Study On Gravity Field And Structural Features Of Wunite Depression In Erlian Basin

The Wunite Depression is located in the Xilinhaote and Dongwuzhumuqin Banner of Inner Mongolia Autonomous Region.It is located in the northern part of the Tengger Sag of the Erlian Basin in the tectonic position.The eastern part of the Sunite Uplift is connected to the Daxinganling Uplift in the west.It is a complex structure.A combination of small lake basins formed by the Mesozoic rift basin.The predecessors have had a certain degree of research work on the structural characteristics,tectonic evolution and faults of the basin and have achieved certain results,but the research is still weak and needs further study.In order to further study the structural characteristics of the Wunite depression,this paper uses the gravity and magnetic data of the area to collect and analyze the geological data of relevant earthquakes and wells,and to process and explain the magnetic data,and obtain different basic maps;The characteristics and causes of the magnetic field in the subsidence area are analyzed,and the local gravity and magnetic anomalies are interpreted.Combined with the previous research work,the characteristics of the magnetic field are systematically analyzed,the fault structure of the area is inferred,the geological significance of the fault is analyzed,and the fault is explained.The structural features,the structural units are divided,and the oil and gas geological features are combined to predict the oil and gas favorable areas.The main conclusions are as follows:(1)The Bougur gravity anomaly in the Wunite depression is generally north-north-eastward,with a north-south direction.The highest anomaly is located in the eastern part of the study area,which is about-55 mGal.The abnormal minimum value is in the middle of the study area.The main part of the trap is approximately-99 mGal.The transition parts with low gravity and high gravity have relatively dense step bands.According to the anomalous characteristics and combined with the existing data,it can be inferred that the research area is a “deep and concave phase” pattern.The residual gravity anomaly in the study area is similar to the Bougur gravity anomaly,and the local anomaly characteristics are more obvious.The high gravity in the study area is caused by the bulge of the front Jurassic basement,and the low gravity is mainly caused by the thicker sedimentary caprocks of the Cenozoic,Jurassic and Cretaceous.The local magnetic anomaly developed in the study area,with the highest anomalous value in the southwest,mainly caused by the Erlian-Hegenshan melange belt.(2)The fault is developed in the Wunite depression,and the fault direction is mainly north-north and north-north-east,followed by east-west and near-east-west.The faults in the northeast trend generally extend long,the fault distance is large,the formation time is early,and the multi-phase tectonic activity is followed.From the stratigraphic distribution,tectonic line direction,and geomorphological features,it can be inferred that the NE-trending and NW-east faults are the main faults in the Unite depression,controlling the sedimentary development of each depression.The faults in the Unite depression are basically high-angle normal faults,and a large number of NE-trending fault depressions form a NE-trending fault zone in a series or parallel combination.(3)By fitting the results of four sections of the study area,it can be seen that there are multiple settlement centers in the Wunite depression,in which the central sag belt is located in the Malajieyinqige depression,the Aladabs depression,and the package.The thick thickness of the Mesozoic and Cenozoic caprocks in the Baoerguoji sag and the Buridun sag is between 2,500 and 3,500 m.The Mesozoic is generally developed with large differences in thickness and localized areas.The difference in the depth of the basement is large,which reflects the pattern of the study area.(4)The Wunite depression can be divided into four tectonic units: the western depression belt,the Sunite uplift belt,the central depression belt and the eastern uplift belt.The central depression zone is the main part of the study area.According to its fault development and stratigraphic distribution,it can be subdivided into 8 sub-structural units.From north to south,it is: Malajielyinqige depression,northern bulge,Aladabus sag,Baoerguoji depression,central bulge,Buridun depression,southern bulge and southern depression.Each sag in the study area basically has a good combination of reservoirs and reservoirs.It is located on the east and south sides of the rupture of the Malagay,and the east side of the Baoerguoji sag.The west side of the Buridun sag and the north side of the southern sag should be further favorable areas for oil and gas exploration.