--> Abstract: Setting, Stratigraphic Architecture, and Diagenesis of Spiculite Platform-to-Basin Systems: Mississippian, South-Central Kansas, by Brian W. Wilhite, Sal Mazzullo, and Wayne I. Woolsey; #90078 (2008)

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Setting, Stratigraphic Architecture, and Diagenesis of Spiculite Platform-to-Basin Systems: Mississippian, South-Central Kansas

Brian W. Wilhite1, Sal Mazzullo2, and Wayne I. Woolsey1
1Woolsey Operating Company, LLC, Wichita, KS
2Department of Geology, Wichita State University, Wichita, KS

The subsurface Cowley Formation (Osagian to Meramecian) in south-central Kansas comprises a thick section of cherty, bank-top spiculite with rare calcareous fossils, that grades seaward to progressively deeper-water (~80-100 m), lenticular to flaser-bedded shaly spiculite in slope settings, and dark shales in basinal settings. Regional log correlations and seismic indicate that the Cowley is an unconformity-bounded depositional sequence, and it is not represented by equivalent rocks in outcrops in SE Kansas and adjoining states. The sequence comprises a very thin, spiculitic TST and mfs overlain by thick, generally progradational spiculite wedges. Higher parts of the bank-top were periodically exposed, and high-frequency sea-level changes imparted a complex pattern to spiculite deposition. Stratigraphic and lithofacies architecture resemble those of immediately underlying and overlying carbonate depositional systems to which lithology of the unit dramatically contrasts. Spiculite deposition was within an erosional embayment wherein slope and bank-top spiculites are overlooked hydrocarbon reservoirs. Porosity types include intra-spicule pores, vugs, and some interparticle pores. Based on petrography and O-Si isotopes, the latter two pore types resulted from post-depositional, subaerial exposure.

Oceanographic circulation and geochemistry within the embayment were such that despite the temperate to warm water, near-equatorial setting, carbonate deposition was suppressed, and what traditionally has been considered to be deep-water spiculites and shales instead were deposited. This model is analogous to the depositional and paleo-oceanographic setting of the spiculitic, Eocene Pallinup Formation of SW Australia. Deposition and areal occurrence of the Cowley therefore reflect the complex interplay of sea-level history, antecedent topography and ocean circulation patterns.

 

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas