Stratigraphical Study on the Mine Series

The Upper Triassic Mine and Atsu series are rspectively developed on the west and southwest sides of Akiyoshi plateau, Yamaguchi Prefecture., The Upper Palaeozoic Chichibu series of the plateau is unconformably overlain on its west side by the Mine series which is in turn generally monoclinal to the northwest except its western marginal part where the series forms a syncline and is delimited by a fault from the phyllitic rocks of Toyogatake in further west., The stratigraphic succession of the Mine series is shown in the table given below : [table] The Hirabara stage begins with the basal limestone conglomerate and consists of clay, shale, sandstone and conglomerate in alternation., A few coal seams are intercalated in its top and basal parts., The lower part of the Momonoki stage is composed of the alternation of thick conglomerate, sandstone and shale with intercalations of main coal seams ; its upper part consists in the main of thick sandstone., The Aso stage consists of the alternating beds of clay, shale, sandstone and a few coalseams in the lower part and mainly of thick massive sandstones in the upper., While the Momonoki stage overlies the Hirabara conformably or slightly para-unconformably in the southern part, the former, overlapping the latter, covers the Upper Palaeozoic Chichibu series directly in the northern part., As may be seen in the following lists, the Aso and Hirabara stages yield marine and brackish shells in various horizons, while the Momonoki contains no shells but a number of plants., FAUNA: Hirabara stage - Trigonia (Minetrigonia) hegiensis SAEKI, Halobia charlyana, Oxytoma zitteli (TELLER), Lima naumanni, Rhynchonella nasai, "Pleurophorus" sp., aff., P., perlongus, Edentula ozawai KOBAYASHI, Cardinia sp., Gervillia sp., Anodontophora sp., Syncyclonema sp., Aso stage- Pecten suzukii KOBAYASHI, Lima naumanni, Pseudomonotis sp., aff., P., spitzbergensis, Anodontophora sp., Pecten sp., Flora: Hirabara stage- Neocalamites carrerei (ZEILLER), Cladophlebis haiburnensis L., and H., Taeniopteris minensis OISHI, Cycadocarpidium swabii NATHORST, Pityophyllum longifolium (NATHORST), Podozamites lanceolatus(L., and H., ), P., schenki HEER, Nageiopsis raetica OISHI., Momonoki and Aso stages- Neocalamites carrerei (ZEILLER), Cladophlebis haiburnensis L., and H., C., nebbensis (BRONGN., ), C., raciborskii ZEILLER, Taeniopteris minensis OISHI, Pityophyllum longifolium (NATHORST), Podozamites lanceolatus (L., and H., ), P., schenki HEER, Cycadocarpidium swabii NATHORST (Momonoki stage), Ginkgoites digitata (BRONGN., ) var., huttoni SEWARD (Momonoki stage), Stenorachis elegans OISHI (Momonoki stage), Dictyophyllum japonicum YOKOYAMA (Aso stage), Nilssonia inouyei YOKOYAMA (Aso stage)., Judging from this floral assemblage the Mine flora corresponds as a whole to that of the Rhaetic of the world., On the other hand Halobia charlyana, Lima naumanni and Rhynchonella nasai which are the significant elements of the Hirabara fauna, occur commonly between the Hirabara stage and the Carnic Halobia bed in the Sakawa basin, province Tosa; Oxytoma zitteli and Trigonia (Minetrigonia) hegiensis are found commonly between the Hirabara stage and the Oxytoma bed in the Sakawa basin; the age of the latter may be Carno-Noric or Lower Noric., Among the Aso fauna, Lima naumanni is contained in the Halobia bed and Pecten suzuki in the Oxytoma bed., Pseudomonotis spitzbergensis is reported from the Carnic bed on Bear Island and the Noric bed at Spitzbergen., Further, it is a noteworthy fact in determining the age of the Aso stage that the fossiliferous sandstone of the Aso strikingly resembles a reddish micaceous sandstone at Kamosho which is located at a distance of about 15 kilometers from the fossil localities of the Aso stage, and the age of the Kamosho sandstone is decided at Noric with the find of Pseudomonotis ochotica in it. [the rest omitted]