## 5 Discussion  
### Source Rock Evaluation  
The evaluation of hydrocarbon source rocks is dependent upon three key factors: organic matter abundance, kerogen type, and organic matter thermal maturity [31, 45, 57, 58, 59, 60, 57]. It should be noted that the field samples are susceptible to the natural environment, which may affect the results of the experimental analyses. Nevertheless, the overall TOC distribution trend is largely consistent with the core data, with the majority of values situated between 0.5% and 1.0%, followed by the 1.0% to 2.0% interval (Figure 10(a)). In accordance with the hydrocarbon source rock evaluation criteria [51], the muddy hydrocarbon source rocks of P1-2\(q\) in the piedmont of southwestern Tarim Basin are deemed to be fair-good hydrocarbon source rocks (Figure 10(b)). The overall Tmax values of P1-2\(q\) hydrocarbon source rocks are notably elevated, with the majority exceeding 490 \({}^{\circ}\)C or falling between 455 \({}^{\circ}\)C and 490 \({}^{\circ}\)C (Figure 9(a)). The kerogen exhibited a dark coloration, with minimal or no fluorescence observed from the vitrinite (Figure 12). It can be concluded that P1-2\(q\) hydrocarbon source rocks have reached  
Figure 11: TOC distribution (**a**) and plot of TOC vs. S1 + S2 (**b**) of Permian Qipan Formation source rocks in the piedmont southwestern Tarim Basin. Figure 10: TIC, \(m/z\) 191, and \(m/z\) 217 mass chromatograms of the Permian Qipan Formation in the piedmont southwestern Tarim Basin. (**a**) Sample from Qipanqucrop section; (**b**) sample from Qimeigan outcrop section. a mature stage, with the organic matter having undergone a high level of evolution. The hydrocarbon-generating parent material of the P1-2\(q\) Formation muddy hydrocarbon source rock in the Well Qiatan-1 is algae and amorphism (Figure 9), and the type of organic matter is Type I. The microcomponents of P1-2\(q\) argillaceous hydrocarbon source rocks in Qimeigan section are only observable as vitrinite. The organic matter is derived from higher plants. The muddy hydrocarbon source rock of P1-2\(q\), which was drilled in the Well Qiatan-1, was developed from a marine environment. The hydrocarbon-generating parent material was algae and amorphous (Figure 10), and the organic matter type was I-II1. Conversely, as a consequence of the late Permian sea retreat, the southwest depression gradually became an inland basin, and the region developed a deltaic phreatic zone with a sea-land transition environment. Moreover, the majority of the organic matter in the samples of P1-2\(q\) in the Qimeigan section were derived from land-sourced clastic material. Isotopic analyses of kerogen carbon in samples from P1-2\(q\) in Qimeigan section indicated a range of \(-\)21.6% to \(-\)23.5%, with the organic matter type identified as Type III. The distribution of saturated hydrocarbon n-alkane peak shapes, the number of main peak carbons, and the content of C27 to C29 rule sterane in biomarker compounds, which are organic compounds that can be used to identify the type of organic matter present. Among the sterane compounds, the principal sources of C27 steranes are algae and plankton, while C29 steranes are derived from algae or terrigenous higher plants [56]. The ortho-alkane peak shapes of the mud hydrocarbon source rocks of P1-2\(q\) are all single peaks, with a reduction in the high-carbon fraction after n-C23. This suggests that the source of organic matter is likely to be lower planktonic organisms. The asymmetric 'V' arrangement of the C27-C29 regular steranes indicates that the hydrocarbon parent material is predominantly derived from algae or aquatic organisms, with varying degrees of mixing with organic matter of terrestrial origin. The organic matter types of the muddy hydrocarbon source rocks of P1-2\(q\)  
Figure 12: Representative photomicrographs for hydrocarbon source rocks of Permian Qipan Formation in the piedmont southwestern Tarm: (**a–f**) Hydrocarbon source socks from the Qimeigan section. (**g**) Hydrocarbon source socks from the Akeqi section.