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Neil J Tabor - One of the best experts on this subject based on the ideXlab platform.
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mixed layer illite smectite in Pennsylvanian aged paleosols assessing sources of illitization in the illinois basin
Minerals, 2021Co-Authors: Julia A Mcintosh, Neil J Tabor, Nicholas A RosenauAbstract:Mixed-layer illite-smectite (I-S) from a new set of Pennsylvanian-aged Illinois Basin underclays, identified as paleosols, are investigated to assess the impact of (1) regional diagenesis across the basin and (2) the extent to which ancient environments promoted illitization during episodes of soil formation. Interpretations from Reichweite Ordering and Δ° 2θ metrics applied to X-ray diffraction patterns suggest that most I-S in Illinois Basin paleosols are likely the product of burial diagenetic processes and not ancient soil formation processes. Acid leaching from abundant coal units and hydrothermal brines are likely diagenetic mechanisms that may have impacted I-S in Pennsylvanian paleosols. These findings also suggest that shallowly buried basins (<3 km) such as the Illinois Basin may still promote clay mineral alteration through illitization pathways if maximum burial occurred in the deep past and remained within the diagenetic window for extended periods of time. More importantly, since many pedogenic clay minerals may have been geochemically reset during illitization, sources of diagenetic alteration in the Illinois Basin should be better understood if Pennsylvanian paleosol minerals are to be utilized for paleoclimate reconstructions.
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palaeoclimate across the late Pennsylvanian early permian tropical palaeolatitudes a review of climate indicators their distribution and relation to palaeophysiographic climate factors
Palaeogeography Palaeoclimatology Palaeoecology, 2008Co-Authors: Neil J Tabor, Christopher J PoulsenAbstract:Abstract Global-scale compilations of palaeoclimate indicators include records of the temporal and spatial occurrence of coal, laterite, bauxite, Vertisols, calcrete, eolianite, and evaporite at the scale of geological stage. These palaeoclimate indicators provide the primary evidence for palaeoclimate change during the Late Palaeozoic, and have been used to infer a long-term climatic transition from humid to arid conditions on equatorial Pangaea from Late Pennsylvanian through Early Permian time. The cause(s) of Late Pennsylvanian–Early Permian climate trends are unknown but must have resulted from climate factors operating on timescales of tectonic change (10 6 –10 7 yr), such as tectonic drift, assembly of Pangaea, orogenesis, and long-term carbon cycling. Although higher-resolution, local- to regional-scale palaeoclimate reconstructions for the Late Pennsylvanian–Early Permian exist, they generally lack the time control necessary for accurate correlation among sites. Nevertheless, these high-resolution palaeoclimate reconstructions provide details about Permo-Pennsylvanian palaeoclimate that are not perceptible in lower-resolution global datasets. These studies indicate that (1) although the Late Pennsylvanian equatorial latitudes were more humid than the Early Permian tropics, there was also considerable variability in the amount and seasonality of rainfall, and (2) there were several short (≪ 1 – 3 Ma) excursions toward relatively more humid climate during the long-term Early Permian transition to aridity in western and central equatorial Pangaea. These higher-resolution climate changes were controlled by climate factors which operated on relatively short timescales (10 4 –10 6 yr) such as continental ice-sheet dynamics, sea-level change and associated changes in land–sea distribution, and variations in palaeoatmospheric P CO 2 . Although lithological indicators and geochemical proxies provide the basis for reconstructing past climate, they seldom provide diagnostic evidence to determine which of the possible climate factors were important. To narrow the possible causes of Late Pennsylvanian–Early Permian climate change, we review and evaluate both conceptual and numerical models that have been previously used to explain Late Palaeozoic climate change in light of the detailed spatial and temporal proxy records from across near-equatorial Pangaea. Our ability to test these models is currently limited by our inability to make accurate correlations among proxy sites due to uncertain dating. Nonetheless, we suggest that on tectonic timescales continental drift, increasing atmospheric P CO 2 , and deglaciation could explain much of the low-latitude climate record, while changing atmospheric P CO 2 and orbitally-driven glacial–interglacial cycles could account for higher-resolution climate variability on Pangaea.
