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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

    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.

  7. Plate Tectonics in the Late Paleozoic

    NASA Astrophysics Data System (ADS)

    Domeier, Mat; Torsvik, Trond

    2014-05-01

    As the chronicle of plate motions through time, paleogeography is fundamental to our understanding of plate tectonics and its role in shaping the geology of the present-day. To properly appreciate the history of tectonics—and its influence on the deep Earth and climate—it is imperative to seek an accurate and global model of paleogeography. However, owing to the incessant loss of oceanic lithosphere through subduction, the paleogeographic reconstruction of 'full-plates' (including oceanic lithosphere) becomes increasingly challenging with age. Prior to 150 Ma ~60% of the lithosphere is missing and reconstructions are developed without explicit regard for oceanic lithosphere or plate tectonic principles; in effect, reflecting the earlier mobilistic paradigm of continental drift. Although these 'continental' reconstructions have been immensely useful, the next-generation of mantle models requires global plate kinematic descriptions with full-plate reconstructions. Moreover, in disregarding (or only loosely applying) plate tectonic rules, continental reconstructions fail to take advantage of a wealth of additional information in the form of practical constraints. Following a series of new developments, both in geodynamic theory and analytical tools, it is now feasible to construct full-plate models that lend themselves to testing by the wider Earth-science community. Such a model is presented here for the late Paleozoic (410-250 Ma). Although we expect this model to be particularly useful for numerical mantle modeling, we hope that it can also serve as a general framework for understanding late Paleozoic tectonics, one on which future improvements can be built and further tested.

  8. 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.

  9. Geochemical evidence for Paleozoic oil in Lower Cretaceous O Sandstone, northern Denver basin

    USGS Publications Warehouse

    Clayton, J.L.

    1989-01-01

    Organic geochemical properties of the oil produced from the Lower Cretaceous O sandstone on the eastern flank of the Denver basin indicate that this oil has been derived from a different source rock than other Cretaceous oils in the basin. O sandstone oil is characterized by low pristane/phytane ratio, high isoprenoid/n-alkane ratios, high asphaltene content, high sulfur content, and slight predominance of even-carbon numbered n-alkanes in the C25+ fraction. These features are evidence of a Paleozoic source and indicate a carbonate rock is the likely source. Preliminary source rock evaluation and correlation data suggest that calcareous black shales and marls of Middle Pennsylvanian (Desmoinesian) age are the source of the O sandstone oil. This is the first reported occurrence of oil from Paleozoic source rocks in a Cretaceous reservoir in the Denver basin. -from Author

  10. Late Paleozoic paleotectonics of the northern Rocky Mountain region

    SciTech Connect

    Peterson, J.A. . Dept. of Geology)

    1993-04-01

    The present-day configuration of northern Rocky Mountain foreland uplifts and basins evolved mainly by middle to late Tertiary time. Many of these structures, however, were inherited from Paleozoic and early Mesozoic tectonic episodes and thus have a long history of influence on sediment source terranes, clastic and carbonate facies distributions, thickness relationships, and diagenetic processes. New structural growth, and renewed older growth, were particularly important during late Paleozoic time, approximately coincident in time with growth of the Ancestral Rocky Mountains. Some features tend to trend with, or are sub-parallel to elements of the Ancestral Rocky Mountains, including the Laramie-Casper Big Horn high, the Powder River, Bighorn, and Wind River sags, and the Alliance-Denver basin. Late Paleozoic growth of these features, and perhaps others, undoubtedly was affected by stresses associated with the Ancestral Rocky Mountains episode. Interpretations, however, depend on careful stratigraphic and sedimentary facies analyses.

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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.

  16. 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.

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

    USGS Publications Warehouse

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

    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.

  18. 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

  19. 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

  20. Evidence from detrital zircons for recycling of Mesoproterozoic and Neoproterozoic crust recorded in Paleozoic and Mesozoic sandstones of southern Libya

    NASA Astrophysics Data System (ADS)

    Meinhold, Guido; Morton, Andrew C.; Fanning, C. Mark; Frei, Dirk; Howard, James P.; Phillips, Richard J.; Strogen, Dominic; Whitham, Andrew G.

    2011-12-01

    The geodynamic history of the Precambrian basement in central North Africa as well as the age and provenance of its sedimentary cover sequence are still poorly constrained. Here we present first detrital zircon ages (obtained by LA-SF-ICP-MS and SHRIMP) from Paleozoic and Mesozoic sandstones of the eastern Murzuq Basin, southern Libya, which unconformably overlie the Saharan Metacraton. Establishing the age and provenance of these sandstones has important implications for our understanding of the evolution of northern Gondwana during the Paleozoic, especially for reconstructions of paleo-source areas and transport paths. Detrital zircons from the sandstones show mainly early Paleozoic to Neoarchean ages with four main age populations, at 2750-2500 Ma (8%), 2200-1750 Ma (16%), 1060-920 Ma (18%), and 720-530 Ma (39%). About 13% of all concordant grains yield ages of 1600-1000 Ma. In addition, there are 9 zircon grains (0.7% of all concordant grains) with ages of 3600-2800 Ma. The presence of a high number of ca. 1 Ga zircons is enigmatic and their origin is controversial. Besides direct sourcing from ca. 1 Ga igneous rocks in eastern Chad and ca. 1 Ga igneous rocks along the southeastern margins of the Congo and Tanzania cratons, recycling of Neoproterozoic sediments containing ca. 1 Ga zircons is another alternative hypothesis to explain the presence of ca. 1 Ga zircons in the Paleozoic sedimentary sequence of central North Africa. The ubiquitous occurrence of ca. 1 Ga zircons in Paleozoic sediments of southern Libya provides insights into the correlation and paleotectonic arrangement of Gondwana-derived terranes, present, for example, in the eastern Mediterranean and in southwestern Europe. Current paleotectonic models of dextral terrane transport along the northern Gondwana margin during the early Paleozoic may need to be revised.

  1. 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.

  2. Geological Evidences For Late Paleozoic Intra-pangea Dextral Shear

    NASA Astrophysics Data System (ADS)

    Muttoni, G.; Kent, D. V.; Abrahamsen, N.; Brack, P.

    The Wegenerian configuration of Pangea at Jurassic times, also known as Pangea A, is not questioned among Earth scientists. Debate exists on its pre-Jurassic configu- ration since Ted Irving (1977 Nature) introduced twenty-five years ago Pangea B by placing Gondwana to the East by 2500km with respect to Laurasia on the basis of paleomagnetic data. Pangea B is mainly necessitated by paleolatitude discrepancy be- tween Africa (Gondwana) and North America (Laurasia), which would overlap by about 1700km if reconstructed in a Pangea A configuration at Early Perian times. West Gondwana/Adria poles support Pangea B in the Early Permian, but allow transi- tion to Pangea A by the end of the Permian in the late stages of the Variscan/Hercynian orogeny (Muttoni et al., 1996 EPSL). Importantly, some of the Early Permian pale- opoles are in igneous rocks and/or from low paleolatitude sites (e.g., Adria), hence making inclination error less likely as an explanation for Pangea B as envisaged by Rochette and Vandamme (2001 Annali di Geofisica). A few Earth scientists tried to seek geological evidence for the pre-Jurassic dextral mega-shear between Gondwana and Laurasia necessary to go from Pangea B or similar configuration to the Pangea A configuration at the time of Atlantic opening in the Jurassic (e.g., Ricou, The Ocean Basins and Margins, Vol. 8, Plenum Press, 1996). Nevertheless, it is fair to say that Pangea B and its tectonic implications have not been broadly accepted but this leaves the problem of the supportive paleomagnetic data unresolved. The ultimate option is to abandon the geocentral axial dipole (GAD) hypothesis by introducing a non-dipole component in the Late Paleozoic paleomagnetic field to explain the paleolatitude dis- crepancy between Africa and North America (Van der Voo and Torsvik, 2001 EPSL). We are not so distressed by the geological consequences of Pangea B to abandon the GAD hypothesis which has been the basis for virtually all tectonic

  3. 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

  4. 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.

  5. 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.

  6. Reconstructing Late Paleozoic exhumation history of the Inner Mongolia Highland along the northern edge of the North China Craton

    NASA Astrophysics Data System (ADS)

    Ma, Shouxian; Meng, Qingren; Duan, Liang; Wu, Guoli

    2014-06-01

    The Inner Mongolia Highland (IMH), along the northern edge of the North China Craton, was considered to be a long-standing topographic highland, whose exhumation history remains elusive. The aim of this study is to reveal Late Paleozoic exhumation processes of the IMH based on an integrated analysis of stratigraphy, petrography of clastic rocks, and U-Pb ages and Hf isotopes of detrital zircons from Permian-Triassic succession in the middle Yanshan belt. The results of the study show that the Benxi Formation, which was originally regarded as a Late Carboniferous unit, proves to be Early Permian in age because it contains detrital zircons as young as ∼298 Ma. The Lower Shihezi Formation is demonstrated to be a unit whose age spans the boundary of the Middle and Upper Permian, constrained by a U-Pb age of 260 ± 2 Ma from a dacite layer. Clastic compositions of conglomerate and sandstone change markedly, characterised by the predominance of sedimentary components in the Benxi-Shanxi Formations, by large amounts of volcanic clastics in the Lower and Upper Shihezi Formations, and by the presence of both metamorphic and igneous clastics in the Sunjiagou-Ermaying Formations. Sedimentary clastics include chert, carbonate, sandstone and quartzite, which may have been derived from Proterozoic to Lower Paleozoic sedimentary covers. Volcanic clasts were directly related to volcanic eruptions, while granite and gneiss grains were sourced from exhumed Late Paleozoic intrusive rocks and basement rocks. Detrital zircon U-Pb ages can be divided into five populations: 2.6-2.4 Ga, 1.9-1.7 Ga, 400-360 Ma, 325-290 Ma and 270-250 Ma. Precambrian detrital zircons are typically subrounded to rounded in shape, implying a recycling origin. Late Paleozoic zircons show oscillatory zones and their Th/U ratios >0.4, suggesting a magmatic origin. Most Phanerozoic zircons have negative εHf(T) values of -3.2 to -25.5, which are compatible with those of Late Paleozoic plutons in the IMH. The

  7. Late Paleozoic basin evolution in the Western Pyrenees

    NASA Astrophysics Data System (ADS)

    Cantarelli, V.; Casas-Sainz, A.; Corrado, S.; Gisbert-Aguilar, J.; Invernizzi, C.; Aldega, L.

    2009-04-01

    Late-Variscan (Late Carboniferous-Early Triassic) evolution in the Axial Zone of the Pyrenees is characterised by continental, intra-mountainous basin formation. These basins are presently preserved in the hangingwall of the main thrusts responsible for the uplift of the Axial Zone (Gavarnie thrust in the western Pyrenees and Nogueres thrust system in the central Pyrenees). Sedimentary sequences filling the Late Variscan basins developed under a post-collisional, strike-slip regime, with thrust-top facies, and evolved toward an extensional setting during Permian times with fluvial and lacustrine facies accompanied by extensive pyroclastic deposition (Gisbert, 1984), still before the onset of widespread extensional sedimentation corresponding to the beginning (Early Triassic) of the Alpine cycle. The continental successions are preserved in basins organised along the E-W direction, parallel to the present-day outcrop of the Axial Zone of the Pyrenees, with limited extension and lengthening in the same direction. Although it is difficult to infer the actual position of the main faults limiting the Late-Variscan basins because of the Tertiary compressional deformation and basin inversion, the main faults limiting these basins are considered to have a WNW-ESE direction, with other oblique or near-perpendicular faults responsible for the occurrence of no-sedimentation areas along-strike of the Axial Zone. Between the Variscan basement (mainly consisting of Devonian limestones and Carboniferous turbiditic Culm facies) and the Alpine sedimentary cover (Early Triassic continental deposits), the Stephanian-Autunian record is a fining-upward lacustrine, 1000-1500 m thick sedimentary succession constituted by dolomitic limestones, conglomerates, sandstones and siltstones. It is organized in four depositional units: Grey Unit (Stephanian B), Intermediate Unit (Stephanian B- Autunian), Lower Red Unit (Autunian) and Upper Red Unit (late Permian). The entire succession is limited

  8. 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.

  9. 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

  10. Simulating Dust Cycling during the Late Paleozoic Ice Age

    NASA Astrophysics Data System (ADS)

    Heavens, N. G.; Mahowald, N. M.; Soreghan, G. S.; Soreghan, M. J.; Shields, C. A.; Albani, S.

    2012-12-01

    sources, but find that our modeling of these processes still cannot explain the full amplitude of variability in the marine records. By making some inferences from the provenance and grain size distribution of the dust deposition records, we reconstruct dust cycling during the termination of extreme glacial conditions in the Early Permian within observational uncertainty. This reconstruction allows a rough estimate of the sensitivity of Early Permian glacial climates to dust as well as radiative forcing. Moreover, the reconstruction highlights potential new areas to explore for non-equatorial marine records of dust deposition, which will improve future assessment of the impact of dust on late Paleozoic climate.

  11. 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.

  12. 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.

  13. 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

  14. 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.

  15. 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.

  16. New Structural, Geochronological and Geochemical Constraints on the Late Paleozoic Geodynamic Evolution of Northwestern Tianshan, NW China

    NASA Astrophysics Data System (ADS)

    Wang, B.; Faure, M.; Cluzel, D.; Shu, L.; Charvet, J.

    2005-12-01

    The Tianshan Belt is one of the main elements of the Central Asia Orogenic collage, which builds up the Eurasian continent during the Paleozoic. The Tianshan Belt is often divided into North, Central and South Tianshan domains, the Yili Block is a continental piece that wedges eastward between the North and Central Tianshan. Our study provides some new structural, geochronological and geochemical evidence to better understand the Late Paleozoic geodynamic amalgamation of the western part of the North Tianshan and the Yili Block. The North Tianshan is composed of relics of oceanic lithosphere and Mid-Carboniferous turbidite. Blocks of serpentinized peridotite, gabbro, pillow basalt, chert and detrital rocks derived from ophiolite make up an ophiolitic mélange, refered to as the `Bayingou ophiolite'. Sedimentological and structural features indicate that this mélange is a sheared olistostrome with exotic blocks, which experienced polyphase tectonic processes. In the ophiolitic mélange, Famennian-Tournaisian radiolarians in chert, N-MORB, OIB and IAT-type mafic rocks with SHRIMP U-Pb age of 325-A7 Ma on Zircon from gabbro, indicate that these ophiolites developed within a Late Devonian to Mid-Carboniferous oceanic basin. This mélange separates the turbidite into two parts. The northern one is deformed by north-verging recumbent folds, and the southern one is characterized by a syn-metamorphic ductile deformation. Sandstone and pelite exhibit a steeply dipping slaty cleavage and a sub-horizontal stretching and mineral lineation. Kinematic criteria indicate ductile dextral shearing. A new 40Ar/39Ar dating on biotite of deformed schist shows that the shearing took place around 250 Ma. The Paleozoic rocks of the Yili Block consist of Carboniferous platform sediments associated with volcanic and volcaniclastic rocks and intruded by granitoids. Geochemical analyses (ICP-MS) on 60 volcanic rocks and granites from 8 representative sections show that (1) these rocks belong

  17. 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.

  18. 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.

  19. 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.

  20. 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

  1. 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.

  2. 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.

  3. 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.

  4. Volcanic Winter and Cold Tropical Uplands in Late Paleozoic Pangaea: A Thought Experiment

    NASA Astrophysics Data System (ADS)

    Heavens, N. G.; Soreghan, G. S.

