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

TL;DR

This study uses non-mass dependent chromium isotopic signatures to identify and analyze Paleoproterozoic impact ejecta deposits, revealing their extraterrestrial origins and providing insights into the nature of the impactors involved.

Contribution

It demonstrates the application of chromium isotope analysis to Paleoproterozoic impact deposits, identifying impact origins and characterizing the impactor types and their possible sources.

Findings

Ejecta deposits are confirmed to be of impact origin.

Graenseso and Zaonega layers contain carbonaceous chondrite components.

Sudbury ejecta show a heterogeneous meteoritic signature.

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 (Graenseso) 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 Graenseso 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 from that of similar age, and 3) the Sudbury ejecta record a complex meteoritic signature, which is different from the Graenseso and Zaonega spherule layers, and could indicate the impact of a heterogeneous chondritic body.