Control of Multi-generation Rotary Normal Faults on Sediment Migration in Rift Basin: An Example from the Early and Middle Jurassic Qaidam Basin

Based on the coupling relations between basins and mountains, interpretation of seismic sections and sedimentary characteristics of basins, the Early Jurassic Qaidam Basin is confirmed as a haft-graben fault basin with characters of "faulting in the south and overlapping in the north", while the Middle Jurassic Qaidam Basin as a haft-graben fault basin with the characters of "faulting in the north and overlapping in the south". Normal faults at the northern margin of the Kunlun Mountains, together with the left-lateral strike-slip Altun Tagh fracture and right-lateral strike-slip Elashan fracture, respectively, controlled the formation of Early Jurassic haft-graben fault basins in the western and eastern Qaidam Basin. Along with the uplift of the Kunlun Mountains expanding toward the north, north-inclined high-angle normal fault planes gradually rotated and rose, which resulted in a tectonic denudation and disappearance of Early Jurassic strata in the southern Qaidam Basin and relics of Early Jurassic strata are remained only in the Lenghu structural and Eboliang structural belts and other belts in the southern Qaidam Basin. Fish-scale-like structures formed at the contact surface between lower Jurassic and basement might result from mutual incision of multi-generation rotary normal faults in turn because of asymmetrical uplift of crust. Uplift in the southwestern Qaidam Basin led to the migration of Middle Jurassic strata to the north and west, and resulted in the formation of inverted haft-graben fault basin. Therefore, the dip of normal faults controlling the Early Jurassic haft-graben fault basins was contrary to that of the Middle Jurassic haft-graben fault basins, and there was a sedimentary migration from the Early Jurassic to Middle Jurassic. It recorded a geological process that the crust of the northern Qinghai—Tibetan Plateau changed from horizontal extension to vertical uplift.