    2014-12-01

    The Late Paleozoic Ice Age (LPIA) was the Earth's most recent icehouse climate prior to the Cenozoic. At present, it is generally accepted that the latitudinal gradient in climate conditions was similar to the present icehouse. High-latitude ice sheets occasionally advanced into the mid-latitudes and retreated once more, but the tropics were warmer or similar in climate to the tropics during the Plio-Pleistocene. Recently, this idea has been challenged by sedimentological evidence of glaciation and dry weathering in upland areas of the tropics as well as geochemical evidence for cold tropical oceans that is consistent with the sedimentological evidence. These observations challenge current qualitative and quantitative models of Late Paleozoic climate, implying tropical climate may have been up to 15 degrees Celsius colder than the present day at some point during the LPIA. Here we consider whether the disparity between evidence for equatorial cold in Pangaea and current models can be explained by explosive volcanic activity associated with events such as the Hercynian orogen or the Kennedy-Connors-Auburn Silicic Large Igneous Province. We find that the necessary radiative forcing for glaciation in low-latitude upland areas could be generated by explosive volcanic activity one to two orders of magnitude greater than the present day, perturbing a baseline climate with mid-latitude glaciation in both hemispheres. Such a forcing would have potentially significant impacts on the carbon cycle and ice sheet dynamics, but these effects are not likely to be unambiguously detectable in the record. Instead, we argue that measurements of mass independent fractionation of S in lacustrine sediments or other deposits sampling meteoric water would be the least ambiguous test of a hypothetical volcanic driver for late Paleozoic cold. This work was supported in part by the National Science Foundation, EAR-1337463.

  5. 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.

  6. 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

  7. Late Paleozoic accretionary complexes on the Gondwana margin of southern Chile: Evidence from the Chonos Archipelago

    NASA Astrophysics Data System (ADS)

    Davidson, John; Mpodozis, Constantino; Godoy, Estanislao; Hervé, Francisco; Pankhurst, Robert; Brook, Maureen

    The late Paleozoic "basement" rocks that crop out along the Pacific side of the Chonos Archipelago (44°-46°S) can be divided into two north-south trending belts: (1) an eastern belt formed of submarine fan-turbidites and subordinate pelagic cherts, each containing well-preserved primary sedimentary structures, and (2) a western belt, mainly formed by strongly foliated mica schists and greenschists. Trace element contents in the cherts and greenschists indicate rocks of oceanic affinity. The structures present within the eastern rock suite are principally subiso-clinal folds (with tectonic imbrication) and locally developed zones of broken formation. The transition from these rocks into the foliated schists appears to be related to a progressive increase in metamorphism and strain associated with the development of westward verging recumbent folds and a flat-lying crenulation cleavage. It is inferred that these structures developed during the construction of a Late Carboniferous-Early Permian accretionary prism (about 260 Ma Rb-Sr ages), although sedimentation may have taken place throughout the upper Paleozoic. Rb-Sr whole-rock isochrons giving Late Jurassic to Early Cretaceous ages for some localities may indicate much later development of S2 structures. Alternatively, they may represent isotopic resetting by hydrothermal effects during the emplacement of transgressive Early Cretaceous granites, one of which gives a new Rb-Sr isochron age of 125±2Ma. This overall scenario seems to be consistent with that reported in the slightly older coastal metamorphic basement north of 34°S and equivalent or younger complexes farther south in the Madre de Dios Archipelago.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Fundamentals of Glacial-Interglacial Variability in Tropical Pangaean Aridity during the Late Paleozoic

    NASA Astrophysics Data System (ADS)

    Heavens, N. G.; Mahowald, N. M.; Soreghan, G. S.; Soreghan, M. J.

    2011-12-01

    Isotopic and sedimentological evidence suggests that the Late Carboniferous and Early Permian Periods were the most recent era of widespread glaciation prior to the Cenozoic; many aspects of the late Paleozoic glaciations remain disputed. Was glacial deposition on Gondwanaland due to a single ice sheet or multiple ice sheets? Did Milankovitch-scale orbital forcing drive expansion and contraction of ice sheets analogous to the Laurentide and Fennoscandian ice sheets? Or were Gondwanan ice sheets more stable, like the East Antarctic ice sheet? Did variability in Gondwanan ice sheet thickness and extent drive the sea level fluctuations evident in tropical cyclothem sequences from the late Paleozoic? One approach to answering some of these broad questions has been to identify and measure various aspects of sedimentary deposits containing dust (paleoloessites etc.) in order to reconstruct aridity at dust sources and sinks and wind patterns along the path between them. Moreover, glacial processes may be very efficient generators of dust particles. Dust deposits appear to have been widespread and thickly accumulating during late Paleozoic time, suggesting the Early Permian may have been the dustiest time in planetary history. There is strong high-frequency variability in dust deposition/wind patterns, possibly driven by Milankovitch-scale orbital variability and related climate feedbacks, and lower frequency variability driven by tectonic and/or other changes. Yet the sign of the correlation of aridity in tropical Pangaea with glacial extent in Gondwanaland and globally cooler climate in general is still unclear. Broadly speaking, some reconstructions (such as those based on dust) favor glacial aridity, while others favor glacial humidity. To investigate the dynamics of aridity in tropical Pangaea, we have designed and implemented simulations of the Earth's climate during the Asselian-Sakmarian of the Permian using the Community Climate System Model. These simulations

  15. 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.

  16. 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.

  17. Paleomagnetism and rock magnetism of Quaternary volcanic rocks and Late Paleozoic strata, VC-1 core hole, Valles Caldera, New Mexico, with emphasis on remagnetization of Late Paleozoic strata

    NASA Astrophysics Data System (ADS)

    Geissman, John W.

    1988-06-01

    Paleomagnetic and rock magnetic data obtained from azimuthally unoriented core samples, collected at approximately 1- to 3-m intervals, of Continental Scientific Drilling Program core hole VC-1 have prompted reinterpretations of the Quaternary volcanic stratigraphy intersected by the bore and have aided in evaluating the thermal regime within late Paleozoic strata attending fluid circulation and mineral deposition during and after development of the Toledo and Valles calderas. The results from Quaternary units (Banco Bonito Obsidian: I = +35.4°, a95 = 2.8° (inclination only determinations), n = 33; Battleship Rock Tuff: D = 359.6°, I = +42.4°, a95 = 2.8°, n = 5 site means (surface sites); VC-1 Rhyolite: I = +39.2°, a95 = 12.8°, n = 7; Upper VC-1 Tuff: I = +37.2°, a95 = 10.7°, n = 13; Middle VC-1 Tuff: I = +42.1°, a95 = 2.1°, n = 39; South Mountain Rhyolite: D = 350.9°, I = +49.9°, a95 = 3.4°, n = 10 (one surface site)) are consistent with isotopic age data, indicating that the entire moat volcanic sequence intersected is less than 650 kyr. Monitoring of natural remanent magnetization (NRM) intensity, NRM directions, directions of magnetizations isolated during progressive demagnetization, median destructive forces, and rock magnetization parameters has identified systematic variations within the thick Banco Bonito Obsidian and VC-1 Tuff units. The Permian Abo Formation, Pennsylvanian to earliest Permian Madera Limestone, and Pennsylvanian Sandia Formation typically contain a moderate positive inclination magnetization component (Abo Formation: I = +52.2°, a95 = 7.4°, n = 16; Madera Limestone: I = +58.4°, a95 = 2.8°, n = 105; Sandia Formation: I = +53.9°, a95 = 4.8°, n = 21); when residing in magnetite, it is usually unblocked in the laboratory by 350°C; when carried by hematite it is unblocked by 550°C. A moderate negative inclination (e.g., Madera and Abo strata: D = 173.1°, I = -46.6°, a95 = 5.5°; n = 47 samples; assuming a north seeking

  18. Eolian delivery of highly reactive iron to the glacial ocean of the late Paleozoic

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    The potential biogeochemical impact of iron-rich dust delivery to the oceans is well recognized for Earth’s recent record but virtually unexplored in deeper time, despite recognition of large ancient dust fluxes. Abundant eolian dust (loess) deposits have been documented in western equatorial Pangaea (western U.S.), dating from the late Paleozoic (300 Ma), a time of known continental-scale glaciation. The role of iron in ancient ecosystems is elucidated by analytical techniques that enable identification of three iron pools within the total iron (FeT) pool: highly reactive (FeHR), poorly reactive, and unreactive. FeHR consists of amorphous and crystalline iron oxides and (oxyhydr)oxides that are readily reactive to H2S on an early diagenetic time scale. FeHR in our ancient sediments is dominated by crystalline oxide forms soluble in a citrate-bicarbonate, Na dithionite (CBD) solution, iron transformed to pyrite (Fepy), and magnetite. If the crystalline oxide phases that we measure in the record at least partially reflect less crystalline, more soluble oxyhydroxide precursors, then ancient FeHR roughly tracks its initial bioavailability and thus can be used as a proxy for potential primary productivity. Here, we report the uniqueness of Fe relationships (enriched FeHR/FeT values and relatively depleted FeT/Al) from a Pennsylvanian (Upper Carboniferous), loess-derived mudrock that accumulated at lowstand (glacial) time within a carbonate buildup of the so-called “Horseshoe Atoll” of the Midland basin (west Texas). This relationship is atypical compared to modern fluvial sediment and soil-derived dust and suggests an enhancement of the reactivity of an internal Fe pool and possible loss of Fe phases through unknown, but extreme biogeochemical processing. Comparisons of our data with other Permo-Carboniferous dusts, pedogenically altered loess, and emerging data on modern dusts suggest that the high values of FeHR/FeT in the mudrock may reflect glacial weathering

  19. 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.

  20. 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.

  1. 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.

  2. 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

  3. 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.

  4. Late Paleozoic strike-slip faults and related vein arrays of Cape Elizabeth, Maine

    NASA Astrophysics Data System (ADS)

    Swanson, Mark T.

    2006-03-01

    Strike-slip faults and related quartz vein arrays of Late Paleozoic-age cut gently-dipping metasedimentary rocks at Cape Elizabeth in southern coastal Maine and formed in response to regional dextral shearing along the Norumbega fault system. Vertical quartz veins up to 20 m wide and 10s of meters long were emplaced orthogonal to the local shear zone-parallel elongation fabric, reflecting strain partitioning during transpression. Earlier veins were reoriented by clockwise rotation toward this NE-trending regional shear direction. The later brittle strike-slip faults are oblique to the regional shear direction and interpreted as a 10-km-scale R-shear array on the southeast flank of the Norumbega fault system. These left-stepping en échelon fault zones consist of the three Two Lights fault zones (˜200 m lengths and up to ˜5 m displacements) and the Richmond Island fault zone (˜1.6 km length and ˜40 m displacement). Displacements on these fault zones have developed fine-grained silicified, obliquely-foliated and laminated cataclasites and locally, millimeter-thin pseudotachylyte fault and injection veins. Individual fault core zones are up to 10s of centimeters thick as part of several complex anastamosing zones of faulting 10s of meters wide. Initial segments within each fault zone are typically terminated with oblique extension fractures in horsetail configurations. The left-stepping en échelon relationships between these segments led to dominantly contractional step-over zones where P-shear linkages created a through-going fault that truncated the ends of the earlier-formed terminated segments. This linkage-growth model for fault zone evolution works toward larger scales and longer fault lengths as displacement accumulates, within a limiting maximum displacement/length ratio characteristic of the host lithologies. Length-frequency data for fault segments within these zones suggest a transition to linkage-dominated growth once fault segments were longer than

  5. 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

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. Late Paleozoic granitic rocks of the Chukchi Peninsula: Composition and location in the structure of the Russian Arctic

    NASA Astrophysics Data System (ADS)

    Luchitskaya, M. V.; Sokolov, S. D.; Kotov, A. B.; Natapov, L. M.; Belousova, E. A.; Katkov, S. M.

    2015-07-01

    An Early Carboniferous (352-359 Ma) U-Pb (TIMS, SIMS) age is established for granitic rocks of the Kibera pluton, quartz sienites of the Kuekvun pluton, and granites from the pebbles in the basement of Carboniferous rocks of the Kuul and Kuekvun uplifts in the Central Chukotka region. These data support the suggestion of granitic magmatism to occur in the region in the Late Paleozoic. The petrogeochemistry of most granitic rocks of the Kibera and Kuekvun plutons is similar to that of I-type granites, and their age coincides with tectonic events of Ellesmerian Orogeny in the Arctic region at the Late Devonian-Early Carboniferous boundary. The Devonian-Early Carboniferous granitic complexes extend to the territories of the Arctic Alaska, Yukon, and Arctic Canada, which indicates a common geological evolution within the Chukotka-Arctic Alaska block, which experienced a motion away from Arctic Canada.

  11. 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

  12. Late Leonardian plants from West Texas: The youngest Paleozoic plant megafossils in North America

    USGS Publications Warehouse

    Mamay, S.H.; Miller, J.M.; Rohr, D.M.

    1984-01-01

    Abundant Permian plant megafossils were discovered in the Del Norte Mountains of Brewster County, Trans-Pecos Texas. The flora is dominated by a new and distinctive type of gigantopteroid leaves. Marine invertebrates are closely associated, and this admixture of continental and marine fossils indicates a deltaic depositional setting, probably on the southern margin of the Permian Basin. Conodonts indicate correlation with the uppermost Leonardian Road Canyon Formation in the Glass Mountains. These are the youngest Paleozoic plant megafossils known in North America; they add an important paleontological element to the classic Permian area of this Continent.

  13. 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.

  14. 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.

  15. Late Paleozoic to Early Mesozoic provenance record of Paleo-Pacific subduction beneath South China

    NASA Astrophysics Data System (ADS)

    Hu, Lisha; Cawood, Peter A.; Du, Yuansheng; Yang, Jianghai; Jiao, Liangxuan

    2015-05-01

    Northeast trending Yong'an Basin, southeast South China Craton, preserves a Permian-Jurassic, marine to continental, siliciclastic-dominated, retroarc foreland basin succession. Modal and detrital zircon data, along with published paleocurrent data, sedimentary facies, and euhedral to subhedral detrital zircon shapes, indicate derivation from multicomponent, nearby sources with input from both the interior of the craton to the northwest and from an inferred arc accretionary complex to the southeast. The detrital zircon U-Pb age spectra range in age from Archean to early Mesozoic, with major age groups at 2000-1700 Ma, 1200-900 Ma, 400-340 Ma, and 300-240 Ma. In addition, Early Jurassic strata include zircon detritus with ages of 200-170 Ma. Regional geological relations suggest that Precambrian and Early Paleozoic detritus was derived from the inland Wuyi Mountain region and Yunkai Massif of the South China Craton. Sources for Middle Paleozoic to early Mesozoic detrital zircons include input from beyond the currently exposed China mainland. Paleogeographic reconstruction in East Asia suggests derivation from an active convergent plate margin along the southeastern rim of the craton that incorporated part of Southwest Japan and is related to the subduction of the Paleo-Pacific Ocean. Integration of the geologic and provenance records of the Yong'an Basin with the time equivalent Yongjiang and Shiwandashan basins that lie to the southwest and south, respectively, provides an integrated record of the subduction of the Paleo-Pacific Ocean along the southeast margin of the South China Craton and termination of subduction of the Paleo-Tethys beneath its southwest margin in Permo-Triassic.

  16. Late Paleozoic-early Mesozoic magmatism in the Cordillera de Carabaya, Puno, southeastern Peru: Geochronology and petrochemistry

    NASA Astrophysics Data System (ADS)

    Kontak, D. J.; Clark, A. H.; Farrar, E.; Archibald, D. A.; Baadsgaard, H.

