Sequence stratigraphy and sedimentary systems in the second and third members of the Qingshankou Formation in the Yingtai region,Songliao Basin

The second and third members of the Qingshankou Formation are believed to be the targets of petroleum exploration in the Yingtai region.The integration of cores and well logs data shows that second and third members of the Qingshankou Formation represent an overall coarsening-upward depositional sequence and/or a slowly falling phase of lake levels.The second and third members of the Qingshankou Formation may be divided into 2 third-order sequences,4 systems tracts,5 parasequence sets and 16 parasequences.Two sedimentary systems have been recognized,i.e.delta and lacustrine sedimentary systems.There are two sources of sediment supply from the west and north,respectively,of which the western source of sediment supply plays a major role and leads to the zonal distribution of sedimentary facies.The sandstones are overlain in bands upon the mudstones,and thus have provided the conditions to form lithologic oil pools.