## 4 Discussion
Moreover, as shown in Figures 9 and 10, northward from Bencha town in Rudong County (SBY12) to the ancient Yellow River Estuary, the particle percentage of biotite and the particle percentage ratio of biotite to muscovite significantly increased, while the particle percentage of weathered mica and the weathering degree of mica (the particle percentage ratio of weathered mica to sum of biotite and weathered mica) significantly decreased. These values were close to those in the ancient Yellow River Estuary. This result indicates that detritus in the region along the coast northward from Bencha town in Rudong County (SBY12) to the ancient Yellow River Estuary were mainly affected by ancient Yellow River detritus. This relationship is also basically consistent with existing research results. For example, [PERSON] considered the area along the coast northward from Jianggang Port to the ancient Yellow River Estuary (close to the SBY13 sample site in Dongtai city in this study) to mainly be affected by the ancient Yellow River [41]. Based on the variation in the montmorillonite content, [PERSON] proposed that detritus along the coast  
Figure 9: Variation in the mica-specific diagnostic indices in the very fine sand fraction of coastal sediments between the Yangtze River Estuary (CJ)) and the ancient Yellow River Estuary (FHH) together with the Subei littoral plain area. (**a**) shows the variation of particle percentage ratio of weathered mica to the sum of biotite and weathered mica (in green), and the variation of particle percentage ratio of biotite to muscovite (in purple). (**b**) shows the variation of particle percentage of biotite (in red) and weathered mica (in blue). northward from Rudong County to the ancient Yellow River Estuary originated from the ancient Yellow River [42]. By applying element geochemistry and heavy mineral methods, [PERSON] et al. suggested that the land-forming process in the Subei littoral plain area was mainly controlled by the ancient Yellow River, with the southern boundary of influence near Xinhai Bore (near sample site SBY11 in this study) [43]. In addition, based on the characteristics of clay mineral assemblages, [PERSON] et al. proposed that sediments from the coast northward from Rudong County to the ancient Yellow River Estuary were dominated by detritus inputs from the ancient Yellow River [45]. In addition, as shown in Figures 9 and 10, compared to the four mica-specific diagnostic indices of the samples southward from SBY10 to the Yangtze River Estuary and northward from SBY14 to the ancient Yellow River Estuary, the index values at sample sites SBY11 and SBY12 were moderate. These results indicate that the main mixed area occurred between these two sites, i.e., SBY11 and SBY12. Detritus were mainly affected both by the Yangtze River and ancient Yellow River at this location. [PERSON] et al. also proposed that between Dongtao Bore (near sample site SBY14) and Xinhai Bore (near sample site SBY11), the surface sediments at Sancang Bore (near sample site SBY12) were mainly mixed Yangtze River and ancient Yellow River sediments [43]. Figure 10: Ranges of the influence of the Yangtze River and the ancient Yellow River on detrital mica in the very fine sand sediments in the Subei littoral plain area. Quantitative Contributions of the Yangtze River and the Ancient Yellow River to Detrital Mics in the Subei Litttoral Plain Area and Indicative Significance  
The quantitative contributions of the Yangtze River and the ancient Yellow River to detrital mica in the very fine sand fraction of the sediments of the Subei litttoral plain area are shown in Table 1. The coefficients of determination (R\({}^{2}\)) are all more than 0.783 (Table 1). All of the variants explained are close to 100 (Table 1). Additionally, these quantitative contribution data are reliable (Figure 11). Thus, the mathematical model of provenance contribution based on mica-specific diagnostic indices for the very fine sand fraction of sediments is reliable.