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

该项目旨在揭示二叠纪-三叠纪边界（约2.5亿年前）大灭绝的原因，这代表了地球历史上最大的生物圈灾难。我们计划收集连续的沉积序列，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本用于地球化学分析对本研究至关重要。在南方4个候选断面中，潮天断面是在1998年冬季初步野外考察的基础上选定的。1999年夏季，我们在川北朝天进行了一次学术钻探，回收了260 m长的岩心样品。嘉陵涧沿江段覆盖了上二叠统从茅坎上至长兴期及下三叠统格里什巴阡期的整个上二叠统。从地表采集了大量的氨类、珊瑚、腕足类、毛藻类等化石样本，露头多，总重约5吨。这些样品于1999年秋运往东京，目前正在进行地球化学分析，包括主要元素组成、碳同位素比和稀土元素组成。特别是，名古屋大学的扫描x射线分析显微镜用于恢复样品化学成分的可视化图像。由于地球化学分析才刚刚开始，结果将在稍后进行总结。根据野外调查和初步室内分析，得出以下新发现：(1)潮田剖面以指标化石为基础，覆盖了上茂坎、五坪阶、甘兴阶及最低格里什巴赫阶化石；(2)取心样品较新鲜，明显优于露头样品；(3)该剖面凝灰岩层多，其层位往往对应特定化石的消失层位。这表明了“羽流冬季”情景（由项目负责人提出），将羽流引起的异常剧烈的火山活动与泛古大陆的分裂联系起来，并将全球环境变化与跨P-T边界的大规模灭绝联系起来。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