## 5 Discussion
### Organic Matter Enrichment Mechanisms and Depositional Models of Various Lithofacies  
To unravel the mechanisms behind organic matter enrichment, Figure 9 presents a correlation analysis between proxies representing various paleoenvironments and TOC content in the study area. Proxies for paleoclimate, such as the Fe/Mn ratio, and redox condition indicators (MoEF and Corg/P) exhibit a robust correlation with TOC content. This suggests that a humid paleoclimate and a relatively reducing ancient sedimentary environment are pivotal factors influencing the enrichment of organic matter. According to previous studies, the deposition period of the Da'anzhai Member shale aligns with the Toarcian Oceanic Anoxic Event (also known as the Jenkyns Event), which was a globally significant geological event in the Early Jurassic and occurred about 183.8 million years ago [46; 54; 55; 56]. It is plausible that the T-OAE, marked by the release of a substantial volume of CO\({}_{2}\) from the Karoo-Ferrar Large Igneous Province, led to a rapid rise in global temperatures, which had a profound impact on the global climate system [57; 58]. This event is linked to worldwide environmental transformations, encompassing the widespread development of anoxia, significant disturbances in the global carbon cycle, and the decline in marine fauna biodiversity [59; 60; 61; 62]. Consequently, T-OAE emerges as a crucial factor contributing to the alterations in paleoclimate and redox conditions in the Da'anzhai Member. Figure 8: The relationship between Al content and (Ni + Cu + Zn) content among different lithofacies of the analyzed Da’anzhai Member shale (ORA: organic-rich argillaceous shale; OPA: organic-poor argillaceous shale; ORM: organic-rich mixed shale; \(n=36,n\)—number of experimental samples; \(p<0.05\)). Simultaneously, the proxy for paleosaninity (Sr/Ba ratio) exhibits a discernible negative correlation with TOC content. In certain terrestrial shale sequences, a positive correlation between the Sr/Ba ratio and TOC content has been observed, as exemplified in the Nanpu sag of the Bohai Bay Basin and the Luchagou Formation of the Santanghu Basin [63; 64]. This positive correlation is typically attributed to higher salinity inducing water column stratification, fostering a reducing environment at the water's bottom, and facilitating the preservation of deposited organic matter. However, in this study, a negative correlation  
Figure 9: The correlation analysis between proxies representing various paleoenvironments and TOC content among different lithofacies of the analyzed Da’anzhai Member shale (ORA: organic-rich argillaceous shale; OPA: organic-poor argillaceous shale; ORM: organic-rich mixed shale; \(n=36\), \(n\)—number of experimental samples; \(p<0.05\)). (**a**) Fe/Mn versus TOC; (**b**) Moef versus TOC; (**c**) Corg/P versus TOC; (**d**) Sr/Ba versus TOC; (**e**) Al versus TOC; (**f**) (Ni + Cu + Zn) versus TOC; (**g**) (Ni + Cu + Zn)/Al versus TOC. is observed between the Sr/Ba ratio and TOC content. This deviation may arise from the Da'anzhai Member primarily depositing in a freshwater to brackish environment, where such salinity conditions may not induce significant water column stratification and the formation of anoxic environments. Instead, salinity likely represents the paleo-depth of the lake in this study. Under conditions of high paleo-depth, weaker evaporation results in lower basin salinity. A higher paleo-depth also creates a relatively reducing environment at the lake bottom, leading to the observed negative correlation between the Sr/Ba ratio and TOC content. Similar phenomena have been reported in previous studies [16; 17]. Proxies representing terrigenous debris input (Al content), paleo-productivity ((Ni + Cu + Zn)), and water column original primary productivity ((Ni + Cu + Zn)/Al) show no significant correlation with TOC content in the study area. As mentioned earlier, the increase in terrigenous debris influx promotes the development of paleo-productivity.