The Research On Transition Structures In Machang Area, Dongpu Depression, Southern Bohaiwan Basin

Combined with the information about the drillings and regional geology and based on fine interpreting for high-quality 3-D seismic profiles in Machang Area,Dongpu Depression, this paper had done a large amout of the explanation maps about 3-D seismic, the structure sketch maps of important layers, the balance geological profiles and the development profiles, etc..The fault systems, defomation styles and configuration in Machang Area had been identified and classified ,and the types, exhibition and function of transition structures were discussed also.This must be useful and importand to study on hydrocarbon exploration and the research on 3-D extension-structure styles.1. Based on the different influence of different fault systems in Machang Area, the three main structure domians can be partitioned: the Machang Zones (including sub-zones of Maxi Zones, Machang Top Zones and Machang Wing Zones, etc.), the Southern Gegangji sub-Depression and the Sanchunji Zones(including Sanchunji Horst Zones and the Northern Sanchunji Deep Step Area) etc..2. Seven local faults systems can be classified: Machang Fault Systems,Madong Fault Systems,Changdong Fault Systems,Sanchunji Fault Systems,Maxi Fault Systems,Xudong Fault Systems and Xuji Fault Systems etc..These Fault Systems not only had important effect on structure domains,styles and arrangement,but exhibited remarkable segmentation.3. Controlling by above fault systems, a lots of different-grade transition structures were developed in Machang Area. The higher-grade transverse transition structures (eg. Nearby profiles L500 and L1200) and lower-grade transition structures (eg. Nearby profiles L900 and L1400) could be identified.4. These transition structures had different evolvement historys in Eogene and controlled mainly by the base structures or ex-exist structures ,the differential extension in Cenozoic Epoch, the fault segmentation along their strike, and extention between the different fault systems etc..5. The varity stress fields in different periods had fundamental contols on the formation and development of these transition structures.Generally, the direction of Eogene stress fields in Machang Area had swinged from NWW-SEE to NNW-SSE.6. This paper also discussed the relationship between the transition structures and hydrocarbon accumulation.