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ABSTRACT: Lithofacies Distribution in Smackover/Haynesville (Oxfordian) Depositional Sequence, MAFLA Area, Northeastern Gulf Coast Basin, U.S.A.

T. C. Boronow, B. E. Prather

Correlation of a basal carbonate unit, a downlap or maximum flooding surface, and approximated time lines in a prograding unit provide the time-stratigraphic framework for mapping the distribution of reservoir, seal, and source lithofacies within the Smackover/Haynesville depositional sequence.

Seismic sequence analysis of offshore data, core control, onshore to offshore regional stratigraphic sections, and time-slice lithofacies maps show this depositional sequence to consist of a deepening-upward transgressive system tract (TST) and a shallowing-upward highstand systems tract (HST).

The TST is composed of predominately lime mudstones and microlaminated mudstones. These mudstones are source rocks for Norphlet and Smackover accumulations and top seals for some Norphlet accumulations. Reservoir rocks in the TST were deposited in high-energy environments localized over paleotopographic highs and around basin margins.

The HST over most of offshore MAFLA is dominated by siliciclastic deposition. In these areas, the HST is characterized by sigmoid clinoform seismic character. The clinoforms result from interbedded carbonates. Source rocks occur in bottomsets and foresets, and grainstones are located in the topsets of these carbonate interbeds. The source rocks are part of a condensed zone deposited in a starved basin and grainstones were deposited at the paleostrandline. Sandstone reservoirs deposited by turbidity currents are found in bottomsets and shoreface sandstones occur in topsets of siliciclastic beds.

The HST in onshore and offshore areas not affected by siliciclastic influx consists of shoaling-upward carbonate to evaporite parasequence sets. Here, grainstone reservoirs are capped by Buckner anhydrite top seals.

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