2020 Fiscal Year Final Research Report
Tropical radiolarian biostratigraphy during the Neogene in the central Indian Ocean and eastern equatorial Pacific
| Project/Area Number |
18K03819
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Multi-year Fund |
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| Section | 一般 |
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| Review Section |
Basic Section 17050:Biogeosciences-related
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| Research Institution | Ibaraki University |
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Principal Investigator |
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| Co-Investigator(Kenkyū-buntansha) |
伊藤 孝 茨城大学, 教育学部, 教授 (10272098)
西 弘嗣 福井県立大学, 恐竜学研究所, 教授 (20192685)
岩井 雅夫 高知大学, 教育研究部自然科学系理工学部門, 教授 (90274357)
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| Project Period (FY) |
2018-04-01 – 2021-03-31
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| Keywords | 中新世 / 放散虫化石 / 生層序 / 出現イベント / 消滅イベント / 同時性と異時性 / インドネシア海峡 |
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| Outline of Final Research Achievements |
Detailed biostratigraphic study of a lower Neogene section with radiolarians from central Indian ODP Site 714 has resulted in the precise correlation of many radiolarian bioevents with calcareous nannofossil and planktonic foraminiferal biostratigraphy. Comparison of results from Site 714 with those of previous studies from the tropical Pacific Ocean enables identification of synchroneity and diachroneity of radiolarian datum events between the tropical Indian and Pacific Oceans. Patterns of synchroneity and diachroneity of first occurrences were different near the middle/late Miocene boundary. Changes in these patterns might to have been influenced by the effective closure of the Indo-Pacific seaway. In contrast, the large majority of last occurrences showed synchroneity from the tropical Indian and Pacific Oceans during the early to late Miocene. This suggests that last occurrences during the early to late Miocene were affected by global climatic or oceanographic events.
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| Free Research Field |
古生物学
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| Academic Significance and Societal Importance of the Research Achievements |
インドネシア海峡が閉塞すると，赤道太平洋の東向きの赤道反流が形成されることによって熱帯・赤道循環の原型が誕生する．熱帯・赤道循環の誕生は，西部太平洋に暖水塊を形成し，日本列島へ北上する黒潮の勢力を一段と強化するため，日本列島を含む太平洋の環境に大きな影響を与えると考えられる． しかしインドネシア海峡の閉鎖した年代は，前期中新世末（17 Ma頃）および後期中新世初期（10 Ma頃）の大きく２つの説があった．本研究によって，効果的に閉塞したのは後期中新世初期（10 Ma頃）である可能性が高くなった．
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