Permian radiolarians from Nishiki Group in Sangun-Chugoku Belt, Southwest Japan

Abstract

Biostratigraphical study of the Nishiki Group was done in the Muikaichi area, Shimane Prefecture, Southwest Japan. The Nishiki Group in the area consists of three formations, namely, the Na, the Nb and the Nc formations, in ascending order. The Na formation (chert facies) includes the upper part of the Albaillella sp. D Assemblage-zone and the Pseudoalbaillella sp. C A-zone (newly denned), while the Nb formation (mudstone facies) is represented mainly by the Pseudoalbaillella sp. C, the Ps. globosa and the Follicucullus monacanthus A-zones. The Nc formation (sandstone facies) and some part of the Nb formation include the lower part of the Fo. scholasticus A-zone. The Nishiki Group in the Muikaichi area is regarded to include the Leonardian and Guadalupian equivalents or the Maokouan based on the radiolarian biostratigraphy. The lower three of these five zones are redefined. A new species is proposed on the basis of paleontologic study of Albaillella sp. D with description of additional three species of Albaillellaria.