Song et al, Marine and Petroleum Eng., 65, p63

  10. 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

    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

  11. Misener sandstone - A complex cyclic sequence

    SciTech Connect

    Shelton, J.W.; Fritz, R.D.; Kuykendall, M.; Hooker, E. )

    1989-08-01

    The Misener sandstone is part of two major transgressive/regressive episodes during the Devonian. The Misener is a prolific reservoir in Oklahoma but is one of the most difficult to predict due to its erratic distribution. Depositional environment, a key to understanding Misener distribution and ultimately reservoir geometry, is determined only by understanding the overall geological setting - petrography, unconformities, stratigraphy, paleogeography, and source. Analyses of composition, textures, and sedimentary features in cores and samples combined with detailed correlation and sequence stratigraphy provide a basic framework for determining Misener facies, which indicate deposition in a marine environment. Types of environment range from tidal ridge to estuarine to tidal flat. Many cores show an overall shallowing-upward Misener sequence and change from a terrigenous to a carbonate regime - from phosphatic sands upward to sandy dolomites. This sequence, compared with the regional configuration of the Woodford Shale, suggests that the Woodford developed in two cycles. The Misener section is genetically equivalent to the lower Woodford transgressive/regressive cycle. A paleogeographic model of the Mid-Continent during Misener deposition shows that with the pre-Woodford paleodrainage system, the most likely source for the Misener is from Simpson subcrops around the Ozark dome; the sand was transported and deposited by west-northwest-trending marine currents. A local model for the Misener is the Kremlin area where sand was deposited in erosional lows before carbonate deposition to form a sequence that reflects both shallowing and facies change.

  12. Salt and ice crystallisation in porous sandstones

    NASA Astrophysics Data System (ADS)

    Ruedrich, Joerg; Siegesmund, Siegfried

    2007-03-01

    Salt and ice crystallisation in the pore spaces causes major physical damage to natural building stones. The damaging effect of these processes can be traced back to physically induced stress inside of the rock while crystallizing. The increasing scientific research done during the past century has shown that there are numerous parameters that have an influence on the weathering resulting from these processes. However, the working mechanisms of the stress development within the rock and its material dependency are still subject to discussion. This article gives an overview of salt and ice weathering. Additionally, laboratory results of various sandstones examined are presented. Salt crystallisation tests and freeze/thaw tests were done to obtain information about how crystallisation weathering depends on material characteristics such as pore space, water transportation, and mechanical features. Simultaneous measuring of the length alternating during the salt and ice crystallisation has revealed detailed information on the development of crystal in the pore spaces as well as the development of stress. These findings can help to understand the damaging mechanisms.

  13. Permeability evolution in sandstone: Digital rock approach

    NASA Astrophysics Data System (ADS)

    Kameda, Ayako

    Permeability is perhaps one of the most important yet elusive reservoir properties, since it poorly correlates with elastic properties, and as a result, cannot be mapped remotely. Physical permeability measurements may be augmented or even partially replaced by numerical experiments, provided that a numerical simulation accurately mimics the physical process. Numerical simulation of laboratory experiments on rocks, or digital rock physics, is an emerging field that may benefit the petroleum industry. For numerical experimentation to find its way into the mainstream, it has to be practical and easily repeatable, i.e., implemented on standard hardware and in real time. This condition reduces the feasible size of a digital sample to just a few grains across. Will the results be meaningful for a larger rock volume? The answer is that small fragments of medium- to high-porosity sandstone, such as cuttings, which are not statistically representative of a larger sample, cannot be used to numerically calculate the exact porosity and permeability of the sample. However, by using a significant number of such small fragments, it may be possible to establish a site-specific permeability-porosity trend, which can be used to estimate the absolute permeability from independent porosity data, obtained in the well or inferred from seismic measurements.

  14. Pressure sensitivity of low permeability sandstones

    USGS Publications Warehouse

    Kilmer, N.H.; Morrow, N.R.; Pitman, J.K.

    1987-01-01

    Detailed core analysis has been carried out on 32 tight sandstones with permeabilities ranging over four orders of magnitude (0.0002 to 4.8 mD at 5000 psi confining pressure). Relationships between gas permeability and net confining pressure were measured for cycles of loading and unloading. For some samples, permeabilities were measured both along and across bedding planes. Large variations in stress sensitivity of permeability were observed from one sample to another. The ratio of permeability at a nominal confining pressure of 500 psi to that at 5000 psi was used to define a stress sensitivity ratio. For a given sample, confining pressure vs permeability followed a linear log-log relationship, the slope of which provided an index of pressure sensitivity. This index, as obtained for first unloading data, was used in testing relationships between stress sensitivity and other measured rock properties. Pressure sensitivity tended to increase with increase in carbonate content and depth, and with decrease in porosity, permeability and sodium feldspar. However, scatter in these relationships increased as permeability decreased. Tests for correlations between pressure sensitivity and various linear combinations of variables are reported. Details of pore structure related to diagenetic changes appears to be of much greater significance to pressure sensitivity than mineral composition. ?? 1987.

  15. Regional variations in provenance and abundance of ice-rafted clasts in Arctic Ocean sediments: Implications for the configuration of late Quaternary oceanic and atmospheric circulation in the Arctic

    USGS Publications Warehouse

    Phillips, R.L.; Grantz, A.

    2001-01-01

    The composition and distribution of ice-rafted glacial erratics in late Quaternary sediments define the major current systems of the Arctic Ocean and identify two distinct continental sources for the erratics. In the southern Amerasia basin up to 70% of the erratics are dolostones and limestones (the Amerasia suite) that originated in the carbonate-rich Paleozoic terranes of the Canadian Arctic Islands. These clasts reached the Arctic Ocean in glaciers and were ice-rafted to the core sites in the clockwise Beaufort Gyre. The concentration of erratics decreases northward by 98% along the trend of the gyre from southeastern Canada basin to Makarov basin. The concentration of erratics then triples across the Makarov basin flank of Lomonosov Ridge and siltstone, sandstone and siliceous clasts become dominant in cores from the ridge and the Eurasia basin (the Eurasia suite). The bedrock source for the siltstone and sandstone clasts is uncertain, but bedrock distribution and the distribution of glaciation in northern Eurasia suggest the Taymyr Peninsula-Kara Sea regions. The pattern of clast distribution in the Arctic Ocean sediments and the sharp northward decrease in concentration of clasts of Canadian Arctic Island provenance in the Amerasia basin support the conclusion that the modem circulation pattern of the Arctic Ocean, with the Beaufort Gyre dominant in the Amerasia basin and the Transpolar drift dominant in the Eurasia basin, has controlled both sea-ice and glacial iceberg drift in the Arctic Ocean during interglacial intervals since at least the late Pleistocene. The abruptness of the change in both clast composition and concentration on the Makarov basin flank of Lomonosov Ridge also suggests that the boundary between the Beaufort Gyre and the Transpolar Drift has been relatively stable during interglacials since that time. Because the Beaufort Gyre is wind-driven our data, in conjunction with the westerly directed orientation of sand dunes that formed during

  16. Ejecta Dynamics during Hypervelocity Impacts into Dry and Wet Sandstone

    NASA Astrophysics Data System (ADS)

    Hoerth, T.; Schäfer, F.; Thoma, K.; Poelchau, M.; Kenkmann, T.; Deutsch, A.

    2011-03-01

    Hypervelocity impact experiments into dry and water saturated porous Seeberger sandstone were conducted at the two-stage light gas accelerator at the Ernst-Mach-Institute (EMI) and the ejecta dynamics were analyzed.

  17. Eccentricity and precession forced cyclicity in the Upper Silurian Williamsport Sandstone Member of the Wills Creek Formation

    SciTech Connect

    Shelton, S.D.; Anderson, E.J. . Dept. of Geology)

    1993-03-01

    The Williamsport Sandstone Member, located at the base of the Wills Creek Formation, contains a complete 5th order sequence, traceable for more than 100 kilometers. This 5th order sequence is initiated with a massive iron-rich sandstone unit. The upper iron-rich sand of the Williamsport Member marks the beginning of the next 5th order sequence. The first 5th order rock cycle, interpreted as the product of the 100 k.y. Milankovitch eccentricity cycle, is divisible into five meter-scale 6th order precessional cycles (PACs). At Cedar Cliff, Maryland, the lithology of each of the five 6th order cycles is distinct. The first cycle (.8m thick) is a massive iron-rich sandstone. The second cycle (.75m thick) is an argillaceous nodular micrite. The third cycle (.75m thick) consists totally of thin-bedded quartz sandstone. The fourth cycle (2m thick) is represented by bedded limestones that thicken upward. The fifth cycle (.6m thick) is very thin-bedded to nodular limestone. This 5th order sequence and most of its internal cyclic elements can be traced over 100 kilometers to Mount Union, Pennsylvania where its facies are largely non-marine. Detailed correlation of these 6th order cycles reveals that the uppermost PAC is missing at Cumberland and Mount Union. At these localities, the prominent iron bed of the next 5th order sequence rests unconformably on the fourth PAC in the sequence. The fifth 6th order cycle was either not deposited or removed by erosion at these proximal localities. The laterally traceable hierarchic cyclic structure in the Williamsport Sandstone is consistent with the Milankovitch forcing model and provides a detailed stratigraphic basis for analysis of lateral patterns of cyclic accumulation in the late Silurian of the central Appalachians.

  18. Siderite (FeCO3)—the Hidden (but Primary) Player in Iron Diagenesis of Non-Marine Sandstones

    NASA Astrophysics Data System (ADS)

    Loope, D.; Kettler, R. M.

    2015-12-01

    Siderite precipitates in reducing pore waters in which iron reduction exceeds sulfate reduction. Abundant siderite should be expected in non-marine strata in which a reductant was present. The Triassic Shinarump Member (Chinle Fm) and Cretaceous Dakota Fm are fluvial and contain siderite in outcrops of floodplain mudstones. Siderite is present in cores of Dakota channel sandstones. Rinded and jointed iron-oxide concretions, Wonderstone patterns, and rhombic, iron-oxide pseudomorphs are present in outcrops of these sandstones. Vascular plants growing on floodplains provided the reductant. Similar concretions, patterns, and pseudomorphs are present in outcropping eolian cross-strata of the Jurassic Navajo Sandstone and in fluvial sandstone of the Cambrian Umm Ishrin Fm. Bleached sandstones indicate reductant was present in both units during late diagenesis. Because Jurassic deserts and Cambrian river systems lacked vascular plants, extra-formational methane was the likely reductant. We interpret the various iron-oxide-cemented phenomena of the Shinarump, Dakota, Navajo, and Umm Ishrin as products of siderite oxidation that accompanied exhumation. In the Navajo, large concretions are enclosed in thick sheaths of iron-oxide cement. Through-going horizontal and vertical joints cut sheaths. Outside concretion sheaths, joints are unassociated with iron-oxide cements, but inside the sheaths, thick cement zones are present on both sides of (still-open) joints. Joints were conduits for oxidizing water entering the concretions. Redox gradients formed on both sides of joints and iron oxide accumulated as Fe+2 diffused from dissolving siderite toward joints and O2 diffused away from joints. Horizontal joints formed <100 m from the land surface. Iron-oxide accumulations on the horizontal joints and on the vertical joints that abut them (see figure) are evidence that siderite oxidation is ongoing and linked to exhumation.

