RESEARCH ON PERMIAN AND TRIASSIC BOUNDARY IN PELAGIC SEDIMENTS

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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.