7.10.4 Iron Speciation and Isotope Perspectives on Palaeoproterozoic Water Column Chemistry

Ancient rocks record the redox conditions of the ocean-atmosphere system through the distribution of iron (Fe) between oxidised and reduced minerals, which can be formulated into a suite of Fe palaeoredox proxies. The bal-ance between Fe and S in a given system reflects the variance in a range of high- and low-temperature sources and sinks. Iron can be delivered by hydrothermal, diagenetic or clastic fluxes and can be buried and removed as Fe-oxide phases, Fe-bearing carbonates such as siderite or ankerite, relatively unreactive silicate phases, which often pass through the sys-tem in detrital form, or as a constituent of pyrite (FeS2) using sulphide sourced by sulphate reduction. Sulphate is delivered to the ocean primarily from continental weathering, which requires that a surface oxidative cycle exists, and rates of sulphate delivery and Fe removal as pyrite should thu