渤海湾盆地渤东凹陷次级洼陷差异演化特征

Differential evolution characteristics of secondary depressions in the Bodong Sag,Bohai Bay Basin

以渤海湾盆地渤东凹陷三维地震精细解释为基础,利用构造剖面复原等方法,探讨次级洼陷结构特征与控洼断裂差异演化过程。研究认为,渤东凹陷共发育6个次级洼陷,凹陷结构由北到南表现为单断半地堑区、半地堑—地堑过渡区、不对称双断地堑区的差异变形规律。渤东凹陷发育3类(伸展、走滑、叠合)、3组(NNE向、NE向、NW向)断裂,NNE—NE向伸展断裂为主干控洼断裂,NW向伸展断裂规模小,切割洼陷,走滑断裂早期局部表现为控沉积的伸展性质,晚期强烈走滑改造地层展布格局。受控洼断裂的差异演化控制,古近纪次级洼陷演化过程可以分为4个阶段:沙四段—孔店组沉积期为初始断陷阶段,NE向伸展断裂为主控,NW向断裂切割洼陷,呈“南北分区”特征,沉积中心位于东北部;沙三段沉积期为强烈断陷阶段,NNE向伸展断裂变为主控,NW向断裂减弱;沙一段—沙二段沉积期为热沉降阶段,NNE向伸展断裂仍为主控;东三段沉积期为断陷强化期,NNE向主控断裂剧烈活动,呈“东西分带”特征,沉积中心已经迁移至西南部。

Based on the 3D seismic interpretation of Bodong Sag,Bohai Bay Basin the structural characteristics of secondary depressions and the differential evolution of depression-controlled faults are discussed by using the methods of structural section restoration.The study shows that there are six sub-depressions in the Bodong Sag,and the sag structure from north to south shows the differential deformation law of single fault and half graben area,half graben-graben transition area and asymmetric double fault graben area.There are three types(extensional,strike-slip and superimposed)and three groups(NNE,NE and NW-trending)faults in Bodong Sag.The NNE-NE extensional faults are mainly dry-controlled depression faults,while the NW-trending extensional faults are small in scale and cut into depressions.In the early stage of strike-slip faults,the extensional nature of controlled deposition is localized,and the distribution pattern of strike-slip reformed strata is strong in the late stage.The evolution process of paleogene sub-depressions can be divided into four stages:the sedimentary period of the 4;Member of Shahejie Formation-Kongdian Formation is the initial fault depression stage,the NE extending fault is the main control,and the NW fault cuts the depression,showing the characteristics of“north and south zone”,and the depositional center is located in the northeast.The sedimentary period of the third Member of Shahejie Formation was a stage of strong fault depression.The NNE extensional fault became the main control and the NW fault weakened.The sedimentary stage of the 1;and 2;Members of Shahejie Formation is thermal subsidence stage,and the NNE extension fault is still the main control.The sedimentary period of the third Member of Dongying Formation is the strengthening period of fault depression,and the NNE main control faults are actively active,showing the characteristics of“east-west zonation”,and the depositional center has moved to the southwest.