Lake Acraman on Eyre Peninsula in South Australia marks huge hit from a 4km meteor 580 million years ago
Lake Acraman is named after 19th Century businessman John Acraman, also credited as being the father of Australian football in South Australia.
The Acraman eroded crater, from outer-space impact about 580 million years ago, was marked by the dry Lake Acraman, 20 kilometres in diameter, in South Australia’s Gawler Ranges on Eyre Peninsula.
Estimates for the crater’s original size vary from 85 to 90 kilometres (with an energy release equal to 5.2 × 106 megatons of TNT) to 35-40 kilometres. The discovery of the crater and its impact debis were first reported in the Science journal in 1986, with shatter cones and shocked quartz being evidence for extra-terrestial impact.
A widespread layer of ejecta (debris) believed to be from the Acraman crater, was found within Ediacaran rocks of the Flinders Ranges 300 kilometres east of the crater and in drill homes from the Officer Basin to the north. The impact would have happened when these areas were shallow Adelaidean Sea, and the ejecta settled into mud on the sea floor.
The ejecta is associated with an iridium anomaly, suggesting it had been contaminated with extraterrestrial material.
The nearness of the crater to the Flinders Ranges and its Ediacara early-life organisms was noted. The effect of the Lake Acraman impact also was linked to evidence of ice glaciers, going back hundreds of million of years, in South Australian locations such as Chambers Bluff in the far north Indulkana Range, the Tillite Gorge near Arkaroola, the northern end of the Flinders Ranges and Mount Gunson north of Port Augusta.
Lake Acraman impact structure, listed on the South Australian heritage register, was named, along with the lake and a creek, after 19th Century businessman John Acraman, also credited as father of Australian football in the colony.
