## 4 Results
### Biomarker Compounds  
The distribution pattern of \(n\)-alkanes in the source rocks of the Shahejie Formation in the Huanghekou Depression was predominantly characterised as the front-peak type, with few samples exhibiting the bimodal type. In the mass chromatogram, at \(m/z\) 85, the distribution of detected \(n\)-alkanes in the Huanghekou Depression samples predominantly ranged from C\({}_{12}\) to C\({}_{33}\), exhibiting distinct variations across different strata. The carbon number distribution of \(n\)-alkanes in E\({}_{3}\)s\({}_{1-2}\) exhibited a relatively comprehensive profile, characterised by a prominent front peak and occasional bimodal features. The main peak ranged from C\({}_{16}\) to C\({}_{25}\), while the odd-even dominance index (OEP) ranged from 0.77 to 1.81 (average: 1.16), and the average chain length (ACL) ranged from 12.67 to 23.50 (average: 17.09) (Table 2). The carbon number distribution of the \(n\)-alkanes predominantly fell within the C\({}_{12}\)-C\({}_{30}\) range in E\({}_{2}\)s\({}_{3}\), exhibiting a front-peak distribution pattern, while some samples displayed a bimodal characteristic, with the main peak ranging from C\({}_{15}\) to C\({}_{23}\), OEP values ranging from 0.84 to 2.08 (average: 1.16), and an ACL ranging from 12.82 to 20.54 (average: 17.78) (Table 2). The analysed samples contained a significant abundance of isoprenoids, including pristane (Pr) and phytane (Ph) (Figure 3 and Table 2). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Well**} & **OEP** & **ACL** & **Ph/nC\({}_{18}\)** & **Pr/nC\({}_{17}\)** & **Pr/Ph** \\  & **Average** & **Average** & **Average** & **Average** & **Average** \\ \hline B25-1 & 1.07 & 17.88 & 0.41 & 0.59 & 1.5 \\ B25-2 & n.d. & n.d. & n.d. & n.d. & n.d. \\ B25-3 & 1.12 & 17.29 & 0.32 & 0.43 & 1.21 \\ B25-5 & n.d. & n.d. & n.d. & n.d. & n.d. \\ B26-1 & 1.35 & 17.39 & 1.68 & 1.4 & 1.24 \\ B27-1 & 1.12 & 18.47 & 0.19 & 0.43 & 2.1 \\ B28-1 & 1.19 & 18.5 & 0.35 & 0.81 & 1.4 \\ B28-2 & 1.14 & 17.65 & 0.28 & 0.49 & 1.77 \\ B29-6 & n.d. & n.d. & n.d. & n.d. & n.d. \\ B29-2 & 1.2 & 16.49 & 0.62 & 0.93 & 1.75 \\ B29-3 & 1.34 & 19.34 & 0.49 & 0.82 & 3.44 \\ B33-1 & 1.1 & 18.24 & 0.46 & 0.47 & 1.45 \\ B34-1 & 1.16 & 17.8 & 0.33 & 0.52 & 0.78 \\ B34-2 & 1.14 & 18.23 & 0.31 & 0.43 & 1.33 \\ B34-3 & 1.14 & 17.76 & 0.28 & 0.43 & 1.35 \\ B34-5 & 1.18 & 15.36 & 0.41 & 1.01 & 1.38 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Related parameters of normal alkanes and isoprenoids in the studied area. Figure 2: Comprehensive evaluation of source rock. (**a**) Plot of \(I_{\rm H}\) versus T\({}_{\rm max}\) evaluating organic matter types; (**b**) TOC content versus rock-eval S\({}_{1}\) + S\({}_{2}\), showing the hydrocarbon generation potential of the samples; and (**c**) plot of vitrinite reflectance versus depth evaluating the maturity of samples from the Shahejie Formation in the Huanghekou Depression. The steranes identified in the Shaheije Formation of the Huanghekou Depression were predominantly regular steranes, rearranged steranes, and 4-methylsteranes. However, the reason for the rearrangement of steranes remains largely unknown. Based on the monitoring of mass chromatograms (\(m/z\) 217), all samples exhibited similar characteristics in the distribution of steranes, primarily featuring the configuration of (20R) -5\(\alpha\)(H), 14\(\alpha\)(H), and 17\(\alpha\)(H). Among these, C\({}_{27}\) steranes had the highest relative content (0.09-0.74%), followed by C\({}_{29}\) (0.04-0.72%) and C\({}_{28}\) steranes (0.06-0.37%), indicating a trend of C\({}_{27}\) > C\({}_{29}\) > C\({}_{28}\) (Figure 4 and Table 3).