The Proterozoic impact record of Australia

Six impact structures of known or probable Proterozoic age have been identified in Australia: (1) the Teague Ring structure in central Western Australia, 30 km in diameter and possibly about 1630 Ma in age; (2) the Spider structure in northern Western Australia, 11 km wide, 13 km long, and probably Meso- to Neoproterozoic in age; (3) the Kelly West structure in the central Northern Territory, possibly between 8 and 20 km in diameter and Neoproterozoic in age; (4) the Strangways structure in the northern Northern Territory, possibly 40 km in diameter and about 1000 Ma in age; (5) the Lawn Hill structure in northwestern Queensland, 20 km in diameter and probably of Neoproterozoic age; and (6) the Acraman structure, probably about 35 to 40 km in diameter and about 590 Ma in age. Discovery of impact structures in exposed gently to mildly deformed stratified Proterozoic rocks in Australia is estimated to be complete or close to complete at diameters equal to or greater than 20 km. From the four known structures with diameter of about 20 km, the estimated area of exposed Proterozoic strata (~1.15 × 10^6 km^2), and the estimated mean time of exposure (~900 Ma), the cratering rate is estimated at (3.8 ± 1.9) x 10^-15 km^-2 y^-1. This estimate for the production of craters greater than or equal to 20 km during the Proterozoic is consistent with the mean cratering rate for the last 3.2 Ga on the Moon, and somewhat below the estimated present cratering rate on Earth.