Depositional Controls on ∆′17O Signatures of Sedimentary Sulfate

Triple oxygen isotope compositions of sedimentary sulfate (triangle ' 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 triangle ' 17O signatures of mid-Proterozoic (ca. 2.0-1.0 Ga) sulfates. We identify a clear depositional control on the magnitude of preserved sulfate triangle ' 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 triangle ' 17O signals, and that the processes within local environments drive much of the observed intraformational variability. Finally, this analysis suggests that triangle ' 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.