北関東那須野原周辺に分布する指標テフラ層

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The purpose of this paper is to present the stratigraphy, distributions and characteristic properties of tephra layers around Nasuno Plain in North Kanto, central Japan. This tephrostratigraphical study is carried out as a basic work for the applicative tephra study which will contribute to volcanology and Quaternary study of this region in late Quaternary.<BR>43 tephra layers deposited in the latter half of middle Pleistocene are identified. The tephra layers derived from nearby volcanoes located in North Kanto are as follows; 12 tephra layers from Nasu Volcano, four tephra layers from Takahara Volcano, 17 tephra layers from Nikko Volcanic Group and one tephra layer from Akagi Volcano. Two widespread tephra layers named APm-U and APm-L (300-350 ka) derived from Momisawadake Volcano in the Hida Mountains are identified. However, the sources of seven tephra layers remain unknown. Ages of these tephra layers are estimated to be younger than 400 ka on the basis of thickness of volcanic soil and ages of several dated tephra layers.<BR>On the other hand, 32 tephra layers formed in late Pleistocene are described. They include the following five well-known widespread tephra layers, that is, AT (22-25 ka), DKP (48 ka), Ng P, Aso-4 (86-90 ka), On-Pm I (80-95 ka). They are derived from distant volcanoes locating in central and southwest Japan. At the same time, 25 local tephra layers from Akagi, Nasu Volcanoes and Nikko Volcanic Group are recognized.
1993-02-25