EARLY FORMATION AND TAPHONOMIC IMPORTANCE OF AUTHIGENIC CLAYS ASSOCIATED WITH EDIACARAN FOSSIL PRESERVATION

The Ediacaran Period represents a critical interval in Earth history encompassing the transition between the Precambrian world and the radiation of animal life in the Paleozoic. The Ediacara Biota—Earth’s earliest fossilized communities of complex, macroscopic life—may represent a key steppingstone in this transition. However, the processes responsible for the fossilization of these soft-bodied organisms—particularly their preservation as three-dimensional casts and molds or “Ediacara-style” preservation—have been longstanding subjects of debate, with a wide range of hypotheses proposed, including the potential role of authigenic pyrite, silica or clays.

In this study, we investigate the taphonomic importance of authigenic clays in the preservation of Ediacaran soft tissues from a range of fossil specimens collected from Ferryland, Newfoundland and the Wernecke and Mackenzie Mountains of NW Canada. Using Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectrometry (EDS), and X-ray diffraction analyses (XRD), we find that early diagenetic chlorite-group clays are commonly present in fossil material. XRD analyses indicate that chamosite, a potential alteration product of berthierine, is present in fossil material from Ferryland. In NW Canada, chamosite is not recorded, likely due to the presence of lower greenschist grade metamorphism, however chlorite potentially derived from chamosite was identified. Using SEM and EDS, we record the presence of early authigenic clays within heterolithic siliciclastic and carbonate matrixes of fossil specimens. These clays are enriched in iron, magnesium and aluminum—cations that are commonly associated with chlorite group minerals. The occurrence of either chamosite or chlorite across all localities, and correlation between the presence of chamosite and interpreted metamorphic regime, may indicate that berthierine was originally present in fossil specimens from all areas. This may indicate that fossilization of Ediacara-style preservation associated with clay-rich lithologies were mediated by authigenic clay formation, as has been suggested for Burgess Shale-type fossil assemblages, suggesting this widespread taphonomic window occurred both in the Precambrian and Phanerozoic.