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paleosol archives of environmental and climatic history in paleotropical western pangea during the latest Pennsylvanian through early permian
Geological Society of America Special Papers, 2008Co-Authors: Neil J Tabor, Isabel P Montanez, Christopher R Scotese, Christopher J Poulsen, Greg H MackAbstract:The stratigraphic and regional distributions of paleosol morphology in latest Pennsylvanian through Early Permian strata in Colorado, Utah, Arizona, New Mexico , Texas, and Oklahoma are presented in this paper. This regional extent corresponds to a paleolatitudinal gradient spanning ~5°S to 10°N. Morphological trends from this region delineate signifi cant and systematic temporal and spatial changes in Permian-Carboniferous paleoenvironment and paleoclimate. The inferred latest Pennsylvanian (Virgilian) through early Early Permian environmental pattern is complex, but it indicates persistently dry, semiarid to arid conditions in Colorado, Utah, and Arizona, at paleolatitudes north of ~2°N, whereas lower paleolatitude (~2°S to 2°N) tropical regions in New Mexico exhibit a stepwise shift from subhumid to semiarid and variably seasonal conditions throughout late Pennsylvanian and the fi rst half of Early Permian (Virgilian through Wolfcampian) time, followed by a subsequent shift to more arid conditions during the latter part of the Early Permian (Leonardian). Notably, strata from the southernmost paleosites, in Texas and Oklahoma, exhibit
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morphology and distribution of fossil soils in the permo Pennsylvanian wichita and bowie groups north central texas usa implications for western equatorial pangean palaeoclimate during icehouse greenhouse transition
Sedimentology, 2004Co-Authors: Neil J Tabor, Isabel P MontanezAbstract:Analysis of stacked Permo-Pennsylvanian palaeosols from north-central Texas documents the influence of palaeolandscape position on pedogenesis in aggradational depositional settings. Palaeosols of the Eastern shelf of the Midland basin exhibit stratigraphic trends in the distribution of soil horizons, structure, rooting density, clay mineralogy and colour that record long-term changes in soil-forming conditions driven by both local processes and regional climate. Palaeosols similar to modern histosols, ultisols, vertisols, inceptisols and entisols, all bearing morphological, mineralogical and chemical characteristics consistent with a tropical, humid climate, represent the Late Pennsylvanian suite of palaeosol orders. Palaeosols similar to modern alfisols, vertisols, inceptisols, aridisols and entisols preserve characteristics indicative of a drier and seasonal tropical climate throughout the Lower Permian strata. The changes in palaeosol morphology are interpreted as being a result of an overall climatic trend from relatively humid and tropical, moist conditions characterized by high rainfall in the Late Pennsylvanian to progressively drier, semi-arid to arid tropical climate characterized by seasonal rainfall in Early Permian time. Based on known Late Palaeozoic palaeogeography and current hypotheses for atmospheric circulation over western equatorial Pangea, the Pennsylvanian palaeosols in this study may be recording a climate that is the result of an orographic control over regionalscale atmospheric circulation. The trend towards a drier climate interpreted from the Permian palaeosols may be recording the breakdown of this preexisting orographic effect and the onset of a monsoonal atmospheric circulation system over this region.
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paleoenvironmental reconstruction from chemical and isotopic compositions of permo Pennsylvanian pedogenic minerals
Geochimica et Cosmochimica Acta, 2002Co-Authors: Neil J Tabor, Isabel P Montanez, Randal J SouthardAbstract:Mineralogical and chemical analysis of Late Pennsylvanian and Early Permian paleosols from the eastern shelf of the Midland basin, north-central Texas, USA, are used to test hypothesized climate change in Late Paleozoic western equatorial Pangea, previously defined independently on the bases of sedimentologic and paleontologic proxies and climate models. The <0.2-μm size phyllosilicate fraction in the studied paleosols exhibits down-profile trends in mineralogy and chemical composition that are consistent with modern weathering profiles suggesting a dominantly pedogenic origin. A stratigraphic trend from kaolinite-dominated profiles in Upper Pennsylvanian paleosols to profiles dominated by smectite and hydroxy-interlayered 2:1 phyllosilicates in Lower Permian paleosols indicates a relatively rapid decrease in soil weathering and leaching in the latest Pennsylvanian followed by a more gradual decrease in leaching throughout the Early Permian. The chemical composition (cation ratios and exchange capacity) of these phyllosilicates further corroborates this shift toward less intensive leaching, presumably in response to climate change from humid to progressively more arid conditions. The phyllosilicates in the <0.2-μm size fraction and contemporaneous pedogenic calcites from the Permo-Pennsylvanian paleosols exhibit a long-term stratigraphic increase in their δ18O values of as much as ∼3.2‰ and ∼5.2‰, respectively. This long-term trend is consistent with a transition throughout the latest Pennsylvanian through Early Permian toward progressively more evaporatively enriched soil waters. Superimposed on the long-term trend is an apparent rapid enrichment (1.5 to 2‰) in phyllosilicate δ18O values immediately above the Pennsylvanian–Permian boundary. Observed oxygen isotope fractionation between the phyllosilicates and calcites within individual paleosols indicate isotopic disequilibrium between mineral pairs. This is attributed to a minor detrital component in the pedogenic clay-dominated phyllosilicate fraction coupled with the effects of seasonality of mineral formation. Inferred δ18O compositions of Late Paleozoic meteoric water (−2‰ to +4‰) are compatible with less intensive soil leaching under conditions of increasing aridity, possibly coupled with a shift in local precipitation from a continental source to a marine source.
