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46581-UFS
Tephrochronology for the 21st Century: Redefining the Bishop Ash Bed

Jeffrey R. Knott, California State University (Fullerton)

The PRF Sabbatical grant provided me an opportunity to complete the proposed tephrochronology project as well as initiate and collect data for another project. The proposed project (Tephrochronology for the 21^st Century) was highly successful and continues. I have collected minor and trace element results from a number of tephra layers using the Time-of-Flight, Laser-Ablation Inductively-Coupled-Plasma Mass Spectrometer (TOF-LA-ICP-MS) showing that the method is precise and accurate enough for use in a large data base (Goal #1 in proposal). These data show that the TOF-LA-ICP-MS methodology accurately determines the concentration of at least 20 elements, including most of the rare earth elements. Using these selected elements, I can statistically determine the differences between the 0.77 Ma Bishop ash bed and the 3.35 Ma tuff of Zabriskie Wash. These differences can also be identified between the 3.28 Ma Nomlaki Tuff and the >3.58 Ma tuff of

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. These results provide a basis to continue using the TOF-LA-ICP-MS for characterizing ash beds from different localities, especially exploration cores.

Based on this success, I have prepared samples of the Wilson Creek Formation for TOF-LA-ICP-MS analyses. The Wilson Creek ash beds present an extremely difficult tephrochronologic problem. These ash beds are critical late Pleistocene stratigraphic markers in the western U.S. Previous studies show that these ash layers are indistinguishable by major elements – future analyses, based on the PRF grant work and conducted by an undergraduate student may provide a major break through in the interpretation of climatic changes in the last 60,000 years.

In addition, I was able to involve 15 students at CSU Fullerton in the preparation of tephrochronology web pages. These web pages will form the basis for online access for researchers to search and determine if tephrochronology will help their research.

Funding from this grant also allowed me to travel to Albuquerque and attend a field trip and meeting; travel to Menlo Park, California to collaborate and collect samples with USGS personnel; travel several times to the Mojave Desert and Mono Lake for field work. I am presently preparing journal manuscripts based on this work.

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