SUBSURFACE MAPPING OF THE MISSISSIPPIAN BLACK HAND SANDSTONE IN EAST-CENTRAL OHIO

New isopach and structure maps of the Black Hand Member of the Mississippian Cuyahoga Formation revise the extent and thickness of the Black Hand in the subsurface of east-central Ohio. In outcrop, the Black Hand is a massive to cross-bedded, medium- to coarse-grained conglomeratic sandstone, bounded by finer-grained marine sandstones and shales of the underlying lower Cuyahoga Formation and the overlying Logan Formation. The unit is a prominent cliff-former in a 135-km outcrop belt running north–south through central Ohio. It dips eastward into the subsurface where it serves as a local aquifer and the deepest underground source of drinking water in several counties. Previous subsurface maps of the Black Hand correlate this unit to the drillers’ “Big Injun,” a term frequently applied to several Mississippian and Pennsylvanian sandstone units, including sandstones in the Logan Formation and the Pennsylvanian Pottsville Group. This project utilized over 1000 geophysical well logs, well cuttings, and outcrops to map the Black Hand in the subsurface and distinguish it from the “Big Injun.” These maps will provide tools for managing ground-water resources and determining casing depths in areas where oil-and-gas drilling is common, and they will aid researchers interested in the hydrogeology, stratigraphy, and sedimentology of the Mississippian in Ohio.