Abstract：Taking the features of seismic reflection as a basis and combining with regional geologic characteristic,the Weizhou-Shigouyi detachment structure that was formed by basement detachment of western Ordos massif from south to north is determined in the paper.On the seismic section it shows multi-layers' parallel reflections above detachment interface,and the chaotic seismic reflection resulted from complex deformation in frontal overthrust nappe has failed to appear,on the plane,the detachment structure formed clear structural discordance with neighboring areas;it came into being after detachment from south to north along coal measure strata nearby T9 interface under the gravity action,under such structural background that,the large scale of overthrust nappe of late Jurassic west massif in east-west direction formed the south part being higher and the north part being lower,its east,west and north boundary connected with neighboring by faults.The structure is composite syncline consisted of exotic sheet and structural deformation is relatively simple.In strongly structore-deformed area of western Ordos massif,the detachment from south to north under the gravity action formed simply structure-deformed and integrite Shigouyi composite syncline overlying on the autochthonous sheets,which has importance to the study of structural history and the arrangement of oil-gas exploration in that area.
