抄録
Jurassic accretionary complex of the Chichibu belt is distributed in the western Akaishi Mountains, central Japan. The Miocene Wada Formation, composed mainly of mudstone with basal conglomerate, is exposed in Minami-Shinano, Iida City, Nagano Prefecture, central Japan. This article reports the occurrences of Permian, Triassic, and Jurassic radiolarians from the Jurassic accretionary complex and Triassic radiolarians from the chert pebbles within the basal conglomerate of the Wada Formation. The chert pebbles are most probably derived from accretionary complex of the Chichibu belt exposed near the distributional area of the Wada Formation. Meanwhile, clasts of Cretaceous-Paleogene chert derived from the Shimanto belt nor metamorphic rock from the Sambagawa belt have never been discovered from the Wada Formation so far. This implies that the Shimanto and Sambagawa belts have not largely exposed in the Miocene in the hinterland of the Wada Formation.
