## 4 The Impact of Sequence Structure on Sedimentary Filling
### The Impact of Mid- and Short-Term Cycles on Sedimentary Microfacies  
Statistical analysis was conducted on the sedimentary microfacies of each short-term cycle (fifth-order cycle) within the fourth-order cycles (Figure 13). The types and proportion of different sedimentary microfacies in each short-term cycle was clarified to analyze the control of mid- and short-term cycles on sedimentary microfacies. The MNG1 cycle can be subdivided into three short-term cycles from bottom to top: SNG1 to SNG3. The sedimentary facies in SNG1 was an alluvial fan, with stream flow deposits accounting for 30%, overflow sand bodies accounting for 40%, and sheet flow deposits accounting for 35%. In SNG2, the proportion of the stream flow deposits and overflow sand bodies decreased to 28% and 20%, respectively, while the proportion of sheet flow deposits increased to 42%. Braided fluvial facies began to appear in SNG2, with braided channel microfacies accounting for 3%, center bar microfacies accounting for 5%, and floodplain microfacies accounting for 2%. In SNG3, the proportion of alluvial fans continued to decrease, while the proportion of braided fluvial facies generally increased. The proportion of stream flow deposits, overflow sand bodies, and sheet flow deposits in the alluvial fans decreased to 21%, 14%, and 10%, respectively. On the contrary, the proportion of braided channels, center bars, and floodplains in the braided river facies increased to 30%, 6%, and 19%, respectively. From SNG1 to SNG3, the base-level gradually rose, resulting in a reduction in the sand bodies and an increase in floodplain microfacies and the mud content.  
The MNG2 cycle can be subdivided into two short-term cycles, named SNG4 and SNG5. During the SNG4 period, almost all alluvial fan facies were transformed into fluvial facies, with stream flow deposits and overflow sand bodies accounting for only 5% and 7%, respectively. A small amount of meandering river facies began to develop during this cycle, with meandering channels and floodplains accounting for 14% and 11%, respectively. The proportion of braided fluvial facies increased, with 27% braided channel, 17% center bars, and 19% floodplain microfacies. In SNG5, the proportion of meandering channels decreased from 14% to 13%, while the proportion of floodplains increased from 11% to 15%. The proportion of braided channels and center bars decreased from 27% to 24%, and from 17% to 14%, respectively. In these two short-term cycles, the base-level was in the rising stage, with a high mudstone content and the total proportion of floodplain facies being over 30%.  
The MNG3 cycle can be subdivided into two short-term cycles: SNG6 and SNG7. From SNG5 to SNG6, the base-level rose and the alluvial fan facies gradually disappeared completely, leaving only meandering and braided fluvial facies. In SNG6, the proportion of meandering fluvial facies (accounting for 57%) began to exceed that of the braided fluvial facies (accounting for 43%). In SNG7, the proportion of meandering fluvial facies increased up to 76%, which was much higher than that of the braided fluvial facies. The main microfacies were floodplains with a high mudstone content in this stage.  
MNG4 can be subdivided into four short-term cycles, from bottom to top: SNG8 to SNG11. Only meandering fluvial facies developed in these four short-term cycles. The base-level reached its maximum between SNG7 and SNG8, with the highest accommodation space and mudstone content. The proportion of the floodplains was relatively high, being up to 68% and 70% in SNG7 and SNG8, respectively. On the contrary, the content of sand bodies was very low in this stage. Starting from SNG8, the base-level began to decrease, with a reduction in mudstone and increase in meandering fluvial channels.