Erect Forests Are Evidence for Coseismic Base-level Changes in Pennsylvanian Cyclothems of the Black Warrior Basin, U.S.A.
Robert A. Gastaldo, Ivana Stevanoviç-Walls, William N. Ware, 2004. "Erect Forests Are Evidence for Coseismic Base-level Changes in Pennsylvanian Cyclothems of the Black Warrior Basin, U.S.A.", Sequence Stratigraphy, Paleoclimate, and Tectonics of Coal-Bearing Strata, Jack C. Pashin, Robert A. Gastaldo
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Examination of the plant taphonomic character and sedimentological processes responsible for preservation of an in situ, erect forest above the Pennsylvanian Blue Creek coal of the Mary Lee coal cycle, Alabama, provides evidence for rapid generation of accommodation space by coseismic subsidence. Standing vegetation is preserved at least to 4.5 m (15 ft) in height above the coal and includes lycopsids, regenerative calamites, tree ferns, and seed ferns (pteri-dospermous gymnosperms); the forest-floor litter is preserved as an adpression assemblage directly above the coal. Sediments entombing the standing trees, burying both the peat mire and forest-floor litter, and casting the erect vegetation consist of rhythmically bedded tidalites. Neap-spring-neap tidalite patterns indicate that entombment occurred on the order of a few decades, whereas burial of the mire and forest-floor litter happened on the order of weeks, if not days. Comparison with documented Holocene rates of eustatic and tectonic base-level changes indicates that eustatic processes alone cannot account for the generation of the accommodation required to provide a basis for the sedimentologic and taphonomic characteristics of the assemblage. Instead, coseismic subsidence of very high magnitude is determined to be the mechanism responsible for preservation. Hence, erect forests buried by estuarine tidal deposits provide evidence for rapid coseismic basinal subsidence. These criteria can be used to identify similar coseismic subsidence events beginning in the middle Paleozoic and provide constraints on the magnitude of event-driven base-level change in various basinal regimes.
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The origin of coal-bearing strata has been debated vigorously for more than a century, and with the emergence of coalbed methane as a major energy resource and the possibility of sequestering greenhouse gas in coal, this debate has never been more relevant. This volume contains 10 chapters on coal-bearing strata of Carboniferous through Tertiary age and is based on a special session that was held at an AAPG Annual Meeting in New Orleans. The contributors to this volume have employed a multitude of approaches ranging from basin analysis to plant taphonomy to support a variety of views on the sequence stratigraphy, paleoclimate, and tectonics of coal-bearing strata.