THE PERMIAN SEQUENCE STRATIGRAPHIC FRAMEWORK AND EVOLUTION OF SEDIMENTARY FACIES AND PALEOGEOGRAPHY IN GUIZHOU AND GUANGXI AREAS

The Permian system which includes the Chuanshanian,the Yangsingian and the Lopingian series can be divided into three series in Guizhou and Guangxi areas of South China.There are two obvious unconformities in the sequence,the one refers to the main episode of the Qiangui epeirogeny in the transitional period at the turn between Chuanshanian epoch and Yangsingian epoch,and another refers to the main episode of Dongwu movement in the transitional period at the turn between Yangsingian epoch and Lopingian epoch,both of which not only forms the evident sequence boundaries of type I but also represents the important changing surfaces of sedimentary facies and paleogeography.Obvious differentiation of depositional facies leads to the formation of a special pattern of paleogeography marked by "platformbasinhilltrough",especially for Lopingian epoch,which is reflected by lots of sedimentary features.For examples,coal measures are developed on the widespread platform,and sponge reefs are developed on the margin of the widespread platform as well as the isolated carbonate platform,furthermore,the period of the evident facies differentiation is corresponding to the development period of reefs,etc.The first episode of Dongwu movement in the transitional period at the turn between Yangsingian epoch and Lopingian epoch results in the great change of the paleogeographic pattern.Seven third order sequences can be discerned in the Permian of the study areas,i.e.,the top part of Carboniferous and the Chuanshanian series form one sequence (SQ₁₉),four sequences which are from SQ₂₀ to SQ₂₃ are discerned in the Yangsingian series,and two sequences which are SQ₂₄ and SQ₂₅ are divided in Lopingian series.The typical drowned event of the carbonate platforms in the transitional period at the turn between Permian and Triassic shows that the top boundary of SQ₂₅ is a obvious drowned unconformity.Therefore,the complex but regular facies changes in time and in space can clearly be illustrated in the series of the maps of sedimentary facies and paleogeography as well as the panel diagrams of sequence stratigraphic framework.