Clay-mineralogical characteristics of soils distributed under warm-temperate forest climate in Nyu Mountains, Fukui Prefecture, Central Japan

Abstract

The vertical distribution of the clay minerals in the profiles of the five soils occurring in the Nyu mountains, namely Dark red soils, Kunimidake series, KNM soil; Dry brown forest soils, Takasu-1 series, TKS soil; Dry brown forest soils (reddish), Tega series, OSI soil; Red soil, Oshibayama series, DAI soil; and Yellow soils, Yada series, MAT soil, compared with Hyperdistri-Rhodic Cambisol, Hyperdistri-Chromic Cambisol, and Hypereutri-Chromic Cambisol of WRB was analyzed quantitatively from the viewpoint of pedogenesis. The results are summarized as follows: Smectite originating in pyroxine andesite which had undergone hydrothermal degradation was altered to chlorite-smectite intergrade in the AB and Bwl horizons, and to chlorite in the A and AB horizons of the KNM soil, suggesting that this soil had been formerly affected by the past warm climate. This intergrade mineral, however, reversely changed to smectite in the surface horizon due to the influence of eluviation of the interlayered hydroxy aluminum of the intergrade mineral under the present cool-temperate climate. The TKS, OSI, and MAT soils, Yellow-Brown Forest soils, were characterized by the presence of chlorite-vermiculite intergrade and chloritization in the surface horizon in terms of clay mineralogy. Based on the clay-mineral composition, the zonal soil under the Warm-temperate deciduous broad-leaved forest climate in the surveyed area was a Yellow-Brown Forest soil. The DAI soil, as paleo-red soil, was formed by the weathering of autochthonous rocks, but the subsurface horizon of the OSI soil, as a paleosol, originated in the loess brought from the Asian continent, based on the clay-mineral composition.