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The AAPG/Datapages Combined Publications Database
CSPG Special Publications
Abstract
Sediment Source, Supply and Dispersal
Sedimentology of the Mainland Nearshore Region of Santa Barbara Channel, California
Abstract
Sediment is introduced to the mainland shelf of Santa Barbara Channel from river discharge at either end. A strong longshore drift system transports relatively coarse-grained sediment around Point Conception at the western end of the channel and moves it eastward along the coast. Several coastal promontories tend to cause deflection of some of this sediment load to the middle and outer shelf. Some fine-grained sediment continues to be transported eastward as a suspension in the surface water layer of the nearshore zone, whereas the coarser grained sediment that is moved offshore as bed load, is subsequently transported westward by prevailing bottom currents in the middle and outer shelf. Alternating areas of lower and higher Holocene sediment accumulation coincide with coarse-grained and fine-grained surficial sediment types, respectively. The total volume of Holocene sediment on the shelf is about 5 × 109 m3, with an average thickness of 8.4 m. The overall areal distribution of surficial sediment consists of 24% sand, 33% silty sand, 21% sandy silt, 18% clayey silt, and 4% silt. Organic carbon and sulfur derived from offshore petroleum seeps is incorporated in the bottom sediment and serves as a tracer for determining transport pathways. The interaction of a persistent longshore drift to the east, coastal promontories, and an offshore current system that flows west and east from the central area off Coal Oil Point imposes a strong imprint on the transport of sediment derived from intermittent river discharge. These conditions result in the winnowing of sediment during transportation, in some sediment accumulation in structural and erosional depressions, and a dominant transport of material from the nearshore zone to the adjacent offshore basin.
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