Abstract:

The mainly developments of sedimentary facies in Quantou Formation of Lishu Sag in Songliao basin are as follows: alluvial fan, braided river, mendering river, shallow water lake and shore shallow water lake etc. Slightly vibration-uplift and subsidence of the basin make it possible to divide it sedimentary evolution into 4 stages; early stage(Quan No.1 interval) is the stage of fault subsidence transited to sag deposition; middle stage(Quan No.2 interval) is the stage of large scale shallow water lakes developed due to great subsidence rate of the basin and weak effects of river alluviation, and sedimentary environment is composed of shallow water lakes, flooding lacunae and a few meandering rivers; later stage(Quan No.3 interval and middle stage of Quan No.4 interval) reservoir intervals were quite developed due to the slow down of regional sedimentation and reinforcement of river effect; during final stage(later stage of Quan No.4 interval)Songliao big lake-basin came into an embryonic form and began to expand due to the effect of the development of the whole basin. Sedimentary evolution of Quantou Formation has experienced a complete sedimentary sequence of river alluvium plain sedimentation representing the sedimentary characteristics of transformational period of Songliao basin fault sag.

Key words: Quantou Formation, sedimentary facies, evolution, Lishu sag