関東平野の地形発達史

貝塚 爽平

doi:10.4157/grj.31.59

The Kanto Plain, in the central part of which Tokyo is situated, is the largest in Japan. This plain is built by the Quaternary series, marine, fluvial and eolian deposits which are considered to be standard series of the Japanese Quaternary.<br> In this paper, first, the author summarized the previous studies on volcanic ash layers, the so-called “Kanto Loam”, which covered almost all of terrce surfaces of the Kantô Plain, then tried to obtain chronological relationships between all of the volcanic ash layers. In the southern Kanto, the Kanto Loam, a part of which is derived from Mt.Fuji, is divided into four beds, and in the northern Kant, that is derived from Mt. Asama and other many volcanoes, into three or four beds. To correlate volcanic ash beds with each other, it is quite effective to trace the characteristic layers such as pumice, scoria or buried soil beds, and also the heavy mineral compositions of the volcanic ashes (Figs. 2 and 3).<br> Secondly, he described the characteristics of landform surfaces in the plain, and chronological horizon of all of them mainly by using relationships between landform surfaces and the volcanic ash beds (Fig. 8). From the a hove mentioned studies, the five stages of landform surfaces, A(Hollocene in age), Du I (upper most Pleistocene), Du b, Dula, and Dl I (middle or Lower Pleistocene), could be classified accordingly.<br> Thirdly, the palaeogeographical maps of each stage of land form surfaces were illustrated (Fig.9) and the evolution of landform of the Kantô Plain was explaind. As can be seen palaeogeographical maps transgression and regression came into being alternately in the Kantô Plain. The landform evolution of the Kantô Plain was, therefore, mainly caused by these transgressions and regressions, but the distribution and the shapes of the landform surfaces were greatly contorolled by the crustal movements in this region since the middle Pleistocene. Broadly speaking, the plain is a large depositional basin surrounded by up-warped belts, in which the southern hilly land shows the greatest upheaval to more than 300 meters since the middle Pleistocene. But precisely speking, there are three down-warped besins. Of the three, the largest one is in the northern part of the Kanto Plain, the second is located in the south-western part and the third is in the Tokyo Bay.

関東平野の地形発達史

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関東平野の地形発達史

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収録刊行物

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