Sedimentary characteristics and spatial differentiations of the sedimentary facies in the Yellow River sub-delta lobes during the different historical periods

Frequent swings and diversions of old channels in lower reaches coexist with the multi-phase overlapping of Yellow River sub-delta lobes. In addition, sedimentary bodies of sub-delta lobes during various developmental stages are known to have undergone overlapping with one another. Experimental analyses of 24 short-column (length of less than 1 m) stations were examined. In addition, due to the influencing effects of swinging of old channels in the Yellow River's lower reaches, sub-delta lobes of the different historical periods were in different evolution stages, including erosion and degradation(Diaokou), scouring and silting balance(Qingshuigou, and Shenxiangou sub-deltas), and sedimentation (current estuary sub-delta). The characteristics of sedimentary bodies, along with scouring and silting of the seabed, were found to have impacts on the sedimentary characteristics of the sub-delta lobes. The sedimentary bodies of the Yellow River Delta (YRD) were divided into three types, after cluster analysis had been completed. Type-I was dominated by the current estuary sub-delta. Their grain-size frequency distribution curves were with an average grain size of 4.43φ, and characterized by moderate sorting, thus indicating that the sediment supply of the Yellow River was the main source, while a trend of sea continuously receiving the continental source supply and silt existed. The sand content of Type-II was significantly higher than that of type I, and its sand composition was greater than 40%. In addition, the frequency accumulation curves were either bimodal or multimodal, with poor sorting. The area was formed by severe erosion and transformation of the original sediment. The long-probability curve of Type-III area was mainly unimodal. The average grain size fluctuated at approximately 5.26φ, with poor sorting, indicating that the sub-delta was in a process of development. The erosion accumulation processes were superimposed. The evolution models of the YRD since 1855 were successfully clarified, providing theoretical references for deposition processes in the YRD.