第四紀地殻変動と先第四紀地殻変動 (第四紀テクトニクス特集)

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The problem discussed in this paper is whether the crustal movements in the Japanese Islands changed in nature or rate during the transition from the Tertiary to the Quaternary periods. The Late Tertiary sedimentary basins gradually migrated under the control of the orogenic movements which had begun in the Early Miocene. The Lower Pleistocene Series deposited in the areas succeeded the Pliocene sedimentary basins. In most parts of the Japanese Islands, a conspicuous break in sedimentation and physiographic development can be recognized between the Early and Middle Pleistocene. Since the Middle Pleistocene, sediments lap off the underlying sediments and form successive terraces, whereas the younger sediments covered the older during the Early Pleistocene. Flat lying Middle Pleistocene and younger terrace formations are striking in contrast to the folded and faulted Early Pleistocene formations, though the intensity of their deformation varies locally. The break between the Early and Middle Pleistocene mentioned above suggests progressive crustal movements since the Neogene and the relative rise of the whole Japanese Islands against sea level though whether diastrophic or eustatic is not yet certain. Concerning the rate of deformation of the Early and Middle Pleistocene formations, the absolute ages of the sediments must be determined and the mechanism of the deformation be elucidated. In Japan, knowledge on the absolute and relative chronology of the Late Cenozoic is now in progress and the interest of structural geologists with regard to the exact age of the tectonics is increasing. More detailed discussion on dated Quaternary crustal movements will become possible in the near future.
日本第四紀学会の論文

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中川久夫
東北大学理学部

第四紀地殻変動と先第四紀地殻変動 (第四紀テクトニクス特集)

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