四国東部および淡路島の海岸平野の原形

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Spread and arrangement of the terraces and the coastal lowlands are controlled by lithology and geological structure of the basements in the Shikoku and Awaji. The coast-line of the western side of the Muroto Peninsula are defined by the two sets of faults, namely the NE-SW set and the N-S set (Fig. 1). The straight coastal line and the capes are the sides and the corners of the faulted blocks respectively, which formed in Middle Miocene and covered by the late-Miocene and the Pliocene formations. The form and spread of the terraces and lowlands are controlled by the topography cut in the pre-Neogene basements. The terraces, the fans and the lowlands in the southern Awaji island are distributed in the area underlain by the unconsolidated Plio-Pleistocene sediments, and are not in the terrain of the Cretaceous Izumi Group and the Granite. The distribution of the Plio-Pleistocene of the coastal plain is controlled by the lithofacies of the Izumi Group and the block movements of the faulted basements (Fig. 2). The Yoshino-gawa valley is a tectonic valley along the Median line, and the downstream of the valley is a wedge shaped graben spread eastward. Since the Upper Pliocene Moriyama formation is the oldest formation cover the basements in the graben, it is concluded that the graben was formed in the Pliocene. Along the northern and southern margins of the graben, the terraces and the fans are developed, and there are several east-west trending faults which cut the terraces and the fans. Judging from the height of the middle terrace gravels (Table 2, Fig. 5) in the belt adjacent to the southern side of the Median line, the blocks east of Wakimachi have tilted down eastward, and the blocks east of Ichiba have subsided since the Gottweiger. The subsided wedge shaped basin filled by the alluvial marine sediments formed the Tokushima coastal plain. As stated above, in these districts the stage of the differentiation of the plains from the mountain regions is the Miocene to Pliocene. It is said that the outlines of the alluvial plains were formed in the Neogene.
日本地質学会の論文
1972-12-25

四国東部および淡路島の海岸平野の原形

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