Mississippian Oolites on West Virginia Dome

Bryan Koehler, Richard Smosna

The West Virginia dome, a positive feature during the Early Mississippian, was submerged during a Meramec-Chester transgression and became the site for ooid sedimentation. The dome's axis trended east-west through Randolph County, West Virginia, where four outcrops of the lower Pickaway Limestone (Greenbrier Group) were studied. Pickaway oolites formed as mobile sand belts that paralleled the dome's axis. In detail, these belts consisted of sand waves up to 2 m in height that migrated north and south under the influence of tidal currents. Along the crest, both flood and ebb currents moved the sediment, whereas farther away flood tides dominated. Sand bodies shoaled upward with time, the sediment becoming coarser grained and better sorted to the top; large wedge-shaped cro s-bed sets gave way to planar bedding; and frequently the ooid shoals were subaerially exposed. Ooids and other grains have been extensively micritized, indicating a slow sedimentation rate, and small-scale ripples record the effect of minor wave action. North of the dome, muddy skeletal sands accumulated in a somewhat restricted gulf. To the south along a very gentle sea floor, the ooid shoals passed into fully marine skeletal sands. On the east, a nearby landmass supplied locally large volumes of detrital quartz. The lower Pickaway was deposited during a single rise and fall of sea level that produced two oolites at each outcrop separated by offshore sediments. This stratigraphic sequence constitutes a fifth-order cycle 7-26 m thick.

AAPG Search and Discovery Article #91023©1989 AAPG Eastern Section, Sept. 10-13, 1989, Bloomington, Indiana.