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3-D Seismic Interpretation of the Paleo-Mississippi Shelf-Margin Delta Offshore Louisiana

Lozano, Felipe A.1
1 Geosciences, University of Houston, Houston, TX.

3D high-quality seismic data covering an area of 8,000 sq. Km along the actual shelf edge offshore Louisiana allowed a detailed mapping of the paleo-Mississippi shelf-margin deltaic system during the last glacioeustatic cycle, ~75,000 years.

Salt-tectonics in the Gulf of Mexico controlled the geomorphology of the shelf edge to slope boundary creating seven salt-withdrawal minibasins in the study area. The paleo-Mississippi system prograded as a big deltaic fan until reaching the shelf edge, at this point the deltaic system split into several lobes that prograded over the different salt-withdrawal minibasins behaving as individual shelf-margin deltas.

Volumetric attributes such as amplitude gradients, coherence, curvature and sweetness were computed to improve the interpretation. Attribute extractions along picked horizons and flattened volumes of the different attributes provided a much accurate 3D image of the deltaic system.

Three salt-withdrawal minibasins were chosen in order to determine and compare the development of the individual shelf-margin deltaic lobes.

Minibasin 1 dip-oriented profiles showed the progradation of a shelf-margin deltaic system with forced regressive geometries followed by a normal regression progradation. 3D seismic attributes extracted from picked horizons revealed a shelf-margin deltaic system characterized by a bypass shelf-to-slope channel system without deposition at the base of the slope.

Minibasin 2 in contrast is characterized by a shelf-margin deltaic channel system linked to a base of slope channel turbidite system. This minibasin follows the fill-spill depositional process and is linked to other two intraslope minibasins to the west and to the east. Corendering amplitude gradient attribute along with sweetness allowed us to detect the presence of a sandy channel system.

Minibasin 3 is characterized by a bypass shelf to slope system with the presence of an incised slope channels linked to a base of slope deep-water deposit. Most-negative and most positive curvature attributes extracted along the picked horizon delineate the presence of the slope channel system and the lobate geometry of the base of the slope deep-water deposit.

In general each of the three minibasins act as an individual depocenter, which has its own size, shape and slope gradient that control the evolution of the shelf-margin deltaic system.


AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009