The Research on Sequence Stratigraphy and Sedimentary Facies of the Member 4 of Yingcheng Formation in Xujiaweizi Depression

The matrix lithology of tight sandstone/gravel reservoirs at the Member 4 of Yingcheng Formation of Xujiaweizi depression in Songliao basin is main target of deep gas prospecting,which includes the upper and the lower of the Member 4 of Yingcheng sequence.During the upper depositional stage,the fault depression is deep and narrow,divided and mutual independent volcanic lake,dominated by the depositional system of alluvial fan facies,fan delta facies(braided delta facies) and flood plain facies;while during the late depositional stage,the fault depression is united and dominated by strongly zonational facies.With the high resolution sequence stratigraphy,the isochronous stratigraphic framework and the depositional evolutional model was built up.The study indicated that structural framework controlled the distribution of various sequence facies in the lake basin.A series of trenches developed in the rim of the fault depression and braided plain,braided delta,fan delta and river delta depositional system developed in the eastern flank to the axial tectonic high.