Late Archean impact spherule layer in South Africa that may correlate with a Western Australian layer

The Late Archean Monteville Formation in the Griqualand West basin (South Africa) contains a single layer rich in distinctive millimeter-size spherules of former silicate melt that have external shapes and/or internal textures similar to well-documented impact spherules such as microtektites in Cenozoic strewn fields and microkrystites in the Cretaceous/Tertiary boundary layer. Most of the Monteville Formation was deposited below storm wave base in a deep shelf environment, yet the spherule layer has wave-formed sedimentary structures and contains intraclasts up to 1.8 m long that could be the product of waves generated by an oceanic impact. The Monteville spherule layer may be part of the same ejecta strewn field as one of two similar spherule layers in the Hamersley basin of Western Australia. Ejecta layers from large impacts therefore have the potential to establish precise time-equivalence between Precambrian successions on different continents and to constrain paleogeographic reconstructions.