| Co-Investigator(Kenkyū-buntansha) |
MOTOYAMA Isao University of Tsukuba, Graduate School of Life and Environmental Sciences, Lecturer (80295295)
YANAGISAWA Yukio Institute of Geology and Geoinformation, Geological Survey of Japan, AIST, Senior Research (10358210)
KANO Kazuhiko Institute of Geology and Geoinformation, Geological Survey of Japan, AIST, Senior Research (40356811)
TANAKA Yuichiro Institute of Geology and Geoinformation, Geological Survey of Japan, AIST, Senior Research (50357456)
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| Research Abstract |
In order to clarify the time and space distribution of the Japanese Cenozoic molluscan species, we have been investigated precise age of each strata which including the type species mainly based on the integrated biostratigraphy and isotopic age such as K-Ar and FT method. We studied the geologic age of Cenozoic strata of Hokkaido, NE Japan, Central Japan, SW Japan, Kyushu and Okinawa Islands., and also compiled published papers described data on the geological age of strata and geologic correlation during the last 10 years. As a result, we can proposed new Cenozoic molluscan biostratigraphical scheme, which will be published in the proceedings of the 9th Pacific Neogene Stratigraphy in August, 2008 (Special issue of the Bulletin of Geological Survey of Japan).
Japanese Paleogene faunas have been compiled from the biochronological aspect, and Miocene molluscan faunas are now divided into the subtropical Akeyo-Kunugidaira fauna (20-16. 4 Ma), the tropical and/or subtropical Yatsuo-Kadono
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sawa fauna (16. 4-15. 3 Ma), the subtropical and/or warm temperate Moniwa fauna (15. 3-15 Ma), the warm-temperate Older Shiobara-Yama fauna (15-11 Ma) and the mild-temperate and/or cool-temperate Younger Shiobara-Yama fauna (11-5. 3 Ma). These faunas can be considered as responses to stepwise cooling stages from tropical to cool-temperate realms, respectively. The Kukinaga fauna, characterized by Arcid-Potamidid fauna, is considered as a relict of the Vicarya-bearing early Miocene fauna. However, we tried once again microfossil biostratigraphy for the Kukunaga Group, and it is still continue to investigate. In addition, we studied the Zushi molluscan fauna which distributed mainly around the Kanto area from the biochronological aspect and concluded it is late Miocene in age based on calcareous nannofossil biostratigraphy.
Consequently, we compiled detailed Cenozoic geological and paleoenvironmtal history of the Japanese Islands in conjunction with the developmental process of the rifting of the Japan Sea. Less
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