Microbial biofilms and the preservation of the Ediacara biota

Abstract

Laflamme, M., Schiffbauer, J.D., Narbonne, G.M., & Briggs, D.E.G. 2011: Microbial biofilms and the preservation of the Ediacara biota. Lethaia, Vol. 44, pp. 203–213. The terminal Neoproterozoic Ediacaran Period is typified by the Ediacara biota (ca. 579–542 Ma), which includes the first morphologically complex macroscopic organisms. Both the taphonomic setting that promoted the preservation of the soft‐bodied Ediacara biota in coarse‐grained sediments, and the influence of associated microbial coatings on this process, have generated debate. Specimens of Ediacaran discs (Aspidella) from the Fermeuse Formation of Newfoundland, Canada, were analysed using environmental scanning electron microscopy (ESEM) and focused ion beam electron microscopy (FIB‐EM) to determine the relationship between the fossil specimens and the surrounding sediment. The presence of chemically distinct (Al–Mg–Fe–K‐ and to a lesser extent S‐rich), finer‐grained sediment (with organized iron sulphides) surrounding the upper and lower margins of the Ediacaran fossils is consistent with elemental analyses of well preserved bacterial biofilms from other localities. ESEM analyses reveal a contrast in the composition of the sediment bound within the discs, which contains a higher concentration of Al, Ca and K, and the purer Si‐rich sediment that forms the surrounding matrix. This suggests that the coarse grained sediment was incorporated into the organism during life. Ediacaran discs were likely surrounded by a bacterial biofilm or thin microbial mat composed primarily of extracellular polymeric substances (or exopolysaccharide) during life, which added structural stability to these frond holdfasts, and facilitated their fossilization. Microbially mediated preservation in Fermeuse‐style Ediacaran taphonomy provides an explanation for the dominance of Aspidella holdfasts in these settings, and suggests that preservation of Ediacaran fossils in the round may be much more prevalent than previously recognized. We suggest that the overwhelming dominance of circular to bulbous forms such as Aspidella in Ediacaran biotas around the world is a direct result of the interplay between microbial ecology and microbially mediated taphonomy. □Aspidella, Ediacaran preservation, environmental scanning electron microscopy, focused ion beam electron microscopy, palaeoecology, taphonomic bias.

Exceptionally preserved fossil assemblages through geologic time and space

“…kerogen) and/or soluble carbonaceous materials (Cai et al, 2012;Schiffbauer et al, 2014b;Stankiewicz et al, 2000), as observed in carbonaceous compressions (Xiao et al, 2002), small carbonaceous microfossils (Butterfield and Harvey, 2012), and organically preserved skeletal fossils . Non-biomineralized tissues are also sometimes preserved in siliciclastic rocks as casts, molds, and impressions (Gutiérrez-Marco and García-Bellido, 2015;Muscente and Allmon, 2013), such as Ediacara-type fossils (Laflamme et al, 2011;Narbonne, 2005).…”

“…Overall, the trend broadly follows the prolonged oxygenation of the ocean-atmosphere system (Gill et al, 2011; and the protracted development of the sediment mixed layer (Tarhan et al, 2015), the zone of sediment homogenized and fluidized via bioturbation by burrowing animals, in the early Paleozoic. These changes in marine environments affected exceptional preservation by promoting scavenging of buried carcasses (Allison and Briggs, 1993); enhancing the seawater concentrations of O 2 and SO 4 2 − used in the main microbial metabolisms of decay (Canfield and Farquhar, 2009;Tarhan et al, 2015); deepening the sedimentary aerobic and sulfate reduction zones in which soft tissues are most aggressively degraded Schiffbauer et al, 2014b); and reducing the prevalence of microbial mats, which facilitate authigenic/diagenetic mineralization by sealing fossils off from oxic or suboxic bottom waters (Gehling, 1999;Laflamme et al, 2011) and preventing efflux of precipitating geochemical species (Callow and Brasier, 2009;. Collectively, these changes impacted the likelihood of organic remains surviving long enough to undergo authigenic/diagenetic mineralization prior to their destruction.…”

Preservation in microbial mats: mineralization by a talc-like phase of a fish embedded in a microbial sarcophagus

“…First, microbial communities can remodel sediments, generating rare but clearly distinguishable features that have been named microbially-induced sedimentary structures (MISS, Gerdes et al, 1993;Hagadorn and Bottjer, 1997;Noffke et al, 2001;Noffke, 2009). MISS have favored preservation of body impressions or the formation of death masks, such as those found in the Ediacaran period (Gehling, 1999;Narbonne, 2005;Laflamme et al, 2011), or footprints of Late Jurassic sauropods (Marty et al, 2010). In addition, the frequent association of bacterial cells with exceptionally preserved fossils supports the link between fossilization and microbial mats.…”

Nanoscale analysis of pyritized microfossils reveals differential heterotrophic consumption in the ∼1.9-Ga Gunflint chert

“…biogeochemistry | taphonomy | paleontology P ervasive pyritization of soft-bodied organisms is rare but may result in remarkable cellular preservation and provide unique biogeochemical and taphonomic information (1)(2)(3)(4)(5). Pyritic microfossils have been reported from several Precambrian strata (e.g., ref.…”