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A deep-towed, side-looking sonar survey of an outer fan, distributary channel near DSDP Sites 614 and 615 on the Mississippi Fan defined three distinct morphologic zones: (1) a relatively “straight” channel zone (sinuosity of 1.1), (2) a channel termination zone, and (3) a splay and “finger-shaped distributary” zone. Boundaries between zones are gradual with no direct connection observed between this channel and the leveed channel that was mapped and drilled farther upfan during DSDP Leg 96.

The sinuous migratory channel of the middle Mississippi Fan changes to a pattern of frequent lateral shifting and abandonment on the lower fan, with one channel being active at any given time. Borings in the upfan part of the lower fan recovered vertical successions of thin channel fill and overbank deposits. Near the distal end of the fan, the channels often bifurcate before merging with a low relief area of assumed laterally extensive “sheet sand” deposition. A significant amount of all the sand-sized sediment that came from the source area onto the Mississippi Fan during the Late Pleistocene was apparently transported to the lower fan.

The middle-fan area of the youngest Mississippi fanlobe is a convex-shaped aggradational body with a sinuous, migratory channel located along its apex. The middle-fan/lower-fan boundary corresponds to a change from the sinuous channel pattern to one of lateral switching and abandonment. Sites drilled in the mid-fan channel indicate an upward-fining fill, commencing with gravel and ending with clay. The overbank deposits are primarily muddy with some silty and very-fine sandy turbidites. Sedimentation rates during the Late Wisconsin age for both the channel fill and overbank areas are about 12 m/1000 yr.

Eight different sedimentary facies recognized in the Mississippi Fan sediments drilled during DSDP Leg 96 are defined on the basis of lithology, sedimentary structures, composition, and texture. Pelagic biogenic sediments are of minor importance volumetrically compared with the dominant resedimented terrigenous facies. Clays, muds, and silts are most abundant at all sites, with some sands and gravels within the mid-fan channel fill and an abundance of sand on the lower fanlobe. Facies distribution and vertical sequences reflect the importance of sediment type and supply in controlling fan development.