A revised seawater sulfate S-isotope curve for the Eocene

Abstract

The sulfur isotope ratio (δ34S) recorded in marine barite is commonly used to estimate secular changes in the sulfur isotopic composition of seawater sulfate (δ34SSO4) throughout Earth's history. The Cenozoic record demonstrates a drastic 5‰ increase in seawater δ34SSO4 during the Early Eocene. However, the gradient of this excursion is based on only a few data points. Taking advantage of a much improved biostratigraphic framework, we redefine the Eocene δ34SSO4 data with a new high-resolution barite based δ34S record between 60 and 30 Ma. Our results show that the rise of δ34SSO4 starts about 3 million years later (~53 Ma) and lasts about 9 million years longer (until 38 Ma) than previously depicted. As such, the gradient of the δ34S curve is ~0.4‰/Myr. The radiogenic strontium isotopic ratio in barite suggests that some of the samples used for the original barite record are affected by diagenetic alteration.