| Project/Area Number |
13640468
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Stratigraphy/Paleontology
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| Research Institution | Yokohama National University |
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Principal Investigator |
MAJIMA Ryuichi Yokohama National University, Faculty of Human and Educational Sciences, Professor, 教育人間科学部, 教授 (30202310)
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| Co-Investigator(Kenkyū-buntansha) |
WADA Hideki Shizuko University, Faculty of Sciences, Professor, 理学部, 教授 (20126791)
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| Project Period (FY) |
2001 – 2003
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| Project Status |
Completed (Fiscal Year 2003)
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| Budget Amount *help |
¥3,900,000 (Direct Cost: ¥3,900,000)
Fiscal Year 2003: ¥1,100,000 (Direct Cost: ¥1,100,000)
Fiscal Year 2002: ¥1,000,000 (Direct Cost: ¥1,000,000)
Fiscal Year 2001: ¥1,800,000 (Direct Cost: ¥1,800,000)
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| Keywords | Japan / Glacio-eustatic change / Early Pleistocene / Chemoautotrophic assemblage / Methane seep / Carbonate concretion / Carbon stable isotope / Regressive facies / 炭素の安定同位体比 / 海退相 / 高鍋層 / 棚層 / 安定同位体比 / ポックマーク |
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| Research Abstract |
Fossil chemoautotrophic assemblages in Japan can be divided into three types, based on species composition, mode of occurrence, and palaeobathymetric distribution. Type 1 is dominated commonly by vesicomyid bivalves and/or tube worms, and characterised by its allochthonous or parautochthonous mode of occurrence in deep-water settings, along with tectonically-or sedimentologically-induced structures such as faults, slumps, diapirs, or debris flows. Some Type 1 assemblages are comparable to modern cold-seep communities around Japan at depths of more than about 500 m, living on scarps and talus deposits, whereas other Type 1 assemblages are seemingly related to slope failures and sediment collapses caused by the drastic decomposition of gas hydrates. Type 2 assemblages are also dominated by vesicomyid bivalves, but usually the species differ from those in Type 1. In contrast with Type 1 assemblages, Type 2 assemblages are characterised by autochthonous occurrences in muddy sediments in le
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ss than 1,000 m water depth. Type 3 assemblages are dominated by Lucinoma and/or Conchocele and are characterised by autochthonous occurrences in muddy sediments at water depths of less than 300 m. No living community comparable with Types 2 and 3 assemblages has yet been observed in the seas around Japan. It is noteworthy that no tectonically-or sedimentologically-induced structures, such as faults, slumps and/or debris-flow deposits, have been observed in and around Type 2 and 3 fossil localities, although the muddy sediments sometimes show brecciated facies that suggest an explosive effusion of methane. Occurrences of Types 2 and 3 may have been synchronous with sea-level changes that triggered methane-hydrate decomposition and/or the upward migration of methane gas. This working hypothesis may also explain why there in no comparable modern community made up of these types : present-day sea level is stable compared to the ancient sea levels when Type 2 and 3 fossil assemblages flourished. Less
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