Abstract:

The third member of Qingshankou Formation in the west clinoform of the Songliao Basin was divided into 3 4th-order sequences (Cg2，Cg1，Cg0)，each of the 4th-order sequence can be divided into lake expanding system tract and lake shrinking system tract, upwardly, the area of Eg2 is the largest, the area of Sg2 was little smaller, which pinch-out line was located in the western part of the west clinoform; The pinch-out line of Eg1 was located in the middle of the west clinoform, and the area of Sg1 was little smaller than Eg1; The pinch-out line of Eg0 was located in the east of the west clinoform region and pinch-out line of Sg0 further migrated toward east. In the profile section, sand-rich delta front and shore-shallow lacustrine sandy beach-bars mostly developed nearby the 3rd or 4th-order sequence boundary, while the main sedimentary microfacies was the mud-rich shore-shallow lacustrine mixed beach which developed nearby the maximum flooding surfaces of the 4th-order sequence. In the plane, the characteristics of microfacies distribution of different 4th sequences system tracts has certain inheritance, and has the obvious difference.

Key words: Songliao Basin, west clinoform, the third member of Qingshankou Formation, high frequency sequence, sedimentary microfacies