The sulfur isotopic composition of Cenozoic pyrite is affected by methane content and depositional environment

Abstract

The sulfur isotopic composition of pyrite (δ³⁴S_pyr) is often used to reconstruct ancient geobiological processes, but recent studies have shown that δ³⁴S_pyr is strongly dependent on local sedimentary environmental conditions. Here we present a global compilation of >3700 published pyrite sulfur isotopic compositions from the past 165 million years, from outcrop as well as marine sediment cores. We show that sediment core δ³⁴S_pyr has a statistically significant relationship with methane content, sedimentation rate, lithology, and proximity from shore, while outcrop δ³⁴S_pyr has distinct distributions depending on categories of depositional water depth and lithology. There are no obvious trends in the average δ³⁴S_pyr from the late Mesozoic to the present, although we suggest that this temporal record is affected by the inherent bias of data compilation. Our study further emphasizes the importance of considering sedimentology and stratigraphic context when using the sulfur isotopic composition of pyrite to infer global environmental changes.