Further Researches on the Tectonic Evolution and Dynamic Setting of the Junggar Basin

There still exist some different opinions concerning the evolution of Junggar basin, an important oil-bearing basin in wes-tern China. An analysis of geophysical data shows that geological structures of Junggar basin in plane and in profile have the foreland basin features. Based on the dynamic setting, the authors utilized the foreland basin systems and pressure-flexure action to divide the evolution of the Junggar basin into five stages: ① collision-basin-forming stage; ② pressure-flexure stage; ③ flexure-depression stage; ④ depression-sedimentation stage and ⑤ foreland basin regeneration stage. From Carboniferous to Permian, the ocean troughs around Junggar massif were closed early or late and continent-continent collision took place. At first, the northeastern part was formed during the late period of Early Carboniferous. Then Kelameili orogenic belt was developed in the northwest during middle and late periods of Late Carboniferous. Finally, the southern part was formed during the late period of Early Permian. With the uplift of marginal mountains, three foreland basin systems were formed in Juggar basin. From Triassic to Palaeogene, the plate squeezing action weakened and Junggar basin gradually entered a depression-subsidence phase from the intense compressive phase. From Neogene to Quaternary, North Tianshan Mountains were uplifted quickly and extensively under the influence of Himalayan movement. The southern part subsided again and formed the regenerated foreland basin from west to east. As a result of such a complex evolution, Junggar basin developed more than one sets of source-reservior-caprock assemblages and multiple periods of hydrocarbon accumulation, which provided favorable conditions for oil and gas accumulation.