Aminostratigraphy and oxygen isotope stratigraphy of marine-terrace deposits, Palos Verdes Hills and San Pedro areas, Los Angeles County, California

Amino-acid and oxygen isotope data for fossils from terraces of the Palos Verdes Hills and San Pedro areas in Los Angeles County, California, shed new light on the ages of terraces, sea-level history, marine paleotemperatures, and late Quaternary tectonics in this region. Low terraces on the Palos Verdes peninsula correlate with the approximately 80-ka and approximately 125-ka sea-level highstands that are also recorded as terraces on other coasts. In San Pedro, the Palos Verdes sand (the deposit on what is mapped as the first terrace by Woodring and others, 1946) was previously thought to be a single deposit; amino-acid, oxygen isotope, U-series, and faunal data indicate that deposits of two ages, representing the 80-ka and 125-ka highstands occur within this unit. Oxygen isotope data show that on open, exposed parts of the Palos Verdes peninsula, ocean waters during the 125-ka highstand were cooler than present (by about 2.3-2.6 degrees C) similar to what has been reported for other exposed coastal areas in California. In contrast, in the protected embayment environment around San Pedro, water temperatures during the 125-ka highstand were as warm or warmer than present. During the 80-ka highstand, water temperatures were significantly cooler than present even in the relatively protected embayment environment of the San Pedro area. Late Quaternary tectonic-uplift rates can be calculated from terrace ages and elevations. Correlation of the lowest terraces around the Point Fermin area shows that the Cabrillo fault has a late Quaternary vertical-movement rate of 0.20 m/ka, based on the difference in uplift rates on the upthrown and downthrown sides of the fault. Elsewhere in the Palos Verdes Hills-San Pedro area, late Quaternary uplift rates vary from 0.32 m/ka to possibly as high as 0.72 m/ka. These rates, which reflect vertical movement on the Palos Verdes fault, are in broad agreement with estimated Holocene vertical rates of movement determined for offshore portions of the fault.