Depositional Turbidity Currents in Diapiric Minibasins on the Continental Slope: Theory, Experiments, and Numerical Simulation* By

The northern continental slope of the Gulf of Mexico is riddled with numerous subsiding diapiric minibasins bounded by ridges, many of which are connected by channels created by turbidity currents. The region is economically relevant in that these diapiric minibasins constitute focal points for the deposition of sand. These deposits in turn serve as excellent reservoirs for hydrocarbons. A better understanding of the ‘‘fill and spill’’ process by which minibasins fill with sediment as the intervening ridges are dissected by canyons may serve to aid in the location of such reservoirs. A theory is developed to describe sediment deposition in minibasins. Two key and heretofore unrecognized aspects of the ‘‘fill and spill’ ’ process are revealed: • The formation of an internal hydraulic jump as a turbidity current spills into a confined basin. • The detrainment of water across a settling interface forming at the top of the ponded turbidity current downstream of the hydraulic jump. It is shown that sufficiently strong detrainment can consume the flow, so that there is no outflow of either water or sediment even with continuous inflow. As the basin fills with sediment, however, overspill is eventually realized. The theory is developed into a numerical model, tested against laboratory experiments. The result is a view of intraslope minibasin sedimentation that has a stronger physical basis than the conceptual models proposed to date