Bhushan M Jayarao - One of the best experts on this subject based on the ideXlab platform.
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prevalence and spatial distribution of salmonella infections in the pennsylvania raccoon procyon lotor
Zoonoses and Public Health, 2016Co-Authors: K J Very, M K Kirchner, Nikki Shariat, W Cottrell, Carol H Sandt, Edward G Dudley, Subhashinie Kariyawasam, Bhushan M JayaraoAbstract:A study was conducted to determine the prevalence and spatial distribution of Salmonella infection in Pennsylvania raccoons (Procyon lotor), common wildlife mammals known to occupy overlapping habitats with humans and domestic food animals. The Pennsylvania Game Commission provided a total of 371 raccoon intestinal samples from trapped and road-killed raccoons collected between May and November 2011. Salmonella was isolated from the faeces of 56 (15.1%) of 371 raccoons in 35 (54%) of 65 counties across Pennsylvania. The five most frequently isolated serotypes were Newport (28.6%), Enteritidis (19.6%), Typhimurium (10.7%), Braenderup (8.9%) and Bareilly (7.1%). Pulsed-field gel electrophoresis (PFGE) analysis of the Salmonella isolates and subsequent comparison to the Pennsylvania Department of Health human Salmonella PFGE database revealed 16 different pulsetypes in Salmonella isolates recovered from raccoons that were indistinguishable from pulsetypes of Salmonella collected from clinically ill humans during the study period. The pulsetypes of seven raccoon Salmonella isolates matched those of 56 human Salmonella isolates by month and geographical region of sample collection. Results from Clustered Regularly Interspaced Short Palindromic Repeats and Multi-Virulence Locus Sequence Typing (CRISPR-MVLST) analysis corroborated the PFGE and serotyping data. The findings of this study show that several PFGE pulsetypes of Salmonella were shared between humans and raccoons in Pennsylvania, indicating that raccoons and humans might share the same source of Salmonella.
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salmonella infections in the common raccoon procyon lotor in western pennsylvania
Journal of Clinical Microbiology, 2008Co-Authors: Justin A Compton, Jason A Baney, Sarah C Donaldson, Beth A Houser, Gary San J Julian, Richard H Yahner, Wayne Chmielecki, Stanley M Reynolds, Bhushan M JayaraoAbstract:Ten Salmonella enterica serotypes were isolated from fecal samples collected from anesthetized raccoons (n = 738) trapped in six Pennsylvania counties from 2003 to 2005. Comparison of raccoon pulsed-field gel electrophoresis (PFGE) pulse type data with the Pennsylvania Department of Health PFGE database revealed that the patterns of seven Salmonella serotypes matched those isolated from humans with salmonellosis.
Howard J Falconlang - One of the best experts on this subject based on the ideXlab platform.
