--> Abstract: High-Resolution Spatial and Temporal Patterns of Sand Accumulation on an Active Highstand Submarine Fan in Santa Monica Basin, Offshore California: Implications for Controls of Deep-Marine Sedimentation; #90063 (2007)

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High-Resolution Spatial and Temporal Patterns of Sand Accumulation on an Active Highstand Submarine Fan in Santa Monica Basin, Offshore California: Implications for Controls of Deep-Marine Sedimentation

 

Romans, Brian W.1, William R. Normark2 (1) Stanford University, Stanford, CA (2) United States Geological Survey, Menlo Park, CA

 

The controls on the sediment distribution and evolution of sand-rich deep-marine systems are commonly attributed to a combination of extrinsic factors that include tectonic setting and activity, changes in eustatic and/or relative sea level, and climatic fluctuations. Investigation of modern settings, where these factors are well understood, can provide a test of models for deep-water depositional systems. The Santa Monica Basin is a small (25 x 50 km) basin in the offshore region of the California Continental Borderland that is fed by two rivers, has high-relief topography in the onshore watershed and a narrow continental shelf reflecting active tectonism in the region. Five late Holocene stratigraphic intervals were correlated over the middle and lower fan and most of the basin plain using a grid of high-resolution seismic-reflection profiles (vertical resolution of 0.5 m) with penetration depths of as much as 70 m. The stratigraphy is tied to a radiocarbon-dated core at ODP Site 1015 in the basin plain and confirms that the rate of sand deposition in the last 4,300 years is only slightly less than during the last glacial maximum.

 

This study shows that the bulk of the sand accumulation is in the middle fan area and is characterized by shifting lobe complexes at the mouth of the Hueneme channel. Additionally, precise sediment thickness maps when integrated with a radiocarbon-dated core sequence permit calculation of changing sediment volume with time. Accumulation rates are generally about one cubic kilometer per 100 years but vary by a factor of five during centennial scale intervals, suggesting an underlying climatic and/or tectonic origin.

 

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