  19. Lower Paleozoic carbonate rocks of Baird Mountains Quadrangle, Alaska

    SciTech Connect

    Dumoulin, J.A.; Harris, A.G.

    1985-04-01

    Lower Paleozoic carbonate rocks in the Baird Mountains quadrangle form a relatively thin (about 550 m), chiefly shallow-water succession that has been imbricately thrust and metamorphosed to lower greenschist facies. Middle and Upper Cambrian rocks - the first reported from the western Brooks Range - occur in the northeastern quarter of the quadrangle, south of Angayukaqsraq (formerly Hub) Mountain. They consist of marble grading upward into thin-bedded marble/dolostone couplets and contain pelagiellid mollusks, acetretid brachiopods, and agnostid trilobites. Sedimentologic features and the Pelagiellas indicate a shallow-water depositional environment. Overlying these rocks are Lower and Middle Ordovician marble and phyllite containing graptolites and conodonts of midshelf to basinal aspect. Upper Ordovician rocks in this area are bioturbated to laminated dolostone containing warm, shallow-water conodonts. In the Omar and Squirrel Rivers areas to the west, the Lower Ordovician carbonate rocks show striking differences in lithofacies, biofacies, and thickness. Here they are mainly dolostone with locally well-developed fenestral fabric and evaporite molds, and bioturbated to laminated orange- and gray-weathering dolomitic marble. Upper Silurian dolostone, found near Angayukaqsraq Mountain and on the central Squirrel River, contains locally abundant corals and stronmatoporoids. Devonian carbonate rocks are widely distributed in the Baird Mountains quadrangle; at least two distinct sequences have been identified. In the Omar area, Lower and Middle Devonian dolostone and marble are locally cherty and rich in megafossils. In the north-central (Nakolik River) area, Middle and Upper Devonian marble is interlayered with planar to cross-laminated quartz-carbonate metasandstone and phyllite.

  20. Geochronology and geochemistry of early Paleozoic igneous rocks of the Lesser Xing'an Range, NE China: Implications for the tectonic evolution of the eastern Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Wang, Zhi-wei; Xu, Wen-liang; Pei, Fu-ping; Wang, Feng; Guo, Peng

    2016-09-01

    This paper presents new zircon U-Pb, Hf isotope, and whole-rock major and trace element data for early Paleozoic igneous rocks of the Lesser Xing'an Range, NE China, in order to constrain the early Paleozoic tectonic evolution of the eastern Central Asian Orogenic Belt (CAOB). Zircon U-Pb dating indicates that early Paleozoic magmatic events within the northern Songnen-Zhangguangcai Range Massif (SZM) can be subdivided into four stages: Middle Cambrian (~ 505 Ma), Late Cambrian (~ 490 Ma), Early-Middle Ordovician (~ 470 Ma), and Late Ordovician (460-450 Ma). The Middle Cambrian monzogranites are K-rich, weakly to strongly peraluminous, and characterized by pronounced heavy rare earth element (HREE) depletions, high Sr/Y ratios, low Y concentrations, low primary zircon εHf(t) values (- 6.79 to - 1.09), and ancient two-stage model (TDM2) ages (1901-1534 Ma). These results indicate derivation from partial melting of thickened ancient crustal materials that formed during the amalgamation of the northern SZM and the northern Jiamusi Massif (JM). The Late Cambrian monzonite, quartz monzonite, and monzogranite units are chemically similar to A-type granites, and contain zircons with εHf(t) values of - 2.59 to + 1.78 and TDM2 ages of 1625-1348 Ma. We infer that these rocks formed from primary magmas generated by partial melting of Mesoproterozoic accreted lower crustal materials in a post-collisional extensional environment. The Early-Middle Ordovician quartz monzodiorite, quartz monzonite, monzogranite, and rhyolite units are calc-alkaline, relatively enriched in light REEs (LREEs) and large ion lithophile elements (LILEs; e.g., Rb, Th, and U), depleted in HREEs and high field strength elements (HFSEs; e.g., Nb, Ta, and Ti), and contain zircons with εHf(t) values of - 7.33 to + 4.98, indicative of formation in an active continental margin setting. The Late Ordovician alkali-feldspar granite and rhyolite units have A-type granite affinities that suggest they formed in

  1. The dangers of taking mud for granted: Lessons from Lower Old Red Sandstone dryland river systems of South Wales

    NASA Astrophysics Data System (ADS)

    Wright, V. Paul; Marriott, Susan B.

    2007-02-01

    Mudrocks are a prominent feature of many ancient dryland successions but they are not always a product of the settling out of suspension load. From studies of the late Silurian-early Devonian Old Red Sandstone mudrocks of South Wales it has been shown that many were not overbank sediments deposited from suspension on floodplains, but were emplaced as sand- and silt-sized aggregates transported as bed load and deposited in sinuous channels and as braid-bar complexes on multi-stage floodplains in dryland river systems. Using the Old Red Sandstone examples criteria are provided for the recognition of similar deposits in the sedimentary record. One important aspect of these mudrocks is that they can represent multiple recycling events and can constitute condensed deposits that may be characteristic of closed alluvial basins with periodically limited sediment supply.

  2. Late Quaternary eolian dust in surficial deposits of a Colorado Plateau grassland: Controls on distribution and ecologic effects

    USGS Publications Warehouse

    Reynolds, R.L.; Reheis, M.C.; Neff, J.C.; Goldstein, H.; Yount, J.

    2006-01-01

    In a semi-arid, upland setting on the Colorado Plateau that is underlain by nutrient-poor Paleozoic eolian sandstone, alternating episodes of dune activity and soil formation during the late Pleistocene and Holocene have produced dominantly sandy deposits that support grass and shrub communities. These deposits also contain eolian dust, especially in paleosols. Eolian dust in these deposits is indicated by several mineralogic and chemical disparities with local bedrock, but it is most readily shown by the abundance of titaniferous magnetite in the sandy deposits that is absent in local bedrock. Magnetite and some potential plant nutrients (especially, P, K, Na, Mn, and Zn) covary positively with depth (3-4 m) in dune-crest and dune-swale settings. Magnetite abundance also correlates strongly and positively with abundances of other elements (e.g., Ti, Li, As, Th, La, and Sc) that are geochemically stable in these environments. Soil-property variations with depth can be ascribed to three primary factors: (1) shifts in local geomorphic setting; (2) accumulation of relatively high amounts of atmospheric mineral dust inputs during periods of land-surface stability; and (3) variations in dust flux and composition that are likely related to changes in dust-source regions. Shifts in geomorphic setting are revealed by large variations in soil texture and are also expressed by changes in soil chemical and magnetic properties. Variable dust inputs are indicated by both changes in dust flux and changes in relations among magnetic, chemical, and textural properties. The largest of these changes is found in sediment that spans late Pleistocene to early Holocene time. Increased dust inputs to the central Colorado Plateau during this period may have been related to desiccation and shrinkage of large lakes from about 12 to 8 ka in western North America that exposed vast surfaces capable of emitting dust. Soil properties that result from variable dust accumulation and redistribution

  3. Late Cenozoic Reverse Faulting in the Fall Zone, Southeastern Virginia.

    PubMed

    Berquist Jr; Bailey

    1999-11-01

    A set of en-echelon reverse faults cut Paleozoic metamorphosed igneous rocks of the Piedmont and overlying late Cenozoic sediments at the Old Hickory Heavy Mineral Deposit in the Fall Zone of southeastern Virginia. Diorite of the eastern Slate Belt was faulted over nearshore to shore-face deposits of the Pliocene Yorktown Formation. These NW-SE-striking faults experienced oblique dip-slip movement with a maximum displacement of up to 6 m on individual faults. Faults tip out along strike and are overlain by distinct cobble beds, suggesting that sediment deposition and faulting were contemporaneous. Deformation at Old Hickory may have been formed by reactivation of existing Paleozoic structures under a regionally extensive compressional stress field parallel to the modern one. PMID:10517887

  4. Late Cenozoic Reverse Faulting in the Fall Zone, Southeastern Virginia.

    PubMed

    Berquist Jr; Bailey

    1999-11-01

    A set of en-echelon reverse faults cut Paleozoic metamorphosed igneous rocks of the Piedmont and overlying late Cenozoic sediments at the Old Hickory Heavy Mineral Deposit in the Fall Zone of southeastern Virginia. Diorite of the eastern Slate Belt was faulted over nearshore to shore-face deposits of the Pliocene Yorktown Formation. These NW-SE-striking faults experienced oblique dip-slip movement with a maximum displacement of up to 6 m on individual faults. Faults tip out along strike and are overlain by distinct cobble beds, suggesting that sediment deposition and faulting were contemporaneous. Deformation at Old Hickory may have been formed by reactivation of existing Paleozoic structures under a regionally extensive compressional stress field parallel to the modern one.

  5. K-Ar dates of Authigenic Illite from the Mississippian Marshall Sandstone, Michigan Basin, USA

    NASA Astrophysics Data System (ADS)

    Meyer, E. E.; Cox, K. J.; Barnes, D. A.

    2015-12-01

    The Michigan basin is an approximately 5 km deep intracratonic basin that is centered over the southern peninsula of Michigan, USA. The basin overlies Proterozoic basement rock and is filled with dominantly Paleozoic sedimentary units. Evidence from diagenetic mineralization and thermal maturity of organic material indicate that past thermal conditions in the basin were anomalously high relative to expected maximum burial temperatures at the current geothermal gradient of 20° C/km. A number of hypotheses have been advanced to explain the anomalous temperature indicators including burial under now eroded sedimentary cover (Cercone and Pollack, 1991) and hydrothermal fluid flow related to the Mesoproterozoic rift that underlies the basin (Girard and Barnes,1995 and others). Here we present K/Ar ages of authigenic illite separated from the Early Mississippian Marshall Sandstone. K/Ar ages of authigenic illite provide temporal constrains on diagenetic process because illite generally forms at temperatures above 100° C, which is in agreement with the formation temperatures estimated for other authigenic components in the Marshall (Zacharias et al., 1993). Samples are from present burial depths of <500 m. Clay separates were analyzed using XRD and were shown to contain abundant illite, with little other clay mineral content and no K-feldspar. A mean age of 272 Ma was measured for three size fractions from a sample from the central basin. This sample had ages that were indistinguishable across three clay size fractions. A second sample from the southern margin of the basin showed a decrease in age with size fraction with 2-1μm illite giving an age of 313±3 Ma and a <0.5 μm illite sample giving an age of 294±3 Ma. This sample may have a small amount of coarse detrital illite that increases the age of the coarse size fraction. Based on the formation conditions interpreted for authigenic illite in the Marshall Sandstone, these dates may record a mid

  6. Diagenesis Along Fractures in an Eolian Sandstone, Gale Crater, Mars

    NASA Technical Reports Server (NTRS)

    Ming, D. W.; Yen, A. S.; Rampe, E. B.; Grotzinger, J. P.; Blake, D. F.; Bristow, T. F.; Chipera, S. J.; Downs, R.; Morris, R. V.; Morrison, S. M.; Vaniman, D. T.; Gellert, R.; Sutter, B.; Treiman, A. H.

