In this paper, the authors performed detailed study of three complete drilling cores from oft-com:office:smarttags" />Songliao Basin. Through the analysis of organism types and provenance when the base-level of the lake was high, it is suggested that the mudstone was formed with abundant organism in deep water and the organism was originated within the lake. When the lake base-level went down, organism in sediments decreased and terrestrial organism was playing a significant role. These results can be also applied to sequence stratigraphic studies in marine deep water environment.