Site U1449: Expedition 354

Abstract

Site U1449 is part of our seven-site transect designed to document turbiditic transport processes and the architecture of deposition in the Middle Bengal Fan at 8°N since the Pleistocene. Sediments will also be used to trace sources of eroded material in the Himalaya and reconstruct erosion rates as a function of climate change. Different structural elements of the sedimentary fan were cored, including a more than 40 m thick levee succession, interlevee sand sheets, and hemipelagic sequences. General lithologic boundaries correlate well with downcore variability in all physical properties and were attributed to major seismic facies types and reflectivity characteristics. In situ and average core seismic velocities are in close agreement, which confirms that the major lithologies were properly sampled and sections not recovered by XCB drilling likely contained unconsolidated sand. Cored sediments allowed us to characterize the sedimentological, physical, and geochemical properties of the material delivered mostly through turbidity currents and likely originating from the Himalayan range. Integration of lithology, physical properties, seismic facies, and geochronological data shows that sedimentation varies over several orders of magnitude between centimeters per thousand years for hemipelagic units that represent a local absence of turbiditic sedimentation and much higher rates for interlevee units and levees that built up rapidly. High accumulation rates of turbiditic deposition in the lower 120 m of Hole U1449A since ~2 Ma were followed by a low-accumulation hemipelagic episode around ~0.8–1.3 Ma. Intercalated levee and interlevee deposits then formed until ~300 ky ago, after which hemipelagic sedimentation dominated again.