Stylolitic Cherts and Radiolarian Fossils in the Imajo Area of the Nanjo Massif, Fukui Prefecture, Central Japan

The Imajo area in Fukui Prefecture，central Ja pan,is under lain by Mesozoic strata such as sandstone， chert， and shale with strike of N 400_500 Wand dip of 500 _700 N. Many sedimentary structures in sandstone tell us the right-way up of beds. Radiolarians extracted from chert and siliceous shale disclose that the sandstone and shale belong to lower to middle Jurassic and the chert mainly to upper Triassic. Based on the radiolarian data， the geologic relation of the strata in the Imajo area to the Tetori Group and to the Samondake Formation is discussed briefly. The chert in this area occasionally bears bedding-parallel seams repeating regularly within individual chert layers. Stylolitization is recognized along the seams resulting in remarkable reduction in thickness of chert layers. These plane structures are described