Correlation of the late Pliocene Mushono-Shiraiwa Tephra Beds in the Kobiwako and Kakegawa Groups to the Kyp-NAll-Jwg4 Tephra Beds in the Niigata region, central Japan

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The correlation of the late Pliocene Mushono Tephra Bed in the Kobiwako Group, the Shiraiwa Tephra Bed in the Kakegawa Group and the Kyp, NAll, Jwg-4 and their correlative Tephra Beds in the Niigata region was performed. The correlation of the Mushono Tephra Bed to the Shiraiwa Tephra Bed was also confirmed by chemical composition of glass shards, especially on the FeO contents of 1.6-1.8% in average. The Mushono-Shiraiwa Tephra Bed was correlative to the Nkw and Dgc Tephra Beds in the Tomikura area, eastern Arai City, the Kyp Tephra Bed in the Higashikubiki area, the Sgs Tephra Bed in the Hachikoku area, the NAll Tephra Bed in the Ojiya area and the Jwg-4 Tephra Bed in the Chuo and Nishiyama Oil Fields. These tephra beds commonly have primary pyroclastic deposits at the base of the beds that can be interpreted as subaqueous fallout origin. These correlative tephras in central Japan cover more than 300x250Km^2 area, which implies one of the prominent eruptions in late Pliocene around 2.35Ma. The source volcanic area can be supposed in the northern Chubu Mountains based on the distribution of the deposits.

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