日本海東部西津軽沖, 久六島東方中層域における第四紀後期の有孔虫群集と珪藻群集

Abstract

We analysed assemblages of diatoms and foraminifera in a late Quaternary sequence from the core MD179-3326G (core length; 5.53 m) recovered at the seabed 325 m depth, east of Kyuroku Island, eastern part of the Japan Sea. We recognized six foraminferal bio-zones which are comparable to those from two sediment cores at the upper slope (around 300 m depth) in the southwestern Japan Sea (off Tottori). The occurrence of Elphidium excavatum suggests that the “Oyashio” cold surface water would have flowed into the Japan Sea through the Tsugaru Strait during the early part of the last deglacial stage. The distribution of Verneuilinulla advena in the Japan Sea was restricted to the northern shallow to intermediate area, which is narrower than that of E. excavatum. Furthermore, the bottom environments of the intermediate part in the Japan Sea could have been different between the east (east of Kyuroku Island) and the northwest (off Tottori) during the early part of the last deglaciation.