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ABSTRACT: Depositional Environments of the Wilcox Group, Texas Gulf Coast: Stratigraphic and Early Diagenetic Signatures

J. A. May, S. A. Stonecipher

Deposition of the late Paleocene-early Eocene Wilcox Group is controversial. Are Wilcox reservoirs entirely of shallow-marine origin, or are basinal turbidites also present? We analyzed over 5000 ft of core from 15 wells along the Texas Gulf Coast to constrain the environments of deposition. We attribute all cores examined to date to 12 subenvironments of the delta plain to continental shelf. These include distributary channel, lake, marine bay, crevasse-splay delta, shoreface, lagoon, tidal flat, tidal channel, distributary-mouth bar, distal bar, prodelta, and shelf. Each subenvironment displays a characteristic well-log signature. Criteria for recognition in core include grain-size variations, physical sedimentary structures, trace fossils, mineralogy, bedding styles, a d vertical sequences, all resulting from the interplay of specific physical, biological, and chemical processes operative in each subenvironment. We did not identify any submarine-fan deposits.

We also attempted to determine the importance of depositional facies and provenance on diagenetic trends. Early diagenetic patterns appear to be related to factors such as sediment texture, detrital composition, organic content, and original water chemistry, which were, in turn, controlled directly or indirectly by depositional environment. Rapid lateral and vertical changes in depositional environments produced markedly different early diagenetic patterns in sand units only a few feet or even inches apart. Thus, diagenetic facies defined on the basis of texture, composition, and cements can be used to complement, and

test, our interpretations of depositional environments based solely on traditional sedimentologic and genetic-sequence criteria.

AAPG Search and Discovery Article #90999©1990 GCAGS and Gulf Coast Section SEPM Meeting, Lafayette, Louisiana, October 17-19, 1990