Ishiga-diagram as a geologic time scale

Ishiga图显示了层状硅质岩的沉积旋回，对评价初级生产力和海洋条件的变化是有用的。在石炭系至侏罗系层状硅质岩序列中已进行了该图解的检验，其中详细的放射虫和牙形刺生物地层年龄已被研究过。沉积旋回由约1 Ma的一级旋回组成，由5个二级旋回组合而成。二级旋回约200年，形成生产力高峰，生产力变化模式随时代不同而不同，上三叠统至下侏罗统出现明显的韵律旋回。石贺图中显示的产能下降与地质界线很好地吻合。因此，初级生产可以与其他大型动物群的凹陷或区分联系在一起。这项研究扩展到地质边界的地球化学检查，如二叠系/三叠系和地质事件，如托尔新世缺氧事件。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的下降和古海洋环境的变化。尽管上二叠统层状硅质岩的生产力逐渐高于中、下二叠统层状硅质岩，但硅质岩颜色变为黑色，有机碳含量明显较高。对中、上二叠统界线进行了地球化学研究，其特征为边缘盆地的缺氧盆地形成。这可能是由于大陆边缘的活火山作用使河流中的营养物质变富而引起的富营养化。Ishiga图可用于评估海洋状况的变化，而远洋和陆源沉积物的地球化学可能是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.