Abstract

The Mississippi Canyon is one of several large canyon systems which have developed seaward of large rivers around the shelf margin of the Northern Gulf of Mexico. High-resolution geophysical and borehole data are combined to re-evaluate canyon geometry and sedimentology. Incision of the canyon appears to have taken place prior to 30,000 years BP. Canyon widening by slope failure and mass-movement processes resulted in arcuate re-entrants containing slumped debris separated by residual knolls. Much of the sediment associated with canyon formation and widening was transported down-slope, by-passing the upper canyon. Thick, laminated pro-deltaic sediments, greater than 30,000 years old, comprise the basal canyon fill. Rapid deposition along the canyon axis began about 19,000 years BP, apparently associated with down-canyon mudflows from a nearby lowstand delta. As canyon filling progressed, mass-movement processes declined, resulting in interbedded pro-deltaic and debris flow sediments. The sediment fill was deposited in a complex cut and fill sequence suggesting a much older canyon than previously thought. Deltaic sedimentation retreated northward away from the canyon at about 7,500 years BP, and since that time a Holocene pelagic drape has been deposited.

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