Upper Pleistocene-to-Holocene Depositional Sequences in the North-Central Gulf of Mexico

Abstract

Upper Quaternary depositional sequences and their systems tracts can be delineated in the Main Pass area using minisparker seismic data. Core collected by the Gulf of Mexico Outer Shelf/Slope Research Consortium (Amoco, ARCO, BP, Chevron, Elf-Aquitaine, Exxon, Marathon, Mobil, and Texaco) sampled these systems tracts on one site in Main Pass 303. At the shelfbreak, a distinct change in depositional style occurs across the latest Wisconsinan sequence boundary. Widespread progradational systems (late highstand systems tract) below become focused into discrete depocenters with predominantly aggradational deposits (lowstand systems tract) above. Focusing was probably a result of localized high subsidence rates due to salt movement, progradation into rapidly deepening water, and, possibly, stabilization of sediment transport paths on the exposed shelf. No age-equivalent submarine canyons are present in this area. The oldest mappable systems tract is a highstand systems tract deposited during stage 3 interstadial and the early-to-middle stage 2 glacial. The overlying transgressive systems tract was deposited coeval with the stage 2-stage 1 transition. It thins in a land-ward direction, except where an updip depocenter was present. At the corehole site, the transgressive systems tract consists of fining-upward deposits ranging from medium-grained sands to clays. The transgressive systems tract includes smallmore » slope-front-fill lenses deposited on the uppermost slope above and adjacent to lowstand deltaic depocenters. These lenses likely comprise silt and clay derived from either reworking of lowstand deltas or sediment bypassing the outer shelf.« less