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Paleo-Reconstruction of Shelf-Slope Margin Along San Emigdio Mountains, Southern San Joaquin Valley, California

Kim R. Butler

Deformation along the San Emigdio Mountains, California, is characterized by large overthrust sheets that carried Eocene through Miocene nonmarine to shallow marine strata over their deeper marine equivalents. The Pleito thrust has at least 20,000 ft of throw and is the major structural feature of this overthrust belt. The upper plate of the Pleito thrust carries an extensively exposed block of three prograding sequences and, along strike, partially exposes the shelf-slope boundaries of these units. Equivalent changes are observed in the subsurface beneath the overthrust.

Total crustal shortening along this region ranges from 25 to 50%, with most of the shortening taken up by the Pleito thrust. The thrust has a low-angle, ramp-and-glide configuration, but on the south, the strata eventually extend downward into basement. The northern boundary to the deformation belt is the White Wolf and Pioneer fold and thrust structures. These features form a transfer zone, where one structure ends and the other feature begins. The amplitude of these folds can be up to 10,000 ft from crest to trough.

Because of the large overthrust of the Pleito thrust, reservoir rocks are found up to 7 mi south of the fault's surface trace in the lower plate. The buried strata lie south and west of producing fields along the White Wolf fault and the Tejon embayment. The complicated stratigraphic changes combined with the thrust-belt structures require retrodeformable crustal profiles to take into account the facies distributions to model the hydrocarbon potential of this lightly explored province.

AAPG Search and Discovery Article #91035©1988 AAPG-SEPM-SEG Pacific Sections and SPWLA Annual Convention, Santa Barbara, California, 17-19 April 1988.