Abstract:
Mass transport deposits (MTDs) in the Ursa region of the northern Gulf of Mexico have low internal reflectivity, high resistivity, high bulk density, and low porosity in comparison to the hemipelagic sediments that bound them. I infer these MTD properties result from enhanced consolidation related to shear deformation. The deviation of physical properties within MTDs, compared to the bounding mud-rich sediments, increases from west to east in the Ursa region. The largest amount of shear-induced densification occurs at the bases of the MTDs resulting in high amplitude basal reflections, and to a lesser extent high amplitude top reflections, in seismic data. While the deformation paths of MTDs (burial and shear) and bounding hemipelagic sediments (burial) differ, comparison of bulk physical properties indicate that all sediments within the Ursa region have similar bulk density-resistivity and void ratio-effective stress behavior. From density and resistivity data and consolidation experiments, I conclude that shear deformation in MTDs in the Ursa region produces denser, more resistive sediments with porosity decreases up to 6 porosity units. This shearing, however, does not change fabric or general deformation behavior at the bed scale (0.1-1 m). The similar resistivity-void ratio-effective stress trends provide a means to infer some of the bulk physical properties (e.g., permeability) of MTDs from information on normally consolidated mud and from the seismic response. Abstract Copyright (2012) Elsevier, B.V.