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

本研究旨在阐明秀岛海峡和朝鲜海峡的开放和关闭与介形类在晚新生代的迁移、消失和演化之间的关系。用于分析现代介形类的表层沉积物样本是从对马岛沿岸封闭的海湾采集的。(嘘，麻生和三浦湾)和大村湾。关于化石。介形类，我采集了上新世科威特组、新泻县、宫崎群、中部山区中新世沉积等样品。在此基础上，结合前人的研究，得出以下四点结论：朝鲜海峡是介形虫更新世中更新世的地理浴场。在上新世科威特组中的间冰期沉积中发现了生活在水深50m以下海域的淡水介形虫种类。尤其是在2.9 Ma左右肯定出现了暖水流入。然而，当时受黑潮影响主要生活在浅海的介形虫种类屈指可数。因此，流入日本海的暖流比今天更弱、更薄。在中上新世的每一次间冰期，都发育了比今天更温暖的中温海水(超过6℃)。在中新世气候最佳时期(约16 Ma)，由于南部海峡开放，强暖流流入日本海，热带至亚热带介形虫物种在日本北部至南部大量繁殖。这些介形虫组合与早中新世晚期(约17-18 Ma)的介形虫组合略有不同。

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).