## 5 Discussion  
### Total Organic Carbon and Organic Matter  
Existing research indicates that, on a horizontal plane, organic matter is more concentrated within the Mianyang-Changing extensional trough compared to outside the trough [17]. Vertically, the Qiong-1 submember shows the highest organic matter content, with a trend of decreasing TOC from the base to the top of the formation. Organic matter in the Qiong 1-1 submember can be observed using scanning electron microscopy (SEM) (Figure 4). Sea level fluctuations further influence the enrichment and preservation of organic matter. Therefore, the Qiongzhusi formation shale is characterized by high organic matter abundance, moderate maturity, and excellent hydrocarbon source rock potential.  
Currently, relevant studies have shown significant variations in the maturity of the Qiongzhusi formation's organic matter. Studies suggest that the overall equivalent R\({}_{\text{o}}\) of the Qiongzhusi formation is generally greater than 2.0%, corresponding to an increasing maturation trend from the central to northern parts of the Sichuan Basin [18]. Asphalt reflectance R\({}_{\text{o}}\) on the northern margin of the Sichuan Basin can locally reach 3.0% to 3.5%. In this study, the maturity of source rocks in well Z201 of the Qiongzhusi formation was  
Figure 4: Organic matter morphology of shale in the Qiongzhusi formation observed using SEM. (**a**) Well Z201, Qiong 1-1 submember, Organic matter; (**b**) Well Z201, Qiong 1-1 submember, Organic matter.  
Figure 3: Standardized rare earth element distribution in the black shale of the Qiongzhusi formation in the southern Sichuan Basin.  
determined using thermal alteration T\({}_{\rm max}\) data from 31 rock samples. The maturity stages of black shale are classified as follows: R\({}_{\rm o}\) < 0.5% and T\({}_{\rm max}\) < 435 \({}^{\circ}\)C indicate an immature stage; 0.5% < R\({}_{\rm o}\) < 1.3% and 435 \({}^{\circ}\)C < T\({}_{\rm max}\) < 475 \({}^{\circ}\)C indicate a mature stage; 1.3% < R\({}_{\rm o}\) < 2% and 475 \({}^{\circ}\)C < T\({}_{\rm max}\) < 500 \({}^{\circ}\)C indicate a high maturity stage; T\({}_{\rm max}\) > 500 \({}^{\circ}\)C indicates an overmature stage, with R\({}_{\rm o}\) ranging from 2% to 3% indicating early over-maturity and from 3% to 4% indicating late over-maturity [19]. For highly evolved source rocks of the Qiongzhusi formation, the overall T\({}_{\rm max}\) measured by rock pyrolysis is less than 435 \({}^{\circ}\)C. However, this does not necessarily indicate that the rock is in an immature stage. The reason is that the source rocks of the Lower Cambrian typically have a conversion rate reaching up to 90%, resulting in lower S\({}_{2}\) values in pyrolysis. This makes the samples susceptible to \"pseudo-peaks\" caused by contaminants, which can obscure the true S\({}_{2}\) peak, leading to an inaccurately low T\({}_{\rm max}\) value. Therefore, this study shows that T\({}_{\rm max}\) fluctuates between 361.63 \({}^{\circ}\)C and 416.00 \({}^{\circ}\)C. S\({}_{1}\) ranges from 0.07 mg\(\cdot\)g\({}^{-1}\) to 3.66 mg\(\cdot\)g\({}^{-1}\), and S\({}_{2}\) ranges from 0.19 mg\(\cdot\)g\({}^{-1}\) to 2.31 mg\(\cdot\)g\({}^{-1}\). The relatively high values of S\({}_{1}\) and S\({}_{2}\) indicate that there is a significant amount of residual hydrocarbons in well Z201 of the Qiongzhusi formation, indicating good hydrocarbon generation potential and suggesting that the organic matter evolution of source rocks has entered a high maturity stage.