分子化石による過去の湧水活動の復元 : 更新統小柴層と大船層の例

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We analyzed lipid biomarkers related to AOM (anaerobic oxidation of methane) that happened in the early Pleistocene (1.7-1.4Ma) cold-seep site, northern part of Miura Peninsula, Pacific side of central Japan. Nineteen samples are obtained from a bedding-normal, 107m-long core consisting of the Koshiba (sandy mudstone and muddy sandstone, above 23m in core depth) and the Ofuna (mudstone, below 23m) Formations. In this core, both the chemoautotrophic bivalves (Lucinoma, Conchocele, Archarax) and ^<13>C-depleted authigenic carbonates (aragonite, MG-calcite, dolomite) occur abundantly. Four important results of this study are summarized as follows. 1) Both archaeal and sulfate reducing bacterial (SRB) biomarkers are recovered in all samples and their ether linkages are well preserved even in 1.7-1.4Ma sediments. 2) High activities of AOM are inferred in 7.1-7.6m and 14.6m in core depths where both archaeal and SRB-biomarkers are distinctly concentrated and greatly depleted in ^<13>C (δ^<13>C less than-100‰ vs. PDB). Those activities happened probably when marine bottoms were in 6.5-7m and 13-13.5m, respectively, where chemoautotrophic bivalves occur abundantly. 3) Two samples obtained from the same horizon 14.6m show an apparent difference in biomarker compositions. This difference may be attributed to a different micro habitats for microbes. 4) The occurrences of biomarkers derived from planktonic archaea are inferred from their δ^<13>C values and relative abundance of 4 kinds of biphytanes. Planktonic archaeal biomarkers are probably recovered from all samples and their concentration rates may be useful as an index of sedimentation rate.
2010-03-31

分子化石による過去の湧水活動の復元 : 更新統小柴層と大船層の例

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