WELLNER, JULIA SMITH, and JOHN B. ANDERSON, Rice University, Houston, Texas
A single delta lobe of what may be the paleo-Mississippi drainage system has been defined, using high-resolution seismic data and platform borings, on the western Louisiana continental shelf in the northern Gulf of Mexico. This deltaic body formed during the highstand of sea level during the last glacial cycle, since marine oxygen isotope stage 5 (~125,000 yr. B. P.) and ending before stage 2 (~20,000 yr. B. P.). The average sediment distribution of the body changes from sand-dominated, identified both in platform borings and as a seismic facies, in the older, northeastern, part of the lobe to mud-dominated in the younger, southwestern, part of the body. The change in preserved sediment distribution implies that there was a change in the sediment load being delivered by the drainage system. The progression of sediments supplied by this system, which drains areas directly affected by continental glaciation, differs from the progression of sediments in other, nonglaciated, systems of the same age in the Gulf of Mexico.