Anaerobic and Aerobic Oxidation of Methane at Late Cretaceous Seeps in the Western Interior Seaway,USA |
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Authors: | Daniel Birgel Jörn Peckmann Sandra Klautzsch Volker Thiel Joachim Reitner |
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Institution: | 1. DFG-Forschungszentrum Ozeanr?nder , Universit?t Bremen , Postfach 330 440, D-28334, Bremen , Germany;2. Geowissenschaftliches Zentrum der Universit?t G?ttingen , Goldschmidtstrasse 3, D-37077, G?ttingen , Germany |
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Abstract: | The Late Cretaceous (Campanian) Tepee Buttes represent a series of conical, fossiliferous limestone deposits embedded in marine shales that deposited in the Western Interior Seaway. The previously suggested origin of the Tepee Buttes at methane-seeps was confirmed by this study. δ13C values as low as ?50‰ of early diagenetic carbonate phases of two Tepee Buttes near Pueblo (Colorado) reveal that methane was the major carbon source. Molecular fossils released from a methane-seep limestone contain abundant 13C-depleted archaeal lipids (PMI, biphytane; δ 13C: ?118 and ?102‰), derived from anaerobic methanotrophs. A suite of 13C-depleted bacterial biomarkers (branched fatty acids; ?73 to ?51‰) reflects the former presence of sulfate-reducing bacteria, corroborating that a syntrophic consortium of archaea and bacteria mediating anaerobic oxidation of methane already existed in Cretaceous times. Molecular fossils also suggest that methane was not exclusively oxidized in an anaerobic process. A series of unusual C34/C35-8,14-secohexahydrobenzohopanes with low δ13C values (?110 and ?107‰) points to the presence of aerobic methanotrophic bacteria at the ancient seep site. |
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Keywords: | methane-seeps carbonates archaea bacteria biomarkers isoprenoids 8 14-secohexahydrobenzohopanes Colorado Cretaceous |
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