Distribution of Surface Sediments from the Southern California Continental Borderlands

L. S. Conner and D. A. Dunn
University of Southern Mississippi, Hattiesburg, Mississippi

Based on sedimentary parameters a delineation of the geographic distribution of sediment types and provinces was determined for the Southern California Continental Borderlands. Data were analyzed for 272 sea bottom sediment samples taken from 44 gravity cores.

Subaqueous bottom sediments in the Borderlands are silty clays, with only minor deposits of sand-silt-clay and clayey silt. One core was taken off the west end of Santa Cruz Island and contained 74.9% sand-sized grains. Cores with higher (10-50%) sand content were found near the offshore islands of Santa Cruz, San Nicholas, Santa Barbara, Santa Catalina, and from atop seamounts in the Borderlands (Lasuen Knoll). Cores primarily taken in the basins of Santa Monica and Santa Catalina were of “Low-clay” content, <50%. Similar cores, though with higher-sand sediments, were obtained from near shore areas and atop shallow-water submarine ridges that separate northwest-southeast trending basins within the Borderlands. Cores of “Low-silt” content, <30% silt, represent a northeast-southwest trend that extends sequentially from Newport Canyon across the southern Santa Catalina Basin to San Clemente Island, and the deeper-water San Nicolas and Tanner Basins that are distal to the mainland coastline. There is no apparent relationship between sediment percentages and water depth. Sediment type appears to be influenced by proximity to a shoreline and by the reworking of deposits atop shallow-water submarine ridges lying between basins.

AAPG Search and Discovery Article #90032©2004 GCAGS 54th Annual Convention, San Antonio, Texas, October 10-12, 2004