Abstract: Pleistocene to Recent Tectonism near Carpinteria, California

DORAN, K. J., K. W. ELLIOTT, W. HAN, L. A. HEBERLE, and J. R. MASSIE

Undeveloped coastal land between Santa Barbara and Ventura California, has recently been rezoned for development. This site, located 2 km east of Carpinteria at the Highway 101 Bailard off ramp, is transected by two, subparallel, ENE-striking, reverse faults. These faults bound a linear topographic "welt" that is 700 m long and 7.5 m high.

Tightly folded shale of the Miocene Monterey Fm. and sandstone of the Pleistocene Santa Barbara Fm. underlie a marine terrace whose basal boulder conglomerate contains fossil boring clams (Pholads) dated at 45 ka. Overlying the conglomerate is 2.5 m of crudely bedded, Late Pleistocene, marine and alluvial sand. Developed on the sand is a bisequent soil having a lower B-C profile, and an upper, A1-A2 profile.

On the southeast side of the site is a northeast-dipping, high-angle, reverse fault that displaces the Monterey Fm., conglomerate, and B-C soil a minimum of 3 m. The upper, A1-A2 horizons do not appear to be offset.

Santa Barbara Fm. is present in boreholes north of the welt, but is absent south of the welt. However, the conglomerate and overlying terrace sands extend across the site and are uplifted by the welt. This indicates that a south-dipping, reverse fault lies along the north side of the welt; displacement on the fault occurred both before the terrace formed, and after the conglomerate was deposited. Therefore, the welt is probably a syntectonic, propagating fold between inward-dipping faults.

Small (mm) scale, north-vergent reverse faults buckle pavement in a parking area and project along the north flank of the welt. These structures, along with aligned ground cracking and anomalous drainage, indicate that at least the northern fault is tectonically active.

Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California