The role of iron in the formation of Ediacaran 'death masks'

The Ediacara biota are an enigmatic group of Neoproterozoic soft-bodied fossils that mark the first major radiation of complex eukaryotic and macroscopic life. These fossils are thought to have been preserved via pyritic death masks mediated by seafloor microbial mats, though little about the chemical constraints of this preservational pathway is known, in particular surrounding the role of bioavailable iron in death mask formation and preservational fidelity. In this study, we perform decay experiments on both diploblastic and triploblastic animals under a range of simulated sedimentary iron concentrations, in order to characterize the role of iron in the preservation of Ediacaran organisms. After 28 days of decay, we demonstrate the first convincing death masks produced under experimental laboratory conditions composed of iron sulfide and probable oxide veneers. Moreover, our results demonstrate that the abundance of iron in experiments is not the sole control on death mask formation, but also tissue histology and the availability of nucleation sites. This illustrates that Ediacaran preservation via microbial death masks need not be a perfect storm of paleoenvironmental porewater and sediment chemistry, but instead can occur under a range of conditions.

Automated summary

In this study, the role of iron in the preservation of Ediacaran organisms is characterized through decay experiments. The results demonstrate that iron can contribute to the formation of death masks, but other factors such as tissue histology and the availability of nucleation sites also play a significant role. This suggests that Ediacaran preservation through microbial death masks can occur under a range of conditions, rather than being solely dependent on the abundance of iron.