Abstract: Climate Model for the Pennsylvanian System of the Contiguous United States

C. Blaine Cecil

Of the allogenic processes of climate, tectonism, and eustasy, climate (changes in the amount and seasonality of rainfall) appears to have been the primary control on sediment flux and the resulting lithostratigraphy of the Pennsylvanian System in the contiguous United States. Long-term climate change occurred at time scales of millions of years. In the Late Mississippian, warm and dry conditions prevailed across the continent, whereas, the east became humid while dry conditions continued in the west during the Pennsylvanian. In addition to the long-term climate change, short-term climatic cycles, at time scales of tens of thousands to hundreds of thousands of years, appear to have controlled both eolian and fluvial sediment flux. Eustatic cycles, at time scales approximating those of the short-term climate cycles, contributed to marine versus nonmarine depositional environments in epicontinental basins.

According to the climate model, Pennsylvanian underclays and coal beds resulted from wet intervals of climate cycles during low stands of sea level. Marine black-shale source rocks also appear to indicate pluvial periods. During these periods, high terrestrial organic productivity provided terrestrial organic matter but restricted siliciclastic influx to marine environments, and black-shale "condensed sections" resulted. Deposition of Pennsylvanian marine carbonates and evaporites occurred during the drier part of the climatic cycles. Maximum fluvial siliciclastic influx occurred when seasonality of rainfall was most pronounced.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994