東北地方内陸盆地の発達に関する問題点

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Most of the inland basins in Northeast Honshu are distributed in the two, the eastern and western, zones between three mountainous zones, Kitakami-Abukuma Massif, Backbone Ranges, and Dewa Hilly Lands. The basins are situated in the axial zones of the synclinorium trending in N-S direction and in the subsided parts of the tilted blocks separated by the tectonic lines stretching in NW-SE direction obliquely to the general structural trend of Northeast Honshu. Marine transgression occurred on the west of the Kitakami-Abukuma Massif in the Early Miocene, and an anticlinorium developed to the Backbone Ranges during the Middle to Late Miocene, then another anticlinorium grew to the Dewa Hilly-Lands during the Late Miocene to Early Pleistocene. The NW-SE trending tectonic lines are thought to be a surficial expression of the deep-seated structure, which has controlled the deposition of the sediments since the early phase of the Miocene transgression. Stratigraphy, geologic structure, and topography vary with the individual basins, though, their development have been affected by the above-mentioned structural patterns. Outlines of geology and geomorphology of the Kitakamigawa, Hanawa, Odate, Takanosu, Yokote, Shinjo, and Yamagata basins are described in the text. As the conclusions: (1) Development of the basins in the northern part of Northeast Honshu commenced in the Late Neogene to Early Pleistocene except the Hanawa, Odate, Yokote and Yamagata basins, in which the main phase of basin-forming movements were estimated to the Early to Middle Pleistocene. (2) General configurations of the basins were completed in the Middle Pleistocene, and fluvial terraces and flood plains have been developed in them. Terraces are poorly developed in the Yokote, Yamagata, Odate, and Hanawa basins, where thick sediments the Late Pleistocene and Holocene have been accumulated beneath the flood plains. (3) Dislocation of the fluvial terraces suggests that the deformation of the basement has continued since Pliocene, though the rate was not uniform. A northward tilting of every block is apparently prevalent in the eastern zone of distribution of the basins, whereas a folding with N-S axes in the western zone. (4) The configuration of the graded plains in the basins suggests that the Middle and Late Pleistocene base levels in the inland areas has been controlled by the sea-level through the fluvial system, and the fluvial process was under the same climatic regimen as in the coastal areas.
日本地質学会の論文
1977-02-21

東北地方内陸盆地の発達に関する問題点

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