SEDIMENTATION IN AN ACTIVE FOLD AND THRUST BELT, SANTA BARBARA BASIN, CALIFORNIA: SPATIAL AND TEMPORAL EVOLUTION OF SEDIMENTATION FROM 1 MA TO PRESENT
The prolific east-west-trending Santa Barbara basin is part of an active fold and thrust belt within the Western Transverse Ranges province. Isopach maps defined by distinctive sequence boundaries and other stratigraphic reference horizons identified on deep-penetration industry multichannel seismic reflection (MCS) data, and high-resolution MCS and USGS towed chirp data document dramatic shifts in location, shape, and accumulation rate of sedimentary depocenters in Santa Barbara Channel during the last 1 Myr. Horizon ages were assigned based on correlation to well-dated ODP Site 893, a previously recognized 1-Ma horizon derived from industry well logs, and interpolation between dated tephra layers, biostratigraphic markers, and isotope stage transitions identified from recovered cores that sample strata back to ~700 ka. Horizons were interpreted and correlated across the eastern and central basin, extending beyond ODP Site 893, then gridded. Isopach thickness maps were created from the gridded horizons, using a 3D velocity model based on approximately two dozen velocity surveys.
Sedimentation rates were highest between 1 Ma and ~790 ka, but then decreased owing possibly to the initiation of subsidence of the crest of the anticline connecting Anacapa Island to the Santa Monica Mountains, resulting in the initiation of the Hueneme fan. Since ~710 ka, sedimentation has been focused within the WNW-ESE-trending offshore footwall basin located between the North Channel and Oak Ridge fault systems. Continued uplift across these two bounding fault systems and further development of the structurally complex northern shelf and south-bounding Mid-Channel anticline is reflected in the 3-dimensional geometry and spatial pattern of sedimentation and constriction of the main central trough. Evolution of these depocenters thus reflects the growth history of faults and folds, and related subsidence, while changes in sedimentation rates reflect the diversion of sediment sourced from the Santa Clara River.