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Title: 対州層群の研究
Other Titles: A study of the Taishu Group
Authors: 高橋, 清
Authors (alternative): Takahashi, Kiyoshi
Issue Date: 25-Dec-1969
Citation: 長崎大学教養部紀要. 自然科学. 1969, 10, p.67-85
Abstract: The Taishu Group, which consists of conformable series of sandstones and mudstones of about 6100-6750 meters in thickness, is stratigraphically divided into the following six formations and represents a major cycle of sedimentation. Upper Lower Shiohama Formation (950m+thick) Yoshigaura Formation (700-1000m thick) Kechi Formation (1500-1700m thick) Wakata Formation (850-900m thick) Sasu Formation (1400-1500m thick) Komoda Formation (800m+thick) a) The Komoda Formation consists of bluish gray fine-grained banded sandstone containing often granules or sometimes thin conglomerate beds and black mudstone or shale. The sandstone bed is mostly an alternation of banded sandstone, 10 to 20cm in thickness, and thin black shale, and occasionally massive, more than 20m in thickness. The sandstone is often ripple-marked and cross-laminated. A thin coaly shale bed occurs between Komo-dahama and Onozaki. Molluscan and plant fossils are found beside the way, north of Kozuki. b) The Sasu Formation is mainly composed of some sandstones, black sandy mudstone, and black mudstone. Many sole marks, being longitudinal current-ridge marks, and other marks are found on the lower surface of sandstone beds, or the upper surface of mudstone beds. Many ripple marks are preserved on the upper surfaces of sandstone beds. Some marine molluscan fossils were reported by S. KANNO (1955) from the Shintomi pit of the Taishu mine. He wrote that the age of the Taishu Group is Upper Oligocene to early Miocene. Some plant fossils occur in the black shale bed in the coast between Kozuki and Kunehama. c) The Wakata Formation consisting of the lower platy banded shale and upper massive mudstone with some interbeded sandstones, is intruded by some intrusive sheets of quartz porphyry. Sabalites taishuensis TAKAHASHI was reported by the author (1958) from Wakata. Its age may be Oligocene. d) The Kechi Formation consists predominantly of black shale and mudstone with some alternating beds of banded sandstone and shale. The upper horizon is occupied often by alternations of sandstone and shale. The upper sandstone is often coarser than that in the lower horizon. Some fossils of mollusca, echinus, and plants are found at many localities, but there are no fossils for determining its geological age. e) The Yoshigaura Formation begins with the predominant alternation of beds of sandstone and shale, getting thin gradually northward and disappearing finally. The mudstone becomes thick in the northern area. The sandstone beds often make some crossbeddings (see text-fig. 6). f) The Shiohama Formation consists of prominent sandstone-beds with thin shale, but in the northern area the shale gets somewhat thicker. The sandstone is white gray color, fine to medium grain, and sometimes massive, containing often sand pipes. No fossils are found. The hornfels rock, thermally altered by the biotite granite, occupies the southeast area of this present district and trends to the northeastward of major anticline and syncline axes. The hornfels rocks are dark brown and very fine, recrystallizing biotite. Quartz porphyry occurs as the intrusive sheets or sills, intruded often into the Sasu and Wakata Formations. There are other intruded igneous rocks, that is, diorite, porphyrite, aplite, granodiorite porphyry, doleritic rock, and fine-grained gabbroic rock. The major structure of the Taishu Group in the east-side area of the Komoda tectonic line, is the large and gentle syncline and anticline trending NE-SW. The northwest side of the Komoda tectonic line is the violent folded and faulted area. The fold axis trends almost NE to NEE, and the fault of NE or NEE trend is the most predominant. In the Taishu mine area, there are two fault systems; one is the normal N-S fault and the other is the reversed strike fault accompanying more or less minor drag folds.
URI: http://hdl.handle.net/10069/16466
ISSN: 02871319
Type: Departmental Bulletin Paper
Text Version: publisher
Appears in Collections:Volume 10

Citable URI : http://hdl.handle.net/10069/16466

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