<専報>対馬の地質とその問題点

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The result of the geological reconnaissance work (Fig. 1), which was performed by KON'NO and MATSUMOTO (1944,unpublished report), is briefly described, since it is essentially correct in the light of up-to-date information. Tsushima consists primarily of the Taishu Group. It is about or over 2500 m thick, consisting of shale and sandstone, with swampy sediments in the lower part, neritic fine-sandy siltstone in the middle, and alternating sandstone and shale, with prominent arenite at several levels, in the upper. The group represents a cycle of sedimentation under deltaic to shallow sea environments. The available evidence of fossils (plants, mollusks, echinoids, etc.) suggests a lower Tertiary age but is not sufficient for further precise age determination. The strata of the Taishu Group show a rather shallow, Jura-type folded structure. Several anticlinoria and synclinoria run en echelon in NE-SW direction, plunging to NE (Fig. 2). The folding is more intense in the northwest. Minor folds, with wave length of 0.5-2 km, show a number of interesting features (Figs. 3-6). The Taishu Group is intruded by sills and dykes of quartz-porphyry and porphyrite and by bosses of granite and smaller bodies of gabbro or diabase. These igneous rocks may be of late Miocene age, as in those of the Goto islands, off northwest Kyushu. Some discussions are extended to the major geological problems related to the islands of Tsushima and surrounding area, such as geological province, geological cycle, basement beneath or under the Taishu Group, younger Tertiary and Quaternary history, petrologic province, and submarine geology.
国立科学博物館の論文
1969-09-13

<専報>対馬の地質とその問題点

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