CONODONT-BASED CORRELATION OF MAJOR CYCLOTHEMS IN LOWER CHEROKEE GROUP (LOWER DESMOINESIAN, MIDDLE PENNSYLVANIAN), OKLAHOMA TO IOWA

The Midcontinent Cherokee Group has historically had problems with lithostratigraphic correlation, and the lower part of the Cherokee Group has been particularly confusing. Recent work recognized 18 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. Of these 18 cyclothems, at least four can be recognized by distinctive conodont morphotypes, and three of these represent major marine transgressions extending across the Midcontinent. All three contain large numbers of Idiognathodus amplificus. The lowest of these (McCurtain) is characterized also by the morphotype I. cf. praeobliquus. The middle cyclothem (Doneley) is the first major cyclothem to yield I. obliquus, and the uppermost cyclothem (Inola) is also characterized by large numbers of I. cf. podolskensis. Utilizing outcrops and long cores in Oklahoma, Kansas, Missouri, and Iowa, the regional extent of these three cyclothems were mapped. The McCurtain cyclothem extends from Oklahoma to the Forest City Basin in northeastern Kansas. The Doneley cyclothem extends from Oklahoma into Iowa, based upon the first appearance of I. obliquus. The Inola cyclothem is the most extensive of the three major lower Cherokee cyclothems, having been identified in nearly all cores in all states. At the base of the succession, the Atokan genus Idiognathoides has been identified in two cores in northeastern Kansas and one core in south-central Iowa, confirming the presence of Atokan strata in the Forest City Basin. Based on these correlations, stratal equivalencies can be established, such as the Bluejacket Coal of Oklahoma with a Bluejacket “A” coal of Kansas, a Weir “B” or “C” coal in Missouri, and a middle Laddsdale coal at its type section in Iowa, at the base of the Inola cyclothem. Another example is the correlation of the Rowe Coal of Oklahoma, Kansas, and Missouri with the Cliffland Coal of Iowa, at the base of the Doneley cyclothem. Biostratigraphic correlation of these extensive marine cyclothems can resolve some of the confusion in lower Cherokee stratigraphy, and should provide the foundation for establishing the sequence stratigraphy and unifying nomenclature for the Midcontinent Cherokee Group.