Regional multichannel seismic data are used to develop a seismic stratigraphic framework for the continental slope-upper Mississippi fan region in the northern Gulf of Mexico. In the Mississippi canyon area, upper Pliocene and Pleistocene paleontologic zones from wells provide age control for major seismic sequence boundaries. A major unconformity and high-amplitude reflector identified as the base of Pleistocene represents a break in sedimentation and probably marks onset of fan deposition. This unconformity and others within the Pleistocene define sequences showing cyclic patterns of deposition, which are related to Pleistocene sea level changes and salt mobilization.

Interpretation of seismic facies and their relationships to sea level changes, glaciations, and salt movement results in a model for the depositional history of the Mississippi fan from the canyon area to the deep-water part of the fan. Low-amplitude, chaotic, onlapping facies are interpreted as slump or debris-flow deposits associated with canyon cutting by retrogressive failure and initiation of large-scale mass movement due to a relative lowering of sea level. High-amplitude, parallel, continuous reflectors at sequence boundaries represent pelagic and hemipelagic sediments associated with a succeeding rise in relative sea level.

In the shelf-upper slope area, isolated salt diapirs influence sedimentation on a localized scale. In the lower slope to upper fan, most Pleistocene section is extensively disrupted by parallel sets of salt ridges that result from differential loading of fan sediments. Shifting depocenters and migratory channel systems funnel sediment through this area onto the lower fan. Salt wedges in the eastern study area appear to represent detached salt masses isolated within the Pleistocene section.

End_of_Article - Last_Page 315------------