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Postglacial sedimentary record of the Southern California continental shelf and slope, Point Conception to Dana Point

By
Christopher K. Sommerfield
Christopher K. Sommerfield
College of Marine and Earth Studies, University of Delaware, Lewes, Delaware 19958, USA
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Homa J. Lee
Homa J. Lee
U.S. Geological Survey, MS 999, 345 Middlefield Road, Menlo Park, California 94025, USA
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William R. Normark
William R. Normark
U.S. Geological Survey, MS 999, 345 Middlefield Road, Menlo Park, California 94025, USA
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Published:
January 01, 2009

Sedimentary strata on the Southern California shelf and slope (Point Conception to Dana Point) display patterns and rates of sediment accumulation that convey information on sea-level inundation, sediment supply, and oceanic transport processes following the Last Glacial Maximum. In Santa Monica Bay and San Pedro Bay, postglacial transgression is recorded in shelf deposits by wave-ravinement surfaces dated at 13–11 ka and an upsection transition from coastal to shallow-marine sediment facies. Depositional conditions analogous to the modern environment were established in the bays by 8–9 ka. On the continental slope, transgression is evidenced in places by an increase in sediment grain size and accumulation rate ca. 15–10 ka, a consequence of coastal ravinement and downslope resedimentation, perhaps in conjunction with climatic increases in fluvial sediment delivery. Grain sizes and accumulation rates then decreased after 12–10 ka when the shelf flooded and backfilled under rising sea level. The Santa Barbara coastal cell contains the largest mass of postglacial sediment at 32–42 × 109 metric tons, most of which occurs between offshore Santa Barbara and Hueneme Canyon. The San Pedro cell contains the second largest quantity of sediment, 8–11 × 109 metric tons, much of which is present on the eastern Palos Verdes and outer San Pedro shelves. By comparison, the mass of sediment sequestered within the Santa Monica cell is smaller at ~6–8 × 109 metric tons. The postglacial sediment mass distribution among coastal cells reflects the size of local fluvial sediment sources, whereas intracell accumulation patterns reflect antecedent bathymetric features conducive for sediment bypass or trapping.

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GSA Special Papers

Earth Science in the Urban Ocean: The Southern California Continental Borderland

Homa J. Lee
Homa J. Lee
U.S. Geological Survey, Menlo Park, California, USA
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William R. Normark
William R. Normark
U.S. Geological Survey, Menlo Park, California, USA
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Geological Society of America
Volume
454
ISBN print:
9780813724546
Publication date:
January 01, 2009

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