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C. Hans Nelson1, David Twichell2, William R. Bryant3, John E. Damuth4, Gita Dunhill5
(1) Department of Oceanography, Texas A & M University, College Station, TX
(2) U.S. Geological Survey, Woods Hole, MA
(3) Texas A&M University, College Station, TX
(4) University of Texas at Arlington, Arlington, TX
(5) University of Colorado, Boulder, CO

Abstract: Salt Neotectonic Activity and Slope Stability Along the Bryant Canyon and Fan Turbidite System Pathway on the Louisiana Continental Margin

GLORIA sidescan sonar imagery, multibeam bathymetry, seismic profiles, and piston cores (3-5 m penetration) outline the pathway and indicate significant neotectonic disruption of a former turbidite system that extends from the continental shelf edge through Bryant Canyon on the slope to Bryant Fan on the continental rise. Radiocarbon ages show some turbidites as young as about 10,150 yr BP, and mass-transport deposits in the upper 4.7 m of cores accumulated between 12,300-3,400 yr. BP. Originally, turbidity currents sourced at the shelf edge passed through the canyon and intraslope basin pathway in a continuous gradient to Bryant Fan. Now, this gradient has been offset by 500 m from basin floor to basin edge down-slope spill points because of continued tectonic movement of the underlying salt. As a result, mass-transport deposits, up to 100 m in thickness, have buried turbidites on the basin floors. When the turbidite system shut off either at the beginning of the Holocene or an earlier sea level rise, salt tectonic effects caused the basin walls to oversteepen and resulted in an overlying layer of mass- transport deposits on the basin floors. The key to understanding whether salt tectonic offsets are 500m per 10,000 years or 100,000 years or more, depends on when the last continuous turbidite pathway was active to Bryant Fan. An analysis of the turbidite stratigraphy on Bryant Fan is necessary to answer this question, determine the present-day slope stability and assess relative severity of geologic hazards in the Bryant Canyon region.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana