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Abstract: X-Ray Computed Tomography of Macroscale Variability in Sediment Physical Properties, Offshore Louisiana

Thomas H. Orsi, Aubrey L. Anderson

Our current understanding of the role of benthic environmental processes in the generation of macroscale (millimeter-to-centimeter) sedimentary structures and the resulting spatial variability of sediment physical properties is limited due primarily to the absence of a suitable quantitative technique for multidimensional analysis at this scale. For this study, we used X-ray computed tomography (CT or CAT scanning), calibrated specifically for conversion to sediment bulk density, to quantify macroscale variations in seafloor sediment structure and physical properties from the Louisiana continental shelf. Dominant sources of macroscale variability in the studied sediments are shells and shell debris; hurricane-driven hydrodynamic forces "homogenize" the upper portions of th seafloor, but in doing so, generate considerable macroscale variability by creating random shell orientations and localized macroscale structures. Millimeter-scale vertical profiles of selected CT statistics reveal macroscale tiering of sediment properties and a notable increase in mechanical compaction (consolidation) at extremely shallow depths below the sediment surface. Interestingly, we observed a nonlinear reduction in physical property variability associated with consolidation that we believe is caused by the presence of pelecypod shells. Shell reorganization in response to increasing overburden pressure results in an immediate decrease in variability. Soon thereafter, a more-or-less stable configuration of the shells is achieved, further compaction of the matrix is prevented, an property variability levels off below this depth.

AAPG Search and Discovery Article #90955©1995 GCAGS 45th Annual Meeting and Gulf Section SEPM, Baton Rouge, Louisiana