CO2 buildup drove global warming, the Marinoan deglaciation, and the genesis of the Ediacaran cap carbonates

What caused ocean/climate changes that drove Marinoan deglaciation, and the subsequent genesis of Ediacaran cap carbonates remains unclear. To address this issue, we examined the Hg records in Ediacaran cap carbonates from shelf to slope depositional settings in exposures from South China. These cap carbonates show higher total Hg (THg) concentrations (4.9 to 405 ppb), most of which are comparable to that observed in carbonates deposited during non-LIPs periods. The lack of THg/TOC anomalies in these cap carbonates suggests that background volcanic activity, rather than a short-term large igneous province event, drove the Marinoan deglaciation. The cap carbonates show positive Delta 199Hg values (0.18 to 0.34 %o) in slope settings and slightly negative to slightly positive Delta 199Hg values (-0.16 to 0.11 %o) in shelf settings, suggesting a binary mixing of seawater-and terrestrial-derived Hg in early Ediacaran Ocean. We infer that the accumulation of greenhouse gases, due to ongoing volcanic emissions of CO2 and enhanced release of gas hydrates, triggered global warming. This warming led to melting of sea ice cover, enhanced terrestrial inputs of alkalis (e.g., K+, Na+, Ca2+, Mg2+), and large-scale dissolution of atmospheric CO2 into seawater, driving widespread deposition of Ediacaran cap carbonates.

Automated summary

The specific causes of ocean/climate changes that led to Marinoan deglaciation and the genesis of Ediacaran cap carbonates are still unknown. This study examines the Hg records in Ediacaran cap carbonates from South China and suggests that background volcanic activity, rather than a short-term large igneous province event, drove Marinoan deglaciation. The study also reveals a binary mixing of seawater- and terrestrial-derived Hg in early Ediacaran Ocean, which could be due to ongoing volcanic emissions of CO2 and global warming. These findings are important for understanding climate changes in Earth's history.