Pedologist

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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.

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Hardened gel-like particles which are rich in alumina and silica were found in pores of volcanic glass in tephras and tephra-derived soils in Hokkaido. They are here named alumina-silica mineraloids because of the major chemical constituents. We investigated the mineraloids collected from 4 tephras at 5 sites. (1) The mineraloids were found in all the horizons studied. They are platy (circular, elliptical and rhombic) and non-platy (massive and spherical) in shape, and the platy shaped ones are dominant. Their average diameter is 109 μm, and the thickness of the platy type is 1/10〜1/15 of the major axis. (2) Clay mineral compsition of the mineraloids differs from that of clay fraction in the same horizon. It is simple and varies with the tephras; halloysite (7 Å), imogolite or a poorly-crystallized layer silicate mineral. (3) SiO_2 and Al_2O_3 contents of the mineraloids range 49〜57% and 29〜44%, respectively. (4) The mineraloids are assumed to be initial weathering products which were formed in the pores of pumice and volcanic glass by preciptation of the dissolved constituents of volcanic glass and other minerals.

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