Neoarchaean impact spherule layers in the Fortescue and Hamersley Groups, Western Australia: stratigraphic and depositional implications of re-correlation

Previously, two layers containing impact melt spherules, the Wittenoom spherule layer and the Carowine spherule layer, exposed in the main outcrop area and Ockover River area, respectively, of the Neoarchaean-Palaeoproterozoic Hamersley Basin of Western Australia, were correlated. Subsequent discovery and study of the Jeerinah spherule layer in the main outcrop area, as well as a new Carawine spherule layer exposure now suggest that the Carowine and Jeerinah spherule layers are correlates, The previous Wittenoom - Carawine correlation was based on the presence of spherules and sedimentological consistency: both layers comprise sediment gravity flows, and the Wittenoom spherule layer was interpreted as the downflow equivalent of the Carawine layer. However, the Jeerinah spherule layer also consists of sediment gravity flows, which could be related to the Corawine layer, Since all three layers reflect events triggered by oceanic impacts, these similarities are not surprising, but they do eliminate sedimentology as a correlation tool, However, two compositional trends suggest that the Carawine and Jeerinah layers are correlates: (i) the textures of their spherules are very similar and are distinctly different from the Wittenoom layer; and (il) only the Corawine and Jeerinah layers contain irregular impact melt particles. The latter observation is strong evidence as irregular particles are unknown in any other early Precambrian spherule layers in Western Australia. While triggered by the some impact, it is unlikely that the Carowine and Jeerinah spherule layers were deposited by the some sediment gravity flows, as they contain very different intraclast populations.