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Seismic Stratigraphic Comparison of DSDP Leg 96 Results with Older Mississippi Fan Lobes, Gulf of Mexico

Paul Weimer, Richard T. Buffler

DSDP Leg 96 drilled the youngest depositional lobe of the Mississippi fan at nine sites. These sites were designed to provide a set of reference cores to help explain the development of Quaternary and older submarine fans. The youngest fan love is dominated by a single, sinuous aggradational channel system, characterized by high-amplitude reflections that represent channel-lag gravels and sands, while adjacent laterally continuous reflections correspond to fine-grained overbank sediments.

Analysis of 12,000 km of multifold seismic data from the Mississippi fan provides a method for comparing the drilling results with the seismic stratigraphy of the nine older Mississippi fan lobes. Sinuous channels and associated facies are present in all older lobes in the middle fan area, although there is a greater diversity in channel/overbank distribution and interpreted depositional processes. For example, four of the lobes have several coeval channels that area fed by separate submarine canyons in the slope, and a bifurcating channel pattern caused by channel avulsion is present in six different lobes along the middle and lower fan. In addition, an important seismic facies consisting of mounded, hummocky, and chaotic reflections is present at the base of six older lobes. This fa ies is more areally restricted than the overlying, well-developed channel/overbank deposits and is interpreted to represent coarse-grained channel sediments deposited during lowering sea level.

Although Leg 96 drilling provides sedimentologic information that can be used for comparison with other fans, this seismic stratigraphic study of the entire Mississippi fan suggests that additional processes were operating that were not explained by the drilling results.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.