鄂尔多斯盆地西缘石沟驿向斜几何学与运动学特征

Characteristics of Geometry and Kinematics of Shigouyi Syncline at West Edge of Ordos Basin

根据高精度的地震资料及钻井数据,以断层相关褶皱为理论依据,对石沟驿向斜进行精细构造解释,进而揭示其几何学和运动学特征,对探究西缘构造变形及形成机制具有重要意义。研究认为:石沟驿向斜东陡西缓,主体呈北北东向构造,具有断距大、发育晚、演化复杂等特征,石炭系以上地层构造相对不发育,但其下部构造复杂,断裂发育,两侧受边界断层控制,东侧沙井子断层为早石炭世正断层,在其上盘沉积下石炭统臭牛沟组,晚三叠世受区域构造运动影响变为上陡下缓的逆断层,这一反转构造使断距差异明显。后缘奥陶系米钵山组粉砂质板岩受区域构造应力的影响,由西向东推覆变形,以石炭系煤层及寒武系泥页岩为顶底界滑脱形成构造楔楔入,导致西翼抬升,且抬升高度与下伏构造楔楔入高度相一致,因此,石沟驿向斜的形成以多期构造相叠加且不断改造最终定型为特征。

According to the theory of fault-related fold,we interpret the structure of Shigouyi syncline in detail and verify its characteristics of geometry and kinematics through seismic and well data with high preci-sion.It has very important meaning to understand tectonic deformation and formation mechanism of west edge of Ordos Basin.Research suggests that Shigouyi syncline is steep in the east of and gentle in the west.It is a NNE direction structure and has the characteristics of large fault throw,late development and complicated evolution.The structure of the reservoirs above Carboniferous is relatively undeveloped,but its lower structure is very complex because of highly developed faults.Both sides of it are controlled by boundary faults.The east Shajingzi fault is a normal one formed in early Carboniferous stage.At that time,Chouniugou Formation of lower Carboniferous deposited on its hanging wall.In late Triassic,it converted into a thrust fault that was upper steep and lower gentle influenced by regional tectonic movement.This inversion structure made significant difference on the fault throw.The silty slate of Miboshan Formation of Ordovician influenced by regional tec-tonic stress in the back is napped from west to east and then formed tectonic wedge by detachment as the top coal of Carboniferous and the bottom argillutite of Cambrian.And then the west wing is lifted,and the uplift amplitude of it is as same as the height of tectonic wedge.Therefore,the formation of Shigouyi syncline is characterized as multiple tectonic movements superimposed and stereotyped finally through continuous re-forming.