Geochemical Characteristics and Geological Significance of Shale in Wufeng-Longmaxi Formations of Hefeng In Western Hunan-Hubei Underwater Uplift

To elucidate the sedimentary environment and provenance background of the Wufeng–Longmaxi Formation in the Shuiquan area of Hefeng, Hubei Province, geochemical analyses were conducted on samples collected from an observed profile. The results indicate that the sedimentation of the Wufeng Formation occurred under predominantly cold and dry climatic conditions, whereas the Longmaxi Formation was characterized by a warm and humid climate. The ratios of Ba/Al and Ba(bio) suggest that the ancient productivity at the base of the Longmaxi Formation was relatively high. During its deposition, the Wufeng Formation experienced an oxidizing to sub-oxic environment, while the Longmaxi Formation exhibited an overall sub-oxic environment. Variations in rare earth elements indicate that the sedimentation rate of the Wufeng Formation was higher than that of the Longmaxi Formation; however, a layer with a significantly slow sedimentation rate is present at the base of the Longmaxi Formation; According to the U/Mo covariance model, the sedimentary environment of the Longmaxi Formation is characterized by a strong retention of water bodies. The characteristics of trace elements and rare earth element compositions and their ratios indicate that the material sources primarily originate from the upper crust, exhibiting a relatively homogeneous source with the main parent rock being felsic granite. The tectonic background of the source area is predominantly characterized by an active continental margin, while also displaying some features typical of continental island arcs.