Microbially induced formation of ooid-like coated grains in the Late Cretaceous methane-seep deposits of the Nakagawa area, Hokkaido, northern Japan |
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| Authors: | Robert Gwyn Jenkins Yoshinori Hikida Yoshito Chikaraishi Naohiko Ohkouchi and Kazushige Tanabe |
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| Institution: | Department of Earth and Planetary Science, University of Tokyo, Tokyo 113-0033, Japan (email: ),;Nakagawa Museum of Natural History, Hokkaido 068-0835, Japan, and;Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Yokosuka 237-0061, Japan |
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| Abstract: | Abstract Ooid-like coated grains are found in the Late Cretaceous methane-seep deposits in the Nakagawa area, Hokkaido, Japan. The coated grains were examined using macro- and microscopic observations, electron-probe microanalysis, and biomarker analysis. They are round- to oval-shaped, with nuclei consisting of fractured sediment and micritic envelopes. The fractures probably occurred as a result of increasing hydrostatic pressure when the sediment was still unconsolidated or weakly consolidated. Biomarker analysis revealed that two types of molecules, crocetane and PMI, are predominant in the hydrocarbon fraction with highly negative carbon isotopic composition as low as −122‰ ( vs Vienna Peedee Belemnite). These data suggest that the coated grains were formed under the influence of anaerobic oxidation of methane, near the sediment/seawater interface. The presence of such grains indicates that methane-containing pore water reached the sea floor at that time. |
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| Keywords: | authigenic carbonate precipitation biomarker fluid flow hydrocarbon seep microbe microbialite |
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