Origin and Hydrocarbon Generation of γ-Alkylbutyrolactones in Permian Shales

The Lucaogou Formation in the Santanghu Basin is notable for its abundance of oxygen-containing compounds, especially the γ-alkylbutyrolactone series (GBLs), which were detected for the first time in the shales. However, the origin and geological significance of these compounds in sediment are unclear. In this study, source rock samples from the Lucaogou Formation in the Santanghu Basin were collected and classified into two categories (high-GBL content (Group H); low-GBL content (Group L)) based on gas chromatography–mass spectrometry. The biomarker results indicate that the medium-chain n-alkanes in Group H are more enriched. In addition, the source rocks of both Group H and Group L were formed in a reducing and salinized sedimentary environment. The Rock-Eval pyrolysis results indicate that Group H has high organic matter abundance and organic matter types of I–II1, illustrating the contribution of submerged algae, whereas Group L has low organic matter abundance and organic matter types II2–III. Based on the above results, the GBLs exhibit typical biogenic characteristics and is likely to originate from specific submerged algae. Thermal simulation experiments further confirm that Group H has a greater hydrocarbon generation. Combined with gas isotope evidence, these findings show that the high abundance of GBLs compounds is effectively preserved during the formation of excellent source rocks and promotes the formation of petroleum.