Episodic Microbial Methanogenesis, Methane Oxidation and Sulfate Reduction in Deep Granite Fractures at Forsmark, Sweden

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• 作者：Henrik Drake^a ; ^{henrik.drake@lnu.se} ; Christine Heim^b ; Martin Whitehouse^c ; Curt Broman^d ; Mats Å ; strö ; m^a
• 关键词：Deep biosphere ; sulfur isotopes ; carbon isotopes ; sulfate reducing bacteria ; anaerobic methane oxidation ; bedrock fractures
• 刊名：Procedia Earth and Planetary Science
• 出版年：2017
• 出版时间：2017
• 年：2017
• 卷：17
• 期：Complete
• 页码：702-705
• 全文大小：269 K
• 卷排序：17

文摘

An extensive microanalytical isotope study of calcite and pyrite has been carried out in bedrock fractures at Forsmark, Sweden. The very large δ13Ccalcite-variation of 103.4‰V-PDB in total (-69.2 to +34.2‰) evidences significant spatial and temporal variability in processes and carbon sources in the deep fracture system during the period when these minerals were formed (Phanerozoic). The substantial δ13Ccalcite-span is mainly methane-related, with heavy and very light δ13C originating from ubiquitous in situ microbial methanogenesis and anaerobic oxidation of methane (AOM), respectively. Co-genetic cubic and framboidal pyrite showed substantial sulfate reducing bacteria (SRB)-related δ34S variation of 95‰V-CDT overall (-29 to +66‰), indicating closed system isotope distillation and point to similar genetic SRB methane-oxidizer relationships as in marine sediments. The depth distribution of the methanogenesis-, SRB- and AOM-signatures are from just below the ground surface down to about 800 m, which marks the deepest occurrence of AOM-related carbonate yet reported from the continental crystalline crust. Biomarkers and fluid inclusions suggest that the microbial activity in the bedrock fractures was closely related to descending surficial fluids and basinal brines rich in organic matter, in at least two pulses (70-80 °C and <50-62 °C).