Through field studies at geophysical anomalies in the Outback of Australia we have identified shock metamorphic features associated with three new impact structures. Field mapping at these sites and others has helped constrain their age and define the structural form. We are currently working to archive much of Eugene Shoemaker's earlier, unpublished work on Australian impact structures and fallout. These studies have helped refine the cratering record in Australia, and to better understand the mechanics of impact cratering.
Shock effects including shatter cones, PDFs in quartz grains, impact melt rocks, and pseudotacylites were identified in deeply eroded granites in the Yilgarn Craton (119˚50’E, 27˚10’S). Geological and geophysical relationships suggest that the original structure was at least 30 km in diameter and was formed during the early Proterozoic.
Glikson is an 18 km diameter impact structure located in the Little Sandy Desert of Western Australia (23˚59’S, 121˚34’E), that would not have been detected were it not for its extremely strong, ring-shaped aeromagnetic anomaly. Shoemaker visited the area in 1996, and he believed Glikson was an impact structure, but he was unable to find any definative shock features. While mapping the structure in 2002, we confirmed Shoemaker’s suspicions and discovered unequivocal shatter cones in Neoproterozoic sandstones. The source of the strong, aeromagnetic anomaly is likely the truncation of a flat-lying sill, and thus, the impact probably postdates the Cambrian mafic events of the Officer Basin.
Amelia Creek is an asymmetrical, 20 X 12 km impact structure in the Davenport Ranges of the Northern Territory (20˚55’S, 134˚50’E). Evidence for an impact origin includes pervasive shatter-coning, planar microstructures in quartz grains, and the development of large autogenic breccias and clastic dikes. The impact occurred between Cambrian and Mesozoic times.