HR: 0830h
AN: OS11A-14    [Abstracts]
TI: Marked Shore-Parallel Variability in Holocene Sediment Thickness Offshore La Jolla, California
AU: * Hogarth, L J
EM: lhogarth@ucsd.edu
AF: Scripps Institution of Oceanography, Vaughan Hall Room #421 University of California San Diego 9500 Gilman Dr SIO 0244, La Jolla, CA 92093-0244 United States
AU: Driscoll, N W
EM: ndriscoll@ucsd.edu
AF: Scripps Institution of Oceanography, Vaughan Hall Room #421 University of California San Diego 9500 Gilman Dr SIO 0244, La Jolla, CA 92093-0244 United States
AU: Babcock, J
EM: jbabcock@ucsd.edu
AF: Scripps Institution of Oceanography, Vaughan Hall Room #421 University of California San Diego 9500 Gilman Dr SIO 0244, La Jolla, CA 92093-0244 United States
AU: Le Dantec, N
EM: nledante@ucsd.edu
AF: Scripps Institution of Oceanography, Vaughan Hall Room #421 University of California San Diego 9500 Gilman Dr SIO 0244, La Jolla, CA 92093-0244 United States
AU: Haas, J
EM: jhaas@ucsd.edu
AF: Scripps Institution of Oceanography, Vaughan Hall Room #421 University of California San Diego 9500 Gilman Dr SIO 0244, La Jolla, CA 92093-0244 United States
AU: Inman, D L
EM: dinman@ucsd.edu
AF: Scripps Institution of Oceanography, CCS Building Room #307 University of California San Diego 9500 Gilman Dr SIO 0209, La Jolla, CA 92037-0209 United States
AU: Masters, P M
EM: pmasters@ucsd.edu
AF: Scripps Institution of Oceanography, CCS Building Room #307 University of California San Diego 9500 Gilman Dr SIO 0209, La Jolla, CA 92037-0209 United States
AB: New CHIRP seismic data indicate that the bathymetry and subsurface structure in the nearshore are not well correlated offshore La Jolla, CA. For example, the thickness of the Holocene transgressive sequence varies along strike in the region from less than 1 m thick offshore Torrey Pines State Reserve in the north to greater than 20 m farther south between the Scripps and La Jolla Canyons. This thickness variability appears to be structurally controlled (i.e., by relief on the transgressive surface). Existing theory and observations show longshore transport of sand in the Oceanside littoral cell occurs from north to south. In the littoral cell sediment is transported by waves and currents and exits the nearshore via the La Jolla submarine canyon system. However, the observed variability in shore-parallel sediment thickness cannot simply be explained by longshore transport. The seismic data, collected in April and November 2002, reveals three areas of relatively thick Holocene sediments: 1) between La Jolla and Scripps canyons, 2) directly north of Scripps Canyon, and 3) within the La Jolla Canyon system on small "inter-canyon highs" or shoals between branches of the canyon. The sediment thickness on the inner shelf systematically thins toward the north away from the canyons. In fact, the observed variability of sediment thickness in the shore-parallel direction (south - north) is larger than that observed cross-shelf (east - west). The spatial correlation of the shoaling transgressive surface and the offshore bathymetric high, together with a left-lateral jog in the right-lateral Rose Canyon Fault in this region, suggest a tectonic control on the shelf morphology that in turn controls Holocene sediment thickness offshore of La Jolla. Convergence as a result of fault geometry engenders uplift and shoaling of the transgressive surface, which also has a bathymetric expression offshore. If correct, this would imply that processes such as wave climate control sediment transport and short-term deposition, but long-term accumulation is tectonically controlled by strain accommodation along the Rose Canyon Fault system. Mount Soledad to the south is another example of pop-up structure associated with a left-lateral jog along the Rose Canyon Fault. We will use the depth to the transgressive surface and the overlying Holocene sediment thickness as inputs to our model to determine the relative importance of the multiple forcing mechanisms on nearshore sediment transport and distribution. We ultimately intend to use this modeling to illuminate the relationship between short-term processes and strata formation.
DE: 4546 Nearshore processes
DE: 4558 Sediment transport
SC: Ocean Sciences [OS]
MN: 2005 Joint Assembly