Systematic decrease of high δ13C values with burial in late Archaean (2.8 Ga) diagenetic dolomite: evidence for methanogenesis from the Crixás Greenstone Belt, Brazil

Remnants of Fe-poor (2700–4400 ppm) dolomite crystals, crystal aggregates, and microconcretions are cryptically distributed within stratiform bodies (tens of metres across) of metamorphic Fe-rich (3–6 wt% Fe) dolomite that occur in graphitic schists of the 2.8 Ga Ribeira˜o das Antas Formation in the Crixás Greenstone Belt, Brazil. Fe-poor dolomite is a diagenetic carbonate formed during burial of organic-bearing, muddy sediments. Using …