四国東部，四万十北帯の上部白亜系チャート : 砕屑岩シーケンスと放散虫生層序

Upper Cretaceous stratigraphic sections including chert-clastic sequences of the North Shimanto Terrane are examined for radiolarian biostratigraphy in East Shikoku. The Amphipyndax pseudoconulus Zone (ApZ: Upper Campanian) and Amphipyndax tylotus Zone (AtZ: Lower Maastrichtian) are newly proposed. ApZ is the interval from the FAB (first appearance biohorizon) of Amphipyndax pseudoconulus to the LAB (last appearance biohorizon) of Dictyomitra koslovae. AtZ is the interval from the LAB of D. koslovae to the LAB of A. pseudoconulus and Dictyomitra formosa. The LAB of D. koslovae is supposed to be the Campanian-Maastrichtian boundary. ApZ is subdivided into Ap1 and Ap2 subzones on the basis of the FAB of A. tylotus. AtZ has At1 and At2 subzones, they are bounded by the LAB of Stichomitra compsa. The polarity of studied accretion prisms are discussed with refer to their radiolarian ages. Ages of clastic sediments are older in northern formations. Based on OPS, accretion of northern formations occurred earlier than southern ones. The plate-subduction that caused the formations took place during the Campanian to early Maastrichtian.