Sedimentary Environment and Organic Matter Enrichment of Lower Cambrian Niutitang Shales in Fenggang Area, Northern Guizhou: A Case Study of Well YF1.

The purpose of this research was to examine the paleoenvironment, hydrothermal activity, and restriction water condition of the Lower Cambrian Niutitang Formation shale gas reservoir in northern Guizhou and analyze the controlling factors for organic matter enrichment. This investigation is based on the geochemical analyses of the total organic carbon (TOC) and major and trace elements from drill core samples of YF1 Well in Fenggang Area, Northern Guizhou. TOC of the Niutitang Formation is mainly distributed between 0.21 and 2.47%. Redox environment indicators (such as V/(V + Ni), V/Cr, and Mo vs U) suggest an anoxic-reducing sedimentary background; water restriction condition indicators (Mo/TOC and Mo-TOC) reveal weakly to moderately restricted water body characteristics; terrigenous debris indicators (Ti/Al and CIA) indicate a gradual increase in terrigenous input under the context of weak chemical weathering; hydrothermal activity indicators (Sr/Ba and Co × Mn) disclose moderate-to-strong hydrothermal influence and weak upwelling influence; and paleoproductivity indicators (biogenic Ba (Ba), biogenic Ni (Ni), and P/Ti) collectively point to high biological productivity. Thus, nutrients introduced by hydrothermal activity establish the material basis for high biological productivity, anoxic-sulfidic environments and weakly to moderately restricted water bodies collectively inhibit organic matter decomposition, and enhanced terrigenous input promotes organic matter sedimentation and preservation. These factors jointly constitute an integrated control framework for organic matter enrichment.