YOUNG SCIENTIST AWARD (DONATH MEDAL): ADVANCING THE GEOCHEMISTRY OF URANIUM IN SEDIMENTARY ROCKS

Uranium is a paleoredox proxy of increasing use and importance for tracking the geobiological co-evolution between life and Earth. The geochemical cycling of uranium in the oceans through Earth’s history is expected to mirror the availability of oxygen, track changes in biological productivity, and be closely linked to the sulfur cycle. The concentration of uranium in seawater reflects oxygen-dependent changes in solubility, and the isotope ratio of uranium (²³⁸U/²³⁵U) reflects variations in isotope fractionation associated with redox-sensitive sources and sinks. Records of uranium concentrations and isotope ratios have been implemented to reconstruct the increase in oxygen in the Earth’s atmosphere and oceans over the last three billion years as well as track transient expansions of anoxic waters connected to major climate perturbations. I will discuss new insights into the behavior of uranium in sedimentary rocks to refine interpretations of uranium cycling and therefore the redox state in past oceans. Specifically, I will evaluate the alteration of carbonate-associated uranium isotope records from early marine diagenesis and present new data of uranium oxidation states in black shales and phosphorites—characterizing two critical sinks of uranium from the ocean.