Life and Death in the Ediacaran: Evolutionary, Environmental and Preservational … – Lidya Tarhan

Life and Death in the Ediacaran: Evolutionary, Environmental and Preservational Dynamics
– Lidya Tarhan
Yale University

The enigmatic fossils of the Ediacara Biota, preserved in upper Ediacaran strata around the world, record the emergence of complex macroscopic life and are a critical stepping-stone to the Cambrian Explosion. Ediacara fossil assemblages consist of soft-bodied organisms of mysterious morphologies and affinities—the majority of which are 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 soft-tissue fossilization. Resolving the mechanisms responsible for Ediacara-style fossilization is essential 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 Ediacara-style fossil assemblages 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 microbially influenced sedimentary structures likewise record early diagenetic silicification. Taphonomic experiments suggest that organic substrates provided by buried macroorganism carcasses and as well as abundant matgrounds permitted these systems to overcome kinetic barriers to silica precipitation, and thereby fostered silicification in upper seafloor sediments. More broadly, these observations indicate that the Ediacara seafloor was shaped by dynamic environmental, ecological and taphonomic processes, including episodic disturbance and obrution, rapid regrowth and macrofaunal colonization of heterogeneous organic matgrounds and early silicification of buried matgrounds and macroorganisms.

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