Peter W. Barnes

Holocene Sedimentation in Tanner Basin, California Continental Borderland

Piston cores collected from Tanner Basin, an outer basin of the California Continenta Borderland, record evidence for hemipelagic and “turbidite” sedimentation that is in accord with Curray9s model for a Holocene sea-level rise. Decreasing amounts of terrigenous sediments were contributed as rising sea level flooded previously exposed banks and shelves and reduced stream gradients on land. Radiocarbon and paleontologic dates provide markers for the computation of sedimentation rates which show that the contributions of biogenic and terrigenous fines have been essentially constant for about the past 7500 years, reflecting a greatly reduced rate of sea-level rise. Carbonate contributions, primarily from foraminifera, appear to have been constant, or nearly so, over the past 12,000 years. This reflects little change in the oceanographic circulation over the outer borderland. Data show that the Holocene record is continuous over the entire basin floor, although variable in absolute magnitude, and that the thickness of hemipelagic material is related to topography. The older concept of a rain of particles producing a uniform veneer without regard to topographic irregularities is not supported, but rather, fines are laterally transported and conform to bathymetry in the same fashion that relief controls the discontinuous “turbidite” sedimentation.