Slope-instability processes caused by salt movements in a complex deep-water environment, Bryant Canyon area, northwest Gulf of Mexico

Abstract

Halokinetic and slope-instability processes have sculpted numerous morphological features on the flanks of the intraslope basins in the Bryant Canyon area. High-resolution geophysical data and long sediment cores (as much as 20 m [66 ft] long) were used to define the time and spatial evolution of sediment failures and their relationship to halokinetic processes. Two episodes of increased salt-tectonic activity are defined: (1) The first acted at the beginning of interglacial oxygen isotope stage 5 as salt adjusted to the abandoned environments of the Bryant and Eastern Canyon systems, and (2) the second occurred during the last glacial period and is characterized by the seaward propagation of salt masses. Three types of slopes are recognized in the intraslope basins: (1) highly inclined slopes with low-relief morphologic features resulting from shallow, translational slump complexes, (2) highly inclined slopes with high-relief morphologic features resulting from deep, rotational slump complexes, and (3) highly inclined slopes dissected by high-relief canyonlike landslide troughs resulting from channelized rotational slumps. The first two slope types occur mainly on the northern flanks of the basins, whereas the third type occurs on the southern flanks. We propose that the slump complexes on types 1 and 2 slopes were triggered by the oversteepening of the flanks by the seaward mobilization of underlying salt masses. The channelized rotational slumps on type 3 slopes are interpreted to result from the development of salt diapir bulges that lead to locally increased gradients on the basin flanks. Most of the sediment failures have been transformed into debris flows and led to the most recent phase of infilling of the basin floors.