东濮凹陷西洼南段下第三系底界及地层组成探讨

An approach to bottom bound and stratigraphy of Lower Tertiary in the south of west sag, Dongpu depression.

通过对东濮凹陷西部洼陷南段的地震资料详细解释，结合沉积学研究，划分出了下第三系与下伏基岩之间的界面。这个界面在地震剖面上表现为下伏反射层系的削截终止和上覆反射层系的上超与下超。界面上、下地层的层速度变化大，反射波组特征差异明显。以往认为该区沙三段和沙四段厚度小（甚至缺失），根据界面之上的反射特征及合成地震记录的地质层位确定，认为区内沙河街组自沙四段至沙一段均发育，但沙四段仅分布于李寨地区以北，最大厚度为５００ｍ。

The bound between Lower Tertiary and basement strata is recognized with detailed interpretation of seismic data and study of sedimentology in this paper. The bound shows that there are the truncated termination of underlying reflectors under the bound and the onlap as well as downlap termination on the bound. The variation of interval velocity and the difference of reflector features are obvious under the bound and on the bound. According to the reflecting character and the geological horizon demarcation of synthetic seismic record over the bound, this paper suggests that Shahejie Formation from first member to fourth member are developed, but the distribution of the fourth member of Shahejie is restrained on the north of Lizhai, and its maximum thickness reaches 500m.