THE GASTROPOD GENUS ARCHITECTONICA (MOLLUSCA) IN THE PLIOCENE OF CALIFORNIA – USING WARM WATER MOLLUSKS TO CORRELATE AND DATE SCATTERED OUTCROPS ACROSS CENTRAL AND SOUTHERN CALIFORNIA

The occurrence of the tropical gastropod genus Architectonica from unnamed Pliocene deposits in the Whittier Hills, Orange County, the “Santa Barbara” Formation at Rincon Point, between Ventura and Santa Barbara counties, and the Cebada fine-grained member of the Carega Sandstone in the Santa Maria District, northern Santa Barbara County, suggests correlation of these scattered warm water faunas. Living Architectonica in the eastern Pacific are not currently found north of Bahîa Magdalena, Baja California, Mexico. Other southern extra-limital species such as the gastropods Crucibulum cyclopium Berry, Turritella gonostoma hemphilli Merriam of Woodring and Bramlette and various larger Conus species at one or more of these sites also support warm tropical conditions.

Fossil collections from the Whittier Hills and Carega Sandstone have been assigned to the Pliocene, but those from the “Santa Barbara” Formation have previously been assigned to the Pleistocene based on correlation with the middle Pleistocene Santa Barbara Formation in Santa Barbara County. Extinct mollusks from the Rincon Point “Santa Barbara” Formation fauna indicate a late Pliocene to early Pleistocene age for the fauna. Therefore all these faunas are of potential late Pliocene age.

Microfossil datums (planktic foraminifers and pollen), and other proxy data well-correlated to oxygen isotope records as well as to the paleomagnetic and cyclostratigraphy records, document a warming event that took place in the Pliocene between 3.3-3.15 Ma [= the "mid'-Pliocene warm event (Gauss chron)]. We suggest that these warm water mollusks are from this time interval, also that specific southern extra-limital, warm-water, mollusks can be used to correlate different formations/outcrops across California, as has already been done for the early to middle Pleistocene in southern California.