二叠-三叠系之交牙形石、火山灰层及生物沉积相序列

This study is choosing representative section from diverse paleogeographical setting and carries out studies of high-resolution conodont biozone, ash-bed and biosedimentary facies through Permian-Triassic boundary. As a result multiply columnar section of every geographic setting will be established. Proceed to the next step comparison of conodont biozones between the sections in diverse geographic setting should make up a spatial succession of conodont biozones in Permian-Triassic boundary interval. Dissection of relationships between ash-beds and conodont biozones could calibrate stratigraphical level of ash-beds and make up an event-stratigraphical succession. So that will provide a credible pattern for dating the ages of P-T boundary and extinct events. Farther in order to establish a succession of biosedimentary phase in Permian-Triassic boundary interval and reconstruct pattern of global biotic extinction and recovery. We would like to match space-time relationships in isochronous stratigraphical framework that is cooperatively controlled both by conodont biozones and by ash beds. Finally to understand the cause of great extinction we should carry out study of catastrophic events in Permian-Triassic boundary interval.

在华南不同的古地理分区内选择具有代表性的剖面，进行高分辨率牙的形石带、火山灰层的特征及生物沉积相研究，首先构建起一个多重的地层柱状。通过解析火山灰层与牙形石带的地层关系，建立各相关的事件地层序列，将火山灰的绝对年龄与牙形石带研究相结合，更精细地建立二叠-三叠系之交的牙形石序列，力争为界面附近的生物灭绝事件模型提供一个新思路。此外，试图在牙形石带和火山灰层联合限定的等时地层格架内，配置生物沉积相的时-空组合关系，厘定生物沉积演化相期，恢复全球性生物灭绝与复苏的节律，考察二叠-三叠纪过度期的灾难事件，探索二叠-三叠系之交的生物大灭绝原因。

在华南二叠-三叠之交的不同古地理分区选定了九条具有代表性的剖面并逐一做了高分辨率的牙形石地层、火山事件地层及沉积相序列的研究工作，取得了如下成果: 1）完成了华南二叠-三叠之交高分辨率牙形石地层研究，在P-T界面附近划分出了5个重要的牙形石带，其区域变化规律充分说明，碳酸盐台地剖面和斜坡区剖面中时常会出现因海平面下降而产生的生物带缺失，而在陆内和远洋盆地的地层序列中则发育连续的完整的牙形石分带序列；2）证实了华南二叠-三叠之交火山灰层来自长英质火山事件，火山起因于亏损地幔不同程度参与的壳源岩浆，火山作用发生在华南陆块周缘遭受碰撞的构造背景下，这充分说明与二叠-三叠生物灭绝事件同时发生的西北利亚玄武岩溢出事件至少不与华南的同期生物大灭绝事件相关；3）通过牙形石地层和全球海平面变化引起的层序地层单元对比发现，二者有高度的耦合性，对比结果充分证明了全球性生物演化受生态环境和全球海平面变化控制。