Development Characteristics Of Neogene-Quaternary Compressional Structures In Bohai Sea Area

Controlled by regional compression events and the disappearance of asthenosphere upwelling,a series of compressional structures were developed in Bohai Sea area in Neogene-Quaternary.Now few related researches were done on this study,which lacks of systematic contrast of space-time difference and analysis of genetic mechanism.Based on 3D seismic data of Bohai Sea area and previous research results,structural analysis and systematical identity have been made for the Neogene-Quaternary compressional structures in Bohai Sea area.Then the evolution processes and dynamic mechanism of those compressional structures were confirmed.Compressional structures can be divided into 2 styles: fold style and fault-fold style.The fold style includes single large-scale anticline and continuous folds,while fault-fold style can be divided into back thrust structures,antiformal negative flower structures and Positive flower structures.Nine Neogene-Quaternary compressional structures were found in Bohai Sea area.Different types of compressional structures have differences in developing strata,long-axis direction and developing position.Based on the strikes of compressional folds,they can be divided into NE,subparallel SN and subparallel EW trending three types.The NE,subparallel SN trending compressional structures were mainly developed near the Tan-Lu Fault Zone in the east of the Bohai Sea area and the subparallel EW trending compressional structures were mainly developed near the Zhangjiakou-Penglai Fault Zone.There were 3 tectonic compression events in Neogene-Quaternary: early Miocene,the end of Pliocene and early Pleistocene.The tectonic compression of the end of Pliocene was reflected in the all areas of Bohai Sea.However,the tectonic compression of early Miocene and Pleistocene was relatively limited which was mainly located in the intersection of Tan-Lu Fault Zone and Zhangjiakou-Penglai Fault Zone in Bodong area.For the compression strength,early Miocene and early Pleistocene were relatively weak,while tectonic compression at the end of Pliocene had considerable differences on compression strength in different areas of Bohai Sea area.The Neogene-Quaternary compressional structures in Bohai Sea area formed under regional compression stress field controlled by surrounding plates and deep dynamic background.The differences in compressional structures of different tectonic events or different location of the same tectonic event,reflected the differences of local stress field under the whole compression background.Because Bohai Sea area lied in dextral strike-slip stress field,the local compressional stress would be derived at the S-shaped bend,left-stepping stepover of strike-slip faults and the reverse S-shape bend sinistral strike-slip faults,which led to the development of local compressional structures and the differences in long-axis strikes,structural patterns and compression strength.