2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 3
Presentation Time: 8:40 AM

The Permian(?) of the Central Appalachian Basin

CECIL, C. Blaine, Smithsonian Institution and US Geol Survey (Emeritus), Reston, VA 20192, DIMICHELE, William, Smithsonian Institution, Washington, DC 20560 and SKEMA, Viktoras, Pennsylvania Geological Survey - retired, Harrisburg, PA 17111, bcecil@usgs.gov

More than 500 m of latest Pennsylvanian or early Permian Dunkard strata occur in central Appalachian basin in the tri-state area of southwest Pennsylvanian, northern West Virginia, and eastern Ohio. The Dunkard, the youngest Paleozoic strata in the Appalachian basin, is comprised of sandstone, shale, mudstone, and minor amounts of limestone and coal. Relatively fine-grained, texturally and mineralogically immature sandstones, tend to have flat, non-erosional, bases. Strata interpreted as paleosols consist of both calcic and noncalcic Vertisols, and coal beds. Megascopically, shales contain substantial amounts of unweathered biotite and muscovite mica. Thin brecciated limestones lack any indication of marine origin. Dunkard strata are virtually devoid of any indication of marine influence.

Characteristics of Dunkard Group strata are indicative of the following: 1) tectonic control on basin configuration, 2) restricted chemical weathering and a long-term dry subhumid paleoclimate, 3) depositional systems decoupled from sea level, 4) lake levels and water chemistry controlled by cyclic variations in rainfall, 5) decreasing occurrence of coal and increasing numbers of calcic paleosols up-section indicative of progressive long-term drying, 6) base level and sedimentary cycles driven solely by climate.

Stratigraphic patterns within the Dunkard Group appear to be consistent with the better understood Pennsylvanian climate cycles. Tectonic uplift and/or low sea levels induced by Permian ice volume decoupled water levels within the basin from eustatic sea level fluctuations. Thus, dry periods associated with high stands and reduced ice volume, as in the Pennsylvanian, resulted in dry subhumid climates and calci paleo-Vertisols in the Dunkard when the basin dried and lakes disappeared. In contrast, pluvial periods associated with increases in ice volume resulted in lacustrine conditions. Rain shadow effects, induced by the rising ancestral Appalachian Mountains in the Early Permian(?), resulted in progressive climate drying in the Appalachian basin.