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ABSTRACT: Evolution of an Upper Jurassic Carbonate/Evaporitic Platform in the Conecuh Embayment, Northeastern Gulf Coast, U.S.A.

Bradford Prather

The time-stratigraphic framework interpreted from approximated time lines within the Smackover/Haynesville depositional sequence is constrained by marker beds, an interpreted maximum flooding surface, and interpreted sequence boundaries. Successive time-slice lithofacies maps constructed along these approximated time lines show an onlapping and retrograding sequence of lithologies characteristic of transgressive systems tract (TST) stratigraphy, followed by several prograding sequences characteristic of stacked highstand systems tract (HST) stratigraphy. Abrupt basinward shift of lithofacies patterns during progradation that appears coincident with exposure of the platform, isolation of intraplatform basins, and subaqueous Buckner salt deposition suggest that generally ri ing sea level during Smackover/Haynesville deposition was interrupted by a sea level lowstand. The resulting stratigraphic relationships suggest the Smackover/Haynesville sequence consists of a TST and two to three stacked HSTs.

Comparison of stratigraphic cross sections, lithofacies maps, and a paleotopographic map of the sub-Smackover transgressive surface show that the distribution of lithofacies within the TST was strongly controlled by two types of sub-Smackover paleotopographic highs: Norphlet dune fields (ergs) and eroded basement rock (inselbergs). Distribution of lithofacies within the HSTs was controlled less by these early paleotopographic features as they became progressively buried during deposition and more by (1) differential compaction around shoal-water facies in the TST, (2) early Louann Salt movement, (3) basement-related faulting, and (4) freshwater influx along the basin rim. The time-stratigraphic framework developed in this study provides constraints on basin evolution and depositional odels that account for the observed distribution of reservoir, seal, and source lithofacies.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990