    2016-01-01

    The Mars Science Laboratory rover Curiosity has been exploring sedimentary deposits in Gale crater since August 2012. The rover has traversed up section through approx.100 m of sedimentary rocks deposited in fluvial, deltaic, lacustrine, and eolian environments (Bradbury group and overlying Mount Sharp group). The Stimson formation lies unconformable over a lacustrine mudstone at the base of the Mount Sharp group and has been interpreted to be a cross-bedded sandstone of lithified eolian dunes. Mineralogy of the unaltered Stimson sandstone consists of plagioclase feldspar, pyroxenes, and magnetite with minor abundances of hematite, and Ca-sulfates (anhydrite, bassanite). Unaltered sandstone has a composition similar to the average Mars crustal composition. Alteration "halos" occur adjacent to fractures in the Stimson. Fluids passing through these fractures have altered the chemistry and mineralogy of the sandstone. Silicon and S enrichments and depletions in Al, Fe, Mg, Na, K, Ni and Mn suggest aqueous alteration in an open hydrologic system. Mineralogy of the altered Stimson is dominated by Ca-sulfates, Si-rich X-ray amorphous materials along with plagioclase feldspar, magnetite, and pyroxenes, but less abundant in the altered compared to the unaltered Stimson sandstone and lower pyroxene/plagioclase feldspar. The mineralogy and geochemistry of the altered sandstone suggest a complicated history with several (many?) episodes of aqueous alteration under a variety of environmental conditions (e.g., acidic, alkaline).

  7. The Middle Jurassic Entrada Sandstone near Gallup, New Mexico

    USGS Publications Warehouse

    Robertson, J.F.; O'Sullivan, R. B.

    2001-01-01

    Near Gallup, New Mexico, the Middle Jurassic Entrada Sandstone consists of, in ascending order, the Iyanbito Member, the Rehoboth Member, and an upper sandstone member. The Rehoboth Member is named herein to replace the middle siltstone member, with a type section located 26 km east of Gallup. The Iyanbito Member has been erroneously equated with the Wingate Sandstone of northeast Arizona, and the Rehoboth Member has been miscorrelated with the Dewey Bridge Member of the Entrada in Utah. The Dewey Bridge is an older unit that does not extend into New Mexico. The Iyanbito Member, east of Gallup, overlies the J-2 unconformity and the eroded tops of the Owl Rock and Petrified Forest Members of the Chinle Formation. The Wingate Sandstone of the Lower Jurassic Glen Canyon Group overlies the J-0 unconformity and the underlying Rock Point Member (topmost unit) of the Chinle Formation in northeast Arizona. Both the Wingate Sandstone and the Rock Point Member are missing east of Gallup below the J-2 unconformity. Similarly, the Wingate is missing southwest of Gallup, near Lupton, Arizona, but the Rock Point Member is present and underlies the Iyanbito from Zuni northward to Toadlena, New Mexico. The Wingate and other formations of the Glen Canyon Group thin and wedge out southward and eastward in northeast Arizona. The J-2 unconformity truncates the Wingate Sandstone and the underlying J-0 unconformity, 5 km north of Toadlena.

  8. Late paternities.

    PubMed

    Cohen, Jean

    2007-06-01

    Late paternities are frequent. Very often these couples ask for medically assisted procreation. In general, it is considered that the couple should not be treated differently from the couple where the father is younger. Recent studies show a certain number of specific risks linked to the late paternities. Doctors and society do not act in the same way towards men and women: a 'sensible age' for women to no longer attempt pregnancy has been set in many countries at 42 years of age, whereas men aged 80 can benefit from IVF attempts and be reimbursed by the state or insurance companies. This is an obvious inequity. PMID:17579995

  9. High-temperature quartz cement and the role of stylolites in a deep gas reservoir, Spiro Sandstone, Arkoma Basin, USA

    USGS Publications Warehouse

    Worden, Richard H.; Morad, Sadoon; Spötl, C.; Houseknecht, D.W.; Riciputi, L.R.

    2000-01-01

    The Spiro Sandstone, a natural gas play in the central Arkoma Basin and the frontal Ouachita Mountains preserves excellent porosity in chloritic channel-fill sandstones despite thermal maturity levels corresponding to incipient metamorphism. Some wells, however, show variable proportions of a late-stage, non-syntaxial quartz cement, which post-dated thermal cracking of liquid hydrocarbons to pyrobitumen plus methane. Temperatures well in excess of 150°C and possibly exceeding 200°C are also suggested by (i) fluid inclusions in associated minerals; (ii) the fact that quartz post-dated high-temperature chlorite polytype IIb; (iii) vitrinite reflectance values of the Spiro that range laterally from 1.9 to ≥ 4%; and (iii) the occurrence of late dickite in these rocks. Oxygen isotope values of quartz cement range from 17.5 to 22.4‰ VSMOW (total range of individual in situ ion microprobe measurements) which are similar to those of quartz cement formed along high-amplitude stylolites (18.4–24.9‰). We favour a model whereby quartz precipitation was controlled primarily by the availability of silica via deep-burial stylolitization within the Spiro Sandstone. Burial-history modelling showed that the basin went from a geopressured to a normally pressured regime within about 10–15 Myr after it reached maximum burial depth. While geopressure and the presence of chlorite coats stabilized the grain framework and inhibited nucleation of secondary quartz, respectively, stylolites formed during the subsequent high-temperature, normal-pressured regime and gave rise to high-temperature quartz precipitation. Authigenic quartz growing along stylolites underscores their role as a significant deep-burial silica source in this sandstone.

  10. Diagenesis and secondary porosity enhancement from dissolution of analcime cement in reservoir sandstones: The Upper Permian Pingdiquan Formation, Junggar basin, northwest China

    SciTech Connect

    Zhaohui, T.; Longstaffe, F.J. ); Parnell, J. )

    1996-01-01

    The Junggar Basin is one of the largest and most important oil-producing basins in China, in which Upper Permian lacustrine oil shales are among the thickest and richest petroleum source rocks in the world. The Upper Permian Pingdiquan Formation was deposited predominantly in fan-delta sequences within a lacustrine setting. The Pingdiquan Formation sandstones constitute the principal oil reservoirs, whereas the interbedded black shales are the predominant oil source rocks. The early diagenetic mineral assemblage in the sandstones comprises siderite, pyrite, analcime, albite, calcite and authigenic quartz as well as trace amount of halite; By contrast, the late diagenetic minerals are characterized by authigenic K-feldspar, ankerite, and minor amounts of mixed-layer clay minerals. Petrographic, mineralogical and available paleoecological data suggest that early authigenic minerals in the sandstones were controlled by alternating periodic fresh water and saline/alkaline water episodes in a lacustrine environment. The cementation of siderite, analcime, calcite and albite occluded the substantial porosity in the sandstones at an early diagenetic stage. However, extensive dissolution of analcime cement and labile detrital feldspars occurred during burial diagenesis, resulting in a significant secondary porosity enhancement in the sandstones and making them very good quality oil reservoirs. The origin of secondary porosity is related to the generation of various organic acids due to organic maturation of the interbedded exceptionally organic-rich oil shales.

  11. Diagenesis and secondary porosity enhancement from dissolution of analcime cement in reservoir sandstones: The Upper Permian Pingdiquan Formation, Junggar basin, northwest China

    SciTech Connect

    Zhaohui, T.; Longstaffe, F.J.; Parnell, J.

    1996-12-31

    The Junggar Basin is one of the largest and most important oil-producing basins in China, in which Upper Permian lacustrine oil shales are among the thickest and richest petroleum source rocks in the world. The Upper Permian Pingdiquan Formation was deposited predominantly in fan-delta sequences within a lacustrine setting. The Pingdiquan Formation sandstones constitute the principal oil reservoirs, whereas the interbedded black shales are the predominant oil source rocks. The early diagenetic mineral assemblage in the sandstones comprises siderite, pyrite, analcime, albite, calcite and authigenic quartz as well as trace amount of halite; By contrast, the late diagenetic minerals are characterized by authigenic K-feldspar, ankerite, and minor amounts of mixed-layer clay minerals. Petrographic, mineralogical and available paleoecological data suggest that early authigenic minerals in the sandstones were controlled by alternating periodic fresh water and saline/alkaline water episodes in a lacustrine environment. The cementation of siderite, analcime, calcite and albite occluded the substantial porosity in the sandstones at an early diagenetic stage. However, extensive dissolution of analcime cement and labile detrital feldspars occurred during burial diagenesis, resulting in a significant secondary porosity enhancement in the sandstones and making them very good quality oil reservoirs. The origin of secondary porosity is related to the generation of various organic acids due to organic maturation of the interbedded exceptionally organic-rich oil shales.

  12. RESERVOIR CHARACTERIZATION OF UPPER DEVONIAN GORDON SANDSTONE, JACKSONBURG STRINGTOWN OIL FIELD, NORTHWESTERN WEST VIRGINIA

    SciTech Connect

    S. Ameri; K. Aminian; K.L. Avary; H.I. Bilgesu; M.E. Hohn; R.R. McDowell; D.L. Matchen

    2001-07-01

    The Jacksonburg-Stringtown oil field contained an estimated 88,500,000 barrels of oil in place, of which approximately 20,000,000 barrels were produced during primary recovery operations. A gas injection project, initiated in 1934, and a pilot waterflood, begun in 1981, yielded additional production from limited portions of the field. The pilot was successful enough to warrant development of a full-scale waterflood in 1990, involving approximately 8,900 acres in three units, with a target of 1,500 barrels of oil per acre recovery. Historical patterns of drilling and development within the field suggests that the Gordon reservoir is heterogeneous, and that detailed reservoir characterization is necessary for understanding well performance and addressing problems observed by the operators. The purpose of this work is to establish relationships among permeability, geophysical and other data by integrating geologic, geophysical and engineering data into an interdisciplinary quantification of reservoir heterogeneity as it relates to production. Conventional stratigraphic correlation and core description shows that the Gordon sandstone is composed of three parasequences, formed along the Late Devonian shoreline of the Appalachian Basin. The parasequences comprise five lithofacies, of which one includes reservoir sandstones. Pay sandstones were found to have permeabilities in core ranging from 10 to 200 mD, whereas non-pay sandstones have permeabilities ranging from below the level of instrumental detection to 5 mD; Conglomeratic zones could take on the permeability characteristics of enclosing materials, or could exhibit extremely low values in pay sandstone and high values in non-pay or low permeability pay sandstone. Four electrofacies based on a linear combination of density and scaled gamma ray best matched correlations made independently based on visual comparison of geophysical logs. Electrofacies 4 with relatively high permeability (mean value > 45 mD) was

  13. Dynamic triggering during rupture nucleation in sandstone

    NASA Astrophysics Data System (ADS)

    Schubnel, Alexandre; Chanard, Kristel; Latour, Soumaya; Petrelis, François; Hatano, Takahiro; Mair, Karen; Vinciguerra, Sergio

    2016-04-01

    Fluid induced stress perturbations in the crust at seismogenic depths can be caused by various sources, such as deglaciation unloading, magmatic intrusion or fluid injection and withdrawal. Numbers of studies have robustly shown their link to earthquake triggering. However, the role of small periodic stress variations induced by solid earth and oceanic tides or seasonal hydrology in the seismic cycle, of the order of a few kPa, remains unclear. Indeed, the existence or absence of correlation between these loading phenomena and earthquakes have been equally proposed in the literature. To investigate this question, we performed a set of triaxial deformation experiments on porous water-saturated Fontainebleau sandstones. Rock samples were loaded by the combined action of steps of constant stress (creep), intended to simulate tectonic loading and small sinusoidal pore pressure variations with a range of amplitudes, analogous to tides or seasonal loading. All tests were conducted at a regulated temperature of 35C and a constant 35 MPa confining pressure. Our experimental results show that (1) pore pressure oscillations do not seem to influence the deformation rate at which the rock fails, (2) they correlate with acoustic emissions. Even more interestingly, we observe a progressive increase of the correlation coefficient in time as the rock approaches failure. The correlation coefficient is also sensitive to the amplitude of pore pressure oscillations as larger oscillations produce higher correlation levels. Finally, we show that, in the last hours of creep before failure, acoustic emissions occur significantly more when the pore pressure is at its lowest. This suggest that the correlation of small stress perturbations and acoustic emissions depend on the state stress of a rock and the amplitude of the perturbations and that emissions occur more likely when cracks are unclamped.

