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(约2.5亿年前)大规模灭绝的原因，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，特别是通过深部钻探，因为这项研究的关键是获得用于地球化学分析的无风化的新鲜岩石样品。1998年冬季，在对中国南部4个候选剖面进行初步野外考察的基础上，选定了朝天剖面。1999年夏天，我们在四川北部朝天进行了一次学术钻探，回收了260米长的钻探岩心样品。嘉林格河段覆盖了整个上二叠统，从上茅口统到长兴统，再加上下三叠统最低的格里斯巴克统。从…表面采集的大量样本，包括菊石、珊瑚、腕足类和褐藻类化石这些样品于1999年秋季运往东京，目前正在接受常量元素组成、碳同位素比值和稀土元素组成等多方面的地球化学分析。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。根据野外调查和室内初步分析，有以下新的发现：1)朝田剖面以化石为基准，涵盖了上茅口统、乌查品系和灿兴系化石，以及最低的格里斯巴克期化石；2)取心样品相当新鲜，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。这提出了“羽流冬季”情景(由项目负责人提出)，它将羽流引起的异常猛烈的火山活动与盘古超大陆的解体联系起来，并与跨越P-T边界的大规模灭绝有关的全球环境变化联系起来。较少

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