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uplands lowlands and climate taphonomic megabiases and the apparent rise of a xeromorphic drought tolerant flora during the Pennsylvanian permian transition
Palaeogeography Palaeoclimatology Palaeoecology, 2020Co-Authors: William A. Dimichele, Howard J Falconlang, Arden R Bashforth, Spencer G. LucasAbstract:Abstract The Late Mississippian and Pennsylvanian have been referred to as the Coal Age due to enormous paleotropical peat accumulations (coal beds). Numerous fossil floras have been collected from these coals, and their associated seat-earth paleosols and roof-shales, over more than two centuries, leading to the inference of vast swampy wetlands covering the Pangean tropics during the Pennsylvanian. In contrast, the Permian tropics are characterized as more arid, with sparser and more heterogeneous vegetation than inferred for the Pennsylvanian. In the tropics, the Pennsylvanian to Permian transition has been described as a changeover from a pteridophyte-dominated “Paleophytic flora”, to a seed-plant dominated “Mesophytic flora. This view notwithstanding, floras dominated by xeromorphic seed plants also are well known from the Pennsylvanian tropics. Some authors have characterized these plants as being occupants of uplands, subsequently transported into basinal-lowland, preservational environments. In this model, uplands are well drained, causing areas of drought under otherwise everwet climates. In this paper, we present an alternative interpretation: that the apparent transition in Pennsylvanian-Permian tropical vegetation reflects two types of taphonomic megabias. First is a preservational megabias, strongly favoring the vegetation of humid climates over that of seasonally dry climates. Accordingly, tropical-plant preservational potential fluctuated in concert with Late Paleozoic Ice Age glacial-interglacial oscillations, and contemporaneous sea-level and climatic changes. Second is an analytical megabias, strongly favoring the discovery and collection of the wetland biome from Pennsylvanian strata, overlooking the less frequently and more poorly preserved drought-tolerant biome. By Permian times, vast wetlands, and their fossil record, had largely disappeared from central Pangea (although continuing in Cathaysia), making drought-tolerant vegetation more “visible” to searchers, without changing its preservational circumstances. We demonstrate that the upland model is untenable, being inconsistent with the principles of plant biogeography and with geological aspects of the fossil record.
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cyclic changes in Pennsylvanian paleoclimate and effects on floristic dynamics in tropical pangaea
International Journal of Coal Geology, 2010Co-Authors: William A. Dimichele, Isabel P Montanez, Blaine C Cecil, Howard J FalconlangAbstract:Abstract Wetland floras narrowly define perceptions of Pennsylvanian tropical ecosystems, the so-called Coal Age. Such wetlands reflect humid to perhumid climate, leading to characterizations of Pennsylvanian tropics as everwet, swampy. These views are biased by the high preservation potential of wetlands. Sedimentation patterns, paleosols, and fossil floras indicate the presence of vegetation tolerant of subhumid to dry–subhumid, perhaps semi-arid climate in basins between peat formation times. Understanding the significance of this seasonally-dry vegetation has suffered from conceptual and terminological confusion. A clearer view has emerged as models for framing the data have improved. Basinal floras typical of seasonally-dry conditions, relatively low soil moisture regimes, are well documented but mainly from isolated deposits. Some of the earliest, dominated by primitive pteridosperms (“Flozfern” floras), occur in clastic rocks between European Early Pennsylvanian coal beds. Later Early Pennsylvanian, fern–cordaitalean vegetation, different from coal floras, is preserved in marine goniatite bullions. Conifers are first suggested by late Mississippian Potoniesporites pollen. About the same time, in North America, broadleaf foliage, Lesleya and Megalopteris occur in basin-margin settings, on drought-prone limestone substrates. The best known, xeromorphic floras found between coal beds appear in the Middle through Late Pennsylvanian, containing conifers, cordaitaleans, and pteridosperms. The Middle Pennsylvanian appearances of this flora are mainly allochthonous, though parautochthonous occurrences have been reported. Parautochthonous assemblages are mostly Late Pennsylvanian. The conifer flora became dominant in western and central Pangaean equatorial lowlands in earliest Permian. Location of the humid–perhumid wetland flora during periods of relative dryness, though rarely discussed, is as, or more, perplexing than the spatial location of seasonally-dry floras through time — wetland plants had few migratory options and possibly survived in small refugia, within and outside of basins. Coupled oscillations in climate, sea level, and vegetation were driven most likely by glacial–interglacial fluctuations, perhaps controlled by orbital cyclicity.
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incised channel fills containing conifers indicate that seasonally dry vegetation dominated Pennsylvanian tropical lowlands
Geology, 2009Co-Authors: Howard J Falconlang, Scott D. Elrick, Philip R. Ames, John W Nelson, Cindy V Looy, William A. DimicheleAbstract:The idea that the Pennsylvanian tropical lowlands were temporally dominated by rainforest (i.e., the Coal Forest) is deeply ingrained in the literature. Here we challenge two centuries of research by suggesting that this concept is based on a taphonomic artifact, and that seasonally dry vegetation dominated instead. This controversial finding arises from the discovery of a new middle Pennsylvanian (Moscovian) fossil plant assemblage in southeast Illinois, United States. The assemblage, which contains xerophytic walchian conifers, occurs in channels incised into a calcic Vertisol below the Baker Coal. These plants grew on seasonally dry tropical lowlands inferred to have developed during a glacial phase. This xerophytic flora differs markedly from that of the typical clubmoss-dominated Coal Forest developed during deglaciation events. Although preserved only very rarely, we argue that such xerophytic floras were temporally as dominant, and perhaps more dominant, than the iconic Coal Forests, which are overrepresented in the fossil record due to taphonomic megabias. These findings require the iconography of Pennsylvanian tropical lowlands to be redrawn.
