--> Abstract: Sequence Stratigraphy of Coastal Plain to Shelf-Slope Facies Tracts: Middle to Upper Pennsylvanian Cleveland and Marmaton Siliciclastics, Western Anadarko Basin, Texas Panhandle, by T. F. Hentz; #90987 (1993).

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HENTZ, TUCKER F., Bureau of Economic Geology, The University of Texas at Austin, Austin, TX

ABSTRACT: Sequence Stratigraphy of Coastal Plain to Shelf-Slope Facies Tracts: Middle to Upper Pennsylvanian Cleveland and Marmaton Siliciclastics, Western Anadarko Basin, Texas Panhandle

The Missourian Cleveland Formation has yielded >435 Bcf of natural gas from low-permeability (<0.1 md) sandstone reservoirs in the western Anadarko Basin. Regional study of the Cleveland and underlying Desmoinesian Marmaton Group siliciclastics established the sequence framework to clarify the vertical and areal occurrence of Cleveland reservoirs, seals, and source rocks. The westerly sourced fluvial and deltaic/nearshore systems of the study interval accumulated in coastal plain, marine-shelf, and proximal shelf-slope settings that were profoundly influenced by syndepositional tectonism.

The study interval consists of three sequences. Sequence 1 is characterized by landward- and seaward-stepping facies stacking patterns on well logs and in cores that define (in ascending order) Marmaton lowstand-wedge and transgressive systems tracts (TST) and a lower Cleveland highstand systems tract (HST). A regionally correlative, organic-rich condensed section at the top of the Marmaton TST, equivalent to the Nuyaka Creek Black Shale Bed of Midcontinent cyclothems and a probable source rock for Cleveland gas, represents a eustatic maximum at the end of the Desmoinesian. A relative sea-level drop with the onset of Sequence 2 deposition initiated development of a sand-rich incised-valley system (IVS) that extended across the Cleveland depositional shelf and basinward of an irregular north-south-trending Cleveland shelf break. Subsequent coastal onlap by thin deltaic systems of the overlying TST marks the start of decreased sediment influx during late Cleveland time, resulting in thinning of parasequences andan increase in carbonate beds in upper Sequence 2 and Sequence 3.

Cleveland gas is trapped in (1) upstructure stratigraphic and porosity/permeability terminations of delta-front and distributary-channel sandstones at the top of the lower Cleveland HST and of upper Cleveland IVS facies and (2) combination traps involving depositional pinch-out of lower Cleveland HST delta-front facies within small, SE-plunging anticlines. Distal delta-front and prodeltaic shales form the seals.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.