Cenozoic multiple faulting and tectonic evolutionin the Liaodong Bay depression
Jia Nan1, Liu Chiyang1, Zhang Gongcheng2, Huang Lei3, Zhao Junfeng1
1. State Key Laboratory of Continental Dynamics/Geology of Department, Northwest University, Xi'an 710069;
2. CNOOC Research Institute, Beijing 100027;
3. Tianjin Branch of CNOOC China Limited, Tianjin 300452
The Liaodong Bay depression is a natural extension of the waters under the Liaohe depression as an important part of the Bohai Bay Basin. Its present-day tectonic pattern is influenced and controlled by Tan-Lu fault system. In this paper, a lot of data and results from the Bohai Sea oil and gas exploration on the tectonic evolution of the Liaodong Bay area features are made by a comprehensive analysis for investigating tectonic evolution and multiple-stage faulting of the Liaodong Bay depression. Cenozoic tectonic transformation is mainly in the role of faulting, uplift and erosion formation and folding, which has an important impact on tectonic evolution in the Liaodong Bay depression. This paper shows that the west area of Liaodong Bay depression was mainly controlled by initial extension and later structural deformations were weaker. To the east, later strik-slip movement significantly transformed the structural framework, forming the Liaodong uplift, which separated the Liaozhong depression and Liaodong depression. In the Early Cenozoic, activity of the Tan-Lu fault in Liaodong Bay depression was not obvious. Initial synrift deposits were superimposed by dextral strike-slip fault from Eocene to Oligocene. From Late Oligocene to Late Neocene, the Tan-Lu fault was only controlled by dextral strike-slip displacement and it did not act as the sedimentary boundary during this period in Liaodong Bay depression. Structural evolution can be divided into three stages: Synrift stage(from Kongdian period to Sha-3 period), late-stage deformation postrift stage(from Sha-2 period to Dongying period)and strike-slip stage(from Guantao period till now). Understanding the change of structural framework after Sha-3 stage is of importance in petroleum exploration of this area.