A circular structural uplift of 3 kIn diameter in sandstone and mudstone of the Abner Sandstone crops out within the McArthur Basin of central Arnhem Land. Northern Territory, Australia. The surrounding area contains little outcrop, but the strata are believed to be flat-lying to gently dipping. An outer annulus of sand (disintegrated sandstone) contains scattered outcrops of fractured and brecciated sandstone generally striking tangentially to the structure and dipping outwards. Silicified sandstone bearing shatter cones crops out in the radially faulted core of the structure. Petrographic analysis of sandstone and breccia from the central area reveals abundant fracturing, and single and multiple sets of closely spaced parallel planar deformation features in quartz. The orientation of these planar deformation features is consistent with impact-produced shock metamorphism. The structure is interpreted as the remnant of the central uplift of a deeply eroded complex impact crater. The crater rim and floor have been removed by erosion, and considerable uncertainty surrounds the original rim dimensions. Comparisons with other terrestrial impact structures allow for a diameter in the range of 7-25 km. The age of the structure is probably pre-Cretaceous, but it could be as old as the Mesoproterozoic (~1400 Ma) age of the target rocks.
