GENESIS OF SOILS DERIVED FROM VARIOUS TYPES OF PARENT ROCK IN SOUTHWESTERN JAPAN : III. Lithological Grouping and Evaluation of Lithology Index and Weathering Index

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Lithological grouping of rock and soil samples was performed using the Fe_2O_3/Al_2O_3 and Al_2O_3/TiO_2 ratios, in one attempt, and Fe_2O_3 and ZrO_2/TiO_2 ratios, in another. By and large, the two grouping s were suitable for the rock samples, and the soil samples were often assigned to the same groups as those of the respective parent rocks. Hence, the lithological features of the parent rocks were considered to be well preserved in the course of profile development. The uniformity of the parent material within the profile was confirmed by the lithology index (LI) and TiO_2/ZrO_2 ratio except for the Yakuno, Niimi-1, Niimi-2, Sekinomiya-1, and Sekinomiya-2 soils. The value of the weathering index (WI) often increased from the C to the B horizon within the profile. But the WI value decreased from the B to the A horizon in eight of the sampled soils. The rejuvenation in the surface soil was ascribed either to the surface accumulation of bases associated with the biological cycling under the forest, or to the surface addition of younger, less clayey materials resulting from colluvial deposition, volcanic ash, or eolian dust.
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