Minibasin dynamics control sediment dispersal on a salt-detached slope: examples from the Northern Gulf of Mexico

Basal welds can halt the downslope translation of minibasins on salt-detached slopes, commonly giving rise to shortening and extension, updip and downdip, respectively, of the obstructed minibasins. How minibasin obstruction influences seafloor topography and thus deep-water sediment dispersal has not been previously investigated, despite it being an important control on hydrocarbon reservoir development. Using a 3D depth-migrated seismic reflection survey that images the mid-to-lower slope of the Northern Gulf of Mexico, we document: (1) minibasin welding and obstruction, and collision and overthrusting of an updip minibasin; and (2) extensional breakaway downdip of the welded minibasin. Using seismic attribute analysis, we show that these minibasin dynamics, controlled seabed relief and sediment dispersal. First, a slope-parallel submarine channel system was deflected perpendicular to the slope by relief generated by minibasin collision and overthrusting. A mass-transport complex (MTC) was subsequently deflected from its previous slope-parallel pathway by relief generated by uplift in the footwall of extensional breakaway-related normal fault. These results challenge traditional fill-and-spill models that consider only vertical subsidence and thus assume laterally static minibasins. Here, we highlight that minibasin mobility and obstruction exert an important influence on the seafloor morphology and hence, on the spatial configuration of deep-water depositional systems. Rather than a predictable response of the deep-water sediment transport system to minibasin obstruction related deformation, the obstruction-triggered seafloor topography changes are complex and locally constrained. Thus, we argue that a three-dimensional, dynamic salt-tectonic framework is required when assessing deep-water sediment dispersal on salt-influenced slopes where minibasin obstruction processes are ubiquitous.