SEQUENCE STRATIGRAPHY AND CYCLOTHEM CORRELATION OF LOWER CHEROKEE GROUP (MIDDLE PENNSYLVANIAN), OKLAHOMA TO IOWA

Despite being one of the most important hydrocarbon- and coal- producing groups in the Midcontinent, little recent work has been done on the sequence stratigraphy and biostratigraphic correlation of the Cherokee Group. Earlier work recognized 28 separate cycles of marine transgression and regression in the Cherokee Group in the Arkoma Basin margin in east-central Oklahoma to the Kansas-Oklahoma border area. Each cycle is a stratigraphic sequence with a base overlying a paleosol (usually beneath a coal) and a top at the exposure surface capping the next higher paleosol. Major cyclothems are characterized by diverse marine biota and abundant conodonts; minor cycles are usually just composed of a coal and regressive clastics. Most major T-R cycles in Oklahoma exhibit relatively distinctive conodont faunas, facilitating correlation northward. My study involves lower Cherokee strata from the base of the Weir-Pittsburg or Tebo coal down to the top of the Mississippian. Preliminary work on lower Cherokee outcrops and long cores allows correlation of the older McCurtain cycle (near the position of the “Riverton” coal) into southern Kansas, and correlation of the younger Inola cyclothem with the type Hackberry Branch (formerly “Seville”) Limestone of Missouri and with a marine interval (“Weir C”) in the Weir Formation in a core to the north. Although the interval from the “Riverton” coal to the top of the Mississippian is far thicker in the Forest City Basin than farther south, the interval from the “Riverton” up to the Tebo coal is thinner in the Forest City Basin than in the shelf area south of the Bourbon Arch. Two hypotheses could explain this situation. The “Riverton” coal in the Forest City Basin core has been misidentified and is actually lower in the section, or the Forest City Basin filled from the north, so that there were more pre-“Riverton” clastics there than to the south. Identification of McCurtain cycle conodonts in the Forest City succession would help constrain the stratigraphic position of the “Riverton” coal and shed more light on its depositional setting.