Dolostone as a reliable tracer of seawater lithium isotope composition

Abstract

The lithium isotope composition (δ7Li) of seawater records important information on the evolution of the carbon and silicon cycles over geologic time. Here we report δ7Li values in a suite of Neogene dolostones (23–3.4 Ma, n = 39) from the South China Sea. Over the Neogene, dolostone δ7Li values have increased from 24.9‰ to 30.1‰, overlapping previously published foraminifera records and documenting seawater δ7Li without applying any isotopic fractionation factor correction. Our results suggest that fabric-retentive dolostones are good proxies for providing seawater δ7Li records even after early diagenesis. Importantly, these results provide a high-resolution dolostone record rather than a foraminifera record to confirm the observed ~5‰ increase in Neogene seawater δ7Li. We predict that early marine diagenetic dolostones with fabric textures abundant in the Proterozoic may record changes in seawater δ7Li and continental weathering, providing great insights into the Precambrian global carbon cycle.