北の陸橋 (日本海沿岸の更新世の古地理と古環境特集号)

概要

論文の詳細を見る
Hokkaido constituted the northern landbridge between Japan and the Asian continent during most of the last glacial, since the Soya Strait, between Hokkaido and Sakhalin, continuously emerged after about 60ka B.P. This paper reconstructs the permafrost environment and vegetation of this northern landbridge from the distribution of fossil periglacial phenomena and pollen data. The edge of the continuous permafrost zone shifted southwards, down to about 45°N in northeast China, and to about 43°N at the southern foot of the Shikhote-Alin' Range in easternmost USSR. The southern boundary of the discontinuous permafrost zone reached about 40°N in Hebei, 44°N in northeast China, and 40°N at the southern foot of Changbai Shan, North Korea. The limit of each zone runs southward from the Pacific side inland, just as the present limit of the permafrost zone does. The lack of typical ice-wedge casts and pingo scars on the one hand, and the richness of soil wedges and palsa scar-like features on the other, in northern and eastern Hokkaido strongly suggest that most of Hokkaido was located in a discontinuous zone of permafrost during the last glacial. The continuous zone seems to have covered only the northernmost part of Hokkaido. The fossil pollen assemblage from the coldest phase (25-20ka B.P.) in Hokkaido is characterized by Larix gmelini, Pinus pumila and Picea (probably P. ezoensis and P. glehnii). Although NAP pollens dominate in several localities, especially in eastern Hokkaido where volcanic activity continued through the last glacial, the dominance of light and dark conifers in the pollen assemblage indicates the spread of boreal forest in the main part of Hokkaido. This suggests that, during the last glacial, Hokkaido was part of the refugia for the taiga zone which consisted of Larix dahurica, very similar to (or synomymous with) species of Larix gmelini. On the assumption of a lowering of the vertical zonation by 1, 500m, the alpine tundra spread down to about 750m a.s.l., thus taiga forest covered the main part of Hokkaido. The vegetation of northern and eastern Hokkaido, which some researchers regard as tundra or forest tundra, seems to have been a complex one made up of patches of coniferous forest, grassland, mire, and alpine tundra.
日本第四紀学会の論文

北の陸橋 (日本海沿岸の更新世の古地理と古環境特集号)

スポンサーリンク

概要

著者

関連論文

スポンサーリンク