| The Jizhong depression is a secondary negative tectonic unit of Bohai Bay basin.For a long time,the formation and evolution of Jizhong depression and its influence on oil reservoir distribution has attracted wide attention of geologists.This paper takes the eastern part of Jizhong depression,including the 3D seismic coverage area of Raoyang sag and the northern part of Jizhong depression,as the object of study.By using 3D seismic and geological data,this paper analyzes the geometry and kinematics characteristics of fault system and the spatial pattern of structural styles in the Cenozoic basin.Combined with the seismic data,drilling data,core analyzes and microscopic slices,this paper aims to study the tectonic evolution of Cenozoic basins,and analyzes the relationship between structural deformation and spatial distribution patterns of the area.The main achievements of this paper are as follows.Three groups of main basement faults control the formation and development of Cenozoic basin.The NE-NNE-striking faults distribute in the whole area and control the Paleogene sedimentary distribution.The main northern faults are all SE-SSE-striking faults,and the fault activity gradually migrates from west to east in Paleogene,which causes the eastward migration of sedimentary center.On the contrary,the majority of the main southern faults are NW-NWW-striking faults,and the fault activity gradually migrates from east to west in Paleogene,which causes the westward migration of sedimentary center.The central Maxi faults belt gradually evolved from strike slip extensional deformation into strike slip deformation to adjust the north-south structural displacement.The tectonic styles of three sets of tectonic layers,E1-2k-E2s4?E2s3-E2s2 and E3s1-E3d are distribute differently,and the spatial patterns of the tectonic styles of the different tectonic layers are different.The E1-2k-E2s4 tectonic layer mainly develops"dustpan-like half graben" tectonic style and part of the area develops the "shovel-like half graben" tectonic style,and the positive flower structure style is developed in the central and north segment of Maxi fault.The E2s3-E2s2 tectonic layer mainly develops"shovel-like half graben" tectonic style in the most part of the area.The "multiple half graben" structural style controlled by shovel or slope faults is developed in Fengheying uplift,Niutuozhen uplift and Hejian buried hill and the positive flower structure style is developed in the central and north segment of Maxi fault.The E3s1-E3d tectonic layer mainly develops "shovel-like half graben" tectonic style.In the meantime,the strike slip flower structure style is developed in Maxi fault.Liuxi area of Raoyang sag develops"asymmetric graben" structural style,which controlled by conjugate major fault.The spatial patterns of the structural styles of the different tectonic layers are different,which can divide into three types:succession type(the boundary faults are syn-rift faults inheriting activity),utilization type(the boundary faults are unchanged but with different polarity activity)and rebirth type(the boundary faults change).The structural style of E2s3-E2s2 mainly superimposed on the E1-2k-E2s4 tectonic layer by succession type and utilization type.The E3s1-E3d tectonic layer superimpose on the E2s3-E2s2 tectonic layer by rebirth type.The combination manner of the main basement faults in E1-2k-E2s4 and E2s3-E2s2 tectonic layers and new secondary faults shows orthogonal rifting feature,reflecting the local extensional stress field in near NW-SE direction.The combination manner of the main basement faults in E3s1-E3d tectonic layers and new secondary faults shows the feature of oblique rifting,which reflects the direction local stress field in near SN direction.The characteristics of the basin rift reflect clockwise rotation of the local tectonic stress field.The metamorphic core develops in the footwall of the detachment fault in Cenozoic basins and the uplift of metamorphic core influences the basin evolution during the Paleogene.During the sedimentary of E1-2k-E2s4,Dachang,Daxing and Cangxi faults extended and developed series of NNE-NE direction half-grabens in the upper plate of the faults.During the end of E2s4,the metamorphic cores in Niutuozhen and Hejian area were uplift,resulted in the bending of fault planes and the erosion of upper Paleogene even middle Neoproterozoic layers.During the sedimentation of E2s3,Dachang,Daxing and Cangxi faults were in slope-plateau type and the multiple half-grabens developed on the upper plate of the faults.At the end of E2s3,Fengheying,Niutuozhen and Hejian metamorphic cores were still in uplifting,causing the detachment faults be further curved and uplifted.Influenced by the uplifting metamorphic cores,the bent upper section of the detachment fault gradually abandoned and ceased to extend.During E3s1-E3d,the secondary faults on the upper plate of the detachment fault either converged or cut the lower section of the original detachment fault and replaced the original detachment as the new boundary fault,and the development range of the basin began to shrink.Tectonic evolution influences the formation and distribution of oil and gas reservoirs.The tectonic activity controls the sedimentary environment,and then controls the stages,zones and zonation of the reservoir forming factors.Tectonic evolution controls the accumulation of hydrocarbon in oil and gas reservoirs.The structural oil reservoirs form in the fault steep slope belt and trough belt.The lithologic and stratigraphic oil reservoirs form in the slope belt and the structural-lithologic oil reservoirs form in transition region from trough to slope.The uplift of metamorphic core influences the formation and development of buried hill oil reservoirs.The early uplift of metamorphic core results in the upper strata to bend and deform,and then form the faulted anticline trap.Source rocks distribute in the troughs of the both wings of the metamorphic core,and the oil and gas are transported along the unconformity surface or oil source fault to the buried hill traps. |
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