The Permian Conodonts in Chert of the Adoyama Formation, Ashio Mountains, Central Japan

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  • 栃木県葛生町のあど山層から産出したコノドントについて
  • トチギケン クズウマチ ノ アドサンソウ カラ サンシュツ シタ コノドント ニ ツイテ

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The Adoyama formation is composed mainly of red, grey, dark grey cherts including sandstone layers. Chert is finely banded in general, and is often intercalated with thin limestone lenses. Just under the Adoyama formation, the Nabeyama formation is conformably underlying, which yields the Permian fusulinids, such as Parafusulina, Pseudofusulina, Schwagerina and Neoschwagerina. Then, the Adoyama formation is undoubtedly the Permian in age. The author collected the samples from only one locality at the base of the Adoyama formation near Kuzu-Machi, Tochigi Pref., Central Japan. Conodonts were obtained by dissolving chert in 5-8% hydrofluoric acid. The author found about 1500 individuals, among which 19 genera and 42 species are described in this paper. Moreover new genus Metapoygnathus is proposed. Characteristic species in this fauna are Gondolella carinata, G. constricta, G. navicula, Gladigondolclla abneptis, G. tethydis and so on. These species have been commonly recognized as the Triassic ones. Polygnathus cf. communis is reported from the Carboniferous, and P. cf mungoensis from the Cretaceous. Both are also included in this fauna. In addition to these, porifera, radiolaria, foraminifera and fish remains are found in the residues of chert.

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