Abstract:Phosphorus is one of the key nutrient elements, which are well associated with sedimentary environment and life evolution. Widespread depositions of phosphorites are coeval with the radiation of skeletonized animals during the Ediacaran-Cambrian transition in South China and global elsewhere, suggesting the good bridge of phosphorus between the sedimentary environment and life evolution. However, sedimentary environment and forming mechanism of phosphorites remain elusive. In order to explore these problems, we conduct aggregation form of phosphate, pyrite morphology, and the composition of rare earth elements (REE) of phosphorites during the early Cambrian Meishucun profile, South China. Our results show that phosphorites are mainly composed of crystalline calcium fluorophosphates, cryptocrystalline calcium fluorophosphates, and iron oxides. The distribution of REE belongs to “hat type” mode, similar to that in the pore-water ferruginous-manganous zone, suggesting that REE is significantly affected by early diagenesis. The absence of framboid pyrite and relatively low Ce/Ce* (0.50~0.82, average 0.70), suggesting that phosphorites are deposited under oxic/dysoxic conditions. The lacking of Eu abnormality (0.92~1.08, average 0.98), indicating phosphorites are not influenced by hydrothermal activity. High Y/Ho ratios of 55.3~74.5 (average 63.6) similar to those of seawater reflect that phosphate is originated from seawater. In combination with widespread oceanic oxygenation, anoxic stratified ocean structure, and intensive upwelling, we infer that phosphorites result from high oceanic phosphate concentrations associate with oceanic oxygenation event and the large fluxes of enriched phosphate contents in reducing deep waters to oxic/dysoxic surface waters by intensive upwelling.