Sequence stratigraphic division and spatio-temporal evolution of the Permian strata in the Wuxia foreland thrust zone in the Junggar Basin

The Wuxia foreland thrust zone on the northwestern margin of the Junggar Basin is characterized by complicated tectonics, severe stratigraphic deformation and modification, incomplete and variable sedimentary systems, and frequent rising and lowering of sea-levels or lake levels, and has recorded the evolution from foreland basin through intracontinental depression to tectonic uplift since the late Hercynian orogeny. The Early Permian strata in the study area primarily consist of volcanic-volcaniclastic rocks and normal clastic rocks. The alluvial fan facies, fan delta facies and lacustrine facies were accentuated during the Middle and Late Permian. The Jiamuhe Formation is made up of the mixed volcanic rocks, volcaniclastic rocks and clastic rocks, which are assigned to the Smith strata with cyclicity. The regional structural unconformity is believed to be the major factor controlling the development of the Permian sequences and sedimentary characteristics. The Permian strata are classified into four second-order sequences and twelve third-order sequences. The model for the spatio-temporal evolution has been constructed for the Permian strata in the Wuxia foreland thrust zone in the Junggar Basin.