Latest Quaternary Regional Sedimentation Processes in the US Gulf of Mexico Exclusive Economic Zone (EEZ)

Abstract

Interpretation of very high-resolution (3.5 kHz) seismic facies reveals that turbidity-current, mass-transport (MTD), and bottom-current depositional processes have all contributed to the regional sediment distribution throughout the U.S. Exclusive Economic Zone (EEZ) in the northern Gulf of Mexico. Piston cores from these deposits confirm the interpretations of these processes and show that most were deposited during Last Glacial sea-level lowstand. The eastern half of the EEZ is dominated by the Mississippi Submarine Fan, which is composed of mud-rich channel-levee complexes on the upper and middle fan, and sandy lobes on the lower fan. Although MTDs were previously mapped from the east side of the fan, our 3.5 kHz data reveals the total distribution of MTDs across the western side. The 3.5 kHz data also shows seismic facies consistent with very sandy deposits throughout the lower fan. In contrast, the western EEZ is dominated by intraslope mini-basin systems, and turbidity currents have deposited large volumes of sands into these basins canyons. Although most of these systems do not traverse the entire intraslope area, the extensive Bryant Canyon system allows turbidity currents to bypass through all the mini-basins via fill-and-spill processes and form the large Bryant Submarine Fan, which extends hundreds of km seaward from the Sigsbee Escarpment. In contrast, the smaller Rio Grande Submarine Fan was deposited in an intraslope plateau. The 3.5 kHz seismic facies and piston cores indicate a sand-rich fan with numerous small, un-leveed channels that appear to show a braided channel system. MTDs are ubiquitous throughout the mini-basins, along the upper continental slope and at the eastern base of the Sigsbee Escarpment. Cores confirm that the majority of MTDs are mostly muddy debris flows with mud clasts of variegated colors, but sandy debris flows also occur in some mini-basins. Deformation, folds and faults in some cores indicate slump or slide deposits. The East Breaks Slide Complex is the largest MTD complex of slump/slide blocks and debris flows and extends from the shelf edge downslope for >100 km. Most MTDs were deposited during the Last Glacial (MIS 2) lowstand. Three large regions of migrating sediment waves occur on the Sigsbee Abyssal Plain and were formed by bottom current circulation of the Loop Current. Sediment waves also occur locally along the base of the Sigsbee Escarpment in conjunction with previously reported erosional furrows.

AAPG Datapages/Search and Discovery Article #90291 ©2017 AAPG Annual Convention and Exhibition, Houston, Texas, April 2-5, 2017