Abstract

Seven depositional sequences, each of which consists of two intermediate-order cyclothems, compose outcrops of the Chase Group (Permian, Wolfcampian) in the mid-continent. Principal reservoir analog facies are restricted mainly to the highstand systems tracts of cyclothems. These facies include subtidal lime sands, deposited mainly in downdip distal ramp settings, and peritidal dolomudstones deposited farther updip on the ramp. The stratigraphic and depositional architecture of the section was controlled by the interplay among paleobathymetry, glacio-eustasy, and periodic syndepositional tectonism. Porous lime sands dominate in the lower part of the Chase Group. The forced regressive, unconformity-bounded sequences within which they occur were deposited during relatively high-magnitude eustatic fluctuations that resulted in marine accommodation increases great enough to preclude peritidal deposition. Porous peritidal facies instead dominate in the upper part of the Chase Group. The sequences within which these normal-regressive deposits are present were deposited during lower magnitude eustatic fluctuations and decreased marine accommodation, which allowed for their eventual progradation across the ramp. Complex porosity heterogeneity is evident within individual depositional sequences and component cyclothems, as well as vertically within the Chase Group.

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