Identification of a Permian foreland basin in the western Junggar Basin (NW China) and its impact on hydrocarbon accumulation

Abstract The piedmont depression in the western Junggar Basin is a typical large-scale thrust belt rich in hydrocarbons, but there is still a debate whether its structural properties relate to a foreland basin. This controversy hinders the understanding of regional hydrocarbon plays, giving rise to this study. As a conclusion, we discovered that - it was a foreland basin in the Permian that accounted for the structural properties of the piedmont depression. The basin was generated by continuous thrusting of the Western Junggar Orogenic Belt against the Junggar–Tuha Plate. This occurred after the formation of the Western Junggar Orogenic Belt in the Carboniferous. The western basin in this study can be divided into five different zones moving from the Western Junggar Orogenic Belt to the internal plate, which are: the foreland thrust belt (the Ke–Bai and Wu–Xia thrust belts), the foreland depression (the western part of the Mahu Sag), the foreland slope (the eastern part of the Mahu Sag), the forebulge (the Dabasong Uplift), and the back-bulge basin (the Western Pen 1 Well Sag). Based on the characteristics of geological structure, and the sedimentary strata of the western Junggar Basin, the evolution of the basin was split into two distinctive stages: the Permian development stage and the Mesozoic–Cenozoic burial stage. Throughout the entire process three suites of hydrocarbon source rocks were developed, regional seal rocks, and four types of trap and reservoir assemblages. The western Junggar Basin should be considered as a typical petroliferous foreland basin.