CHEMICAL ANALYSIS OF WESTERN OKLAHOMA ASH BEDS USING THE ELECTRON MICROPROBE

This project was developed through two separate courses offered at Oklahoma State University (OSU) in the School of Geology and the Department of Plant and Soil Sciences, and is an example in which faculty in different departments teaching different courses can provide ideas for successful undergraduate research.

Near Waynoka in NW Oklahoma, several meters of volcanic ash have been documented, which may have been either derived from the Long Valley caldera in California or the Yellowstone caldera in Wyoming. Both volcanoes have been shown to have deposited ash well into regions of Western Oklahoma, however, little data have been acquired to determine exactly which volcano these sediments were derived from.

One of the authors of the poster was introduced to this ash bed during a field trip for a Soil Genesis class. After an ash sample was collected and made into thin sections, it was analyzed and imaged using the OSU Electron Microprobe. Materials present in the ash include glass, sanidine, and zircon. Backscattered electron images show the ash contains 100 µm-sized vesicles and ~40 µm-sized zircon grains. The initial goal of the study was to qualitatively identify the specific elements that are in the sample to acquire a “chemical signature” for the ash. From that signature, it is proposed that additional research be done on samples from each perspective source caldera to attempt to match this unknown ash sample. Future studies have been planned to attempt to identify the source of this ash, including obtaining ash from areas of Yellowstone and Long Valley and dating the zircon grains present in the Oklahoma ash beds.