抄録
The interglacial sediments of the Shimosueyoshi Stage (Riss-Wurm interglacial Stage) were found in the Nopporo hill of the Ishikari plain and named "Nishinosato bed". The Nishinosato bed consists of sand, gravel, tuffaceous silt and clay. From the studies of its pollen, diatom, foraminifera, heavy mineral, molluscan fossil and topographic feature, a cycle of sedimentation was revealed in this bed. This represents the transgression and regression during the Riss-Wurm interglacial Stage. Based on the present study, the geological history of this area is summarized as follows: 1) Before the Mindel-Riss interglacial Stage, the area was invaded by shallow sea water except the Mt. Shirahata area and then a part of the Nopporo formation was deposited. 2) Under the cold climate of the Riss glacial Stage, the Takeyama gravel bed of fluvial origin was deposited and the Wattsu valley was digged. 3) Thereafter, due to the transgression in the Shimosueyoshi Stage, the sea level was upheaved 55 m high and then the Nishinosato formation was deposited. 4) After the regional erosion during the Wurm glacial Stage, there was deposited the Kakuta bed, which consists of pumice and loam. 5) During the latest Warm glacial Stage, pumice, fall, flow and welded tuff from the Shikotsu volcano covered the area. Continuously, under the periglacial cold climate, the Hiroshima glavel bed was formed. 6) With the regression of the Wurm glacier, the Ishikari plain was invaded again by the sea water.
