Abstract: The Pearl River Mouth Basin is a hotspot to the study of deep-water sedimentation and petroleum exploration in the South China Sea. This study is contributed to the mixed depositional system developed from late Oligocene to Middle Miocene, based on seismic, logging and cuttings data. This mixed depositional system is characterized by the mixtures of different proportions of carbonate and siliciclastic debris. In the vertical sequence, there are three types of lithofacies, i.e. mutational, tapered and alternated types. Based on seismic reflections and lithofacies characteristics, the formation of the mixed depositional system may be further divided into four stages and three mixing processes: the stage 1 of in-situ mixing; the stage 2 of mixing at facies border; and the stage 3 and 4 of punctuated mixing. It is proposed in this paper that these mixed depositional sequences developed in a siliciclastic-dominated environment, may be significant to the formation of potential petroleum reservoirs and has implications for deep-water petroleum exploration in the South China Sea