SHIPP, R. CRAIG, Shell Development Company, Houston, TX

ABSTRACT: Late Pleistocene Mississippi River Canyons: Slope Turbidite Systems in Western Mississippi Canyon and Atwater, Northern Gulf of Mexico

Three large submarine canyons associated with the late Pleistocene Mississippi River cross the continental slope in western Mississippi canyon and Atwater protraction areas. Analysis of both 2-D and 3-D seismic data shows four major depositional events. First, the study area is floored by an extensive ponded fan package, which onlaps salt-induced paleobathymetric relief. Second, the easternmost and oldest Southwest Pass Canyon is a large leveed-channel system that is deposited on the underlying ponded fan. Third, Old Timbalier Canyon cut a v-shaped, erosional bypass channel into the ponded fan to the west of southwest Pass canyon. Old Timbalier canyon subsequently was infilled by mass transport directed from both margins toward the channel thalweg. Fourth, the westernmost and youngest Young Timbalier Canyon cut a more extensive bypass channel, whichhas infilled in several discrete stages and forms a significant bathymetric depression (Mississippi Trough) across the present-day slope. Each canyon is an updip feeder of recently identified Mississippi Fan lobes on the continental rise and abyssal plain (fan channels 14-17 of Weimer, 1989). Therefore, these canyons represent slope conduits between the ancestral Mississippi River mouth at the shelf margin and their equivalent deepwater fan lobe during the last three episodes of meltwater discharge.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.