Permian Radiolarians and Spicules from Conglomerate of the Lower Jurassic Kuruma Group in Itoigawa, Niigata Prefecture, Central Japan

Abstract

Conglomerate of the Lower Jurassic Kuruma Group contains microfossil-bearing clasts. In the present study, these microfossils were investigated via the hydrofluoric acid (HF)-etched surfaces of the clasts and residues produced during acid treatment. As a result, Permian (mainly Guadalupian–Lopingian) radiolarians were obtained from mudstone and chert clasts; spicules of indeterminate age were obtained from the chert clasts. The mudstone clasts were derivable from the Akiyoshi, Ultra-Tamba, Maizuru, and/or Hida-Gaien belts or equivalent units, while the spicule-dominated chert clasts likely originated from the Akiyoshi belt or equivalent units. Except for tuff and acidic volcanic rocks, the clast components of the Kuruma Group in this study are similar to the component rocks of the Akiyoshi belt.