## 5 Discussion
### Depositional Palaeenvironment
#### 5.2.3 Palaeoclimate and Peat Swamp Facies  
Concentrated precipitation of lake water or sea intrusion in hot arid climates may lead to the precipitation of Sr as SrSO\({}_{4}\), resulting in higher Sr content in sediments and lower Sr content in humid climates. [PERSON] found that Sr/Cu can be used to analyze the palaeoclimate. Sr/Cu = 1.0-10.0 indicates a humid climate and Sr/Cu > 10.0 indicates \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline
**Samples** & **Sr/Ba** & **Th/U** & **V/(V+Ni)** & **Cu/Zn** & **Sr/Cu** & **Al2O3/TiO2 C** & **GI** & **TPI** & **GWI** & **VI** & **VI** & **V/I** \\ \hline
15R & 0.66 & 2.63 & 0.54 & 1.77 & 1.29 & 34.51 & 0.35 & – & – & – & – & – \\ C1 & 17.61 & 0.17 & 0.66 & 0.37 & 13.46 & 9.04 & 0.97 & 4.25 & 0.83 & 0.37 & 2.22 & 3.43 \\ C2 & 16.24 & 2.30 & 0.86 & 0.20 & 15.24 & 7.37 & 2.15 & 5.07 & 0.75 & 0.46 & 2.00 & 3.78 \\ C3 & 6.86 & 2.70 & 0.80 & 0.58 & 5.62 & 23.99 & 0.11 & 4.19 & 0.91 & 0.83 & 1.42 & 3.23 \\ C4 & 3.97 & 2.00 & 0.85 & 0.55 & 3.12 & 25.35 & 0.17 & 2.88 & 0.91 & 0.70 & 1.88 & 2.30 \\ C5 & 3.68 & 2.15 & 0.89 & 0.36 & 3.99 & 12.27 & 0.07 & 2.72 & 0.85 & 0.60 & 2.00 & 2.14 \\ C6 & 2.46 & 1.43 & 0.83 & 0.56 & 2.26 & 11.40 & 0.04 & 4.63 & 0.62 & 0.53 & 1.51 & 3.59 \\ C7 & 11.24 & 1.73 & 0.81 & 0.45 & 8.82 & 26.73 & 0.32 & 4.31 & 0.93 & 0.34 & 2.51 & 3.72 \\ C8 & 13.56 & 1.74 & 0.76 & 0.55 & 8.38 & 41.25 & 0.84 & 4.12 & 0.66 & 0.45 & 2.91 & 3.06 \\
15P & 2.42 & 2.75 & 0.76 & 0.53 & 2.51 & 21.28 & 0.02 & – & – & – & – & – \\ C9 & 5.33 & 0.69 & 0.78 & 1.83 & 1.55 & 34.90 & 0.86 & 5.21 & 0.49 & 0.54 & 1.40 & 3.46 \\
15F & 2.56 & 1.09 & 0.92 & 0.55 & 2.20 & 31.89 & 0.11 & – & – & – & – & – \\ Average & 7.22 & 1.78 & 0.79 & 0.69 & 5.70 & 23.33 & 0.50 & 4.15 & 0.77 & 0.54 & 1.98 & 3.19 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Deposition palaeenvironmental parameters of the No. 15 coal and non-coal samples. an arid climate [83]. The Sr/Cu ratios of the No. 15 coal samples are in the range of 1.0-10.0, except for C1 and C2 with Sr/Cu >10.0, indicating that the palaeoclimate is humid. The Sr/Cu ratios of the C1 and C2 samples are greater than 10, which is probably due to transgression, and the resulting increase in Sr content is a potential cause of this high ratio. The tissue preservation index-geliification index (TPI-GI), groundwater index-vegetation index (GWI-VI), vitrinite/inertinite ratio (V/I), and the (CaO+MgO+Fe\({}_{2}\)O\({}_{3}\))/(SiO\({}_{2}\)+Al\({}_{2}\)O\({}_{3}\)) ratio of coal (C-value) can be used to characterize peat swamp environments [84; 85; 86; 87; 88; 89]. The TPI-GI diagram in Figure 13 shows that the coal samples fall in the transgressive area of the Back Barrier region, indicating that the peat swamp environment is mainly affected by transgressive action. The GWI-VI diagram shows that the coal samples fall within the bog area (Figure 13). The (CaO+MgO+Fe\({}_{2}\)O\({}_{3}\))/(SiO\({}_{2}\)+Al\({}_{2}\)O\({}_{3}\)) ratio of coal (C-value) is typically used to indicate the media conditions during peat accumulation, where a C-value of 0.23 is the boundary between marine and terrestrial facies [90; 11; 91]. The C-values of the No. 15 coal samples are greater than 0.23, except for C3-C6 with C-values less than 0.23 (Table 7), suggesting that C3-C6 belong to terrestrial facies peat swamp, whereas the remaining samples are influenced by seawater. However, the total sulfur content (S\({}_{\text{t,d}}\)) of C3-C6 ranges from 2.80% to 3.98%, with an average of 3.24% (Table 2), and the organic sulfur contents of all samples are higher than 2.00%, indicating that they had been affected by seawater during peat swamp accumulation. According to research results of depositional facies in the southeastern Qinshui Basin [92; 93; 94], the No. 15 coal is assumed to belong to the coastal zone depositional system.