孤北洼陷沙三、四段沉积体系分析

孤北洼陷沙三、四段主要发育七种碎屑岩沉积体系，以冲积扇、扇三角洲和湖底扇为主。沉积体系的分布与沙河街组沉积时期的古构造关系密切，陡坡断阶带控制了沉积体系的展布方向；延伸至洼陷带的次级同生断裂，不仅对扇三角洲和湖底扇相带起分隔作用，还控制了扇体的形态和发育厚度。以此作指导，在陡坡带、洼陷带及低隆起带预测了有利的岩性圈闭。

Analysis on sedimentary system in Es3 and Es4 of Gubei subsag

Seven kinds of clastic sedimentary systems are developed in Es 3 and Es 4 of Gubei subsag, which are dominated by alluvial fan, fan delta and sublacustrine fan. The distribution of these sedimentary systems have close relationship with the palaeostructure in Shahejie period, the faulted bench of abrupt slope, controls their spread direction. Secondary contemporaneous fault extented to subsag belt not only separates the facies belts of fan delta and sublacustrine fan,but also controls the morphology and growing thickness of fans. Guided by that, favorable lithological trap is predicted in the belts of abrupt slope, subsag and low uplift.