Description: The backscatter data were collected during R/V SONNE Cruise SO244. For processing of the backscatter information, all data recorded during turns of the ship were eliminated before gridding to a 20 m cell size throughout the study area.

Description: Overpressures measured with pore pressure penetrometers during Integrated Ocean Drilling Program (IODP) Expedition 308 reach 70% and 60% of the hydrostatic effective stress (View the MathML source) in the first 200 meters below sea floor (mbsf) at Sites U1322 and U1324, respectively, in the deepwater Gulf of Mexico, offshore Louisiana. High overpressures are present within low permeability mudstones where there have been multiple, very large, submarine landslides during the Pleistocene. Beneath 200 mbsf at Site U1324, pore pressures drop significantly: there are no submarine landslides in this mixture of mudstone, siltstone, and sandstone. The penetrometer measurements did not reach the in situ pressure at the end of the deployment. We used a soil model to determine that an extrapolation approach based on the inverse of square route of time (View the MathML source) requires much less decay time to achieve a desirable accuracy than an inverse time (1/t) extrapolation. Expedition 308 examined how rapid and asymmetric sedimentation above a permeable aquifer drives lateral fluid flow, extreme pore pressures, and submarine landslides. We interpret that the high overpressures observed are driven by rapid sedimentation of low permeability material from the ancestral Mississippi River. Reduced overpressure at depth at Site U1324 suggests lateral flow (drainage) whereas high overpressure at Site U1322 requires inflow from below: lateral flow in the underlying permeable aquifer provides one mechanism for these observations. High overpressure near the seafloor reduces slope stability and provides a mechanism for the large submarine landslides and low regional gradient (2°) offshore from the Mississippi delta.

Description: The continental slope of the northern Gulf of Mexico seaward of the Mississippi Delta is characterized by very rapid Quaternary sedimentation. Thick sequences of underconsolidated muds and mudstones are present, which are severely overpressured. In the Ursa Basin, Site U1322 of the Integrated Ocean Drilling Program (IODP) provided an excellent coring record of interleaved fine-grained turbidites and hemipelagic sediments, in part severely affected by submarine slumping and sliding after deposition. Cores were continuously sampled and analyzed for anisotropy of magnetic susceptibility (AMS), to elucidate the effects of different transport mechanisms and degree of settling and consolidation on magnetic fabric properties. Generally AMS ellipticity increases with depth irrespective of transport mode, due to loss of porosity. Samples from slumped mass transport deposits (MTD), however, have higher AMS if compared to immediately overlying nonslumped material. MTD samples dominantly show triaxial magnetic fabrics whereas those found in nonslumped sediments are much more oblate. Long axes of the fabric ellipsoid reflect the direction of eastward to southward suspension transport in samples not overprinted by sliding or slumping. Short ellipsoid axes in non-slumped material are vertical, and thus parallel to the axis of maximum uniaxial shortening. In the MTD samples, many short ellipsoid axes are inclined, reflecting an overprint of the uniaxial shortening by bedparallel shearing induced by the slumping. Shear and MTD transport direction deduced from the fabrics is top to- SE, downslope along the morphological axis of Ursa Basin. Generally we show that magnetic fabrics of muds and mudstones are sensitive recorders of sedimentary and tectonic processes, and can be used to reconstruct essential

Description: Multibeam bathymetric data were acquired during R/V SONNE Cruises SO104, SO244, and R/V Marcus G. Langseth Cruise MGL1610. The datasets were individually processed and gridded with grid cell sizes of 75 m. For the combined grid, depth information from SO244 was used wherever possible. If no SO244 data were available, MGL1610 data were preferred over SO104 data. The backscatter data were collected during R/V SONNE Cruise SO244. For processing of the backscatter information, all data recorded during turns of the ship were eliminated before gridding to a 20 m cell size throughout the study area.