渤海湾盆地惠民凹陷临商断层特征及其活动机制

Characteristics and Faulting Mechanism of Linshang Fault in the Huimin Sag,Bohai Bay Basin

临商断层为济阳坳陷惠民凹陷内部NE向展布的控洼断层之一,详细地分析这些断层的活动性对于深入了解古近系沙河街组沙三段开始沉积以来惠民凹陷的差异分化具有重要的意义。本文通过详细解剖临商断层的几何学特征,不同时期、位置的断层活动性,并结合新生代以来渤海湾盆地的构造演化,得出以下认识:①临商断层的雏形为一右旋走滑正断层。②断层的主枝由西往东活动速率逐渐增强,而分枝断层则表现为中间强、两侧弱。③时间上的差异性表现为古近系沙河街组沙三段沉积期—古近系沙河街组沙二段沉积期断层的活动性较强,在古近系沙河街组沙二段沉积期达到最高值,而后逐渐减弱,古近系东营组沉积期出现小规模的增强,新近系馆陶组沉积期断层活动性达到最低值,新近系明化镇组沉积期断层活动性开始增强。④空间上断层活动的差异主要是由于该断层走滑过程中形成的同向走滑断层的位置造成的,而时间上的差异性与渤海湾盆地新生代的构造演化具有较好的一致性。

Linshang fault is one of the NE-striking faults which controls the Huiming Sag in the Bohai Bay Basin. The writers tried to analyze the activity of these faults for understanding differentiation of the Huimin Sag after the depositing of the Member 3 of the Paleogene Shahejie Formation. By analyzing the fault geometry,activity of different stages and segments of the Linshang fault,and the related Cenozoic structural evolution of the Bohai Bay Basin,this paper gets some new conclusions as following：① The prototype of the Linshang fault is a dextral transtensional fault. ② The movement rates of the main segment gradually increases from west to east,and movement rates of the branch faults decrease from center to both sides. ③ The movement rates of the fault are stronger during the depositing of the Member 3 to Member 2 of the Paleogene Shahejie Formation,reaching to the maximum during the depositing of the Member 2 of the Paleogene Shahejie Formation,then gradually decreasing,increasing a little during depositing of the Paleogene Dongying Formation,reaching to the minimum during depositing of the Neogene Guantao Formation,and increasing during depositing of the Neogene Minghuazhen Formation. ④ The difference of the fault activity at the different segments were controlled by the location of strike-slip fault in the same direction which formed with the strike-slipping of the Linshang fault,and the differences at different stages of fautling are consistent with the Cenozoic structural evolution of the Bohai Bay Basin.