    The Inner Arc domain, the easternmost magmatic manifestation of the post-Paleozoic Central Andean orogeny in southeastern Peru and western Bolivia, comprises a remarkably diverse assemblage of plutonic and volcanic rocks, many of which would be more characteristic of ensialic rifts or collisional mountain belts than of Andean-type convergent plate boundaries. Marked petrologic contrasts with the more homogeneous Main Arc domain, which underlies the westerly provinces of the orogen, have been maintained since the initiation of Andean orogeny in the Late Triassic. Constraints on the chronology and petrogenesis of the early stages in the protracted evolution of the Inner Arc and its Permian antecedents are provided herein by, respectively, KAr and RbSr geochronologic data and major and minor element analyses of representative pre-Cretaceous igneous rocks of the Cordillera de Carabaya, southeastern Peru. Our studies confirm the following sequence of magmatic events, which temporally overlapped with the initial stages of Andean orogeny: i) Intrusion of the gabbroic-to-granitic San Gabán (Corani) complex, a calc-alkaline, but crustally contaminated, suite that cores an extensive area of high-grade, low-pressure metamorphism in lower Paleozoic strata. The complex has been assigned to the mid-Paleozoic, but its age remains poorly defined. The foliated, markedly peraluminous, two-mica granites of the smaller Limacpampa pluton may also have been emplaced during the Paleozoic, but a Triassic age is favored on the basis of our RbSr data. ii) Eruption of alkali basaltic lavas of the Lower Permian Mitu Group along the northeastern margin of a longitudinal ensialic rift that developed in response to extensional tectonism in the interval between the pre-Andean ("late Hercynian") and Andean orogenies. iii) Emplacement of large granitoid plutons (Coasa, Limbani, and Aricoma centers), with I-Caledonian affinities, along the northeastern boundary of the Mitu rift during the

  17. Petrogenesis and Geodynamic Significance of Late Precambrian-Early Paleozoic Metagranites in Istranca (Strandja) Zone, NW Pontides, Turkey

    NASA Astrophysics Data System (ADS)

    Yilmaz Sahin, Sabah; Aysal, Namık; Gungor, Yıldırım; Peytcheva, Irena; Neubauer, Franz

    2014-05-01

    The existence of Cadomian arc magmatism in Istranca Zone within the Western part of the Pontides was determined according to new zircon U-Pb dating and whole-rock geochemical analysis of the Çatalca and İhsaniye metagranites. Magmatic evolution of the Late Precambrian-Early Paleozoic metagranites in Istrandja Zone related to the Cadomian orogeny along the northern Gondwana margin. The Istranca zone is composed of metamorphic basement intruded by large granitic bodies and overlain by a Paleozoic-Mesozoic meta-sedimentary cover. The metamorphic rocks of the Istranca zone extend from Bulgaria, Istranca Mountains to NW Turkey and reach the area near Istanbul (Çatalca region). The Çatalca and İhsaniye metagranites have a subalkaline, high-K calc-alkaline and peraluminous character. Trace element geochemistry displays decreasing normalized concentrations from large-ion lithophile (LIL) elements to high field strength (HFSE) elements and from light (LREE) to heavy rare earth elements (HREE). A negative Eu anomaly is both types of metagranites. On tectonic discrimination diagrams, the samples from both metagranites plot in the subduction-related fields. The SHRIMP-II U-Pb zircon ages of the Çatalca metagranite range from 534.5 ± 4.7 Ma to 546.0 ± 3.9 Ma and LA-ICP-MS U-Pb zircon dating yields 535.5 ± 3.6 Ma age for the İhsaniye metagranite. The new ages together with the geochemical constraints allow a new geodynamic interpretation for the Istranca zone and we compare these metagranites with other Upper Ediacaran to Lower Cambrian granitoids of Turkey and Alpine-Himalayan orogenic belt. We deduce an origin of these elements from the northern Gondwana-Land margin.

  18. Structural evolution of the Irtysh Shear Zone: implication for the Late Paleozoic amalgamation of multiple arc systems in Central Asia

    NASA Astrophysics Data System (ADS)

    Li, Pengfei; Sun, Min; Rosenbaum, Gideon

    2015-04-01

    The NW-SE Irtysh Shear Zone represents a major tectonic boundary in the Central Asian Orogenic Belt, recording the amalgamation history between the peri-Siberian orogenic system and the Kazakhstan orogenic system. The structural evolution and geodynamics of this shear zone is still poorly documented. Here we present new structural data complemented by chronological data in an attempt to unravel the geodynamic significance of the Irtysh Shear Zone in the context of accretion history of the Central Asian Orogenic Belt. Our results show three episodes of deformation for the shear zone. D1 foliation is locally recognized in low strain area and recorded by garnet inclusions, whereas D2 is represented by a sub-horizontal fabric and related NW-SE lineation. D3 is characterized by a transpersonal deformation event, to form a series of NW-SE mylonitic belts with sinistral kinematics, and to overprint D2 fabric forming regional-scale NW-SE upright folds. A paragneiss sample from the shear zone yielded the youngest detrital zircon peaks in the late Carboniferous, placing a maximum age constraint on the deformation, which overlaps in time with the late Paleozoic collision between the Chinese Altai and the intraoceanic arc system of the East Junggar and West Junggar. We interpret three episodes of deformation to represent orogenic thickening (D1), collapse (D2) and thickening (D3) in response to this collisional event. Sinistral shearing (D3) together with the coeval dextral shearing in the Tianshan accommodate eastward extrusion of the Kazakhstan orogenic system during the late Paleozoic amalgamation of the Central Asian Orogenic Belt. Acknowledgements: This study was financially supported by the Major Basic Research Project of the Ministry of Science and Technology of China (Grant: 2014CB440801), Hong Kong Research Grant Council (HKU705311P and HKU704712P), National Science Foundation of China (41273048, 41273012) and a HKU CRCG grant. The work is a contribution of the Joint

  19. 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.

  20. Paleomagnetism of the Santa Fé Group, central Brazil: Implications for the late Paleozoic apparent polar wander path for South America

    NASA Astrophysics Data System (ADS)

    Brandt, Daniele; Ernesto, Marcia; Rocha-Campos, Antonio Carlos; Dos Santos, Paulo Roberto

    2009-02-01

    Paleomagnetic and rockmagnetic data are reported for the Floresta Formation (Santa Fé Group) of the Sanfranciscana Basin, central Brazil. This formation represents the Permo-Carboniferous glacial record of the basin and comprises the Brocotó (diamictites and flow diamictites), Brejo do Arroz (red sandstones and shales with dropstones and invertebrate trails), and Lavado (red sandstones) members, which crop out near the cities of Santa Fé de Minas and Canabrava, Minas Gerais State. Both Brejo do Arroz and Lavado members were sampled in the vicinities of the two localities. Alternating field and thermal demagnetizations of 268 samples from 76 sites revealed reversed components of magnetization in all samples in accordance with the Permo-Carboniferous Reversed Superchron. The magnetic carriers are magnetite and hematite with both minerals exhibiting the same magnetization component, suggesting a primary origin for the remanence. We use the high-quality paleomagnetic pole for the Santa Fé Group (330.9°E 65.7°S; N = 60; α95 = 4.1°; k = 21) in a revised late Carboniferous to early Triassic apparent polar wander path for South America. On the basis of this result it is shown that an early Permian Pangea A-type fit is possible if better determined paleomagnetic poles become available.

  1. Tracing trends in erosion and exhumation during the Middle-Late Paleozoic tectonic evolution of the Farewell terrane, SW Alaska

    NASA Astrophysics Data System (ADS)

    Hampton, B. A.; Malkowski, M. A.; Bradley, D. C.; Fujita, K.; O'Sullivan, P. B.

    2010-12-01

    mono- and polycrystalline quartz, plagioclase, as well as a strong lithic volcanic component reflective of arc and recycled origin source areas. At present, much of the stratigraphic and structural evolution of Farewell terrane has yet to be documented however, preliminary provenance trends from the Dillinger and Mystic subterrane may reflect an initial stage of exhumation and detrital contributions from sources areas along the eastern and central Uralian Seaway (e.g. Baltica, Siberia, and Taimyr regions). Provenance trends from the uppermost strata in the Farewell may reflect and introduction of detritus from the northern or western margins of Laurentia potentially reflecting a paleogeographic location in the central to western Uralian seaway by Late Paleozoic time. Alternatively, it could be argued that the younger parts of the Mystic subterrane have been linked with Laurentia since origin and have no geologic or paleogeographic link with the older parts of the Farewell terrane.

  2. 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.

  3. 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

  4. 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

  5. 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

  6. 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.

  7. 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.

  8. 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

  9. 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.

  10. 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

  11. Stable isotope geochemistry of sediment-hosted groundwater from a Late Paleozoic Early Mesozoic section in central Europe

    NASA Astrophysics Data System (ADS)

    Barth, S. R.

    2000-08-01

    The boron isotopic composition, in combination with oxygen, hydrogen and sulfur isotopes and hydrochemical tracers, is utilized to investigate the evolution of groundwaters from a Late Paleozoic (Permian) to Early Mesozoic (Triassic) section of the sedimentary cover in central Europe (N Switzerland-SW Germany). Four distinct groundwater types have been identified: (a) saline groundwater from Permian (Rotliegend) sediments ( δ11B=+13.7 to +33.0‰, δ18O=-6.7 to -5.3‰, δD=-53.4 to -37.8‰, δ34S=+16.4 to +17.1‰); (b) brackish to saline groundwater from Lower Triassic (Buntsandstein) sediments ( δ11B=+6.4 to +22.3‰, δ18O=-10.3 to -6.9‰, δD=-71.8 to -60.5‰, δ34S=+18.2 to +18.4‰); (c) fresh to saline groundwater from Middle Triassic (Muschelkalk) sediments ( δ11B=-10.2 to +7.7‰, δ18O=-11.8 to -8.8‰, δD=-86.6 to -63.0‰, δ34S=+15.8 to +21.4‰); and (d) saline groundwater from Upper Triassic (Keuper) sediments ( δ11B=+26.3‰, δ18O=-6.4‰, δD=-41.2‰, δ34S=+16.1‰). As evidenced by B-O-H-S stable isotope and hydrochemical (e.g. Na/Cl, Br/Cl, Ca/SO 4, (Ca+Mg)/SO 4, K/B, and Li/B) constraints, interactions with sedimentary host rocks and inter-aquifer mixing have contributed to the evolution of the investigated groundwaters.

  12. 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.

  13. 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.

  14. 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

  15. Kaolinite, illite and quartz dissolution in the karstification of Paleozoic sandstones of the Furnas Formation, Paraná Basin, Southern Brazil

    NASA Astrophysics Data System (ADS)

    Melo, Mário Sérgio de; Guimarães, Gilson Burigo; Chinelatto, Adilson Luiz; Giannini, Paulo César Fonseca; Pontes, Henrique Simão; Chinelatto, Adriana Scoton Antonio; Atencio, Daniel

    2015-11-01

    Karstification processes in sandstones of the Furnas Formation, Silurian to Devonian of the Paraná Basin, have been described since the mid-twentieth century. However, some geologists still doubt the idea of true karst in sandstones. Studies carried out in the Campos Gerais region, Paraná State, Southern Brazil, aimed at investigating the nature of erosion processes in Furnas Formation and the role of the dissolution in the development of their notorious erosive features and underground cavities. These studies have led to the recognition of dissolution macro to micro features ('furnas', caves, ponds, sinks, ruiniform relief on cliffs and rocky surfaces, grain corrosion, speleothems, mineral reprecipitation and incrustation). The analysis (scanning electron microscopy, energy dispersive spectrometry and x-ray diffractometry) of sandstones and their alterites has indicated significant dissolution of clay cement along with discrete quartz grain dissolution. This mesodiagenetic cement (kaolinite and illite) is dissolved and reprecipitated as clay minerals with poorly developed crystallinity along with other minerals, such as variscite and minerals of the alunite supergroup, suggesting organic participation in the processes of dissolution and incrustation. The mineral reprecipitation usually forms centimetric speleothems, found in cavities and sheltered rocky surfaces. The cement dissolution associated with other factors (fractures, wet weather, strong hydraulic gradient, antiquity of the landforms) leads to the rock arenisation, the underground erosion and the appearance of the karst features. Carbonate rocks in the basement may locally be increasing the karst forms in the overlying Furnas Formation. The recognition of the karst character of the Furnas Formation sandstones has important implications in the management of underground water resources (increasingly exploited in the region), in the use of the unique geological heritage and in the prevention of geo

  16. 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.

  17. 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.

  18. 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

  19. 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.

  20. Detrital Zircon Ages from Late Jurassic-Early Cretaceous Myrgovaam Basin Sandstones (Rauchua Trough), Western Chukotka, NE Russia

    NASA Astrophysics Data System (ADS)

    Miller, E. L.; Toro, J.; Gehrels, G.; Tuchkova, M.; Katkov, S.

    2004-12-01

    Late Jurassic to Early Cretaceous Myrgovaam Basin sediments (previously Rauchua Trough) are regionally significant because of the stratigraphic constraints they provide on the age and progression of deformation in the Chukotka fold belt, a possible along-strike continuation of the Alaskan Brooks Range fold-and-thrust belt. Existing descriptions of the structural and stratigraphic relations of Myrgovaam Basin sediments to underlying strata are contradictory. Some maps portray the basin fill as deposited unconformably over deformed Triassic and Jurassic strata of the Chukotka fold-belt. In other publications, the deposits are described as structurally detached and imbricated by N-verging thrust sheets (Baranov, 1996). Field studies reveal that underlying strata are tightly folded compared to overlying strata and that the contact is a structural discordance not an unconformity. More locally, we observed arkosic sandstones typical of the Myrgovaam Basin interbedded with underlying Late Jurassic strata or present as submarine channel deposits cut into older rocks, suggesting an original stratigraphic relationship. To reconcile these observations we suggest regional deformation post-dates deposition of Myrgovaam Basin deposits, and that the disharmony in deformational style between underlying thin-bedded Triassic sandstones and shales and (stratigraphically) overlying massive quartzites, is due to their different mechanical properties. Petrographic studies indicate that fine-grained Triassic-early Jurassic sandstones represent a distal recycled orogen source, while Myrgovaam Basin sandstones originated from a proximal orogenic source containing granitoid and crystalline basement rocks (microcline, biotite, muscovite and fragments of multiply deformed schist) and intermediate to felsic volcanic rocks. Laser Ablation ICPMS was used to date zircons (100 grains) from sandstones of the Myrgovaam Basin and compare them to those in Triassic sandstones (300 grains) and verify

  1. Oil-impregnated outcrops and their relationship to petroleum generation in late Paleozoic Eagle basin, northwestern Colorado

    SciTech Connect

    Waechter, N.B. )

    1989-09-01

    Oil-impregnated outcrops of Mississippian and Pennsylvanian rocks are present in widely separated areas of the Eagle basin. Along the northeast margin of the fault-bounded Eagle basin, oil-impregnated arkosic sandstones of the lower Minturn Formation (Desmoinesian) are interbedded with black, organic-rich shales that provided a local source for the oil. Algal mounds in the lower Minturn Formation in this area contain oil residue. Oil residue is also present in the Mississippian Leadville formation in several parts of the basin, both in paleokarst-related vugs and intergranular porosity in oolite grainstones. The Leadville formation was sourced by overlying organic-rich shales of the Belden Formation (Morrowan-Atokan). Under Pennsylvanian-Permian arkosic sandstones near the southwestern margin of the basin are not adjacent to potential source rocks. The Schoolhouse Tongue of the Weber Sandstone is heavily stained in many areas over its 50 mi of outcrop exposure. Numerous arkosic sandstones in the underlying Maroon Formation are also sained. Faults bounding intrabasinal horst blocks were conduits for upward oil migration, and the horsts may have provided the trap. Oil is also present in overlying Triassic and Jurassic sands in this area, supporting the theory of vertical migration up faults. Oil residue is also present in the Maroon Formation 40 mi to the southeast in the Crystal River Valley. Secondary porosity from dissolution of calcite cement preceded oil emplacement. Beaching of normally red-brown sandstones is ubiquitous with the oil residue and probably represents reduction and partial removal of iron by acidic, reducing fluids generated from the Belden Shale.

  2. 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

  3. Coordinated strike-slip and normal faulting in the Southern Ozark dome of Northern Arkansas: Deformation in a late Paleozoic foreland

    USGS Publications Warehouse

    Hudson, M.R.

    2000-01-01

    Structures that formed on the southern flank of the Ozark dome, in the foreland of the late Paleozoic Ouachita orogeny, have received little modern study. New mapping of the western Buffalo River region of northern Arkansas identifies diversely oriented faults and monoclinal folds that displace the generally flat lying Mississippian Boone Formation over a 180 m elevation range. Kinematic measurements and spatial relations reveal the presence of both east-striking normal faults and broader northeast-striking dextral strike-slip fault zones that acted in a coordinated fashion to accommodate constrictional strain, in which north-south extension was balanced by vertical and east-directed shortening. North-south extension in the Buffalo River region probably reflects Pennsylvanian-Early Permian deformation within the flexural forebulge of the developing Ouachita orogeny, which closed progressively westward along the southern margin of the craton.

  4. 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.

  5. 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., Jr.; 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.

  6. 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.

