Mechanism and sedimentary responses of oblique faults: A case study of Jiyang Depression, Bohai Bay Basin

Oblique faults played an important role in the structural deformation of superimposed basins, which resulted in oblique rifting and controlled the sedimentary system in some ways. The systematic mechanism analyses showed that three contemporaneous deformations and one multiphase deformation controlled the generation of oblique faults, including contemporaneous pure shear, simple shear, general shear, and multiphase pure shear by oblique extension/compression. The activity features of oblique faults in the Jiyang Depression ever since Mesozoic were determined on the basis of 3D seismic data interpretation, plane and section analyses of fault and kinematic parameter calculations, combined with regional tectonic evolution. The oblique faults showed reverse oblique-slip in the Indosinian compressional stress field, normal oblique-slip in the Yanshanian simple shear, and normal oblique-slip in the Himalayan extensional stress field. In addition, there were also some normal oblique-slip faults under general shear and inherited oblique-slip faults under oblique extension by stress field transformation. The activities of oblique-slip faults controlled the lateral migration and stacking of fan bodies at the margin of the basin and the dispersion and spreading of sedimentary systems. As the sedimentary response to oblique-slip, the sedimentary imbricates and inclined anticlines formed by the oblique faults' strike slipping in three dimensions were dissected. Several false appearances in judging the faults' slip direction by sedimentary fan body were discussed, which demand intensive studies on secondary structures or regional tectonic evolution.