Discovery of the manganese carbonate rock yielding late Early Permian radiolarians in the Nishiki Group, Akiyoshi Belt, Southwest Japan

Abstract

We identified a Permian manganese-bearing carbonate layer within the siliceous shales of the Nishiki Group in the Akiyoshi Belt, Southwest Japan. The Nishiki Group is an accretionary complex composed of massive sandstones, mudstones, and Permian radiolarian-bearing siliceous shales and bedded cherts. In this paper, we present the initial descriptions of the newly discovered Permian manganese carbonates. They contain well-preserved early Permian radiolarians, including Albaillella asymmetrica and Pseudoalbaillella cf. ishigai. Although Jurassic radiolarian-bearing manganese carbonate nodules have been documented in the accretionary complexes of Japan, those of Permian age have not been described until now. In addition, we present U-Pb ages of detrital zircons extracted from the Nishiki Group sandstones, which yield a weighted mean age of 268.7±2.1 Ma, slightly younger than the age of the radiolarians in the Nishiki Group.