Abstract
A possible approach to the origin of sediments in the Osaka Group is discussed on the basis of chemical analysis. The study area is located at the margin of the sedimentary basin of the Osaka Group distributed on the Uji hills, where the Aodani
Gravels, the Joyo A Gravels, the Joyo B Gravels and the Uji Gravels are observed. Chemical analysis of the whole samples were carried out using an X-ray fluorescenc spectrometer, and biotites in the sediments were analyzed using an electron probe micro analyzer (EPMA).
The sediments of the Uji Gravel could not be well discriminated from those of the Joyo A Gravels and/or the Joyo B Gravels by means of contents of Sr and Rb in the XRF analysis, which were useful in the soil discrimination. However, the contents of FeO and MgO (or the MgO/FeO ratios) of the biotites in the fine sediments and/or weathered granitic gravels were effective to the discrimination.
The analytical results were compared with the biotites in the granitic rocks and their weathered products, which were distributed in the hinterlands, by means of the MgO/FeO ratios. As the results, it was presumed that the Joyo A Gravels and the Joyo B Gravels were characterized by the weathered products which had been derived from the Yagyu-type granites, whereas the Uji Gravels included the weathered products which had been derived from the Shigaraki-type granites.
