A quantification of the effect of diagenesis on the paleoredox record in mid-Proterozoic sedimentary rocks

Abstract Iron speciation in ancient sedimentary rocks is widely used to reconstruct oceanic redox conditions over geological time, specifically assess the extent of oxic, euxinic (anoxic containing sulfide), and ferruginous iron) conditions. We explore how post-depositional processes can skew particular geochemical signals rock record. One such process when aqueous sulfide—including that produced sediment column—reacts with iron, converting non-sulfide, highly reactive iron minerals iron-sulfide minerals; this lead increased preservation as pyrite an overestimation seafloor euxinia. show higher (>5 wt%) total content are more buffered effect thus a reliable indicator true water-column When considering past, we estimate euxinia mid-Proterozoic may have been much fourfold less than previously thought—more line other recent paleoredox proxies not based on minerals. Marine sulfate concentrations were equivalent Proterozoic–Neoproterozoic oceans, suggesting time period was particularly susceptible alteration, explaining suggested for interval.