Geometry and Depositional Sequences of the Mississippi Canyon, Gulf of Mexico

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, ap arently 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.