Ishiga-diagram as a geologic time scale

石贺图解显示了层状硅质岩的沉积旋回，可用于评价初级生产力的变化和海洋条件。在石炭纪至侏罗纪层状硅质岩序列中对该图解进行了检验，在此之前对详细的放射虫和牙形石生物地层年龄进行了检验。沉积旋回由一级旋回组成。1 Ma，这是5个二级循环的组合。二阶循环是ca。200 kys，形成一个产能高峰期，产能变化方式因时代而异，上三叠统-下侏罗统出现了明显的韵律旋回。Ishiga图中显示的产能下降与地质边界相吻合。因此，初级生产力可以与其他大型动物群的下降或区别联系起来。本研究扩展到地质边界的地球化学检查，如二叠纪/三叠纪和地质事件，如Toarcian缺氧事件。这是因为这些事件的标志是有机黑色页岩的出现，这表明放射虫生产力和古海洋环境的变化。尽管晚二叠世层状硅质岩的生产力逐渐高于中、下二叠世，但硅质岩颜色变为黑色，有机碳含量明显较高。中、上二叠统界线的地球化学特征表明，该界线以边缘盆地缺氧成盆为特征。这可能是由于大陆边缘的活火山活动使河流营养物富集而引起的富营养化所致，石贺图可用于评价海洋条件的变化，而远洋和陆源沉积物的地球化学可作为系统研究地球环境的基础。

Ishiga-diagram displays sedimentary cycles of bedded cherts and is useful for evaluation of change of primary production and oceanic condition. Examination of this diagram has been carried out in the Carboniferous to Jurassic bedded cherts sequence, where detailed radiolarian and conodonts biostratigraphic age was examined previously. The sedimentary cycles consists of first order cycle of ca. 1 Ma, and this is a combination of 5 second order cycles. The second order cycle is ca. 200 kys, and form a peak of productivity.Mode of change in productivity varies in ages, and significantly rhythmic cycles appeared in Upper Triassic to Lower Jurassic. The decrease in productivity shown in the Ishiga-diagram well coincides to the geologic boundary. Thus primary production can be linked to depression or distinction of the other macro-fauna.This research was expanded to the geochemical examination of the geologic boundary, such as Permian/Triassic and geologic event e.g. Toarcian anoxic event. This is because these events are marked by appearance of organic black shales, which show depression of radiolarian productivity and paleooceanic environmental change. Although the productivity of bedded cherts in the Uppermost Permian gradually became relatively higher than the Middle and Lower Permian, cherts color change into black and includes significantly high contents of organic carbon. The Middle and Upper Permian boundary was also geochemically examined and that was characterized by anoxic basin formation in marginal basin. This might be caused by eutrophication by supposed enrichment of river-born nutrient supply by active volcanism of the continental margin.Ishiga-diagram is useful for evaluation of the oceanic condition change, and geochemistry of the sediments both pelagic and terrigenous may be fundamental for systematic examination of the earth environment.