  7. 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

  8. 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

  9. Elemental and Sr Nd Pb isotopic geochemistry of Late Paleozoic volcanic rocks beneath the Junggar basin, NW China: Implications for the formation and evolution of the basin basement

    NASA Astrophysics Data System (ADS)

    Zheng, Jianping; Sun, Min; Zhao, Guochun; Robinson, Paul T.; Wang, Fangzheng

    2007-03-01

    The basement beneath the Junggar basin has been interpreted either as a micro-continent of Precambrian age or as a fragment of Paleozoic oceanic crust. Elemental and Sr-Nd-Pb isotopic compositions and zircon Pb-Pb ages of volcanic rocks from drill cores through the paleo-weathered crust show that the basement is composed mainly of late Paleozoic volcanic rock with minor shale and tuff. The volcanic rocks are mostly subalkaline with some minor low-K rocks in the western Kexia area. Some alkaline lavas occur in the central Luliang uplift and northeastern Wulungu depression. The lavas range in composition from basalts to rhyolites and fractional crystallization played an important role in magma evolution. Except for a few samples from Kexia, the basalts have low La/Nb (<1.4), typical for oceanic crust derived from asthenospheric melts. Zircon Pb-Pb ages indicate that the Kexia andesite, with a volcanic arc affinity, formed in the early Carboniferous (345 Ma), whereas the Luliang rhyolite and the Wucaiwan dacite, with syn-collisional to within-plate affinities, formed in the early Devonian (395 and 405 Ma, respectively). Positive ɛNd( t) values (up to +7.4) and low initial 87Sr/ 86Sr isotopic ratios of the intermediate-silicic rocks suggest that the entire Junggar terrain may be underlain by oceanic crust, an interpretation consistent with the juvenile isotopic signatures of many granitoid plutons in other parts of the Central Asia Orogenic Belt. Variation in zircon ages for the silicic rocks, different Ba, P, Ti, Nb or Th anomalies in the mafic rocks, and variable Nb/Y and La/Nb ratios across the basin, suggest that the basement is compositionally heterogeneous. The heterogeneity is believed to reflect amalgamation of different oceanic blocks representing either different evolution stages within a single terrane or possibly derivation from different terranes.

  10. 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

  11. 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.

  12. Seven Post-Pennsylvanian Structural Events in the Dry Hills and Northern Osgood Mountains: Evidence of Late Paleozoic Tectonism and New Getchell Fault Offset Data

    NASA Astrophysics Data System (ADS)

    Taylor, W. J.; Siebenaler, S.; Cashman, P.; Trexler, J.; Davydov, V.

    2008-12-01

    An incomplete understanding of the number and style of deformational events in north-central Nevada complicate economic and stratigraphic studies. To help unravel this structural history, we mapped and measured structures in the Dry Hills, northern Osgood Mountains, Humboldt County, Nevada. This research identified at least seven Pennsylvanian age or younger deformational events. The location was selected because it contains the Roberts Mountain allochthon (RMA), the Pennsylvanian (IP) to Permian (P) age Etchart Formation that was deposited atop the RMA, and the Golconda allochthon (GA). Measured folds and faults provide evidence of at least four deformational events that occurred between emplacement of the RMA and GA. Evidence for Late Paleozoic deformational events was recently well documented in other regional locations, but this location is farther north than previous studies. This research is also important because it provides information about the style and regional extent of these tectonic events. Structural mapping and data analysis reveal that the Etchart Formation contains four upright fold sets (SE-, NNW-, SSW-, NE-trending, in chronologic order) and three fault sets (N-striking normal, ENE-striking thrust, NNE-striking thrust), which may relate to the three youngest fold sets. The relative ages of the folds and faults are constrained via cross-cutting relationships, overprinting, and the oldest fold set being confined solely to the lowest stratigraphic unit within the Etchart Formation. These structures developed prior to and during emplacement of the GA. Two angular unconformities, the C5 and P1 angular unconformities of Trexler et al. (2003), are newly recognized in the area. The SW-trending fold set underlies the C5 unconformity. The P1 unconformity is angular indicating a deformational event and has been confirmed with fusulinid-based ages. The P1 and C5 unconformities correlate to other locations in northern Nevada implying regional scale late

  13. 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

  14. Zircon U-Pb geochronology and petrogenesis of the Late Paleozoic-Early Mesozoic intrusive rocks in the eastern segment of the northern margin of the North China Block

    NASA Astrophysics Data System (ADS)

    Cao, Hua-Hua; Xu, Wen-Liang; Pei, Fu-Ping; Wang, Zhi-Wei; Wang, Feng; Wang, Zi-Jin

    2013-06-01

    Zircon U-Pb dating and whole-rock geochemical analysis have been undertaken on Late Paleozoic-Early Mesozoic intrusive rocks of central Jilin Province, NE China, with the aim of constraining the tectonic evolution of the eastern segment of the northern margin of the North China Block (NCB) during the Late Paleozoic-Early Mesozoic. Zircon U-Pb dating indicates that Late Paleozoic-Early Mesozoic magmatic events can be subdivided into four stages: Middle Permian (~ 270 Ma), Late Permian (259-255 Ma), Early Triassic (~ 249 Ma), and Late Triassic (~ 222 Ma). The Middle Permian magmatic event formed peraluminous garnet-bearing monzogranites, indicative of formation under a compressional tectonic regime related to collision between the NCB and the Songnen-Zhangguangcai Range Massif. The Late Permian magmatic event formed gabbros and syenogranites, a bimodal association that is typical of magmatism within post-collisional extensional setting. The Early Triassic magmatic event formed adakitic monzogranites, suggesting that they formed from magmas derived from partial melting of a thickened mafic lower crust. The Late Triassic magmatic event formed a series of mafic-ultramafic intrusive rocks, together with coeval granitoids in adjacent regions, and make up a typical bimodal association suggesting that they formed under an extensional environment related to the final amalgamation of the NCB and the Songnen-Zhangguangcai Range Massif. Taken together, we conclude that the northern margin of the NCB underwent multiple orogenic events between the Middle Permian and the Late Triassic, with final amalgamation of the NCB and the Songnen-Zhangguangcai Range Massif occurring in the Early Triassic, an event that led to the final suturing of the Solonker-Xra Moron-Changchun zone.

  15. 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.

  16. 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.

  17. Blueschist metamorphism and its tectonic implication of Late Paleozoic-Early Mesozoic metabasites in the mélange zones, central Inner Mongolia, China

    NASA Astrophysics Data System (ADS)

    Zhang, Jinrui; Wei, Chunjing; Chu, Hang

    2015-01-01

    Blueschists in central Inner Mongolia are distributed as layers and blocks in mélanges including the southern zone in Ondor Sum area and the northern zone in Manghete and Naomuhunni areas. They have been attributed to the subduction of Early Paleozoic oceanic crust. Blueschists from Ondor Sum and Naomuhunni are characterized by occurrence of sodic amphibole coexisting with epidote, albite, chlorite, calcic amphibole (in Ondor Sum) and muscovite (in Naomuhunni). Blueschists in Manghete contain porphyroblastic albite with inclusions of garnet and epidote in a matrix dominated by calcic-sodic amphibole, epidote, chlorite, albite and muscovite. Phase equilibria modeling for three blueschist samples using pseudosection suggest that the AlM2 contents in sodic amphibole can be used as a good barometer in the limited assemblage involving sodic amphibole + actinolite + epidote + chlorite + albite + quartz under pressures <4-6 kbar, while this barometer is largely influenced by temperature and bulk Fe2O3 contents in the actinolite-absent assemblage sodic amphibole + epidote + chlorite + albite + quartz of higher pressure and the AlM2 contents are not pressure-controlled in the albite-absent assemblage sodic amphibole + epidote + chlorite + quartz under pressures > 7-10 kbar. In the sodic amphibole-bearing assemblages, the NaM4 contents in sodic amphibole mainly decrease as temperature rises, being a potential thermometry. The calculated pseudosections constrain the P-T conditions of blueschists to be 3.2-4.2 kbar/355-415 °C in Ondor Sum, 8.2-9.0 kbar/455 °C-495 °C in Manghete and 6.6-8.1 kbar/420-470 °C in Naomuhunni. These P-T estimates indicate a rather high geothermal gradient of 18-25 °C/km for the blueschist metamorphism, being of intermediate P/T facies series. Available zircon U-Pb age data suggests that the protoliths of blueschists were formed later than Late Paleozoic-Early Mesozoic and metamorphosed soon afterwards. An alternative interpretation for the

  18. 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

  19. 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.

  20. Petrogenesis and geodynamic setting of Neoproterozoic and Late Paleozoic magmatism in the Manzhouli-Erguna area of Inner Mongolia, China: Geochronological, geochemical and Hf isotopic evidence

    NASA Astrophysics Data System (ADS)

    Gou, Jun; Sun, De-You; Ren, Yun-Sheng; Liu, Yong-Jiang; Zhang, Shu-Yi; Fu, Chang-Liang; Wang, Tian-Hao; Wu, Peng-Fei; Liu, Xiao-Ming

    2013-05-01

    U-Pb dating and Hf isotopic analyses of zircons from various granitoids, combined with major and trace element analyses, were undertaken to determine the petrogenesis and geodynamic setting of Neoproterozoic and Late Paleozoic magmatism in the Manzhouli-Erguna area of Inner Mongolia, China. The Neoproterozoic granitoids are mainly biotite monzogranites with zircon U-Pb ages of 894 ± 13 Ma and 880 ± 10 Ma, and they are characterised by enrichment in large ion lithophile elements (LILEs; e.g., Rb, Ba, K) and light rare earth elements (LREEs), depletion in high field strength elements (HFSEs; e.g., Nb, Ta, Ti) and heavy rare earth elements (HREEs). The Late Devonian granitoids are dominantly syenogranites and mylonitised syenogranites with zircon U-Pb ages of 360 ± 4 Ma, and they form a bimodal magmatic association with subordinate gabbroic rocks of the same age. The Late Devonian syenogranites have A-type characteristics including high total alkalis, Zr, Nb, Ce and Y contents, and high FeOt/MgO, Ga/Al and Rb/Sr ratios. The Carboniferous granitoids are mainly tonalites, granodiorites and monzogranites with U-Pb ages varying from 319 to 306 Ma, and they show very strong adakitic characteristics such as high La/Yb and Sr/Y ratios but low Y and Yb contents. The Late Permian granitoids are dominated by monzogranites and syenogranites with zircon U-Pb ages ranging between 257 and 251 Ma. Isotopically, the ɛHf(t) values of the Neoproterozoic granitoids range from +4.3 to +8.3, and the two-stage model ages (TDM2) from 1.2 to 1.5 Ga. The Late Devonian granitoids are less radiogenic [ɛHf(t) from +12.0 to +12.8 and TDM2 from 545 to 598 Ma] than the Carboniferous [ɛHf(t) from +6.8 to +9.5 and TDM2 from 722 to 894 Ma] and Late Permian granitoids [ɛHf(t) from +6.1 to +9.4 and TDM2 in the range of 680-895 Ma]. These data indicate (1) the Neoproterozoic granitoids may have been generated by melting of a juvenile crust extracted from the mantle during the Mesoproterozoic

  1. Late Paleozoic crustal history of central coastal Queensland interpreted from geochemistry of Mesozoic plutons: The effects of continental rifting

    USGS Publications Warehouse

    Allen, C.M.; Wooden, J.L.; Chappell, B.W.

    1997-01-01

    The eastern margin of Australia is understood to be the result of continental rifting during the Cretaceous and Tertiary. Consistent with this model, Cretaceous igneous rocks (granites to basalts) in a continental marginal setting near Bowen, Queensland are isotonically retarded, having isotopic ratios similar to those of most island arcs (Sri = 0.7030-0.7039, ??Nd = +6.46 to +3.00 and 206Pb/204Pb = 18.44-18.77, 207Pb/204Pb = 15.552-15.623, and 208Pb/204Pb = 37.90-38.52). These isotopic signatures are much less evolved than the Late Carboniferous-Permian batholith that many Cretaceous plutons intrude. As rocks ranging in age from about 300-100 Ma are well exposed near Bowen, we can track magma evolution through time. The significant change of magma source occurred much earlier than the Cretaceous based on the fact that Triassic granites in the same area are also isotonically primitive. We attribute the changes of magma composition to crustal rifting during the Late Permian and earliest Triassic. The Cretaceous rocks (actually latest Jurassic to Cretaceous, 145-98 Ma) themselves show compositional trends with time. Rocks of appropriate mineralogy for Al-in-hornblende geobarometry yield pressures ranging from 250 to 80 MPa for rocks ranging in age from 145 to 125 Ma, respectively. More significantly, this older group is relatively compositionally restricted, and is Sr-rich, and Y- and Zr-poor compared to 120-98 Ma rocks. This younger groups is bimodal, being comprised principally of basalts and rhyolites (granites). REE patterns for a given rock type, however, do not differ with age tribute these relatively subtle trace element differences to small differences in conditions (T, aH2O) at the site of melting. Cretaceous crustal rifting can explain the range of rock types and the spatial distribution of rocks < 120 Ma in a longitudinal strip between and overlapping with provinces of older Cretaceous intrusions. A subduction-related setting is assigned to the 145-125 Ma

  2. 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.

  3. Geochronology, petrogenesis, and tectonic setting of Neoproterozoic and Late Paleozoic granitoids of the Manzhouli-Ergun area of Inner Mongolia, China

    NASA Astrophysics Data System (ADS)

    Gou, J.; Sun, D.; Fu, C.; Ren, Y.; Liu, X.

    2012-12-01

    U-Pb dating and Hf isotopic analysis of zircons from various granitoids, combined with major and trace element analysis, was undertaken to determine the petrogenesis and geodynamics of Neoproterozoic and Late Paleozoic magmatism in the Manzhouli-Ergun area of Inner Mongolia, China. Neoproterozoic granitoids are mainly composed of biotite monzogranite with zircon U-Pb ages of 880 ± 10 and 894 ± 13 Ma, and are characterized by enrichment in LILE and LREE relative to HFSE and HREE with negative Nb, Ta, P and Ti anomalies. Late Devonian granitoids are dominantly composed of syenitegranite and mylonitized syenitegranite with zircon U-Pb age of 360 ± 4 Ma, and show a bimodal magmatic association and A-type granitiod geochemical characteristics including high total alkalis, Zr, Nb, Ce and Y contents and high FeOt/MgO, Ga/Al and Rb/Sr ratios. Carboniferous granitoids consist principally of tonalite, granodiorite and monzogranite with U-Pb ages varying from 320 to 306 Ma, and show the strongest adakitic characteristics such as high La/Yb and Sr/Y ratios but low Y and Yb contents. Late Permian granitoids are dominated by granodiorite and monzogranite with zircon U-Pb ages ranging between 257 and 251 Ma and show low Sr and Yb content characteristic of Himalaya-type granitoid. Isotopically, the ɛHf(t) values of Neoproterozoic granitoids range from +2.30 to +4.14 and two-stage model ages (TDM2) vary from 1.5 to 1.6 Ga, Late Devonian granitoids display values less radiogenic [ɛHf(t) from +11.95 to +12.77 and TDM2 from 546 to 599 Ma] in comparison to Carboniferous granitoids [ɛHf(t) from +7.82 to +8.47 and TDM2 from 791 to 832 Ma] and Late Permian granitoids [ɛHf(t) from +6.70 to +7.35 and TDM2 in the range of 813-855 Ma]. These data indicate that Neoproterozoic granitoids may have generated in equilibrium with an amphibolitic (plagioclase + amphibole) residue at depths of 30-40 km and are most likely associated with the accretion of Ergun microcontinent block to the

  4. 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.

  5. 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.

  6. Paleozoic paleomagnetism and northward drift of the Alexander terrane, southeastern Alaska.

    USGS Publications Warehouse

    Van Der Voo, R.; Jones, M.; Gromme, C.S.; Eberlein, G.D.; Churkin, M., Jr.

    1980-01-01

    Paleozoic limestone, greywacke, sandstone, mudstone, red beds and volcanic rocks of the Alexander terrane, SE 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 N America, the paleomagnetic results are compared to those for the N 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 terrance (55.5 N, 133.5 W). Better matching can be obtained for a paleoposition of the terrane at about 40 N, 120 W, in the present position of western Nevada and NE California. In addition, an in situ 25o clockwise rotation of the terrane is required to restore it to its original position.-Authors

  7. 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

  8. 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.

