INFLUENCE OF SEDIMENT ROUTING MORPHOLOGY AND GRAIN-SIZE PARTITIONING ON DEEP-MARINE STRATIGRAPHIC RECORDS: INSIGHTS FROM QUATERNARY SYSTEMS OF SOUTHERN CALIFORNIA

The morphology and history of sediment routing influences the composition and grain-size distribution of clastic detritus delivered to depositional basins. The morphology of sediment-routing systems evolves as a result of external environmental change in concert with autogenic processes such as delta-lobe switching. Here, we combine latest Pleistocene to Holocene records of the terrestrial-to-marine sediment flux history of the Western Transverse Ranges of Southern California with depositional records from offshore basins to study the influence of sediment-routing evolution on preserved stratigraphy. The Santa Barbara Basin (SBB) and Santa Monica Basin (SMB) are both fed sediment from the Santa Clara River and adjacent catchments in the Western Transverse Ranges. Cosmogenic radionuclide analyses of sand samples collected near river-catchment outlets constrain millennial-scale denudation rates and sediment delivery to the offshore sinks. Sediment cores recovered from deep Ocean Drilling Program (ODP) boreholes in SBB and SMB combined with regional grids of 2D seismic-reflection data allow for the construction of a deep-marine chronostratigraphic framework since ~30 ka.

Both marine sinks are characterized by terrigenous sediment deposition over the past ~30 ka; however, SBB is mud-dominated whereas SMB contains mud and thick-bedded (>50 cm) fine- to medium-grained turbidite sand beds. The routing of coarse-grained material into SMB persisted through significant climatic and sea-level change of the past ~30 ka. Catchment-integrated denudation rates compared with depositional rates indicate that the terrestrial segments of the system store negligible amounts of sediment at millennial timescales and that post-LGM transgressive erosion may have contributed significant volumes of sediment to SMB.