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.
AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California