Statistics of Depressions Covering the Northern Gulf of Mexico Salt-Minibasin Province: Drivers and Strength of Bathymetric Self-Organization

Abstract

The bathymetry of the northern Gulf of Mexico is strongly influenced by diapirism of subsurface salt. A competition between salt dynamics and the depositional mechanics of sediment laden density flows over geological timescales controls the scale of seafloor depressions, which are the dominant bathymetric features of the margin. Salt domes create topographic highs, and salt removal to the domes creates topographic lows, with sediment deposition driving the gravitational dynamics. The strength of bathymetric self-organization into depressions is inferred through analysis of a vast bathymetric data set made public by the U.S. Bureau of Ocean and Energy Management. Depression geometric scales follow Pareto distributions, and their tail indexes aid inference of the strength of bathymetric self-organization, with lower tail indexes linked to greater self-organization. A comparison is made of margin subregions defined by pseudo-flow drainage density maps, which inversely relates to the pre-deformation thickness of subsurface salt. Tail indexes of distributions decrease with the thickness of the underlying salt. This is linked to the merger of depressions, which is enhanced when depressions can grow wider and deeper, as occurs over thick salt fields, and the development of salt structure. The manner of self-organization results in most of the margin's ponded sediment accommodation residing in relatively few depressions that have reliefs exceeding 100 m. This relief is sufficient to induce sedimentation from even the thickest turbidity currents, which can further drive gravitational dynamics. The bathymetric complexity of depressions is also greatest over regions with the thickest salt, further supporting enhanced self-organization.