A revised seawater sulfate S-isotope curve for the Eocene

Abstract

The sulfur isotope ratio (δS) recorded in marine barite is commonly used to estimate secular changes in the sulfur isotopic composition of seawater sulfate (δS) throughout Earth's history. The Cenozoic record demonstrates a drastic 5‰ increase in seawater δS 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 δS data with a new high-resolution barite based δS record between 60 and 30 Ma. Our results show that the rise of δS 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 δS 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.