Bryant Canyon Turbidite System Pathway on The Louisiana Continental Slope, Northern Gulf of Mexico

Twichell, D.C., USGS, Woods Hole, MA, C. H. Nelson, Texas A&M Univ, College Station, TX, J. E. Damuth, Univ. Texas at Arlington, Arlington, TX, H. C. Olson, Univ. of Texas Institute for Geophysics, Austin, TX ,and G. Dun hill, Univ. Colorado, Boulder, CO

Abstract

GLORIA sidescan imagery, multibeam bathymetry, seismic profiles, and piston cores (3-5 m penetration) reveal the near surface geology of a former turbidite system offshore Louisiana that extends from the continental shelf edge across the slope to a deep-sea fan on the continental rise. The turbidite system pathway is narrow (<2 km) and some turbidites have been sampled where it crosses shallow salt deposits, but the pathway broadens where it crosses basin floors that are largely covered by muddy mass-transport deposits and some coarse silt turbidites.

Radiocarbon ages show turbidites have accumulated until about 10,150 yr. BP, and mass-transport deposits in the upper 4.7 m of cores have accumulated 12,300-3,400 yr. BP. Since turbidity currents sourced at the shelf edge passed through this system, it has been modified so that the thalweg no longer has a continuous down-slope gradient: some basin floors are more than 500 m deeper than the spill point on the basin's down slope side. Mass-transport deposits, which may reach 100 m in thickness, result from the continued tectonic movement of the salt. These deposits appear to have buried turbidites in the basin floors. We propose an intraslope basin conceptual model where an active channel feeds a ponded basin sand lobe; once the basin becomes filled the sand lobe is overlain by a bypass channel. When the turbidite system is shut off, salt tectonic effects cause the basin walls to oversteepen and result in an overlying layer of mass-transport deposits on the basin floor. Finally the sequence is overlain by a high-stand hemipelagic drape.