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.

参考新的微生物年代学，特别是硅藻生物年代学，从生物地层学和古动物地理学的角度对北陆地区分布的新近纪软体动物化石进行了研究。北陆地区的新近纪软体动物群可分为四种：1）。黑濑谷动物群（早中新世晚期；16.5 - 15.5Ma），2）七尾动物群（中中新世早期；15.5 - 14Ma），3）乙川动物群（晚中新世；约9ma），和4）Omma动物群（上新世晚期到更新世早期；2-1Ma)，可以假设这些动物群在热带至亚热带（16,5-15,5Ma）、暖温带（15.5-14Ma）、温和至冷温带（约9Ma）和混合气候下繁盛。分别为亚寒带至冷温带和暖温带。其中，乙川动物群可归为日本特有动物群，可能是在中新世海水冷却期间建立的。虽然乙川动物群被认为是冷水型动物群，但一些温水起源的残余软体动物元素表明该动物群是温和至冷温带动物群。与近代亲潮（亲潮洋流）类似的近寒带海洋环境首次出现可能是在上新世时期。因此，北陆地区中新世至早更新世的动物区系变化与可能在中新世晚期至早更新世期间逐渐发生的全球范围变冷相吻合。