Australasian Science Magazine

By Stephen Luntz

An asteroid impact structure found in the north-east of South Australia is the third largest known asteroid impact site, displacing the Chicxulub crater responsible for the extinction of dinosaurs.

“It is possible the asteroid impact dates back to the late Devonian period 360 million years ago, a time of major mass extinction,” says Dr Andrew Glikson of the Australian National University’s School of Archaeology and Anthropology.

Last year Glikson announced the discovery of a crater 84 km in diameter at Talundilly in south-western Queensland. The crater is thought to be 125 million years old, coinciding with a period of major volcanic activity in the Indian and Pacific Oceans.

Dr Tonguc Uysal of the University of Queensland, who has been studying potential geothermal resources nearby in the Cooper Basin, became aware of the work and alerted Glikson to the presence of shocked quartz in drills 4 km deep at some locations.

Shocked quartz is considered a tell-tale sign of an asteroid impact as it requires forces stronger than those experienced in earthquakes or volcanoes. Glikson confirmed its presence in the East Warburton Basin over a 30,000 km2 area – up to 200 km across – suggesting that the source was an asteroid 10–20 km in diameter.

Glikson says the Cooper Basin has been drilled so many times it is “like Swiss cheese”, providing extensive samples to study. Deep seismic anomalies provide further support for the theory through evidence of uplift that is now buried under millions of years of strata.

Glikson says that a geophysical anomaly in the West Warburton Basin has “almost identical geophysics” to its counterpart in the East Warburton Basin, and is studying whether it is also the result of an asteroid impact.

As events in Russia proved this year, incoming objects often break up prior to contact. This can occur as a result of gravitational interactions rather than atmospheric effects, producing twin craters.

Uncertainty remains about the timing of the impact. “The uranium–lead ages indicate it is at least 298 million years old, but the crystals can be reset by subsequent events and it is possible it is actually 360 million years old,” says Glikson. Several other large impact craters date from the same time, but this would be the largest of the cluster.

If accepted the finding, published in Tectonophysics, along with Talundilly would give Australia six of the 16 largest known impact craters, along with several disputed sites.