惠民凹陷沙河街组四段与三段分界线的讨论

惠民凹陷传统的地层分层，一般将沙四段与沙三段的分界线放在盘河砂体与厚长页岩之间，厚长页岩中发育了后长金星介等沙四段典型的生物化石。通过惠民地区沙河街组层序地层学分析，结合沉积学特征分析、区域性层序地层对比和古地磁绝对年龄测定等研究，惠民凹陷沙四段与沙三段的分界线应放在盘河砂体沉积与沙三段油页岩段之间，且盘河砂体与沙三段油页岩之间存在一个三级层序界面，盘河砂岩和厚长页岩在沉积剖面上构成了一个完整的沉积旋回，区域上也具有良好的对比性。

Discussion on the boundary of Sha3 and Sha4 of Huimin Depression

According to the traditional stratigraphic division in Huimin Depression , the boundary separating the fourth member ( Sha4) and the third member( Sha3) of Shahejie Formation lies between Pan-he sandbody and thick-long shales because the Cypris postilon-ga, the typical fossils of Sha4, was developed in the thick-long shales. Through the analysis of sequence stratigraphy, sedimentol-ogy, regional sequence correlation and palaeomagnetic geochro-nology of Shahejie Formation, the boundary of Sha4 and Sha3 should be placed between Panhe sandbody and oil shale of Sha3 in Huimin Depression. A third order sequence boundaries exist between Panhe sandbody and oil shale of Sha3 member,and between Panhe sandbody and thick-long shales make up a complete sedimentary cycle on sedimentary profile, and a good correlation in the region.