Chert breccia, its occurrence and radiolarian fossils in the Hichiso- Mugi area, central Mino Terrane, central Japan

Abstract

A detailed geological survey has revealed that the chert breccia conformably covers the Jurassic sandstone in the Hichiso-Mugi area. It shows that the chert-clastic sequence in the Kamiaso Unit consists of Early Triassic banded claystone, Middle Triassic to early Middle Jurassic chert, Middle Jurassic siliceous shale and shale, late Middle to Late (?) Jurassic turbidite and sandstone, and chert breccia in the ascending order. On the basis of field and laboratory evidence and the knowledge of the currently active subduction zones, the sedimentary process of chert and chert-limestone breccia formation is discussed. Clasts of the breccias came from the uppermost part of accretionary complex and were supplied to the trench by submarine current in a submarine canyon or gravitational sliding on it. -from English summary