Polycyclic aromatic compounds in crude oil as proxies for Permian Tarim large igneous province activities

Large igneous provinces (LIPs), a critical area in Earth science, are closely related to paleoenvironmental evolution and biodiversity. The Permian Tarim large igneous province (TLIP) provides an ideal laboratory for correlational research. Previous reports show that the TLIP formed ∼300–262 Ma. Based on igneous lithology and the upper limit of single magmatic activity (<5 Ma), the TLIP can be divided into five main magmatic episodes. Core logging, seismic sections, lithofacies observations, and in-situ calcite U-Pb dating indicate diabase intrusions and a hydrothermal upwelling event (∼295.9–273 Ma) resulted from TLIP magmatic activity. The results indicate that polycyclic aromatic compounds (PACs) in oil are powerful proxies of magmatic intrusion and hydrothermal activity in the Permian TLIP. The existing diabase intrusion (EDI) samples show a higher concentration of high-molecular-weight (HMW) PACs (≥5-ring PACs) and greater combustion-derived PAC ratios. The distribution coupling between the diabase intrusion and PACs indicates that the HMW PACs are mainly derived from the cycloaddition reactions by the pyrogenic source (i.e., diabase intrusion). The conversion of phenanthrene (Phe), biphenyl (Bp), and dibenzothiophene (DBT) series compounds indicates that the oil is altered by hydrothermal activity. The hydrogenium and sulfur carried by the hydrothermal upwelling process promote the heteroatom incorporation of PACs. The cycloaddition and heteroatom incorporation reactions of PACs during the formation of LIPs offer a new perspective for evaluating their impact. PACs serve as effective proxies for LIPs and may also contribute to biological crises associated with LIPs.