EDIACARAN SOFT-BODIED PRESERVATION BY MICROBE-PARTICLE INTERACTIONS

The terminal Neoproterozoic Ediacaran period is typified by the Ediacara biota (ca. 575-542 Ma), which includes the first morphologically-complex macroscopic organisms in Earth history. Both the taphonomic setting that promoted the preservation of the soft-bodied Ediacara biota in coarse-grained sediments, and the influence of microbial coatings on this process, have generated much debate. Several specimens of Ediacaran discs (Aspidella) from the Fermeuse Fm. of Newfoundland, Canada, were analyzed under Environmental-SEM, revealing the relationship between the fossil specimens and the casting sediment. The presence of chemically distinct (Al-Mg-Fe-Ti-K and to a lesser extent S-rich), finer-grained sediment surrounding the upper and lower margins of the Si-rich Ediacaran fossils is highly consistent with elemental analyses of well preserved bacterial biofilms and suggests that a bacterial biofilm promoted their preservation. Furthermore, Ediacaran discs were likely entombed within a bacterial extracellular polymeric substance (EPS) during life, which added structural stability to these frond holdfasts. Our analysis confirms the importance of microbially-mediated preservation in Fermeuse-type Ediacaran preservation, provides an explanation for the dominance of Aspidella holdfasts in these taphonomic settings, and provides an ecological explanation for the biased preservation of Aspidella in Fermeuse-style preservation around the world.