Abstract
Orthoquartzite fragments were firstly found from Miocene formation overlying Joetsu metamorphic rocks in Minakami district. The conglomerate which yields these orthoquartzite fragments is mostly composed of sandstone fragments, but those of shale hornfels, chert, felsic rocks, altered dacitic rocks, altered basalt and crystalline schist are included. In spite of the durable lithology, the orthoquartzite fragments posses a high roundness (0.34〜0.73) in comparison with the other fragments. This indicates that they are reworked fragments from pre-Neogene formations. The Tokurazawa Formation distributed in the Joetsu district is one of probable source of these orthoquartzite fragments, because many orthoquartzite fragments have been found from the Lower Cretaceous Tetori Group with which the Tokurazawa Formation is a correlative.
