The Yanshanian Structural Characteristics And Their Control On The Basin In Huanghua Depression

Huanghua depression is the Mesozoic and Cenozoic superimposed basin based on North China Craton,its pre-tertiary oil reservoir has become an important exploration fild.Yanshan Era is the important revolutionary period in the eastern part of north China,its tectonic development not only determines the stratigraphic distribution and sedimentary pattern of Yanshan Era,but also controls the erosion and transformation of Paleozoic and Triassic strata,and has an important influence on the basin pattern of Cenozoic.By analysis of the geometry and kinematics of Yanshanian tectonic development features,reveals the ancient tectonic framework and basin development characterisics in Yanshan era.This is beneficial to provide guidance of oil and gas exploration of pre-tertiary oil reservoir in Huanghua depression.The Mesozoic of Huanghua basin can be divided into three structural sub-layer:lower-middle Triassic,lower-middle Jurassic and lower Cretaceous,missing upper Triassic,upper Jurassic and upper Cretaceous as a whole.The original stratum of lower-middle Triassic in Huanghua Depression are distributed all the basin,mainly extending in NWW direction,and the sedimentary thickness is over 1400m.The stratigraphic denudation is serious in the north and central of the basin,affected by tectonic movement in Indosinian-Yanshanian-Himalayan periods.Residual stratum are mainly distributed in the south,extending in NE and nearly EW direction,others are only distributed in Chenghai area and Jiannan sag in the north-central of the basin.The original stratum of lower-middle Jurassic are distributed in the south and middle part of the basin,extending in NE direction,nearly SN direction and EW direction,its maximum sedimentary thickness is in Xuhei area(about 1300m).After the tectonic movement resconstruction,the residual stratum are widely distributed in the south,with stratum missing in Qikou area,Beidagang area,Chadian area and other areas in the middle and north of the basin.The original stratum of the lower Cretaceous are thicker in the middle and north of the basin,distributed in NE direction and nearly EW direction.The maximum sedimentary thickness is more than 1,100m.Under the influence of late yanshanian compression and the fault tilting movement in Cenozoic,denudation is strong in the middle and north of the basin.The residual strata are mainly distributed in the north of Kongdian-Yanshan area.In present,the main faults developed in the Mesozoic of Huanghua depression are NNE(NE)trending faults and NWW trending faults,NNE(NE)trending faults are mainly tensile faults with strike-slip faults,NWW trending faults are mainly tensile faults and reverse faults.The main faults also can be divided into three types according to its activity types:die out early faults,sustainable active faults and advanced cutting faults.There are four tectonic styles developed in the Mesozoic of Huanghua depression such as compression,strike-slip,extension and inversion.Based on the study of residual stratigraphic characteristics,fault development characteristic and tectonic style in the Mesozoic,the Mesozoic of Huanghua depression can be divided into five tectonic zones by NWW trending faults(Haihe-Xingang fault,Yangerzhuang-yangsanmu fault)and SN-trending strike-slip zone(Qijiawu strike-slip fault and Yanan strike-slip fault).?area:NNE trending developed in this area,and the residual lower-middle Jurassic and lower Cretaceous are widely distributed in the east of it,there are developed single thrusting fault.?area:There are developed NNE(NE)and NWW trending faults in this area,also developed compressional structure style and extending structure style,such as extrusion duplex structure,thrust imbricate fan,thrusting triangle belt,warped fault block,“horst-graben”structure.The lower Cretaceous are widely distributed and the lower-middle Jurassic is partially residual.?area:NWW trending faults develop in this area,lower-middle Triassic,lower-middle Jurassic and lower Cretaceous is partially residual,there are developed compressional structure style and extending structure style,such as thrust imbricate fan,sliding fault terrace,“horst-graben”structure.?area:NNE(NE)trending faults are developed in this area,the lower-middle Triassic,lower-middle Jurassic are widely distributed and the lower Cretaceous is partially residual.there are developed compressional structure style and extending structure style,compressional structure style includes paleoanticline,thrusting imbricate fan and thrusting triangle belt,extending structure style is characterized by the combination of“horst-graben”.?area:NNE trending main faults,EW trending and NNE trending secondary faults were developed in here,lower-middle Triassic is widely distributed and the lower-middle Jurassic is partially residual.Compressional structure style includes thrust imbricate fan,extending structure style are developed.In addition,strike-slip structure are developed in?to?area,and negative inversion are developed in?to?area.According to the division of structure layer and the restoration of paleotectonic pattern,Yanshan Movement can be divided into three stages.In Early Yanshanian stage(J₁₊₂),the huanghua depression showed intermantane depression was subjected to regional multiway compression stress field,such as nearly SN and NW-SE compression.On the basis of inheriting the NWW structure pattern of the indosinian age,NNE(NE)trending faults were thrusting,such as Cangdong fault,Xuxi fault,and so on.Cangxian uplift and other compressive fold began to develop,The basin showed intermontane depression,?higher in the north,lower in the south?.Under the controlling of NWW and NNE(NE)trending thrusting faults and folds,stratum are distributed in the south of Qikou paleoanticline and the east of northern basin,tending in NE,nearly SN,nearly EW direction,elsewhere the stratum are eroded.In Middle Yanshanian stage(J₃+K₁),the basin was in the regional extension and sinistral strike-slip stress field,which was manifested as a fault basin with tectonic pattern of?higher in the south and lower in the north?,at the early stage,the active thrust faults were mainly extensional,and Chadian fault and Dashentang fault were active.By the controlling of NNE(NE)and NWW trending extensional faults,the stratum are distributed in the north and middle part of the basin,trending in NE and EW direction.The stratum suffered erosion in the south of Kongdian-Yanbei.In Late Yanshanian(K₂),under the regional stress background of NW-SE compression,the basin was lifted as a whole and strata suffered from denudation..