WAS THERE A CONFLICT AT THE NEOPROTEROZOIC-CAMBRIAN BOUNDARY: EVIDENCE FROM SULFUR ISOTOPE COMPOSITION?

Abstract

Based on evaporite sequences of the Irkutsk amphitheater, it is shown that sulfur in the Vendian-Lower Cambrian sedimentary sulfates displays a very wide scatter of sulfur isotope ratios and enrichment in heavy sulfur up to average values of δ34S ≈ +(27–30)‰. These features are related to sulfate reduction, which is distinctly expressed like other secondary alterations in the studied sections. Average δ34S values reflect the dynamics of isotopic effects rather than the initial sulfur composition of the oceanic water. The Irkutsk amphitheater can be considered natural model of sulfur isotopic variations in ancient evaporites. Existing concepts of the sulfur isotopic composition of Cambrian oceans need to be revised.