The terminal Neoproterozoic was a period of time in Earth history that was characterised by severe environmental turbulence. At least two major, global glaciations between ca. 700-580 Ma might have acted as evolutionary bottlenecks that led to a rapid diversification of several lineages of single celled and, eventually, multicellular organisms. A large bolide impact in present day southern Australia at around 580 Ma could also have affected the evolution and diversification of microphytoplankton, at least on a local scale (Grey et al. 2003). The appearance of more than 50 ornamented acritarchs above the impact ejecta layer provides an excellent potential for these organisms to be used in biostratigraphy.
The Ediacaran System is defined by its lower boundary occurring between the glacial deposits from the last major glaciation, the Marinoan glaciation, and the overlying cap carbonate, and by the base of the Cambrian System. This system is not very well known and in terms of fossil studies it is just in its infancy. Palynomorph assemblages containing organic walled microfossils, mainly acritarchs and prokaryotic organisms, are recovered from numerous drillholes located in southern Australia. Preliminary studies of a large number of acritarch samples from more than 30 drillcores (Grey 2005) have resulted in a subdivision of the middle Ediacaran into biozones based on the first appearance of index species and characteristic assemblages. Additional studies of drillcores from the Officer Basin in Australia will aid in the correlation between different basins in Australia and hopefully also global correlation. The studies of the Murnaroo 1 succession indicate a consistency with the previously examined boreholes and allow more accurate recognition of the acritarch biozones.
Grey, K., Walter, M.R. & Calver C.R., 2003: Neoproterozoic biotic diversification: Snowball Earth or aftermath of the Acraman impact? Geology, v. 31.
Grey, K., 2005, in press: Ediacaran Palynology of Australia. Australasian Association of Palaeontologists, Memoirs, v. 31.
2005. 61- p.