Amorphous Components of Buried Humic Soils among the Upper Member of Ashitaka “Loam” Formation, Latest Pleistocene Tephras, Central Japan

Abstract

It is the main interest of this paper how amorphous matters of humic horizon had changed on burial. Samples from several buried humic horizons among the Upper Member of Ashitaka “Loam” Formation, about 14, 000-30, 000 years old, were studied in comparison with those from the recent humic soils lying on them. The followings were obtained from determination of apparent and if possible net charges of allophane, humus, and layer-silicates, and from extraction of free oxydes with hydrogen peroxyde diggestion and sodium bicarbonate-sodium citrate-sodium dithionite treatment.
1) Contents of allophane and amorphous sesquioxydes extracted with the last mentioned treatment are abundant and uniform through the profile.
2) Activities measured of alumina both free and of allophane decrease with depth.
3) Apparent and net activities of humus also diminish continuously with progressive burial, the former falling even into zero level in the lowest horizons.
4) Gibbsite formation found its maximum phase in the upper horizons.
5) Relative abundance of silica took place in the lower horizons, thus resulting in formation of halloysite and decrease in net positive activity of allophane.