Figure 8
From: Exceptional sulfur and iron isotope enrichment in millimetre-sized, early Palaeozoic animal burrows

This block diagram proposes a pathway for generating disparate δ56Fe and δ34S values between TPS, PTs and isolated framboids. We consider a scenario in which pyrites form from a finite reservoir of pore water hydrogen sulfide as well as dissolved ferrous iron. Early precipitating pyrite will acquire isotopic signatures that represent a natural kinetic fractionation effect. In the case of δ34S, bacterial sulfate reduction generates H2S-δ34S that is approximately 30‰ lighter than seawater sulfate-δ34S (Early Ordovician seawater ~ +40‰45). In accordance with this mechanism, the dissolved Fe-δ56Fe will be on average − 0.5‰ lighter compared to the seawater dissolved Fe-δ56Fe, which is proposed to lie around 0.0‰. The heavy isotope ranges for both iron and sulfur are typical for Raleigh-type fractionation within a closed diagenetic system (see text for discussion).