Abstract: A New Model for the Miocene-Pliocene Turbidite System at San Clemente, CA

BUSBY, CATHY J., and HILARIO CAMACHO^*, Department of Geological Sciences, University of California, Santa Barbara, CA 93106; andBEN KNELLER, Department of Earth Sciences, The University of Leeds, LS2 9JT, UK

The lower Capistrano Formation at San Clemente State Beach is used as a field laboratory by university and industry training courses every year. Numerous publications from 1971 tol996 have interpreted the outcrop there as (1) a submarine fan deposit, dominated by (2) numerous narrow channels that migrated laterally with time. We instead interpret the San Clemente State Beach outcrop to represent a single nonfan channel that extended down a low-gradient continental slope. Our detailed photomosaics show that this channel was wide and shallow, not narrow and deep, and it aggraded vertically through time. Siltstone "drapes" within this wide channel record deposition from low-density turbidity currents marginal to the channel axis, concurrent with deposition from high-density turbidity currents along the channel axis. Work in progress on other outcrops of the lower Capistrano Formation in the San Clemente area suggests that the San Clemente State Beach outcrop represents only one of a series of wide and shallow deepwater channels. The slope deposits that intervene between channels lack tne soft-sediment deformational structures typical of moderate- to high-gradient continental slopes. We suggest that a modern analogue to these low-gradient slope channels occurs in the Porcupine Seabight of the European Atlantic margin (Kenyon and others, Oceanol. Acta, 1978). We are using the Capistrano Formation outcrops to develop a predictive model for three-dimensional heterogeneities in nonfan turbidite channels.

AAPG Search and Discovery Article #90935©1998 AAPG Pacific Section Meeting, Ventura, California