Deep-Water Traction Current Sedimentation in the Lower Silurian Longmaxi Formation Siliceous Shales, Weiyuan Area, Sichuan Basin, China, Using Nano-Resolution Petrological Evidence

Despite the shale revolution triggering global shale oil and gas exploration, our understanding of the sedimentary environments of deep-water organic-matter-rich shale remains unclear. Hence, we analyzed the sedimentary environment and facies of some siliceous shales at the bottom of the Longmaxi Formation in the Weiyuan area of the Sichuan Basin, China. Nano-resolution petrological characterization and genesis analysis of the siliceous shales were conducted using the nano-resolution petrologic image datasets. We identified these siliceous shales as the microbial mats formed by the deep-water traction current sedimentation. The microbial mat's formation and burial diagenesis processes were divided into seven stages. The silt-grade bioclastic beach deposits initially, colonizing the mud-grade siliceous microbes and forming the siliceous microbial mat. Subsequently, the carbohydrate-rich microbes thrive in sediment voids, forming the carbohydrate-rich microbial mat. Additionally, SOM undergoes the four stage of burial diagenesis process, progressing from the kerogens to the pre-oil bitumen generation and ultimately transforming into the porous pyrobitumen and the nonporous pyrobitumen. The study deepens the understanding of the deep-water traction current sedimentation and has implications for guiding shale gas exploration and development.