Distribution and Rates of Terrigenous Sediment Accumulation on the Hueneme Submarine Fan in the Late Holocene (4.3 Ka-Present), Santa Monica Basin, California

Deep-marine basins are the final sink for terrigenous sediment delivered to the ocean and, as such, contain a record of factors that influenced their origin, transport, and deposition. The distribution and rates of sediment accumulation, however, are not uniform within a basin. Intrinsic and dynamic geomorphic entities (e.g. channels, levees, channel-mouth lobes, basin plain, etc.) influence the dispersal of subsequent sedimentation events. To adequately assess past external factors sediment accumulation must be integrated with spatial distribution information. In addition, the sink for the sediment flux must be closed, i.e., all of the input can be tallied for the assessment. The Santa Monica Basin is a small (25 x 50 km) deep-water basin in the offshore region of the California Continental Borderland that is fed by two major rivers, has high-relief topography in the onshore watershed and a narrow continental shelf reflecting active tectonism in the region. The Hueneme submarine fan dominated the terrigenous-derived sediment in Santa Monica Basin throughout the Holocene and is the focus of this study. Five stratigraphic intervals were correlated over the middle and lower fan and most of the basin plain using a grid of high-resolution seismic-reflection profiles that provide vertical resolution of up to 0.5 m and penetration depths of as much as 70 m. This stratigraphy is tied to a radiocarbon-dated core at ODP Site 1015 in the basin plain providing an explicit time scale for the late Holocene (4.3 Ka present). This study provides for the first time an estimate of the volumes of sediment delivered to Santa Monica Basin during the late Holocene The integration of precise sediment thickness maps with a radiocarbon-dated core sequence at ODP Site 1015 shows that sediment delivery to the basin is punctuated and is highly variable at millennial scales. Accumulation rates for the mapped stratigraphic intervals vary by a factor of five during the late Holocene, which is a relative highstand in sea-level with very little change. The assessment of volume- based accumulation rates reveal a more complex history than using sedimentation rates solely from ODP Site 1015 and suggest climatic and/or tectonic controls on the rate variability.