Bakakas Mayika et al. (2020) inferred δ13C heterogeneity in Paleoproterozoic oceans based on the chemostratigraphic and sedimentologic study of a single drillcore of the Francevillian Group (FG) of Gabon, considered to record the end of the ca. 2.22–2.06 Ga Lomagundi carbon isotope excursion (LCIE). The authors concluded that while the shallowmarine carbonates with highly positive δ13C values record enhanced primary productivity or evaporitic conditions, the deep-water facies reflect steady-state operation of the global carbon cycle with ~0. δ13C values. If this interpretation is valid, there was no LCIE, and the end of the ”event” was merely a facies shift toward deeper-water settings recognized in Gabon and elsewhere at the end of the LCIE. However, this interpretation relies on a suite of assumptions about the depositional setting and geochemical data that are open to question. We outline several lines of evidence suggesting that all available data are consistent with the basin-scale and global nature of the chemostratigraphic signals recorded by the FG.
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