福井県大野市大納地域からの後期ジュラ紀アンモノイドの産出と九頭竜地域手取層群の対比再検討

Ammonoid fossils including Tithonian Parapallasiceras sp. are newly discovered from the Kurotodo Formation of the Tetori Group in the Ono area of the Kuzuryu district, Ono City, Fukui Prefecture in the Hida Gaien Belt, Central Japan. Based on this find, the Kurotodo Formation can now be correlated with the Early Tithonian Kamihambara Formation in the Kamihambara area of the same district, despite its previous assignment to the Middle Jurassic(Bathonian-Callovian)Kaizara Formation of the Kuzuryu Subgroup(lower part of the Tetori Group)in the Hida Belt. Similar lithological successions ranging from Oxfordian to Barremian in age, including ammonoids-bearing Oxfordian and Tithonian formations referred to the early and middle transgressions(stage Ib and IIa)of the Tetori Group, are recognized throughout the Mana-Ono and Nagano-Kamihambara areas in the Hida Gaien Belt and are, at least partly, synchronous with the main part of the Itoshiro Subgroup(middle part of the Tetori Group)of the Itoshiro area of the Kuzuryu district in the Hida Belt. The Kaizara Formation and its equivalents, representing the early transgression(stage Ia:Bathonian to Callovian)of the Tetori Group, is probably confined within the Hida Belt, contrary to the hitherto accepted view that it is distributed widely not only in the Hida Belt but also in the Hida Gaien Belt.