Mass-independent isotope effects in Archean (2.5 to 3.8 Ga) sedimentary sulfides determined by ion microprobe analysis

We report sulfur isotope anomalies with Delta(33)S, the deviation from a mass-dependent fractionation line for the three-isotope system (S-34/S-32 VS. S-33/S-32), ranging up to +/-2parts per thousand within individual Archean sedimentary sulfides from a variety of localities. Our measurements, which are made in situ by multicollector secondary ion mass spectrometry, unequivocally corroborate prior bulk measurements of mass-independent fractionations (MIF) in sulfur and provide additional evidence for an anoxic atmosphere on the Earth before similar to2 Ga. This technique also offers new opportunities for exploring ancient sulfur metabolisms preserved in the rock record. The presence of MIF sulfur in sulfides from a >3.8-Ga Fe-rich quartzite from Akilia (island), West Greenland, is consistent with a marine sedimentary origin for this rock. Copyright (C) 2003 Elsevier Science Ltd.