PALEOGENE PALEOSOL OCCURRENCES IN THE SANTA MONICA MOUNTAINS, SANTA ANA MOUNTAINS AND IN THE SAN JOAQUIN HILLS, SOUTHERN CALIFORNIA

In southern California, Paleogene lateritic paleosols are exposed in the Santa Monica and Santa Ana Mountains, and the San Joaquin Hills. In the San Joaquin Hills, the paleosol studied consists of a red and white mottled kaolinitic horizon overlain by a kaolinite horizon, and a pallid horizon. Dissolved, etched and pitted monocrystalline quartz grains float in the kaolinitic matrix in the aforementioned horizons and disaggregation of polycrystalline quartz along crystal boundaries is evident. In the Santa Monica Mountains, the paleosol consists of intensely weathered arkose overlain by a mottled reddish and white kaolinite-rich interval. Iron pisolites and a silicified interval of pisolites in a kaolinite matrix cap the paleosol. In the Santa Ana Mountains, much of the paleosol in one section examined consists of iron pisolites in a kaolinitic matrix overlain by weathered arkose. Iron pisolites, mottled red and white kaolinite zones, white kaolinite-rich zones, and partially dissolved quartz grains in the paleosols are consistent with oxisol development. Chemical data also support interpretations that the paleosols are oxisols. Samples from the Santa Monica Mountains and the San Joaquin Hills are enriched in total Al₂O₃ and Fe₂O₃ and total Fe₂O₃ content is in some instances similar to an oxisol sample from the Ione Formation of central and northern California. Additionally, the Fe₂O₃ to Al₂O₃ ratio in a sample from the San Joaquin Hills is indicative of an oxisol. Correlation between sections is based on stratigraphic similarities although age assignments for the palesols are not firm. Refined age dates for the southern California sections are needed to determine whether the paleosols correlate with those of the Ione Formation.