Organic and inorganic geochemical investigations were carried out on samples of Kimmeridge Clay from Yorkshire, UK, to examine the Fe-S-C dynamics that created them. These samples have variable bulk and molecular compositions reflecting differing redox conditions, inputs of iron, and organic matter quantity/quality (TOC up to 18wt%, Type I-II/III kerogen). Reactive iron (FeR) availability is a controlling factor on the sequestration of sulphur into inorganic and organic fractions (Raiswell et al., 1993). Organic matter sulphurisation has economic implications but can also bias the interpretation of organic biomarkers (Kohnen et al., 1991). It has been suggested that sulphide buffering by FeR strongly influences biomarker preservation in bitumen (Reinhardt et al., 2018, on isorenieratene). The effect of individual FeR fractions sulphurisation is investigated. In particular, magnetite does not appear to act as FeR in many samples. This could potentially be a function of the terrigenous input (e.g. magnetite grain size), or caused by its lower reactivity affecting its pyritisation behaviour in less persistently reducing environments. Examining the behaviour of FeR fractions under different conditions and their effects on organic matter sulphurisation is essential to improving our understanding of FeR and biomarker proxies and their biases.


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