Studies on classification, dating and genetic environments of paleosols in cold climatic regions, north Japan

The buried periglacial paleosols，involutions and earth hummocks，are often observed in Hokkaido and northeastern honshu，north Japan。The tephrochronological studies of the Late Pleistocene periglacial phenomena are carried out and the paleopedology in the investigation area is also discussed.In the Tokachi Plain of the eastern Hokkaido，fossil periglacial paleosols in the Late Pleistocene such as involutions were found at many places in the buried volcanic ash soils.Ages of these pale-osols are considered to be well correlative to the cold climatic stages of the Late Pleistocene revealed by plant opal analyses and by floral assemblages.A sporadic permafrost is distributed in the vicinity of Tokachi-mitsumata，northernmost Tokachi District.This relict permafrost(ca.1.3-4.0 m deep and ca.26，500平方公尺in area)is know only on the NNW steep slope of above 830-886m in altitude.Since the^&lt；14&gt；C dating made on wood sample collected in the lowermost level of the frozen layer indicate 4，540 105yrs。B.P..Annual soil temperature at 0.5米depth is-4.3°C.The morphology and nature of the involutions in the buried volcanic ash soils，sporadic permafrost and earth hummocks；and their geographical distribution are briefly given in this report。

The buried periglacial paleosols, involutions and earth hummocks, are often observed in Hokkaido and northeastern honshu, north Japan. The tephrochronological studies of the Late Pleistocene periglacial phenomena are carried out and the paleopedology in the investigation area is also discussed.In the Tokachi Plain of the eastern Hokkaido, fossil periglacial paleosols in the Late Pleistocene such as involutions were found at many places in the buried volcanic ash soils. Ages of these pale-osols are considered to be well correlative to the cold climatic stages of the Late Pleistocene revealed by plant opal analyses and by floral assemblages.A sporadic permafrost is distributed in the vicinity of Tokachi-mitsumata, northernmost Tokachi District. This relict permafrost (ca.1.3-4.0m deep and ca.26,500m^2 in area) is know only on the NNW steep slope of above 830-886m in altitude. Since the ^<14>C dating made on wood sample collected in the lowermost level of the frozen layer indicate 4,540 105 yrs. B.P.. Annual soil temperature at 0.5m depth is -4.3゜C.The morphology and nature of the involutions in the buried volcanic ash soils, sporadic permafrost and earth hummocks; and their geographical distribution are briefly given in this report.