PULL-APART TECTONIC AND HYDROCARBON PROSPECTING IN BOHAI BAY AND ITS NEARBY AREA

area is in the east part of Bay Basin,and experienced rifting,transfer and post-rifing phases in Tertiary. Half graben and half horsts are the basic units during rifting phase. According to the oritntation and dip of boundary faults between half graben and half horst,there were three groups of half graben in and nearby area, the first occurred in its south-western part (Huanghua Depression), most of half graben's boundary faults dipped eastwards;the second happened in its middle and south area (Chengning up-lift and Jiyang Depression and south part in area),most of graben boundary faults dip southward;the third in its northeastern area (Liaohe Depression,and northeast Bohai),most of half graben boundary faults dip westwards. In the transfer phase between rifting and post-rifting, thick strata of Dongying Formation formed in Bozhong and Qikou Sags (overstacked on Bozhong half graben and Qikou half graben),and horsts begun subsided during this phase. Post-rifting mainly occurred in Miocene and Pliocene and Quaternary,and formed Guantao, Minghuazhan and Pingyuan Formations. During the whole evolution, subsidence and sedimentary center migrated from southwest to Qikou Sag for south-west belt and from Damingtun Sag in northeast and Changwei Sag in southeast to Bozhong Sag respectively. All these phenomena show area is a pull-apart basin involved mantle activity in Tertiary. Many rich source-rock half grabens formed during pull-apart rifting,and lower part Dongying formed in transfer phase is potential. In Quaternary area was inverted by Tanlou movement,and formed a lot of traps in Bozhong area,particully along east part of Bozhong Depression. We here named the movement as Bohai Movement. Controlled by tectonic history, there are three kinds of local background for trap development,those over horsts,along horsts and in sag.