Abstract: To clarify the development and evolutionary processes of the large delta complex and slope system on the southern margin of the South China Sea, this paper, based on the interpretation of 2D seismic profile from the region, quantitatively describes the evolution of the Paleo-Rajang Delta in the Zengmu Basin. Key parameters such as the clinoform migration angle $\alpha$, clinoform accretion thickness to clinoform accretion distance ratio $\sigma$, pro-delta width $l$ and pro-delta slope angle $\beta$ are selected to describe the evolution process of the delta. The study explores the controlling effects of various factors on this process. The main body of the delta has undergone five stages of evolution: 1) the early stage of continental shelf delta, forming an oblique prograding clinoforms; 2) the rapid advance stage. when the delta evolved to the marginal shelf delta, and the inflection point trajectory of the prograding clinoforms rose at a medium-high angle while $l$ was small but $\beta$ was large; 3) the stable accretion stage. when the depositional center moved to the slope, and the inflection point of the prograding clinoforms rose at a medium angle while the front of $l$ and $\beta$ were unchanged; 4) the stage of slow progradation. when the inflection point of the prograding clinoforms presented a low angle of progradation while $l$ and $\beta$ gradually decreased; 5) late stage of shelf delta progradation. when climatic conditions coupled with source supply and sea level change affected the rate of change of accommodation $A$ and the rate of sediment supply $S$ and ultimately jointly controled the evolution of the deltaic system and its slope migration.

Key words: South China Sea, Zengmu Basin, Paleo-Rajang Delta, delta complex, sedimentary characteristics, development pattern, controlling factors