INVESTIGATING THE EARLY NEOPROTEROZOIC SEAWATER SULFUR ISOTOPE RECORD

The sulfur isotope record of sedimentary sulfate and sulfide minerals is a powerful tool for both chronostratigraphy and for tracking the redox evolution of the oceans over Earth’s history. It is widely thought that an oxygenation event occurred in the Ediacaran Period (635–541 Ma), broadly coinciding with early animal evolution and diversification, but geochemical data increasingly imply oxygenation of the oceans may have occurred earlier in the Neoproterozoic. And whereas abundant sulfur isotope data exists for the Ediacaran Period, few records have been published for the interval spanning from the late Mesoproterozoic to the onset of Cryogenian glaciation (~1000 to 720 Ma). Here we report new carbonate associate sulfate (CAS) sulfur isotope data from latest Mesoproterozoic to early Neoproterozoic sedimentary successions in Siberia, northwest Canada, and Svalbard, with the aim of populating this poorly documented interval of the sulfur isotope record and better understanding the nature of the marine sulfur cycle across a potentially critical interval in the history of ocean oxygenation. Previously reported sulfur isotope data suggested relatively low δ³⁴S_sulf values in the early Neoproterozoic, in contrast to the much higher values that occur following the Cryogenian glaciations and in the latest Ediacaran. However, our data show another prominent high in δ³⁴S_sulf that begins at the end of the Bitter Springs anomaly (c. 800 Ma) and culminates with values approaching 40‰.