## 5 Discussion
### Source Rock Characteristics
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Formation**} & \multirow{2}{*}{**Lithology**} & **Type of** & **TOC (Average)** & **S\({}_{1}\) + S\({}_{2}\) (Average)** & **HI (Average)** & **T\({}_{\max}\)** \\  & & & **Organic Matter** & & & \\ \hline J\({}_{2}\)_kz_ & DM & III and II\({}_{2}\) & 0.01–2.96 (1.08) & 0.04–6.92 (1.56) & 11.68–79.00 (55.55) & 430–546 \\ J\({}_{2}\)_kz_ & CM & III & 0.62–33.1 (16.94) & 14.91–76.38 (45.60) & 52.00–54.00 (166.83) & 431–446 \\ J\({}_{2}\)_kz_ & CO & III & 42.62–53.75 (45.47) & 43.78–71.37 (56.73) & 83.17–16.07 (118.53) & 425–432 \\ J\({}_{1}\)_y_ & DM & III and II\({}_{2}\) & 0.01–15.30 (28.2) & 0.11–42.03 (68.19) & 10.00–90.010 (144.64) & 405–503 \\ J\({}_{1}\)_y_ & CM & III & 11.13–36.86 (21.83) & 10.04–94.11 (33.10) & 79.00–302.00 (140.44) & 428–443 \\ J\({}_{1}\)_y_ & CO & III & 21.65–68.23 (37.91) & 17.18–59.49 (33.27) & 70.00–245.00 (1041.99) & 435–462 \\ T\({}_{3}\)_t_ & CM & III & 16.2–29.6 (2.08) & 1.43–10.88 (3.30) & 46.00–278.00 (102.86) & 429–445 \\ T\({}_{3}\)_h_ & CM & II\({}_{2}\) and III & 0.26–7.29 (1.84) & 0.11–88.84 (14.07) & 16.00–189.63 (80.79) & 439–469 \\ \hline \hline \end{tabular} Note: DM = Dark mudstone, CM = Carbonaceous mutostone, CO = Coal, TOC = total organic carbon (wt.%), S\({}_{1}\) = soluble hydrocarbon content; S\({}_{2}\) = pyrolysis hydrocarbon content; HI = hydrogen index, T\({}_{\max}\) = pyrolysis temperature corresponding to the highest point of P\({}_{2}\) peak (\({}^{\circ}\)C).  
\end{table} 
Table 6: Total organic carbon parameters of the source rocks in the northern structural belt (modified from [PERSON] et al., 2019 [44] and [PERSON] et al., 2022 [94]). The results of gas chromatograms (GCs) are characterized by a none odd-even predominance of the Jurassic source rocks (CPI: 1.17-1.22) and an even predominance of the Triassic source rocks (CPI: 1.10; Figure 4 and Table 2), reflecting a higher thermal maturity of the Triassic source rocks compared with that of the Jurassic source rocks [10; 19]. The isomerization ratios of C\({}_{29}\) steranes \(\beta\beta/(\beta\beta+\alpha\alpha)\) and C\({}_{29}\) steranes 205/(205 + 20R) are common thermal maturity characterization parameters with an equilibrium value being at 0.9% Ro [17; 104]. The results show higher maturity of Triassic source rocks than that of Jurassic source rocks, with some of them exceeding the end point of isomerization (Figure 8B). Methylphenanthhrene with the methyl group at the \(\alpha\)- position will be transformed into a more stable one at the \(\beta-\) position with increasing maturity. [PERSON] et al. (1982) [105] proposed methyl phenanthrene indexes (MPI-1, MPI-2) to measure the maturity of organic matter. These ratios are sensitive to thermal evolution but may become inefficient for high-maturity oils. Methyl phenanthrene ratios (F\({}_{1}\), F\({}_{2}\)) with greater applicability at higher levels of maturity. The F\({}_{1}\) and F\({}_{2}\) values of the Jurassic source rocks and Triassic source rocks are, on average, 0.48 and 0.27 and 0.61 and 0.34, respectively (Table 2 and Figure 8C). The calculated maturities from F\({}_{1}\) and F\({}_{2}\) values of the two types of sources are the average of 0.96% Rc and 0.89% Rc and 1.32% Rc and 1.1% Rc (Table 2), respectively, indicating the higher maturity of Triassic source rocks than the Jurassic source rocks. The calculated % Rc is the same as the measured Ro (Figure 12) and the basin modeling results (Figure 13).