Abstract: Extension of the Western Transverse Ranges Zone of Cenozoic Block Rotations North of the Santa Ynez Fault

Katherine J. Whidden, Steve P. Lund, David J. Bottjer

New paleomagnetic data from the region north of the Santa Ynez fault and south of the Big Pine fault shows that this area has been rotated approximately 90°. This region is interpreted to be an extension of the western Transverse Ranges block of 90° (clockwise) rotation defined by Luyendyk and co-workers. Paleomagnetic results are from 29 Class I (alpha 95<20°, good characteristic remanence) and Class II (alpha 94>20°, good characteristic remanence) sites collected from 5 localities. Samples were collected from the Juncal Shale, Cozy Dell Shale, and Matilija Sandstone of middle Eocene age and from shales of the Gaviota-Sacrate Formation of late Eocene age. The middle Eocene samples had a low blocking temperature remanence interpreted to be goethite, and a hig blocking temperature (>600°) characteristic remanence interpreted to reside in hematite. The late Eocene samples also had the low blocking temperature goethite overprint, and a characteristic remanence with a blocking temperature between 500° and 550°, interpreted to be magnetite. The results show a clockwise rotation of 70° to 90°.

Reconstruction of this extended rotated domain indicates a western source for the Juncal and Matilija formations. Paleocurrents in these units show a northerly source, which becomes a westerly source when rotated. This western source reflects large-scale uplift in the distal fore-arc/accretionary prism region of the convergent margin.

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