1988 Fiscal Year Final Research Report Summary
Sedimentological Study of the Relation between the Decomposition and Maturation of Organic matter and Formation of Authigenic Minerals during Early Stage of Diagenesis
| Project/Area Number |
62470045
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
地質学一般
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| Research Institution | University of Tokyo |
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Principal Investigator |
TADA Ryuji Faculty of Science, University of Tokyo, 理学部, 助手 (30143366)
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| Co-Investigator(Kenkyū-buntansha) |
KAKUWA Yoshitaka College of General Education, University of Tokyo, 教養学部, 助手 (70124667)
WATANABE Yoshio Faculty of Tokyo, University of Tokyo, 理学部, 助手 (70182962)
UTADA Minoru University Museum, University of Tokyo, 総合研究資料館, 助教授 (50012406)
IIJIMA Azuma Faculty of Science, University of Tokyo, 理学部, 教授 (90011501)
MATSUMOTO Ryo Faculty of Science, University of Tokyo, 理学部, 講師 (40011762)
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| Project Period (FY) |
1987 – 1988
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| Keywords | Organic carbon / Diagenesis / Carbonate minerals / Gas hydrate / 酸素同位体組成 |
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| Research Abstract |
This research porject includes two major thema. One is the origin of organic matter in sediments and the mechanism of fluctuation of the content. The other is the genetic relation between gas-hydrate and formation of authigenic carbonates.
The mechanism of the concentration and dispersion of organic matter (organic carbon) in sediments was investigated using the sedimentological and geochemical techique including sedimentary structure- and texture-analyses and the major, minor, and rare earth element geochemistry. Results of this theme was reported last year and published in the University Journal.
The second theme was focused on the nature of natural gas hydrate, factors controlling the variation of carbon and oxygen isotopic composition of authigenic carbonates, and gas-hydrate related phenomena in sedimentary sequence. The importance of gas hydrate had long been ignored or minimized by geologists, but the present study has stressed the potential importance of gas hydrate both in sedim
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entary and diagenetic processes.
If the production rate of biogenic methane is large enough to make the interstitial water supersaturated with respect to methane, the "excess methane" could form ice-like methane hydrate under a certain pressure-temperature condition. Gas hydrate concentrates more 80 relative to ambient water. General trend of the depletion of 180 of the interstitial water may be interpreted as the result of hydrate formation. Upon further burial, methane hydrate would finally decompose and supply the sediments with large amounts of methane and 180-enriched water. Detrital ferric iron is reduced, and methane is "oxidized" (anaerobic oxidation), then alkalinity of the interstitial water is expected to increase dramatically. This seriese of reaction leads to the precipitation of heavyoxygen, Fe-bearing carbonated, usually siderite.
The present study found such unusual siderite from several under-the sea core samples taken from the continental margin offshore Shikoku and SE America and the Neogene siliceos rocks in Aomori and Yamagata Prefectures. Less
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