ABSTRACT: Pliocene-Pleistocene Depocenter Distribution and Shelf Break Progradation, Northwest Offshore Louisiana

LI, RONG, and JOEL S. WATKINS, Department of Geophysics, Texas A&M University, College Station, TX

Interpretation of 4,000 line miles of seismic data, covering an area between 910 degrees 60'W to 940 degrees 00'W longitude and 280 degrees 00'N to 290 degrees 00'N latitude, reveals the sedimentation patterns underneath the continental shelf. Seven Pliocene-Pleistocene paleohorizons were mapped using the first occurrence paleotops: Trimosina A, Hyalinea balthica, Angulogerina B, Lenticulina 1, Globoquadrina altispira, Buliminella 1, and Textularia X.

The sediment distribution in this area is controlled by different structural features. Between 93 degrees W and 93 degrees 40'W, three east-west-trending fault zones are the most pronounced structural features. The master fault is located between 28 degrees 20'N and 28 degrees 30'N and extends about 60 mi in the downdip direction. It controls sediment distribution for the interval from Lent 1 to Trim A. The expansion index approaches 5. The fault toe merges with a broad shale uplift near the Trim A and Hyal B shelf edge. Largest depocenters from Ang B to Lent 1 are located on the downthrown side of this fault. The second fault zone trend is located between 27 degrees 50'N and 28 degrees 10'N. The maximum thickness in the Hyal B-Trim A interval occurs at the downthrown side of this fau t. The third fault trend is located between 28 degrees 30'N and 28 degrees 40'N. This fault is much smaller than the first fault zone and it mainly controls depocenters from Lent 1 to Glob Alt. Salt diapirism was active during this interval. A series of salt spines occurs in the region between 93 degrees W and 92 degrees W. Large scale growth faults did not develop here. Maximum sediment deposition occurs in interdiapiric basins as a result of the salt withdrawal. This region contrasts with the region between 93 degrees W and 93 degrees 40'W, which is dominated by salt anticlines and salt sheets, and where large growth faults are well developed. Around 92 degrees W, another large growth fault with a long glide plane is observed with a depocenter on its downthrown side.

The distribution of depocenters of different periods coincides with the trends of prograding paleoshelf edges and growth fault trends related to failure at shelf edges. A portion of Trim A paleoshelf edge is controlled by a landward fault zone. Hyal B and Ang B paleoshelf edges are related to the fault trend between 27 degrees 50'N and 28 degrees 10'N. Both this fault trend and the second fault trend control the location of Lent 1 paleoshelf edge. The Bulli 1 paleoshelf edge is along a belt of salt diapirs.

Thickest Pliocene-Pleistocene depocenters are in middle shelf-lower slope environments. Depocenters from Trim A to Lent 1 are in an outer shelf environment; and Glob Alt-Tex X are in upper slope environments.

AAPG Search and Discovery Article #91014©1992 AAPG GCAGS and GC-SEPM Meeting, Jackson, Mississippi, October 21-23, 1992 (2009)