  14. Depositional setting, structural style, and sandstone distribution in three geopressured geothermal areas, Texas Gulf Coast

    SciTech Connect

    Winker, C.D.; Morton, R.A.; Ewing, T.E.; Garcia, D.D.

    1983-01-01

    Three areas in the Texas Gulf Coastal Plain were studied using electric logs and seismic-reflection data to interpret their depositional and structural history and to compare their potential as geopressured-geothermal reservoirs. The Cuero study area, on the lower Wilcox (upper Paleocene) growth-fault trend, is characterized by closely and evenly spaced, subparallel, down-to-the-basin growth faults, relatively small expansion ratios, and minor block rotation. Distributary-channel sandstones in the geopressured lower Wilcox Group of the South Cook fault block appear to be the best geothermal aquifers in the Cuero area. The Blessing study area, on the lower Frio (Oligocene) growth-fault trend, shows wider and more variable fault spacing and much greater expansion ratios and block rotation, particularly during early Frio time. Thick geopressured sandstone aquifers are laterally more extensive in the Blessing area than in the Cuero area. The Pleasant Bayou study area, like the Blessing area, is on the Frio growth-fault trand, and its early structural development was similar rapid movement of widely spaced faults resulted in large expansion ratios and major block rotation. However, a late-stage pattern of salt uplift and withdrawal complicated the structural style. Thick geopressured lower Frio sandstone aquifers are highly permeable and laterally extensive, as in the Blessing area. In all three areas, geopressured aquifers were created where early, rapid movement along down-to-the-basin growth faults juxtaposed shallow-water sands against older shales, probably deposited in slope environments. Major transgressions followed the deposition of reservoir sands and probably also influenced the hydraulic isolation that allowed the build up of abnormal pressures. 26 refs., 49 figs., 8 tabs.

  15. Paleogeography of Southwest Gondwana Boundary During the Upper Paleozoic

    NASA Astrophysics Data System (ADS)

    Tomezzoli, R. N.

    2005-05-01

    Current results are summarized from the southwest Gondwana boundary, from rocks from La Pampa province, Argentina. This area is the westward part of an orogenic belt, known as Sam Frau geosincline or Cordón de las Gondwánides and may represent the suture zone between the Gondwana and Patagonia terranes. This collision model is still uncertain and there are many controversies related to the age of the deformation of this belt. Paleomagnetism and the exploration of the magnetic fabric signatures (AMS) can be useful to evaluate the regional deformation and a better understanding of the assembly, deformation, and fragmentation of Gondwana / Pangea. A systematic paleomagnetic study was done in the Cerro Centinela: 36/deg S, 67/deg W, belong to the Choiyoi Group and consist of Lower Paleozoic volcanic rocks. In this paleomagnetic study is present results from 19 sites (84 specimens), sampled from the base to the top in different layers. Samples were demagnetized with thermal procedures. A high un¬blocking temperature component carried by hematite was defined between 580° C and 680° C, showing very good within site consistency (alpha 95<15° and k>20). Remanent magnetization ranges around 1500 mA m-1. In all samples it was possible to isolate one component with the same behavior and positive inclination. These stable remanent magnetization were group into two different Population: 1 and 2, clearly separated. Population 1 (from sites 1 to 12) in situ mean direction is: D=146°, I=63.5°, alpha 95=4°, k=104, N=12. Population 2 (from sites 13 to 19) in situ mean direction is: D=164°, I=42°, alpha 95=4°, k=197, N=7. Reversed characteristic remanence magnetization suggesting that the magnetization was acquired during the Kiaman interval, in accordance with their age. Two high quality paleomagnetic poles were computed for each population on the basis of the in situ remanence directions. The corresponding PP are for Population 1: 63° S, 353° E, Alpha 95=7 and K=44

  16. New geochronologic and stratigraphic evidence confirms the paleocene age of the dinosaur-bearing ojo alamo sandstone and animas formation in the San Juan Basin, New Mexico and Colorado

    USGS Publications Warehouse

    Fassett, J.E.

    2009-01-01

    Dinosaur fossils are present in the Paleocene Ojo Alamo Sandstone and Animas Formation in the San Juan Basin, New Mexico, and Colorado. Evidence for the Paleo-cene age of the Ojo Alamo Sandstone includes palynologic and paleomagnetic data. Palynologic data indicate that the entire Ojo Alamo Sandstone, including the lower dinosaur-bearing part, is Paleocene in age. All of the palynomorph-productive rock samples collected from the Ojo Alamo Sandstone at multiple localities lacked Creta-ceous index palynomorphs (except for rare, reworked specimens) and produced Paleocene index palynomorphs. Paleocene palynomorphs have been identified strati-graphically below dinosaur fossils at two separate localities in the Ojo Alamo Sand-stone in the central and southern parts of the basin. The Animas Formation in the Colorado part of the basin also contains dinosaur fossils, and its Paleocene age has been established based on fossil leaves and palynology. Magnetostratigraphy provides independent evidence for the Paleocene age of the Ojo Alamo Sandstone and its dinosaur-bearing beds. Normal-polarity magnetochron C29n (early Paleocene) has been identified in the Ojo Alamo Sandstone at six localities in the southern part of the San Juan Basin. An assemblage of 34 skeletal elements from a single hadrosaur, found in the Ojo Alamo Sandstone in the southern San Juan Basin, provided conclusive evidence that this assemblage could not have been reworked from underlying Cretaceous strata. In addition, geochemical studies of 15 vertebrate bones from the Paleocene Ojo Alamo Sandstone and 15 bone samples from the underlying Kirtland Formation of Late Creta-ceous (Campanian) age show that each sample suite contained distinctly different abundances of uranium and rare-earth elements, indicating that the bones were miner-alized in place soon after burial, and that none of the Paleocene dinosaur bones ana-lyzed had been reworked. ?? U.S. Geological Survey, Public Domain April 2009.

  17. Sandstone Diagenesis at Gale Crater, Mars, As Observed By Curiosity

    NASA Astrophysics Data System (ADS)

    Siebach, K. L.; Grotzinger, J. P.; McLennan, S. M.; Hurowitz, J.; Kah, L. C.; Edgett, K. S.; Williams, R. M. E.; Wiens, R. C.; Schieber, J.

    2014-12-01

    The Mars Science Laboratory rover, Curiosity, has encountered a significant number of poorly-sorted and very well-lithified sandstones along its traverse on the floor of Gale Crater. We use images from the hand-lens imager (MAHLI) and elemental chemistry from the ChemCam laser-induced breakdown spectroscopy instrument (LIBS) and the alpha-particle x-ray spectrometer (APXS) to begin to constrain the diagenetic history of these sandstones, including lithification and possible later dissolution. Investigation of MAHLI images reveals that the sediments are poorly-sorted and show very low apparent porosity, generally less than ~5%. However, in some cases, such as the Gillespie Lake sandstone identified in Yellowknife Bay, this apparent porosity includes a significant fraction of void spaces larger than typical sediment grain sizes (~30% by number or 75% of void spaces by area). One possible explanation of these larger pits is that they represent recent removal of soft intraclasts by eolian abrasion. Another possibility is that later diagenetic fluids caused dissolution of more soluble grains, and production of secondary porosity. Investigation into the elemental chemistry of the sandstones has shown that they have a relatively unaltered basaltic bulk composition in spite of possessing a variety of secondary minerals and amorphous material, indicating isochemical diagenetic processes. The chemistry and mineralogy of the cement is not immediately evident based on the initial analyses; there is not a high percentage of salts or evaporative minerals that may easily cement near-surface sandstones. Furthermore, these sandstones lack textures and compositions consistent with pedogenic processes, such as calcrete, silcrete, or ferricrete. Instead, they may record burial and cementation at depth. Cement composition may be constrained through comparison to terrestrial basaltic sandstones, and studying chemical variations along ChemCam and APXS transects of the rocks.

  18. Remagnetization and tectonic rotation of Upper Precambrian and Lower Paleozoic strata from the Desert Range, southern Nevada

    NASA Astrophysics Data System (ADS)

    Gillett, Stephen L.; van Alstine, David R.

    1982-12-01

    the regional geology suggests the Desert Range strata were essentially horizontal throughout the Paleozoic. The total observed relative rotation is 44°±5°, representing absolute counterclockwise rotation (27°±4°) of the northern part of the Desert Range, and absolute clockwise rotation (17°±5°( of the southern part. The only unit in the Desert Range sequence that may retain a primary magnetization is the late Precambrian Rainstorm Member of the Johnnie Formation. The characteristic magnetization of this unit exhibits two polarities and probably resides in specular hematite; after correction for 18° of counterclockwise rotation, the resulting pole (5°N, 151°E) is near other late Hadrynian poles from North America.

  19. Detrital zircon U-Pb geochronology, Lu-Hf isotopes and REE geochemistry constrains on the provenance and tectonic setting of Indochina Block in the Paleozoic

    NASA Astrophysics Data System (ADS)

    Wang, Ce; Liang, Xinquan; Foster, David A.; Fu, Jiangang; Jiang, Ying; Dong, Chaoge; Zhou, Yun; Wen, Shunv; Van Quynh, Phan

    2016-05-01

    In situ U-Pb geochronology, Lu-Hf isotopes and REE geochemical analyses of detrital zircons from Cambrian-Devonian sandstones in the Truong Son Belt, central Vietnam, are used to provide the information of provenance and tectonic evolution of the Indochina Block. The combined detrital zircon age spectra of all of the samples ranges from 3699 Ma to 443 Ma and shows with dominant age peaks at ca. 445 Ma and 964 Ma, along with a number of age populations at 618-532 Ma, 1160-1076 Ma, 1454 Ma, 1728 Ma and 2516 Ma. The zircon age populations are similar to those from time equivalent sedimentary sequences in continental blocks disintegrated from the East Gondwana during the Phanerozoic. The younger zircon grains with age peaks at ca. 445 Ma were apparently derived from middle Ordovician-Silurian igneous and metamorphic rocks in Indochina. Zircons with ages older than about 600 Ma were derived from other Gondwana terrains or recycled from the Precambrian basement of the Indochina Block. Similarities in the detrital zircon U-Pb ages suggest that Paleozoic strata in the Indochina, Yangtze, Cathaysia and Tethyan Himalayas has similar provenance. This is consistent with other geological constrains indicating that the Indochina Block was located close to Tethyan Himalaya, northern margin of the India, and northwestern Australia in Gondwana.

  20. Carbon dioxide in the Paleozoic atmosphere: Evidence from carbon-isotope compositions of pedogenic carbonate

    NASA Astrophysics Data System (ADS)

    Mora, Claudia I.; Driese, Steven G.; Seager, Paula G.

