Cretaceous Tugulu group bottom sediments and unconformity characteristics of Chepaizi uplift,Junggar basin

Situated in the northwestern margin of the Junggar basin,Chepaizi uplift is an important secondary tectonic unit.Tectonic movement of Cretaceous sediments was mainly controlled by late Jurassic Yanshan Ⅱ curtain.By analyzing sedimentary characteristics of Tugulu group bottom,combined with geophysical,coring and logging data,the studies believe Cretaceous Tugulu group overlapping(angular unconformity)is deposited on top of bedrock under the Carboniferous system,with low angle unconformity surface,developed alluvial fan-fan delta-lacustrine depositional system and big residual thickness variance.The sediments are mainly of black-gray,green-gray breccias and boulder-clay.The gravel is mainly composed of igneous breccias.According to the datum(lake level)is located below the surface of the basin slope break period,residual alluvial fan roots fan channel fill,it can be classified as low-level alluvial fan depositional model.