Discussion On The Coupling Relationship Between Shallow Structure And Deep Processes In The Bohai Cenozoic Basin

The Bohai Cenozoic basin is a part of the Bohai Bay basin,and thus they have a close relationship.The Bohai Bay basin is developed with typical Cenozoic rift basin,and the Bohai was its deposition and subsidence center since Oligocene.During the rift period,faults developed in a profound way,and the basin subsided.During the post-rift period,the whole area subsided,and had the feature of accelerated subsidence.In this thesis,through the method of balanced cross-sections,we used several profiles and made an analysis of the shallow structure in the Bohai Cenozoic basin.Based on this,combined with the results and data of the deep structure,like seismic tomography,we made a contrast of the coupling relationship between the shallow structure and deep processes,aimed to probe into the dynamic mechanism of Bohai basin.The characteristics of structural styles in each Cenozoic depression and temporal-spatial variation faults were analyzed based on previous studies.It shows that the development of faults is generally controlled by extension,and influenced by slip-faults only after Oligocene.Choosing 6 sections which were basically perpendicular to the tectonic trends of the Bohai sea,we made an estimation of the extension proportions,and the rate of subsidence of the Bohai sea was also calculated.The results suggested that in the uplifting period during the 4th Member of the Shahejie Formation and the Kongdian Formation,the Bohai sea area has several depositional or subsiding centers,and the rates of subsidence were slow and barely the same to each other;during the third Member of Shahejie Formation,the rate of subsidence were the fastest,and during the Dongying stage,they became slower again,and the depositional or subsiding centers had transited to the Bozhong Depression.In the depressing period,intensively subsidence or deposition around the Bozhong Depression was obviously higher than normal.Combined with the latest deep structure data,it was concluded that the development of faults was influenced by the Mesozoic tectonic framework;the formation of the faulted basin was the joint result of the Pacific plate's continuous back moving and the India-Tibet collision.Accelerated subsidence since Oligocene,is the most direct result of the rapid cooling of the lithosphere after the subduction frontier of the Pacific plate moved to the east.