The PI proposes to examine the hypothesis that a series of extreme dry fogs probably delivered a large quantity of sulfate to the northern High Plains, North America, during the peak of the Great Basin volcanism ~ 28 million years ago. The hypothesis is based on a unique type of stable isotope signature, an array of positive sulfate 17O anomalies found in Oligocene volcanic ash beds in the region. This discovery and the proposed interpretation have generated interest, as well as debates on the possibility of past abnormal atmospheric events being recorded by rocks versus alternative explanations of the sulfate 17O anomalies. The PI and his students will (1) map out the spatial heterogeneity of sulfate deposition and isotope compositions at the type locality of the Gering Formation, (2) examine the sedimentological, mineralogical, and diagenetic factors that resulted in the preservation of the anomalous sulfate in the Gering Formation, (3) study a depositional sequence of normal playa sulfate at Wolf Butte, Nebraska, to compare to the abnormal sequence in Scotts Bluff, Nebraska, and (4) establish a temporal pattern of volcanic sulfate deposition in a neighboring locality: Badlands National Park, South Dakota. The aim of these tasks will be to provide sedimentological and geochemical evidence to constrain particular chemical pathways, deposition mode, climatic condition, and diagenetic processes that may be responsible for the 17O-anomalous sulfate in many of the ash beds in the northern High Plains. This project will provide students opportunities to learn a broad spectrum of Earth science, as well as provide the general public educational materials at popular national monuments and parks. If indeed a series of extreme dry fogs occurred in the past, studying these unusual geological events will help civilization prepare for the next big one.
