Electrical Structure Characteristics of the Dunhuang Basin in the Northeastern Margin of the Tibetan Plateau and Implications for Hydrocarbon Exploration

The overall degree of fundamental petroleum geological work in the western Dunhuang Basin is relatively low compared with the eastern part. Since the discovery of source rocks in the Lower-Middle Jurassic (J_1-2) with favorable hydrocarbon shows in the Wudun Sag by Wells Xican-1 and Dun-1, the hydrocarbon accumulation conditions and exploration prospects of the coeval sags in the western basin have also received increasing attention. To investigate the distribution characteristics of the Jurassic and the main tectonic framework in the Qingtai Sag and its adjacent areas, a 100 km-long Continuous Electromagnetic Profiling (CEMP) profile was acquired, yielding an electrical structure model within the upper 5 km beneath the western Dunhuang Basin. Comprehensive interpretation integrated with regional gravity and magnetic data indicates that the study area as a whole exhibits a tectonic framework of “two depressions, one uplift and one slope”, which, from south to north, are the Aksay Depression, Sanweishan Uplift, Andun Depression, and Yumenguan Slope. A total of seven faults were identified along the profile: F₁ and F₂ are the southern and northern boundary faults of the Sanweishan Uplift, respectively; F₃ is the Maotoushan Fault; F₄ is the Ruoqiang - Hongliuyuan Fault; F₆ is the North Altun Fault; and F₇ and F₈ are inferred faults. The Qingtai Sag is characterized by a half-graben geometry with a faulted northern margin and an onlapping southern margin. The Jurassic exhibits distinct low-resistivity electrical characteristics, with a thickness of approximately 1 500~2 000 m and a northward-shifted depocenter; the Proterozoic crystalline basement occurs at a burial depth of approximately 2 500~3 500 m. This study provides a reliable geophysical basis for hydrocarbon resource evaluation and future exploration deployment in the western Dunhuang Basin. The northern depocenter of the Qingtai Sag and the local structures controlled by the F₇ fault are identified as priority exploration targets for future hydrocarbon exploration.