The Palaeogeomorphologic Reconstruction Of Es4s In Zhuangxi Area, Bohai Bay Basin

The paper restores the palaeogeomorphology and analyzes the sedimentary environment during the period of the upper part of 4th member of Shahejie Formation (Es4s) in Zhuangxi area.Based on the strata analysis, using 1D basin modeling and the balanced-section technique eroded thickness and compacted thickness are recovered.It is necessary to make dip correction in steep slope belt with dip angle up to 45°. We calculates its true thickness and plots contour map after truth thickness correction. From the end of Es4s to now the compaction rate ranges during 30%～50%. Original thickness is 1.5-2 time the residual thickness.During the late sedimentation, slight denudation occurs mainly in the top of Gubei low swell and the Northeastern side of Zhuangxi burial hill. And denudation thickness is not more than 40meters because denudation widely occurs in Jiyang depression and Zhuangxi area is surrounded by arches.There are several low swells and subsags including Gubei low swell ,Zhuangxi burial hill and other four peripheral secondary subsag. Among them two secondary subsags in the western and eastern side of Gubei low swell develop well with Es4 thickness up to 400 meters. The rudiment of the two secondary subsags is formed with the Es4 thickness not more than 200meters.It is concluded that beach and bar facies develop favorably in the top and gentle slope area of Gubei low swell and the edge of Zhuangxi burial hill.