美濃帯西部の泥岩から産出したトリアス紀新世放散虫化石群集

Abstract

Late Triassic radiolarian fossils composed of genera Canoptum and Latium have been obtained from the western part of the Mino terrane, which is characterized by Mesozoic subduction complex, central Japan. The study area is underlain by a melange named the Otaki Unit which consists of basalt, limestone, chert and sandstone blocks and mudstone matrix. Although the sandstone yields Late Triassic bivalve Monotis, the age of the unit has remained unknown. The radiolarians obtained from the mudstone matrix of the melange unit show that the formation of the unit was Late Triassic and that the unit is one of the oldest in the Mino terrane.A Late Triassic unit has been reported to crop out only in the most northwestern most area of the Mino terrane and occupies the structurally highest portion of the subduction complex. The existence of the Late Triassic unit in the study area also gives important information for the discussion of the structure of the terrane.