Sedimentary microfacies and evolution of the 4th member of the Quantou Formation in the Yongping region, southern Songliao Basin

The 4th member of the Quantou Formation in the Yongping region, southern Songliao Basin is divided, in terms of core examination, sedimentary structure, mineralogy and well logs, into lake and meandering delta facies, including two sedimentary subfacies such as shallow lake and delta front subfacies, and three sedimentary microfacies such as shallow lake mud, subaqueous distributary channel and interdistributary bay microfacies. With the aid of the division and correlation of the layers and sand sets based on the closely-spaced well patterns of JF-229 well field, the 4th member of the Quantou Formation may be subdivide into 12 layers or 9 phases of channels. The delta front deposits once persisted in the study area during the early stage of the deposition of the 4th member of the Quantou Formation. There occurred a short period of transgressive-regressive lake cycles during the deposition of the 10th layer, followed by the delta front deposits again. At the end of the deposition of the 4th member of the Quantou Formation, the wide-spread transgressions were initiated during the deposition of the 4th layer. Finally a sedimentary model is presented for the 4th member of the Quantou Formation, and thus may provide evidence for the delineation of the favourable reservoir sandstones in the Yongping region.