Abstract
The Akashi-Harima area stratigraphically belongs to the Osaka group of Plio-Pleistocene age, which is composed of gravel beds, sand beds and clay beds formed in marine or fresh water environments. Clay mineral compositions of the clay beds were determined by the X-ray diffraction method, D.T.A. and optical microscopy. The results will be summarized as follows.
1) Abundant clay minerals of the clay beds are montmorillonite, metahalloysite, illite and chlorite.
2) Generally speaking, clay beds formed in the fresh water environment contain larger amounts of montmorillonite and smaller amounts of chlorite and illite near seashore than around hinterland.
3) There is a reverse relation between the quantity of montmorillonite and that of illite in the profile of fresh water clay beds (Ma 0). Chlorite is only contained in the Ma 1 clay beds around hinterland.
The sedimentary environment, where these clay minerals were formed, are discussed on the basis of geological and experimental results described above.
