CONODONT BIOSTRATIGRAPHY IN RELATION TO CYCLOTHEM CORRELATION OF THE LOWER CHEROKEE GROUP (MIDDLE PENNSYLVANIAN), OKLAHOMA TO IOWA

Cyclothems in the Middle Pennsylvanian Cherokee Group have a history of difficult correlations and nomenclatural problems. Recent work recognized 17 separate named cycles of marine transgression and regression (cyclothems) in the lower Cherokee Group from the Arkoma Basin margin in east-central Oklahoma to the Kansas-Oklahoma border area. Several of the more major cyclothems are characterized by distinctive conodont morphotypes. More recent work has identified similar successions of morphotypes in Kansas, Missouri, and Iowa. Four of the more major cyclothems in the lower Cherokee seem to be regionally extensive across the Midcontinent, in ascending order: McCurtain, Doneley, Inola, and post-Wainwright. In Oklahoma, the McCurtain cyclothem contains Idiognathodus cf. praeobliquus, which is found above “Riverton” coals in cores in southeastern Kansas and the Forest City Basin. The Doneley cyclothem contains I. cf. obliquus, which is found in a core from the Forest City Basin, and above the Cliffland coal in Iowa. The Inola cyclothem contains I. cf. podolskensis, which is found in the type Hackberry Branch (formerly “Seville”) Limestone and above the “Weir C” coal (of the Weir Formation) in Missouri, in a core from the Forest City Basin, and above a middle Laddsdale coal in Iowa. From these observations, the McCurtain cyclothem may include a post-Riverton marine unit, the Doneley cyclothem may include the post-Cliffland marine zone of Iowa, and the Inola cyclothem may include the Hackberry Branch Limestone, a marine zone in the Weir Formation, and a middle Laddsdale coal cycle. In Oklahoma, all Idiognathodus forms from the post-Wainwright cyclothem have fewer, coarser ridges on their Pa elements than do older Cherokee conodonts. Similar conodonts above an upper Laddsdale coal in Iowa suggest correlation with the post-Wainwright cyclothem, extending this significant faunal change northward. At the base of the section, the Atokan genus Idiognathoides occurs low in a core from the Forest City Basin. Biostratigraphic correlation of extensive marine cyclothems resolves some confusion in Cherokee stratigraphy, and, combined with wire-line log and seismic data, should help establish the sequence stratigraphy and a unifying nomenclature for the Midcontinent Cherokee Group.