Journal
GEOLOGY
Volume 39, Issue 4, Pages 307-310Publisher
GEOLOGICAL SOC AMER, INC
DOI: 10.1130/G31526.1
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- National Aeronautics and Space Administration [NNX08AI29G]
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We report the discovery of the Paraburdoo spherule layer, which consists entirely of replaced impact-produced melt spherules. It is distal ejecta from a large impact close to the Archean-Proterozoic boundary in the Hamersley Basin of Western Australia. The spherule layer occurs in the Paraburdoo Member of the Wittenoom Formation and was deposited ca. 2.57 Ga (date via U-Pb age interpolation) in a deep shelf environment. The layer consists of microkrystites rich in plagioclase and ferromagnesian crystals, replaced by K-feldspar and a phlogopite-like sheet silicate, respectively. The skeletal textures indicate rapid cooling of a melt with mafic to ultramafic composition and suggest oceanic target rocks. The Paraburdoo spherule layer is 2 cm thick, normally graded, and was probably deposited by suspension settling, as there is no evidence of reworking; it is strikingly similar to the Reivilo spherule layer in the Griqualand West Basin (South Africa), appears to provide a third impact-related high-resolution stratigraphic correlation between these two basins, and points to a high frequency of large impacts around the Archean-Proterozoic boundary.
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