湘东南晚三叠世-侏罗纪沉积特征及盆地性质和成因机制

关于湘东南晚三叠世-侏罗纪沉积盆地性质存在挤压相关类前陆盆地及断陷盆地等不同认识。沉积物分布及岩相特征研究表明:湘东南晚三叠世-早侏罗世早期为海相-海陆交互相沉积环境, 早侏罗世晚期-中侏罗世早期为陆相沉积环境; 晚三叠世盆地为分布于茶陵-郴州大断裂东侧(上盘)的北北东-近南北向狭长海湾, 早侏罗世开始盆地向东、西两侧扩展; 晚三叠世-侏罗纪沉积横向上覆于相对较老的地层之上, 表明湘东南晚三叠世-侏罗纪盆地不是南北向挤压形成的类前陆拗陷盆地。结合区域构造背景, 提出盆地的形成主要与区域南北向挤压下先期北北东向断裂产生东西方向伸展有关, 一定程度上印证了印支运动构造线为北北东向。海相至陆相的演化过程暗示研究区以南在早侏罗世晚期开始因区域南北向挤压形成了东西向隆起, 说明盆地发育后期伸展活动的同时却处于区域挤压拗陷构造背景之中, 反映出晚三叠世-侏罗纪盆地演化期间华南地区伸展/挤压构造体制具复杂的时空变化。 

SEDIMENTARY CHARACTERISTICS, BASIN TYPE AND DYNAMIC MECHANISMS DURING LATE TRIASSIC-JURASSIC IN SOUTHEASTERN HUNAN PROVINCE

There are different standpoints such as para-foreland basin and down-faulted basin about the Late Triassic-Jurassic basin in southeastern Hunan.Distribution of the sediments and lithofacies character show information as follows: there existed marine and marine-terrigenous sedimentary environment during Late Triassic-early Early Jurassic in southeastern Hunan,while continental sedimentary environment during late Early Jurassic-early Middle Jurassic;the Late Triassic basin was a NNE-SN trending narrow and long bay along the east side of Chaling-Chenzhou fault,and the basin expanded to east and west since Early Jurassic;the Late Triassic-Jurassic sediments covered crosswise on older layers.All the above indicated that the Late Triassic-Jurassic basin in southeastern Hunan wasnt a para-foreland depressive basin controlled by NS-compression.Combined with regional tectonic setting,the authors bring forward recognition as follows: the forming of the basin was mainly related with the EW-extention of NNE-trending faults under regional SN-compressional stress field,which confirmed that the lineament trend of Indosinian Movement in southeast Hunan was NNE;above evolution from marine to continental suggested that a EW-trending uplift formed to south of the study area since late Early Jurassic under regional S-N-compression,and that the study area was in a regional depressive tectonic setting when the basin extended in late development stage.These render the complex extensional or compressional space-time variation of tectonic regime when the Late Triassic-Jurassic basins developed in south China.