Stratigraphy and Paleoenvironments of the Middle and Upper Pleistocene in Naganuma Area, the Eastern Ishikari Low Land, Hokkaido Japan

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  • 北海道中央部石狩低地帯東縁長沼地域の中 : 上部更新統層序と古環境
  • ホッカイドウ チュウオウブ イシカリ テイチタイ トウエン ナガヌマ チイキ ノ チュウ ジョウブ コウシントウ ソウジョ ト コカンキョウ

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Abstract

The Neogene deposits the Oiwake, Umaoi, Yamanegawa, Kita-naganuma, and Moseushi Formations are distributed in the Naganuma area eastern area of the Ishikari Low Land. We studied these formations and estimated the paleoenvironments and deposition times based on the analysis of foraminiferal assemblages, volcanic, ash and pollen fossil assemblages. Then we concluded the following facts. 1) All the Formations distributed in this are contact with unconformity each other. 2) Pyroclastic layers on the section in the Naganuma area are correlated with the pyroclastic fall deposits named Mpfa1, Mpfa3, Aso-4, Aafa2 (Toya), Aafa4, and the pumice fall deposit belonging to the Hayakita Formation due to feature of facies, grain assemblage compositions, chemical composition of volcanic glass, and stratigraphy. 3) The Umaoi and Yamanegawa Formations were deposited in the warmer period of the Middle Pleistocene MIS11 and 9. 4) The deposition time of Mpfa1 in the Kita-Naganuma Formation was cold and high moor such as the Latest Glacial Maximum.

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