Oxygen Isotope Stratigraphy and Carbon and Nitrogen Isotopes of Sedimentary Organic Matter of ODP Site 1015, Santa Monica Basin: Proxies for Sediment Origin.

The Santa Monica Basin (938m depth), a Southern California Inner Borderland basin, is a closed basin, fed by the Santa Barbara littoral cell. Ocean Drilling Program (ODP) Site 1015 was drilled in the basin plain area and penetrated through a 150-meter late Quaternary sedimentary section. The sediments recovered at Site 1015 are grouped into a single lithostratigraphic unit consisting of three alternating sedimentary units: medium- to fine-grained sand, silty clay, and nanofossil clay. We present oxygen, carbon and nitrogen isotope data from the top 120m of the core. The oxygen data provide a stratigraphic and climatologic context for the carbon and nitrogen values of the three sediment types and allow for a correlation between the origin of the sediment based on the source of the organic matter and climatic and hydrographic fluctuations. Intervals of climatic change (increase in sea level) and increased storm activity are characterized by numerous beds of sediment barren of microfossils and rich in Pinus sp. pollen and corresponding to higher (terrestrial) C isotope signatures. The combined oxygen, carbon, nitrogen, pollen and microfossil data suggest that during times of low and rising sea level the basin was fed from a mainly terrestrial source, likely the Santa Clara river.