東京低地および新潟平野沖積層の生層序区分と堆積環境

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We have studied four boring cores of alluvium with the aid of the methods of pollen-analysis and diatom-analysis. Two of them were collected from two stations of Koto-ku located in Tokyo Lowland. And other two were collected from Akatsuka-kiyama, Niigata city (B-NO.22 well) and Kurotori, Kurosaki Village Nishikanbara District Niigata Prefecture (B-NO. 24 well), both of which are located in the Niigata Plain. As a result of the writers study, the biostratigraphic division and sedimentary environment of the alluvium in these area have been considered as follows. (1) According to pollen-analysis, the alluvium in the Tokyo Lowland was classified into three formations, namly the Yurakucho one, the Upper Nanagochi one and the Lower Nanagochi one, since the uncomformable relationship was presumed between them. And the one in the Niigata Plain was also divided into three formations, namely the Upper Shirane one, the Middle Shirane one and the Lower Shirane one, since the unconformable relationship was presumed between them like to the former. According to the paloeoclimatic analysis considered from the result of the pollen-analysis, it may be assumed that these formations deposited during the course of transgression and regression after the maximal phase of Wurmian glaciation. (2) According to diatom-analysis, however, the alluvium in the Tokyo Lowland was divided into two formatins, namely the Yurakucho one and the Nanagochi one. On the other hand, the one in the Niigata Plain was divided into three parts like to the case of pollen-analysis. In the former, the diatom assemblage of the Yurakucho one (Lower clay bed) show the marine sediments in the bay bottom, where the circulation of water was comparatively a weak or rather stagnated, assigning to the maximal phase of Jomonian transgression. And the one of the Nanagochi one show the deposition in the bay bottom, where the water was so much variable strongly influenced by fresh water and changeable. The alluvium in the Niigata Plain has no evidence of marine diatom fossil in spite of their other view of sedimentation during the course of the transgression. (3) From the similar results of the pollen-analysis and diatom-analysis in the Niigata Plain, it may be safely considered that the Upper Shirane formaiion, Middle one and Lower one in the Niigata Plain are respectively correlated to the Yuraku-information, the Upper Nanagochi one and the Lower Nanagochi one, divided based upon a result of the pollen-analysis in the Tokyo Lowland. Then, based upon the diatom-analysis, it may be recognized that the Upper Shirane formation is correlated to the Yurakucho one and either both of the Middle Shirane formation and the Lower one, or only the Middle one might be correlated to the Nanagochi formation in the Tokyo Lowland. (4) It may be considered that the absence of the marine fossil in the alluvium of the Niigata Plain was resulted from the fact, which the mouth of bay came to be closed by sand bar or sand dune during the course of the invasion of marine water into the bay. Moreover, it may be assumed that this phenomenon might be an important condition discriminating the forming process of the alluvial plain in the Japan Sea coastal area from those in the Pacific coastal one.
日本地質学会の論文
1972-12-25

東京低地および新潟平野沖積層の生層序区分と堆積環境

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