柴东地区早中侏罗世沉积充填与分布规律

Depositional filling and distribution rules of Early-Middle Jurassic in eastern Qaidam Basin

针对柴东地区中、下侏罗统残余地层分布复杂、原始沉积分布认识不一等问题,充分利用侏罗系野外露头勘查、钻井(孔)、地震等成果资料,通过露头引层、钻井(孔)标定地震以及地震相、低速异常识别等技术手段,明确研究区中、下侏罗统残余地层分布规律;通过野外地质剖面实测、岩心描述,系统研究早、中侏罗世地层沉积特征和充填演化规律,结合中新生代盆—山演化关系,恢复研究区早、中侏罗世古沉积体系。研究结果表明,柴东地区下侏罗统仅分布于红山凹陷,分布面积约为640 km2;中侏罗统分布于红山—小柴旦、尕西—鱼卡、霍布逊和德令哈等6个残留凹陷,尕丘、大柴旦、欧南等凹陷不发育中、下侏罗统。柴东地区早侏罗世表现为冲积扇—辫状河—辫状河三角洲—浅湖—辫状河三角洲的沉积充填演化特征,主要物源来自北方的祁连山,次要物源来自南侧的柴南隆起;中侏罗世处于拗陷沉积阶段,表现为扇三角洲—辫状河三角洲—湖泊的水进半旋回沉积充填演化特征。

In allusion to the problems encountered in research such as the complex distribution of residual middle-lower Ju?rassic,inconsistent knowledge about original depositional filling,etc.,the residual strata distribution of the middle-lowerJurassic was made clearly according to the Jurassic outcrop profile,drilling and seismic data and combined with the techni?cal methods including drilling calibration,seismic facies analysis and low velocity anomaly detection. Strata sedimentarycharacteristics and evolution law of filling during Early-Middle Jurassic were studied systematically by field geological pro?file measurement and core description. Palaeo-sedimentary system of the middle-lower Jurassic in the study area was re?covered combined with evolution relationship between Meso-Cenozoic basin and mountain. The research results show thatthe residual lower Jurassic distributed only in Hongshan sag of eastern Qaidama Basin with an area of about 640 km2;the re?sidual middle Jurassic distributed in six sags such as Hongshan-Xiaochaidan,Gaxi-Yuqia,Hobson and Delingha,and themiddle-lower Jurassic did not appear in Gaqiu,Dachaidan and Ounan areas. The depositional filling systems in Early Ju?rassic of eastern Qaidam Basin are characterized by alluvial fan,braided river,braided river delta,shallow lake and braidedriver delta,and their source came mainly from north Qilian mountain,secondarily from the south Chainan Uplift. The mid?dle Jurassic developed while Qaidam Basin depressed and its depositional systems changed as follows:fan delta,braidedriver delta and sub-lacustrine transgressive cycle.