示標テフラによる黒ボク土の生成開始時期の推定 : 十和田火山テフラ分布域蔦沼地区を例にして

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Using opal phytolith analysis and humus analysis, we have determined the relationship between humus properties and vegetation history on accumulated volcanic ash soils at Tsutanuma, Towadako-cho, in the area of Holocene Towada volcanic ash. These data coupled with time marker tephras allow a discussion of the basal age of the Kuroboku Soils (Andosols) and the human impact on forests. After the Late glacial substage, Brown weathered tephra (B. W. T.), Chuseri pumice (Cu, about 5,400 y. B. P.) and Towada a tephra (To-a, about 1,000 y. B. P.) accumulated at Tsutanuma. Here, the section is divided into three soil stratigraphic units with each of the tephras as the basal horizon. The three soil units are called the Tsutanuma B. W. T. Soil (Unit III), the Tsutanuma Chuseri Soil (Unit II) and the Tsutanuma Towada a Soil (Unit I). Every soil unit did not show Kuroboku Soils characteristics and developed under a broad leaf forest. Therefore, all units are Brown Forest Soils-like volcanic ash soils. This indicates that Brown Forest Soils-like volcanic ash soils formed under broad leaf forest at Tsutanuma during the Holocene. At present, the Tsutanuma area is covered by forest which dose not result in Kuroboku Soils. It seems, therefore, that the formation of Kuroboku soils at Tsutanuma will depend on a change from forest to grassland in the future. The continuation of forest vegetation during the Holocene at Tsutanuma depended on no human impact. As human advancement to the Tsutanuma area was very late (because of an unfavorable environment), the climax of natural vegetation was maintained. Volcanic activity, resulting in accumulation of tephra at a few thousand intervals, only caused transitory damage to forest vegetation and could not be the decisive factor that controlled the change in the vegetation pattern.
地学団体研究会の論文
1994-09-25

示標テフラによる黒ボク土の生成開始時期の推定 : 十和田火山テフラ分布域蔦沼地区を例にして

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