Abstract: Late Cenozoic Tectonics of the East Ventura Basin, Transverse Ranges, California
Robert S. Yeats, Gary J. Huftile, Leonard T. Stitt
The east Ventura Basin originated in middle Miocene as a rift bounded on the southwest by the Oak Ridge-Simi Hills structural shelf and on the northeast by a granitic ridge parallel to the San Gabriel fault. This fault began accumulating right slip 10 to 12 m.y. ago at a rate of 6 to 9 mm/yr, slowing to 1 mm/yr in the Quaternary. North of the Santa Clara River, rifting ended before deposition of the Miocene-Pliocene Towsley Formation. South of the river, the rift axis shifted southwest toward the Oak Ridge-Simi Hills shelf as the Towsley accumulated against a normal-fault ancestor of the Santa Susana fault. A change to horizontal compression occurred with deposition of the Pliocene Fernando Formation, when the Newhall-Potrero anticline developed as a southwest-verging fault-propagatio fold. The Pico anticline to the southeast and the Temescal and Modelo anticlines to the northwest may have a similar origin. Tectonic inversion and displacement on the southwest-verging Santa Susana fault began 0.5 to 0.6 Ma with appearance of locally derived clasts in the upper Saugus, and continues today, along with the San Cayetano fault farther west. Also active are northeast-verging backthrusts and a segment of the San Gabriel fault which now acts as a northeast-dipping oblique-slip reverse fault. Northeast-trending transverse structures divide the present deformation zone into segments. These are (1) the Modelo lobe of the San Cayetano fault, (2) the northwest Santa Susana fault, Newhall-Potrero anticline, and backthrusts to the north, (3) the Pico anticline flanked by the San Gab iel and Santa Susana reverse faults, and (4) the Sylmar basin.
AAPG Search and Discovery Article #90981©1994 AAPG Pacific Section Meeting, Ventura, California, April 27-29, 1994