Chromium isotope evidence in ejecta deposits for the nature of Paleoproterozoic impactors

1Bérengère Mougel, 1,2Frédéric Moynier, 1Christa Göpel, 3,4Christian Koeberl
Earth and Planetary Science Letters 460, 105-111 Link to Article [https://doi.org/10.1016/j.epsl.2016.12.008]
1Institut de Physique du Globe de Paris, Université Sorbonne Paris Cité, CNRS UMR 7154, Paris, France
2Institut Universitaire de France and Université Paris Diderot, Paris, France
3Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria
4Natural History Museum, Burgring 7, A-1010 Vienna, Austria
Copyright Elsevier

Non-mass dependent chromium isotopic signatures have been successfully used to determine the presence and identification of extra-terrestrial materials in terrestrial impact rocks. Paleoproterozoic spherule layers from Greenland (Grænsesø) and Russia (Zaonega), as well as some distal ejecta deposits (Lake Superior region) from the Sudbury impact (1849±0.3 Ma) event, have been analyzed for their Cr isotope compositions. Our results suggest that 1) these distal ejecta deposits are all of impact origin, 2) the Grænsesø and Zaonega spherule layers contain a distinct carbonaceous chondrite component, and are possibly related to the same impact event, which could be Vredefort (2023±4 Ma) or another not yet identified large impact event from that of similar age, and 3) the Sudbury ejecta record a complex meteoritic signature, which is different from the Grænsesø and Zaonega spherule layers, and could indicate the impact of a heterogeneous chondritic body.

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