Coevolution of the environment and life driving the Early Cambrian phosphogenesis in South China

Global phosphogenic events occurred during the Ediacaran−Cambrian transition, which coincided with dramatic marine environmental changes and the Cambrian Explosion. However, the interaction mechanisms of multiple spheres driving phosphogenesis during this critical interval remain poorly understood. To elucidate the links between environmental evolution, biological activity, and the oceanic phosphorus cycle, this study presents systematic petrographic observations and multiproxy geochemical analyses of the Early Cambrian (Fortunian Stage) phosphorites from the Yangtze Block, South China. The results demonstrate that the Fortunian phosphorites occur in two distinct lithological units. The lower unit formed under cold and arid climatic conditions with intense upwelling, with phosphorus mainly from deep seawater, whereas the upper unit records a warm and humid climate, accompanied by enhanced chemical weathering, decreasing upwelling intensity, and a shift toward a predominantly terrigenous phosphorus supply. The lower unit is characterized by an oxic water column overlying anoxic-ferruginous bottom waters, coupled with vigorous biological activity and high primary productivity, leading to phosphorus enrichment primarily through the biological pump. In contrast, the upper unit was deposited under a suboxic water column overlying anoxic-euxinic bottom waters, accompanied by decreased biological activity and low primary productivity, with phosphorus enrichment dominated by Fe-redox pumping. Synergistic variations in redox conditions, biological activity, and primary productivity promoted phosphorus enrichment. Sustained sea-level rise and volcanic activity likely accelerated the transformation of the sedimentary environment and drove the shift in phosphorus enrichment mechanisms from biological pump dominance to Fe-redox pumping dominance. This study elucidates the dynamic response of phosphogenesis to the coevolution of the environment and life during the Ediacaran−Cambrian transition.