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Abstract: Plio-Pleistocene Depocenter Distribution and Shelf Break Progradation, Northwest Offshore Louisiana
Rong Li, Joel S. Watkins
Interpretation of 4000 line miles of seismic data, covering an area between 91° 60W to 94° 00W longitude and 28° 00N to 29° 00N latitude, reveals the sedimentation patterns underneath the continental shelf. Seven Plio-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°W and 93°40W, three East-West trending fault zones are the most pronounced structural features. The master fault is located between 28°20N and 28°30N and extends about 60 miles 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°50N and 28°10N. The maximum thickness in the Hyal B - Trim A interval occurs at the downthrown side of this fault. The third fault trend is located between 28°30N and 28°40N. 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 occur in the region between 93°W and 92°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°W and 93°40W, which is dominated by salt anticlines and salt sheets, and where large growth faults are well developed. Around 92°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°50N and 28°10N. 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 Plio-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.
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ACKNOWLEDGMENTS AND ASSOCIATED FOOTNOTES
Department of Geophysics Texas, A&M University, College Station, Texas 77843
Copyright © 1999 by The Gulf Coast Association of Geological Societies