Abstract
SUMMARY In the western Ventura Basin in southern California, marine turbidites in the Pico Formation are exposed along Santa Paula Creek in a southeast-dipping homocline. The section is about 3 km thick and contains normal and reverse polarity that was acquired before the development of the homocline. Although the sediment contains a secondary component of normal polarity that cannot be removed entirely by thermal or alternating-field demagnetization, the mean declination for 26 sites (12 normal polarity, 14 reverse polarity) shows a clockwise rotation of 19.8d± 9.0d that is similar to the rotation recorded in the Saugus Formation, a coeval, non-marine deposit in the eastern Ventura Basin that was studied by Levi et al. (1986). The partial overprint of the secondary component of normal polarity results in a mean inclination for each polarity that does not match the inclination of an axial dipole field (the inclination is too steep in normal polarity and too shallow in reverse polarity); still, the inclination for the combined sites is close to the expected inclination (52.0d versus 53.9d). Overall, turbidites in the Pico Formation are suitable for a magnetostratigraphic investigation, but caution is required if the palaeomagnetic data are to be used in a tectonic study.
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