Open AccessConstraining the Fluid History of a CO 2 ‐H 2 S Reservoir: Insights From Stable Isotopes, REE, and Fluid Inclusion Microthermometry
Author(s) -
Zwahlen Carmen,
Hollis Cathy,
Lawson Michael,
Becker Stephen P.,
Boyce Adrian,
Zhou Zheng,
Holland Greg
Publication year - 2019
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2018gc007900
Subject(s) - anhydrite , geology , petrography , calcite , carbonate , geochemistry , stable isotope ratio , isotopes of carbon , sulfate , dissolution , hydrothermal circulation , sulfur , mineralogy , redox , total organic carbon , environmental chemistry , chemistry , inorganic chemistry , paleontology , gypsum , physics , organic chemistry , quantum mechanics
Reservoirs that host CO 2 ‐H 2 S‐bearing gases provide a key insight into crustal redox reactions such as thermochemical sulfate 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 (δ 13 C), oxygen (δ 18 O), and sulfur (δ 34 S) stable isotope data can disentangle the fluid history of the world's largest CO 2 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 δ 13 C with both δ 34 S and δ 18 O that may be coupled to two different processes. The first trend was interpreted to reflect the coupled dissolution of anhydrite and reduction to elemental sulfur 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 CO 2 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.