Study of the Volcanogenic sequences in the Daijima and Nishikurosawa Age

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1:Results of the stratigraphical and volcanogeologic study of the Daijima and Nishikurosawa Age are as follows; (1)Based on the fossil plants and marker beds, most of the Nozoki Formation in the type locality,northern end of the Shinjo basin,is correlated with the Daijima Formation in the Oga Peninsula. (2)It was considered that the Sugota and Ohmori Formations were the strata showing contemporaneous heterotopic facies,and both of them were correlated to the latest stage of the Nishikurosawa Age. However,the Sugota Formation is overlaid by the Ohmori Formation. The Sugota Formation is correlated with NN4-5 zones of the calcareous nannofossil biostratigraphy. (3)The emplacement of basaltic rocks in the Akita-Shonai Oil Field in the Nishikurosawa Stage occurred for the duration of the formation of the Sugota Formation. (4)The large-scale felsic volcanism in the graben of the area along Sagae River begun after NN6 zone. (5) The Daijima Formation(Huzioka,1959)is newly defined in this study.2:Results of the facies analysis of the basaltic Sunakobuchi Formation,Formed during the back-arc opening stage,shows that the strata was formed by the phreatomagmatic eruptions near seashore.3:There are chemical similarities between the basaltic rocks formed prior or posterior to the formation of Kuroko deposits in the Hokuroku district and that of the Sunakobuchi Formation. Both of them are similar to back arc basalt. It is considered that heavy metals in Kuroko fluids were extracted from basaltic rocks. The vesicularity at the rim of submarine basalts of the Sunakobuchi and Nanatani Formations is higher than that of basalts from the Yurihara Oil and Gas Field.