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Abstracts: Magnetic Stratigraphy of the Type Matilija Sandstone and Cozy Dell Shale (Middle Eocene), Ventura County, California


The Matilija Sandstone (2000 feet of turbidites, shallow marine sandstones, and terrestrial redbeds) and the overlying Cozy Dell Shale (3600 feet of deepwater shales and turbidites) are prominently exposed all along the western Transverse Ranges in Ventura and Santa Barbara counties. The lower Matilija A Sandstone yields Domengine-aged molluscs, but the upper Matilija yields "Transition" molluscs. The Cozy Dell Shale yields P11 and P12 planktonic foraminifera, and CP13b, CP13c, and lower CP14a nannofossils. Over 150 magnetic samples were taken in the type exposures of both of these formations P along Highway 33 near Matilija Hot Springs, north of Ojai. Although many samples were overprinted and had to be rejected, a majority of samples yielded 2 a stable remanence that passed both a fold test and reversal test. Like other pre-Miocene units in the region, these rocks showed a 90 degree clockwise rotation. Based on the biostratigraphic data, the magnetic pattern is correlated with Chrons C19r-C21n (42-47 Ma). Contrary to sequence stratigraphic r interpretations (Campion et al., 1994, 1996), these units are time-transgressive, since the underlying Juncal Formation is as young as nannofossil zone CP14a (no older than 43 Ma) in western Santa Barbara County, making the Matilija and Cozy Dell formations at least 4-6 million years older in the east than they are to the west.

Search and Discovery Article #90945©1997 AAPG Pacific Section Meeting, Bakersfield, California