豊州累層群の地史學的研究(II)
スポンサーリンク
概要
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In the central and northern parts of Oita prefecture, Kyushu, younger Cenozoic rocks are exposed extensively., They rest mainly on a basement of Paleozoic strata, and granites of the Ryoke type and partly on metamorphic rocks of Sambagawa type and the Cretaceous Onogawa group., They are composed of volcanic, pyroclastic and sedimentary rocks., From fossil and other evidence, they are dated as Miocene to recent., They represent a complicated history of volcanic activity and sedimentation, both of which are closely related., The history comprises four major geologic cycles, each of which is distinguished by the following criteria:(1) In volcanic cycles, (a) changes in rock types and modes of activity (flow type or explosive type) and (b) changes in dimension and in geographical position of activity., (2) In sedimentary cycles, (a) lateral and vertical changes in sedimentary facies, that strongly reflect the formation of basins by tectonic movements; (b) changes in dimension and in the geographical position of the basins., On the basis of these cyclic records, the younger Cenozoic rocks are grouped into four stratigraphic units; the Usa (F in age), the Sekinan (G-H), the Oita (I) and Kuju (J-K) groups in ascending order., The 2nd and the 4th groups correspond to the Setouchi and the Sanin volcanic series respectively, so far as the volcanism is concerned., As the volcanic series corresponding to the 1st and the 3rd groups has been neglected heretofore, it should be sought more extensively in Southwest Japan or elsewhese., This paper offers some evidence concerning the origin of the Oita-Kumamoto line, one of the major tectonic lines in Kyushu.,
- 日本地質学会の論文
- 1953-08-25