Basinal dimensional trends in Gulf of Mexico minibasin geometry

Abstract:

Minibasins are halokinetic structures which are the product of differential sediment loading atop a ductile salt substrate. Their subsidence is driven via the coevolution of depositional and tectonic processes. Minibasins have a global distribution, including dominating the northern deepwater Gulf of Mexico basin. Through the employment of a 12 m resolution bathymetry dataset of the northern deepwater Gulf of Mexico acquired from 3D seismic by the US Bureau of Ocean Energy Management (BOEM), in conjunction with numerical modelling of salt response to perturbations, this investigation seeks to derive the mechanisms by which differential sediment loading in a complex natural environment with variable salt substrate thickness induces differing rates and magnitudes of minibasin subsidence, and how the interplay of these processes affects the resultant minibasin morphology.

By fitting ellipses to the minibasin rims, per the application of the least squares method, in order to quantify their features, it can be seen that minibasins proximal to the sediment source trend towards higher eccentricities (e) than those located distally. We hypothesize that this elongation of the major semi-axis (a) relative to the minor semi-axis (b) is a product of sediment supply. Minibasins located proximally receive an increased sediment supply which impels minibasins in the direction of flow to coalesce to form elongate basins, which is illustrated by the azimuths (θ) of the semi-major axes (a) trending in the NW-SE direction, and the existence of multiple loci of subsidence within the elongated minibasins. This is further evidenced by the centroids of the minibasins having a relatively uniform distribution throughout the extent of the dataset, implying that distal minibasins are not amalgamating to form elongated minibasins due to a lack of sediment supply, rather than there being a sparser distribution of minibasin centroids distally. The ellipse fitting method also revealed that basins with thicker salt substrates, and therefore greater relative subsidence, had higher basin rim rugosities, due to landslides induced by subsidence driven oversteepening of the minibasin walls. These findings presented herein, allow for the attainment of a greater understanding of the processes governing minibasin formation and halokinesis.