Abstract: Large accumulations of phosphorite in the Ediacaran worldwide witnessed the second phosphogenic event in the Earth
history. However, there is no generally acknowledged geochemical model for this event so far. Given that precipitation of phosphate is
controlled by seawater redox conditions, explore the cause-and-effect relationship between the phosphorite deposits and seawater
chemistry is critical to testify the model of sedimentary geochemistry. This can help to understand the large scale phosphorite deposits
worldwide across this transitional time interval. In this study, the REE+Y data of phosphorite-associated carbonates from different
facies demonstrate that the Doushantuo phosphorites were deposited in suboxic conditions with intermittent oxidization. The redox
condition of the Ediacaran seawater was unstable and the redox boundary dynamically fluctuated from shallow to deep water conditions.
This greatly increased the space and opportunity for the deposition of phosphorite, leading to the great phosphogenic event during the
Ediacaran-Cambrian transition.

Key words: South China, Ediacaran, phosphorite, REE, redox