LIFE AND DEATH IN THE EDIACARAN: EVOLUTIONARY, ENVIRONMENTAL AND PRESERVATIONAL DYNAMICS

The enigmatic fossils of the Ediacara Biota, preserved in upper Ediacaran strata around the world, record the emergence of complex macroscopic life and are likely a critical stepping-stone to the Cambrian Explosion. Ediacara fossil assemblages consist of soft-bodied organisms of enigmatic morphologies and affinities, and which are predominantly exceptionally preserved as casts and molds in sandstones (“Ediacara-style” preservation). One of the longest-standing debates in life history and Precambrian geology revolves around the nature of this extraordinary mode of fossilization. Resolving the processes responsible for Ediacara-style fossilization is critical to accurately reconstruct the affinities, community structure and paleoenvironment of these ancient organisms; gauge the fidelity of the Precambrian fossil record and determine the place of the Ediacara Biota in the emergence of complex animal life on our planet.

Petrographic, paleontological and geochemical evidence from a range of Ediacara-style fossil assemblages of Ediacaran and Cambrian age indicates that these fossils are commonly associated with pervasive early diagenetic silica cements, suggesting that silica cementation played a pivotal role in their exceptional fossilization. Moreover, Ediacara-style assemblages commonly include microbially mediated sedimentary structures that likewise record early diagenetic silicification. Taphonomic experiments suggest that organic substrates provided by buried macroorganism carcasses and as well as microbial biofilms and matgrounds permitted these systems to overcome kinetic barriers to silica precipitation­­, and thereby fostered silicification in upper seafloor sediments. More broadly, these coupled geologic and experimental observations indicate that the Ediacara seafloor was shaped by dynamic environmental, ecological and preservational processes.