Abstract: Sequence-Stratigraphic Analysis of Correlative Outcropping and Subsurface Chase Group Strata

Cyclic facies in the Wolfcampian Chase Group in Hugoton-Guymon fields, which account for 90% of Mid-continent gas reserves, were deposited in a tectonically quiescent setting. In contrast, outcropping Chase Group strata in Kansas and Nebraska were deposited along the still-active Nemaha Uplift. Studies of these outcrops indicate the development of 7 regionally correlative depositional sequences. Although these strata were deposited during known Southern Hemisphere glaciation, the mechanism driving cyclicity (i.e., glacioeustatic vs. tectono-eustatic) inherently is equivocal because of syndepositional tectonism. This study proposes to compare cyclicity in outcropping and subsurface chase Group strata in these contrasting tectonic settings, from study of two cores in Hugoton-Guymon fields (in-hand), so as to separate the eustatic and tectonic signatures in this section. This study also addresses the genesis and regional sequence-stratigraphic architecture of this prolific reservoir unit.

Outcrop-to-subsurface correlations of component formations will be done by comparing subsurface logs to outcrop gamma-ray logs. Then, depositional facies and cyclicity in the cores will be described and compared to those recognized in outcrops. Facies, cycles, recognition of subtle unconformities, and overall diagenetic history, including porosity evolution and timing of dolomitization, will be evaluated by thin-section petrography, SEM, and stable isotope (O-C) geochemistry. Cycles that are found to be correlative across the state therefore likely are of glacio-eustatic origin; those remaining cycles present only in the outcrop area likely are of tectonic origin.  

AAPG Search and Discovery Article #90940©1997 AAPG Foundation Grants-in-Aid