津軽半島南東部に分布する鮮新統 : 下部更新統の有孔虫化石群集

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Foraminiferal fossils from the Pliocene Tsukushimoriyama Formation and lower Pleistocene Daishaka Formation in the southeastern Tsugaru Peninsula, Northeast Japan, are examined. Twelve species of planktonic foraminifers were identified among 13 samples. The occurrence of Neogloboquadrina pachyderma (dextral) and a radiometric age of the Otakizawa Tuff Member in the Tsukushimoriyama Formation suggest that the geological age of the formation is the Late Pliocene. The Daishaka Formation is assigned to the Lower Pleistocene on the basis of coiling direction of N. pachyderma and K-Ar ages of the formation. One hundred and sixteen species of benthic foraminifers were identified among 20 samples. Q-mode cluster analysis shows that these samples are divided into four clusters. The samples from the Tsukushimoriyama Formation belong to Clusters 1 and 2. The stratigraphic distributions of these clusters suggest that the middle and upper parts of the Tsukushimoriyama Formation deposited on upper bathyal zone in cool- and mild-temperate areas, respectively. The samples from the Daishaka Formation belong to Clusters 2, 3 and 4. Their stratigraphic distributions indicate that the formation changed in the depositional depth from middle to outer sublittoral zone to upper bathyal zone. Although the most of the formation was deposited under cool- or mild-temperate condition, a short interval in the upper part was affected by warm current. This influence might represent one of the intermittent inflows of the paleo-Tsushima Warm Current to the Japan Sea.
2005-09-28

津軽半島南東部に分布する鮮新統 : 下部更新統の有孔虫化石群集

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