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. 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, were therefore analyzed. Nano-resolution petrological characterization and genesis analysis of the siliceous shales studied were conducted using nano-resolution petrologic image datasets. We identified these siliceous shales as microbial mats formed by deep-water traction current sedimentation. The microbial mats’ formation and burial diagenesis processes were divided into seven stages. The silt-grade bioclastic carpet deposits initially, colonizing mud-grade siliceous microbes and forming the siliceous microbial mat. Subsequently, carbohydrate-rich microbes thrive in sediment voids, forming the carbohydrate-rich microbial mat. Additionally, SOM undergoes four stages of burial diagenesis process, progressing from kerogens to pre-oil bitumen generation and ultimately transforming into porous pyrobitumen and nonporous pyrobitumen. This study will improve the understanding of deep-water traction current sedimentation and has implications for guiding shale gas exploration and development.