堆積岩無機物の研究  [in Japanese] Studies on sedimentary inorganic rocks : A review  [in Japanese]

During the last fifteen years. the study on sedimentary inorganic rocks has made remarkable progress in Japan. The genetical studies have been emphasized, especially on weathering and diagenesis. The Japanese weathering researchers have mainly studied the weathering envelopes produced in Quaternary volcanic ash deposits and granitic rocks. They showed that the kaolin-bearing ones cover the entire Japanese Islands, and clarified the detailed mineralogical and chemical changes in weathering process. Diagenesis has been studied on several categories of the sediments. The Neogene to Cretaceous pyroclastic sediments were classified into five diagenetic zones which are characterized by authigenic zeolites or albite. Zonal distribution of them has been regionally recognized and was classified into four types which were formed under different geothermal gradients. The sediments were changed chemically accompanying the zeolitization. The silica diagenesis was clarified in the Neogene siliceous sediments; siliceous organisms change diagenetically from amorphous to quartz through opal-CT. Clay mineral diagenesis also occur in the Neogene argillaceous sediments. A gradual change of mixed layered clay minerals was commonly found in the intermediate facies from the smectite facies to the chlorite-illite facies. The study on carbonate nodules in fresh water environments was successful in clarifying their genetical conditions based on the mode of occurrence and chemical analyses.