Salt tectonic evolution and hydrocarbon accumulation of Kuqa foreland fold belt, Tarim Basin, NW China

Abstract Thick salt beds in the Lower Tertiary were developed in the Kuqa foreland fold belt of the northern Tarim Basin. The salt beds controlled the structural deformation and hydrocarbon accumulation of the belts. Because of the salt beds, the Meso-Cenozoic structures of the Kuqa foreland fold belts can be divided into three major tectono-sequences: suprasalt structures, salt bed structures and subsalt structures. Suprasalt structures include thrusts and fault-related folds. Salt bed structures are dominated by salt pillows, allochthonous salt sheets, salt welds and fish-tail structures. Subsalt structures mainly include imbricated thrust belts, duplex structures, fault-related folds and pop-up structures. Formation of the salt structures in the Kuqa foreland fold belts is controlled by compression, gravitational gliding and gravitational spreading. The basin-mountain coupling and compression resulted in intense shortening of the fold belt. The rising of the South Tianshan Mountains caused the gravity gliding and gravity spreading. Plastic flow deformation of the salt beds resulted in salt thickening from the mountain front to the south of the fold belt. The thick salt bed accumulated in the Klasu and Qiulitag structural belts, and controlled the distribution of the salt-related structural traps and oil–gas pools. The structural traps have a bearing upon salt beds in the Kuqa foreland fold belts. The source rocks are mainly located below the salt beds, which can act as excellent cap rocks and seal the gas pools. The subsalt beds are the favorable places for hydrocarbons to accumulate.