十勝層群本別・足寄層の花粉化石層序

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Thick Neogene to Quaternary deposits, the Tokachi Group, are distributed extensively in the Tokachi Plain, eastern Hokkaido. The lower part of this Group, the Honbetsu, Ashoro and Ikeda Formations were investigated with pollen analysis. Two pollen zones, Picea-Tsuga-Alnus Zone and Fagus-Alnus Zone were discriminated, and each zone was subdivided into Subzones I〜III in ascending order. 1. Picea-Tsuga-Alnus Zone (Latest Miocene〜Early Piocene) is generally characterized by high frequencies of fossil pollen Picea, Tsuga, Alnus and Juglans originated from temperate〜cool temperate slope forest. In Subzone II, pollen frequencies of broad leaf trees such as Ulmus〜Zelkova, Quercus, Tilia and Carpinus are reratively higher than those of Subzones I and III. 2. Subzone I in Fagus-Alnus Zone (Early Pliocene) is characterized by high frequencies of fossil pollen Fagus, Alnus, Tsuga and Picea originated from temperate〜cool temperate forest. It was a transitional stage from Picea-Tsuga-Alnus Zone to Subzone II in Fagus-Alnus Zone which is dominated with Fagus and Alnus. Climatic condition of Subzoue II is represented warmer and moister than that of Subzone I. However, the pollen assemblage obtained from Subzone III (Late Pliocene) suggests that it deteriorated to cool climatic condition. The characteristic of Fagus-Alnus Zone is correlated with that of Pliocene Hukagawa Group which are distributed in the Takikawa and Hukagawa district, Hokkaido.
地学団体研究会の論文
1988-09-25

十勝層群本別・足寄層の花粉化石層序

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