Study of the Volcanogenic sequences in the Daijima and Nishikurosawa Age

1 . Daijima和Nishikurosawa时代的地层和火山地质研究结果如下：(1)根据化石植物和标志层，在新真盆地北端的模式区域，野崎组的大部分与大贺半岛的Daijima组具有对应关系。(2)认为宿田组和大森组为同生异位相地层，均与西黑泽时代晚期相对应。然而，Sugota组被Ohmori组覆盖。苏戈塔组与NN4-5带钙质纳米化石生物地层有关。(3)秋田油田西黑泽期玄武岩侵位发生在须田组形成期间。(4) Sagae江边地堑的大规模长英质火山活动开始于NN6带之后。(5) Daijima组（Huzioka,1959）是本研究中新定义的地层。2：弧后打开阶段形成的玄武岩Sunakobuchi组的相分析结果表明，该地层是由靠近海岸的呼吸岩浆喷发形成的。3：北陆地区黑子沉积形成前后的玄武岩与Sunakobuchi组的玄武岩具有化学相似性。两者都与弧后玄武岩相似。认为黑子流体中的重金属是从玄武岩中提取出来的。Sunakobuchi组和Nanatani组海底玄武岩边缘的水泡性高于Yurihara油气田的玄武岩。

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.