孙吴—嘉荫盆地沾河断陷构造变形及其对沉积作用的制约

Structural Deformation of Zhanhe Fault Depression and Its Constrains on Sedimentation in Sunwu-Jiayin Basin,NE China

为了揭示孙吴—嘉荫盆地的构造特征、构造变形及其对沉积作用的制约,本文对沾河断陷的地震剖面进行了精细地质解释和相应的研究工作。沾河断陷为孙吴—嘉荫盆地的一个一级构造单元,自白垩纪开始主要经历了2个构造变形阶段:下白垩统宁远村组—淘淇河组上段下部沉积时期为NW—SE向伸展作用阶段,形成NE向大型犁式正断层及由其控制的箕状断陷,盆地连续接受沉积,断陷的沉降中心始终位于控陷正断层上盘靠近断层的部位,断陷盆地的规模与沉积范围随着控陷断层规模和断距的增大逐渐扩展,盆地具有裂谷盆地的性质;下白垩统淘淇河组上段上部—新近系孙吴组沉积时期为NW—SE向挤压作用阶段,形成反转构造、断层传播褶皱和走滑构造。在反转作用过程中,早期伸展断陷受到强烈改造,不仅在断层上盘靠近断层的部位形成大型反转背斜,而且使远离控陷断层的断陷缓坡带发生旋转式隆升,盆地的沉降中心迁移到盆地中间部位;随着反转背斜的隆升速率逐渐大于断陷缓坡带的隆升速率,盆地的沉降中心也逐渐向盆地的NW侧迁移,盆地绝大部分区域的沉降速率、沉积速率始终大于隆升速率,地层是连续沉积的,不存在沉积间断。仅在永安村组—鱼亮子组沉积时期,反转背斜带较高部位的隆升速率大于沉积速率,形成一系列超覆不整合,使永安村组、太平林场组和鱼亮子组的部分地层在构造高部位缺失。孙吴—嘉荫盆地在NW—SE向挤压作用阶段处于活动大陆边缘的陆内区域,盆地性质应属于陆内挤压坳陷盆地。孙吴—嘉荫盆地与松辽盆地在构造演化方面存在差异,晚期NW—SE向挤压作用的强度较弱,与挤压作用相伴沉积的生长地层的厚度远小于松辽盆地的坳陷层。与松辽盆地相似,孙吴—嘉荫盆地规模较大的断陷中白垩系—新近系为一套连续沉积建造。

The Sunwu-Jiayin basin is a Mesozoic-Cenozoic continental basin which superimposed on the Late Paleozoic orogenic belt between the North China plate and the Siberian plate.In order to reveal the structural characteristics,structural deformation and its constrains on sedimentation in Sunwu-Jiayin basin,this paper has carried out detailed geological interpretation and corresponding research on the seismic profile of Zhanhe fault depression.The Zhanhe fault depression is a first-order structural unit in the Sunwu-Jiayin basin.It has experienced two tectonic deformation stages since the Cretaceous:1)The NW-SE trending extension occurred during the depositional period of Ningyuancun Formation to the lower strata of the upper member of the Taoqihe Formation of the Lower Cretaceous,forming a large NE-trending listric normal fault and the half-graben.The basin received sediment continuously,and the subsidence center of the fault depression was always located near the fault on the hanging wall of the depression-controlling normal fault.The scale and depositional range of the basin gradually expands with the increase of the scale and offset of the depression-controlling faults,and the basin has the properties of a rift basin.2)The NW-SE trending compression occurred during the depositional period of the upper strata of the upper member of the Taoqihe Formation of the Lower Cretaceous to Sunwu Formation of Neogene,forming inversion structures,fault-propagation folds and strike-slip structures.The early extensional fault depression was strongly reformed during the inversion process,which not only formed a large-scale inversion anticline near the fault on the hanging wall of the depression-controlling fault,but also caused a rotary uplift of the half-graben gentle slope zone far from the depression-controlling fault.The subsidence center migrated to the middle of the basin.As the uplift rate of the inversion anticline was gradually greater than the uplift rate of the half-graben gentle slope belt,the subsidence center of the basin also gradually migrated to the NW side of the basin.The subsidence rate and deposition rate in most areas of the basin are always higher than the uplift rate.The strata are deposited continuously without depositional discontinuity.The uplift rate of the higher part of the inversion anticline was greater than the deposition rate during the depositional period of Yongancun Formation to Yuliangzi Formation,and a series of overlying unconformities were formed,which made some strata of the Yongancun Formation,Taipinglinchang Formation and Yuliangzi Formation missing at the structural high.The Sunwu-Jiayin basin was located in the intracontinental area of the active continental margin during the NW-SE compression stage,and the properties of the basin should belong to the intracontinental compression-depression basin.There are differences in the tectonic evolution between the Sun Wu-Jiayin basin and the Songliao basin.The intensity of the late NW-SE trending compression is weaker,and the thickness of the growth strata deposited with the compression is much smaller than that of the depression strata in the Songliao basin.Similar to the Songliao basin,the Cretaceous-Neogene in the large-scale fault depression of the Sunwu-Jiayin basin is a set of continuous sedimentary formations.