    1991-10-01

    Stable carbon-isotope compositions of pedogenic carbonate occurring in three clay-rich vertic paleosols within Paleozoic red-bed successions in central Pennsylvania provide a record of past pedogenic environments and can be used to estimate CO2 pressure (PCO2) of the Paleozoic atmosphere. The δ13C values of carbonate nodules from paleosols in the deltaic lower Bloomsburg Formation (Upper Silurian) reflect the contribution of carbon from marine groundwater or fossils, coupled with low biological activity. The δ13C values of carbonate rhizocretions from stratigraphically high paleosols in the Bloomsburg Formation, and in the alluvial Catskill (Upper Devonian) and Mauch Chunk (Upper Mississippian) Formations, suggest an extensive C3 flora and significant contribution of atmospheric CO2. Paleozoic atmospheric CO2 levels inferred from δ13C of pedogenic carbonate are significantly higher than present levels.

  1. 1st paleomagnetic investigation of Nubia Sandstone at Kalabsha, south Western Desert of Egypt

    NASA Astrophysics Data System (ADS)

    Mostafa, R.; Khashaba, A.; El-Hemaly, I. A.; Takla, E. M.; Abdel Aal, E.; Odah, H.

    2016-06-01

    Two profiles have been sampled from the Nubia Sandstone at Aswan, south Western Desert: the 1st profile has been taken from Abu Aggag Formation and the 2nd one was from Sabaya Formation (23.25 °N, 32.75 °E). 136 oriented cores (from 9 sites) have been sampled. Abu Aggag Formation is of Late Cretaceous (Turonian) and Sabaya Formation is of early Cretaceous (Albian-Cenomanian). The studied rocks are subjected to rock magnetic measurements as well as demagnetization treatment. It has been found that hematite is the main magnetic mineral in both formations. Four profile sections from Abu Aggag Formation, yielded a magnetic component with D = 352.7°, I = 36.6° with α95 = 5.2° and the corresponding pole lies at Lat. = 82.8 °N and Long. = 283.1 °E. Five profile sections from Sabaya Formation, yielded a magnetic component with D = 348.6°, I = 33.3° with α95 = 5.8° and the corresponding pole lies at Lat. = 78.3 °N and Long. = 280.4 °E. The obtained paleopole for the two formations lies at Lat. = 80.5 °N and Long. = 281.7 °E. The obtaind magnetic components are considered primary and the corresponding paleopole reflects the age of Nubia Sandstone when compared with the previously obtained Cretaceous poles for Egypt.

  2. A New Basal Sauropodomorph Dinosaur from the Lower Jurassic Navajo Sandstone of Southern Utah

    PubMed Central

    Sertich, Joseph J. W.; Loewen, Mark A.

    2010-01-01

    Background Basal sauropodomorphs, or ‘prosauropods,’ are a globally widespread paraphyletic assemblage of terrestrial herbivorous dinosaurs from the Late Triassic and Early Jurassic. In contrast to several other landmasses, the North American record of sauropodomorphs during this time interval remains sparse, limited to Early Jurassic occurrences of a single well-known taxon from eastern North America and several fragmentary specimens from western North America. Methodology/Principal Findings On the basis of a partial skeleton, we describe here a new basal sauropodomorph dinosaur from the Lower Jurassic Navajo Sandstone of southern Utah, Seitaad ruessi gen. et sp. nov. The partially articulated skeleton of Seitaad was likely buried post-mortem in the base of a collapsed dune foreset. The new taxon is characterized by a plate-like medial process of the scapula, a prominent proximal expansion of the deltopectoral crest of the humerus, a strongly inclined distal articular surface of the radius, and a proximally and laterally hypertrophied proximal metacarpal I. Conclusions/Significance Phylogenetic analysis recovers Seitaad as a derived basal sauropodomorph closely related to plateosaurid or massospondylid ‘prosauropods’ and its presence in western North America is not unexpected for a member of this highly cosmopolitan clade. This occurrence represents one of the most complete vertebrate body fossil specimens yet recovered from the Navajo Sandstone and one of the few basal sauropodomorph taxa currently known from North America. PMID:20352090

  3. Mixed fluvial systems of the Messak Sandstone, a deposit of the Nubian lithofacies, southwestern Libya

    NASA Astrophysics Data System (ADS)

    Lorenz, John C.

    1987-11-01

    The Messak Sandstone is a coarse-grained to pebbly, tabular-crossbedded deposit of the widespread nubian lithofacies. It was deposited during Late Jurassic and/or Early Cretaceous time at the northern edge of the Murzuq basin, in southwestern Libya. Although the sedimentary record is predominantly one of braided fluvial systems, a common subfacies within the formation is interpreted to record the passage of straight-crested sand waves across laterally migrating point bars in sinuous rivers, similar to parts of the modern Ganga and Yamuna rivers. Because the sand waves were larger on the lower parts of the point bar, lateral migration created diagnostic thinning-upward cosets of tabular crossbeds, as well as fining-upward grain-size trends. Common thick, interbedded claystones, deposited in associated paludal and lacustrine environments, and high variance in crossbed dispersion patterns, also suggest the local presence of sinuous fluvial systems within the overall braided regime. The Messak Sandstone contains some of the features that led to the proposal of an unconventional low-sinuosity fluvial environment for the Nubian lithofacies in Egypt, and the continuously high water levels of this model may explain channel-scale clay drapes and overturned crossbeds in the Messak. However, most of the Messak characteristics are incompatible with a low-sinuosity model, suggesting instead that the fluvial channels in the Murzuq basin alternated between braided and high-sinuosity channel patterns.

  4. Fault-related Silurian Clinton sandstone deposition in Ohio

    SciTech Connect

    Coogan, A.H. )

    1988-08-01

    Mapping the thickness of the Silurian Clinton sandstone reservoir and associated shale, sandstone, and carbonate facies in the subsurface of 40 counties in eastern Ohio reveals a general correspondence between major patterns of deposition and the location of faults that strike parallel with or subparallel to the depositional trends. Clinton delta-front sandstones, which occur along a line from Hocking and Perry Counties, through Knox, Holmes, and Wayne Counties northeast to Lake County, Ohio, parallel a line of major change in magnetic intensity in the basement, which is interpreted here to be the juncture between the more stable, less subsiding central Ohio carbonate bank and the more subsiding western edge of the Appalachian basin. The principal Clinton deltaic lobes occur in east-central and northeastern Ohio. The Clinton sandstone interval is thinner and starved of coarse clastic sediment close to the Rome trough, which is located along the southeasternmost Ohio border. Sediment distribution patterns indicate that deltaic deposits of Clinton sandstone were captured in the subsiding Rome trough at the border of southern Ohio during the Early Silurian. Farther north, deltaic sediments spread out across eastern Ohio to reach an elongate depocenter caused by minor subsidence at the central Ohio platform edge. There, deltaic sands intermittently filled the delta-edge trough, and spilled out as thin shelf sands onto the more stable platform, a site of predominantly mixed shale and carbonate deposition during the Early Silurian.

  5. Development geology study of Weber sandstone, Rangely field, Colorado

    SciTech Connect

    Jackson, W.D.; Bowker, K.

    1989-09-01

    The Pennsylvanian-Permian Weber Sandstone formation is the major producing horizon at the giant Rangely field, Rio Blanco County, Colorado. The Weber has been separated into six lithofacies using core descriptions, core analyses, optical and scanning-electron microscopy, x-ray diffraction, and special-core analyses. Two of the lithofacies (eolian) are productive. The subarkosic laminated sandstones (which have the best reservoir quality) have an average Boyle's Law porosity of 9.7%. Permeability varies directionally on a small scale because of differential cementation within the graded laminae; the very fine-grained portion of the laminae is more tightly cemented by carbonate minerals than are the fine-grained portions. Permeability along the laminae averages 1.2 md; permeability across the laminae is less than 1 md. The second productive lithofacies is massive (bioturbated) and more thoroughly cemented than the first; it is also composed of fine and very fine-grained sandstones. These massive subarkosic sandstones have an average porosity of 7% and permeability averaging less than 1 md. Fractures alter permeability in portions of the field. The remaining four lithofacies (fluvial) are not productive and act as intraformational permeability barriers. Arkosic sandstones, arkosic siltstones, shales, and rare carbonates comprise this group. The relationship of the lithofacies to the depositional environment and the recognition of them on electric logs has allowed correlations across the field. This has proven an important contribution to the management of the current CO{sub 2} flood.

  6. Numerical analysis of sandstone composition, provenance, and paleogeography

    SciTech Connect

    Smosma, R.; Bruner, K.R.; Burns, A.

    1999-09-01

    Cretaceous deltaic sandstones of the National Petroleum Reserve in Alaska exhibit an extreme variability in their mineral makeup. A series of numerical techniques, however, provides some order to the petrographic characteristics of these complex rocks. Ten mineral constituents occur in the sandstones, including quartz, chert, feldspar, mica, and organic matter, plus rock fragments of volcanics, carbonates, shale, phyllite, and schist. A mixing coefficient quantities the degree of heterogeneity in each sample. Hierarchical cluster analysis then groups sandstones on the basis of similarities among all ten mineral components--in the Alaskan example, six groupings characterized mainly by the different rock fragments. Multidimensional scaling shows how the clusters relate to one another and arranges them along compositional gradients--two trends in Alaska based on varying proportions of metamorphic/volcanic and shale/carbonate rock fragments. The resulting sandstone clusters and petrographic gradients can be mapped across the study area and compared with the stratigraphic section. This study confirms the presence of three different source areas that provided diverse sediment to the Cretaceous deltas as well as the general transport directions and distances. In addition, the sand composition is shown to have changed over time, probably related to erosional unroofing in the source areas. This combination of multivariate-analysis techniques proves to be a powerful tool, revealing subtle spatial and temporal relationships among the sandstones and allowing one to enhance provenance and paleogeographic conclusions made from compositional data.

  7. Transport of engineered silver (Ag) nanoparticles through partially fractured sandstones.

    PubMed

    Neukum, Christoph; Braun, Anika; Azzam, Rafig

    2014-08-01

    Transport behavior and fate of engineered silver nanoparticles (AgNP) in the subsurface is of major interest concerning soil and groundwater protection in order to avoid groundwater contamination of vital resources. Sandstone aquifers are important groundwater resources which are frequently used for public water supply in many regions of the world. The objective of this study is to get a better understanding of AgNP transport behavior in partially fractured sandstones. We executed AgNP transport studies on partially fissured sandstone drilling cores in laboratory experiments. The AgNP concentration and AgNP size in the effluent were analyzed using flow field-flow fractionation mainly. We employed inverse mathematical models on the measured AgNP breakthrough curves to identify and quantify relevant transport processes. Physicochemical filtration, time-dependent blocking due to filling of favorable attachment sites and colloid-facilitated transport were identified as the major processes for AgNP mobility. Physicochemical filtration was found to depend on solute chemistry, mineralogy, pore size distribution and probably on physical and chemical heterogeneity. Compared to AgNP transport in undisturbed sandstone matrix reported in the literature, their mobility in partially fissured sandstone is enhanced probably due to larger void spaces and higher hydraulic conductivity.

