Carbon and Nitrogen Stable Isotopes of Sedimentary Organic Matter From the Santa Monica Basin

The California Continental Borderland is a tectonically active area, characterized by 23 basins located at different distances from sources of terrigenous sediment, local intermittent rivers and coastal upwelling zones and thus displaying different sedimentation sources and processes. The Santa Monica Basin (938m depth), a Southern California Inner Borderland basin, is a closed basin and fed by the Santa Barbara littoral cell. During sea level lowstands, the littoral cell is inactive and the canyon was fed directly by the Santa Clara River, which is presently not dammed and is known to be capable of generating hyperpycnal flows during ENSO related floods. 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. Samples of the drill core from the top 60 meters of sediment was obtained and analyzed at ~50cm intervals to obtain a high-resolution record of organic matter distribution and isotope record within the different intervals. The δ13C values of total organic carbon (TOC) and δ15N values, as well as the C/N ratio were obtained and used to differentiate between marine and terrestrial sediment inputs to the basin. Additionally, the TOC data may indicate if highstand and lowstand deposits show significant compositional differences.