Paleo-Oceanography and Depositional Framework of the Cowley Facies in South-Central Kansas: Solution to the ÒCowley ProblemÓ

Brian W. Wilhite¹, S. J. Mazzullo², I. Wayne Woolsey¹, Dean Pattisson¹, Dennis Hedke¹, Marc Summervill¹, and Kimberly DimmickÐWells¹. (1) Woolsey Operating Co., LLC, Wichita, KS 67202, (2) Department of Geology, Wichita State University, Wichita, KS 67260 [email protected]

The origin and setting of the Cowley ÒfaciesÓ is a long-standing problem in Kansas geology. The Cowley is present in a localized subsurface area in Barber and adjoining counties, where it comprises a thick section of bioturbated, lenticular to flaser-bedded spiculite and dark-gray/black-to-green shale with accessory replacive chert and only minor carbonate rocks. It is an unconformity-bounded unit sandwiched by Osagian rocks below and Meramecian strata above. Based on sub-regional log correlations and analysis of a continuous core through the entire preserved Mississippian section, it appears that these rocks were deposited as progradational, relative low-stand wedges within a restricted embayment. This embayment was a paleotopographic feature that formed as a result of erosion of underlying Osagian rocks, and it encompassed a large area in Barber and adjoining counties. Cowley facies are not present outside of this embayment in the immediate study area.

Oceanographic circulation and geochemistry within the embayment were such that despite the temperate to warm water, near-equatorial setting of the study area, carbonate deposition was suppressed, and what traditionally has been considered to be deep-water spiculites and shales instead were deposited in a range of environments from shallow to relatively deep water (~80Ð100 m). This model is directly analogous to the depositional and paleo-oceanographic setting of the Eocene Pallinup Formation of southwestern Australia, where spiculite and associated deposits likewise are present. Accordingly, deposition and areal occurrence of the Cowley reflects the complex interplay of sea-level history, antecedent topography, and ocean circulation patterns.