第四紀研究

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In southern Kyushu, there are distributed Late Cenozoic formations which were deposited from the Early Miocene to the Latest Pleistocene period. The formations consist mainly of lava, tuff breccia, tuff and occasionally intercalate beds composed of siltstone or claystone deposited in the lacustrine and shallow marine. Among them, siltstone and claystone bads commonly include macro and micro plant fossils.
In the present paper the writers have examined the plant fossil bearing beds on the basis of stratigraphy and fossil evidence. As a result of the investigation, five major pollen assemblage zones can be distinguished in ascending chronological order. They are as follows;
1) Metasequoia zone. Most of the pollen grains shown as Taxodiaceae in Figs. 3 and 4 are regarded as Metasequoia because of the abundance of fossil leaves of the Metasequoia sp. in the Nagano Formation and the Daiwa Member of the Koriyama Formation. The Arcto-Tertiary element such as Metasequoia is characteristic of this zone. The age may be assigned to the period from the Late Pliocene to the Early Pleistocene.
2) Fagus zone. Cool-temperate deciduous broad leaved trees and conifers such as Fagus, Ulmus and/or Zelkova, Pinus, Abies and Tsuga are characteristic of this zone. The age may be considered to be the Early-Middle Pleistocene.
3) Cryptomeria-Sciadopitys-Alnus zone. Temperate coniferous forests, coexisting with Alnus, Juglans and Corylus, dominated and Cryptomeria increased later. This zone occupies a relatively warm period in the Middle-Late Pleistocene.
4) Cryptomeria zone. This is characterized by a predominance of temperate conifers such as Cryptomeria and Abies suggesting a cool and damp climate. The age is considered to be the Late Pleistocene.
5) Pinaceae zone. This is yielding of such sub-arctic or cool-temperate coniferous taxa as Picea, Pinus and Tsuga. This may indicate a cold and dry climate during the Latest glaciation period.

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The pollen assemblages, macroscopic remains (seed, fruit, leaf, etc.), and wood remains obtained from the Latest Pleistocene peat bed at Harabun, Tochigi Prefecture, ca. 20, 000y.B.P., resemble each other in occurrence of such remarkable taxa, as Pinus subgen. Haploxylon, Picea, Larix, Betula, and Alnus. The forests are characterized by a dominance of Pinus koraiensis and Picea, accompanied by Larix and Betula platyphylla. Wood anatomy shows that Picea includes two groups, but P. cf. shirasawae is identified or the basis of cone morphology These indicate the upper cool-temperate to lower subalpine climate. From these facts and the previous reports it is inferred that such forests spread out widely in the northern Kanto region during the last glacial maximum.

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