阿武くま山地中央部における第四系と植物化石群 最終氷期における東北南部の植生変遷の一例

Abstract

The Quaternary strata in the environs of Takine town in the central part of the Abukuma Mountains can be classified as shown in Table 1 and Figure 3. The Saru-uchi I Formation and the Saru-uchi II Formation are considered assignable to the Last Glacial Age on the basis of radiocarbon dates, regional tephra, paleomagnetic data and plant fossil assemblages (macroscopic and pollen fossils), and the Ishigami Formation to Early Holocene in age on the basis of radiocarbon date and plant fossil assemblages (macroscopic and pollen fossils).The Saru-uchi I Formation can be represented by a plant fossil assemblage zone Sr-1 of local significance. The Saru-uchi II Formation is classified into three local plant fossil assemblage zones, Sr-2, Sr-3 and Sr-4, in ascending order. The plant fossil assemblages characterizing the Sr-1 and Sr-4 zones seem to represent stadial floras and the one characterizing the Sr-2 zone an interstadial flora, all during the Last Glacial Age in the southern Tohoku District. And, the plant fossil assemblages characterizing the Sr-3 zone may represent a flora with intermediate characters between the stadial and interstadial floras. The Sr-2 zone is nearly suited to the Ts-b magnetozone containing an excursion, and assigned to ages of about 34, 000 to 30, 000 years B.P. as the results of radiocarbon dating.The plant fossil assemblages in the zones of Sr-1 and Sr-4 may represent the vegetation closely resembling to that of the subalpine zone in the central Honshu, and those in the zone of Sr-2 may represent a vegetation composed of taxas of the subalpine and montane zones in the central Honshu of Japan. The plant fossil assemblages in the zone of Sr-3 may represent the vegetation which contains the elements of the subalpine zone more abundantly than those of the montane zone.Finally, the characters of flora and vegetation in the southern Tohoku District during the Last Glacial Age are tentatively considered, based on the plant fossil assemblages from some areas.