--> Architecture of Pennsylvanian Carbonate Shelf, Midcontinent, USA--Cycle Hierarchy and Reservoir Development, by W. L. Watney, J. C. Youle, J. A. French, J. H. Doveton, and W. J. Guy; #90986 (1994).

Datapages, Inc.Print this page

Abstract: Architecture of Pennsylvanian Carbonate Shelf, Midcontinent, USA--Cycle Hierarchy and Reservoir Development

W.L. Watney, J.C. Youle, J.A. French, J.H. Doveton, W.J. Guy

Three orders of cyclicity are recognized in Middle and Upper Pennsylvanian carbonate-dominated strata in the Midcontinent, USA. Long-term, 3rd-order cycles consist of 4 to 5 successive intermediate-scale, 4th-order (0.2 to 0.5 Ma) cycles, each varying from a few to 30 m thick. The 3rd-order cycles are distinguished by either regional backstepping and lateral accretion of successive intermediate-scale sequences of shifts in the stacking pattern and accompanying changes in the character of the 4th-order cycles. Backstepping during the late Desmoinesian and early Missourian is delimited by prominent condensed sections. Third-order cycles end with reduced sediment accommodation space accompanied by shelf incisement and sediment bypassing. This longer-term cyclicity is also traceable acros the shelf through continuous profiles of Th/U ratios reflecting changing redox patterns, particularly expressed in deeper-water carbonate facies and paleosols.

The 4th-order cycles are unconformity-bounded, regionally correlatable, and temporally distinct depositional sequences. Each is commonly comprised of flooding units, condensed sections, and late-highstand deposits. Thickness, lithofacies, and early diagenesis of these intermediate-scale sequences are closely related to elevation, slope, and configuration of the shelf. Late-highstand carbonates include meter-scale, 5th-order grainstone-bearing cycles (small-scale sequences and parasequences) that exhibit offlap and onlap relationships associated with local inferred topography. These high-frequency cycles produce distinctive vertical and lateral reservoir compartmentalization. Stratal geometries of these grainstones are very similar along depositional strike at similar inferred elevatio s on the shelf resulting in a proposed "strandline grainstone model."

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994