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Pennsylvanian uplands were forested by giant cordaitalean trees
Geology, 2004Co-Authors: Howard J Falconlang, Arden R BashforthAbstract:The precise timing of when upland terrains first became forested is highly controversial. Pennsylvanian palynoflora and megaflora transported into marine highstand deposits imply that emergent topographic highs may have supported cordaitalean forests. The discovery of a new Pennsylvanian (Bolsovian) plant assemblage in southwest Newfoundland confirms this hypothesis and allows the architecture of these upland trees to be reconstructed in detail. The assemblage includes several hundred calcareously permineralized stumps, trunks, and branches, and represents the remains of shallowly rooted cordaitalean trees that were ≤48.5 m high when mature. The fossils occur in alluvial conglomerates that constitute a 10-km-diameter outlier on the margins of the paleoequatorial Variscan foreland. The paleogeographic setting together with plant taphonomic inferences strongly indicate that these giant trees were transported from nearby upland alluvial plains and deposited in an elevated intermontane basin. This interpretation is supported by analysis of rootstock morphology, which implies tree growth in thin soils consistent with an alluvial gravel substrate. This improved understanding of Pennsylvanian upland forests has important implications for geochemical modeling of the global carbon cycle.
George E Gehrels - One of the best experts on this subject based on the ideXlab platform.
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linking late paleozoic sedimentary provenance in the appalachian basin to the history of alleghanian deformation
American Journal of Science, 2006Co-Authors: William A. Thomas, Thomas P Becker, George E GehrelsAbstract:The Pennsylvanian and Permian strata in the Appalachian basin are generally interpreted to be the erosional record of the Alleghanian orogeny. Advances in our understanding of the kinematic and tectonic history of the Alleghanian orogen from study of the orogenic interior have not been integrated into interpretations of the late Paleozoic stratigraphic record. This comparative study of detrital-zircon U-Pb ages from the youngest preserved synorogenic deposits in the Alleghanian foreland (Permian Dunkard Group) to previously published ages from Early and Middle Pennsylvanian-age deposits reveals a subtle, but perhaps significant, shift in the detrital-zircon-age population. The Permian detrital-zircon ages lack 1700 to 1900 Ma and Archean-age grains characteristically present in the Pennsylvanian-age deposits, which are interpreted to indicate recycling of the lower Paleozoic passive margin. Instead, the Permian detrital-zircon-age populations are representative of the ages of rocks within the Appalachian orogenic interior. This change in the detrital-zircon-age population correlates temporally to a shift from transpressionally-inspired oblique deformation during the Pennsylvanian to foreland-vergent contraction during the Early Permian. The study demonstrates the utility of detrital-zircon dating in sedimentary basins associated with complex and protracted tectonism beyond what can be ascertained by petrographic techniques alone.
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detrital zircon evidence of laurentian crustal dominance in the lower Pennsylvanian deposits of the alleghanian clastic wedge in eastern north america
Sedimentary Geology, 2005Co-Authors: Thomas P Becker, William A. Thomas, Scott D Samson, George E GehrelsAbstract:Abstract The late Paleozoic Alleghanian orogeny culminated with the continent–continent collision between Laurentia and Gondwana in the construction of the supercontinent Pangea. Within the Appalachian basin, the sedimentological record of the early stages of the continental collision is preserved as late Mississippian-age siltstones and mudstones that mark the end of carbonate production. An upward transition to coarse, quartz-rich, cratonward-prograding, fluvial deposits of Pennsylvanian age is cited to mark the initiation of continental collision and cratonward advancement of the tectonic load. Seven samples of early Pennsylvanian (early-middle Morrowan) sandstones and conglomerates from the Appalachian basin were collected along the orogen from eastern Pennsylvania to central Alabama for U–Pb dating of detrital zircons. All of the samples reveal a dominance of zircons with ages that can be attributed to crust-forming events in Laurentia. A small percentage of the detrital zircons have ages (530–680 Ma and 2000–2200 Ma) that correspond to the Pan-African/Brasiliano orogenic belts and Trans-Amazonian/Eburnian cratons typical of Gondwanan crust. Although recycling of pre-orogenic strata may disproportionately bias the detrital-zircon population toward ages of Laurentian affinity, the dominance of the Laurentian “signature” in the Appalachian basin along strike suggests that the early components of the Alleghanian orogen were composed mainly of recycled Laurentian crust. Detrital-zircon populations are not indicative of substantial incorporation of Gondwanan crust in the orogenic highlands. On the basis of the timing of dextral displacement along shear zones in the Appalachian hinterland, the early Pennsylvanian clastic deposits preserved in the Appalachian basin likely correspond to transpressional exhumation of the Laurentian margin, consistent with hypotheses of oblique collision between Gondwana and Laurentia in the late Paleozoic.
