HR: 1330h
AN: OS52B-0916    [PDF]
TI: Variations in accumulation rate of late Quaternary turbidite deposits in Santa Monica Basin, offshore southern California
AU: Piper, D J
EM: DPiper@nrcan.gc.ca
AF: Geological Survey of Canada Atlantic, Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, NS B2y 4A2 Canada
AU: * Normark, W R
EM: wnormark@usgs.gov
AF: US Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 United States
AU: McGann, M
EM: mmcgann@usgs.gov
AF: US Geological Survey, 345 Middlefield Road, Menlo Park, CA 94025 United States
AB: The Santa Monica Basin off southern California provides an ideal setting to study the effects of sea-level change and turbidity current initiation styles on turbidite depositional processes along a narrow continental margin. It is the perfect sink: all sediment delivered through multiple submarine canyons along its northern margin remains within the basin, except for quantifiable advection of shelf mud to the south. High-resolution deep-tow boomer data, which provides stratigraphic detail (to 50-cm resolution) for the upper 20 to 80 m of basin fill, permits mapping of a series of reflectors across the basin floor and onto the lower basin slopes. Age control for the upper basin fill at ODP Site 1015 is provided by 11 new radiocarbon dates, back to 31 ka (radiocarbon years) at 98 m. The average sediment-accumulation rate during the Holocene of 2.4 m/ka is about half the peak lowstand accumulation rate of 4.7 m/ka. During oxygen isotope stage 3, the accumulation rate was 2.5 m/ka (based on two dates), comparable to the Holocene rate. Additional dates from samples taken with conventional piston cores on the basin slopes confirm age assignments and stratigraphic correlation based on the boomer data. Basin floor reflectors in the turbidite fill can be traced from ODP Site 1015 to as much as 40 m above the floor of the basin at both the western and southeastern margins. Intervals of thick sands on the basin floor have correlative fine-grained turbidites on the basin margins, whereas intervals with only thin sands on the basin floor lack identifiable turbidites. Volume estimates of sediment accumulation can thus be made for individual time slices, allowing identification of periods of shelf trapping (e.g., 7.5 - 4 ka), preferential mid-fan deposition from high-density turbidity currents (e.g., 4 - 1.5 ka) and preferential basin-plain deposition from thick turbulent flows (e.g., 1.5 - 0 ka).
DE: 3022 Marine sediments--processes and transport
DE: 3099 General or miscellaneous
DE: 4299 General or miscellaneous
DE: 4558 Sediment transport
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting