Sequence strata and coal accumulation of lower and middle Jurassic formation from southern margin of Junggar Basin,Sinkiang,China

The middle and lower Jurassic in southern margin area of Junggar basin was divided into 5 sequences based on analyses of exploration lines,well,logging curve,paleontology,field outcrop profiles and seismic reflective.Lowstand,lacustrine transgressive and highstand systems tracts were subdivided by the stacking patterns of stratigraphy,changes of lithology and lithofacies.The sequence stratigraphic correlation in well-tie sections made it possible to construct the regional stratigraphic framework.Fan delta,delta,lacustrine and peat swamp sedimentary system facies were identified by fully applying the drilling,logging,palaeontology and field outcrop profiles data.The architecture,evolution,distribution of sedimentary faces of the middle and lower Jurassic in southern margin area of Junggar Basin was analyzed.The coal-accumulation features in sequence stratigraphic framework was clarified.Coal bed vertical distribution was controlled by the sequence architecture pattern.Coal bed is developed in the early lowstand systems tract and in the late highstand systems tract,and coal bed transverse distribution is controlled by the sedimentary environment.