Spatial and Temporal Evolution of Sedimentation in Santa Barbara Basin, California, from 1.0 Ma to Present

C. J. Marshall¹, C. C. Sorlien², C. Nicholson², R. J. Behl¹, and J. P. Kennett^2
1California State University, Long Beach, CA, [email protected], [email protected]
²University of California, Santa Barbara, CA, [email protected], [email protected], [email protected]

Isopach maps derived from high-quality grids of seismic reflection profiles document dramatic shifts in location, shape, and accumulation rate of sedimentary depocenters in Santa Barbara Basin during the last 1 Myr. Isopach maps are defined by distinctive sequence boundaries and other stratigraphic horizons identified on deep-penetration industry multichannel seismic (MCS) data, and high-resolution MCS and USGS towed chirp data acquired during 2005 and 2008 research cruises. Horizon ages were assigned based on correlation to the well-dated ODP Site 893, and interpolation between dated tephra layers, biostratigraphic markers, and MIS climate transitions identified from oxygen isotopic analysis. We also used a published 1-Ma horizon. 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, first in two-way travel time (twtt), then converted to depth and volume. Over much of the basin, average sediment accumulation rates (uncorrected for compaction) since 1 Ma are remarkably high (~1.0 to 1.5 m/kyr). Rates were highest between 1 Ma and ~500 ka in the central portion of the Santa Barbara Channel (near ODP Site 893), but then decreased owing possibly to diversion of sediment into Santa Monica Bay with the initiation of the Hueneme fan. Since ~710 ka, most basin sedimentation has been focused within the WNW-ESE-trending offshore trough located between the North Channel and Oak Ridge fault systems. Within this principal depositional trough, greatest sediment accumulation occurs in narrow, km-scale marginal bands adjacent to the two bounding fault systems. Evolution of these depocenters reflects the growth history of faults and folds and related structural loading, subsidence, and the development of seafloor morphology. Shifts in basin depocenters, sedimentation rates, or sediment facies may also be related to changes in bathymetry, relief of the uplifted Santa Ynez highlands, and the size and location of catchment areas for sediment supply.

AAPG Search and Discovery Article #90088©2009 Pacific Section Meeting, Ventura, California, May 3-5, 2009