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XUE, LIANGQING, and WILLIAM E. GALLOWAY, University of Texas at Austin, Austin, TX

ABSTRACT: Sequence Stratigraphic and Depositional Framework of the Paleocene Lower Wilcox Strata, Northwest Gulf of Mexico Basin

The lower Wilcox (LW) strata comprise a single genetic sequence and are subdivided into four subsequences (I-IV, from oldest to youngest) based on regional flooding surfaces. The LW sequence is bounded by maximum flooding surfaces associated with the Big Shale at the top and Midway marine shale at the bottom, and is dated at 56.5 Ma and 59.0 Ma. The LW sequence shows extensive shelf-margin progradation, high sedimentation rate, and thick progradational parasequences.

LW depositional systems are outlined on the basis of the net-sandstone isopach maps, which are contoured using a log database of about 500 wells. Subsequence I includes several fluvial-dominated delta systems, reflecting the initial progradation of the LW depositional episode. Subsequence III contains the classic Rockdale delta system, Cotulla barrier-bar system, and strand plain system described by Fisher and McGowen. Subsequence III is the turning point of the depositional styles within the LW genetic sequence. The progradational patterns of sequences I and II were replaced by the retrogradational style of subsequence III, which contains deposits of wave-dominated delta, strand plain, barrier-bar, lagoon, and shelf-slope systems. Subsequence IV also shows a wave-dominated style. Sev ral wave-dominated delta systems migrated landward. The delta-type evolution in the Houston embayment (major depocenter) from fluvial-dominated through wave-modified, to wave-dominated and backstepping delta systems reflects the progression from progradational subsequences I and ll to retrogradational subsequences III and IV.

AAPG Search and Discovery Article #90989©1993 GCAGS and Gulf Coast SEPM 43rd Annual Meeting, Shreveport, Louisiana, October 20-22, 1993.