Abstract: A Comparison of Surface and Subsurface Structure,Elwood Oil Field, Santa Barbara County, California

BARTLETT, W. L., Department of Geological Sciences, University of California, Santa Barbara 93106

Elwood oil field in Goleta, California, was one of the first oil fields in California to produce oil commercially from the lower Miocene Vaqueros Formation. Discovered in 1928 by field mapping, the oil field reached its peak production in 1930. The oil field straddles the shoreline, extending eastward onto Ellwood Mesa and westward into the offshore. Recent field work along the beach and sea cliffs of Ellwood Mesa along the eastern part of Elwood oil field yielded detailed surface stratigraphy and structure of the middle Miocene Monterey Formation. Thus, from the surface to a depth of 600 m, the structure of the Monterey Formation in the Elwood oil field is mainly anticlinal, complexly deformed by faulted, chevron folds associated with two major east-west striking, oblique-slip faults. The folds plunge generally eastward and are offset by minor northeast- striking, oblique-slip faults.

By contrast, interpretations from well data and old field maps indicates that the subsurface structural trap in the Vaqueros Formation is a relatively broad, east-west trending anticline with a shallow central saddle, both east and west closure, and a faulted northern flank.

Between the Vaqueros and Monterey formations is the comparatively incompetent Rincon Formation, a mudstone unit that accommodates the disparate styles of the formations above and below it by thickening and thinning. The disharmonic relationship between the relatively simple structure in the subsurface and the complex faulting and folding of the overlying Monterey Formation is a characteristic deformation style in the western Transverse Ranges of southern California.

AAPG Search and Discovery Article #90935©1998 AAPG Pacific Section Meeting, Ventura, California