NEW CORRELATIONS IN RACCOON CREEK GROUP (ATOKAN AND LOWER DESMOINESIAN) OF INDIANA AND SOUTHERN ILLINOIS

New understandings of Middle Pennsylvanian stratigraphy in Indiana and adjacent Illinois have arisen from three decades of collective investigations of active coal mines, cores and other borehole records, literature review, and conodont study. Among our findings (in descending stratigraphic order), the black, phosphatic Carrier Mills Shale occurs the length of the outcrop belt in Indiana, where it had been termed Logan Quarry Shale at the north end. The Stonefort Limestone and underlying black shale and coal also are regionally continuous, at least toward the south. The Holland Limestone appears to be lenticular, either deposited in flooded estuaries, or incised by later valley formation. The name Silverwood Limestone is discarded because of inadequate stratigraphic context in its type area.

The Minshall, Buffaloville and Lewisport coals are closely if not exactly correlative and underlie the Perth/Curlew Limestone, close to the Atokan-Desmoinesian boundary. The Upper and Lower Block Coals are highly lenticular in their type area northeast of Terre Haute, and their southward correlation remains in question. The Lead Creek Limestone is regionally widespread, but comprises perhaps as many as three cycles of marine incursion. The underlying Mariah Hill (IN) and Dunbar (KY) coals are approximate equivalents. All of these units are lenticular.

The ultimate goal of this research is to unify bed, member, and formation terminology throughout the Illinois basin.