## 4 Results and Discussion
### Geochemistry Features as Indication for Organic Matter Input and Depositional Conditions
#### 4.2.1 Depositional Environment
They discovered that the higher plant samples are located close to the C\({}_{29}\) corner, whereas the plankton samples are situated closed to the C\({}_{27}\) corner. The equivalent regions in the triangle's center are home to the gulf, bay, and terrigenous sediments, which receive organic inputs from plankton and/or higher plants (Figure 7). C\({}_{29}\) regular sterane accounted for a relatively large proportion of the samples selected in this study. The C\({}_{29}\)% value of the coal sample is 56.1%. The C\({}_{29}\)% value of carbonaceous mudstone samples is 37.0%-63.6%, with an average of 50.4%. C\({}_{29}\)% in dark mudstone samples ranges from 33.5% to 68.3%, with an average of 44.3%. The depositional environment of samples is mainly a terrestrial and shallow water environment, as shown in Figure 7.  
Figure 5: Relationship between TS and TOC for coal-measure source rock. Terpane parameters are also commonly used as biomarker parameters to characterize the depositional environment. For example, gammacerane is a sign of stratification of a depositional water body [39], and its ratio to C\({}_{30}\) propane can usually characterize the salinity of a water body [40; 41]. The gammacerane index (GI = Ga/C\({}_{30}\)H) of coal-measure source rock samples is generally low, and because the environmental water body formed by coal-measure source rocks is shallow and turbulent, and the possibility of water stratification is small, only some dark mudstone samples can identify gammacerane. The gammacerane index is between 0.07 and 0.28, with an average of 0.19 (Table 1). The lower gammacerane index indicates the low salinity freshwater depositional environment, which is the same as the above conclusion. Dibenzothiophene (DBT) and phenanthrene (P) in aromatic hydrocarbon parameters can indicate the depositional environment. The DBT/P ratio combined with the Pr/Ph ratio can divide the depositional environment and lithology of source rock samples, which is an effective parameter to distinguish marine and continental source rocks. [PERSON] et al. Figure 6: Cross-plot of Pr/nC\({}_{17}\) vs. Ph/nC\({}_{18}\) for coal-measure source rocks (after [PERSON] et al., 2006 [36]). Figure 7: Ternary plot of regular steranes, showing the normalized abundance of C\({}_{27}\), C\({}_{28}\) and C\({}_{29}\) sterane isomers and their depositional facies (after [PERSON] and [PERSON], 1979 [37]). (1995) [42] developed a practical approach for determining the depositional environment of crude oil and source rocks by combining the ratios of dibenzothiophene (DBT) to phenanthrene (P) and pristane to phytane. It is widely accepted that marine source rocks have high DBT values and low phenanthrene content, while continental source rocks have low DBT values and high phenanthrene content. The DBT/P ratio of coal-measure source rock samples is very low, all lower than 0.1, with an average of 0.05 (Table 1). Figure 8 shows that all of the source rock samples were deposited in a continental environment, mostly a lacustrine environment with little sulfur.