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Salinized lacustrine shale (SLS) represents a frontier in the global quest for unconventional hydrocarbon resources. The impact of terrigenous input, which includes terrigenous organic matter (OM) and detrital matter, on the deposition and hydrocarbon potential of SLS is still controversial. Here, we examine this issue using the newly discovered SLS within the Paleogene Biyang Depression, employing a combination of organic petrographic and geochemical analyses. A high influx of terrigenous input (terrigenous OM and detrital matter) promotes the formation of SLS. On the one hand, terrigenous higher plants emerge as the primary source of OM in the SLS, as indicated by the dominance of terrigenous macerals (e.g., terrigenous liptinite) and the abundance of plant-derived biomarkers (e.g., tricyclic terpanes). Additionally, a portion of the OM may originate from bacteria. On the other hand, the rapid input of detrital matter improves the preservation of OM, resulting in the deposition of SLS with high total organic carbon (TOC) contents and low hydrogen index (HI) values. The findings of this study contribute to a deeper understanding of SLS deposition and provide guidance for regional hydrocarbon exploration. [ABSTRACT FROM AUTHOR]

Salinized lacustrine shale (SLS) represents a frontier in the global quest for unconventional hydrocarbon resources. The impact of terrigenous input, which includes terrigenous organic matter (OM) and detrital matter, on the deposition and hydrocarbon potential of SLS is still controversial. Here, we examine this issue using the newly discovered SLS within the Paleogene Biyang Depression, employing a combination of organic petrographic and geochemical analyses. A high influx of terrigenous input (terrigenous OM and detrital matter) promotes the formation of SLS. On the one hand, terrigenous higher plants emerge as the primary source of OM in the SLS, as indicated by the dominance of terrigenous macerals (e.g., terrigenous liptinite) and the abundance of plant-derived biomarkers (e.g., tricyclic terpanes). Additionally, a portion of the OM may originate from bacteria. On the other hand, the rapid input of detrital matter improves the preservation of OM, resulting in the deposition of SLS with high total organic carbon (TOC) contents and low hydrogen index (HI) values. The findings of this study contribute to a deeper understanding of SLS deposition and provide guidance for regional hydrocarbon exploration.

Salinized lacustrine organic-rich shale (SLORS) in the Paleogene has been considered as one of the most important shale oil reservoirs in China. Although deposition of the Paleogene SLORS in East China is generally concomitant with marine incursions, the influence of marine incursions on the algal-microbial community, paleoenvironment and shale oil potential of SLORS is still controversial. Here we examine this issue using a case of the Paleogene Biyang Depression (Nanxiang Basin) in East China, based on the integration of bulk geochemical, mineralogical, organic petrographic, biomarkers, elemental geochemical, and shale reservoirs analyses. Marine incursions were occurred during deposition of the SLORS in the Paleogene Biyang Depression as evidenced by the presence of marine organisms and marine-derived biomarkers (24- n -propylcholestanes). Lake transgressions, global sea-level rise, and extensional tectonic setting were responsible for the occurrence of marine incursions. The algal-microbial community change is associated with marine incursions, from dominance of green algae with a weak influence of marine incursions to dominance of red (brown) algae and coccolithophores with a strong influence of marine incursions, accompanied by enhanced bacterial activity. With the stronger influence of marine incursions, higher salinity, more reducing conditions, higher productivity, and lower detrital influx were present in the paleo-lake, resulting in the deposition of SLORS with higher shale oil potential, which was characterized by higher free shale oil contents, more abundant pores and fractures in nano- to micro-meter scale, and higher brittle mineral contents. In summary, our data suggest that marine incursions have a positive influence on the development of biodiversity in paleo-lakes, and the deposition of SLORS with high shale oil potential. Therefore, the influence of marine incursions should be fully considered during the palaeoecological reconstruction and the shale oil exploration of SLORS, especially during high sea-level stages. In addition, the results provide guidance for future profitable shale oil exploration in East China and other similar areas. • The occurrence of marine incursions was evidenced by multiple parameters. • The change of algal-microbial community was affected by marine incursions. • The influence of marine incursions on paleoenvironment was revealed. • Depositional model of SLORS influenced by marine incursions was established. • The marine incursions had a positive impact on the shale oil potential of SLORS. [ABSTRACT FROM AUTHOR]