Thrust and fold tectonics and the role of evaporites in deformation in the Western Kuqa Foreland of Tarim Basin, Northwest China

The Kuqa foreland between the Tarim basin and the Tianshan Mountains is rich in oil and gas. Based on field work and seismic profiles, the structural styles and their formation mechanisms were determined, and the role of evaporites in the deformation was demonstrated. The main structural styles in the overburden are detachment folds, large scale nappes, triangle zones, gentle and wide synclines, fault-propagation folds and pop-ups. The main structures in the substrate are small-scale thrust faults, duplexes, pop-ups and fault-bend and fault-propagation folds, and formed mainly at the end of the Pliocene under north-south compression. The evaporite layer in the lower section of the Paleogene is the decollement zone for the disharmonic deformations in the overburden and in the substrate. The detachment along the evaporite layer made it possible for compressive stresses to be transmitted farther in the overburden than in the substrate. Deformation in the overburden is more extensive than in the substrate at the leading edge of deformation. At the trailing edge of deformation, the structural highs in the overburden closely correspond to those in the substrate, which is of significance for petroleum exploration in the western Kuqa foreland.