The first member of the Qingshankou Formation (Qing Member 1) is rich in oil and gas resources and represents the first lacustrine transgression period, during which the lake basin area reached its maximum. This study utilizes major and trace element analyses, along with pyrolysis, to investigate the sedimentary environment and mechanisms of organic matter enrichment in the hydrocarbon source rocks of the Heiyupao Depression Qing Member 1. The results indicate that the hydrocarbon source rocks in this area exhibit good to excellent organic richness, mainly comprising Type I and Type II₁ organic matter, and are at a high stage of maturity. Furthermore, the paleoclimate conditions during the Qing Member 1 period in the study area were characterized by a warm and humid climate, with an open lake basin and freshwater to brackish water conditions. The water was low in oxygen, suboxic to anoxic, and had relatively high primary productivity. Multiple marine transgressions occurred during the Qing Member 1, transporting substantial nutrients into the lake, which promoted algal blooms in the water. The correlation analysis of TOC content in the Qing Member 1 shale and various indicators shows that the enrichment of organic matter in the study area is primarily influenced by paleoproductivity and paleosalinity, while paleoclimate, paleoredox conditions, and paleowater are not the main controlling factors for organic matter enrichment in the area. Organic matter only accumulates under relatively high salinity and paleoproductivity conditions. Event-driven marine transgressions also play an essential role in enhancing paleoproductivity. Therefore, the organic matter enrichment model in the study area is more aligned with a productivity-driven model. Finally, a comprehensive organic matter enrichment model of hydrocarbon source rocks in the Qing Member 1 of the Heiyupao Depression is proposed.

The Late Permian was a critical interval in geological history, during which dramatic changes occurred in the Earth’s surface system, and a set of black rock series rich in organic matter and silicon, the Dalong Formation, was deposited in the northeastern Sichuan Basin. We conducted a detailed sedimentological and petrological investigation integrated with (major and trace) element contents in the deep-water sequence of the Xibeixiang and Jianfeng sections. It demonstrates the source of silicon, tectonic background, and sedimentary environment of the Dalong Formation, and explores the influence of hydrothermal activities on organic matter enrichment. The results show that the upper part of the Dalong Formation contained more radiolarians in the Xibeixiang section compared to the Jianfeng section. Hydrothermal proxies such as Eu/Eu*, Al-Fe-Mn diagram, Al/(Al + Fe + Mn), and Lu_N/La_N suggest a biotic origin for the chert in the Dalong Formation in the Xibeixiang and Jianfeng sections, while the Xibeixiang section was slightly affected by hydrothermal activities. The La-Th-Sc diagram and the La/Sc and Ti/Zr crossplots point to a continental island arc and active continental margin origins for the Xibeixiang and Jianfeng sections. Combined with previous research, the silicon of the Dalong Formation in the northeastern Sichuan Basin is mainly derived from biological sources. The Xibeixiang section was affected by a small amount of hydrothermal fluid due to its proximity to the Paleo-Tethys Ocean and continental island arcs. Furthermore, the enrichment of organic matter was predominantly driven by high productivity, with minimal impact from hydrothermal activities. These insights hold significant research value and practical implications for shale gas exploration in the Sichuan Basin.

Strategic breakthroughs have been made in the exploration and evaluation of Gulong shale oil in the Songliao Basin. However, the Heiyupao Depression, located near the Gulong Depression, hosts a thick section of the Qingshankou Formation shale that has not been extensively studied. This paper presents novel insights into the lithofacies characteristics, depositional environment, and reservoir features of the Qingshankou Formation shale in the Heiyupao Depression, with a specific focus on the origin and maturation of organic-rich shale. Four core wells were drilled, and 152 core samples were analyzed through a variety of techniques, including rock type classification, mineral composition, TOC content, rare earth elements, rock pyrolysis, organic matter type determination, and CT scanning. Results indicate that the Qingshankou shale is dominated by felsic compositions and Type I kerogen, with organic maturity varying across the section. Based on lithology, sedimentary structures, mineralogy, and organic matter abundance, five distinct lithofacies are identified: high-organic mud-rich felsic shale, high-organic sand-rich felsic shale, medium-organic sand-rich felsic shale, medium-organic massive shale, and low-organic sand-rich felsic shale. Notably, the Type A lithofacies (high-organic mud-rich felsic shale) is identified as a primary source rock due to its intergranular and organic matter pores, albeit with low porosity and poor connectivity. In contrast, the Type E lithofacies (low-organic sand-rich felsic shale) have high porosity, well-developed micro- and nano-scale pores, and strong connectivity, marking them as the primary reservoirs. The characteristics of this region differ significantly from those of Gulong shale oil, requiring different extraction strategies. The mineral composition of such shale is predominantly felsic rather than mixed. The findings not only provide theoretical support for the exploration of complex lacustrine shale in the Songliao Basin but also offer valuable insights for the resource development of similar non-marine shale systems worldwide.