Uranium isotope compositions of biogenic carbonates - Implications for U uptake in shells and the application of the paleo-ocean oxygenation proxy.

ABSTRACT: The application of U isotopes in carbonates as a paleo-ocean oxygenation proxy is based on the critical assumption that the calcareous shell-building organisms incorporate U into their shells without fractionation relative to the U isotopic composition of ambient seawater. Recent studies claim a small, but resolvable, isotopic offset during abiotic and biogenic aragonite precipitation, whereas no isotope fractionation has been recorded during calcite precipitation. Although aragonite is meta-stable and not preserved over geological timescales (>1 Myr) and U precipitates during diagenesis, the U isotope composition of biogenic aragonite is important because aragonite precipitation is an important U sink to carbonate sediments. In contrast, low-magnesium calcite (LMC) is preserved over geolo

SUBMITTER: Livermore BD 

PROVIDER: S-EPMC7611457 | biostudies-literature | 2020 Oct

REPOSITORIES: biostudies-literature