  8. Shahejie-Shahejie/Guantao/Wumishan and Carboniferous/Permian Coal-Paleozoic Total Petroleum Systems in the Bohaiwan Basin, China (based on geologic studies for the 2000 World Energy Assessment Project of the U.S. Geological Survey)

    USGS Publications Warehouse

    Ryder, Robert T.; Qiang, Jin; McCabe, Peter J.; Nuccio, Vito F.; Persits, Felix

    2012-01-01

    This report discusses the geologic framework and petroleum geology used to assess undiscovered petroleum resources in the Bohaiwan basin province for the 2000 World Energy Assessment Project of the U.S. Geological Survey. The Bohaiwan basin in northeastern China is the largest petroleum-producing region in China. Two total petroleum systems have been identified in the basin. The first, the Shahejie&ndashShahejie/Guantao/Wumishan Total Petroleum System, involves oil and gas generated from mature pods of lacustrine source rock that are associated with six major rift-controlled subbasins. Two assessment units are defined in this total petroleum system: (1) a Tertiary lacustrine assessment unit consisting of sandstone reservoirs interbedded with lacustrine shale source rocks, and (2) a pre-Tertiary buried hills assessment unit consisting of carbonate reservoirs that are overlain unconformably by Tertiary lacustrine shale source rocks. The second total petroleum system identified in the Bohaiwan basin is the Carboniferous/Permian Coal–Paleozoic Total Petroleum System, a hypothetical total petroleum system involving natural gas generated from multiple pods of thermally mature coal beds. Low-permeability Permian sandstones and possibly Carboniferous coal beds are the reservoir rocks. Most of the natural gas is inferred to be trapped in continuous accumulations near the center of the subbasins. This total petroleum system is largely unexplored and has good potential for undiscovered gas accumulations. One assessment unit, coal-sourced gas, is defined in this total petroleum system.

  9. Estimation of uranium migration parameters in sandstone aquifers.

    PubMed

    Malov, A I

    2016-03-01

    The chemical composition and isotopes of carbon and uranium were investigated in groundwater samples that were collected from 16 wells and 2 sources in the Northern Dvina Basin, Northwest Russia. Across the dataset, the temperatures in the groundwater ranged from 3.6 to 6.9 °C, the pH ranged from 7.6 to 9.0, the Eh ranged from -137 to +128 mV, the total dissolved solids (TDS) ranged from 209 to 22,000 mg L(-1), and the dissolved oxygen (DO) ranged from 0 to 9.9 ppm. The (14)C activity ranged from 0 to 69.96 ± 0.69 percent modern carbon (pmC). The uranium content in the groundwater ranged from 0.006 to 16 ppb, and the (234)U:(238)U activity ratio ranged from 1.35 ± 0.21 to 8.61 ± 1.35. The uranium concentration and (234)U:(238)U activity ratio increased from the recharge area to the redox barrier; behind the barrier, the uranium content is minimal. The results were systematized by creating a conceptual model of the Northern Dvina Basin's hydrogeological system. The use of uranium isotope dating in conjunction with radiocarbon dating allowed the determination of important water-rock interaction parameters, such as the dissolution rate:recoil loss factor ratio Rd:p (a(-1)) and the uranium retardation factor:recoil loss factor ratio R:p in the aquifer. The (14)C age of the water was estimated to be between modern and >35,000 years. The (234)U-(238)U age of the water was estimated to be between 260 and 582,000 years. The Rd:p ratio decreases with increasing groundwater residence time in the aquifer from n × 10(-5) to n × 10(-7) a(-1). This finding is observed because the TDS increases in that direction from 0.2 to 9 g L(-1), and accordingly, the mineral saturation indices increase. Relatively high values of R:p (200-1000) characterize aquifers in sandy-clayey sediments from the Late Pleistocene and the deepest parts of the Vendian strata. In samples from the sandstones of the upper part of the Vendian strata, the R:p value is ∼ 24, i.e., sorption processes are

  10. Estimation of uranium migration parameters in sandstone aquifers.

    PubMed

    Malov, A I

    2016-03-01

    The chemical composition and isotopes of carbon and uranium were investigated in groundwater samples that were collected from 16 wells and 2 sources in the Northern Dvina Basin, Northwest Russia. Across the dataset, the temperatures in the groundwater ranged from 3.6 to 6.9 °C, the pH ranged from 7.6 to 9.0, the Eh ranged from -137 to +128 mV, the total dissolved solids (TDS) ranged from 209 to 22,000 mg L(-1), and the dissolved oxygen (DO) ranged from 0 to 9.9 ppm. The (14)C activity ranged from 0 to 69.96 ± 0.69 percent modern carbon (pmC). The uranium content in the groundwater ranged from 0.006 to 16 ppb, and the (234)U:(238)U activity ratio ranged from 1.35 ± 0.21 to 8.61 ± 1.35. The uranium concentration and (234)U:(238)U activity ratio increased from the recharge area to the redox barrier; behind the barrier, the uranium content is minimal. The results were systematized by creating a conceptual model of the Northern Dvina Basin's hydrogeological system. The use of uranium isotope dating in conjunction with radiocarbon dating allowed the determination of important water-rock interaction parameters, such as the dissolution rate:recoil loss factor ratio Rd:p (a(-1)) and the uranium retardation factor:recoil loss factor ratio R:p in the aquifer. The (14)C age of the water was estimated to be between modern and >35,000 years. The (234)U-(238)U age of the water was estimated to be between 260 and 582,000 years. The Rd:p ratio decreases with increasing groundwater residence time in the aquifer from n × 10(-5) to n × 10(-7) a(-1). This finding is observed because the TDS increases in that direction from 0.2 to 9 g L(-1), and accordingly, the mineral saturation indices increase. Relatively high values of R:p (200-1000) characterize aquifers in sandy-clayey sediments from the Late Pleistocene and the deepest parts of the Vendian strata. In samples from the sandstones of the upper part of the Vendian strata, the R:p value is ∼ 24, i.e., sorption processes are

  11. Provenance of Permian Malužiná Formation sandstones (Hronicum, Western Carpathians): evidence from monazite geochronology

    NASA Astrophysics Data System (ADS)

    Vozárová, Anna; Konečný, Patrik; Vďačný, Marek; Vozár, Jozef; Šarinová, Katarína

    2014-10-01

    The Permian Malužiná Formation and the Pennsylvanian Nižná Boca Formation are Upper Paleozoic volcano- sedimentary complexes in the Hronicum nappe system. Sandstones, shales and conglomerates are the dominant lithological members of the Malužiná Formation sequence. Detrital monazites were analysed by electron microprobe, to obtain Th-U-Pb ages of the source areas. The majority of detrital monazites showed Devonian-Mississippian ages, ranging from 330 to 380 Ma with a weighted average of 351 ± 3.3 (2σ), that correspond well with the main phase of arcrelated magmatic activity in the Western Carpathians. Only a small portion of detrital monazites displayed Permian ages in the range of 250-280 Ma, with a significant maximum around 255 Ma. The weighted average corresponds to 255 ± 6.2 Ma. These monazites may have been partially derived from the synsedimentary acid volcanism that was situated on the margins of the original depositional basin. However, some of the Triassic ages (230-240 Ma), reflect, most likely, the genetic relationship with the overheating connected with Permian and subsequent Triassic extensional regime. Detrital monazite ages document the Variscan age of the source area and also reflect a gradual development of the Hronicum terrestrial rift, accompanied by the heterogeneous cooling of the lithosphere.

  12. Analysis of radiation exposure for naval personnel at Operation Sandstone. Technical report

    SciTech Connect

    Thomas, C.; Goetz, J.; Stuart, J.; Klemm, J.

    1983-08-15

    Radiation environments are reconstructed for Task Group 7.3 ships and the residence islands of Enewetak and Kwajalein Atolls resulting from the three nuclear detonations comprising Operation SANDSTONE (April-May 1948). Secondary (late-time) fallout was the source of virtually all of the radioactive contamination on the ships and islands, most of which resulted from Shots X-RAY and YOKE. Fallout from Shot ZEBRA was minimal. From the reconstructed free-field radiological environments, an equivalent personnel film badge dose is calculated and compared to actual dosimetry data obtained during the operation. Calculated doses and dosimetry are consistent, although most of the calculated and film badge doses are below film badge threshold.

  13. Paleozoic evolution of active margin basins in the southern Central Andes (northwestern Argentina and northern Chile)

    NASA Astrophysics Data System (ADS)

    Bahlburg, H.; Breitkreuz, C.

    The geodynamic evolution of the Paleozoic continental margin of Gondwana in the region of the southern Central Andes is characterized by the westward progression of orogenic basin formation through time. The Ordovician basin in the northwest Argentinian Cordillera Oriental and Puna originated as an Early Ordovician back-arc basin. The contemporaneous magmatic arc of an east-dipping subduction zone was presumably located in northern Chile. In the back-arc basin, a ca. 3500 meter, fining-up volcaniclastic apron connected to the arc formed during the Arenigian. Increased subsidence in the late Arenigian allowed for the accomodation of large volumes of volcaniclastic turbidites during the Middle Ordovician. Subsidence and sedimentation were caused by the onset of collision between the para-autochthonous Arequipa Massif Terrane (AMT) and the South American margin at the Arenigian-Llanvirnian transition. This led to eastward thrusting of the arc complex over its back-arc basin and, consequently, to its transformation into a marine foreland basin. As a result of thrusting in the west, a flexural bulge formed in the east, leading to uplift and emergence of the Cordillera Oriental shelf during the Guandacol Event at the Arenigian-Llanvirnian transition. The basin fill was folded during the terminal collision of the AMT during the Oclóyic Orogeny (Ashgillian). The folded strata were intruded post-tectonically by the presumably Silurian granitoids of the "Faja Eruptiva de la Puna Oriental." The orogeny led to the formation of the positive area of the Arco Puneño. West of the Arco Puneño, a further marine basin developed during the Early Devonian, the eastern shelf of which occupied the area of the Cordillera Occidental, Depresión Preandina, and Precordillera. The corresponding deep marine turbidite basin was located in the region of the Cordillera de la Costa. Deposition continued until the basin fill was folded in the early Late Carboniferous Toco Orogeny. The basin

  14. PROGRESSIVE VENTILATION OF THE OCEANS - POTENTIAL FOR RETURN TO ANOXIC CONDITIONS IN THE POST-PALEOZOIC

    SciTech Connect

    Wilde, Pat; Berry, William B.N.

    1980-09-01

    After the ventilation of the residual anoxic layer in the late Paleozoic (Berry and Wilde, 1978) a return to ephemeral anoxic conditions in the ocean is suggested by anoxic sediments found in the Mesozoic cores of the deep-sea drilling program (Schlanger and Jenkyns 1977, and Theide and Van Andel 1977). A preliminary physical oceanographic model is presented to explain the development of oxygen depleted layers in mid-waters below the surface wind-mixed layer during non-glacial climates. The model shows the range of temperature, salinity and density values for hypothetical water masses for two climatically related oceanographic situations: Case A where bottom waters are formed at mid-latitudes at the surface salinity maxima, and Case B where bottom waters are produced at high latitudes but not by sea-ice formation as in the modern ocean. The hypothetical water masses are characterized by examples from the modern ocean and extrapolation to non-glacial times is made by eliminating water masses produced by or influenced by sea-ice formation in modern glacial times. The state of oxidation is made by plotting the model water masses on an oxygen saturation diagram and comparing the relative oxygen capacity with modern conditions of zonal organic productivity. The model indicates for Case A (high latitude temperatures above 5°C) two oxygen, depleted layers in the equatorial regions (1) from about 200m to the depth of completed oxidation of surface material separated by an oxygenated zone to (2) a deep depleted zone along the base of the pycnocline at 2900 M. The deep depleted zone extends along the Case A pycnocline polarward toward the high latitude productivity maximum. For case B with a pycnocline at about 1500m the deep anoxic layer is not sustained. Considerations of density only, suggest that neutral stratification and the potential for overturn is enhanced for climates transitional between Case A and Case B where the density contrast between major water masses

  15. Global Warmth and Nutrient Trapping Enhance End-Paleozoic Euxinia in an Earth System Model

    NASA Astrophysics Data System (ADS)

    Meyer, K. M.; Kump, L. R.; Ridgwell, A.

