GASTROPODS AND OSTRACODES OF THE WAUCOBI LAKE BEDS: SIGNIFICANCE FOR PLIOCENE CLIMATE IN THE EASTERN SIERRA NEVADA, CALIFORNIA

The fossil record in lacustrine sediments allows the reconstruction of high resolution climate change. The Pliocene Waucobi Lake beds cropping out in Owens Valley, CA provide an excellent opportunity to reconstruct the paleoclimate for the eastern Sierra Nevada. In this study two localities were analyzed for fossil gastropod, ostracode, and bivalve variability on a cm scale over a ~2 m interval. The distribution of gastropods and ostracodes are used in this study as a climate signal for the Sierra Nevada.

The Waucobi beds are composed primarily of clay. Previous studies record alternating saline/alkaline (closed lake) and freshwater conditions (open lake) based on zeolites. Ostracodes occur in many beds throughout the succession. However, several discrete beds preserve freshwater species of gastropods (Valvata sincera, Planorbia parvus, Paludina integra), ostracodes (Candona rawsoni, Cyprideis beaconensis, Limnocythere ceriotuberosa, Fabaeformiscandona acuminata), and bivalves. These beds containing gastropods were interpreted as freshwater events. The presence of ostracode assemblages occurring in some gastropod beds suggests that interruptions of saline conditions (closed lake) occurred more commonly than indicated by past studies of low stratigraphic resolution. Further examination of the interpreted stratigraphic relationship of the Waucobi lake beds to the fossil record suggest the paleoclimate for the region is tied to the rainshadow of the Sierra Nevada and arid conditions for the western Great Basin were underway during the Pliocene.