东营凹陷沙河街组三段—二段下亚段沉积层序及成因

根据地震、岩性及电性等特征,东营凹陷沙河街组三段—二段下亚段可划分为 3个三级层序。底部层序(SSⅠ)相当于沙河街组三段下亚段,低位体系域不发育,只发育湖侵体系域和高水位体系域,受早期构造沉降和气候控制。中部层序(SSⅡ)代表的是沙河街组三段中亚段沉积,与底部层序具有类似特征。SSⅠ,SSⅡ均为T-R旋回的沉积。顶部层序(SSⅢ)代表沙河街组三段上亚段-二段下亚段沉积,发育低水位体系域、水侵体系域和高水位体系域,是一完整的旋回。SSⅢ是在构造活动相对较弱,气候相对干旱、水体供应不足的条件下形成的。

ORIGIN AND SEDIMENTARY SEQUENCE OF Es3-Es2 IN SHAHEJIE FORMATION OF DONGYING DEPRESSION

Member Ⅲ-lower submember of Member Ⅱ in Shahejie Formation of Dongying Depression can be divided into Ⅲ third-order sequences on the basis of seismic data,lithology and electric characteristics etc.The bottom of sequence(SSI) corresponds to the lower submember of Member Ⅲ of Shahejie Formation,characterized by lowstand system tracts undeveloped,only lacustrine transgression system tracts and highstand system tracts developed,all of theses are controlled by the early tectonic subsidence and climate.Middle sequence(SSⅡ) represents the mid-submember sedimentation of Member Ⅲ in Shahejie Formation and has similar nature of the bottom sequence.SSI and SSⅡ are all T-R cyclic sedimentation.Top sequence(SSⅢ) representing sedimentation of the upper submember of Member Ⅲ-lower submember of Member Ⅱ in Shahejie Formation(forming Lowstand system tracts,water transgression system tracts and highstand system tracts) is a complete cycle.SSⅡ was formed under the conditions of tectonic activity relatively weak,climate relatively dry and water supply insufficiently.