## 4 Results and Discussion
### Braided Archetype  
Considering the sedimentary evolution process of the river system, the braided river archetype (Figure 8) is established, which takes the element as the basic unit and represents the end channel-fill stacking arrangements preserved in the strata during the continuous evolution. Three contact combination relationships between different elements are recorded: (1) one combination has a genetic relationship at the same period; (2) one combination has no genetic relationship at the same period; and (3) one combination has no genetic relationship at different periods; the dimensions of channel belt scales in this study are quantitatively characterized. The establishment of the archetype is helpful to understand the architecture and evolution of a coarse sandy-gravelly braided river system under a temperate continental monsoon climate. As an upward-stacking evolutionary pattern of overall fineness, the braided river archetype mainly includes the fluvial channel (fluvial channel associated with bar and erosionally based fluvial channel); bank-attached laterally accreting bar; mid-channel downstream accreting bar; abandoned channel; and floodplain. The upward-stacking element associations constitute the archetype: (1) The combination of the fluvial channel and downstream accreting bar with a genetic relationship at the same period usually occurs in the middle part of the channel in the lower part of the archetype, and the two elements are bounded laterally by the fine-grained fill associated with lateral accretion at the bottom of the channel. Downstream accretion bars involve mainly downstream accretion but include lateral and upstream accretion. The sediment thickness of the channel is similar to that of the bar in the independent period, and mud plug fillings are common. (2) The combination of a fluvial channel and a bank-attached laterally accreting bar with a genetic relationship at the same period usually occurs at the edge of the channel in the lower part of the archetype. The laterally accreting bar is adjacent to the river bank, and the dip directions of the internal bedding point to the opposite side of the river bank. The channel has an indistinctly symmetrical shape, with the development of fine-grained fills associated with lateral accretion and mud plug filling and sometimes fine-grained fills. (3) The combination of an erosionally based fluvial channel and a bank-attached laterally accreting bar usually occurs in the lower part of the archetype. As the erosionally based fluvial channel occurs at the same time or after the bar deposition but before the next large filling event, it belongs to the combination with no genetic relationship in the same period. There are two forms of erosion channels: independent small channels or large channels with migration superposition. A small channel is mainly filled with mud, and the thickness is smaller than that of the bar deposit in this period. Large channels sometimes erode the sediment of bars in the early period, and channel linear muds at the bottom and mud plugs at the top are common. (4) The combination of floodplains covering abandoned channels usually occurs at the end of the archetype and represents the combination with no genetic relationship in different periods and the end of the sedimentary event. To better apply the braided channel prototype to quantitatively characterize the width of the channel belt, we establish an empirical relationship among the mean bankfull channel depth (d\({}_{\text{m}}\)), bankfull channel depth (d), and bankfull channel width (W\({}_{\text{b}}\)) by using 14 groups of channel measurement data with genetic relationships (Figure 9, Table 2):  
\[\text{d}_{\text{m}}=0.617\text{ d},\text{W}_{\text{b}}=56.025\text{ d}_{\text{m}}{}^{0.9656} \tag{1}\]  
Figure 8: (**A**) A comprehensive evolution model for the Quaternary braided river system in the study area; (**B–E**) four combination types and internal structure characteristics of adjacent elements.