Study on the cause of the Earth's greatest mass extinction

该项目旨在揭示二叠纪-三叠纪界线的原因（约。2.5亿年前）大规模灭绝，这是地球历史上最大的生物圈灾难。我们计划收集一个连续的沉积序列，记录P-T边界周围的长期环境变化，特别是通过深钻，因为获得无风化的新鲜岩石样品进行地球化学分析对本研究至关重要。1998年冬季，在华南地区4个候选断面中，通过前期野外调查，选定了朝天断面。1999年夏季，我们在四川北方朝天进行了一次学术钻探，获得了260 m长的钻芯样品。沿着嘉陵江的剖面覆盖了上二叠统从茅岗阶顶部至长兴阶的整个地层，以及下三叠统格里斯巴赫阶底部。在地表采集到大量的菊石、珊瑚、腕足动物和梭虫化石， 关于我们 e露头使样品总重量约为。这些样品于1999年秋季运往东京，目前正在进行各方面的地球化学分析，包括主要元素组成、碳同位素比和稀土元素组成。特别地，名古屋大学的扫描X射线分析显微镜用于恢复样品的化学组成的可视化图像。由于地球化学分析工作刚刚开始，成果将在以后进行总结。（1）朝天剖面的标志化石包括上茅口阶、五茶坪阶、长兴阶和格里斯巴赫阶。（2）取心样品新鲜，比露头样品好得多，3）该剖面有许多凝灰岩层，其层位往往与特定化石的消失层位相对应。这表明了“羽冬季”情景（由项目负责人提出），将羽引起的异常暴力的火山活动与盘古超大陆分裂以及与P-T边界上大规模灭绝相关的全球环境变化联系起来。少

This project was aimed to reveal the cause of the Permo-Triassic boundary (ca. 250 million years ago) mass extinction which represents the greatest biospheric catastrophe in the Earth's history. We planned to collect a continuous sedimentary sequence that recorded the secular environmental change around the P-T boundary, particularly by deep-drilling, because it is critical for this study to obtain weathering -free fresh rock samples for geochemnical analyses. Out of 4 candidate sections in South China, the Chaotien section was chosen on the basis of preliminary field research in winter of 1998. We conducted an academic drilling at Chaotien in northern Sicuan province in summer of 1999 and recovered 260 m long drilled core samples. The section along the Jialingian river covers the entire Upper Permian series from top Maokoan to Changhsingian plus the lowest Griesbachian of Lower Triassic. Numerous samples including ammonoid, coral, brachiopod and fusulinid fossils collected from surfac … More e outcrops made the total sample weight ca. 5 tons.These samples were shipped to Tokyo in Fall of 1999 and are currently under geochemical analyses in various aspects including major element composition, carbon isotope ratio plus rare earth element composition. In Particular, the Scanning X-ray Analyzing Microscope of the Nagoya Univ. is used for recovering visualized images of chemical composition of the samples. As the geochemical analysis has just started, results will be summarized later on.According to the field research and preliminary indoor analyses, the following new observations were made ; 1) The Chaotien section covers fossiliferous Upper Maokoan, Wuchapingian and Canhsingian plus the lowest Griesbachian on the basis of index fossils, 2) the cored samples are quite fresh, much better than those from the outcrop, 3) This section has many tuff layers whose horizons often correspond to the disappearance horizon of particular fossils. This suggests the "Plume Winter" scenario (proposed by the project leader) that connects plume-induced extraodinarily violent volcanism with the Pangean supercontinent breakup, and with the global environmental change associated with mass extinction across the P-T boundary. Less