Coastal sedimentation

Abstract

The distribution and dispersal patterns of sand-size particles has been investigated along a portion of the California coast south of San Francisco. The effectiveness of long-term, net littoral transport in the area has been evaluated through hydrodynamic considerations and through considerations of the dispersal patterns of sand. The distribution and dispersal patterns presented are based upon results of a vector analysis of the raw heavy mineral da ta, Four sedimentary provinces have been delineated. One blankets the continental shelf in the area studied and represents premodern sediment deposited during the last major regression and transgression of the sea. The remaining three represent Holocene deposits on the pre-modern sediment. The latter are only of local extent and are contiguous with their sources. These mineralogical changes along the coast preclude the existence of net littoral transport under present conditions. This conclusion agrees well with that predicted by hydrodynamic considerations. The contrasting picture presented by the widespread, relatively homogeneous pre-modern province and the localized, varied Holocene deposits is pximarily due to changes in littoral transport attendant with the rise in sea level to its present position.