Morphology and formation mechanism of pyrite induced by the anaerobic oxidation of methane from the continental slope of the NE South China Sea |
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| Institution: | 1. School of Earth and Environment, Leeds University, LS2 9JT, United Kingdom;2. Institute of Petroleum Engineering, Heriot-Watt University, Edinburgh EH14 4AS, United Kingdom;3. The Lyell Centre, Heriot-Watt University, Research Avenue South, Edinburgh EH14 4AP, United Kingdom;4. Instituto Colombiano del Petróleo, Ecopetrol, Bucaramanga, Colombia;1. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan, Hubei 430074, PR China;2. School of Earth Science, China University of Geosciences, Wuhan, Hubei 430074, PR China;3. National Institute for South China Sea Studies, Haikou, Hainan 571100, PR China;4. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan, Hubei 430074, PR China;5. Department of Geology, University of Cincinnati, Cincinnati, OH 45221, USA;1. School of Earth Science and Geological Engineering, Sun Yat-sen University, Guangzhou 510275, China;2. School of Marine Sciences, Sun Yat-sen University, Guangzhou 510006, China;3. Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering, Guangzhou 510006, China;4. Institut für Geologie und Paläontologie, Westfälische Wilhelms-Universität Münster, Münster 48149, Germany;5. South China Sea Bio-Resource Exploitation and Utilization Collaborative Innovation Center, Guangzhou 510006, China;6. Guangzhou Marine Geological Survey, Guangzhou 510760, China;7. Center of Deep Sea Research, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071, China;8. Institut für Geologie, Universität Hamburg, Hamburg 20146, Germany;9. Department für Geodynamik und Sedimentologie, Universität Wien, 1090, Wien, Austria |
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| Abstract: | In order to understand the response of authigenic pyrite to gas hydrate geo-systems, pyrite tubes or rods at the sulfate–methane transition (SMT) zone of core GC10 from the northern continental slope of the South China Sea (SCS) were investigated. In situ X-ray diffraction (XRD) results show that the pyrite tube consists of pyrite micro-crystals with trace amount of graphite in the inner tube. Scanning electron microscope (SEM) observations of pyrite tubes indicate various aggregations in the form of framboidal, euhedral, and colloidal pyrite microcrystals. Typical framboidal pyrite is considered as packing of octahedral microcrystals. Interestingly, many framboids in the tubes consist of round or irregular microcrystals and have an outer crust that consists of secondary pyrite. The size of the framboids in the inner wall of the tube is larger than that in the middle wall or foraminifer-filled pyrite. High-resolution transmission electron microscopic (HRTEM) images show marcasite lamellae defects in the spherulitic pyrite crystals, which reveal different solution conditions during the pyrite precipitation. Nano-foil-like graphitic carbon was observed to be closely associated with the pyrite spherules. The occurrence of both marcasite layers and nano-foil-like graphitic carbon suggest that the migration of methane from deep sediment. It is suggested that the formation of pyrite serves as a catalyst during the reaction from methane to elemental carbon under the anaerobic oxidation of methane. Meanwhile, this reaction results in local acidification of the solution inside the pyrite tubes, which favors marcasite lamellae growth on the host pyrite substrate. |
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| Keywords: | Pyrite Marcasite Spherule Framboid Anaerobic oxidation of methane AOM South China Sea |
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