--> Abstract: Middle Pennsylvanian Transcontinental Epeiric Systems of the USA, by C. Blaine Cecil, Frank T. Dulong, and Ronald R. West; #90039 (2005)

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Middle Pennsylvanian Transcontinental Epeiric Systems of the USA

C. Blaine Cecil1, Frank T. Dulong1, and Ronald R. West2
1 US Geological Survey, Reston, VA
2 Kansas State University, Manhattan, KS

The stratigraphy of Middle Pennsylvanian cycles in low latitudes of Pangea (USA) can be generalized as follows: 1) low-stand continental-scale mineral paleosols unconformably overlain by coal beds in the east and central USA and fine-grained eolianites in much of the west 2) transgressive tidalites at basin margins and organic-rich shale in basin centers, 3) coarsening upward siliciclastic sediments in the east that grade westward into open marine limestones (central and western USA).

Temporal and spatial stratigraphic analyses indicate the following: 1) pedogenesis during relatively wet glacial low stands when permanent high pressure over ice caps and nearly stationary polar fronts confined the Intertropical Convergence Zone to the thermal equator; peat formed during maximum low pressure (maximum ice), 2) when sea level rose, lingering low pressure coupled with the absence of wind driven circulation resulted in dysoxia and black shale deposition in shallow epeiric seas, 3) as ice sheets disappeared, cross-equatorial monsoonal circulation developed in response to seasonal heating of land and air masses over both hemispheres of Pangea. During the final stage of sea level rise, a dry subhumid climate (monsoonal circulation) replaced the humid equatorial climate and increased surface winds initiated wind-drive circulation in epeiric seas. The dry subhumid climate of the thermal equator increased siliciclastic influx (prograding deltas in the eastern USA) whereas open marine carbonates were deposited in arid to semiarid latitudes (western USA). Spatial and temporal changes in paleoclimate, therefore, appear to best explain the lithostratigraphy of Pennsylvanian cycles; glacioeustacy and tectonics controlled accommodation space.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005