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Neogene molluscan biostratigraphy and paleoecology of the Hokuriku district

北陆地区新近纪软体动物生物地层学和古生态学

基本信息

批准号：
61540564
负责人：
OGASAWARA Kenshiro
金额：
$ 1.28万
依托单位：
TOHOKU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1986
资助国家：
日本
起止时间：
1986 至 1987
项目状态：
已结题

项目摘要

Neogene molluscan fossils distributed in the Hokuriku district have been studied from the view points of biostratigraphy and paleozoogeography in refer to the new microbiochronology, in particular the Diatom biochronology.The Neogene molluscan faunas of the Hokuriku district can be divided into four as 1). the Kurosedani fauna (late Early Miocene; 16.5 - 15.5Ma), 2) the Nanao fauna (early Middle Miocene; 15.5 - 14Ma), 3) the Otogawa fauna (Late Miocene; ca. 9ma), and 4) the Omma fauna (Late Pliocene to Early Pleistocene; 2-1Ma), respectively.These faunas can be assumed that the faunas had been fourished under the tropical to subtropical (16,5-15,5Ma), warm-temperate (15.5-14Ma), mild to cool-temperate (ca. 9Ma) and mixed of subboreal to cool-temperate and warm-temperate, respectively. Among them, the Otogawa fauna can be assigned to the Japanese endemic one which might be established during Miocene sea-water cooling. Although the Otogawa fauna has been considered to the cold-water type, some molluscan elements which are survivals of the warm-water origin suggest that the fauna is mild to cool-temperate ones. The first appearence of the subboreal marine environment which is comparable to those of the Recent Oyashio (Oyashio Current) might be in the Pliocene time. Consequently, faunal changes of the Miocene to the Early Pleistocene of the Hokuriku district well corresponded to worl-wide cooling that was probably taking place gradually through the late Miocene to early Pleistocene.

本文从生物地层学和古动物地理学的角度，结合新的微生物年代学，特别是硅藻生物年代学，对北陆地区新近纪的软体动物化石进行了研究，将北陆地区新近纪的软体动物群划分为4个区系：1）.黑濑谷动物群（早中新世晚期; 16.5 - 15.5Ma）;南尾动物群（中中新世早期; 15.5 - 14 Ma）;这些动物群可能分别在热带-亚热带（16.5 - 15.5Ma）、暖温带（15.5- 14 Ma）、温和-冷温带（约. 9 Ma）和亚寒带-冷温-暖温混合带。其中，Otogawa动物群属于日本特有动物群，可能建立于中新世海水冷却期。虽然Otogawa动物群一直被认为是冷水型的，但一些暖水起源的幸存的软体动物成分表明，该动物群是温和到冷温带的。与现代Oyashio（Oyashio海流）相当的亚寒带海洋环境的首次出现可能是在上新世。因此，北陆地区中新世至早更新世的动物群变化与中新世晚期至早更新世可能逐渐发生的全球性降温相对应。