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地質学雑誌
Vol. 48 (1941) No. 577 P 469-490

記事言語:

http://doi.org/10.5575/geosoc.48.469

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The Lower Carboniferous deposits in the Kitakami Mountainland, though apparently widely developed, have not yet been studied in detail, owing to the complicated structure, rarity of important fossil, and perhaps also to the frequent lateral changes of rock-facies., It is therefore desirable to observe their succession and lithic character as minutely as possible to elucidate their true natrue., For this purpose, the valley of Kotubo near Setamai, Kesen-gori, Iwate Prefecture, was selected where these deposits are thrown into only a broad anticline and exposed almost completely., Their succession has been studied precisely and lithic character of each layer or bed observed in detail., The complex exposed along this valley may be divided into six groups (I-VI)., Of these, I-V represent the Ohdaira series of Onuki and are conformable to one another, while VI is the Coral Limestone of the same author and probably transgressive to the older ones., Lithologically, groups I and III are composed of clayslate and II and IV mainly of schalstein ; V is represented by sandstone and VI by more or less thick limestone., It is remarkable that the Ohdaira series contains abundant pyroclastic material such as schalstein and porphyritic tuff., As to the geological age of the Ohdaira series, the lower part of group III may not be younger than Etroeungtian as suggested by the presence of Spirifer verneuili MURCH., but a Productus of the Semireticulati group is met with at a horizone 70 m higher than the S., verneuili bed and may indicate the Tournaisian age of this part of the complex., Another higher horizon in III yields some corals, among which an Amplexus resembling Lower Tournaisian A., coralloides Sow., will favor this supposition., The upper limit of this complex is not precisely determinable in age, probably being unconformably overlaid by the Coral Limestone which is thought from its very rich coral fauna to be Upper Viseen age., There are doubtless represented Upper Tournaisian sediments, and moreover, as suggested by a great thickness of the Ohdaira series, it is probable that some Lower viseen deposits are also contained in the uppermost part of the series, though no positive fossil, evidence is available at present.,

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