EVIDENCE OF AN AIR BURST ORIGIN FOR THE SOUTH AUSTRALIAN EDEOWIE GLASS

Haines et al. (Geology, 2001) proposed that the c. 700 ka Edeowie glasses that occur along the western margin of the Flinders Range in South Australia were formed during an impact event with an asteroid or comet, possibly the result of intense heating beneath an air burst. However, Macdonald et al. (LPSC, 2004) suggested that the twisted slabs of dark glass mixed with local sand and siltstones might have been formed by lightning strikes.

Glasses very similar in morphology to the Edeowie glasses also occur in the Chilean Atacama Desert near the town of Pica (Schultz et al., Geology, 2022). Based on the dynamic process of formation (as well as evidence of extremely high temperatures), these glasses have been attributed to a series of low-altitude air bursts approximately 12,000 years ago. Equally important, these glasses contain relict mineral grains and rock fragments that indicate the bolide most likely originated in the outer solar system, probably a comet. The similarity between the Edeowie and Pica glasses prompted a much closer examination for similar exotic inclusions.

SEM/EDS analyses of the Edeowie glass revealed novel iron sulfides (with similar occurrences and morphologies to those found in the Pica glasses and CI carbonaceous chondrites), carbon-bearing perovskite, melilite, and other Ca-Al-Ti-rich phases as xenoliths in the Edeowie glass. The phases suggest that these glasses could have formed during an air burst of a body similar to the one responsible for the Chilean event.

Haines et al. (2001) reported possible planar deformation features (PDFs) in quartz from the Edeowie glass indicative of a hypervelocity shockwave that fully coupled to the ground. This is not expected during an above-ground air burst. Although we are not confident of the identification of shocked quartz presented, we have observed other phases (including Fe-Ti oxides and zircons) that exhibit evidence of shock. These minerals might have been "pre-shocked" and inherited from the bolide or target sediments (note that the Edeowie glasses are found down-drainage from exposures of ejecta from the large Proterozoic Acraman impact structure).