関東山地秩父帯北部の低変成度帯からのジュラ紀放散虫

概要

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The northern part of the Chichibu belt in the Kanto Mountains, central Japan, comprises three lithologic units : Kashiwagi unit consisting mainly of lowgrade metamorphosed siliceous tuff and mudstone, Kamiyoshida unit of sandstone and mudstone with subordinate amounts of exotic blocks such as chert, greenstone and limestone, and limestone, and Kazahaya-toge unit of alternation of sandstone and mudstone. Middle to Late Jurassic radiolarians were newly found from the Kashiwagi unit of the northern marginal part of the Chichibu belt. They are Archaeodictyomitra sp., Eucyrtidiellum sp., Hsuum sp., Pantanellium sp., Parvicingula sp., Podobursa sp., Pseudodictyomitra sp., Stichocapsa sp., Syringocapsa sp. and some unidentified nassellarians. This radiolarian assemblage including the genus Eucyrtidiellum and Pseudodictyomitra indicates the involvement of middle to late Jurassic sediments in the unit. Hence it is concluded that the formation and metamorphic process of the Chichibu belt occured during and after the accretion continued at the late Jurassic, respectively.
国立科学博物館の論文
2001-12-22