STRATIGRAPHIC ANALYSIS OF THE TWO MILE LIMESTONE OF THE LATE PENNSYLVANIAN CONEMAUGH FORMATION IN THE PROPOSED PENNSYLVANIAN STRATOTYPE AREA, SOUTHERN WEST VIRGINIA

The Twomile Limestone of I.C. White (1885) is an important stratigraphic marker along the southeastern margin of the Dunkard Basin where marine units and persistent coal beds are absent. The Twomile limetone is a mapable unit up to 2 m thick whose stratigraphic relationships have been uncertain. Early workers tentatively correlated the Twomile with the Ames Limestone (White, 1885; Krebs and Teets, 1914) whereas more recently it has been suggested to be equivalent to the Brush Creek Limestone (Henry and others, 1979). Recent stratigraphic analysis of the upper Allegheny and Lower Conemaugh strata in southern West Virginia (Martino, in review) has led to the development of a high resolution stratigraphic framework that supplements conventional key beds such as coals beds and marine units with laterally persistent, well-developed paleosols. Paleosols were identified using field criteria for recognition including consisted primarily of variegated hackly mudstones that exhibited horizonization, soil structure, and (in some cases) root traces. In this study, seventeen outcrops were measured and their component facies described. These exposures occur mainly along Rt. 119, I-79 and I-77 and cover a 25 mile transect from McCorkle northward through the Charleston area. The Twomile limestone was found to occur from 29-36 m above the Upper Freeport Coal in the southern portion of the study area, and that the Upper Freeport is truncated northward by fluvial incision associated with the Mahoning Sandstone. Throughout its extent, the Twomile limestone is underlain by well-developed single or compound paleosols 1.4-3.15 m thick. The presence of vertic features and red hues suggest well-drained conditions that may have been associated with a sealevel lowstand. Similar Glenshaw paleosols have been interpreted as interfluvial sequence boundaries toward the west of the stratotype area (Martino, in review). Rising sea level may have raised the water table and initiated lacustrine deposition. Correlation from the stratotype area westward into Kentucky where nine-paleosol bounded allocycles are distinguishable suggests that the sea level highstand with which the Twomile was associated was most likely the Brush Creek, or possibly the Cambridge marine event.