Paleoceanographic environment synergistic controls on V-U enrichment in Early Cambrian marine shales from the Yangtze Block

• In-situ S isotopes and pyrite morphology constrain V-U enrichment conditions • V-U enriched under euxinic, high productivity, low salinity, warm-humid condition in semi-restriction basin. • Key factors for V-U enrichment include oxygen depletion, material supply, OM preservation, microbial activities, and terrigenous flux. Vanadium-uranium enrichment in marine shales has been extensively documented. However, the synergistic controls on the enrichment under various paleoceanographic conditions remain poorly understood. The Early Cambrian marine shales in the Lower Yangtze Block represent a typical vanadium-uranium rich stratum, providing an ideal subject to address this knowledge gap. To elucidate the paleoceanographic controls on vanadium-uranium enrichment, we conducted an integrated multi-proxy investigation of the Early Cambrian Hetang Formation, combining sedimentary sequence analysis, petrographic observations, whole-rock geochemistry, and in-situ sulfur isotopes. Results suggest that vanadium and uranium are preferentially enriched in a euxinic, semi-restricted basin characterized by high paleoproductivity, low salinity, and a warm-humid paleoclimate. The euxinic conditions were crucial for the reduction and precipitation of vanadium-uranium. A semi-restricted basin configuration helped maintain redox stratification and moderate hydrographic exchange, which ensured a sustained elemental supply and their subsequent preservation. Sea-level fluctuations, in conjunction with high paleoproductivity, governed the accumulation and preservation of organic matter, which in turn enhanced vanadium-uranium enrichment via adsorption and complexation. Furthermore, reduced salinity likely promoted microbial activity and adsorption capacity, while a warm and humid paleoclimate boosted both productivity and terrigenous flux. These factors acted in concert to ultimately determine the degree and distribution patterns of vanadium and uranium enrichment. This understanding provides crucial insights into the differential enrichment of redox-sensitive elements in marine basin systems.