Sedimentary filling characteristics and evolution process from Permian to middle Triassic in South Guizhou and Middle Guangxi

Based on identifying the sequence surface and analyzing the sequence stratigraphy of outcrops and well data,this paper regularized the stratigraphic classification of different facies from Permian to middle Triassic in south Guizhou and middle Guangxi.The Permian-middle Triassic strata in the study area can be divided into 2 super sequences and 19 third-order sequences.Taking super sequence system tracts as the mapping units,the authors drew the tectonic-sequence lithofacies paleogeographic map,which shows depositional facies distribution pattern of different stages from Permian to middle Triassic.This paper analyzed the filling processes at three evolution stages from Permian to middle Triassic in the study area,i.e.,stage of rift valley basin of passive margin,stage of rift valley basin of back-arc,stage of foreland basin.On such a basis,a model of sedimentary filling and dynamic evolution during the process of relative sea level change was constructed,which shows that the lowstand period was the alternate basin-upheaval stage,the transgression period was the formation stage of alternate platform-basin,and the highstand period was the typical sedimentary pattern of alternate platform-basin during the period of the passive continental margin rift basin and the backarc rift basin from Permian to middle Triassic in south Guizhou and middle Guangxi.From middle Triassic,affected by Indosinian movement,the sedimentary pattern of alternate platform-basin was ended and transformed into the sedimentation of turbidite of foreland basin.