Earth Sciences Seminar Series

Kim Lau,University of Wyoming
“Tracking Anoxia in Ancient Oceans: Insights from uranium isotopes”

Abstract:
Oxygenation and deoxygenation of the oceans strongly influences organic carbon burial, habitability for marine biota, and biogeochemical cycling of nutrients and critical redox-sensitive elements. Methods for reconstructing anoxia through Earth history include various paleontological, sedimentological, biomarker, and inorganic geochemical indicators. Of these, inorganic geochemical proxies—a broad category that includes concentrations of redox-sensitive elements and their isotopic ratios—offer the potential to track redox conditions across a range of temporal and spatial scales. Uranium isotopes (²³⁸U/²³⁵U) have emerged as a useful proxy for reconstructing the redox conditions of the Earth’s oceans and atmosphere based upon the large isotopic fractionation between reduced U(IV) and oxidized U(VI). Variations in ²³⁸U/²³⁵U, particularly when recorded in carbonate sediments, can track global trends in marine oxygenation and de-oxygenation. It is unique from other proxies because reduction primarily occurs at the sediment-water interface, and this sensitivity makes U isotopes especially relevant for the habitability of benthic animals. While the U isotope proxy is already a promising tool for understanding Earth’s environmental transitions, rapid development continues to refine the accuracy of interpretations of ²³⁸U/²³⁵U records. In this talk, I will present an overview and key examples of U isotopes as a paleoredox proxy in the rock record and discuss new insights from diagenetic modeling that will advance interpretations of these records.

All welcome.