  9. 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

  10. Petrogenesis of late Paleozoic volcanic rocks from the Daheshen Formation in central Jilin Province, NE China, and its tectonic implications: Constraints from geochronology, geochemistry and Sr-Nd-Hf isotopes

    NASA Astrophysics Data System (ADS)

    Yu, Qian; Ge, Wen-Chun; Yang, Hao; Zhao, Guo-Chun; Zhang, Yan-Long; Su, Li

    2014-04-01

    We present geochronological, geochemical, whole-rock Sr-Nd and zircon Hf-isotopic data for late Paleozoic volcanic rocks from the Daheshen Formation in central Jilin Province, northeastern China, and constrain the petrogenesis of the volcanic rocks and late Paleozoic tectonic evolution of the northern margin of the Northern China Craton, which is regarded as the eastern segment of the Central Asian Orogenic Belt (CAOB). Lithologically, the Daheshen Formation is composed mainly of rhyolite, rhyolitic tuff, dacite and andesite, with minor basalt. The zircons from three rhyolites, two dacites, one rhyolitic tuff and one basalt are euhedral-subhedral, display oscillatory zoning and have high Th/U ratios (0.50-2.28), implying a magmatic origin. LA-ICP-MS zircon U-Pb age data indicate that the volcanic rocks from the Daheshen Formation formed during Late Carboniferous-Early Permian time (302-299 Ma). Geochemically, late Paleozoic volcanic rocks have SiO2 = 52.13-81.77 wt.% and K2O = 0.86-6.88 wt.%, belonging to mid-K to high-K calc-alkaline series. These rocks are characterized by enrichment in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), and depletion in high field strength elements (HFSEs, such as Nb, Ta, and Ti) and heavy rare earth elements (HREEs), with affinities to igneous rocks forming in an active continental margin setting. All volcanic rocks have depleted Nd isotopic compositions (ɛNd(t) = + 2.4 to + 2.5 for the basalts and + 5.8 to + 7.1 for the andesites and dacites, respectively). In situ Hf isotopic results of zircon from the rhyolites show that they have ɛHf(t) = - 1.1 to + 10.6. All these geochemical features indicate that the andesites, dacites, and rhyolites likely originated from the partial melting of Meso-Neoproterozoic accreted lower crust (Hf and Nd model ages (TDM2) of 1384-662 Ma and 1061-800 Ma, respectively). In contrast, the basalts were derived from the partial fusion of a depleted lithospheric mantle that

  11. 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

  12. 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

  13. Provenance and origins of a Late Paleozoic accretionary complex within the Khangai-Khentei belt in the Central Asian Orogenic Belt, central Mongolia

    NASA Astrophysics Data System (ADS)

    Hara, Hidetoshi; Kurihara, Toshiyuki; Tsukada, Kazuhiro; Kon, Yoshiaki; Uchino, Takayuki; Suzuki, Toshiya; Takeuchi, Makoto; Nakane, Yuki; Nuramkhaan, Manchuk; Chuluun, Minjin

    2013-10-01

    We have investigated the petrography, geochemistry, and detrital zircon U-Pb LA-ICPMS dating of sandstone from the Gorkhi Formation of the Khangai-Khentei belt in the Ulaanbaatar area, central Mongolia. These data are used to constrain the provenance and source rock composition of the accretionary complex, which is linked to subduction of the Paleo-Asian Ocean within the Central Asian Orogenic Belt during the Middle Devonian to Early Carboniferous. Field and microscopic observations of the modal composition of sandstone and constituent mineral chemistry indicate that the sandstone of the Gorkhi Formation is feldspathic arenite, enriched in saussuritized plagioclase. Geochemical data show that most of the sandstone and shale were derived from a continental margin to continental island arc setting, with plutonic rocks being the source rocks. Detrital zircon 206Pb/238U ages of two sandstones yields age peaks of 322 ± 3 and 346 ± 3 Ma. The zircon 206Pb/238U age of a quartz-pumpellyite vein that cuts sandstone has a weighted mean age of 339 ± 3 Ma. Based on these zircon ages, we infer that the depositional age of sandstone within the Gorkhi Formation ranges from 320 to 340 Ma (i.e., Early Carboniferous). The provenance and depositional age of the Gorkhi Formation suggest that the evolution of the accretionary complex was influenced by the intrusion and erosion of plutonic rocks during the Early Carboniferous. We also suggest that spatial and temporal changes in the provenance of the accretionary complex in the Khangai-Khentei belt, which developed aound the southern continental margin of the Siberian Craton in relation to island arc activity, were influenced by northward subduction of the Paleo-Asian Ocean plate.

  14. Libyan Paleozoic: A review of the factors limiting hydrocarbon potential

    SciTech Connect

    Kanes, W.H.; Mairn, A.E.M.; Aburawi, R.M.

    1988-08-01

    Of the three main Paleozoic basins - Ghadames, Murquz, and Kufra - only the Ghadames and its continuation into Algeria, the Illizi (or Fort Polignac) basin, has yielded hydrocarbons in significant quantity. The Paleozoic on the Cyrenaica platform and basement of the Sirte basin has a potential not fully considered. The paleogeography of the Paleozoic system is reviewed to illustrate the extent to which inherited and reactivated basement-controlled structures have influenced later Paleozoic sedimentation and hence the distribution of source rocks, reservoirs, and seals. In all instances, the source rocks are restricted to shales of the Tanezufft Formation or occur in the Upper Devonian Aouinet Oeunine Formation. Multiple fine-grained sequences serve as seals in all the fields. The reservoirs range from the well-cemented but highly fractured Cambrian-Ordovician Gargaf sandstones to the Acacus-Tadrart clastics to the fine-grained Lower Carboniferous Tahara Sandstone. The principal plays are associated with minor structures, and stratigraphic trapping mechanisms play a minor role. The average field size (excluding the Sirte basin) is approximately 80 million bbl of recoverable oil. Paleozoic structural plays in the Sirte basin and the Cyrenaica platform include reactivated infra-Cambrian faults. The lower Paleozoic accumulations of the Murzuq basin are tied to large structures. With the exception of local areas in the Ghadames basin, the Paleozoic succession remains a stratigraphic frontier province - still incompletely explored but with several interesting possibilities for large amounts of stratigraphically trapped hydrocarbons.

  15. 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

  16. 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

  17. 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

  18. 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

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. Late Paleozoic to Triassic magmatism in the north-central High Andes, Chile: New insights from SHRIMP U-Pb geochronology and O-Hf isotopic signatures in zircon

    NASA Astrophysics Data System (ADS)

    Hernández González, Álvaro; Deckart, Katja; Fanning, Mark; Arriagada, César

    2014-05-01

    The Chilean High Andes (28o- 31oS) comprises a vast number of late Paleozoic - Triassic granitoids which give information about the last stages of Gondwana assemblage. Particularly, previous studies determined two tectonic configurations during this time: subduction related compressional setting (late Carboniferous - Late Permian) and non-subduction post-collisional extensional setting (Late Permian - Triassic), as the last stage of Gondwana assemblage. However, new O-Hf isotopic data along new U-Pb SHRIMP ages in zircon have shown that this model should be modified and updated to the new analytical data available. δ18O values indicate a strong change in the tectonic configuration approximately 270 Ma (earliest middle Permian) and thus, units can be divided into 2 mayor groups: late Carboniferous to earliest middle Permian and middle Permian to Triassic. The oldest group shows slightly low values of ɛHfi (ca. +1 to -4) with high δ18O (ca. >6.5 o/oo), indicating an elevated supracrustal component and the addition of less radiogenic continental-like material, which along significant residence time (TDM2: Mesoproterozoic) can be interpreted as magmas formed at depth in a subduction-related continental arc, and contaminated with supracrustal material and/or oceanic sediments transported through the subducted slab to the mantle-wedge. Subsequently, middle Permian - Triassic rocks show a wider range of ɛHfi values (ca. +3 to -3) with relatively low, mantle-like δ18O (ca. 4.5-6.5 o/oo), indicating a source of magmas without the addition of supracrustal material for some plutons, whilst for others, a slight input. The higher positive values of ɛHfi can be related to the influence of new juvenile material in the source of some magmas. This isotopic data can be interpreted as rocks formed as the result of melting of an old thinned mafic crust (with mantle-like δ18O values characteristic of this type of rocks) with limited addition of supracrustal material; in

  4. 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.

  5. Microbial Sand Chips in Transgressive Sandstones of the Precambrian: An Example from the Late Paleoproterozoic Dahongyu Formation at the Huyu Section of Nankou Town, Beijing, China

    NASA Astrophysics Data System (ADS)

    MEI, Mingxiang; MENG, Qingfen; GAO, Jinhan

    It is often difficult to identify the primary structures induced by microbes in terrigenous clastic rocks because the direct evidence indicative of the microbe is generally absent. Both sandstone strata of the transgressive system tract and sandy-muddy dolomite strata with stromatolite of the high-stand system tract make up the regular succession of sedimentary facies for the Late Paleoproterozoic Dahongyu Formation at the Huyu Section of Nankou Town in the northwestern suburb of Beijing, China. This characteristic has become the main criterion to divide the Dahongyu Formation into three third-order sequences. There is an odd type of sand chips in sandstone beds of the transgressive system tract of the Dahongyu Formation. The peculiar sand chip, similar to the carbonate intraclast, may indicate the development of microbial mats on the depositional surface of the Precambrian terrigenous clastic deposits. The chips together with palimpsest ripples and wrinkle structures form series of matground structures. The special configuration and features of these structures is a typical indication of the development of microbial mat in the Precambrian sandstones. Therefore, the discovery of the microbial sand chip and related matground structures is beneficial for the further study of similar sedimentary structures, particularly for those generally known as the oldest trace fossils of metazoa in the Precambrian. It also shows that there is some evidence indicative of microbial activity in terrigenous clastic rocks, the matground structures (the primary sedimentary structure of a fifth category) in the Precambrian, in addition to microbial sedimentary structures in carbonates such as the stromatolite. These unique sedimentary structures are important for reconstruction of the Precambrian sedimentary environments. The diversity of microbial metabolism results in the production of an immense amount of biomass, which has a global widespread distribution. Before the biological

  6. Age and petrogenesis of late Paleozoic granites from the northernmost Alxa region, northwest China, and implications for the tectonic evolution of the region

    NASA Astrophysics Data System (ADS)

    Zhang, Wen; Pease, Victoria; Meng, Qingpeng; Zheng, Rongguo; Wu, Tairan; Chen, Yan; Gan, Lisheng

    2016-01-01

    The Wudenghan, Huhetaoergai and Zhuxiaobuguhe plutons, northern Alxa region, in the southern Central Asia Orogenic Belt are dated by U-Pb zircon to 383 ± 3, 356 ± 3 and 286 ± 2 Ma, respectively. The late Devonian Wudenghan monzogranite, a highly fractionated I-type granite with ɛ Nd(t) (-0.2 to -0.1) and very low (87Sr/86Sr) t (0.704719-0.706113), is from mantle-derived magmas and shows volcanic arc characteristics. The early Carboniferous Huhetaoergai granodiorite with medium-K calc-alkaline peraluminous characteristics represents a volcanic arc granite generated from partial melting of lower continental crust combined with mantle-derived input. The early Permian Zhuxiaobuguhe pluton, an unfractionated calc-alkaline granodiorite with moderately low ɛ Nd(t) (-2.0 to -1.1) and low (87Sr/86Sr) t (0.708370-0.708462), was likely derived from partial melting of the mafic lower crust of a paleo-volcanic arc and represents a post-collisional granite. Our revised tectonic evolution of the region includes (1) northward subduction of the oceanic crust represented by the Engger Us Ophiolitic Belt and formation of the late Devonian Wudenghan monzogranite, (2) northward subduction of the ocean between the Huhetaoergai and Zhusileng tectonic zones and the formation of the Huhetaoergai volcanic arc granite during the early Carboniferous and (3) the emplacement of the Zhuxiaobuguhe pluton in the early Permian during post-collisional extension.

  7. Diagenesis of deeply buried Eagle Mills sandstones. Implications for paleo-fluid migration and porosity development

    SciTech Connect

    Dawson, W.C.

    1995-10-01

    Eagle Mills strata (Triassic-Jurassic) unconformably overlie the Paleozoic basement complex and thus, form the basal sedimentary unit within the Gulf Coast basin. Jurassic-aged basaltic dikes and sills have intruded Eagle Mills strata. These sedimentary and igneous rocks are the earliest record of Gulf of Mexico rifting. Deeply buried (15,000 to 18,000 ft.) Eagle Mills sandstone have subarkosic and sublithic modal compositions. These sandstones exhibit evidence of a complex and prolonged diagnetic history, including: early chlorite cementation; early quartz and feldspar overgrowths; early calcite and dolomite cementation; dissolution of framework grains and early carbonate cements; kaolinite precipitation; late ferroan carbonate cementation; albitization; late chlorite and anhydrite replacement; saddle dolomite cementation; and pyritization. Pyrobitumens coat early chlorite rim cements indicating that most diagenesis post-dated hydrocarbon migration. Secondary porosity development coincided with a later burial dissolution event. The Eagle Mills paragenetic sequence records progressive burial into a high-temperature diagenetic regime where thermochemical sulfate reduction was the dominant process. Marked shifts in paleo-water chemistry are recorded by the Eagle Mills diagenetic sequence. Pervasive dissolution of detrital feldspars in some Eagle Mills sandstones provides unequivocal petrographic evidence for deep-seated sourcing of diagenetic fluids, which migrated along faults, and contributed to the diagenesis of overlying Mesozoic strata. These petrographic analyses support interpretations of geochemical/fluid-flux data for the Mesozoic Gulf Coast basin.

  8. Petrogenesis of Late Paleozoic volcanics from the Zhaheba depression, East Junggar: Insights into collisional event in an accretionary orogen of Central Asia

    NASA Astrophysics Data System (ADS)

    Li, Di; He, Deng-fa; Santosh, M.; Tang, Jie-yun

    2014-01-01

    The Carboniferous to Permian period marks an important transition from accretion to collision in the East Junggar terrane, NW China. Field and Well Fuqian-1 well core data from the Zhaheba depression provide a better window for understanding the magmatic process during this period and its implications for the continental growth of Central Asia. Field investigations reveal structural features characterized by NE-SW compression, with lithology composed of basic and intermediate-felsic volcanic rocks and pyroclastic rocks. The core samples from Well Fuqian-1 show dominantly basalt, basaltic andesite, dacite and minor pyroclastic rocks. We report zircon SHRIMP U-Pb ages of 276.0-279.8 Ma from rhyolites and zircon LA-ICP-MS U-Pb ages of 315.4-317.4 Ma from dacite and basaltic andesite. Our data suggest that the volcanic rocks from surface exposures and the well cores of Well Fuqian-1 formed in the Early Permian and the Late Carboniferous, respectively. The Late Carboniferous mafic rocks have geochemical characteristics similar to the intercalated Early Permian felsic rocks. The mafic rocks show low initial 87Sr/86Sr (0.703162-0.703783) and high ɛNd(t) (5.5-7.5), enrichment in LREE and some LILEs (such as Rb and Th) as well as HFSEs (such as Zr, Y), and depletion in Nb, Ta and Ti. Furthermore, they also display lower Sm/Th (1.6-8.4) and higher Th/Y (0.03-0.12) ratios than those of MORB, and variable Th/Zr (0.004-0.016), Ba/Th (61-839), Ba/La (6.13-48.77) and Ba/Nb (10-101) ratios. The geochemical data suggest that these rocks were derived dominantly from a 5-10% partial melting of a mainly garnet-rich with minor spinel-bearing Iherzolite mantle source metasomatized by slab-derived fluids. The felsic rocks are rich in silica (SiO2 = 57.43-78.07%) and alkalis (K2O + Na2O = 5.33-9.28%) and possess high TFe2O3 (0.70-6.95%) contents and Ga/Al ratios, and low CaO (0.18-5.11%) and MgO (0.13-2.02%) contents. They represent typical high-medium-K calc-alkaline A-type rhyolite

  9. 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.

