REVIEW OF RECENT DEPOSITIONAL PROCESSES ON THE MISSISSIPPI FAN, GULF OF MEXICO

The Mississippi Fan is a large Plio-Pleistocene deposit that covers roughly the eastern half of the deep Gulf of Mexico basin. Sidescan sonar imagery, high-resolution seismic profiles, and cores have shed new light on the sedimentary processes that have shaped the surface of this fan since the latest Pleistocene. A sinuous leveed channel extends from the mouth of Mississippi Canyon for approximately 350 km, and smaller channels extend away from this main channel to the distal edges of the fan. Turbidity currents and debris flows have been transported along the sinuous channels to the distal edge of the fan where they form elongate sandy deposits parallel to the channel axes. The sidescan imagery shows numerous channels with their associated sandy deposits, and C¹⁴ dates indicate that this style of deposition was active until 9-11 ka. Large mass-transport deposits derived from the continental slope in or around Mississippi Canyon cover the proximal part of the Mississippi Fan completely burying part of the channel that fed turbidites and debris flows to the distal fan prior to 9-11 ka. High-resolution sidescan sonar images show barchan dune-like features and northwest trending linear furrows, which indicate active reworking of the fan surface by northwest flowing bottom currents. This broad suite of data suggest a progression from deposition of channelized turbidites and debris flows prior to 9-11 ka to channel-filling mass-transport deposits at the onset of the Holocene rise in sea level to the present reworking of these older sediments by bottom currents.