THE TECTONIC FRAMEWORKS OF BOHAI GULF AND COASTAL BASINS, CHINA

The Bohai Gulf Coastal Basin covers an area of 200,000 sq. km. an important oil and gas province of China It is a polycyclic superimposed basin. Its history of development can be subdi-vided into four stages: 1) Late proterozoic parageosycline Stage(Sinian). 2) Early Palaeozoic cratonic stage (Lower Cambrian-Middle Ordovician). 3) Late Palaeozoic intracratonic coal-bearing sequences stage(Middle Carboniferous-Permian). 4) Mesozoic and Cenozoic taphrogenic rifting and subsidence stages. During the Paleogene rifting stage, three NNE trough systems and three nearly E-W trough systems were initiated as the results of regional extensional stresses. Central rift valleys,low angle gravity faults and a series of wedgeshaped troughs were developed symmetrically surrounding the "Bohai Mantle Plume".The rifting troughs were extended and widened gradually.During the Neogene, a large saucer-shaped sedimentary basin was developed as a thick blanket covering the whole areas either of the Paleogene troughs or the Palaeozoic-Sinian highs. Oil and gas fields are mainly distributed in the Paleogene trough systems controlled by the Rifting Zones.Tertiary structural traps such as Shengli oilfield, Gudao Oilfield and Dagang oilfield are large oil pools.Sinian-Palaeozoic buried-hill traps beneath the Tertiaty unconformity such as Renqiu Oilfield is also a giant Oilfield of the Bohai Gulf Coastal Basin.