    2007-12-01

    The end-Permian mass extinction occurred during an interval characterized by global warmth and falling atmospheric oxygen levels. Although the cause of the extinction remains unresolved, geochemical evidence suggests that the event coincided with widespread anoxia and possible euxinia (anoxic and sulfidic waters). A combination of warm surface ocean temperatures, low atmospheric oxygen content, and high O2 demand in the deep ocean likely induced anoxia. Anaerobic organic matter remineralization by bacterial sulfate reduction then produced euxinic conditions. Phosphate release from surface sediments and decreased phosphate burial under a sulfidic water column further enhanced oceanic euxinia through positive feedbacks to primary productivity. We hypothesize that late Paleozoic climate and geography favored marine euxinia, a potential kill mechanism for the extinction event. Here we use earth system modelling to explore the physical and biogeochemical conditions necessary for the development of intense euxinia during the end-Permian. We use the end-Permian configuration of GENIE (www.genie.ac.uk), an energy-moisture-balance atmospheric model coupled to a 3-D, non-eddy-resolving, frictional geostrophic model to investigate the transition to marine anoxia and euxinia in a greenhouse world. Equilibrium model simulations over a range of oceanic phosphate concentrations relate oceanic nutrient status to the buildup of euxinia and attendant hydrogen sulfide release to the atmosphere. Addition of a marine nitrogen cycle suggests that microbial denitrification reduces, but does not prevent H2S buildup. Deep-ocean hydrogen sulfide appears with a doubling of phosphate, and localized photic zone euxinia develops with a tripling of phosphate. The greatest surface water H2S concentrations are observed in upwelling zones and in the Paleo-Tethys Ocean, where nutrient trapping results in elevated phosphate concentrations. Significant hydrogen sulfide fluxes to the atmosphere result

  16. Plumbotectonic aspects of polymetallic vein mineralization in Paleozoic sediments and Proterozoic basement of Moravia (Czech Republic)

    NASA Astrophysics Data System (ADS)

    Slobodník, Marek; Jacher-Śliwczyńska, Katarzyna; Taylor, Matthew C.; Schneider, Jens; Dolníček, Zdeněk

    2008-02-01

    A regional isotopic study of Pb and S in hydrothermal galenas and U-Pb and S in potential source rocks was carried out for part of Moravia, Czech Republic. Two major generations of veins, (syn-) Variscan and post-Variscan, are defined based on the Pb-isotope system together with structural constraints (local structures and regional trends). The Pb-isotopic compositions of galena plot in two distinct populations with outliers in 206Pb/204Pb-207Pb/204Pb space. Galena from veins hosted in greywackes provides a cluster with the lowest Pb-Pb ratios: 206Pb/204Pb = 18.15-18.27, 207Pb/204Pb = 15.59-15.61, 208Pb/204Pb = 38.11-38.23. Those hosted in both limestones and greywackes provide the second cluster: 206Pb/204Pb = 18.37-18.44, 207Pb/204Pb = 15.60-15.63, 208Pb/204Pb = 38.14-38.32. These clusters suggest model Pb ages as Early Carboniferous and Triassic-Jurassic, the latter associated with MVT-like deposits. Two samples from veins hosted in Proterozoic rocks lie outside the two clusters: in metagranitoid (206Pb/204Pb = 18.55, 207Pb/204Pb = 15.64, 208Pb/204Pb = 38.29) and in orthogneiss (206Pb/204Pb = 18.79, 207Pb/204Pb = 15.73, 208Pb/204Pb = 38.54). The results from these two samples suggest an interaction of mineralizing fluids with the radiogenic Pb-rich source (basement?). The values of δ34S suggest the Paleozoic host rocks (mostly -6.7 to +5.2‰ CDT) as the source of S for hydrothermal sulfides (mostly -4.8 to +2.5‰ CDT). U-Pb data and Pb isotope evolutionary curves indicate that Late Devonian and Early Carboniferous sediments, especially siliciclastics, are the general dominant contributor of Pb for galena mineralization developed in sedimentary rocks. Plumbotectonic mixing occurred, it is deduced, only between the lower and the upper crust (the latter involving Proterozoic basement containing heterogeneous radiogenic Pb), without any significant input from the mantle. It is concluded that in the Moravo-Silesian and Rhenohercynian zones (including proximal

  17. Paleozoic and Paleoproterozoic Zircon in Igneous Xenoliths Assimilated at Redoubt Volcano, Alaska

    NASA Astrophysics Data System (ADS)

    Bacon, C. R.; Vazquez, J. A.; Wooden, J. L.

    2010-12-01

    Historically active Redoubt Volcano is a basalt-to-dacite cone constructed upon the Jurassic-early Tertiary Alaska-Aleutian Range batholith. New SHRIMP-RG U-Pb age and trace-element concentration results for zircons from gabbroic xenoliths and crystal-rich andesitic mush from a late Pleistocene pyroclastic deposit indicate that ~310 Ma and ~1865 Ma igneous rocks underlie Redoubt at depth. Two gabbros have sharply terminated prismatic zircons that yield ages of ~310 Ma. Zircons from a crystal mush sample are overwhelmingly ~1865 Ma and appear rounded due to incomplete dissolution. Binary plots of element concentrations or ratios show clustering of data for ~310-Ma grains and markedly coherent trends for ~1865-Ma grains; e.g., ~310-Ma grains have higher Eu/Eu* than most of the ~1865-Ma grains, the majority of which form a narrow band of decreasing Eu/Eu* with increasing Hf content which suggests that ~1865-Ma zircons come from igneous source rocks. It is very unlikely that detrital zircons from a metasedimentary rock would have this level of homogeneity in age and composition. One gabbro contains abundant ~1865 Ma igneous zircons, ~300-310 Ma fluid-precipitated zircons characterized by very low U and Th concentrations and Th/U ratios, and uncommon ~100 Ma zircons. We propose that (1) ~310 Ma gabbro xenoliths from Redoubt Volcano belong to the same family of plutons dated by Aleinikoff et al. (USGS Circular 1016, 1988) and Gardner et al. (Geology, 1988) located ≥500 km to the northeast in basement rocks of the Wrangellia and Alexander terranes and (2) ~1865 Ma zircons are inherited from igneous rock, potentially from a continental fragment that possibly correlates with the Fort Simpson terrane or Great Bear magmatic zone of the Wopmay Orogen of northwestern Laurentia. Possibly, elements of these Paleoproterozoic terranes intersected the Paleozoic North American continental margin where they may have formed a component of the basement to the Wrangellia

  18. Barents Sea Paleozoic basement and basin configurations: Crustal structure from deep seismic and potential field data

    NASA Astrophysics Data System (ADS)

    Aarseth, Iselin; Mjelde, Rolf; Breivik, Asbjørn Johan; Huismans, Ritske; Faleide, Jan Inge

    2016-04-01

    The Barents Sea is underlain by at least two different basement domains; the Caledonian in the west and the Timanian in the east. The transition between these two domains is not well constrained and contrasting interpretations have been published recently. Interpretations of new high-quality magnetic data covering most of the SW Barents Sea has challenged the Late Paleozoic basin configurations in the western and central Barents Sea as outlined in previous studies. Two regional ocean bottom seismic (OBS) profiles were acquired in 2014. This new dataset crosses the two major directions of Caledonian deformation proposed by different authors: N-S direction and SW-NE direction. Of particular importance are the high velocity anomalies related to Caledonian eclogites, revealing the location of Caledonian suture zones in the northern Barents Sea. One of the main objectives with this project is to locate the main Caledonian suture in the western Barents Sea, as well as the possible Barentsia-Baltica suture postulated further eastwards. The collapse of the Caledonian mountain range predominantly along these suture zones is expected to be tightly linked to the deposition of large thicknesses of Devonian erosional products, and later rifting is expected to be influenced by inheritance of Caledonian trends. The P-wave travel-time modelling is done by use of a combined ray-tracing and inversion scheme, and gravity- and magnetic modelling will be used to augment the seismic model. The preliminary results indicate high P-wave velocities (mostly over 4 km/s) close to the seafloor as well as high velocity (around 6 km/s) zones at shallow depths which are interpreted as volcanic sills. The crustal transects reveal areas of complex geology and velocity inversions. A low seismic impedance contrast between the sedimentary section and top crystalline basement makes identification of this interface uncertain. Depth to Moho mostly lies around 30 km, except in an area of rapid change in

  19. Laser Ablation Split Stream (LASS) U-Pb & Lu-Hf Isotope Analysis of Detrital Zircons from the Old Red Sandstone, NW Svalbard: Implications for Northern Caledonian Paleogeography

    NASA Astrophysics Data System (ADS)

    Beranek, L. P.; Gee, D. G.; Fisher, C. M.

    2015-12-01

    The Svalbard archipelago consists of three Caledonian provinces that were assembled by thrusting and transcurrent faulting during the Silurian and Devonian in a location directly northeast of the Greenland Caledonides. Syn- to post-orogenic alluvial strata, referred to as the Old Red Sandstones, filled pull-apart basins adjacent to the transcurrent faults and comprise cover assemblages that help constrain the timing of the Caledonian orogeny. To further investigate the tectonic history and paleogeography of the Raudfjorden-Liefdefjorden-Woodfjorden area of Spitsbergen, NW Svalbard, we analyzed rock samples of the Old Red Sandstones and underlying Precambrian basement complexes for detrital zircon analysis. Laboratory studies of the Old Red Sandstones include the novel Laser Ablation Split Stream (LASS) technique, which allows for simultaneous U-Pb & Lu-Hf isotope analysis of zircon crystals. Lower Devonian Red Bay Group strata contain a range of early Neoproterozoic to Neoarchean detrital zircons with prominent age peaks c. 960, 1050, 1370, 1450, 1650, and 2700 Ma; subordinate Ordovician (c. 460-490 Ma) and Cryogenian (c. 650 Ma) detrital zircons occur in a subset of the samples. Underlying Precambrian metasedimentary rocks are composed of similar earliest Neoproterozoic to Neoarchean age populations, which argues for much of the Red Bay Group to be derived from local basement rocks during thrusting and other faulting. The U-Pb ages and Hf isotope compositions of Paleozoic to Neoarchean detrital zircons are consistent with Arctic crustal evolution, and support the hypothesis that northwestern and northeastern provinces of the Svalbard Caledonides are extruded fragments of the northeast Greenland allochthons. The new Hf isotope results further allow paleogeographic and stratigraphic comparisons with rock assemblages proximal to the North Atlantic Caledonides during the Silurian-Devonian, including the Pearya terrane of Ellesmere Island, Alexander terrane of NW

  20. Effective Thermal Conductivity Modeling of Sandstones: SVM Framework Analysis

    NASA Astrophysics Data System (ADS)

    Rostami, Alireza; Masoudi, Mohammad; Ghaderi-Ardakani, Alireza; Arabloo, Milad; Amani, Mahmood

    2016-06-01

    Among the most significant physical characteristics of porous media, the effective thermal conductivity (ETC) is used for estimating the thermal enhanced oil recovery process efficiency, hydrocarbon reservoir thermal design, and numerical simulation. This paper reports the implementation of an innovative least square support vector machine (LS-SVM) algorithm for the development of enhanced model capable of predicting the ETCs of dry sandstones. By means of several statistical parameters, the validity of the presented model was evaluated. The prediction of the developed model for determining the ETCs of dry sandstones was in excellent agreement with the reported data with a coefficient of determination value ({R}2) of 0.983 and an average absolute relative deviation of 0.35 %. Results from present research show that the proposed LS-SVM model is robust, reliable, and efficient in calculating the ETCs of sandstones.

