和泉山脈の和泉層群上部白亜系に混在する再堆積ジュラ紀・白亜紀前期放散虫

Jurassic and Early Cretaceous radiolarians were extracted from the fine turbidites of the Amphipyndax tylotus Zone of the Izumi Group, Izumi Mountains. Studied fine turbidites, composed of the sandy mudstones and pebbly mudstones, are intercalated in the channel-fill coarse clastic beds. Autochthonous radiolarian assemblages, characterized by Amphipyndax tylotus, are correlative with those of the Early Maastrichtian age. Co-occurred bivalves are coincide with the autochthonous radiolarian age. Among the allocthonous radiolarians, Tricolocapsa plicarum, T. conexa and Stylocapsa catenarum are Middle Jurassic indexes, and Transhsuum maxwelli group, Ristola dhimenaensis are Middle to latest Jurassic indexes. The other reworked materials whose final appearances are known within Middle Cretaceous include Archaeodictyomitra excellence, Wrangellium depressum, W. puga and Thanarla (?) conica. All of these Jurassic and Early Cretaceous species also occurred in the fine clastic sediments of the Mino-Tanba accretionary complexes. By microscopic observations of thin sections and etched slabs of the sediments, we confirm that the Middle Jurassic to Early Cretaceous radiolarians are extracted from the siliceous mudstone fragments included in the pebbly mudstones. Gravels and small fragments of chert-hornfels that contain crystallized radiolarian shells are also found from the studied pebbly mudstone. The mudstone clasts that contain Middle Jurassic and Early Cretaceous radiolarians were probably derived from the accretionary complexes of the Mino-Tanba Belt. The crystallized radiolarian-bearing gravels and clasts of chert-hornfels are possible to be derived from the thermal metamorphosed sediments of the Ryoke Belts.