Tracing the evolution of the earth system through an isotopic record of proterozoic sulfate

Beginning with the oxygenation of the surface environment and concluding with Snowball Earth glaciations and diversification of animals, the Proterozoic Earth witnessed some of the most dramatic shifts to the Earth System. These transitions are burdened with many unanswered questions largely surrounding the composition of the atmosphere and nature of the biosphere. Sulfate has the ability to document many of these changes in the sedimentary record through its isotopes. Specifically, recent analytical advances over the past few decades have opened new abilities to constrain atmospheric chemistry, identify specific microbial metabolisms and gauge the size of the biosphere. In this thesis an isotopic record of Proterozoic sulfate is presented where over 400 samples from 35 different formation spanning Earth’s earliest evaporites at 2.35 Ga to Ediacaran aged deposits were measured for both major (δ18O, δ34S) and minor (∆17O, ∆33S) isotopes. Neoproterozoic samples deposited in the immediate aftermath of the Marinoan Snowball Earth reveal a dynamic sulfur cycle through ∆17O, δ34S and ∆33S results. I expand the current footprint of the ∆17O anomaly, which has been one of the major pillars in support of the Snowball Earth Hypothesis. Through expanding to three new paleo-continents in North America, Brazil and Norway I provide further evidence that deglaciation from the Marinoan was rapid and synchronous. Further, these results lay a foundation to interrogate the post-Marinoan sedimentary record for local, global or globally local perturbations to the Earth System. Contrasting highly dynamic Cryogenian records, I explore the mid-Proterozoic through sulfates from the 1.4 Ga Sibley Group. Here similar large ∆17O anomalies similar to the Cryogenian are observed, However, in the absence of any evidence of glaciation, these results imply a significantly smaller biosphere generating oxygen at this time, and likely over much of the mid-Proterozoic. To obtain a more synoptic view of the Proterozoic I complement Cryogenian and Sibley data sets with 32 other formations spanning the Proterozoic. This comprehensive record depicts dramatic changes to the Earth system through five unique Proterozoic stages. What stands out is that underlying many of these changes may be dramatic shifts in the size of the biosphere and marine sulfate reservoir.

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