Ediacaran ice-rafting and coeval asteroid impact, South Australia: insights into the terminal Proterozoic environment

• Published in: Australian journal of earth sciences 2010-01, Vol.57 (7), p.859-869
• Main Authors: Gostin, V. A., McKirdy, D. M., Webster, L. J., Williams, G. E.
• Format: Article
• Language: English
• Subjects: Adelaide Geosyncline; Ediacaran; evolution; glaciation; ice rafting; impacts; Officer Basin; South Australia
• ISSN: 0812-0099; 1440-0952
• DOI: 10.1080/08120099.2010.509408

Isolated quartzose pebbles, clusters of quartz granules, orthogonal aggregates of poorly sorted quartzose coarse sand, and ovoid pellets (≤2 mm long) of quartz silt occur in hemipelagic marine mudstone of the mid-Ediacaran Bunyeroo Formation exposed in the Adelaide Geosyncline (Adelaide Rift Complex), and ovoid pellets of quartz silt in cores of the correlative marine Dey Dey Mudstone from deep drillholes in the Officer Basin, South Australia. This detritus is interpreted respectively as dropstones, dumps, and frozen aggregates dispersed by sea ice possibly of seasonal origin, and till pellets transported by glacial ice. The ice-rafted material in the Bunyeroo Formation only has been found 500 km northwest of the impact site. The Acraman impact took place at a low paleolatitude (∼12.5°) and would have adversely affected the global environment. The stratigraphic observations imply, however, that the impact occurred during, but did not trigger, a cold interval marked by sea ice and glacial ice, although the temporal relationship with Ediacaran glaciations elsewhere in Australia and on other continents is unclear. Release from the combined environmental stresses of a frigid, glacial climate near sea-level and a major impact in low latitudes may have been a factor influencing subsequent Ediacaran biotic evolution.