  1. Plane shock wave studies of Westerly granite and Nugget sandstone

    SciTech Connect

    Larson, D.B.; Anderson, G.D.

    1980-12-01

    Plane shock wave experiments were performed by using a light-gas gun on dry and water-saturated Westerly granite and dry Nugget sandstone. Changes in the slopes of the shock velocity versus particle velocity curves at 2 to 3 GPa and 1 to 2 GPa for dry granite and for dry sandstone, respectively, are attributed to the onset of pore collapse. However, there is little apparent loss of shear strength in either dry rock over the stress range of the experiments (i.e., 9.3 GPa in Westerly granite and 9.2 GPa in Nugget sandstone). Agreement between the shock wave data and quasistatic, uniaxial strain data for the dry rock implies the absence of rate-dependence in uniaxial strain. The shock data on saturated granite agree well with those for dry granite, thus suggesting there was no loss in shear strength as a result of pore pressure buildup.

  2. Optical coherence tomography for vulnerability assessment of sandstone.

    PubMed

    Bemand, Elizabeth; Liang, Haida

    2013-05-10

    Sandstone is an important cultural heritage material, in both architectural and natural settings, such as neolithic rock art panels. The majority of deterioration effects in porous materials such as sandstone are influenced by the presence and movement of water through the material. The presence of water within the porous network of a material results in changes in the optical coherence tomography signal intensity that can be used to monitor the wetting front of water penetration of dry porous materials at various depths. The technique is able to detect wetting front velocities from 1 cm s(-1) to 10(-6) cm s(-1), covering the full range of hydraulic conductivities likely to occur in natural sandstones from pervious to impervious.

  3. Factors controlling localization of uranium deposits in the Dakota Sandstone, Gallup and Ambrosia Lake mining districts, McKinley County, New Mexico

    USGS Publications Warehouse

    Pierson, Charles Thomas; Green, Morris W.

    1977-01-01

    Geologic studies were made at all of the uranium mines and prospects in the Dakota Sandstone of Early(?) and Late Cretaceous age in the Gallup mining district, McKinley County, New Mexico. Dakota mines in the adjacent Ambrosia Lake mining district were visited briefly for comparative purposes. Mines in the eastern part of the Gallup district, and in the Ambrosia Lake district, are on the Chaco slope of the southern San Juan Basin in strata which dip gently northward toward the central part of the basin. Mines in the western part of the Gallup district are along the Gallup hogback (Nutria monocline) in strata which dip steeply westward into the Gallup sag. Geologic factors which controlled formation of the uranium deposits in the Dakota Sandstone are: (1) a source of uranium, believed to be uranium deposits of the underlying Morrison Formation of Late Jurassic age; (2) the accessibility to the Dakota of uranium-bearing solutions from the Morrison; (3) the presence in the Dakota of permeable sandstone beds overlain by impermeable carbonaceous shale beds; and (4) the occurrence within the permeable Dakota sandstone beds of carbonaceous reducing material as bedding-plane laminae, or as pockets of carbonaceous trash. Most of the Dakota uranium deposits are found in the lower part of the formation in marginal-marine distributary-channel sandstones which were deposited in the backshore environment. However, the Hogback no. 4 (Hyde) Mine (Gallup district) occurs in sandy paludal shale of the backshore environment, and another deposit, the Silver Spur (Ambrosia Lake district), is found in what is interpreted to be a massive beach or barrier-bar sandstone of the foreshore environment in the upper part of the Dakota. The sedimentary depositional environment most favorable for the accumulation of uranium is that of backshore areas lateral to main distributary channels, where levee, splay, and some distributary-channel sandstones intertongue with gray carbonaceous shales and

  4. Diagenesis, compaction, and fluid chemistry modeling of a sandstone near a pressure seal: Lower Tuscaloosa Formation, Gulf Coast

    USGS Publications Warehouse

    Weedman, S.D.; Brantley, S.L.; Shiraki, R.; Poulson, S.R.

    1996-01-01

    Petrographic, isotopic, and fluid-inclusion evidence from normally and overpressured sandstones of the lower Tuscaloosa Formation (Upper Cretaceous) in the Gulf Coast documents quartz-overgrowth precipitation at 90??C or less, calcite cement precipitation at approximately 100?? and 135??C, and prismatic quartz cement precipitation at about 125??C. Textural evidence suggests that carbonate cement dissolution occurred before the second phases of calcite and quartz precipitation, and was followed by precipitation of grain-rimming chlorite and pore-filling kaolinite. Geochemical calculations demonstrate that present-day lower Tuscaloosa Formation water from 5500 m depth could either dissolve or precipitate calcite cements in model simulations of upward water flow. Calcite dissolution or precipitation depends on PCO2 variability with depth (i.e., whether there is one or two-phase flow) or on the rate of generation of CO2 with depth. Calculations suggest that 105-106 rock volumes of water are required to flow through the section to precipitate 1-10% calcite cement. Compaction analysis suggests that late-stage compaction occurred in normally pressured sandstones after dissolution of carbonate cements, but was hindered in overpressured sandstones despite the presence of high porosity. These results document the inhibition of compaction by overpressured fluids and constrain the timing of pressure seal formation. Modeling results demonstrate that the proposed paragenesis used to constrain timing of pressure seal formation is feasible, and that most of the cement diagenesis occurred before the pressure seal became effective as a permeability barrier.

  5. Paleotectonic controls on deposition of Niobrara formation, Eagle sandstone, and equivalent rocks (Upper Cretaceous), Montana and South Dakota

    SciTech Connect

    Shurr, G.W.; Rice, D.D.

    1985-05-01

    The deposition of the Niobrara Formation, Eagle Sandstone, and equivalent Upper Cretaceous rocks was controlled by paleotectonic activity on lineament-bound basement blocks in Montana and South Dakota. Linear features observed on Landsat images provide an interpretation of lineament geometry that is independent of stratigraphic data. Paleotectonism on lineament-bound blocks is documented in three areas that were located in distinctly different depositional environments. In central Montana, coastal and inner-shelf sandstones and nonmarine coastal-plain and wave-dominated delta deposits reflect paleotectonic control by lineaments trending north-south, east-west, northwest, and northeast. In the northern Black Hills, chalks and outer-shelf sandstones reflect control by lineaments trending north-south, northwest, and north-east. In central South Dakota, erosion and deposition of chalk and calcareous shale on a west-sloping carbonate ramp were controlled by lineaments that generally trend northeast and northwest. Paleotectonism on lineament-bound blocks characterized four tectonic zones located in the Late Cretaceous seaway; the western foredeep, the west-median trough, the east-median hinge, and the eastern platform. The regional geometry of all four tectonic zones appears to be related to the geometry of the convergent plate margin on the west. Paleotectonic activity on lineament-bound blocks may have been the result of horizontal forces related to the convergent margin and to vertical forces related to the movement of the North American plate.

  6. Diagenetic pathways for sandstones: The role of initial composition

    SciTech Connect

    Harris, N.B.

    1995-09-01

    The initial composition of a clastic section is critical in determining the diagenetic reactions that a sandstone will undergo during burial, reactions which strongly influence its reservoir properties. The role of initial composition is illustrated for Middle Jurassic sandstones of northwest Europe (including the Brent sandstone of the North Sea) and Tertiary sandstones of the Gulf of Mexico. The composition of the former evolves from arkose to quartz arenite, with massive dissolution first of plagioclase and subsequently K-feldspar. As the bulk composition changes, the suite of clay minerals changes from kaolinite-dominated to illite-dominated, suite of clay minerals changes from kaolinite-dominated to illite-dominated, typically accompanied by a pronounced decrease in permeability. The Gulf of Mexico sandstones are also initially arkoses. Their composition, however, evolves toward a mixture of quartz and compositionally pure albite. Kaolinite remains the dominant authigenic clay within the sandstones; however detrital clays change from a Na-rich, smectitic mixed layer clay to a K-rich, illitic mixed layer clay. The contrasting diagenetic pathways result from differing mineralogy in the clastic section. The smectite-rich mudstones in the Gulf of Mexico provide a powerful sink for potassium and source of sodium. The resulting low potassium activity results in K-feldspar dissolution; it also prevents illite formation, while high sodium activity stabilizes albite. The Middle Jurassic clastic section in northwest Europe contains relatively little smectite, thus lacks the potassium sink and sodium source. Sodium activity is low, so plagioclases preferentially dissolve. K-feldspars also dissolve, but the potassium here is available for illite formation.

  7. Microbial contamination of two urban sandstone aquifers in the UK.

    PubMed

    Powell, Karen L; Taylor, Richard G; Cronin, Aidan A; Barrett, Mike H; Pedley, Steve; Sellwood, Jane; Trowsdale, Sam A; Lerner, David N

    2003-01-01

    Development of urban groundwater has historically been constrained by concerns about its quality. Rising urban water tables and overabstraction from rural aquifers in the UK have led to a renewed interest in urban groundwater, particularly the possibility of finding water of acceptable quality at depth. This study assessed the microbial quality of groundwater collected from depth-specific intervals over a 15-month period within the Permo-Triassic Sherwood Sandstone aquifers underlying the cities of Nottingham and Birmingham. Sewage-derived bacteria (thermotolerant coliforms, faecal streptococci and sulphite-reducing clostridia) and viruses (enteroviruses, Norwalk-like viruses, coliphage) were regularly detected to depths of 60 m in the unconfined sandstone and to a depth of 91 m in the confined sandstone. Microbial concentrations varied temporally and spatially but increased frequency of contamination with depth coincided with geological heterogeneities such as fissures and mudstone bands. Significantly, detection of Norwalk-like viruses and Coxsackievirus B4 in groundwater corresponded with seasonal variations in virus discharge to the sewer system. The observation of low levels of sewage-derived microbial contaminants at depth in the Triassic Sandstone aquifer is explained by the movement of infinitesimal proportions of bulk (macroscopic) groundwater flow along preferential pathways (e.g., fissures, bedding planes). The existence of very high microbial populations at source (raw sewage) and their extremely low detection limits at the receptor (multilevel piezometer) enable these statistically extreme (microscopic) flows to be traced. Rapid penetration of microbial contaminants into sandstone aquifers, not previously reported, highlights the vulnerability of sandstone aquifers to microbial contamination. PMID:12502063

  8. Microbial contamination of two urban sandstone aquifers in the UK.

    PubMed

    Powell, Karen L; Taylor, Richard G; Cronin, Aidan A; Barrett, Mike H; Pedley, Steve; Sellwood, Jane; Trowsdale, Sam A; Lerner, David N

    2003-01-01

    Development of urban groundwater has historically been constrained by concerns about its quality. Rising urban water tables and overabstraction from rural aquifers in the UK have led to a renewed interest in urban groundwater, particularly the pos