Tectonic feature and evolution mechanism of central anticline belt of Dongying Sag, Bohai Bay Basin

The present of plastic substances such as evaporate beds in the 4th member (Es⁴) of the Shahejie Formation and the over-pressured mudstone layers in the 3rd member (Es³) of the Shahejie Formation in the Dongying Sag provides the necessary material foundation for the application of Cantilever theory in this area.Since the late Es⁴ period,the loading state in the east of the Dongying Sag as well as its deformation resembled a plastically-founded cantilever which was based on the underlying cream salt layer,fixed on the southern Guangrao Uplift and free on the northern Chennan Fault.With its own gravity and the growing load of overburden sediments,the amplitude of sinking in the free end was gradually increasing,making the basin look like a dustpan.During the sinking,plastic substances kept flowing and aggregating,forcing the overburden layer to arch and finally forming the central anticline belt.Then the cantilever split into two parts which performed individually and continued to drive the evolution of the Dongying Sag.