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Miniaturized biosignature analysis reveals implications for the formation of cold seep carbonates at Hydrate Ridge (off Oregon, USA)
1Geoscience Centre (GZG), University of Göttingen, Göttingen, Germany
2Leibniz-Institut für Meereswissenschaften (IfM-GEOMAR), Kiel, Germany
Abstract. Methane-related carbonates from Hydrate Ridge typically show several macroscopically distinguishable phases, namely whitish aragonite, lucent aragonite, and gray micrite. The relationship of these phases to particular microorganisms or biogeochemical processes is as yet unclear. We used a miniaturized biomarker technique on mg samples, combined with factor analysis and subsequent electron microprobe analysis, to study lipid biomarkers and chemical compositions of the individual phases. This allows us to identify particular mechanisms involved in the formation of the different carbonate precipitates. Our combined analysis of biomarkers and petrographic traits shows that most of the lipids related to the anaerobic oxidation of methane (>90% by weight) are concentrated within only a minor compartment (~20% by volume) of the Hydrate Ridge carbonates (whitish aragonite). The patterns indicate that the whitish aragonite represents fossilized biofilms of methanotrophic consortia, whereas the precipitation of the lucent aragonite does not seem to be directly controlled by microorganisms. The gray micrite shows a partly Mg-calcitic mineralogy, higher pyrite contents, and a much higher proportion of allochthonous biomarkers. The formation of these precipitates is interpreted to reflect periodic methane-rich fluid pulses that disrupted the sediments and promoted the growth of the respective methanotrophic consortia along fluid pathways.
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Citation: Leefmann, T., Bauermeister, J., Kronz, A., Liebetrau, V., Reitner, J., and Thiel, V.: Miniaturized biosignature analysis reveals implications for the formation of cold seep carbonates at Hydrate Ridge (off Oregon, USA), Biogeosciences Discuss., 4, 4443-4458, 2007. Bibtex EndNote Reference Manager
