MAGNETIC STRATIGRAPHY AND TECTONIC ROTATION OF THE MIDDLE PALEOCENE SAN FRANCISQUITO FORMATION, TRANSVERSE RANGES, CALIFORNIA

The San Francisquito Formation consists of about 4000 m of deep-marine to shallow-marine sandstones and shales, which crop out in many places in the Transverse Ranges. It ranges in age from latest Cretaceous to late Paleocene, although no single section spans that entire interval of time, and most sections are chopped up by faults. We sampled the most complete available section (2000 m of middle-upper Paleocene members D, E, and F of Kooser, 1982) along Elizabeth Lake Canyon road. After removal of overprints, a stable remanence held in magnetite was obtained. The uppermost part of member D, and all of members E and F were reversed in polarity. They yield a mean direction of D=204.9, I=-51.1, a95=9.8, which suggests about 30 degrees of clockwise tectonic rotation, consistent with other results in this part of the Transverse Ranges. The inclination is not significantly different from present inclination, suggesting minimal northward translation of these rocks. Based on the presence of middle Paleocene molluscs (including the index taxon Turritella peninsularis), we correlate the reversed strata of members D-E with magnetic Chron C26r (58.0-61.0 Ma), although it is possible it correlates with Chron C27r (61.3-62.5 Ma).