Review of Boundaries of U.S. Midcontinent Stages in the Pennsylvanian of Indiana

This paper discusses the placement of Pennsylvanian Stage boundaries in Indiana: Morrowan-Atokan; Atokan-Desmoinesian; Desmoinesian-Missourian, and Missourian-Virgilian. Although these boundaries mark important biostratigraphic events, their identification is hampered by the discontinuous nature of correlative horizons and by insufficient and often controversial biostratigraphic data. The placement of the Morrowan-Atokan boundary has been the most inconsistent because of difficulties in the correlation of rock units in the lower part of the Raccoon Creek Group. The base of the St. Meinrad Coal Member, corresponding to the boundary between SR (Schulzospora rara-Laevigatosporites desmoinesensis) and NG (Microreticulatisporites nobilis-Endosporites globiformis) miospore zones appears to be the most suitable placement. The Perth Limestone Member of the Tradewater Formation, or in the absence of this limestone, the top of the Minshall/Buffaloville Coal Members of the Tradewater Formation marks the Atokan-Desmoinesian boundary, corresponding to the boundary between the RD (Radiizonates difformis) and MI (Cadiospora magna-Mooreisporites inusitatus) miospore zones. The West Franklin Limestone Member occurs at the boundary between the Desmoinesian and Missourian. The Missourian-Virgilian boundary occurs in the upper part of the Mattoon Formation, above the Cohn Coal Member, but its precise placement in Indiana is difficult because of insufficient biostratigraphic data in the uppermost part of the Pennsylvanian section.