Lateral Variations in Log, Core, and Seismic Attributes of a Mass Transport Deposit in the Mars-Ursa Region, Mississippi Canyon, Northern Gulf of Mexico

Derek E. Sawyer¹, Craig Shipp², Peter B. Flemings¹, Jan Behrmann³, Cedric M. John⁴, and Expedition 308 Shipboard Scientific Party
¹ Penn State University, University Park, PA
² Shell, Houston, TX
³ Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
⁴ University of Santa Cruz, Santa Cruz, CA

Physical properties and logging-while-drilling (LWD) data from IODP Expedition 308 Sites U1324, U1323, and U1322 (during the summer of 2005) reveal significant lateral differences within a prominent mass transport deposit (MTD). The MTD occurred ~20 kya, lies ~100 meters below the seafloor, is ~40-90 meters thick, and covers an area of at least 900 km2 in the Mars-Ursa Region of the Mississippi Canyon protraction area. It is easily recognized in high-resolution 3-D and conventional exploration 3-D seismic data by a sharp, stepped basal detachment surface, and internal chaotic to semi-transparent seismic facies. Despite the similar internal seismic facies however, the bulk physical properties vary from site-to-site. At Site U1322, higher shear strength, porosity, higher core deformation, and LWD resistivity distinguish the MTD relative to the surrounding undeformed sediments. At Site U1323 the MTD is characterized by increased LWD resistivity as well. However, 10 km to the west-southwest at Site U1324, no significant offsets are observed in shear strength, porosity, or LWD resistivity, and only minor core deformation is observed. Seismic attributes such as coherency slices and interval amplitude extractions generally correspond to this variation in the bulk physical properties. Coherency slices and interval amplitude extractions between the top and base of the MTD reveal sinuous flow pathways and rafted blocks in the area of Site U1322 and U1323. However, no such features are observed around Site U1324.