Keywords: 
• delta /
• river mouth process /
• differentiated fluid /
• mouth bar

Abstract: Lacustrine delta in QW area of Shanganning basin has a different characteristic from other traditional deltas. Subaqueous distributary channel sandbodies and mouth bars are well developed here, and mouth bar complexes locate both at the beginning and the end parts of the subaqueous distributary channels, these sandbodies build up the framework of the delta front. Sediments of subaqueous distributary channels are distinguishable from those in distributary channels of delta plain as those in thickness, depositional structures and well-logging curvesect. After reviewing the past researches on river mouth processes and comparing with some other similar studies, this paper introduces the concept of river mouth processes of differentiated fluid and different mouth bars respectively, and attempts to explain the developing mechanism of the lacustrine delta in QW area with this theory. The differentiated fluid is characterized by vertical loads and speed differentiated distribution, and mainly controlled by climate and quantities of sediments supporting. The results of river mouth processes are affected by basin structure and bottom geometry which may result in those stable moving forward or rapid downcutting of subaqueous distributary channels after the river water flew into the basin. Two different types of mouth bars can be distinguished by connecting microfacies or facies association. long drived subaqueous distributary channels and its terminal mouth bar complex together with the ordinary mouth bar complex may be the most important responses to the river mouth processes of differentiated fluid.