松辽盆地南部乾安地区上白垩统青三段高分辨率层序地层及沉积特征*

综合利用岩心和测井资料,系统总结了松辽盆地南部乾安地区上白垩统青山口组三段高分辨率层序界面的识别标志,建立了高分辨率层序地层格架,对高分辨率层序地层格架内地层叠置特征进行了探讨,并进一步分析了层序地层格架内河道砂体展布特征及沉积相演化规律。识别出冲刷面、底部滞留沉积和滑塌沉积3种高分辨率层序界面识别标志,以及泥岩颜色转换和含油性变化2类辅助性证据,在此基础上将青三段划分为2个三级层序(SQ1,SQ2)、13个四级层序(HFSQ1-HFSQ13),层序内可进一步划分出湖侵体系域(LTST)和湖退体系域(LRST)。四级层序体系域内识别出单向加深A1型、单向加深A2型、单向变浅B型、复合对称C1型和复合对称C2型共5类四级层序结构;三级层序湖平面升降可划分为4个阶段,各阶段内四级层序组合模式各不相同。根据砂体连井对比和平面相分析成果,结合体系域阶段划分,在研究区青三段高分辨率层序地层格架内共总结出4类沉积模式。其中,湖退体系域早期沉积模式砂体分区叠置,河道平面呈分支树杈状。湖退体系域晚期沉积模式砂体规模最大,整体连片叠置,河道平面呈网络交织状,分流河道间湾在河道间呈零星点状分布。湖侵体系域早期沉积模式砂体规模较小,孤立分布,河道平面呈分支树杈状。湖侵体系域晚期沉积模式砂体规模最小,零星分布,河道平面呈曲流状—分支树杈状。

High-resolution sequence stratigraphy and sedimentary characteristics of the Member 3 of Qingshankou Formation of Upper Cretaceous in Qian'an area,south Songliao Basin

Integrated with core and logging data,the recognition marks of high resolution sequence stratigraphic boundary of the Member 3 of Qingshankou Formation of Upper Cretaceous in Qian'an area of south Songliao Basin is summarized systematically. The high￣resolution sequence is established. Moreover, the stacking pattern of the strata in the framework of high-resolution sequence stratigraphy is discussed and the characteristics of sand distribution and disciplines of sedimentary facies evolution in the sequence framework is analyzed. Several conclusions are made as follows. Three sequence boundaries and two supporting evidences have been recognized in the study area,such as erosion surface,stranded sediments at the bottom of the deposit,slump deposit, switched color of mudstone and differences in petroliferous. Then the Member 3 of Qingshankou Formation is divided into two 3^rd-order sequences(SQ1,SQ2)and thirteen 4^th-order sequences(HFSQ1-HFSQ13),and each of the sequence can be divided into lake transgressive system tract(LTST)and lake regressive system tract(LRST). Five types of the 4^th-order sequence structure have been recognized in the system tract. The process of lake level fluctuation can be divided into four stages,and the combination model of 4^th-order sequences in each stage is different. Based on the analysis of sand correlation in cross-section and facies distribution, according to the phase division of lake level fluctuation,four types of sedimentary model have been recognized in the framework of high-resolution sequence stratigraphy. Each model has its unique sand distribution feature in vertical direction and shape in horizontal direction.