## 4 Results and Interpretation
### Organic Geochemistry
#### 4.5.2 Hopanoids and Steroids  
In this study, the m/Z 191 mass chromatogram features are basically similar. The relative abundance of hopanes is higher than that of tricyclic terpen (Figure 8a-d). The C\({}_{29}\)/C\({}_{30}\) 17a (H) propane ratios of the samples are between 0.38 and 0.54 (average 0.46; Table 3). Previous studies have suggested that this is a typical feature of clastic source sedimentary rocks [29; 30]. As the molecular energy of Ts 18a(H)-trisnorhopane is higher than that of Tm 17a(H)-trisnorhopane, the stability of Ts is higher than that of Tm. With the increase in maturity, the value of Ts/(Ts + Tm) increases gradually [31]. The Ts/(Ts + Tm) values of the samples are between 0.46 and 0.89 (average 0.70), reflecting the high thermal maturity of the source rock (Table 4). Previous studies have also shown that with the increase in the organic matter maturity, the ratio of C\({}_{30}\) montane/C\({}_{30}\) hopane (C\({}_{30}\)M/C\({}_{30}\)H, moreatane/hopane) decreases from 0.8 to below 0.1 [16]. The C\({}_{30}\)M/C\({}_{30}\)H values of these samples are between 0.11 and 0.19 (average 0.14), reflecting a high thermal maturity (Table 4). The C\({}_{31}\)R/C\({}_{30}\)H propane ratio is used to distinguish marine and lake environments. The C\({}_{31}\)R/C\({}_{30}\)H propane ratios of organic matter in marine environments are generally higher than 0.25, but the ratio of organic matter in lake environments is generally lower [16]. The C\({}_{31}\)R/C\({}_{30}\)H propane ratios of the extracts from the Hengtongshan Formation range from 0.15 to 0.33 (average 0.22). According to the lithofacies results of the Hengtongshan Formation samples, the strata feature the characteristics of continental lakes, so the lake environment may have been invaded by sea water. The cross plot of the C\({}_{31}\)R/C\({}_{30}\)H propane ratio parameter and Pr/Ph ratio (Figure 9) supports this conclusion. Figure 8: The m/z 191 (**a–d**) and m/z 217 (**e–h**) mass chromatogram of saturated hydrocarbons of the Hengtongshan Formation samples in the Tonghua Basin. Figure 9: Hopane and isoprenoid ratios of the extracted oil samples, adapted from [16]. Gammacerane was initially considered to be a high-salinity indicator [32]. It is also thought to be related to increases in salinity in marine and lacustrine environments [21]. The gammaacreane index (GI=gammacerane/\(\alpha\)\(\beta\)C\({}_{30}\) propane) of the extracted samples of the Hengtongshan Formation reflects a high-salinity, reducing environment [16] (Figures 8a-d and 10). In this study, the m/Z 217 mass chromatogram of saturated hydrocarbons in 38 samples from the Hengtongshan Formation shows a series of distributions of diastereanes and steroids. Among these compounds are conventional steroids C27, C28 and C29, which are related to the source of the parent materials of organic matter (Figures 8e-h and 11; Table 4). Previous studies have found that the conventional steroids C\({}_{\text{27}}\), C\({}_{\text{28}}\) and C\({}_{\text{29}}\) are all specific to different sources of organic matter, and the relative proportions among them can be used to study the contribution of various types of organic matter in shale oil [33]. Figure 11: Ternary diagram of the relative proportions of steroids C27, C28 and C29 (the relationship between the organic matter input and the depositional environment [33]. Figure 10: Plot of the Gammacerane index and Pristane/Phytane of the extracted oil samples, adapted from [16]. The relative proportions of the steroids C\({}_{27}\), C\({}_{28}\) and C\({}_{29}\) (C\({}_{29}\): 33.70-60.9%, average 46.08%; C\({}_{28}\): 8.5-26.4%, average 21.07%; and C\({}_{27}\): 25.04-41.59%, average 32.67%; Table 4; Figure 11) were calculated in the Bengtongshan Formation.