  10. 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

  11. Petrogenesis and tectonic setting of the Late Paleozoic Xing'an complex in the northern Great Xing'an Range, NE China: Constraints from geochronology, geochemistry and zircon Hf isotopes

    NASA Astrophysics Data System (ADS)

    Dong, Yu; Ge, Wenchun; Zhao, Guochun; Yang, Hao; Liu, Xiwen; Zhang, Yanlong

    2016-01-01

    To determine the petrogenesis and tectonic setting of the Late Paleozoic Xing'an complex in the northern Great Xing'an Range (GXR), northeastern China, we undertook zircon U-Pb dating and geochemical analyses (major and trace elements, and Hf isotopic compositions) on samples obtained from the complex. The Xing'an complex is composed mainly of the Xinshali (XSL), Ershihao (ESH), Xinnangou (XNG) and Xing'an Station (XAS) plutons. The U-Pb zircon ages measured by secondary ion mass spectrometry (SIMS) and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) indicate that the Xing'an complex was emplaced in three stages, represented by the ∼358 Ma XSL, ∼308 Ma XNG/XAS, and ∼294 Ma ESH plutons. The XSL pluton is composed mainly of gabbro diorites (SiO2 = 53.49-56.81 wt.%; MgO = 4.60-5.52 wt.%) of the mid-K calc-alkaline series. These rocks are weakly enriched in large ion lithophile elements (LILEs) and light rare earth elements (HREEs), and depleted in high field strength elements (HFSEs, e.g., Nb, Ta, and Ti) and heavy rare earth elements (HREEs), with εHf(t) values of +4.07 to +7.59. Based on these geochemical and isotopic features, we propose that the magma of the XSL pluton was derived from partial melting of depleted lithospheric mantle that was metasomatized by subducted slab-derived fluids. The ESH and XSL plutons have similar geochemical compositions and zircon Hf isotopic values, thereby indicating a common petrogenesis. In contrast, the XNG and XAS plutons comprise syenogranites and monzogranites that are geochemically similar to I-type granites based on their high SiO2 (67.93-74.98 wt.%) and Na2O + K2O (7.12-9.20 wt.%) contents, low MgO (0.33-1.14 wt.%) content, enrichment in LILEs (e.g., Rb, Th, U, K) and LREEs, and depletion in Nb, Ta, Ti and P. The positive εHf(t) values (+6.34 to +12.72) of the XNG and XAS plutons and their corresponding Hf two-stage model ages of 1149 Ma to 484 Ma indicate that the parental magma was derived

  12. 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

  13. 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.

  14. 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.

  15. The Lower Cretaceous Chouf Sandstone of Lebanon: Tracking Caledonian tectonism in a Tethyan sediment

    NASA Astrophysics Data System (ADS)

    Asmar, Chloé; Schneider, David A.; Grasemann, Bernhard; Nader, Fadi H.; Tari, Gabor

    2014-05-01

    The Chouf Sandstone is a clastic rock sequence within the Cretaceous succession of Lebanon. Generally, the formation consists of shales, sandstones and shallow water, low-energy limestones with local volcanic horizons and lignites. The typical Chouf Sandstone is dominated by monocrystalline quartz (85-95%) indicating well-sorted sandstone deposited in fluvial to deltaic/littoral environments. The thickness of the Chouf Sandstone is variable, ranging from just a few meters to almost 700 m thick showing prominent lateral facies changes locally. Isopach maps of the Chouf Sandstone reveal systematic variations which could be interpreted as the result of deposition in extensional half-grabens at the margin of a large basin. The overlying Lower Cretaceous neritic carbonate formations do not record any major thickness variations and therefore the Chouf Sandstone may be interpreted as a Lower Cretaceous syn-rift clastic sequence. LA-ICPMS U-Pb geochronology was conducted on detrital zircons from the Chouf Sandstone sampled along the Qartaba Anticline (Mount Lebanon). With the exception of a few Archean outliers, the resulted ages fell into three broad populations: i) a small Paleoproterozoic population, ii) a Grenvillian population, and iii) a Pan-African population (575-650 Ma). One single zircon is slightly younger then the Pan-African population, yielding a 206Pb/238U age of 491 ± 5 Ma. Zircon (U-Th)/He dating on the same samples records cooling through a nominal closure temperature of 180°C and yields Late Ordovician to Early Silurian ages (440-465 Ma), regressed from triplicates of zircon from seven samples across the anticline. Typically, the youngest detrital age that is obtained by U-Pb geochronology, represents a maximum estimate for the depositional age. However, in our study the ca. 490 Ma zircon U-Pb age is interpreted as the age of primary deposition in an Early Paleozoic basin. Combined with the zircon (U-Th)/He cooling ages, our data may suggest the

  16. 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.

  17. 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

  18. 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.

  19. 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.

  20. 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

  1. 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

  2. Paleoclimatic and paleomagnetic constraints on the Paleozoic reconstructions of south China, north China and Tarim

    NASA Astrophysics Data System (ADS)

    Shangyou, Nie

    1991-10-01

    Paleomagnetic and paleoclimatic data provide the most useful latitudinal constraints for plate reconstructions. Distributions through the Paleozoic of five types of climatically sensitive sediments (coals, evaporites, reefs, dolomites and limestones) for south China, north China and Tarim are shown on 15 maps that include 1578 reliable data points. These paleoclimatic data agree reasonably well with available paleomagnetic directions, although significant divergence between the two exists for the Early Paleozoic. These data indicate the following: (1) South China was in low latitudes during the entire Paleozoic, with a subtropical position in the Cambrian. (2) North China also remained near the equator in the Early and Late Paleozoic, except for the Ordovian and the Late Permian when extensive evaporites suggest slightly higher latitudinal positions, while its Middle Paleozoic position is uncertain due to the missing stratigraphie record. (3) In south China, local tectonics appears to have played a dominant role in determining paleogeography and therefore marine sedimentation, especially after the Late Ordovician-Early Silurian, because the areal coverage of marine sediments through time is distinctly different from what would be expected from published global sea-level curves. (4) Paleoclimatic and paleomagnetic data are compatible with biogeographic data which suggest that south China was part of eastern Gondwana in the Early Paleozoic, but was widely separated from Gondwana in the Late Paleozoic, and the split between the two probably happened in the Devonian, giving rise to a major break-up unconformity in central south China.

  3. Paleozoic cratonal/miogeoclinal stratigraphy in the western Mojave Desert

    SciTech Connect

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

    1991-02-01

    Detailed mapping of metasedimentary rocks by many workers in the western Mojave Desert, California, has revealed Paleozoic lithologies of cratonal/miogeoclinal affinity. These exposures are metamorphosed, highly strained, and dismembered, and sit as roof pendants to Mesozoic and Tertiary intrusive rocks. In most outcrops no diagnosis fossils are preserved. Age correlation of these units is based, therefore, solely on similarities to lithologic packages outside the region. Despite the complex tectonic history this area has suffered since the late Paleozoic paleogeographic elements trend southwest into the region from where they are last clearly defined near the California-Nevada border. Dolomitic and calcitic marbles, quartzites, and biotite schists make up a major part of the stratigraphy in many areas. The stratigraphy and lithology of these units strongly suggest that they are correlative with late Precambrian-Cambrian units in the Death Valley region. Possible Ordovician and Devonian marbles also are present within some sections; at least one locality contains stromatoporoids of probable Devonian age. Calcite marbles tentatively correlated with lithologically similar Permian units in the Death Valley area are also represented and appear to be depositionally overlain by Mesozoic( ) shallow-marine and are-derived clastic rocks. Although the western Mojave Desert region has experienced compressional, transcurrent, and extensional deformation since late Paleozoic, our current understanding and restoration of this deformation history does not significantly alter the general southwest Paleozoic paleogeographic trends known to exist farther east.

  4. 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

  5. Geology of a stratigraphically complex natural gas play: Canyon Sandstones, Val Verde Basin, southwest Texas. Topical report, January-October 1993

    SciTech Connect

    Laubach, S.E.; Clift, S.J.; Hamlin, H.S.; Dutton, S.P.; Hentz, T.F.

    1994-07-01

    The report examines the influence of stratigraphy, diagenesis, natural fractures, and in situ stress on low-permeability, gas-bearing sandstone reservoirs of the Paleozoic Ozona and Sonora Canyon Sandstones of the Val Verde Basin, Texas. The main stratigraphic controls on distribution and quality of Canyon Sandstone reservoirs are submarine fan depositional patterns. These patterns are revealed in regional facies and maximum sandstone maps. Siderite cement is key to good within-sandstone reservoir quality. Natural fractures are widespread in both Ozona and Sonora Canyon sandstones. They could be future targets for advanced drilling methods, and they need to be taken into account in hydraulic fracture treatment design and reservoir management.

  6. 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

  7. 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.

  8. 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.

  9. 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.

  10. Paleozoic crudes of Tomsk province

    SciTech Connect

    Smol'yaninova, N.M.; Mashukova, Z.I.; Nemirovskaya, G.V.

    1983-01-01

    The Paleozoic crudes typically have low densities at 20/sup 0/C, low contents of resins, high viscosities at 20/sup 0/C, rather high solid points, and high contents of solid paraffins. The Paleozoic crudes are in no way inferior in quality to the Mesozoic crudes of Tomsk province, and are even better in some respects (yields of high-V.I. and medium-V.I. oils). They can be processed with either a fuel/lube or petrochemical refining scheme. Finds that the crudes from the Ostaninsk and SeveroOstaninsk fields, in terms of their paraffin and sulfur contents and other indexes, are similar to the Jurassic crudes of the Zhetybai field on the Mangyshlak peninsula. These 2 crudes and the Chkalovsk crude, even though the high wax contents offer problems in production and transportation, can serve as good raw materials for fuel and oil production, and also for the manufacture of liquid and solid paraffins.

  11. 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.

  12. 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

  13. 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

  14. Paleozoic orogens in New England, USA

    USGS Publications Warehouse

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

  15. 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.

  16. Demarcation of a Late Cretaceous(. ) thrust belt near Railroad Valley and Pine Valley in east-central Nevada

    SciTech Connect

    Cameron, G.J.

    1986-08-01

    Older-over-younger low-angle faults occur within a north-south-trending belt that includes the Pancake, Fish Creek, Diamond, and Carlin/Pinon Ranges in east-central Nevada. Collectively, these ranges form the western boundary of Nevada's only oil-producing basins, Railroad Valley and Pine Valley. These structures lie parallel to, but are east of and distinct from, the Roberts Mountain thrust. The faults involve eastern assemblage Paleozoic rocks in both upper and lower plates. The Chainman Shale is commonly the surface of decollement. A Late Cretaceous and possibly younger age is assigned to the faults, based on evidence that the Late Cretaceous Newark Canyon Formation is locally overridden by Paleozoic rocks in the Diamond and Pancake Ranges. The areal extent of this thrust belt was assessed using systematic lithostratigraphy from measured sections. This method was found useful and necessary owing to the disruptive influence of younger basin-and-range block faults on the earlier structures. Lithostratigraphic parameters used include formation thicknesses, color logs, grain-size logs, chert horizons, and quartz sandstone zones within Ordovician to Devonian rocks. It is reasoned that the boundaries of displaced blocks will show relatively sharp gradients of change in a number of lithostratigraphic parameters within the Paleozoic section.

  17. "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

  18. 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.

  19. Late Devonian to early carboniferous turbidite facies and basinal development of the Eastern Klamath Mountains, California

    NASA Astrophysics Data System (ADS)

    Watkins, Rodney

    1986-08-01

    The Late Devonian to Early Carboniferous Bragdon Formation, Eastern Klamath Mountains, California, is a thick turbidite sequence deposited as a submarine fan complex within an arc-related basin. Laminated mudstone and less abundant "classical" turbidites comprise most of the lower part of the Bragdon and represent a lower fan environment. Amalgamated beds of normally graded to massive sandstone and pebbly sandstone occur throughout the Bragdon but are most abundant in its upper half, where they are associated with very thick channel-fill beds of pebbly sandstone and conglomerate. The upper half of the Bragdon Formation represents a mid fan to upper fan environment, and it also includes closely interbedded "classical" turbidites interpreted as interchannel or levee deposits. An upper slope facies of bioturbated mudstone with an Early Carboniferous fauna occurs at the top of the formation. Clastic material in the Bragdon Formation indicates little contemporaneous vulcanism and was probably derived from Lower Paleozoic metasediments which were uplifted to the north. Deposition of the Bragdon was initiated by rifting and subsidence of an underlying Middle Devonian arc complex. Infilling of the resulting basin during the Late Devonian and Early Carboniferous is indicated by overlap of turbidite facies across Middle Devonian arc deposits and by an upward stratigraphic trend in the Bragdon from lower fan to upper fan and slope environments.

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. Paleozoic and Mesozoic stratigraphy and oil potential of Western Desert

    SciTech Connect

    Khalil, N.A.; Young, D.; Nairn, A.E.M.

    1983-03-01

    The depocenter of the Paleozoic basin in western Egypt lies in the northwestern part of the Western Desert. The depositional axis of the basin, where thicknesses in excess of 2800 m (9200 ft) have been recorded, has a northwesterly trend to the vicinity of the Siwa Oasis. A less well-defined shallower basin with a northerly trend lies to the southwest. Farther east, a possible Paleozoic basin lies in the Abu Gharadig area where 1300 m (4265 ft) of sediments were drilled. Following the deposition of the Paleozoic section, there was a marked hiatus; the time of Hercynian movements for Permian and Triassic beds is absent. Uplift and the presence of volcanics dated in Permian-Carboniferous time are indicative of Hercynian tectonic activity. Further tectonic uplift accompanied by faulting and marine regression is dated from late Kimmeridgian time to the beginning of the Cretaceous, when transgression began once again. The dominant feature, new in the Western Desert, was the development of an east-west extensional basin, the Abu Gharadig basin, in Cretaceous time. The trough became less distinctive in Cenozoic times when a further trough, the Tiba basin, developed north of the ridge. Production from the northern Western Desert until recently has been disappointing. Exploration results from the Paleozoic Section have yielded little, but the existence of a marine section suggests that the area northeast of Siwa still has potential. The thick deeply buried Jurassic marine sequence in the Western Desert may be the source for at least part of the production from Cretaceous horizons in the Abu Ghradig, Alamein, and Razzak oil and gas fields.

  5. Paleozoic basins in West Africa and the Mauritanide thrust belt

    NASA Astrophysics Data System (ADS)

    Villeneuve, Michel

    2005-10-01

    The evolution of the Paleozoic basins of West Africa is strongly depending on the structuration of the different belts which are surrounding the West African Craton. We distinguish the "Taoudeni Basin" located in the center of the craton from the basins located on the West African Craton margin (Tindouf, Tamale and several troughs limiting the western side of the Taoudeni Basin). Other basins are located on top of the Pan-African or Hercynian belts (Bové, Kandi, Ouallen in Semmen and Diourbel basins) or on top of the Proterozoic shields (The Ghana basins). Some are evidenced underneath the Mesozoic-Cenozoic coastal basins (Bové and Ghana basins). The sedimentation started with the Marinoan glacial event (620-580 Ma) and ended with the carbonates of the Early Carboniferous. The main tectonic or climatic events that occurred during this period are registered by the sediments. Among them are, the "Série pourprée glaciogenic deposits, the Pan-African II tectonic event (550-500 Ma) which affects the southwestern part of the Taoudeni Basin, the Late Ordovician glaciogenic event, the Early Silurian marine transgression, the Early Devonian marine regression and the Hercynian tectonic event (330-270 Ma) which affects the Paleozoic basins located on the western and northern parts of the West African Craton. The second part of this paper is devoted to a synthetic review of the Mauritanides Belt which is extending from Southern Senegal to the Moroccan High Atlas. This belt includes both old Pan-African belts and Paleozoic sediments (belonging to the western part of the Bové, Taoudeni and Tindouf basins) tectonised and metamorphosed during the Hercynian orogen. The third part points out the close relationships between the Paleozoic basins and the main tectonic event for the main periods of the West African Craton evolution.

