A eukaryote assemblage intercalated with Marinoan glacial deposits in South Australia

Daniel le Heron, David Alderton, Margaret Collinson, Nathalie Grassineau, Sykes Dan, A.E. Trundley

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Composite hematite–silica structures recovered from a siltstone bed in the Elatina Formation of South Australia include (1) sub-circular to whorl-shaped forms, (2) elongate to half-moon-shaped forms and (3) and lozenge-shaped forms locally linked into chains. They range from 200 to 500 µm in diameter and are interpreted as eukaryote tests. Evidence for internal etching of a calcite core of some tests indicates that at least some of the hematite–silica fabrics were acquired through replacement. Carbon isotope values of −20‰ δ13C are suggestive of precipitation by microbial activity, and imply a change in ambient fluid chemistry associated with a pH reduction. The tests occur within sandstone beds that were deposited on a tidally modulated braidplain during the Marinoan glaciation at the end of the Cryogenian. The quartz grains in the sandstone sample lack the typical textures (surface striae, internal fractures or irregular grain boundaries) expected for glacially transported material. Thus, on textural grounds we argue that the eukaryote tests represent a proglacial ecosystem during a late Cryogenian snowball Earth event.
Original languageEnglish
Pages (from-to)560-568
Number of pages9
JournalJournal of the Geological Society
Issue number3
Early online date5 Feb 2016
Publication statusPublished - May 2016

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