Authigenic carbonates in methane seeps from the Norwegian sea: Mineralogy, geochemistry, and genesis |
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| Authors: | A Yu Lein A I Gorshkov N V Pimenov Yu A Bogdanov P Vogt O Yu Bogdanova V M Kuptsov N V Ul’yanova A M Sagalevich M V Ivanov |
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| Institution: | (1) Shirshov Institute of Oceanology, Russian Academy of Sciences, Nakhimovskii pr. 36, 117851 Moscow, Russia;(2) Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry (IGEM), Russian Academy of Sciences, Staromonetnyi per. 35, 109017 Moscow, Russia;(3) Institute of Microbiology, Russian Academy of Sciences, pr. 60-letiya Oktyabrya 7/2, 117811 Moscow, Russia;(4) Naval Research Laboratory, Code 7420, 20375 Washington DC, USA |
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| Abstract: | Authigenic carbonates in the caldera of an Arctic (72°N) submarine mud volcano with active CH4bearing fluid discharge are formed at the bottom surface during anaerobic microbial methane oxidation. The microbial community
consists of specific methane-producing bacteria, which act as methanetrophic ones in conditions of excess methane, and sulfate
reducers developing on hydrogen, which is an intermediate product of microbial CH4 oxidation. Isotopically light carbon (δ13Cav =−28.9%0) of carbon dioxide produced during CH4 oxidation is the main carbonate carbon source. Heavy oxygen isotope ratio (δ18Oav = 5%0) in carbonates is inherited from seawater sulfate. A rapid sulfate reduction (up to 12 mg S dm−3 day−1) results in total exhausting of sulfate ion in the upper sediment layer (10 cm). Because of this, carbonates can only be
formed in surface sediments near the water-bottom interface. Authigenic carbonates occurring within sediments occur do notin situ. Salinity, as well as CO
3
2−
/Ca and Mg/Ca ratios, correspond to the field of nonmagnesian calcium carbonate precipitation. Calcite is the dominant carbonate
mineral in the methane seep caldera, where it occurs in the paragenetic association with barite. The radiocarbon age of carbonates
is about 10000 yr. |
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