  6. Paleozoic to Jurassic terrane accretion along the northeastern margin of Tibet plateau

    NASA Astrophysics Data System (ADS)

    Neubauer, Franz; Liu, Yongjiang; Genser, Johann; Ren, Shoumai

    2010-05-01

    The Tibet plateau is considered to have been constructed by a number of basement terranes accreted to the Eurasian margin during Paleozoic to Mesozoic times, and accretion is interpreted to have progressed southwards. The northern margin, exposed in Altyn and Qilian Mountains, is generally considered as an Lower Paleozoic orogen including previously subducted ultra-high successions (Yin and Harrison, 2000; Xiao et al., 2009). Previous tectonic models of the Qaidam block and adjacent mountain ranges at the northeastern margin of the Tibet plateau assumed a minor role of Indosinian tectonism in that region, and firm evidence was only reported from eastern Kunlun Mountains (e.g., Liu et al., 2005). Based on four sources of new data, we propose that the Indosinian tectonism was much more widespread in the northeastern Qaidam block and adjacent mountain ranges, Altyn and Qilian Mts., as believed before and we propose a new tectonic model. The new data sources comprise: (1) 40Ar/39Ar dating of detrital white mica of Jurassic to Pliocene sandstones from the north-eastern Qaidam basin fill; (2) interpretation of Ordovician, Devonian and Jurassic sedimentary successions, from which we interpret the Jurassic successions as intramontane molasse to the Indosinian orogen; (3) 40Ar/39Ar dating of detrital white mica in recent rivers from the southern Qilian Shan revealing possible basement sources in the Qilian Shan draining towards the Qaidam basin; and (4) structural study of basement rocks and subordinate 40Ar/39Ar mineral ages of metamorphic basement rocks. An Ordovician greywacke exposed in the eastern Qaidam basin (W of Delinghua) yields three 40Ar/39Ar age groups of detrital white mica: 900-922, 610-654 and 527-554 Ma. Furthermore, similar old age groups centering at ca. 670 and 1010 Ma are virtually widespread in recent rivers from Qilian Mountains and clearly demonstrate the presence of Panafrican and Grenvillian tectonic elements in the southern Qilian Mts. at the

  7. 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

  8. 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.

  9. The maturation history of the Paleozoic hydrocarbon system of the Arabian platform

    SciTech Connect

    Bishop, R.S.

    1995-08-01

    This poster defines the Paleozoic hydrocarbon system of the Arabian Platform, presents an interpretation of its thermal and burial history and uses those results to describe the maturation history of the Lower Silurian source rock. Geohistory analysts were used to delineate source rock kitchens and to guide searches for previously unrecognized sources. The Paleozoic hydrocarbon system is one of the areally largest hydrocarbon systems in the world and one of the least drilled. It contains one of the world`s largest gas fields, is one of the largest potential gas resources on earth, and contains one of the largest emerging oil plays. It is present in both the Zagros Foldbelt and the Arabian Platform. The Lower Silurian Qusaiba source and the Triassic Sudair regional seal define the boundaries of the system. The Paleozoic hc 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 deposition of a regional seal; (4) Mesozoic charging primarily from the Lower Silurian sources; and (5) re-initiation of maturation of Paleozoic sources and charging of the Zagros compressional traps during Neogene collision with Eurasia. We have also interpreted the filling history of North Dome to explain why it contains gas rather than oil. A combination of late trap growth and late gas generation apparently displaced the previously resident oils and left a trap with a gas rich in condensate. The Silurian may have been exhausted by this time, thus indicating that other sources may have contributed significantly to North Dome.

  10. 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.

  11. 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.

  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. PMID:11088546

  13. 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.

  14. Petrographic compositions of Paleozoic coals of Mongolia

    NASA Astrophysics Data System (ADS)

    Jargal, Luvsanchultem; Erdenetsogt, Bat-Orshikh

    2016-04-01

    In Mongolia, the deposition of coal bearing strata commenced in Pennsylvanian, and continued in Upper Permian, in Lower-Middle Jurassic and finally in Lower Cretaceous time. Pennsylvanian coal seams were deposited in Western Mongolia, where peat formation was initially developed in the southernmost part and later gradually shifted to northward. By the Late Permian, the locus of coal formation had changed and main peat accumulation took place in southern Mongolia. Lower-Middle Jurassic coal was accumulated in western, northern and eastern Mongolia. During this time, peat forming condition was comparatively stable in entire Mongolia. In the Early Cretaceous, thick and extensive coal was formed in the Eastern Mongolia. Due to this general trend of peat accumulation, coal rank decreases from west (bituminous) to east (lignite). The significant portion of Pennsylvanian and Upper Permian coal reserves, existed in western and southern Mongolia, are coking coal. Thus, petrographical studies of the coals are notably important. However, previous studies of Paleozoic coals have been sparse, and only few deposits have been conducted. The maceral compositions of Western Mongolian Pennsylvanian coals such as Khushuut, Maanit, Khurengol, Zeegt, Tsagaangol, Nuurstkhotgor, Khartarvagatai and Olonbulag were studied. The results show that the coals are dominated by vitrinite (45 vol.% to 71 vol.%) and inertinite (28 vol.% to 53vol.%) macerals. Liptinite contents are low, less than 4 vol.%. In addition, vitrinite reflectance values (Rmax in oil) of Khushuut (1.85%), Maanit (0.92%), Khurengol (1.4%), Zeegt (0.86%), Tsagaangol (3.6%), Nuurstkhotgor (0.9%), Khartarvagatai (1.1%) and Olonbulag (1.7%) were determined. Upper Permian coals in southern Mongolia (Tavantolgoi, Nariinsukhait, Jargalant, Tsagaantolgoi, Buduuniikhyar) are dominated by vitrinite (55 vol.% to 78 vol.%) and inertinite macerals (19 vol.% to 44 vol.%). Liptinite contents range from 1 vol.% to 7 vol.%. The vitrinite

  15. Geochemistry and petrology of greenstones from the Erdenetsogt formation, central Mongolia: New evidence for a middle Paleozoic mantle plume

    NASA Astrophysics Data System (ADS)

    Ganbat, E.; Ishiwatari, A.; Demberel, O.

    2012-12-01

    This research presents evidence of the plume-related formation of greenstones from the Erdenetsogt Formation (EF) hosted by Tsetserleg terrane of middle Paleozoic Hangay-Hentey accretionary complex, which is central part of the Central Asian Orogenic Belt (CAOB). Our new data can support middle Paleozoic evolution of plume-related magmatism of the paleo-oceanic plate and its accretionary processes, which significantly contributed to the continental growth of CAOB. EF is mainly made up of intensively deformed oceanic plate stratigraphy such as radiolarian/ribbon chert, red and green quartzites (metachert), fine to medium-grained sandstone, siltstone with minor amount of limestone, and some basaltic greenstones which have been discovered lately during geological mapping in the south Hangay region. The upper unit of this formation was dated by late Devonian conodonts from the chert. However, the chemistry of greenstones in this region has not been studied yet except brief study by Orolmaa (2008). The studied samples include metabasalts, dolerites, microgabbros, and occasional meta-picrites with mostly subophitic, intersertal, and partly intergranular textures. The common assembledge of phenocrysts is clinopyroxene (well-preserved in all greenstones) and plagioclase (replaced by albite). Also completely altered olivine containing relict Cr-spinel observed from metapicrite and porphyritic metabasalt. The composition of the primary clinopyroxene (augite) and Cr-spinel were analyzed by electron microprobe and bulk rock major and trace elements by XRF. On the basis of Ca +Na vs. Ti and Ca vs. Ti+Cr discrimination diagrams, clinopyroxenes display tholeiitic magma type and non-orogenic affinity. The relict spinels are 20-250 μm in size. The Al2O3 wt.% vs. TiO2 wt.% variation of the spinels corresponds to the transitional affinity of OIB and MORB. The Cr and Mg numbers of the spinels show very limited values ranging from 55 to 68 and from 0.3 to 0.6, respectively, and

  16. 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.

  17. (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

  18. 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.

  19. Late Paleozoic transcurrent tectonic assembly of the central Appalachian Piedmont

    NASA Astrophysics Data System (ADS)

    Valentino, David W.; Gates, Alexander E.; Glover, Lynn

    1994-02-01

    Recent investigations in south-eastern Pennsylvania and northern Maryland have demonstrated a major anastomosing strike-slip shear system. The Pleasant Grove-Huntingdon Valley shear system emerges from beneath the coastal plain cover at Trenton, New Jersey, and extends to the area west of Baltimore, Maryland, where it is overlain by the Culpepper Mesozoic rift basin. The sense of offset across this system is dextral. In the Susquehanna River region and north of the shear zone, the rocks of the Octoraro Formation contain evidence for two metamorphisms and deformations prior to strike-slip shearing, whereas south of the shear zone the Peters Creek Formation contains evidence for only one. The discordance in metamorphic and deformational history across the shear zone suggests the now juxtaposed rocks originated in different parts of the orogen. Although conclusive ages for the strike-slip deformation do not exist at this time, the timing of deformation is loosely constrained where the shear system crosscuts known Taconian structures in the Piedmont. Comparison of deformation style with other regions in the Appalachian suggests the Pleasant Grove-Huntingdon Valley shear system is related to Alleghanian transcurrent tectonics in the Piedmont. Palinspastic reconstruction of the Pleasant Grove-Huntingdon Valley shear system reveals fundamental problems in current tectonic models for the central Appalachian Piedmont. A minimum of 150 km of dextral offset is proposed for the Pleasant Grove-Huntingdon Valley shear system based on reconstruction of the Cambrian-Ordovician shelf edge between northern Maryland and southeastern New York. Displacement of this magnitude can account for the previously proposed tectonic models that portray a failed Iapetan rift block and microcontinent that contains the Baltimore Grenvillian massifs. Even though a history of early orthogonal collision is preserved within discrete structural blocks, transcurrent shearing has greatly influenced the distribution of those blocks. Models not including the strike-slip component of tectonic assembly need serious reconsideration, as evidence grows that the magnitude of orogen-parallel displacement is equal to or larger than the orthogonal component.

  20. Distribution and erosion of the Paleozoic tectonic unconformities in the Tarim Basin, Northwest China: Significance for the evolution of paleo-uplifts and tectonic geography during deformation

    NASA Astrophysics Data System (ADS)

    Lin, Changsong; Yang, Haijun; Liu, Jingyan; Rui, Zhifeng; Cai, Zhenzhong; Zhu, Yongfeng

    2012-03-01

    The distribution and erosional features of the Paleozoic major tectonic unconformities in the Tarim Basin, and their genetic relation to the development of paleo-uplifts as well as the evolution of geodynamic settings, are documented in this paper based on the integral analysis of seismic, drilling, and outcrop data. During the Paleozoic, the Tarim Basin underwent three major tectonic deformation stages, which resulted in three angular unconformities and in significant changes in basin geomorphology and paleogeography. The tectonic deformation at the end of the Middle Ordovician was characterized by development of the southern central paleo-uplift, the northern depression, and the southeastern Tangguzibasi depression in the basin. The thickest denudation belts of the unconformity (Tg5-2) are distributed mainly along the thrust structural highs. A stronger deformation event took place at the end of the Late Ordovician and formed a huge uplift along the southwestern and southeastern basin margins and the western part of the Tabei uplift along the northern basin margin, producing an extensive angular unconformity (Tg5) with maximum erosion thickness of 1500-2000 m. This tectonic event resulted in an abrupt change in overall geography of the basin, from a deepwater marine environment at the late stages of the Late Ordovician to a littoral and neritic basin in the Early Silurian. The deformation that occurred at the end of the Middle Devonian was the strongest in the Paleozoic. It generated the most widespread angular unconformity (Tg3) within the basin and led to extensive erosion, with maximum denudation thickness of 3000-5000 m in the northern and northeastern parts of the basin. The topography of the basin during the late Devonian was characterized by a high in the northeast and a low in the southwest, forming an embayment basin opening to the southwest during the Early Devonian to Carboniferous. The transgression in general from southwest to northeast deposited

  1. 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

  2. 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.

  3. 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.

    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).

  4. (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.

  5. 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

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. Log interpretation of shaly sandstones

    SciTech Connect

    Baker, J.F.

    1988-01-01

    The determination of water saturation from electrical resistivity measurements to evaluate the potential of reservoirs is a fundamental tool of the oil industry. Shaly sandstones are difficult to evaluate because clays are conductive and they lower the resistivity of the rock. A review of shaly-sandstone research concerning ''volume-of-shale'' equations reveals three theoretical categories: (1) laminated clay equations, (2) dispersed clay equations, and (3) equations that assume that the effect of the clays on the conductivity measurement is directly related to water saturation. A new model for predicting the relative amounts of laminated and dispersed shales and accounting for their effects according to their abundance can be used for any sandstone, clean or shaly. Equations representing each of the three theoretical categories and the new equation were tested on cored Wilcox sandstones from two wells. Cores were analyzed to determine the volume and distribution of clays and to correlate porosity with the well logs.

  11. 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.

  12. 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

  13. 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

  14. 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.

  15. 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

  16. 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

  17. 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.

  18. 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.

  19. 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.

  20. Hydrocarbon discoveries in Paleozoic Solimoes basin, Upper Amazon region, Brazil

    SciTech Connect

    Apoluceno, N.; Ferreira, A.; Tsubone, K.

    1989-03-01

    The Solimoes basin, previously known as Upper Amazon basin, is located in northern Brazil and has a prospectable area of more than 300,000 km/sup 2/. The Purus arch, a regional positive feature, separates this basin from the Amazonas basin. As far as the basin geology is concerned, the Solimoes basin is strikingly different from its neighboring basin due to certain structural and stratigraphic peculiarities. Between the Late Jurassic and Early Cretaceous the basin was affected by regional compressional tectonics that generated a series of northeast-southwest-oriented trends. The exploration play in the basin is classic wrench tectonics - elongated dome structures on upthrown blocks of en echelon reverse faults. Despite the problems of working in a tropical forest, Petrobras has made a systematic exploration campaign in the basin since the early 1970s. This effort was compensated by the discovery of two important hydrocarbon-bearing areas: Jurua gas province in 1978 and the Urucu River oil, gas, and condensate province in 1986. The latter, whose commercial oil production was initiated in July 1988, is considered an important marker in the petroleum exploration history of Brazil, particularly with respect to the Paleozoic basins, which total more than 3 million km/sup 2/ of the country's territory.

  1. 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.

  2. 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.

  3. 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)

  4. 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

  5. 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.

  6. 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.

  7. 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

  8. 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.

  9. 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.

  10. 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.

  11. Paleozoic geology of the New Madrid area

    SciTech Connect

    Schwalb, H.R.

    1982-09-01

    Thick sections of sedimentary rocks occupy two grabens, the Reelfoot Rift and the Rough Creek Graben. Early sediments of Middle Cambrian and sub-Mt. Simon (Lamotte) deposition are found in the grabens, but do not crop out in the area. Growth faulting continued to deepen the Rough Creek Graben and possibly the Reelfoot Rift during much of the Paleozoic interval. Renewed tectonic activity, probably occurring during the Mesozoic Era, uplifted the Pascola Arch near the center of the Reelfoot Rift and also renewed uplift of many structural features and fault zones, some of which were displaced in a direction opposite to earlier movements. Erosion then removed thousands of feet of sediment from the area, and beveled the Pascola Arch. Igneous plutons were injected into the Precambrian basement rocks and some penetrated into the sedimentary section and formed dikes and sills. Subsidence followed with the formation of the Mississippi Embayment where Cretaceous and Tertiary sediments collected and buried the Pascola Arch. The area remains seismically active to the present day.

  12. Quantitative analysis of sandstone porosity

    SciTech Connect

    Ferrell, R.E. Jr.; Carpenter, P.K.

    1988-01-01

    A quantitative analysis of changes in porosity associated with sandstone diagenesis was accomplished with digital back-scattered electron image analysis techniques. The volume percent (vol. %) of macroporosity, quartz, clay minerals, feldspar, and other constituents combined with stereological parameters, such as the size and shape of the analyzed features, permitted the determination of cement volumes, the ratio of primary to secondary porosity, and the relative abundance of detrital and authigenic clay minerals. The analyses were produced with a JEOL 733 Superprobe and a TRACOR/NORTHERN 5700 Image Analyzer System. The results provided a numerical evaluation of sedimentological facies controls and diagenetic effects on the permeabilities of potential reservoirs. In a typical application, subtle differences in the diagnetic development of porosity were detected in Wilcox sandstones from central Louisiana. Mechanical compaction of these shoreface sandstones has reduced the porosity to approximately 20%. In most samples with permeabilities greater than 10 md, the measured ratio of macroporosity to microporosity associated with pore-filling kaolinite was 3:1. In other sandstones with lower permeabilities, the measured ratio was higher, but the volume of pore-filling clay was essentially the same. An analysis of the frequency distribution of pore diameters and shapes revealed that the latter samples contained 2-3 vol% of grain-dissolution or moldic porosity. Fluid entry to these large pores was restricted and the clays produced from the grain dissolution products reduced the observed permeability. The image analysis technique provided valuable data for the distinction of productive and nonproductive intervals in this reservoir.

