广西黎塘孤立台地吉维特阶-法门阶碳酸盐台地生态系到菌藻生态系的演变及其意义

自泥盆纪埃姆斯期, 广西受陆内裂陷影响, 形成碳酸盐台地与台沟间列的构造格局.吉维特期开始, 六景及相邻的黎塘一带逐渐形成孤立台地的沉积背景.吉维特期, 六景剖面的民塘组为以竹节石为特色的礁前斜坡生态系, 尽管目前没有出露生物礁, 从礁前角砾岩可以恢复曾经存在的礁生态系.而黎塘一带塘家湾组为以珊瑚、层孔虫、腕足类为主要特色的台地生态系.弗拉斯期, 六景剖面的谷闭组则为少量珊瑚、腕足、层孔虫为特色的局限-半开放台地生态系.黎塘一带的桂林组仍为以珊瑚、层孔虫、腕足类为主要特色的台地生态系.六景、黎塘地区自法门期开始发生生态系突变, 六景剖面的融县组和黎塘一带的东村组发育藻礁丘或藻席为特色的藻生态系.该生态系的突变是F-F生物群集绝灭造成的生物类群突变的结果.生态系的特征也与吉维特-弗拉斯期烃源岩的形成、演化密切相关. 

Transformation from Devonian Givetian Carbonate Platform to Famennian Bacteria-Algae Ecosystem in Litang Isolated Platform, Guangxi,and Its Significance

The carbonate platforms and the intraplatform troughs resulted from intracontinental rifting were simultaneously developed in Guangxi since the Emsian stage of Devonian. An isolated platform was found to occur at Liujing and Litang areas in central Guangxi since the Givetian stage. A fore-reef slope ecosystem characterized by tentaculites was identifiable in Mintang Fm. in Liujing during the Givetian stage. The occurrence of the reef ecosystem was inferred by the reef congregates in Mintang Fm. rather than the reef outcrop. The carbonate platform ecosystem in the Givetian Tangjiawan Fm. in Litang is composed of corals, stromatopoidea and brachiopoda. An ecosystem of a restricted and partly-open platform developed in Frasinan Gubi Fm., characterized by a small proportion of corals, brachiopoda and stromatopoidea. Frasnian Guilin Fm. in Litang is shown to be an ecosystem of a carbonate platform composed of corals, brachiopoda and stromatopoidea. An abrupt ecosystem change was observed to occur at the boundary between Frasnian and Famennian. Ecosystems of Rongxian Fm. in Liujing and Dongcun Fm. in Litang of Famennian are composed of algae reef and algae sheet. The ecosystem variation was proposed to result from the well known F-F faunal mass extinction. These ecosystem features are closely related to the forming and the evolution of the source rocks in this region.