CARBONATE U-TH AGE CONSTRAINTS FOR ASHES 1–4 OF THE WILSON CREEK FORMATION, MONO BASIN, CALIFORNIA

The Wilson Creek Formation is the Late Pleistocene lithostratigraphic unit of the Mono Basin, California (Lajoie, 1968). The age model of the Wilson Creek Formation relies on the depositional ages of 19 tephra that are, apart from one, derived from volcanic centers in the Mono Basin (Marcaida et al. 2014). These tephra are named by their reverse depositional order—i.e., Ash 1 is the youngest, and Ash 19 is the oldest—and grouped into five tephra sets.

The older three tephra sets that include Ashes 8–19 have been the focus of recent dating efforts. However, there has been less attention placed on the two younger tephra sets, especially the set comprising Ashes 1, 2, 3, and 4.

Here we present carbonate uranium-series ages that constrain the depositional ages of Ashes 1–4. We measured these ages on lacustrine carbonates that precipitated before or after the deposition of each tephra. Hence the ages represent minimum or maximum age constraints. The results of this work suggest the following: that Ash 1 was deposited between 15.1 ± 0.1 ka and 16.1 ± 0.1 ka, and that Ashes 2–4 were deposited between 17.0 ± 0.4 ka and 20.2 ± 0.2 ka. We will discuss the implications of these age constraints for the lake fluctuation and volcanic history of the Mono Basin, and we will discuss how they compare to estimates derived from the age model of Benson et al. (1998), which was underpinned by ¹⁴C ages measured on lacustrine carbonates. Our uranium-series dating results spotlight a new, viable path towards refining the age model of the Wilson Creek Formation.

Lajoie, K.R., 1968, Quaternary Stratigraphic and Geologic History of Mono Basin, Eastern California: University of California, Berkeley, 271 p.

Marcaida, M., Mangan, M.T., Vazquez, J.A., Bursik, M., and Lidzbarski, M.I., 2014, Geochemical fingerprinting of Wilson Creek formation tephra layers (Mono Basin, California) using titanomagnetite compositions: Journal of Volcanology and Geothermal Research, v. 273, p. 1–14, doi:10.1016/j.jvolgeores.2013.12.008.

Benson, L. V., Lund, S.P., Burdett, J.W., Kashgarian, M., Rose, T.P., Smoot, J.P., and Schwartz, M., 1998, Correlation of Late-Pleistocene Lake-Level Oscillations in Mono Lake, California, with North Atlantic Climate Events: Quaternary Research, v. 49, p. 1–10, doi:10.1006/qres.1997.1940.