岡山縣小田郡稻倉村地方の所謂硯石層群について

On the Inkstone Group of Inakura-mura District, Oda-gun, Okayama Ptefecturer, Japan

Imamura Sotoji

Kusumi Hisashi

廣島大學地學研究報告

Geological report of the Hiroshima University

The Inkstone group of Inakura-mura district, Oda-gun, Okayama Prefecture rests unconformably on folded Chichibu PaIaeozoic slate formation and meta-diabase, and is overlaine by rhyolite flow ＆ so-called Neogene Tertiary conglomerate formation with unconformity. The Inkstone group can be divided into 2 formations with disconformity, Upper(Ishizuchiyama red tuff) ＆ Lower, while the latter subdivided into the upper Yamaji shale ＆ the Iower, Nishinotani conglomerate. The general stratigraphy of this district is as follows．
Nishinotani conglomerate ＆ Ishizuchiyama red tuff with no organic remains are characterized by some amount and a large amount of red tuff respectively, while Yamaji shale with no red tuff contains rare plant & abundant fossils as non-marine gastropods, pelecypods and Estherites the last of which is the first discovery in the Inkstone group of Japan. Though palaeontological study on the Inakura fauna has not yet been completed, some types of our Estherites (Estherites cf. kyongsangensis K. ＆ K., E. cf. kyongsangensis var. medialis K. ＆ K. ＆ E. cf. naktongensis K. ＆ K.) are known to be common with those in the Naktong ＆ Silla groups in Korea, but no Naktong-Wakino types of Trigonioides, Plicatounio ＆ Brotiopsis are discovered in Inakura fauna. Nishinotani conglomerate ＆ Yamaji shale will probably correspond to the upper sub-group, while Ishizuchiyama red tuff to the upper sub-group of the Inkstone group in the western Nagato defined by Prof. T. Matsumoto(1948). The Inakura Inkstone group will correspond to the upper part of Naktong group ＆ the lower part of Silla group in Korea.
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jpn

廣島大學理學部地學教室

[ISSN] 0073-2303

[NCID] AN00213676