Abstract:

In order to explore the relationship between the anomalous subsidence during the post-rift stage in the central and northern
Bohai Bay Basin and the process of the western pacific plate subduction, we collected and compiled data from 27 wells and one seismic
profile and a geological cross-section. We also simulated the strain rate of the crust during the syn-rift stage and the anomalous
subsidence during the post-rift stage for each borehole by using the back-stripping technology and the strain rate inversion method. Thesubsidence events. The average tectonic subsidence rate is 4.6 m/Ma during the first episode (60~42 Ma), corresponding to Ek-Es4, is
5.5~30.5 m/Ma during the second episode (42~36 Ma), corresponding to Es3-Es2, and is 14.7~54.7 m/Ma during the third episode
(36~24.6 Ma), corresponding to Es1-Ed. There are obvious differences between the observed tectonic subsidence and the simulated
subsidence during the post-rift stage in the study region, which indicate the anomalous subsidence. The anomalous subsidence in the
northern region is about 100~200 m and is about 500~700 m in the central Bohai sea region, the anomalous subsidence during the
post-rift stage increases towards the sea. The post-rift anomalous subsidence was probably caused by the subduction of the Pacific Plate,
which induced a down-drag force due to the flow of the deep mantle material. Therefore, the anomalous subsidence in Bohai Bay Basin
might be related to dynamic subsidence.

Key words: Bohai Bay Basin, Cenozoic, backstripping, the strain rate of inversion, dynamic subsidence