Chromium isotopes track redox fluctuations in Proterozoic successions of the Chapada Diamantina, São Francisco craton, Brazil

Abstract The Chapada Diamantina region in the São Francisco craton of eastern Brazil is composed sedimentary successions containing both Mesoproterozoic and Neoproterozoic carbonate levels, making it a key natural laboratory for understanding fluctuations Earth's biogeochemical cycles during its middle age. ca. 1.4–1.2 Ga Caboclo Formation stromatolites yielded unfractionated δ53Crauth (authigenic) (~−0.54‰ to +0.08‰). Ediacaran cap carbonates phosphatic Salitre Formation, on other hand, fractionated reaching as high +0.51‰, suggesting input 53Cr-rich Cr(VI), first delivered through meltwater-induced post–snowball Earth fluctuating redox conditions then weathering mobilization under fully oxygenated environment. acquired data set highlights very distinct throughout Proterozoic reinforces suggestion that after Cryogenian global glaciations, atmosphere hydrosphere became progressively Ediacaran-Cambrian transition.