The episode of widespread organic carbon deposition marked by a peak in black shale sedimentation during the Palaeoproterozoic is also reflected in a relative abundance of exceptionally abundant graphite deposits of this age. Worldwide anoxic/euxinic sediments were preserved as a deep crustal reservoir of both organic carbon, and sulphur in accompanying pyrite, both commonly >1 wt.%. The carbon- and sulphur-rich Palaeoproterozoic crust interacted with mafic magma to cause Ni-Co-Cu-PGE mineralization over the next billion years, and much of the uranium currently produced is from Mesoproterozoic deposits nucleated upon older Palaeoproterozoic graphite. Palaeoproterozoic carbon deposition has thus left a unique legacy of both graphite deposits and long-term ore depositions.
- carbon isotopes