The 30,000 square km area located in the Cooper basin (700km from Adelaide) is believed to be 300 million years in age, that is, late Carboniferous. The actual impact zone, the zone covered in ejecta and spherules from the impact, is 200km across and displays evidence of shock metamorphism across the entire area. (Shock metamorphism is also known as impact metamorphism and refers to heating and deformation from a shock wave during an impact event).
If this feature is confirmed as a crater, it will be the 3rd largest ever found, with the top two spots going to Vredefort crater in South Africa (298km) and the Sudbury crater in Canada (250km).
The site was discovered in a drilling programme – the impact zone is buried under 4km of younger sediment making it difficult to study. Researcher Andrew Glikson and his team originally thought that the terrane was volcanic in origin. When they determined the scale of the feature, they realised it could be nothing less than a large impact event.
The impact would have occurred when Australia was still part of the Gondwana super-continent, and the team believes that the impact was so large it would have had catastrophic global impacts. Whilst the team at this stage believe the zone to be 300 million years old, further research may push the date back even further, possibly to the Late Devonian extinction event.
Image: Shocked quartz from the Suvasvesi South impact structure, by Martin Schmieder