--> ABSTRACT: Depositional Patterns and Shelf-Margin Styles of a Lowstand Slope Fan Systems Tract, Offshore Louisiana, by Bruce E. Bowen, J. Pacht, B. L. S. Shaffer; #91003 (1990).

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ABSTRACT: Depositional Patterns and Shelf-Margin Styles of a Lowstand Slope Fan Systems Tract, Offshore Louisiana

Bruce E. Bowen, J. Pacht, B. L. S. Shaffer

A complete spectrum of facies from deep-water fans to updip deltaics and fluvial sediments occurs in the Pliocene-Pleistocene lowstand fan systems tracts of the Gulf of Mexico. Seismic data, well logs, and biostratigraphy have been used to delineate and map the upper Pliocene slope fan systems tract, commonly referred to as the Lenticulina 1 interval. This tract contains sands that are major hydrocarbon producers in the southern part of the Louisiana shelf. Both a ramp margin and a growth fault modified ramp margin can be recognized in this unit. Large submarine fans with well-developed channel levee complexes occur basinward of the growth fault margin. The sands in these sediments typically are thin-bedded and highly lenticular. On the upside of the growth faults, the sl pe fan sediments can be chronostratigraphically correlated to deltaics by using the encasing condensed sections that have been defined by biostratigraphy. The sands in the deltaics are coarsening-upward cycles, occasionally blocky, are generally thicker bedded than the downdip fan deposits. Updip, the semicontinuous to continuous reflectors of the deltaic sediments are replaced by highly discontinuous reflectors with variable amplitude characteristic of upper delta plain or fluvial deposits. A different set of facies is characteristic of the ramp margin. Extensive slope fan sediments are rarely developed and the updip deltaic wedge tends to be thicker and is characterized by slumping along the seaward margin. The deltaics occur in an area that extends about 100 mi along strike and 75 mi n the dip direction.

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