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

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.