  13. 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.

  14. Block Island fault: a Paleozoic crustal boundary on the Long Island platform

    USGS Publications Warehouse

    Hutchinson, Deborah R.; Klitgord, Kim D.; Detrick, R. S.

    1985-01-01

    A major fault cutting through most of the crust can be identified and mapped on the Long Island platform using multichannel seismic reflection profiles and magnetic data. The fault, here called the Block Island fault (BIF), strikes north-northeast, dips westward at low angle, and does not resemble the thin-skinned thrust faulting observed in the foreland of the Appalachians. The BIF is located within the hinterland of the Appalachian mountain belt in the collision zone between Africa and North America. We present several interpretations but favor one in which the fault originated as an east-verging mid–late Paleozoic thrust fault, possibly related to the collision of Avalon or Meguma with North America. It was probably reactivated during early Mesozoic continental breakup and again in the Late Cretaceous and Tertiary, causing the steeply dipping postrift New Shoreham fault to form, either as an antithetic (normal) or splay (reverse) fault.

  15. 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

  16. Tectonic evolution of Early Paleozoic island-arc systems and continental crust formation in the Caledonides of Kazakhstan and the North Tien Shan

    NASA Astrophysics Data System (ADS)

    Degtyarev, K. E.

    2011-01-01

    The extended Saryarka and Shyngyz-North Tien Shan volcanic belts that underwent secondary deformation are traced in the Caledonides of Kazakhstan and the North Tien Shan. These belts are composed of igneous rocks pertaining to Early Paleozoic island-arc systems of various types and the conjugated basins with oceanic crust. The Saryarka volcanic belt has a complex fold-nappe structure formed in the middle Arenigian-middle Llanvirnian as a result of the tectonic juxtaposition of Early-Middle Cambrian and Late Cambrian-Early Ordovician complexes of ensimatic island arcs and basins with oceanic crust. The Shyngyz-North Tien Shan volcanic belt is characterized by a rather simple fold structure and consists of Middle-Late Ordovician volcanic and plutonic associations of ensialic island arcs developing on heterogeneous basement, which is composed of complexes belonging to the Saryarka belt and Precambrian sialic massifs. The structure and isotopic composition of the Paleozoic igneous complexes provide evidence for the heterogeneous structure of the continental crust in various segments of the Kazakh Caledonides. The upper crust of the Shyngyz segment consists of Early Paleozoic island-arc complexes and basins with oceanic crust related to the Saryarka and Shyngyz-North Tien Shan volcanic belts in combination with Middle and Late Paleozoic continental igneous rocks. The deep crustal units of this segment are dominated by mafic rocks of Early Paleozoic suprasubduction complexes. The upper continental crust of the Stepnyak segment is composed of Middle-Late Ordovician island-arc complexes of the Shyngyz-North Tien Shan volcanic belt and Early Ordovician rift-related volcanics. The middle crustal units are composed of Riphean, Paleoproterozoic, and probably Archean sialic rocks, whereas the lower crustal units are composed of Neoproterozoic mafic rocks.

  17. 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

  18. 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.

  19. 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.

  20. U-Pb age and Hf isotopic data of detrital zircons from the Devonian and Carboniferous sandstones in Yimin area, NE China: New evidences to the collision timing between the Xing'an and Erguna blocks in eastern segment of Central Asian Orogenic Belt

    NASA Astrophysics Data System (ADS)

    Han, Guoqing; Liu, Yongjiang; Neubauer, Franz; Bartel, Esther; Genser, Johann; Feng, Zhiqiang; Zhang, Li; Yang, Mingchun

    2015-01-01

    New U-Pb age data and Hf isotope systematics on zircons from Middle Devonian and Lower Carboniferous units from NE China provide evidence for the depositional age of these poorly constrained units as well as for the timing of the collision between the Erguna (Ergun in some references) and Xing'an blocks in the eastern end of Central Asian Orogenic Belt (CAOB). The detrital zircons from the Devonian and Carboniferous sandstones yielded similar age spectra in probability diagrams showing three distinct peaks at ∼450 Ma, ∼500 Ma and ∼540 Ma, respectively, along with Proterozoic and Archean age groups, except for a relatively young age population at ∼360 Ma detected for zircons from the Hongshuiquan Fm. The dating results suggest that the depositional time of the Niqiuhe Fm. should be younger than Late Silurian, as indicated by the youngest 422-Ma detrital zircon from this Fm., and that of the Hongshuiguan Fm. with a youngest detrital age of ca. 338 Ma, is younger than Middle Mississippian (Visean), which is in accordance with those inferred from biostratigraphic data. These dominant age groups are widely found in the Erguna and Xing'an blocks, it is suggested that the sediments of the studied sandstones from Niuqiuhe and Hongshuiquan Fms come mainly from the Erguna and Xing'an blocks. The εHf (t) value of dated zircons from our sandstones has a wide range (-21 to 16), which shows a mixed signature of that from Paleozoic granitoids in Xing'an block (6-17) and Erguna block (-2 to 6), indicating that Erguna and Xing'an blocks had connected before the Middle Devonian deposition of the Niqiuhe Fm. (422 ± 5 Ma). Combined with the age data, we suggest that the Erguna and Xing'an blocks started to accrete at ∼540 Ma, reached the peak of collision at ∼500 Ma, and went into the post-collision stage from ∼490 to ∼450 Ma. The study provides more evidences and constraints for the early Paleozoic evolutions of the inter-continental block amalgamations and

  1. 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

  2. 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.

  3. Geochronology and geochemistry of Paleozoic plutons in the Alxa Terrane: petrogenesis and tectonic implications

    NASA Astrophysics Data System (ADS)

    Liu, Qian; Zhao, Guochun

    2016-04-01

    Situated between the Tarim Craton and the North China Craton (NCC), the Paleozoic magmatic record in the Alxa Terrane places important constraints on the accretionary orogenesis of the southern Paleo-Asian Ocean (PAO) forming the southern section of the Central Asian Orogenic Belt. New results of LA-ICPMS zircon U-Pb ages and whole-rock major- and trace-element compositions reveal two groups of diorites and granitoids in the Alxa Terrane. One group consists of diorites and granitoids that were emplaced at 458-440 Ma, characterized by lower Al2O3/TiO2 ratios and higher TiO2 contents, implying high temperature - low pressure crystallization conditions and a shallow source region. In contrast, the second group consists of granitoids that were formed at 417-407 Ma, displaying low high rare earth elements, very high Sr/Y ratios and mostly positive Eu anomalies, suggesting low temperature - high pressure crystallization conditions and source regions at deep crustal levels where garnet is stable in the residual phase. Both of two groups are mostly calc-alkaline to high-K calc-alkaline, and depleted in Nb, Ta and Ti and enriched in Ba, K and Sr, suggesting an arc affinity related to a PAO oceanic subduction regime since the Late Ordovician. Both zircon ɛHf(t) and whole-rock ɛNd(t) values decrease from 458 Ma to 440 Ma but increase from 417 Ma to 407 Ma, whereas whole-rock initial 87Sr/86Sr ratios display an opposite trend. Such an isotopic change suggests a tectonic switch from an advancing to a retreating subduction setting in the Early Devonian. Compiled with previous studies, we suggest that the early Paleozoic magmatic arc existing in the Alxa Terrane represented the western extension of the super-large early Paleozoic active continental margin on the northern margin of the NCC.

  4. Do Low 15N Values in Paleozoic Epeiric Basins Indicate High Rates of N Fixation?

    NASA Astrophysics Data System (ADS)

    Tuite, M. L.; Macko, S. A.

    2011-12-01

    As a consequence of the high energetic requirements of dinitrogen (N2) fixation, organic N produced by diazotrophic microorganisms typically exhibits δ15N values similar to atmospheric N2 (approximately 0%). Because the δ15N of organic-rich Paleozoic epeiric basin sediments often has values in the vicinity of 0%, it is frequently asserted that N2 fixation was the primary source of new reactive N for productivity. There are two broad reasons why recourse to widespread and intensive N fixation as the primary source of the organic N is problematic. First, there are substantial physiological and ecological constraints on marine N fixation that limit its extent in modern oceans primarily to open ocean basins. Second, preservation of an unaltered isotopic signature of diazotrophy in underlying sediments is not a likely outcome of oxic and anoxic diagenetic alteration and repeated cycles of mineralization and assimilation. Constraining the sources of reactive N for primary productivity is critical to understanding the N cycle in Paleozoic epeiric seas. In this study we report δ15N values from high organic matter Middle Ordovician through Late Devonian dysoxic and euxinic basinal sediments. We propose a nitrogen isotope mass balance model that incorporates the microbial ecology of a stratified water column and the biochemical stoichiometry of primary production and organic matter diagenesis. Results from the model support our contention that high rates of N fixation over extended time periods were not the cause of depleted nitrogen isotope values in organic-rich Paleozoic basinal sediments. Rather, the depleted values were a consequence of a diminished role for nitrification and subsequent N loss via denitrification and anammox, and the preferential preservation of a substantially 15N-depleted chlorophyll-influenced lipid fraction. The model may be applicable to earlier and later geological periods where high organic matter sediments feature depleted δ15N values.

  5. Geochemistry and geochronology of Paleozoic intrusions in the Nalati (Narati) area in western Tianshan, Xinjiang, China: Implications for Paleozoic tectonic evolution

    NASA Astrophysics Data System (ADS)

    Xu, Xue-Yi; Wang, Hong-Liang; Li, Ping; Chen, Jun-Lu; Ma, Zhong-Ping; Zhu, Tao; Wang, Ning; Dong, Yun-Peng

    2013-08-01

    The Nalati (Narati) area in the Chinese western Tianshan is characterized by abundant Paleozoic intrusions, including granites, diorites and gabbros. They are not only indicators of the interaction between crust and mantle, but also useful clues for tracing the tectonic history of the Tianshan Orogen. Most Early Paleozoic granitoids (biotite monzonitic granites and muscovite granites) of this study are from the Yili Block. The biotite monzonitic granites (mixed-source-derived I-type granites) have a zircon U-Pb age of 497.0 ± 5.9 Ma, indicating the time of the subduction of the Terskey Oceanic crust in the Late Cambrian. The 427.2 ± 5.7 Ma Zircon U-Pb age of the S-type muscovite granites let us interpret that these granites may have been formed during the crust thickening process after the collision between the Yili Block and the Nalati Block. In western Tianshan the Late Paleozoic biotite granites, muscovite granites, quartz diorites, biotite monzonitic granites, granodiorites and alkali granites have respectively a LA-ICPMS zircon U-Pb age of 371.8 ± 6 Ma, 357.2 ± 7.5 Ma, 313.9 ± 2.5 Ma and 296.9 ± 2.4 Ma. The biotite granites display I-type geochemical features and are considered to have been derived from a lower continental crust source. The muscovite granites have a pronounced S-type affinity and are considered to have been formed by the partial melting of thickened continental crust after the collision between the Central Tianshan Belt and the South Tianshan Belt. The quartz-diorites are adakite-like and have an I-type affinity, which are considered to have been formed by partial melting of a delaminated lower crust in a post-orogenic extension setting. The granodiorites also show some typical geochemical features of adakite. Their formation is considered to be related to the lower crustal delamination and the ascending of asthenosphere after the collision event. The alkali granites show an A-type granite affinity. They may have been formed in a within

  6. Ophiolitic mélanges in crustal-scale fault zones: Implications for the Late Palaeozoic tectonic evolution in West Junggar, China

    NASA Astrophysics Data System (ADS)

    Chen, Shi; Pe-Piper, Georgia; Piper, David J. W.; Guo, Zhaojie

    2014-12-01

    The Baijiantan and Darbut ophiolites in West Junggar are exposed in steep fault zones (>70°) containing serpentinite mélange, in contact on either side with regionally distributed Upper Devonian-Lower Carboniferous ocean floor peperitic basalts and overlying sedimentary successions. The ophiolitic mélanges show classic structural features created by strike-slip faulting and consistent shear sense indicators of left-slip kinematics. Sandstone blocks within the mélanges resemble the surrounding sediments in lithology and age, indicating that the ophiolitic mélanges consist of locally derived rocks. The ophiolitic mélanges therefore originated from left-slip fault zones within a remnant basin and are not plate boundaries nor subduction suture zones. Sandstone is the youngest lithology involved in the mélange and provides a maximum age for the mélange of 322 Ma, whereas stitching plutons are younger than 302 Ma. Multiple clusters in zircon ages from single gabbro blocks in the mélange at ~375, ~360, ~354, and ~340 Ma are inconsistent with accretionary incorporation of subducting ocean crust but rather suggest that episodic movement of the faults provided pathways for magma from the mantle into magma chambers. Late Paleozoic tectonic evolution of West Junggar involved Late Devonian to Carboniferous relative motion between the Junggar block and West Junggar ocean basin, which triggered the left-slip fault zones within a remnant ocean basin, along which the oceanic crust was disrupted to form linear ophiolitic mélanges. Final filling of this remnant ocean basin and its dismemberment by strike-slip faulting occurred in the late Carboniferous, followed by crustal thickening by juvenile granites at the Carboniferous-Permian boundary.

  7. Neoproterozoic-Early Paleozoic tectonic evolution of the western part of the Kyrgyz Ridge (Northern Tian Shan) caledonides

    NASA Astrophysics Data System (ADS)

    Degtyarev, K. E.; Ryazantsev, A. V.; Tretyakov, A. A.; Tolmacheva, T. Yu.; Yakubchuk, A. S.; Kotov, A. B.; Salnikova, E. B.; Kovach, V. P.

    2013-11-01

    The conducted comprehensive study of the western part of Kyrgyz Ridge provided new data on the structure, composition and age of Precambrian and Early Paleozoic stratified and igneous complexes. The main achievements of these studies are: (1) the establishment of a wide age spectrum, embracing the interval from the Neoproterozoic to the end of the Early Ordovician, for the clastic-carbonate units composing the cover of the Northern Tian Shan sialic massif; (2) the reconstruction and dating of Early and Late Cambrian ophiolite complexes formed in suprasubduction settings;(3) the discovery and dating of the Early-Middle Ordovician volcano-sedimentary complex of island-arc affinity; and (4) proof of the wide occurrence of Late Ordovician granitoids, some of which bear Cu-Au-Mo ores. The intricate thrust-and-fold structure of the western part of the Kyrgyz Ridge, formed in several stages from the Middle Cambrian (?) until the end of the Middle Ordovician, was scrutinized; the importance of the Early Ordovician stage was demonstrated. The intrusion of large batholiths in the early Late Ordovician accomplished the caledonide structural evolution. Formation of Neoproterozoic and Early Paleozoic caledonide complexes, which were possibly related to the protracted and entangled evolution of the active continental margin, ceased by the Late Ordovician.

  8. 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

  9. 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

  10. Early Paleozoic magmatic events in the eastern Klamath Mountains, northern California

    SciTech Connect

    Wallin, E.T.; Mattinson, J.M.; Potter, A.W.

    1988-02-01

    New U-Pb zircon ages for nine samples of tonalite and pegmatitic trondhjemite from the Trinity ophiolite and associated melange reveal a complex history of magmatic activity extending back into the earliest Cambrian, much older than previously believed. Earlier investigations, based on limited data, recognized lower Paleozoic crustal elements in the eastern Klamath terrane (EKT) ranging in age from Middle Ordovician to Early to Middle Devonian. The new work in the Yreka-Callahan area of the EKT confirms the Ordovician (440-475 Ma) and younger ages, but reveals for the first time the presence of tonalitic rocks that crystallized during a narrow time interval at about 565-570 Ma. The authors also recognize younger, Late Silurian magmatism at 412 Ma. In the context of available mapping, these ages indicate that the Trinity ophiolite is broadly polygenetic because parts of it yield crystallization ages that span approximately 150 m.y. Superjacent dismembered units of probable early Paleozoic age may be tectonostratigraphically equivalent to the Sierra City melange in the northern Sierra Nevada.