相馬古生層(福島県,北東部阿武隈山地)の二畳系にみられる古生代末の地殻変動について
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概要
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In this paper the writer deals with the description of stratigraphy and geological structures, and tectonic movement during the permian period of the Soma palaeozoic deposits. The rocks of the Permian system in this area are divided into seven members by the writer (fig. 1 & 2). Uwano slate member (U₁), Uwano sandstone and slate member (U₂),Ōashi lower conglomerate (O₁), Ōashi slate and sand stone member (O₂), Ōashi upper conglomrate (O₈), Yumiorezawa slate and sandstone member (Y₁), Yumiorezawa slate member (Y₂). The following is a simplified and precisely stratigraphy in decending order. Yumiorezawa formation: consisting of the Y₁ and Y₂ members, about 350m thick. Fossils unknown. Ōashi formation: consisting of the O3 member in the upper part, intercalating some fossilferous limestone lenses, the O₂ in the middle, and the O₁ in the lower, about 350m thick. Important fossils: Lepidolina, Yabeina, Verbeekina, Pseudodoliolina, Parafusulina, Waagenophyllum, Wentzeloides, etc.. These fossils are restricted in their occurence to the upper and middle parts. Uwano formation: consisting of the U₁ and the U₂ members. Pseudoschwagerina was collected at two hirzones. The geological structures in the Permian system of the present deposits may be devided into two units in the deformation and destruction. The pre-Permian deposits are extensively overlain by the Uwano formation which constitutes a synclinorium with the axis of north-north-east, and the dips of 40 degree to 90. The Uwano synclinorium is overlain by the Ōashi-Yumiorezawa basin structure consisted of two formation, both of which represent low dips of 5 degree to 30 all over the basin in sharp contrast with the general trend of the U -synclinorium, with exception of the vicinity of tectonic line and disturbed region. Judging from the sedimentary facies of the Ōashi formation, it can be inferred that the sediments were formed in shallow water within wave action, and that the basement complex kept to rapidly sinking down during deposition of the Ōashi formation. The Ōashi formation is thicker in the east and south east than in the west, thining out or gradually grading into the sandstone and the slate of thin alternation of Y₁ member in the west side of the given deposits. The ŌashiYumiorezawa basin structure is differ from the Dwano synclinorium, in its less complexeous geological structure. Differences between these feature are more remarkable in the east. Observation of outcrops also testified this structural feature. There is the other fact that the constituent rocks of the Oasi conglomerates consist of granitic rocks, volcanic rocks, subangular pebbles of black slate, biotite hornfels and myronitic silisious rock. Such coarse material had deposited from time to time untill the close of the Lepidolina epock in the Soma district. All that can be inferred in the Soma district are the backland situated to the east side of the present district, and uplifted abruptly after dose of the Dwano epock. This unknown backland continuousely supplied the Ōashi formation with a large quantity of coarse material, and were from time to time worn low. They were mobile areas. Supply of such coarse sediments came to the end at the close of the LŌŌepidolina epock. Continuously the slates of the Toyoma type representing enviroment of closed sea kept on deposition during the Late Permian.
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- 1973-03-15
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