## 5 Discussion  
### Paleenvironment Reconstruction  
#### 5.1.1 Paleoclimate and Weathering  
Paleoclimate and weathering conditions play a significant role in influencing the influx of terrigenous debris, salinity conditions, and redox conditions [45]. In this study, two proxies were employed to characterize paleoclimate and weathering conditions (Table 4, Figure 4). Fe/Mn was selected as a proxy for paleoclimate, while the CIA was used for a quantitative description of weathering conditions. CIA values of 80-100, 70-80, and 50-70 reflect strong, moderate, and weak degrees of chemical weathering in sediment source regions, respectively [5]. Simultaneously, under different climatic conditions, Fe and Mn elements display different enrichment tendencies. Hot and dry climatic conditions lead to increased evaporation from lakes, resulting in Mn enrichment of lacustrine deposits. Conversely, a humid environment leads to Fe concentrations in contemporaneous sediments in the form of Fe(OH)\({}_{3}\). Elevated Fe/Mn ratios indicate warm and humid climatic conditions [16; 23]. The CIA values for the Da'anzhai Member shale in the study area range from 61.8 to 84.1 (average: 77.6), with average values of 75.9, 78.1, and 78.9 for ORA, OPA, and ORM, respectively. This indicates that the basins of detrital sources in the three lithofacies are undergoing moderate weathering, and there is no significant difference in weathering conditions among the different lithofacies. Simultaneously, the Fe/Mn ratio in the Da'anzhai  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Depth** & **TOC** & **51V** & **52 Cr** & **59 Co** & **60 Ni** & **63 Cu** & **66 Zn** & **88 Sr** & **95 Mo** & **137 Ba** & **238U**  
Member shale in the study area ranges from 4.6 to 242.7, with an average of 116.1. The Fe/Mn ratio in this study is similar to that reported by [PERSON] et al. (2023), indicating a similar paleoclimate condition [16]. However, there are significant differences in the Fe/Mn ratio among different lithofacies shales. In general, ORM has the highest Fe/Mn ratio (average of 148.5), followed by OPA (average of 133.7), and ORA has the lowest Fe/Mn ratio (average of 90.4), indicating different paleoclimate conditions for the formation of different lithofacies. The climate during the formation of ORM was the most humid, followed by OPA, and the environment during the formation of ORA was the most arid. Generally, a certain correlation is expected between weathering conditions and paleoclimate, with a wet paleoclimate often associated with strong weathering conditions. However, in this study, Fe/Mn ratios and CIA values do not exhibit a clear correlation (Figure 5). Similar patterns were reported in the studies by [PERSON] et al. (2022) and [PERSON] et al. (2023) on the Da'anzhai Member in the Sichuan Basin, suggesting that weathering processes may not have a significant impact on the input of raw materials at a basin scale [16; 46]. In summary, the Da'anzhai Member shale in the study area was deposited in a warm and humid environment, and the watershed of the shale clastics source was undergoing strong weathering. While examining different lithofacies, it becomes evident that weathering processes do not exhibit significant differences, whereas notable distinctions emerge in paleoclimate conditions.