Contribution of siderite–water interaction for the unconventional generation of hydrocarbon gases in the Solimões basin,north-west Brazil |
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| Institution: | 1. Department of Geosciences, Physics of Geological Processes, University of Oslo, Norway;2. University Grenoble Alpes, CNRS, ISTerre, CS 40700, F-38058 Grenoble Cedex 9, France;3. Institut für Mineralogie, University of Münster, Corrensstrasse 24, 48149 Münster, Germany;4. The Institute for Geoscience Research (TIGeR), Department of Chemistry, Curtin University, Perth 6845, Australia;5. Department of Earth Sciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, The Netherlands;1. Key Laboratory of Nano-minerals and Pollution Control of Anhui Higher Education Institutes, Hefei University of Technology, Hefei 230009, China;2. Institute of Environmental Minerals and Materials, School of Resources and Environmental Engineering, Hefei University of Technology, Hefei 230009, China |
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| Abstract: | Hydrocarbon gases with unconventional carbon isotopic signatures were observed in the Solimões sedimentary basin in north-west Brazil. Siderite contents measured with a new Rock-Eval methodology in the drill-cuttings samples of the Famenian source rock were found to decrease with the increase of gas maturity and with the occurrence of the gas isotopic anomalies. Triassic diabase intrusions induced heating of the source rock, which likely resulted in the gradual oxidative dissolution of siderite as suggested by the observation of etch pits on the siderite surfaces. It is proposed that ferrous iron from the carbonate was involved in a redox reaction with water producing ferric iron and H2, then reducing CO2 and yielding an inverse correlation between siderite content and gas maturity. Alternatively, hydrogenation of highly mature kerogen by H2 derived from siderite could explain the production of 13C-rich CH4. Mass balance considerations suggest that these mechanisms may account for a significant fraction of the hydrocarbon gases generated from the Famenian source rock in the Solimões basin. |
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| Keywords: | Siderite Hydrothermal Solimões Abiotic Hydrocarbon gases Reducing conditions |
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