柴达木盆地北缘中生代盆地性质研究——对大柴旦凹陷的解剖

Characteristics of Mesozoic Basin of the Northern Qaidam:A Case Study on Dachaidan Depression

柴达木盆地北部地区的中生代地层是柴达木盆地油气勘探的重点层系之一。利用地震剖面解释成果和野外地质资料绘制了侏罗纪与白垩纪的地层残余分布图和断裂分布图;利用平衡剖面对地震剖面进行了平衡恢复,恢复了侏罗纪与白垩纪的原始与剥蚀后形态。通过对中生代各期(主要是侏罗纪和白垩纪)残余地层、断裂的分布和地震剖面构造演化的综合分析,认为柴达木盆地北部地区中生代经历了三个不同性质的盆地演化阶段:早侏罗世为伸展环境下的(箕状)断陷盆地,主要表现为一系列小型断陷盆地群;中侏罗世—早白垩世为伸展型坳陷盆地;晚白垩世末盆地受挤压整体隆升,形成古隆起。

The Mesozoic strata are the key of hydrocarbon target in the northern Qaidam Basin.Combined the seismic data and geologic field materials,the residual distribution maps of Jurassic and Cretaceous strata and the fault system maps were generated. Meanwhile,the cross sections before and after erosion in Jurassic and Cretaceous times were revealed by cross section restoration.Based on the synthetic analyses of Jurassic and Cretaceous residual strata distribution,faults systems and cross-section evolution,we proposed that the northern Qaidam Basin experienced three phases of basinal evolution during the Mesozoic：A series of small faulted-basins developed in the Early Jurassic northern Qaidam in an extensional environment;Afterwards,these small faultbounded basins were covered by a larger depression basin in the Middle Jurassic to Early Cretaceous;During the Late Cretaceous,the northern Qaidam basin was reversed and wholly uplifted,resulting in formation of palaeo-uplifts.