The Southernmost Branch of the Lucia Canyon System Offshore Central California: New Insights From High-resolution AUV Bathymetry and Chirp Sub-bottom Profiles

The Lucia Canyon system originates from the edge of a narrow shelf approximately 2 km offshore central California. Five of the six feeder canyons to the Lucia Canyon head adjacent to the main Lucia Canyon and merge on the upper slope. The southernmost branch of the Lucia Canyon, informally referred herein as the Lucia Chica, heads approximately 30 km to the south where the shelf is wider; the Lucia Chica merges with the Lucia Canyon farther down the slope (approximately 1800 m water depth) than the more northerly feeder canyons. The Lucia Chica system is more sinuous, less incised, and smaller in width than the other channels of the Lucia Canyon System. The Lucia Chica represents the latest sedimentation in the structurally confined Sur Basin on the continental slope offshore central California. In contrast to the other canyon systems which direct sediment down the slope, the Lucia Chica veers along the slope. The main channel of the Lucia Chica reaches a depocenter in 1000m water depth where it avulses resulting in varying sinuousity of multiple channel segments and complex depositional architectures. In order to study the mid-slope deposition of the Lucia Chica, we recently conducted a high-resolution multibeam bathymetry, chirp sub-bottom profile, and sidescan survey of the Lucia Chica using an Autonomous Underwater Vehicle (AUV) developed by the Monterey Bay Aquarium Research Institute (MBARI). The resulting bathymetry has a lateral resolution of 1m and a vertical precision of 0.3 m, and the sub-bottom profiles achieve penetrations of up to 40 m. These new data have improved interpretation of the complex sedimentation recognized in low- frequency industry 2D seismic-reflection data archived at the USGS and in surface-towed boomer profiles of the Sur Basin. The AUV survey was conducted with the vehicle at 50 m above the sea floor. The varying confinement and relief of the Lucia Chica sinuous channels is buried by 3 to 4 meters of hemipelagic drape. A new, foraminifera 14C calibrated-age date from a vibracore of this hemipelagic layer yields a sediment accumulation rate of 33.4 cm/ka, indicating that the Lucia Chica was last active about 12 ka at the late OIS 2 rising of sea level.