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Description
The geology, stressing Late Quaternary sediment over-burden, and hydrocarbon seep activity were mapped offshore Santa Barbara, California. Investigation of a 400-square km area included interpretation of approximately 365 km of seismic reflection profiles and data from approximately 4,000 jet, dart, and core samples. The geologic structure consists of a southerly-dipping homocline which was formed during Early Pleistocene and extends to the southern foothills of the Santa Ynez Mountains. Middle Pleistocene tectonism caused by north-south compression deformed the homocline by superimposing folds and high-angle faults which parallel the main tectonic structural trend of the Northern Borderland and Western Transverse Ranges. Approximately 1.3 x 109 m3 of Late Quaternary sediment occurs as a thin discontinuous veneer on the continental shelf in the study area. The Late Quaternary sediment distribution was found to be directly influenced by bedrock topography and indirectly by glacio-eustatic effects, tectonics, and the hydraulic regime. Sediments were found to thin along topographic highs related to such structures as up-thrown fault blocks and anticlinal crests (Mesa, Rincon, and Red Mountain Anticlines). Increase in sediment thickness is confined to synclinal troughs (Carpinteria Syncline), bedrock depressions (paleofluvial channels), faulted and down-dropped blocks, and dammed shoreward of topographic highs associated with structures such as anticlines (Rincon Anticline, Red Mountain Anticline). Hydrocarbon seeps are still active on the continental shelf in the study area. Recorded seeps from historical industry data and those interpreted from high resolution profiles were found to correlate with underlying geologic structure and variations in thickness of unconsolidated sediments. Approximately 80% of the 312 recorded seeps are found within 200 m of a mapped major fold axis or fault. Most seeps are also found in areas with less than 10 m of unconsolidated sediment overburden.
