石狩平野西部地下における更新統の貝化石群と層序区分

概要

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The study of the subsurface geology in the Ishikari Lowland has progressed to exploit the subsurface water (YAMAGUCHI et al., 1964; YAMAGUCHI, 1970). In the western part of this area, ten observatory stations for ground water level have been founded. As a result of the geological and paleontological examinations of the boring core samples at the stations, the subsurface Pleistocene deposits are discriminated as follows; the horizon correponding to the Shimonopporo Formation of Early to Middle Pleistocene and the Hachiken, Yamaguchi and Tarukawa Beds of the latest Pleistocene in ascending order.The presence of the horizon corresponding to the Shimonopporo Formation under the Ishikari Alluvial Plain gives an important key to solve the geoloogical sequences between the Nopporo and Ishikari Hills. Among the three beds which unconformably overlie the horizon corresponding to the Shimonopporo Formation, the Hachiken and Tarukawa Beds are assigned respectively to the Götweiger and Päudorfel Interstadials on the basis of 14C age determinations and paleoclimate analyses of molluscan and pollen fossils.