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Published October 2018 | Supplemental Material
Journal Article Open

Cenozoic record of δ^(34)S in foraminiferal calcite implies an early Eocene shift to deep-ocean sulfide burial

Abstract

Understanding the changes in, and drivers of, isotopic variability of sulfur in seawater sulfate (δ^(34)S_(SO4-sw)) over geological time remains a long-standing goal, particularly because of the coupling between the biogeochemical sulfur and carbon cycles. The early Cenozoic has remained enigmatic in this regard, as the existing seawater sulfate isotopic records appear to be decoupled from the well-defined carbon isotope composition of the ocean. Here, we present a new Cenozoic record of sulfur isotopes, using carbonate-associated sulfate hosted in the calcite lattice of single-species foraminifera. The vastly improved stratigraphy afforded by this record demonstrates that carbon and sulfur cycles, as recorded by their isotopes, are not fully decoupled in the early Cenozoic. With a model driven by partial coupling of the carbon and sulfur cycles, we demonstrate that a change in sulfur isotopic fractionation of the pyrite burial flux best explains the large increase in δ^(34)S_(SO4-sw) ~53 million years ago (Ma) and the subsequent long steady state. We suggest that the locus of pyrite burial changed from shallow epicontinental seas and shelf environments to more open-ocean sediments around 53 Ma. Loss of extensive shelf environments corresponds to Cretaceous–Palaeogene sea-level changes and tectonic reorganization, occurring as the Himalayan arc first collided with Asia.

Additional Information

© 2018 Springer Nature Limited. Received: 4 February 2018; Accepted: 5 July 2018; Published online: 13 August 2018. We thank M. Vautravers for her expertise with Palaeogene foraminifera and S. Misra, G. Antler and W. Fisher for helpful discussions and advice. This work was supported by a 'Small Sulfur' NERC grant (NERC NE/H011595/1), the ERC (ERC StG 307582, CARBONSINK to A.V.T.) and a NERC studentship to V.C.F.R. Author Contributions: V.C.F.R. designed the cleaning tests, did the lab work and analysis for trace element analysis and sulfur isotopes, and wrote the model and the paper. G.P. advised on the cleaning tests, did sulfate and sulfur isotope preparation and analysis, was heavily involved in the modelling and wrote the paper. A.L.S. provided equipment and fruitful discussions. S.A. picked the foraminifera for the stable isotope analyses. A.V.T. provided extensive advice and funding at all stages, had the idea for the shift in ^(34)ε_(SO4-pyr) and wrote the paper. J.F.A. provided guidance and lab equipment for lab work and analysis, advised extensively on the model and wrote the paper. Data availability: The authors declare that all the data and MATLAB codes supporting the finding of this study are available within the article and its supplementary information files. The authors declare no competing interests.

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Created:
August 23, 2023
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