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Pennsylvanian climatic events and their congruent biotic responses in the central Appalachian Basin

By
David K. Brezinski
David K. Brezinski
Maryland Geological Survey, 2300 St. Paul Street, Baltimore, Maryland 21218, USA, and Section of Invertebrate Paleontology, Carnegie Museum of Natural History, 4400 Forbes Avenue, Pittsburgh, Pennsylvania 15213, USA
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Albert D. Kollar
Albert D. Kollar
Section of Invertebrate Paleontology, Carnegie Museum of Natural History, 4400 Forbes Avenue, Pittsburgh, Pennsylvania 15213, USA
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Published:
January 01, 2011

Abstract

Pennsylvanian strata of western Pennsylvania exhibit evidence of a hierarchy of paleoclimatic changes. Long-term (107 years) climate trends reflect plate movement and tectonic events. These long-term trends are overprinted by changes of much shorter duration (100–400 k.y., and 10–20 k.y.). During deposition of the Pottsville and Allegheny formations (Bashkirian-Moscovian), the Appalachian climate exhibited perhumid to humid situations during periods of glacial advance, and humid to dry subhumid conditions during glacial retreats. Marine faunas and coal swamp floras during this interval of time exhibited a remarkably consistent taxonomic and ecological structure. Tetrapod amphibian faunas were highly aquatic. When the Cone-maugh Group was deposited, the ancient Appalachian climate became progressively drier. Glacial stages were dry subhumid and during deglaciation semiarid to arid. This reduction in precipitation produced changes in coal-forming floras, as lycopsid-dominated assemblages gave way to tree fern–dominated associations. Coincident with this climatic drying, tetrapod faunas became highly terrestrial in the basin. During the deposition of the Monongahela Group, the Appalachian climate returned to humid conditions during glacial periods. However, there is evidence of drier subhu-mid conditions during the intervening interglacial episodes as indicated by the pervasive presence of mudcracked nonmarine limestones. Nested lacustrine cycles within the Monongahela Group indicate short-term alternations between wet and dry periods that may have been driven by Earth’s precession. Coal-forming mires continued to be dominated by tree ferns, and vertebrate faunas tended to be found within fluvial lake environments. The latest Pennsylvanian and/or early Permian strata exhibit a return to Conemaugh-like deposition as evidenced by the pervasiveness of redbeds, dry climate floras, and highly terrestrial vertebrate faunas.

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GSA Field Guide

From the Shield to the Sea

Richard M. Ruffolo
Richard M. Ruffolo
GAI Consultants, Inc. Pittsburgh Office 385 East Waterfront Drive Homestead, Pennsylvania 15120-5005 USA
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Charles N. Ciampaglio
Charles N. Ciampaglio
Wright State Universityâ?"Lake Campus 7600 Lake Campus Drive Celina, Ohio 45822 USA
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Geological Society of America
Volume
20
ISBN electronic:
9780813756202
Publication date:
January 01, 2011

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