The Pliocene Fukagawa Group which lies unconformably over the Middle Miocene Nishitoppu Group is divided into the Chippubetsu and Itchan Formations in ascending order in the Tadoshi Hills, north of Fukagawa City. Examination of tephra zonation and pollen assemblages shows that the lower and the upper parts of the Chippubetsu Formation are correlated with the upper part of the Horokaoshirarika Formation and the Ichinosawa Formation, respectively and the Itchan Formation with the Bibaushi Formation. The Horokaoshirarika, Ichinosawa and Bibaushi Formations are the type sequences of the Fukagawa Group distributed on the opposite side of the Tadoshi Hills in the northern part of the Ishikari Alluvial Plain. The Tokachi Group is a standard sequence of the Pliocene in Hokkaido, and is divided into four formations; the Honbetsu, Ashoro, Ikeda and Shibusan Formations in ascending order. From the molluscan fauna and the pollen assemblages it shoud be possible to correlate the Chippubetsu and the lower part of the Itchan Formation with the upper part of the Honbetsu Formation, and the upper part of the Itchan Formation with the Ashoro Formation and the lower part of the Lower Ikeda Formation. The Fukagawa Group is unquestionably Pliocene in age as shown in Table 4.

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