Rapid recovery of Ediacaran oceans in the aftermath of the Marinoan glaciation

Abstract. The termination of Cryogenian glaciations would have undoubtedly impacted the chemistry of Neoproterozoic oceans, with possible consequences for life; but the extent and duration of this impact are poorly constrained. In this study, we use the lithium (Li) isotope composition of Ediacaran cap dolostones from South Australia (Nuccaleena Formation) and China (Doushantuo Fm) to investigate changes in ocean chemistry that followed the Marinoan deglaciation. The effect of diagenesis was evaluated and while the Nuccaleena Fm is likely to have preserved the primary composition of cap dolostone deposition, the offset in Li isotope ratios observed for the Doushantuo Fm could possibly reflect partial overprinting by diagenetic fluids. The Li isotope composition of Ediacaran seawater was estimated and we suggest it was similar to that of late Cenozoic oceans for most of the cap dolostone deposition. Using a box model for the oceanic Li cycle, we show that at the onset of deglaciation, the supply of riverine Li to the oceans was up to 50 times the modern flux. The modelled riverine Li isotope composition suggests that continents resembled modern high-latitude regions during this time. This episode was short-lived (up to 1 Myr) and the subsequent supply of riverine Li was similar to modern conditions, both in flux and isotope composition, for the whole duration of cap dolostone deposition. These results suggest that Ediacaran oceans and continents rapidly recovered from the Marinoan glaciation to reach environmental conditions similar to the late Cenozoic. From the standpoint of the Li oceanic budget, the Ediacaran oceans in which complex lifeforms emerged may have not been that different from our modern oceans.