Structural Characteristics And Evolution Of Daqing Placanticline In The Northern Songliao Basin

Songliao Basin is located in the Northeast of China,straddling the Heilongjiang,Jilin,Liaoning Province and Inner-Mongolia autonomous region.It is a large oil-gas-bearing sedimentary basin forming during Mesozoic-Cenozoic era.The basement of Songliao Basin is composed of Paleozoic and Precambrian metamorphic rocks.The Daqing placanticline has been highly concerned for a long time because of its abundant oil-gas resources,and It belongs to the second-order structural unit in the central depression,which is a first-order structural unit of the Songliao Basin.On the basis of summarizing the predecessors' information and the detailed geological interpretation of 2D and 3D seismic profiles,based on the latest research results of basin tectonics,growth fault-related fold theory and balanced section techniques,the paper analyses the Daqing placanticline's main structural styles,the different structural assemblage characteristics and its constrains on the sedimentary fillings.The study indicates that the Daqing placanticline is a large compressional anticline forming during Mesozoic-Cenozoic era,with the characteristics that the west wing is steep and the east wing is slow.It is composed of shallow and deep part of structure.The shallow part of structure includes thrust fault and compression-reversion anticline structure associated with contraction setting,normal fault and graben-horst associated with extensional setting,and palm tree structure associated with strike-slipsetting.The deep part of structure includes half-graben controlled by listric normal fault,domino normal fault and rollover anticline developed in the hanging wall of half-graben associated with extensional setting.The deformation of the Daqing Placanticline is always accompanied by sedimentation,in the meantime tectonic activities control the stratigraphic sequence and sedimentary fillings.The growth strata contain Nenjiang-Mingshui Formation in the Northern Daqing Placanticline,Member4 of Nenjiang Formation-Mingshui Formation in the middle of Daqing Placanticline and Member 5 of Nenjiang Formation-Mingshui Formation in southern Daqing Placanticline.Based on seismic interpretations,(1)the thickness of growth strata gradually increases from high position to low position of structure and have characteristic wedge shaped sedimentation;(2)the dip angle of growth strata of the anticline gradually decreases from the old to the new and some of the strata are gradually onlaped the higher parts of the anticline.On the basis of analyzing structural features,Timing and processes of structural deformation,the stage of nearly NWW-SEE compression in Songliao Basin begun from the deposition of the Nenjiang Formation to the deposition of the Mingshui Formation,leading to form the Daqing Placanticline.The different part of anticline of Daqing Placanticline have different forming mechanism,timings,heights and uplift rates.Daqing placanticline has experienced three structural evolution stages:(1)the continuously uplifting stage of Daqing Placanticline during the depositional period of the Upper Cretaceous Nenjiang Formation;(2)the continuously uplifting stage of Daqing Placanticline,with the transference stage of high position of structure in the north and middle part during the depositional period of Sifangtai Formation;(3)the continuously to the feeble uplifting stage of Daqing Placanticline during the depositional period of Mingshui Formation.