Print this pageTWICHELL, D. C.3, C. H. NELSON1, J. E. DAMUTH2, and G. DUNHILL1
1USGS, Menlo Park, CA
2Univ. Texas at Arlington, Arlington, TX
3USGS, Woods Hole, MA
Abstract: Bryant Canyon Turbidite System Pathway On The Louisiana Continental Slope
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 which are largely covered by muddy mass-transport deposits and some coarse silt turbidites. Radiocarbon ages show turbidites accumulated until about 10,150 yr 13P, and mass-transport deposits in the upper 4.7 m of cores 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 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, and 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.
AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas