INITIAL GEOCHRONOLOGIC FRAMEWORK, STRATIGRAPHIC CORRELATIONS, AND PALEOENVIRONMENTAL INTERPRETATION OF THE WAUCOBA LAKE BEDS, INYO COUNTY, CALIFORNIA – A MULTIDISCIPLINARY SPOT CHECK USING TEPHROCHRONOSTRATIGRAPHY, 40AR/39AR DATING AND MICROPALEONTOLOGY

Ten tephra and two microfossil samples were collected from Duchess canyon, Waucoba lake beds, Inyo County, California (37° 10' 33"N, -118° 11' 26"W). Chemical fingerprinting of volcanic glass shards by electron microprobe resulted in the initial identification of the 2.57-2.22 Ma tuffs of the Badlands and 2.22- 2.14 Ma tuffs of Blind Springs Valley. Bracketing ⁴⁰Ar/³⁹Ar dates from sanidines additionally support the approximate age ranges of these marker tephra. Further, major and minor elemental characterization of these tephra permits correlation to highly chemically similar volcanic ash deposits throughout the lake basin and southwest region. These widespread, compositionally related tephra are derived from the Glass Mountain eruptive area, which lies roughly 129 kilometers NW from the study site.

Microfossil samples were also collected to obtain additional age control and for paleoenvironmental interpretation including shift rates of local and regional hydrologic and climate events. Two fossiliferous beds lie between the age-constrained tephra layers. The ostracodes Limnocythere ceriotuberosa, Ilocypris sp., and Candona spp. are sparsely present in the lower deposit proximal to the tuffs of the Badlands deposit. This assemblage suggests a freshwater environment with seasonally cooler temperatures (most likely resulting from snowmelt from the Sierra Nevada), as well as low dissolved oxygen content. Ostracodes are much more abundant in the bed underlying the tuffs of Blind Springs Valley deposit. In addition, the assemblage is more diverse. Cytherissa laucustris was also observed along with the above-mentioned taxa. When found with Limnocythere ceriotuberosa, Cytherissa laucustris indicates high frequency climate variability. This species also indicates that the lake waters were cool and slightly saline suggesting Pleistocene cooling. The diatom Navicula sp. also has been noted in the same environment.

Additional work needs to be conducted to further confirm these interpretations and to refine the chronologies. New work will include identification of diatom, fish, and gastropod fossils, plus additional ostracode species. Results from magnetostratigraphic analyses (currently underway) will lend additional support and refine age determinations, and corroborate paleoclimate data.