Depositional Controls on ∆′¹⁷O Signatures of Sedimentary Sulfate

Triple oxygen isotope compositions of sedimentary sulfate (∆′¹⁷O) have been applied as a tracer of past primary productivity, pO₂ and pCO₂. However, large intraformational variability and debate surrounding how such signatures are produced and preserved has limited the understanding of this record. Here we explore what controls ∆′¹⁷O signatures of mid-Proterozoic (ca. 2.0–1.0 Ga) sulfates. We identify a clear depositional control on the magnitude of preserved sulfate ∆′¹⁷O signatures, with Proterozoic terrestrial environments preserving the most negative and variable signatures and marine environments displaying values near modern marine sulfate. Our results strongly suggest that local depositional setting influences the magnitude of preserved ∆′¹⁷O signals, and that the processes within local environments drive much of the observed intraformational variability. Finally, this analysis suggests that ∆′¹⁷O signatures of carbonate associated sulfate in concert with sedimentological observations may offer a powerful tool to identify basin restriction and non-marine settings throughout the geologic record.