著者

阿久津 純

出版者

地学団体研究会

雑誌

地球科學 (ISSN:03666611)

巻号頁・発行日

no.33, pp.1-11, 1957-06-30

被引用文献数

3

---

The stratigraphy of the Kanto Loam formation, its relation with the river terraces, volcanics which produced the many pumice beds, and the correlation of the formation with adjacent regions have been studied. The results are summarized as follow. From the lithofacies of the formation, features of sedimentation, and heavy mineral components, four membe s were recognized, these are named in descending order, A_1, A_2, A_3 and A_4; each one is separated by diastems. Each member is characterized by intercalating several pumice beds which are good guides in the stratigraphy of the formation and the correlation of the river terraces. Al member is characterized by the Shichihonzakura and Imaichi pumice beds, A_2 by the Kanuma and A_3 by the Mamiana and the. Moka, respectively. The intermittent deposition of the Kanto Loam formation and formation of the river terraces are intimately related with each other. There are no deposits of the Kanto Loam formation on the Kinushima terrace. The Tawara terrace is covered by the A_1 member and the Takaragi by the A_1 and A_2 members. The Hoshakuji, the highest river terrace, is covered by the A_1, A_2 and A_3 members. The Higher Terrace which was the depositional plane of the Kawasaki formation, is covered by all four members of the formation, but the greater part of the Higher Terrace, lacks the lower members (A_3, A_4). From the distributions and thicknesses of the pumice beds as well as from the mineralogical and lithological characters, it is inferred that the Shichihonzakura and Imaichi pumice beds are aeolian deposits, and are products of the Nantai volcanic eruptions, similarly the Kanuma is considered a product of the Akagi, the Mamiana of the Nikko and the Moka of the Takahara volcanic eruptions, respectively. From the stratigraphical and mineralogical as well as topographical characters, the Kanto Loam formation in the said area is correlated with the formations in the environs of Maebashi City, Gunma Prefecture and Southern Kanto region. A_1 member is correlated with the Upper Loam member of Maebashi and the Tachikawa Loam of Southern Kanto. A_2 member corresponds to the Middle Loam member and is a little younger than the Musashino Loam. A_3 member may be correlated with the Shimosueyoshi Loam. The Quaternary history, related to the deposition of the Kanto Loam formation, is briefly discussed.