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

Abstract : 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 (Graensesø) and Russia (Zaonega), as well as some distal ejecta deposits (Lake Superior region) from the Sudbury impact (1,849±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 Graensesø and Zaonega spherule layers contain a distinct carbonaceous chondrite component, and are possibly related to the same impact event, which could be Vredefort (2,023±4 Ma) or another not yet identified large impact event 2 from that of similar age, and 3) the Sudbury ejecta record a complex meteoritic signature, which is different from the Graensesø and Zaonega spherule layers, and could indicate the impact of a heterogeneous chondritic body.
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Bérengère Mougel, Frédéric Moynier, Christa Göpel, Christian Koeberl. Chromium isotope evidence in ejecta deposits for the nature of Paleoproterozoic impactors. Earth and Planetary Science Letters, Elsevier, 2017, 460, pp.105-111. ⟨10.1016/j.epsl.2016.12.008⟩. ⟨insu-02917511⟩



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