The Sequence Stratigraphical Fcatures of the Intracontinental Strike-Slip Basin—— Xianfeng Basin in Yunnan Province, Southwest China

Key words: 
• terrestrial basin /
• strike-slip structure analysis of sequence /
• stratigraphy

Abstract: The difference between intracontinental basin and marginal basin exists in many aspects, such astectonic settings, depositional scale, infilling pattern, paleomotography, sediment components and sedi-mentary sequences.The intracontinental basin is characterized by multi-sedinent-sources, multi-sediment| system, narrow lateral facies extension and rapid facies alternation.The Xianfeng basin is a Tertiaryfaulted intracontinental basin in Yunnan Province, Southwest China.This paper studied its infilling se-quence, sedimentary framework, structure framework and the loacal tectonic setting.Furthermore, thefeatures of an intracontinental basin under a strike-slip tectonic setting and the sequence characters werediscussed.Bwsides the features appearing in all inland basins, the Xianfeng basin showed a clear strike-slip character.it controlled the variation of accomadtion and the evolution of sediment source providingpattern.The infilling sequences were charactorized by the migration of the depositional cen along theboundary faults, the lateral onlap of sediment system and the active infilling along the mqjor axis of thebasin.Through carefully study, four types of sruface have been recognized to divide the sequence and thesystem tracts: tectogenesis surface(TCS), tectonic stress field transition surface(T TS).large-scale flood-ing surface(FDS) and coal bed surface(CBS).On the basis of sequence surfaces listed the above, the in-filling sequence could be divided into two sequences.LST, TST, HST and AST were recognized.Coal-bearing sequences were well developed in the Xianfeng basin, mainly appearing in the upper part of LSTand HST.Coal bed M 8 spreaded on a whole basin scale with the depth as thick as 236.6m.As we allknow, a coal bed is a sensitive indicator which reflects the fluctuation of alke surface and water depth.Therefore, the locally spreaded coal beds are the ideal surfaces to determine a parasequence and parase-quence sets.in addition, it should be pointed out that the tectonic movement plays a great role in tehbasin infilling including tectonic subsidence, strike-slip movement and tectonic inversion.