--> Abstract: Contrasting Styles and Common Controls on Middle Mississippian and Upper Pennsylvanian Carbonate Platforms in the Upper Midcontinent, U.S.A., by W. Lynn Watney, Evan K. Franseen, Alan P. Byrnes, and Susan E. Nissen; #90039 (2005)

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Contrasting Styles and Common Controls on Middle Mississippian and Upper Pennsylvanian Carbonate Platforms in the Upper Midcontinent, U.S.A.

W. Lynn Watney1, Evan K. Franseen2, Alan P. Byrnes3, and Susan E. Nissen3
1 Kansas Geological Survey, Lawrence, KS
2 University of Kansas, Lawrence, KS
3 Kansas Geological Survey, University of Kansas, Lawrence, KS

Middle Mississippian Osagean shelf and shelf margin lithofacies bordering the northern Anadarko Basin are dominated by heterozoan carbonates including sponge-spicule rich facies and early formation of chert. Chert increases southward from nodules in shallow, restricted inner shelf areas to extensive, thick chert beds deposited on an open marine shelf margin. Decameter-scale sequences are commonly delineated by glauconite beds and subaerial exposure. Early to post-Mississippian subaerial exposure diagenesis resulted in sponge spicule dissolution, vuggy porosity in moldic-rich rocks, and autobrecciation.

In contrast, Upper Pennsylvanian carbonates contain abundant photozoan carbonates and are dominated by decameter-scale, unconformity-bounded sequences deposited on a shallow inclined ramp and shelf margin. Widespread oolite and grainstone shoals were commonly deposited during punctuated, high frequency forced regressions where early subaerial exposure resulted in pervasive moldic lithofacies and paleosol development.

Both carbonate settings were affected by block fault movement at a scale of 1-10's of km, linked to basement lineaments. Block faulting influenced locations of shelf edges and caused segmentation of the ramp/shelf profile, which created differences in lithofacies, thicknesses, and stratal architecture across segments. Recurrent structural movement created blocks where strata were preferentially preserved, locus areas for thick accumulations of sponge spiculite and oolite reservoir deposits, and topographic highs that were subjected to subaerial exposure. Later meteoric water influx and possible basinal fluid migration are also closely associated with lineaments. Integrated geological, petrophysical, and geophysical studies are providing a clearer picture of the complex creation of hydrocarbon plays and the variable reservoir properties of each system.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005