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Abstract: New Digital Geologic Map of the San Rafael Mtn. 7.5 Minute Quadrangle (Santa Barbara County, CA) and a New Interpretation of the Camuesa Fault

STANLEY, R., U. S. Geological Survey, Menlo Park, CA; J. VEDDER, U.S. Geological Survey, Menlo Park, CA

A digital (ARC/INFO), 1:24,000-scale geologic map of the San Rafael Mtn. quadrangle was compiled from older mapping, new photogeologic interpretations, and new field investigations. Geologic features shown on the map include (1) thick sequences of unnamed Upper Cretaceous bathyal marine sandstone, mudstone, and conglomerate; (2) an unnamed Miocene sandstone unit that rests in angular unconformity on Mesozoic rocks, contains molluscan fossils of the "Temblor Stage," and yielded a 87Sr/86Sr minimum age of 19.7 +0.1 Ma on molluscan shell material; (3) Miocene Monterey Formation composed of siliceous fine-grained strata with sandstone interbeds and Saucesian, Relizian, and Luisian benthic foraminifers; (4) Miocene volcaniclastic rocks and several small diabase intrusions of presumed Miocene age; (5) the apparent western termination of the Big Pine fault, North Branch, near a diabase dike that intrudes Upper Cretaceous strata about 2.5 km south of San Rafael Mtn.; and (6) the laterally persistent Big Pine fault, South Branch, a N-dipping reverse fault that separates moderately deformed Upper Cretaceous strata on the north from overturned and intensely folded Monterey Formation on the south.

Near Santa Cruz Creek in the southern part of the quadrangle, the Camuesa fault has a meandering trace but generally strikes NW and dips SW. This fault separates the Franciscan Complex and associated serpentinite on the SW from overturned argillite and sandstone of the Jurassic and Lower Cretaceous(?) Espada Formation on the NE. About 2-3 km NW of Santa Cruz Creek near Peachtree Canyon, the Camuesa fault appears to be truncated by a WNW-striking, NNE-dipping angular unconformity at the base of the unnamed Miocene sandstone unit.

 

 

AAPG Search and Discovery Article #90911©2000 AAPG Pacific Section and Western Region Society of Petroleum Engineers, Long Beach, California