--> ABSTRACT: Significance and Application of Genetic Unit Mapping of Permian-Pennsylvanian Clastics on Eastern Shelf, by John L. Thoma; #91026 (2010)

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Significance and Application of Genetic Unit Mapping of Permian-Pennsylvanian Clastics on Eastern Shelf

John L. Thoma

Upper Pennsylvanian to middle Permian strata on the Midland basin Eastern shelf reflect an overall period of marine transgression. Persistent terrigenous influx produced extensive regressive clastic prisms, and periodic flooding of shelf areas during marine transgressions terminated regressive phases and produced conditions favorable for carbonate and black shale deposition. The resulting sequence argues favorably for extrabasinal or eustatic controls on transgression and a combination of eustatic and tectonic controls on regression.

Each regressive phase exhibits a shelf and basin component. Sediments in the shelf component result primarily from a fluvial depositional environment, whereas sediments in the basin component are the product of marine, deltaic, and submarine depositional environments.

Bounded by transgressive carbonate and black shale, each regressive clastic prism represents a genetic sequence of strata (GSS). Within each GSS are locally definable bodies of sediments, typically sandstone packages, which can be correlated as genetic increments of strata (GIS). Multiple sandstone members frequently occupy a GIS. Extensive subsurface control within the study area allows for definition of four GSS and numerous associated GIS.

The basin component of any given GSS exhibits an upward-coarsening sequence reflecting four primary depositional environments that can be localized on a GSS isopach map: basin floor, toe-of-slope, slope, and delta environments. Identification of reservoir geometries inherent to these environments was achieved through modeling of Sweetwater, Conger, Lake Trammel, and Group 4000 fields.

Use of the genetic approach to mapping and interpretation of Eastern shelf Permian-Pennsylvanian clastics enables early identification of areas of interest along with an ordered reliable means of localizing and evaluating associated prospects.

AAPG Search and Discovery Article #91026©1989 AAPG Southwest Section, March 19-21, 1989, San Angelo, Texas.