Sedimentary environments and lithofacies characteristics of fine-grained sediments in typical continental basins in China

The sedimentary environments of fine-grained sediments and the spatio-temporal distribution patterns of the fine-grained lithofacies are identified as primary factors governing the enrichment and high yield of shale oil. Starting from previous relevant studies, we investigate the sedimentary environments and primary characteristics of fine-grained sediments in typical continental basins in China, including the Songliao, Bohai Bay, Ordos, and Junggar basins. The findings suggest that: (1) Fresh-to-brackish-water lacustrine basins typically contain claystones, siltstones, and transitional lithologies between them, showing the presence of silty, clayey, and organic laminae. In contrast, the lagoon and saline lakes mostly develop fine-grained carbonate rocks and mixed fine-grained sedimentary rocks, characterized by calcite (dolomite) laminae and the laminae of clayey marls. (2) Different evolutionary stages of continental basins developed the occurrence of varying assemblages of fine-grained lithofacies. Fine-grained sedimentary rocks formed during rifting are characterized by lithofacies assemblages rich in carbonate minerals, while organic-rich shale layers formed during depression are dominated by the assemblage of feldspathic and clayey sedimentary rocks. (3) Primary mechanisms for shale deposition in lacustrine basins include suspension settling, aeolian input, turbidity flows, hyperpycnal plumes, and muddy debris flows. (4) Continental shale oil in China exhibits diverse types. It boasts abundant resources in the Mesozoic-Cenozoic continental basins such as Songliao, Ordos, Junggar, and Bohai Bay basins serving as important targets for shale oil exploration and exploitation. (5) Future research on the sedimentary settings and lithofacies of fine-grained sediments should be focused on astronomical cycles to establish systematic and effective parameters and criteria for identifying paleosedimentary environments. Furthermore, it is essential to develop classification schemes and sedimentary models for the fine-grained sedimentary lithofacies of shale, interbedded, and mixed types in continental basins to effectively predict the spatio-temporal distributions of these lithofacies. Physical and numerical simulations of the sedimentary origin and processes of fine-grained sediments are recommended to examine the sediments' coupled physical, chemical, and biological depositional processes, as well as its formation and development mechanisms. Additionally, it is necessary to pay attention to data integration, in-depth data mining, artificial intelligence (AI), big data, and computer aided technology to investigate the distribution patterns of fine-grained sediments.