Abstract
A profile of buried red colored soil covered with volcanic ash layer was newly found on the northern foot-slode of Mt. Tsukuba where present bio-climatic condition is transitional from warm-temperate lucidophyllus to cold temperate deciduous bload-leaved forest climate. The red colored soil is derived from colluvial slope-deposit consisting of stone and gravel of gabbro, which are highly weathered to give heavy clay texture. The profile has a horizon sequence of IIA_1/IIBt/IIC_1/IIC_2. The organic matter content is very low (less than 1%), the soil reaction is strong acid and the degree of base saturation is less than 30%. The activity ratio (Fe_o/Fe_d) and crystallinity ratio [(Fe_d-Fe_o)/Fet] range from 0.10 to 0.03, and from 0.51 to 0.70, respectively, showing that the soil belong to red soil. The clay mineralogical composition mainly consists of halloysite (10 A) and metahalloysite with some goethite. The chemical and clay-mineralogical properties of this red colored soil coinside quite well with those of relic red soils of Southwest Japan which are generally recognized as palaeo-red soils formed under the warmer past bio-climatic condition of the last inter-glacial epoch. It is, therefore, concluded that this buried red colored soil may be considered to be a fossil red soil.
