Permian Sequence Stratigraphy and Basin Evolution in South of China

Key words: 
• South China /
• sequence stratigraphy /
• basin analysis /
• unstable sedimentation

Abstract: Sequence stratigraphy is an important method of basin analysis.Permian is an important evolution stage of Hercynian-Indo-Chinese Basin in the South China.The tectonic environment of the basin is under an extensional condition as a whole and the sedimentary basin can be divided into two classes including craton basin and extension rift basin.After the Dongwu movement,there exist squeezing foreland basin and arc rear basin due to partial basin environment changes.There are special characteristics in sequence stratigraphy of different sedimentary basin because the structural site sedimentation rate and geometry are different and they influence and control the sea level change.Permian system in the south China consists of eleven sequences corresponding to 3rd order cvcle and two supersequences corresponding to 2nd order cycle.Supersequence of Lower Permian is a complete cycle.Qixia epoch is composed of three sequences (S1-S3) corresponding to sea level rising stage of 2nd order cycle,Maokou epoch also consists of three sequences (S4-S6) corresponding to sea level descending period.The largest transgression period is in Lower Maokou epoch.The supersequence of Upper Permian is not complete only corresponding to a sea level rising period of 2nd order cycle The characteristics of sequences or supersequences are different not only in material constitution and geometry,but also in structure,composition and the boundary surface form,and it demonstrates that the types,evolution and characters of the basin have tightly inherent relationship. According to tectonic role,sedimentary characteristics,sea level change,sequence stratigraphy texture and paleogeography,the evolution of Hercynian Indo Chinese sedimentary basin in the south China can be divided into five stages and respectively corresponding to five 2nd order sea level change cycles.It indicates a process from the basin forming,developing to consuming with clear rhythm.The evolution of Permian sedimentary basin is in the transition process from mature stage to consuming stage.The basin in the south China comes into holaspid period in Lower Permian.The main proofs are:(a) the transgression field of the sea is the largest in this stage;(b) the deep water area of the extension basin is the largest;(c) there is the strongest basic volcanic activity of Hercynian Indo during Dongwu movement stage,and it cause this area to be protruded and disintergrated,the transgression field of the sea shortened and finally the property of some basin changed.The basic characteristics of the Permian basin are that a northwest extension basin is between two large cratons Yangzi and Huaxia and the development of the two cratons are not balanced.The central tension basin is formed by rifting again along Caledonian junction belt.This palaogeography framework is very similar to that of Caledonian.Therefore,we consider that the tectonic environment of Upper Palaeozoic era basin in the south China is not a stable craton environment.