黔南地区中二叠世碳酸盐台地边缘沉积演化及古海洋意义*

华南地区二叠纪为东特提斯地区一个大型碳酸盐台地。中二叠世茅口亚世,上扬子碳酸盐台地经历了从全盛到萎缩的重要转折。黔南地区地处该台地南缘,是通过地层结构及其变化探讨台地演化控制因素的最佳地区。文中选取黔南罗甸纳水和沫阳2个代表性剖面,通过对茅口组的岩石类型和骨屑颗粒组合统计分析,从碳酸盐生产工厂的角度开展研究。野外和室内研究共识别出15种岩石类型、5种沉积相和6种骨屑颗粒组合,并恢复了各组合对应的碳酸盐生产工厂的特征。沉积相及碳酸盐生产工厂分析表明,黔南地区自晚孤峰期开始经历了由热带浅水、暖水工厂到热带较深水、温凉水工厂的明显转变,表现为孤峰阶上部开始出现较深水沉积。这一碳酸盐生产工厂的转变现象在华南地区孤峰期—早冷坞期普遍存在,表现为台地萎缩、台地边缘被淹没。中二叠世晚孤峰期至晚二叠世吴家坪期是全球重大地史转折期,光合作用生物遭受重创、海洋生态环境急剧恶化,上述碳酸盐生产工厂的急剧转变与当时热带浅海碳酸盐生产工厂被抑制或破坏有关。

Sedimentary evolution of the Middle Permian carbonate platform margin in southern Guizhou and its palaeo-oceanographic implications

South China,part of Eastern Tethys,developed a huge carbonate platform in the Permian. During the Maokouin Subepoch of the Middle Permian,the carbonate platform experienced a transition from its prosperity to shrink. The southern Guizhou was located at the southern margin of the carbonate platform. It is a good area for discussing the controlling factors of platform evolution by analysis of stratigraphic structure and its variation. In this study,we selected the typical Nashui and Moyang sections of Luodian,southern Guizhou and studied on their carbonate factory by analyzing rock types and skeletal association statistics. As a result,15 rock types,5 sedimentary facies and 6 skeletal associations are recognized by field and indoor research. The carbonate factory features of the skeletal associations were also rebuilt. The results show that a distinct transition from tropical,shallow and warm water factory to tropical,deep and cool water factory occurred starting from the late Kuhfengian in the southern Guizhou,manifested as the beginning occurrence of deep water sediments in the upper Kuhfengian Stage. This transition was widespread from the Kuhfengian to the early Lengwuan in South China,manifested as the shrink of the carbonate platform and the drowning of the platform margin. The late Kuhfengian of the Middle Permian to the Wuchiapingian of the Late Permian was a significant turning point of global geological history where the photosynthetic organisms suffered heavy losses and the marine ecological environment deteriorated sharply. The drastic change of the carbonate factory was related to the inhibition or destruction of the shallow tropical carbonate factory.