aFine-Scale Relief on The Floor of Upper Redondo Fan Valley: Multibeam Bathymetry And Chirp Reflection Profiles from The MBARI Mapping AUV in San Pedro Basin, Offshore Southern California

Normark, William R.¹, C. K. Paull², D. W. Caress³, W. Ussler³, R. Keaton³, R. Sliter⁴ (1) United States Geological Survey, Menlo Park, CA (2) Monterey Bay Aquarium Research Institute, Moss Landing, (3) Monterey Bay Aquarium Research Institute, Moss Landing, CA (4) U.S. Geological Survey, Menlo Park, CA

Establishing modern analogs for turbidite reservoirs has been difficult as a result of limited techniques for obtaining outcrop-scale data, e.g., at scales of one meter for sandy facies in deep water. Erosional and depositional bedforms at outcrop scale were imaged on the floor of the upper Redondo fan valley using the Autonomous Underwater Vehicle (AUV) developed by the Monterey Bay Aquarium Research Institute (MBARI). The Mapping AUV obtained high-resolution multibeam bathymetry (vertical resolution of 0.3 m and horizontal footprint of 1.5 m at 100 m survey altitude) and chirp seismic-reflection profiles (vertical resolution of 0.1 m) across the channel floor in water depths of 600 m to 700 m.

The one-meter contour interval for the bathymetry generated by the Redondo survey is unprecedented in its detail and provides key insights into processes operating along turbidity-current channels. Distinct trains of large scours with widths ranging from tens to a few hundred meters and depths of 20 m are common on the fan valley floor. Some of the scour features are mud draped, and vibracores obtained with the MBARI ROV Tiburon show that the shallowest sand bed under the mud drape was deposited about one kya. If observed in cross section only, these scours would probably be misidentified as a thalweg channel. Flow stripping at a sharp bend in the most recently active (e.g., no mud drape) channel within the Redondo fan valley has formed transverse sediment waves with 10 m heights and wavelengths from 100 to 250 m.