Print this pageAAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Examining Deep-Water Channel-Levee Development with High-Resolution Seafloor Data: Insights from the Lucia Chica System, Offshore Central California
(1) Dept. of Geological Sciences, Stanford University, Stanford, CA.
(2) Chevron Energy Technology Company, San Ramon, CA.
(3) Monterey Bay Aquarium Research Institute, Moss Landing, CA.
(4) U.S. Geological Survey, Menlo Park, CA.
The Lucia Chica, a tributary channel system of the Lucia Canyon, offshore central California, was imaged using the Monterey Bay Aquarium Research Institute’s (MBARI) Autonomous Underwater Vehicle (AUV) in order to investigate seafloor and subsurface morphologies associated with a low-relief channel-levee system in ~1000 m water depth. While processes of initial channel and levee development are well established in fluvial settings, detailed examples are lacking for deep-sea systems. The majority of previously investigated deep-water channel-levee systems are much larger than the channels imaged in the Lucia Chica, and the initial deposits of these larger systems are either eroded, compacted, or below the resolution of available imaging. In this dataset, the unprecedented high-resolution multibeam bathymetry (1 m lateral resolution) and chirp sub-bottom profiles (11 cm vertical resolution) reveal a series of avulsed channels with varying sinuosity, relief, continuity, and levee morphologies over an area of ~70 km2. Sediment packages and erosional surfaces associated with the channels and levees are correlated between chirp profiles and the multibeam bathymetric image to determine the sequence of channel-levee development. In the Lucia Chica, channels appear to have initiated as trains of scours that eventually coalesced into continuous channel thalwegs carved by erosional turbidity currents. Initial turbidity current flows in the youngest channels eroded and bypassed the study area, creating scours which align down-slope. Continued channel incision and stepped lateral migration led to the development of terraces, complex levee stratigraphy, and morphologies associated with inner and outer bends of sinuous channels. The inner bend levee stratigraphy indicates that the channel position migrated in discrete shifts, as opposed to continuous channel migration associated with lateral accretion. Overbank sediments aggraded on the terraces as the thalweg incised and moved laterally to a new channel position. Later flows, stripped from the youngest channel, were deposited in avulsed channels and overbank areas. These flows reactivated most of the avulsed channels but unevenly filled the oldest channel, leaving a train of elongate depressions on the seafloor. Results from this high-resolution examination of channel-levee morphology provide an unprecedented improvement in understanding of deep-water channel migration and levee development.