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The superimposed basin must have undergone the changes of regional stress field. Study on the nature and switch of regional stress field of superimposed basin is very useful to understanding its stress state and tectonic events during its formation and evolution. As sensitive markers of small stress changes, joint and shear fracture, characterized by consistency of ori-entation over wide area, can be used to reconstruct paleostress state and its evolution. Detailed observations and analysis on the orientations, geometrical patterns, sequences of joints and shear fractures and their chronological relation to faults and folds show that, the NEE-SWW systematic joints and NNW-SSE systematic joints developed in the Mesozoic and Cenozoic strata are much more prominent than NW-SE systematic joints and shear fractures with different orientations. And the NWW-SEE and NW-SE systematic joints formed later than NEE-SWW systematic joints but earlier than shear fractures with different orientations. According to the rela-tionships between joint and shear fractures and stress, the NEE-SWW systematic joints are in-ferred to result from lateral weak extension caused by the late Cretaceous regional uplift, while the NNW-SSE and NW-SE systematic joints are interpreted as syn-tectonic deformation relating to strong N-S compression in the Neogene. But some conjugate shear fractures occur probably due to sinistral strike-slip faulting in the Kuqa depression. At the beginning of the Neogene, the stress field changed and the maximal principal stress s1 switched from vertical to horizontal.
The superimposed basin must have undergone the changes of regional stress field. Study on the nature and switch of regional stress field of superimposed basin is very useful to understand its stress state and tectonic events during its formation and evolution. Detailed observations and analysis on the orientations, geometrical patterns, sequences of joints and shear fractures and their chronological relation to faults and folds show that, the NEE-SWW systematic joints and NNW-SSE systematic joints developed in Mesozoic and Cenozoic strata are much more prominent than NW-SE systematic joints and shear fractures with different orientations. And the NWW-SEE and NW- SE systematic joints formed later than NEE-SWW systematic joints but earlier than shear fractures with different orientations. According to the rela-tionships between joint and shear fractures and stress, the NEE-SWW systematic joints are in-ferred to result from lateral weak extension caused by the late Cretaceous regional uplift, while the NNW-SSE and NW-SE interpreted as syn-tectonic deformation relating to strong NS compression in the Neogene. But some conjugate shear fractures occur probably due to sinistral strike-slip faulting in the Kuoqa depression. At the beginning of the Neogene, the stress field changed and the maximal principal stress s1 switched from vertical to horizontal.