Triple oxygen and multiple sulfur isotope constraints on the evolution of the post-Marinoan sulfur cycle

- We present new Δ17O and coeval 33,34,36S data of Neoproterozoic aged barite from NW Canada.
- Through a dynamic 1-box model we demonstrate the sulfate source to global barites was global seawater.
- Results suggest a diminished marine sulfate reservoir in the aftermath of the Marinoan glaciation.

Triple oxygen isotopes within post-Marinoan barites have played an integral role in our understanding of Cryogenian glaciations. Reports of anomalous ΔO17 values within cap carbonate hosted barites however have remained restricted to South China and Mauritania. Here we extend the ΔO17 anomaly to northwest Canada with our new measurements of barites from the Ravensthroat cap dolostone with a minimum ΔO17 value of −0.75‰. For the first time we pair triple oxygen with multiple sulfur isotopic data as a tool to identify the key processes that controlled the post-Marinoan sulfur cycle. We argue using a dynamic 1-box model that the observed isotopic trends both in northwest Canada and South China can be explained through the interplay between sulfide weathering, microbial sulfur cycling and pyrite burial. An important outcome of this study is a new constraint placed on the size of the post-Marinoan sulfate reservoir (≈0.1% modern), with a maximum concentration of less than 10% modern. Through conservative estimates of sulfate fluxes from sulfide weathering and under a small initial sulfate reservoir, we suggest that observed isotopic trends are the product of a dynamic sulfur cycle that saw both the addition and removal of the ΔO17 anomaly over four to five turnovers of the post-Marinoan marine sulfate reservoir.