| Project/Area Number |
18540465
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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 | National Museum of Nature and Science, Tokyo |
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Principal Investigator |
TANIMURA Yoshihiro National Museum of Nature and Science, Tokyo, National Museum of Nature and Science, Departmet of Gelogy and Paleontology, Chief Curator (80141985)
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| Project Period (FY) |
2006 – 2007
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| Project Status |
Completed (Fiscal Year 2007)
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| Budget Amount *help |
¥3,830,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥330,000)
Fiscal Year 2007: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000)
Fiscal Year 2006: ¥2,400,000 (Direct Cost: ¥2,400,000)
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| Keywords | circum-Pacific region / lake / diatom / development |
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| Research Abstract |
Well preserved lacustrine Actinocyclus species occurred abundantly from Early to Middle Miocene diatomite from the Japanese Islands: Chojabara Formation in Iki Island, Yamatoda Formation in Noto-Nakajima, Piston-core RC12-394 from Yamato-Bank in the Sea of Japan, and Ouchi Formation in Miyagi. Their contribution to several horizons of Chojabara Formation account for nearly 99% of the total diatom valves.
Based on a comparison of the morphological characteristics of the Actinocyclus species with thirteen Actinocyclus species described from Miocene diatomite in the North American Continent, the species from the Japanese islands have classified tentatively into eight morphological types. The morphologic types have not been so far identified with the thirteen species. However, the common-abundant occurrences of the species of the species in both western part of North American Continent and the Japanese Islands is confirmed, and this evidence strongly suggested that development of lacustrine Actinocyclus species in the Early to Middle Miocene occurred nearly simultaneously in the circum-Pacific region ; namely it is highly probable that development and later rapid decline of Actinocyclus species in the Miocene were common events in the circum-Pacific region.
Although an age-model making is needed for making a complete biostratigraphic framework based on the lacustrine diatoms in the circum-Pacific region, the above evidences provide very basic data/information in a procedure to make the framework. In this study, a strict simultaneity in the development of Actinocyclus species between the Japanese Islands and the North American Continent is not confirmed, and an ecological/environmental factor(s) controlling the development and later decline of the species are still unsolved.
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