Ishiga-diagram as a geologic time scale

石贺图显示了层状燧石岩的沉积旋回，可用于评价原生生产和海洋条件的变化。在石炭纪到侏罗纪的层状燧石层序中对这张图进行了检查，在那里详细的放射虫和牙形刺生物地层年龄已经被检查过。沉积旋回由约1 Ma的一级旋回组成，这是5个二级旋回的组合。第二个订单周期约为200个键，并形成一个生产力高峰。上三叠统—下侏罗统生产力变化方式不同，有明显的节律旋回。石贺图井显示的产能下降与地质边界一致。因此，初级生产可以与其他大型动物群的衰退或区分联系起来。该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。这是因为这些事件以有机黑色页岩的出现为标志，表明放射虫生产力的下降和古海洋环境的变化。虽然上二叠统层状燧石的产率逐渐高于中、下二叠统，但其颜色逐渐变黑，有机碳含量明显增高。对中、上二叠统边界进行了地球化学研究，发现盆地边缘以缺氧盆地为特征。这可能是由富营养化引起的，这是由于大陆边缘的活火山作用使河流中的营养物质供应增加。石贺图可用于评价海洋条件的变化，而海洋和陆源沉积物的地球化学可能是系统考察地球环境的基础。

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.