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

Abstract

Triple oxygen isotopes within post-Marinoan barites have played an integral role in our understanding of Cryogenian glaciations. Reports of anomalous ∆ 17 O values within cap carbonate hosted barites however have remained restricted to South China and Mauritania. Here we extend the ∆ 17 O anomaly to northwest Canada with our new measurements of barites from the Ravensthroat cap dolostone with a minimum ∆ 17 O 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

Bacterial sulfur disproportionation constrains timing of Neoproterozoic oxygenation

“…DR4c). Such a composition is inconsistent with the recently determined positive δ 34 S and ∆ 33 S composition of the post-Marinoan seawater sulfate reservoir (Crockford et al, 2016;Sansjofre et al, 2016). Therefore, we conclude that an α net of 0.95 produces the best model solution.…”

A productivity collapse to end Earth’s Great Oxidation

“…While this scenario is difficult to disprove sedimentologically, it would require abnormally low rates of microbial sulfur cycling to prevent the removal of Δ 17 O-anomalous SO 4 and abnormally high rates of continental SO 4 inputs to maintain a continuous supply of SO 4 that carried negative Δ 17 O anomalies; such a state has been inferred only for the exceptional oceanographic case of a meltwater lens following deglaciation of the Marinoan Snowball Earth (44). The alternative "remobilization" scenario 1, in which the SO 4 in Costello Formation macrobarites was derived from Kasegalik Formation SO 4 -bearing minerals, places age constraints between 2,018.5 ± 1.0 Ma and 2,015.4 ± 1.8 Ma on Δ 17 O signatures.…”

Snowball Earth climate dynamics and Cryogenian geology-geobiology

“…4 ) are Sturtian in age ( 159 , 160 ), whereas all known occurrences of barite (BaSO 4 ) in cap dolostones are Marinoan ( 91 , 155 , 161 – 163 ). Nearly all the isotopic evidence for anomalous atmospheric CO 2 comes from the shorter Marinoan cryochron ( 86 ) or its aftermath ( 84 , 85 , 87 – 91 , 162 , 163 ). This reflects the absence in the Sturtian of glaciolacustrine calcite and postglacial barite and the incomplete development of Sturtian cap-carbonate sequences, discussed later.…”