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Growth Patterns of Deep-Sea Fans Revisited: Turbidite-System Morphology in Confined Basins of the Quaternary Borderland

J. A. Covault and B. W. Romans
Chevron ETC, San Ramon, CA, [email protected], [email protected]

This study characterizes growth and morphologies of late Pleistocene-Holocene turbidite systems and complexes in the southeastern Gulf of Santa Catalina and northern San Diego Trough, offshore southern California. From north to south, the San Mateo, Oceanside, and Carlsbad canyon-channels supplied sediment to the basins. An extensive grid of industry multichannel and USGS high-resolution deep-tow seismic-reflection data show that the late Pleistocene-Holocene basin fill includes eight turbidite systems: three each composing the Oceanside and Carlsbad turbidite complexes and two composing the San Mateo turbidite complex. We determined relative timing of turbidite-system growth phases since Oxygen Isotope Stage 6 from seismic-reflection-based correlations and radiocarbon age dates younger than 45 ka.

Morphologies of turbidite systems and complexes were quantified according to volume, area, maximum thickness, length, and width. There is a positive linear relationship between the ratio of turbidite-system volume to area and maximum thickness. Volumes of sediment sufficient to extend turbidite systems to the margins of their basins resulted in thick systems. Conversely, insufficient volumes resulted in thinner systems. Within each turbidite complex, component systems are progressively more areally extensive and thin. This is most likely a result of progressive turbidite deposition “healing” relatively high-relief bathymetry. The growth and morphologies of turbidite depositional units in the California Borderland and in similar settings, such as the western Gulf of Mexico, are greatly influenced by relatively meager volumes of sediment supplied and receiving-basin confinement, and are distinctively different from longer-lived units in enormous, unconfined ocean basins with sediment supplied from extensive terrestrial drainages. Results of this study provide insights into the distribution and morphology of the largest detrital accumulations on Earth, which can be directly applied to predictive models of turbidite-architecture development in confined receiving basins.

AAPG Search and Discovery Article #90088©2009 Pacific Section Meeting, Ventura, California, May 3-5, 2009