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    Rights statement: This is the peer reviewed version of the following article: Zwahlen, C., Hollis, C., Lawson, M., Becker, S. P., Boyce, A., Zhou, Z., & Holland, G. (2019). Constraining the fluid history of a CO2‐H2S reservoir: Insights from stable isotopes, REE, and fluid inclusion microthermometry. Geochemistry, Geophysics, Geosystems, 20, 359–382. https://doi.org/10.1029/2018GC007900 which has been published in final form at https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GC007900 This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving.

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Constraining the fluid history of a CO2-H2S reservoir: Insights from stable isotopes, REE and fluid inclusion microthermometry

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<mark>Journal publication date</mark>01/2019
<mark>Journal</mark>Geochemistry, Geophysics, Geosystems
Issue number1
Volume20
Number of pages24
Pages (from-to)359-382
Publication statusPublished
Early online date19/12/18
Original languageEnglish

Abstract

Reservoirs that host CO2-H2S bearing gases provide a key insight into crustal redox reactions such as thermochemical sulphate reduction (TSR). Despite this, there remains a poor understanding of the extent, duration and the factors limiting this process on a reservoir scale. Here we show how a combination of petrography, fluid inclusion, rare earth element (REE) and carbon (δ13C), oxygen (δ18O) and sulphur (δ34S) stable isotope data can disentangle the fluid history of the world's largest CO2 accumulation, the LaBarge Field in Wyoming, USA. The carbonate hosted LaBarge Field was charged with oil around 80 Ma ago, which together with nodular anhydrite, represent the reactants for TSR. The nodules exhibit two distinct trends of evolution in δ13C with both δ34S and δ18O that may be coupled to two different processes. The first trend, was interpreted to reflect the coupled dissolution of anhydrite and reduction to elemental sulphur and the oxidation of organic compounds and associated precipitation of calcite during TSR. In contrast, the second trend was interpreted to be the result of the hydrothermal CO2 influx after the cessation of TSR. In addition, mass balance calculations were performed to estimate an approximate TSR reaction duration of 80 ka and to identify the availability of organic compounds as the limiting factor of the TSR process. Such an approach provides a tool for the prediction of TSR occurrence elsewhere and advancing our understanding of crustal fluid interactions.

Bibliographic note

This is the peer reviewed version of the following article: Zwahlen, C., Hollis, C., Lawson, M., Becker, S. P., Boyce, A., Zhou, Z., & Holland, G. (2019). Constraining the fluid history of a CO2‐H2S reservoir: Insights from stable isotopes, REE, and fluid inclusion microthermometry. Geochemistry, Geophysics, Geosystems, 20, 359–382. https://doi.org/10.1029/2018GC007900 which has been published in final form at https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GC007900 This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving.