EP12A-04
Linking Slope Sedimentation, Gradient, Morphology, and Active Faulting: An Integrated Example from the Palos Verdes Slope, Southern California Borderland

Monday, 14 December 2015: 11:15
2005 (Moscone West)
Katherine L Maier1, Daniel S Brothers1, Charles K Paull2, Mary McGann3, David W Caress2 and James E Conrad4, (1)US Geological Survey, Santa Cruz, CA, United States, (2)Monterey Bay Aquarium Research Institute, Watsonville, CA, United States, (3)USGS Pacific Coastal and Marine Science Center Menlo Park, Menlo Park, CA, United States, (4)USGS Western Regional Offices Menlo Park, Menlo Park, CA, United States
Abstract:
Seafloor gradient variations associated with restraining and releasing bends along the active (1.6–1.9 mm/yr) right-lateral Palos Verdes Fault appear to control Holocene sediment thickness, depositional environment, and morphodynamic processes along a section of the continental slope offshore Los Angeles, California. Autonomous underwater mapping vehicle (AUV), remotely operated vehicle (ROV), and shipboard methods were used to acquire a dense grid of high-resolution chirp profiles (150 m line spacing; 11 cm vertical resolution), multibeam bathymetry (2 m grid), and targeted sediment core samples (<2 m length). Detailed interpretation of Holocene deposits in the chirp profiles combined with radiocarbon dating and laser particle-size analyses allow correlation of Holocene sediment thickness and seafloor gradient with sediment gravity flow deposits. Holocene down-slope flows appear to have been generated by mass wasting processes, primarily on the upper slope (~100–200 m water depth) where shipboard multibeam bathymetry reveals submarine landslide headwall scarps in a region that has been isolated from terrigenous sediment sources throughout the Holocene. Submarine landslides appear to have transformed into sandy and organic-rich turbidity currents that created up-slope migrating sediment waves, a low relief (<5 m) fault-bounded channel, and a series of depocenters. A down-slope gradient profile and a Holocene isopach down-slope profile show that the primary depocenter occurs within a small pull-apart basin associated with a decrease in seafloor gradient of ~1.5°. Holocene sediment-flow deposits vary in number, thickness, and character with subtle changes in seabed gradient (<0.5°) and depositional environment. These results help quantify morphodynamic sensitivity to seafloor gradients and have implications for down-slope flow dynamics, deep-water depositional architecture, Holocene sediment, nutrient, and contaminant transport, and turbidite paleoseismology along other margins.