SEDIMENTATION IN AN ACTIVE FOLD AND THRUST BELT, SANTA BARBARA BASIN, CA: SPATIAL AND TEMPORAL EVOLUTION OF SEDIMENTATION FROM 1.0 MA TO PRESENT

The offshore Santa Barbara Basin (SBB) fold and thrust belt provides an excellent opportunity to study the relation between tectonics, accommodation space, and sediment supply on basin stratigraphy in a dynamic continental margin setting. It also provides constraint on the timing and impact of key tectonic events on the Quaternary southern Californian margin. Seismic stratigraphy and isochore maps reveal shifts in location, shape, and accumulation rate of sedimentary depocenters in SBB during the last 1 Myr and a major reduction of sediment supply at ~500 ka that likely marks major diversion of the Santa Clara River to the Santa Monica Basin and inception of the Hueneme submarine fan. Distinctive sequence boundaries and other stratigraphic horizons identified on deep-penetration industry marine multichannel seismic (MCS) reflection data, and high-resolution MCS and USGS towed chirp data acquired during 2005 and 2008 research cruises provide the basis for stratigraphic and isochore analysis. Horizon ages are assigned by correlation and interpolation between ODP Site 893, a previously recognized 1-Ma horizon, dated tephra layers, biostratigraphic markers, and MIS climate transitions identified from oxygen isotopic analysis of recovered cores that sample strata back to ~700 ka. Isochore maps were created from gridded horizons, first in two-way travel time, then converted to depth and volume. Sedimentation rates were highest between 1 Ma and ~500 ka, but then decreased sharply with a marked change in stratal architecture. Since ~710 ka, sedimentation was localized within a WNW-ESE-trending offshore trough located between the North Channel and Oak Ridge fault systems and westward into the central basin. Continued uplift across these two bounding fault systems and development of the structurally complex northern shelf and south-bounding Mid-Channel anticline is reflected in the 3 dimensional geometry and spatial pattern of basin sedimentation and constriction of the main central trough. Evolution of these depocenters thus reflects the growth history of faults and folds, and related subsidence and development of seafloor morphology, while changes in sedimentation rates reflect either an unlikely decrease in the sediment load of the Santa Clara River or its tectonic divergence and initiation of the Hueneme Fan.