Structural Transect Across Ventua Basin and Western Transverse Ranges

Jay S. Namson

A retrodeformable cross section that integrates surface and subsurface data across the Ventura basin and western Transverse Ranges illustrates the structural style and evolution of Oligocene to Holocene age structures. Three deformational events are recognized: Oligocene to early Miocene compression, late Miocene through Pliocene normal faulting, and Pleistocene to Holocene compression. Oligocene to early Miocene compression caused uplift and formation of a large antiform north of the Santa Ynez fault in the central part of the range. This antiform is interpreted to be a ramp-related fold associated with movement on a southwest-verging blind thrust fault. Late Miocene through Pliocene age normal faulting along the Oak Ridge fault formed the southern boundary of the Ventur basin. The basin formed by simple block rotation along the normal fault and was filled by up to 6 km of Pliocene and Pleistocene clastic sediment. During Pleistocene to Holocene compression, the Ventura basin and western Transverse Ranges were deformed by both north- and south-verging thrust faults and related folds. The Ventura Avenue anticline is interpreted to be the result of imbricate thrust faulting in the Rincon and Monterey formations. Along the Oak Ridge trend, thrust-related folds rotated and reactivated the late Miocene and Pliocene age normal faults. A restoration of the regional transect documents 34% or 35 km of shortening by thrusting and folding during the Pleistocene to Holocene phase of compression.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.