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ABSTRACT: Displacement Transfer Between Surface Reverse Faults and Blind Thrusts, Ventura Basin, California

Gary J. Huftile

Techniques of balancing structural cross sections are found to be applicable to structures in the western Transverse Ranges. Horizontal

shortening on structures that are detached from the lower crust at the brittle-ductile transition must be accommodated on surface reverse faults or folds related to blind thrusts. In a mature oil basin like the Ventura basin, future oil exploration targets could depend on the understanding of blind thrusting and related structures. The Red Mountain and San Cayetano faults form the northern border of the Ventura basin. Movement expressed near the surface on the Red Mountain fault is transferred, across a tear fault at its eastern end, to a south-vergent blind thrust beneath Ojai Valley and Sulphur Mountain. From Ojai Valley east to Sespe Creek, horizontal shortening is taken up on both the San Cayetano fault and the blind thrust system. Much of the folding related to the blind thrust i overthrust by the San Cayetano fault and is expressed at the surface only by vertical to overturned bedding of Pliocene strata in the footwall block of the San Cayetano fault. East of Sespe Creek, across a tear fault, shortening is entirely taken up on the San Cayetano fault.

To the south, horizontal displacement is transferred from the Oak Ridge fault basinward to the Rincon-Ventura Avenue fold belt along a decollement in Miocene mudstones; oil is produced from both structural trends.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990