Crockford Proterozoic Triple Oxygen Isotopes

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 of ∆’17O signatures and debate surrounding how they are produced and eventually preserved has limited the understanding of this important geochemical record. Here we explore depositional controls on ∆’17O signatures of mid-Proterozoic (≈2.0-1.0 Ga) sulfates. We identify a clear depositional control on the magnitude of preserved ∆’17O sulfate signatures, with Proterozoic terrestrial environments preserving the most negative and variable signatures and marine environments displaying values near modern marine sulfate with less overall variability. Our results strongly suggest that local depositional settings influence the magnitude of preserved ∆’17O signals, and the processes within those environments drive much of the observed intraformational variability. Finally, this analysis suggests that ∆’17O signatures in concert with sedimentological observations may offer a powerful tool to identify basin restriction and non-marine settings throughout the geologic record.