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渤海湾盆地始新统沙四段(沙河街组四段)形成时的构造背景特点决定了它的复杂性、多变性和多样性。沙四段在其建组剖面分为沙四上、中和下三个亚段。随着新钻井的增多和研究的不断深入,渤海沙四段层序地层的认识也在不断加深。渤海以前的沙四段基本没有分出亚段,只是分出了南北两种类型。现在认为渤海发育完整的沙四段,分为上下两个亚段,下部为蒸发盐湖相沉积,上部为正常的砂泥岩沉积。南部发育完整的沙四段,北部只钻遇了沙四上亚段,可能缺失沙四下亚段;上下亚段以假整合接触,南北地层是统一的,而不是两种类型。沙四下亚段相当于济阳坳陷典型沙四段中、下两个亚段。沙四段分为继承和残留两种类型,二者有很大的差别。沙四段下亚段不具备生油能力,上亚段发育完整的生储盖组合,可以形成自生自储的油气田,是深层勘探的重要方向之一。
The tectonic background of the Eocene Shasi Section of the Bohai Bay Basin (the fourth member of Shahejie Formation) determines its complexity, variability and diversity. Sha four sections in the section of its formation is divided into sand four, and in the next three sub-segments. With the increase of new drilling and the deepening of research, the understanding of sequence stratigraphy in the fourth member of Bohai Sea is also deepening. Before the Bohai Sea Sha4 segment basically no sub-sub-section, but separated from the north-south two types. It is now believed that the fourth member of the Shahejie Formation, which is well developed in the Bohai Sea, is divided into upper and lower sub-segments. The lower part is the sedimentary salt lake and the upper part is normal sandstone and mudstone. In the southern part of Shahejie Formation, only the upper reaches of Shasi IV were encountered in the northern part of Shahejie Formation, and the fourth member of Shahejie Formation may be missing in the northern part of Shahejie Formation. The sub-fourth member of Shahejie Formation is equivalent to the middle and lower two sub-members of Shahejie Formation in Jiyang Depression. Sha four segments is divided into two types of inheritance and residual, the two are very different. The lower segment of the fourth member of the Shahejie Formation does not have the ability to generate oil, and the complete reservoir-cap assemblage developed in the upper segment can form a self-generated oil and gas field, which is one of the important directions for deep exploration.