Study on migration, disappearance and evolution of Ostatcoda with relation to the opening and clostire of the Tsushima and Korean Straits during the late Cenozoic

本研究的目的在于阐明竹岛海峡和朝鲜海峡的开合与晚新生代介形虫的迁移、消失和演化之间的关系。用于分析最近介形类的表层沉积物样本采集于对马岛沿岸的封闭海湾。（Shush， Aso和三浦湾）和大村湾。有关化石。介形虫，我收集了新泻县上新世Kuwae组、宫崎组、中新世Chugoku山等矿床的样品。基于这些结果，并考虑到早期的研究，我得出了以下四个结论：自更新世中期以来，朝鲜海峡一直是甲壳类生物的地理浴场。日本封闭湾的优势种与朝鲜和中国封闭湾的优势种不同。在中上新世Kuwae组间冰期沉积中发现了生活在水深小于50 m海域的水介形虫种。特别是在2.9 Ma左右，肯定发生了暖水流入。然而，在当时黑潮的影响下，只有少数介形虫种主要生活在浅海。因此，流入日本海的暖流比今天更弱、更薄。中上新世各间冰期均发育比今天温度高（6℃以上）的温带中间水域。然而，本研究并未明确水的流入路径。在中新世气候最适宜时期（约16 Ma），由于南部海峡开阔，暖流强流入日本海，日本北部至南部的热带至亚热带介形类繁盛。这些介形虫组合与早中新世晚期（约17-18 Ma）的介形虫组合有所不同。

The aim of this study is to clarify the relationships between the opening and closure of the Thushima and Korean Straits and migration, disappearance and evolution of Ostracoda during the late Cenozoic. Surface sediment samples for the analysis of recent Ostracoda were collected from enclosed bays along the Tsushima Island. (Shush, Aso and Miura Bays) and Omura Bay. Concerning fossil. Ostracoda, I collected samples from the upper Pliocene Kuwae Formation, Niigata Prefecture, the Miyazaki Group, Miocene deposits in the Chugoku Mountains and so on. Based on these results and taking account of earlier studies, I led to the four conclusions as follows;The Korean Strait has been a geographic bather far embayment ostracodes alter the middle Pleistocene. Namely dominant species in Japanese enclosed bays are different from those in Korean and Chinese enclosed baysWarm water ostracode species living in marine areas shallower than 50 m in water depth were recognized in the interglacial deposits of the middle Pliocene Kuwae Formation. Especially, warm water inflows occurred certainly at about 2.9 Ma. However, there are only a few ostracode species which lived dominantly in shallow seas under the influence of the Kuroshio Current at that time. Thus warm water currents having flowed into the Japan Sea were weaker and thinner than today.Temperate intermediate waters warmer than today (more than 6 ℃) were developed in each interglacial period of the Middle Pliocene. However, inflow routes of the waters were not clarified in this study.Tropical to subtropical ostracode species were flourished through the northern to southern Japan during the Miocene climatic optimum (ca. 16 Ma) because the southern strait opened widely and strong warm water currents flowed into the Japan Sea. These ostracode assemblages were somewhat different from those in the late Early Miocene (ca. 17-18 Ma).