鳥取平野の形成過程

NDLデジタルコレクション 被引用文献1件

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タイトル別名
  • Process of the Formation of Tottori Plain

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説明

Tottori Plain is situated at the coastal strip of San'in district facing the southwestern part of Japan Sea, consisting of alluvial fans, flood plains, deltas and coastal dunes. The terraces fringing the plain are divided into three groups, namely High, Middle and Low terraces. The topographic surface of the High terraces (Yokomakura surface) develops locally along the margin of the plain. The Middle one of in this area are subdivided into two of different levels: the one of higher level is considered to be a depositional surface, and the lower one an erosional. The result of detailed examination of the boring data in this plain is summarized as following succesion in descending order: Alluvial deposits 0-45 m: sand and gravel (A_5), soft clay with humic soil (A_4), sand and silt (A_3), fossil bearing soft clay (A_2), alternation of sand and clay (A_1); Diluvial deposits 0-50m: gravel clay and silt gravel (D_1-D_3). After the maximum phase of regression in the Wurmian stage, the buried river terrace and fossil valley have been reclaimed by post-glacial sediments. In these, the Furumi formation (A_2) has partly yielded some molluscan fossils indicating the brackish depositional environment. The alluvial soft clay may be accumulated rapidly in the inland bay under brackish water during the so-called Yurakucho transgression. The Tottori plain had been remarkably subsided during the late Pleistocene. Judging from the data of geodesic measurements during the latest 80 years and the distributions of archaeological relics, the crustal movements have been rather continuous since the Pleistocene age down to the present.

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