黔南桂中地区二叠纪—中三叠世沉积充填特征及演化过程

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

对野外露头、钻井剖面进行了层序界面识别和层序地层分析,重新厘定了研究区二叠系—中三叠统不同相区的地层划分对比方案,将研究区二叠系—中三叠统划分出2个超层序和19个三级层序;以超层序体系域为编图单元,编制了研究区二叠纪—中三叠世层序岩相古地理图,系统揭示了研究区二叠纪—中三叠世各超层序的不同体系域的相带发育规律;分析了研究区二叠纪—中三叠世3个盆地演化阶段(被动陆缘裂谷盆地阶段、弧后裂谷盆地阶段、前陆盆地阶段)的盆地充填特征,并建立了相对海平面升降过程中的沉积充填过程及动态演化模式,提出了研究区被动陆缘裂谷盆地阶段和弧后裂谷盆地阶段的低位期为盆-隆相间期,海侵期为台-盆相间的建设期,高位期为台-盆相间格局定型期,中三叠世的受印支运动破坏了台-盆相间格局,转化为前陆盆地的浊积岩沉积。

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.