| Abstract: | Oxygen is crucial for the origin and early evolution of eukaryotes. However,the oxygen levels in the atmosphere and shallow ocean of Mesoproterozoic have been poorly constrained,with varying viewpoints including persistent low(equals to <0.1%~1% of the present atmosphere level,PAL),relatively high(>4%~8% of PAL),and dynamic variation. In order to further constrain the redox conditions in shallow waters where eukaryotes inhabited,the Ce anomaly of the peritidal carbonates from lower Member 4 of the Mesoproterozoic Wumishan Formation in North China was investigated. The results show that the significant negative Ce anomalies(Ce/Ce*=0.82±0.11,n=10)occurs in the carbonate of the lower Member 4 of the Wumishan Formation with the thickness of about 150 m. The carbonate formation with the significant negative Ce anomaly is interlayered between the carbonates with inconspicuous positive Ce anomalies,which may represent a pulsed oxygenation in shallow seawater with a duration of ~5 Ma(~1480-1475 Ma). It reflects that the redox conditions of Mesoproterozoic shallow seawater fluctuated greatly rather than stable at low or relatively high level of oxygen. The results are helpful to determine the evolution of redox state of the Mesoproterozoic shallow sea,and it provides important information for studying the influence of redox state of seawater on the evolution of early eukaryotes. |
