Uranium isotope compositions of mid-Proterozoic black shales: Evidence for an episode of increased ocean oxygenation at 1.36Ga and evaluation of the effect of post-depositional hydrothermal fluid flow

摘要

Highlights ? U isotope data from black shales point to increased ocean oxygenation at 1.36Ga. ? A U isotope mass-balance model suggests 25% seafloor anoxia during this event. ? Elevated Mo and U enrichments in these shales also support an oxygenation event. ? Post-depositional hydrothermal alteration can affect U isotopes in black shales. Abstract We report U isotope data for marine black shales of the early Mesoproterozoic Velkerri Formation (Roper Group) and late Paleoproterozoi