SEQUENCE STRATIGRAPHY AND CORRELATION OF MIDDLE CHEROKEE GROUP (MIDDLE PENNSYLVANIAN, EARLY DESMOINESIAN) CYCLOTHEMS FROM OKLAHOMA TO IOWA

Late Desmoinesian (Marmaton Group) cyclothems have been studied throughout the Midcontinent, yet little modern work has been done on the detailed tracing of stratigraphic sequences (cyclothems) in the underlying Cherokee Group across the Midcontinent shelf. Earlier work by T. R. Marshall has determined the cyclothem succession and conodont faunas of the most complete Cherokee succession at the Arkoma basin margin in northeastern Oklahoma, and he has initiated biostratigraphic correlation of the lower Cherokee Group across the Midcontinent. My study focuses on the middle Cherokee, which extends from the base of the Weir-Pittsburg Coal up to the base of the Croweburg Coal, beneath the widespread and well-known Verdigris Limestone, and includes several named cyclothems.

Preliminary findings have revealed that the lithostratigraphic Tiawah Limestone is more genetically complicated than originally thought. In its type area in northeastern Oklahoma, the lower part of the Tiawah Limestone represents the regressive limestone of a cyclothem (Tiawah), which includes a dark conodont-rich shale above the Tebo coal at the base. The upper part of the Tiawah Limestone, above a rubbly, conodont-poor limestone that appears to represent an exposure surface, is the transgressive limestone of an overlying cyclothem. Directly above this is another conodont-rich black shale that contains abundant Gondolella, a genus found elsewhere only in certain offshore shales, where it is typically widespread, thus is used as an indicator for certain specific offshore shales. In west-central Missouri, what is called the Tiawah Limestone plus associated dark marine shale above the Tebo coal have yielded abundant conodonts, but no Gondolella. The next younger cyclothem, above 8.5 feet of terrestrial clastics capped by an underclay, has Gondolella-bearing shale above a coal that is in the position of the Scammon Coal of Kansas and Missouri. Thus the Tiawah Limestone here is equivalent to only the lower type Tiawah of Oklahoma, while the paleosol and clastics underlying the Scammon Coal appear to be equivalent to the rubbly exposed zone in the middle of the type Tiawah, and the Scammon Coal and overlying marine unit are equivalent to the cyclothem that includes the upper type Tiawah Limestone of Oklahoma.