Spatio‐temporal distribution and genetic mechanism of Paleogene extension amounts in the Liaodong Bay, Bohai Bay Basin

Based on seismic interpretation of 18 regional 3D high-resolution seismic sections across Liaodong Bay, extension amounts, extension rates and extension coefficients of different seismic sections from the south to the north are calculated by employing balanced section technique. Then, spatio-temporal distribution of extension amounts is characterized and interpreted. Finally, the analysis of genetic mechanism is conducted and analysed. The results indicate that tectonic evolution in the Paleogene of Liaodong Bay is characterized by episodic extension. Furthermore, spatio-temporal distribution of extension amounts is relatively uneven. In terms of space, extension amounts are mainly caused by extensional displacement of main depression-controlled boundary faults and syn-depositional faults in the depression. In addition, extensional amounts along main depression-controlled boundary faults are characterized by larger displacement. In terms of time, the periods for horizontal extensional movement can be divided into three stages: The Palaeocene-Early Eocene (Kongdian Formation-third member of Shahejie Formation), Middle-Late Eocene-Early Oligocene (first and second member of Shahejie Formation) and Middle-Late Oligocene (Dongying Formation). Among them, extension during the Palaeocene-Early Eocene occurs both in the north and south of Liaodong Bay. However, extension intensity in the north is stronger than that in the south. Extension intensity in the middle and north during Middle-Late Eocene-Early Oligocene obviously increases. In contrast, it is dominated by strike-slip movement during depositional period of Dongying Formation. Therefore, extension intensity is characterized by significant inheritance. Spatial-temporal distribution of extension amounts is predominantly controlled by tectonic evolution and associated tectonic deformation.