REVISION OF STRATIGRAPHIC NOMENCLATURE AND RECLASSIFICATION OF THE MORROWAN, ATOKAN, DESMOINESIAN, MISSOURIAN, AND VIRGILIAN STAGES IN IOWA

Correction of several long-standing miscorrelations of the Missourian succession in Iowa, Kansas, Missouri, and Nebraska; several relatively recently named units (e. g. Pammel Park Limestone, East Peru Limestone, Clanton Creek Limestone, Farlington Limestone, Mulberry Coal) in Iowa; the lack of documented and relatively well-exposed and easily accessible type and reference sections in the state; the reorganization and recorrelation of the Iowa Cherokee Group using a conodont biostratigraphic framework; and recent stratigraphic revisions in neighboring states of Missouri, Illinois, Kansas, and Oklahoma, has necessitated a revision of Pennsylvanian stratigraphic nomenclature in Iowa. The most recent comprehensive revision of stratigraphic nomenclature of the Pennsylvanian in Iowa was done by Ravn and others in 1984.

Since Scott and Muscatine counties in southeastern Iowa are structurally part of the Illinois Basin, we will follow the most recent revisions of the Tri-State Committee on Correlation of the Pennsylvanian System in the Illinois Basin, for stratigraphic nomenclature in this part of the Iowa Pennsylvanian. This now includes strata of the Caseyville Formation of the Raccoon Creek Group, which replaces the older McCormick Group and lower Kewanee Group. The upper part of the abandoned Kewanee Group is unnamed at this time. The upper Raccoon Creek Group now includes the abandoned Abbott Formation and the lower part of the abandoned Spoon Formation.

Most of the rest of the Pennsylvanian of Iowa (approximately the southwestern one third of the state) occurs in the Midcontinent Basin, thus ‘Midcontinent' stratigraphic nomenclature will be used for areas outside of Scott and Muscatine counties of Iowa. Pennsylvanian units within the Midcontinent Basin include in ascending order the Morrowan, Atokan, Desmoinesian, Missourian, and Virgilian stages.