“…This progression was also found in the Dales Gorge Member, where siderite spheres and rhombohedra occur near each other. Such features suggest that some siderite formed during the diagenetic (biological or non-biological), and subsequent metamorphic, oxidation of microbial biomass to CO 2 /bicarbonate coupled to the reduction of Fe(III), followed by reaction of the product Fe 2+ aq with sediment pore-water bicarbonate (Johnson et al, 2008;Heimann et al, 2010;Köhler et al, 2013;Halama et al, 2016). Importantly, in most cases, the C, O, Fe, and Sr isotope compositions of IF carbonates clearly preclude formation in equilibrium with seawater .…”