MAZZULLO, S. J., and CHELLIE S. TEAL, Wichita State University, Wichita, KS
Interbedded carbonates and siliciclastics in the Chase Group (Permian, Wolfcampian) are exposed continuously from southern Nebraska. across Kansas, and into northern Oklahoma. The section comprises seven relatively high-frequency, low-accommodation depositional sequences, deposited on a gently-sloping ramp, at a time of known southern hemisphere glaciation-deglaciation as well as mild tectonism in the study area. Each depositional sequence consists of two intermediateorder transgressive-regressive cycles, the "cyclothems" of typical midcontinent terminology that are separated by relative lowstand deposits of marginal-marine shales. Depositional sequences are separated by weakly developed paleosols in siliciclastic redbeds, which represent periods of lowstand subaerial exposure.
The main reservoir-analog facies are mostly present in the HSTs of each sequence, and include shallow-marine carbonate sands in distal ramp settings, and dolomitized peritidal deposits in proximal ramp settings. The sands dominate in the lower part of the Chase Group, whereas peritidal dolomites are more common in the upper part. Pore types variously include interparticle and moldic pores, vugs, intercrystalline porosity (in dolomites), and microporosity. The occurrence and complex geometry of porous units is analogous to that in the Hugoton gas field.
AAPG Search and Discovery Article #90915©2000 AAPG Rocky Mountain Section, Albuquerque, New Mexico