Elevated Phosphorus Concentrations in Shallow Oceans as a Trigger for the 1.57-Ga Oxygenation Event

Abstract

Enhanced continental phosphorus (P) input into the oceans has been proposed as a potential trigger for the 1.57 Ga oxygenation event; however, uncertainty remains due to the absence of direct evidence for seawater P concentrations. Here, we investigate shallow marine carbonate rocks of the Gaoyuzhuang Formation in the North China Platform, using the carbonate-associated phosphate (CAP) proxy to directly reconstruct seawater P levels at that time. Two significant CAP/(Ca + Mg) increases correspond with rises in I/(Ca + Mg) during the oxygenation event suggesting that elevated seawater P concentrations were important in triggering the oxygenation event. Furthermore, a concurrent positive shift in ε_Nd(t) values from −12.3 to −0.9 suggests that a transition in weathering source rocks from intermediate to mafic lithologies significantly contributed to the elevated P fluxes to the oceans during the oxygenation event. This study provides new insights into assessing seawater P levels and their role in the mid-Proterozoic oxygenation events.