LUO Jinxiong;HE Youbin;WANG Dan;LI Weiyang;WEN Jing
The Permian of Songkan section at Tongzi County, Guizhou Province is a typical section in South China, which is composed of the Qixia, Maokou, Longtan and Changxing Formations with a thickness of 484.02m. The field measurements and lab studies show that the rock types of this section are rather simple, including limestones, shale, dolostones and siliceous rocks. Limestones can be further divided into bioclastic limestones, bioclastic-bearing limestones, microcrystalline-fine crystalline limestones and eyeball shaped limestones. The eyeball shaped limestones were mainly developed in the lower part of the Qixia Formation and the middle to lower parts of Maokou Formation. They were formed by the interaction of sedimentation and diagenesis under the influence of upwelling. The dolostones are dominated by calcitic dolostones distributed in patches. They were mainly developed in Qixia and Maokou Formation, and probably formed by burial dolomitization. Siliceous rocks can be divided into two types of the nodule-, lump-and band-like rocks and the bedded siliceous rocks, which were formed by metasomatism; and the source of silicon is related to the hydrothermal activity. According to the analyses of lithology, palaeontology, sedimentary structures and geochemistry, two kinds of sedimentary environments were identified. They include the shore zone and the carbonate platform, and locally there are shallow banks in the platform. The analysis of the sedimentary environment evolution indicates that two sedimentary cycles of transgression and regression occurred in the Permian. The first transgression began in the Early Qiaxia Age, ended in the Late Maokou Age. In the Early Longtan Age, the second transgression began and lasted until the Late Changxing Age.
