Does uranium speciation control uranium isotope signatures in marine sedimentary rocks? Advancing the paleoredox proxy

Uranium (U) speciation controls its reactivity and transport in environmental systems and is modulated by redox conditions. U enrichment and isotopic composition in sedimentary rocks are a promising proxy to reconstruct Earth’s oxygenation. However, interpretation of U systematics is based on poorly constrained assumptions of U burial pathways. We propose to determine U spatial distribution and characterize its speciation using HERFD-XANES within well-characterized, U-rich sedimentary rocks that were deposited under a range of reducing marine environments. Previous work on phosphorites showed the prevalence of U(V) and spatial heterogeneity of U species, suggesting multiple burial pathways during deposition. However, to explore how U(V) impacts the paleoredox proxy, characterization needs to be done in concert with isotope characterization. This work will link the variability in U speciation with U isotope values, advancing reconstructions of paleoredox conditions.