Structural Styles In Dongpu Paleogene Extensional Faulted Depression

Based on the study of regional geology, earthquake and drilling data, as well as the theories and methods of structural analysis in extensional faulted basin, the geological setting, characteristics structural styles in extensional linkage fault systems and superimposed types in Dongpu extensional faulted depression are studied. The transfer structural types, feature and mechanism, and local extensional structural styles and their relation with hydrocarbon occurrence are reanalyzed systematically and discussed.Discussion on six problems is emphasized as follows in this paper.(1) The basic feature of east-west zoning and south-north partition in Dongpu faulted depression are controlled by Paleogene activity of Lanliao fault, which induced the structural deformation in the hanging wall, forming the structural framework of one uplift between two depressions and one gentle slope. Based on the activity difference of faults and lateral accommodation zones, Dongpu faulted depression is divided into three segments, including northern, middle, and southern segment.(2) Complex fault systems developed in Dongpu faulted depression. The structural style of extensional linkage fault system was showed as narrow fault step belt in Lanliao fault zone. Centrel fault zone is the most complex structure: anthitic and synthetic conjugate secondary normal fault systems formed at the late of extensional fault linkage, including compound graben system, compound horst system and graben-horst superimposed complex fault block group. In the western slope, there are mainly mild fault steps and reverse"y"style fault combined by master faults and secondary faults in cover strata.(3) The major superimposed structureal types in different periods in Dongpu depression are inherited and interference type. Inherited types are developed in Pucheng subdepression and Qianliyuan sub depression convergent types developed in Liutun, Haitongji, Nanhejia and Menggangji subdepression, while inherited and interference composite type developed in Gegangji subdepression.(4) Based on redefind concepts of transfer structure and its classification scheme, transfer structures identified in Dongpu fault depression include 2 first order transverse accommodation zones, 3 secondary transverse accommodation zones, 8 three-level transverse accommodation zone and transfer zone, in which there are 2 types of accommodation zones, 5 types of transfer zones, 1 compound type of accommodation zone and transfer zone.(5) There are 5 types of local extensional structures in Dongpu faulted depression:①folds and fault blocks relative to normal fault, such as Pucheng rollover anticline and Langzhongji antiform structure formed in graben, fault step and fault block superimposed by graben and horst;②local structures relative to shear movement, such as Maogang negative flower structure and left-lateral en echlon extensional fault blocks arranged in external side of major strike slip fault;③local inverted structure related to compressed shorten movement;④salt structures and⑤eroded fault block hills.(6) Relation between structural styles and hydrocarbon occurrence are summarized. Superimposed structural types of different period control formation condition of source beds; extensional folds is the favored petroleum structure; complex fault-block groups are the major petroleum units; accommodation zones affect the distribution of source rock and development of reservoir, becoming the favored petroleum accumulation area.