Magnetic stratigraphy and tectonic rotation of the Middle Eocene Matilija Sandstone and Cozy Dell Shale, Ventura County, California: implications for sequence stratigraphic correlations
The Matilija Sandstone and Cozy Dell Shale in the western Transverse Ranges of California record a long history of Eocene regression from deep marine turbidites to non-marine red shales and then transgression to deep marine shales in a rapidly subsiding tectonic basin. In its type area along the Ventura River north of Ojai, the Matilija Sandstone consists of over 800 m of deep marine to non-marine sandstones, and the Cozy Dell Shale contains over 760 m of deep marine shales and turbidite sandstones. Paleomagnetic sampling of these rocks yielded a stable magnetic remanence which passed both a fold test and a reversal test; some samples were reversed at NRM after dip correction. Based on calibration from planktonic microfossils, the Matilija Sandstone spans the interval from Chron C21r to early Chron C20r (46.0-48.5 Ma), and the Cozy Dell from late Chron C20r to C19r (46.0-42.0 Ma). The samples show a tectonic rotation of approximately 85±18° clockwise, consistent with previous results reported for this tectonic block. Previous sequence stratigraphic correlations of these rocks are inconsistent with this chronostratigraphy. None of the sequence boundaries predicted from these sections matches the global sequence chart.