Thomas P Becker - One of the best experts on this subject based on the ideXlab platform.
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linking late paleozoic sedimentary provenance in the appalachian basin to the history of alleghanian deformation
American Journal of Science, 2006Co-Authors: William A. Thomas, Thomas P Becker, George E GehrelsAbstract:The Pennsylvanian and Permian strata in the Appalachian basin are generally interpreted to be the erosional record of the Alleghanian orogeny. Advances in our understanding of the kinematic and tectonic history of the Alleghanian orogen from study of the orogenic interior have not been integrated into interpretations of the late Paleozoic stratigraphic record. This comparative study of detrital-zircon U-Pb ages from the youngest preserved synorogenic deposits in the Alleghanian foreland (Permian Dunkard Group) to previously published ages from Early and Middle Pennsylvanian-age deposits reveals a subtle, but perhaps significant, shift in the detrital-zircon-age population. The Permian detrital-zircon ages lack 1700 to 1900 Ma and Archean-age grains characteristically present in the Pennsylvanian-age deposits, which are interpreted to indicate recycling of the lower Paleozoic passive margin. Instead, the Permian detrital-zircon-age populations are representative of the ages of rocks within the Appalachian orogenic interior. This change in the detrital-zircon-age population correlates temporally to a shift from transpressionally-inspired oblique deformation during the Pennsylvanian to foreland-vergent contraction during the Early Permian. The study demonstrates the utility of detrital-zircon dating in sedimentary basins associated with complex and protracted tectonism beyond what can be ascertained by petrographic techniques alone.
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detrital zircon evidence of laurentian crustal dominance in the lower Pennsylvanian deposits of the alleghanian clastic wedge in eastern north america
Sedimentary Geology, 2005Co-Authors: Thomas P Becker, William A. Thomas, Scott D Samson, George E GehrelsAbstract:Abstract The late Paleozoic Alleghanian orogeny culminated with the continent–continent collision between Laurentia and Gondwana in the construction of the supercontinent Pangea. Within the Appalachian basin, the sedimentological record of the early stages of the continental collision is preserved as late Mississippian-age siltstones and mudstones that mark the end of carbonate production. An upward transition to coarse, quartz-rich, cratonward-prograding, fluvial deposits of Pennsylvanian age is cited to mark the initiation of continental collision and cratonward advancement of the tectonic load. Seven samples of early Pennsylvanian (early-middle Morrowan) sandstones and conglomerates from the Appalachian basin were collected along the orogen from eastern Pennsylvania to central Alabama for U–Pb dating of detrital zircons. All of the samples reveal a dominance of zircons with ages that can be attributed to crust-forming events in Laurentia. A small percentage of the detrital zircons have ages (530–680 Ma and 2000–2200 Ma) that correspond to the Pan-African/Brasiliano orogenic belts and Trans-Amazonian/Eburnian cratons typical of Gondwanan crust. Although recycling of pre-orogenic strata may disproportionately bias the detrital-zircon population toward ages of Laurentian affinity, the dominance of the Laurentian “signature” in the Appalachian basin along strike suggests that the early components of the Alleghanian orogen were composed mainly of recycled Laurentian crust. Detrital-zircon populations are not indicative of substantial incorporation of Gondwanan crust in the orogenic highlands. On the basis of the timing of dextral displacement along shear zones in the Appalachian hinterland, the early Pennsylvanian clastic deposits preserved in the Appalachian basin likely correspond to transpressional exhumation of the Laurentian margin, consistent with hypotheses of oblique collision between Gondwana and Laurentia in the late Paleozoic.
