The existence of this impact structure was deduced from the discovery of its ejecta layer within late Precambrian shales of the 590-million-year-old Bunyeroo Formation in the Adelaide geosyncline, South Australia. This layer contains abundant shocked quartz grains and small shatter cones. The ejecta were found in outcrops and drill cores over several hundred kilometers. These outcrops led scientists to the Acraman structure in South Australia, which was shortly thereafter confirmed as an impact structure, and as the source crater of the Bunyeroo impact ejecta layer. The diameter of the Acraman structure is at least 90 kilometers, with some outer arcuate features at 150 kilometers diameter. Impact ejecta have been found at distances of up to 450 kilometers from the Acraman structure. The center of the structure is occupied by the 20-kilometer-diameter, hexagonal Lake Acraman, a dry salt lake (white feature slightly left of the center). It is not quite clear if the semicircular Lake Gairdner and Lake Everard, which can be seen in the upper part of the image, are part of the impact structure or not. If they are, Acraman would have a diameter of about 160 kilometers.
Space shuttle image STS88-704-16.