EAGER: Development of Tellurium Stable Isotopes as Paleoredox Indicator

点击翻译按钮获取中文摘要

Tellurium (Te) is a toxic element that is used in photovoltaic solar panels, is concentrated in some mine wastes, and is a key constituent of some types of gold ore deposits. Its chemical properties vary with conditions: In oxygen-poor, "reducing" conditions it tends to be immobilized in solid forms, but when exposed to atmospheric oxygen it can dissolve in water. In the modern environment, measurements that detect when and where Te transitions from its oxidized, mobile form to its reduced, immobile form can help us predict its mobility and toxicity. Such measurements should also improve understanding of Te-bearing ore deposits. In piecing together the history of life on earth, measurements of ancient rocks that reveal the presence or absence of Te oxidation can provide evidence for changes in biologically critical oxygen concentrations in the earth's atmosphere and oceans over time. This project will develop a new way to trace Te oxidation and reduction, using novel measurements of small variations in Te stable isotope ratios (128Te/125Te). This new geochemical tool should be useful in a range of applications aimed at modern environments, ore deposits, and earth history. A doctoral student will be trained in advanced geochemistry applied to both ancient rocks and the modern environment. The project plans to recruit an undergraduate student from an underrepresented group in STEM; the student will be introduced to the field of environmental geochemistry. K-12 students will learn to collect and analyze river waters to determine if seeps from a local coal ash impoundment affect river water quality.The objectives of this exploratory project are to establish if (1) isotopic shifts occur in modern weathering environments and (2) if Te stable isotopes can serve as a paleoredox proxy of Precambrian oxygenation. The new analytical method uses hydride generation MC-ICPMS and a double spike (120Te and 124Te) to obtain highly precise measurements of 128Te/125Te ratios while requiring very small amounts of Te (10 ng). Measurements of modern soils, weathered shales and mine tailings will reveal the magnitude of 128Te/125Te shifts imparted during redox cycling in active weathering environments. Measurements of ancient ironstones, shales, and paleosols will provide a record of Te isotopic shifts, or lack thereof, in ancient environments. Te isotopes should provide a new paleoredox proxy with an intermediate redox threshold between those of the U isotope and Cr isotope proxies, and thus, may provide new insights into O2 levels during the Neoproterozoic. Such a tool could provide valuable information about the rise of oxidizing conditions and the proliferation of multicellular life.