Study on paleoenvironment during the Last Glacial in the Tokachi Plain and Hidaka Range

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1. On the basis of tephrochronology, sedimentation and downcutting by rivers are examined in some rivers of Tokachi Plain and Hidaka Mountains, particularly for the Oxygen Isotope Stage 5〜3.2. Eolian dust had been produced and transported from the bare ground of Hidaka Mountains to Tokachi Plain during the Last Glacial, indicating the tundra environment of the Mountains.3. Paleohydrological study of fluvial gravels reveals that the discharge of rivers during the Last Glacial should have been almost same as that of at present. This result indicates that a sedimentation during the Last Glacial had been resulted from the abundant supply of load.4. Mountain permafrost was examined by the indicative landform of rockglacier and the present climatic condition obtained from own observation. Permafrost is possibly distributed at present in the summit area of the Hidaka Mountains around Mt. Poroshiri.5. Fossil periglacial phenomena in the Tokachi plain was examined with special reference to permafrost condition of the Last Glacial. Past climate was examined in relation to summer temperature.