Abstract: Structural Model for the Gato Canyon Field, Santa Barbara Channel, California

Edwin B. Edwards, R. G. Heck

Studies of the Gato Canyon field in the northern Santa Barbara Channel show that the structure is a complexly faulted asymmetric anticlinal fold in Monterey and older rocks. The field is cut by a multitude of north-dipping imbricate thrust faults and a north-dipping roof thrust near top Monterey that exhibits a normal rather than reverse sense of offset (back thrust). A south-dipping monocline of Sisquoc and younger rocks lies basinward of the core of the Monterey structure. These features are characteristic of passive roof duplex structures. Passive roof duplex structures develop at thrust fronts where, because of mechanical problems inherent in trying to shorten a thick section overlying a thick, less competent unit, the competent (hanging wall) rocks are uplifted and transported ba k toward the hinterland relative to the footwall rocks.

At Gato Canyon, the passive roof duplex consists of superimposed south-verging thrust slices containing highly deformed Monterey (early to late Miocene), Rincon (early Miocene) and Sespe (Oligocene) rocks creating an antiformal stack. Sisquoc (late Miocene) sediments make up the hanging wall of the roof thrust that marks the upper limit of the antiformal stack, and have been passively uplifted to make room for emplacement of the underlying thrust sheets.

The age of top Monterey in this area is 5.7 (+.1) Ma. Estimated age of initiation of post-Monterey tectonism is about 4.9 Ma. This earliest activity appears to have resulted in only minor structural deformation. Onset of south-vergent thrusting and passive uplift of Sisquoc rocks took place at the end of Sisquoc deposition, about 3.5 Ma, with the major part of structural development occurring between then and top "Repettian" (early Pliocene) around 1.9 Ma. Subsequent structural events have produced a gentle south-dipping monocline in sediments younger than 1.9 Ma.

AAPG Search and Discovery Article #90981©1994 AAPG Pacific Section Meeting, Ventura, California, April 27-29, 1994