## 5 Discussion
### Main Controlling Factors and Enrichment Patterns of Organic Matter  
To clarify the controlling effects of the paleodepositional environment on the enrichment of organic matter in the study area, this study fitted the indicators of paleoclimate, redox conditions, paleosalinity, paleoproductivity, and paleowater depth mentioned earlier with TOC to determine which factors control the enrichment of organic matter (Figure 13).  
In terms of paleoclimate, the TOC (Total Organic Carbon) content in the study area shows a certain negative relationship with the Sr/Cu ratio. There is no significant relationship with the CIA (Chemical Index of Alteration). Higher Sr/Cu values are associated with more pronounced decreases in TOC values. This indicates that during the deposition of Ying IV, when the climate was relatively arid, precipitation decreased, leading to lower levels of biological activity and less favorable conditions for the enrichment of organic matter. In contrast, when the climate was warm and humid, it was more conducive to the proliferation of life, especially with increased rainfall, which led to higher reproduction rates of aquatic organisms. As a result, the conditions were more favorable for the enrichment of organic matter, leading to higher organic carbon content. Regarding redox indicators, TOC shows a certain positive relationship with the V/(V + Ni) ratio. This suggests that the enrichment of organic matter is partly controlled by the redox conditions of the water body. Better reducing conditions in the water body are more favorable for the enrichment and preservation of organic matter. Using the Cu/Zn ratio as an indicator, the water body environment is determined to be reduced, with no significant differences in the degree of reduction. Therefore, there is no clear relationship with TOC. Paleosalinity is also an important factor affecting the enrichment of organic matter. When salinity increases, the vertical salinity gradient in the lake rises, leading to stratification of the water body. In such conditions, organic matter is less likely to be consumed and decomposed in the high-salinity water, thus, being preserved. The TOC content in Ying IV mudstone of the study area shows a certain negative relationship with the Sr/Ba ratio. There is no signifi  
Figure 13: Relationship between TOC and paleoclimate (**a-c**), redox conditions (**d,e**), paleosalinity (**f,g**), paleoproductivity (**h**), and paleowater depth (**i**) parameters.  
cant relationship with the Ca/(Ca + Fe) ratio. This indicates that although higher salinity improves the preservation conditions for organic matter, the high salinity also inhibits the survival and reproduction of organisms in the lake. As a result, the organic matter content does not increase significantly and may even decrease slightly. Since the overall water depth of the paleolake in the study area is characterized by a deep-lake environment, there is no significant relationship between water depth fluctuations and TOC content.  
Paleoproductivity is the foundation for the enrichment of organic matter. Since the four indicators used to assess paleoproductivity (P/Ti, Ni/Ti, Cu/Ti, and Zn/Ti) show consistent vertical variations, P/Ti is selected as the representative indicator of paleoproductivity. The positive relationship between P/Ti and TOC indicates that the organic matter content in sediments increases with higher paleoproductivity, providing a rich source of organic carbon. Volcanic activity also occurred during the sedimentary period of Ying IV. The volcanic hydrothermal fluids and volcanic ash generated by the volcanic activity provided abundant nutrients for the lake, thereby increasing the lake's paleoproductivity. Meanwhile, the deep lake environment, which was predominantly reducing, facilitated the preservation of organic matter. As a result, organic-rich source rocks were formed through sedimentation, with the enrichment pattern being a productivity-dominated model (Figure 14).