RESEARCH ON PERMIAN AND TRIASSIC BOUNDARY IN PELAGIC SEDIMENTS

这项工作的重点是在日本西南部的层状硅质岩序列的二叠纪和三叠纪的边界调查。层状硅质岩是典型的深海远洋沉积物，被认为是一个连续的、无缝的记录器。这是因为它们比浅海沉积物更容易受到侵蚀，而浅海沉积物则受到陆源物质局部通量的污染。通过生物地层学、沉积学、地球化学和稳定同位素等研究，对该界线两侧的海洋环境进行了评价，发现即使在远洋环境下，硅质碳酸盐在界线处也大部分灭绝，生态系统得到了彻底的改造。这一生物事件发生在晚二叠世放射虫大量繁殖之后，放射虫大量提供有机质，可能是由好氧盆地向缺氧盆地转变和生态系统变化的触发因素。边界以上的有机黑色泥岩是阐明海洋条件变化的重要标志层，即硫稳定同位素检测表明其具有高的初级生产力和氧化的沉积环境。与标准陆相页岩相比，该有机质黑色泥岩还显示富集Ti、Th和Zr，这表明可能受到大陆溢流玄武岩活动的影响。二、三叠系界线的合作研究，对地球表面生物地质系统产生了一些新的认识，这些认识将在下一个项目中得到检验。

This work has focused on an investigation of the Permian and Triassic boundary in bedded chert sequences of Southwest Japan. Bedded cherts are typical pelagic deep marine sediments which were regarded to be a continuous and seamless recorder. This is because they were rather exempted from an erosion than those of the shallow marine sediments where an invasion of the local flux of terrigenous materials were contaminated. Biostratigraphical, sedimentologic, geochemical and stable isotopic examinations have been carried out which resulted in an evaluation of the oceanic condition across this boundary.Even in a pelagic condition, siliceous planktons mostly extinct at the boundary, and ecologic system was wholly innovated. This bio-event followed Late Permian radiolarian blooming of which dominant supply of organic materials might be a trigger of shifting from oxic basin to anoxic one and change of ecological system. Organic black mudstones occurred above the boundary is an important key bed to elucidate change of oceanic condition ; namely this indicated high primary production and oxic depositional environment indicated by sulfur stable isotopic examination. This organic black mudstone also indicated enrichment in Ti, Th and Zr in comparison with standard continental shales which suggested possible effect from the activity of continental flood basalts. Co-operative research on the Permian and Triassic boundary produced some new ideas on bio-geo-system of the earth surface which will be examined in next project.