Highstand Fans And The
Myth Of Accommodation Space: The Sand Is Just in Somebody Else’s Deep-water
Backyard in The California Borderland
Covault, Jacob A.1,
William R. Normark2, Stephan A. Graham1 (1) Stanford
University, Stanford, CA (2) United States Geological Survey, Menlo Park, CA
Contrary to traditional sequence stratigraphic models, lowstand
fans are only part of the turbidite depositional
record, and this analysis reveals that a comparable amount of coarse clastic sediment has been deposited in California borderland deep-water
basins regardless of eustatic sea-level position.
Sedimentation rates and periods of active sediment transport for deep-water turbidite systems contributing to the southeastern Gulf of
Santa Catalina and San Diego Trough have been determined for the last 40 ky using an extensive grid of high-resolution and industry multichannel seismic-reflection data. A regional
seismic-reflection horizon (approximately 40 ka) has been correlated across the
work area using radiocarbon age dates from the Mohole borehole and USGS piston
cores. This study focused on the deposits fed by (from north to south) the Oceanside, Carlsbad, and La Jolla canyons within the Oceanside littoral cell. The Oceanside system has contributed
sediment to San Diego Trough from 40 ka to 13 ka, and the Carlsbad system from 30 ka to 10
ka. The La
Jolla
system was active over two periods, from approximately 75 ka to 37 ka, and from
19 ka to the present. One or more of these turbidite
systems have been active regardless of sea-level position. Shelf width between
the canyon-head and the littoral zone is the primary control on turbidite-system activity. For example, highstand
fan deposition occurs when a majority of the sediment within the Oceanside littoral cell is
intercepted by one of the canyon heads, presently La Jolla Canyon.