--> Abstract: Sequence Stratigraphy, Systems Tracts, and Mapping Strategies for the Subsurface Middle and Upper Pennsylvanian of the Eastern Shelf, by A. Cleaves; #90994 (1993).

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CLEAVES, ARTHUR, Oklahoma State University, Stillwater, OK

ABSTRACT: Sequence Stratigraphy, Systems Tracts, and Mapping Strategies for the Subsurface Middle and Upper Pennsylvanian of the Eastern Shelf

Effective subsurface mapping of siliciclastic and carbonate depositional systems in middle and upper Pennsylvanian rocks of north-central Texas requires the delineation of vertical generic intervals that are compatible with the mechanism causing cyclic sedimentation in the region. Earlier studies of the Strawn, Canyon, and Cisco groups on the Eastern shelf have used the format method for defining genetic intervals. This method involved correlating regionally persistent, presumably marine transgressive, carbonate markers and generating isolith maps based on the total thickness of a lithology between the tops of the carbonates. It was assumed that all lithologic changes within an individual cycle resulted from facies changes, and that all of the cycles together represented a conformable stacking of units derived from deltaic-lobe switching or local Ouachita tectonism.

Sequence stratigraphic analysis of the Strawn-Cisco interval indicates that these cyclothemic deposits contain numerous disconformities and represent type 1 sequences. Phosphatic black shale units constitute the interval of maximum glacio-eustatic inundation on the shelf for each cycle and should be used as the genetic unit boundaries. Distinct disconformity surfaces are very difficult to identify except beneath the incised valley-fill facies in these cycles, and the genetic interval, often less than 150-ft thick, usually cannot be resolved by means of typical seismic lines. Care should be exercised so that the highstand systems tract and lowstand systems tract of each cycle are identified and mapped as separate exploration fairways.

AAPG Search and Discovery Article #90994©1993 AAPG Southwest Section Meeting, Fort Worth, Texas, February 21-23, 1993.