The Ediacara member of the Rawnsley quartzite: The context of the Ediacara assemblage (late precambrian,flinders ranges)

The Ediacara fossil assemblage occurs widely in the Flinders Ranges, South Australia, in a single, readily mappable stratigraphic interval—the Ediacara Member of the Rawnsley Quartzite, which is part of the Pound Subgroup of the Wilpena Group. The Member occurs low in the Rawnsley Quartzite and consists of siltstones, medium‐ to thick‐bedded sandstones, and heterolithic units of intercalated siltstone and sandstone. Features such as rhythmical bedding and flaser bedding, interference and flat‐topped ripples, winnowed coarse sand residues, abundant clay galls, and rare desiccation cracks suggest that the heterolithic siltstone/sandstone units represent intertidal deposits. The rich body‐fossil assemblage occurs chiefly in these deposits of probable intertidal origin, and for the most part appears to represent organisms stranded by the tide away from their normal habitat. Associated bioturbation structures include horizontal, penetrative (post‐depositional) burrows, but vertical dwelling burrows have not been found; the Pound Subgroup evidently pre‐dates their widespread appearance.

The Rawnsley Quartzite appears to have been deposited during cycles of marine transgression, with the Ediacara Member inferred to have accumulated in environments varying from shallow shelf to tidally influenced lagoons sheltered by barrier bars.