Abstract
The Daisen volcanic ash formation is widely distributed in Tottori Prefecture, Southwest Japan. According to the San-in Quaternary Research Group, this formation is divided into four members ; upper, middle, lower and the lowermost volcanic ash members consisted. The lowermost volcanic ash members of about thirty layers are found at Okachi, Kurayoshi C. Tottori Prefecture. The thirty layers consisted of pumices, loams and pyroclastic flows are divided into eight units, namely, a, b, c, d, e, f, g and h units from the lower to the upper due to the unconformity planes, The eight units are classified into four groups according to the soil colours, namely, the first group (unit a), the second group (units b and c), the third group (units d, e, f, and g) and the fourth group (unit h). We have studied the mineralogical, clay mineralogical and soil micromorphological properties of the above mentioned volcanic ash formations by means of X-ray diffraction analysis, differential thermal analysis, electron-microscopic observations and electronprobe microanalysis. The results of the analyses are summarized in Table 1.
