Sulfate 17O Anomalies in Cenozoic Volcaniclastic Deposits in the Northern High Plains, North America

PI计划检验这样一种假设，即在2800万年前的大盆地火山活动高峰期，一系列极端干燥的雾可能向北美北部高平原输送了大量的硫酸盐。这一假设是基于一种独特的稳定同位素特征，即在该地区渐新世火山灰床中发现的一系列正硫酸盐17O异常。这一发现和提出的解释引起了人们的兴趣，以及关于岩石记录过去异常大气事件的可能性与硫酸盐17O异常的其他解释的争论。PI和他的学生将(1)绘制出葛林组类型区域的硫酸盐沉积和同位素组成的空间异质性，(2)检查导致葛林组异常硫酸盐保存的沉积学、矿物学和成岩因素，(3)研究内布拉斯加州Wolf Butte的正常playa硫酸盐沉积序列，并将其与内布拉斯加州Scotts Bluff的异常序列进行比较。(4)在邻近的南达科他州荒地国家公园（Badlands National Park）建立火山硫酸盐沉积的时间格局。这些任务的目的是提供沉积学和地球化学证据，以限制可能导致北部高平原许多灰层中17o -异常硫酸盐的特定化学途径、沉积模式、气候条件和成岩过程。该项目将为学生提供学习广泛的地球科学的机会，并在受欢迎的国家纪念碑和公园提供一般的公众教育材料。如果过去确实发生过一系列极端的干雾，研究这些不寻常的地质事件将有助于人类文明为下一次大雾做好准备。

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.