Stratigraphic Framework Of Deep Strata In The West Of Xujiaweizi Fault Depression In The North Of Songliao Basin

Based on a mass of previous achievements, the thesis has studied the stratigraphic framework of the strata in the west of Xujiaweizi fault depression with the fundamental principle and methods of sequence stratigraphy, combining modern geophysical theory and tectonic theory, and has got some elementary conclusions.The strata in the west of Xujiaweizi fault depression is divided into 4 super-sequences and 8 third-order sequences according to the contact relations of the strata which are reflected from seismic section, drilling data and log data. Accordingly the stratigraphic framework is set up in the west of Xujiaweizi fault depression.The tectonic characteristics of the critical boundaries of stratigraphic framework and structure evolution are studied through the establishment of structure map and structural history profile. The strata in the west of Xujiaweizi fault depression were controlled by NNW Xuxi fault, and volcanic outbreak accompanied the fault activities. The anticline and fault-nose are the main and vast trap. A majority of traps are influenced by fault, and locate on the edge of faults and the top of paleo-bulges. The structure evolution process experienced 4 stages: intensively faulting period, the period transformed from fault depression to sag, depression period and compaction fold period.According to the analysis of the sedimentary characteristics of third-order sequences, it is thought that volcanic facies is the main sedimentary environment in Huoshiling formation and in the first section of Yingcheng formation. In the lower section of Shahezi formation, the upper section of Shahezi formation and the forth section of Yingcheng formation, the main sedimentary environment is fan delta facies, deep and semi-deep lake facies and delta facies respectively. Fluvial facies develops in Denglouku formation. Besides, systems tract is studied in third-order sequences which filled with clastic rocks. An intact third-order sequence is divided into lowstand systems tract, transgressive systems tract and highstand systems.The development of sequence in Xujiaweizi fault depression is controlled by tectonic factor, climate factor, sediments supply rate, lake-level change and volcanic outbreak. The tectonic factor is the main affecting factor in faulting period, but in the period transformed from fault depression to sag, climate factor becomes more significant. All the above factors comprehensively interact each other to affect the periodical change of base-level and accommodation, in turn, control the development of sequence and the features of its internal structure.It concludes that the favorable zones for prospecting locate at Zhaozhouxi bulge, Changde bulge, Zhongneipao bulge and overlap area of Xuxi fault, which is educed by the synthetical study of tectonic characteristics, sequence sedimentary characteristics, source-reservoir-caprocks assemblage and overlap trap.