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＜departmental bulletin paper＞
Litho-and bio-facies of limestones of the Upper Triassi Tanoura Formation in the Kuma Mountains
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| Abstract | This paper describes lithologic and sedimentary features of limestones of the Upper Triassic (mainly Carnian) Tanoura Formation in the central part of the Chichibu Terrane in the Kuma Mountains. An in...terpretation on their depositional environment is also given. Limestones of the Tanoura Formation occur in the upper mudstone member of the lower subformation and are thin-bedded, occasionally massive, interbedded with and merging laterally into calcareous siltstone and mudstone. They consist of oosparite oolitic intrasparite, oolitic biosparite and sandy calcarenite, with subordinate intercalations of calcisiltite and micrite. They are well-washed, mostly lacking matrices and are cemented with drusy fibrous calcite. Fine-grained limestones often contain terrestrial sands. Oolite is most predominant throughout the seguence, and ooid nuclei are mostly calcisiltite or micrite that are found very commonly as intraclasts. Intrasparite also occurs at many horizons and contains intraclasts of at least several kinds that are all very similar or analogous to the rock types of the members of the Tanoura limestones. Skeletal limestones are rather subordinate in occurrence and their main constituents are fragments of sessile benthos such as crinoids, brachiopods and bryozoas. Calcarenite, calcisilitite and micrite appear to be composed of skeletal debris mechanically disintegrated. The lithologic and sedimentary features of the Tanoura limestones suggest their deposition in such an environment of very shallow, strong current agitation as the present oolite shoals that are mostly less than 5 m in depth. In the last part of this paper is given the comparison of the litho-and bio-facies between the Tanoura limestones and the coeval limestones of the Konose Group (KANMERA, 1969) of the Sambosan Belt that are associated with radiolarian chert and basaltic volcanic rocksshow more |
| Table of Contents | I. まえがき II. 田浦眉の層序概要 III. 田浦層石灰岩の産状 IV, 石灰岩の岩石記載 V. 田浦層石灰岩の特徴と堆積学的考察 VI. 三宝山帯の同時代石灰岩との比較 / |
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| Created Date | 2021.11.01 |
| Modified Date | 2022.06.20 |