Sedimentary environment and shale gas exploration potential of Lower Cambrian Niutitang Formation in northern Guizhou

The Lower Cambrian Niutitang Formation is one of the major marine carbonaceous shale horizons in southern China, which is widely distributed in northern, central and eastern Guizhou with stable horizons. The Niutitang Formation is mainly composed of black carbonaceous mudstone, which is thin-bedded and horizontally bedded. Its components are mainly clay minerals, quartz and a small amount of carbonaceous components and pyrite. Compared with the mean values of Australian Post-Archean Shale (PAAS), the contents of V, Mo, and U in the mudstone of Niutitang Formation are higher, while the contents of Co, Cu, Zn, and Th are lower. The content of AU, as well as the element content ratios of V/Cr, Ni/Co, U/Th, and V/(V+Ni) indicate that the sedimentary environment of the black mudstone in the Niutitang Formation is in a state of hypoxia reduction. The (La/Yb)_N ratio is significantly greater than 1, with a large degree of differentiation between light rare earth elements and heavy rare earth elements, indicating a low deposition rate. The TOC abundance of the mudstone in the Niutitang Formation is high, at the stage of high maturity to over maturity, with a high content of brittle minerals, and an effective thickness of approximately 30 to 100 meters. In conclusion, the black mudstone of the Niutitang Formation in northern Guizhou Province possesses good material conditions for the formation of shale gas reservoirs, indicating its promising potential for shale gas exploration.