The Study Of Décollement Structures In Southern Jiyang Depression Since Late Mesozoic

Dongying and Huimin Sag are in southern of research area Jiyang depression, which is a half graben depositing mainly in late Meso-Cenozoic inside Bohai Bay. Dongying Sag is the primary research area being rich of data. Based on the model founded by field observation, mathematical simulation and qualitative physical interpretation, the response of geophysics on décollement structure is established. The possibility of gravity gliding happening is studied by dynamics analysis. Geology, seismic, well logging, other documents, forward modeling, inverse modeling, and stress analysys on the key profile, the strata where décollement structure occured are analyzed. The deep fault plane of the Chennan Fault is drawn by geometrography.The result shows that the fault plane of Chennan Fault extends horizon towards the deep of lithosphere in depth of 12km. Comparing with the deep décollement structure in West Shandong Rise, both of Dongying half-graben and the"Domino-shape"half-grabens in West ShanDong Rise are confirmed to be on hanging wall of the same deep décollement. The décollement plane occurred in the slope of Dongying half-graben, with position between Archean and early Palaeozoic, and lower Palaeozoic and upper Palaeozoic. 616 geologic profile indicate that the footwall of Chennan Fault drags and pulls overlying. The new model of décollement structure in shallow layer is as following: first it occurred in uncomformity surface and disconformity surface, second it developed between incompetent rock and competent rock of sedimentary rock. The extensional décollement half-graben is composed of shallow level décollement fault and deep level décollement fault, and the slip mainly occured after late Mesozoic.