Tectonic Influence on the Generation of Cyclic Steps by Turbidity Currents Offshore San Mateo Point, Southern California Borderland

H. F. Ryan¹, J. A. Covault², H. J. Lee¹, C. K. Paull³, and D. W. Caress^3
1U. S. Geological Survey, Menlo Park, CA, [email protected], [email protected]
²Chevron ETC, San Ramon, CA, [email protected]
³Monterey Bay Aquarium Research Institute, Moss Landing, CA, [email protected], [email protected]

Net-erosional cyclic steps and net-depositional sediment wave fields are interpreted from very high-resolution bathymetry and seismic-reflection profiles offshore of San Mateo Point in the southern California borderland between Los Angeles and San Diego. These bedforms were likely created by turbidity currents flowing down the informally named San Mateo channel during glacio-eustatic sea-level lowstands. Folds at the seafloor associated with the offshore San Mateo thrust fault influenced the formation of the cyclic steps and sediment waves by creating abrupt differences in both bed slope and bottom roughness.

A large turbidite complex has formed at the distal end of the San Mateo channel despite the fact that the drainage basin near San Mateo Point is relatively small and there is no obvious well-developed river-submarine canyon system. Near San Mateo Point, the drainage basin is dominated by relatively weak Tertiary sedimentary rocks that are uplifting at rates as high as 0.2 mm/yr (Grant et al., 1999). These rocks, which include the Capistrano Formation, are prone to extensive landsliding and may provide the sediment source for the turbidity currents. As a result of the uplift and subsequent erosion of sediment within a steep, localized drainage basin, the San Mateo submarine channel system has effectively transported significant volumes of sediment from the continent to deeper waters during sea-level lowstands.

AAPG Search and Discovery Article #90088©2009 Pacific Section Meeting, Ventura, California, May 3-5, 2009