A non-thermogenic source of black carbon in peat and coal

•Photochemically produced formulas are observed in peats using FTICR-MS.•Low rank coal contains photochemically produced molecular formulas.•Fusinitic macerals in coal may be partly derived from non-thermogenic black carbon.

Black carbon previously observed in peats has been attributed to various forms of pyrogenic carbon. However, a recent report has shown that a non-pyrogenic source of BC-like molecules can be obtained photochemically from dissolved organic matter. In this study, we examined well-known coal-forming peats located in the USA by solid-state 13C NMR and ultrahigh resolution mass spectrometry to evaluate the contribution of photochemically produced organic matter. The presence of photochemically produced organic matter was observed in all the peat samples and suggests that photochemically induced precipitation is pervasive. To determine if these “photo” materials survive maturation, we examined a low-rank coal from the Gippsland Basin, Australia, and the presence of “photo” materials was observed, indicating that these materials are geologically preserved. Results from this study indicate that photochemically produced materials are important sources of black carbon and aliphatic like compounds to coals and possibly Type III kerogens. It is possible that these materials are precursors to ubiquitously occurring fusinite, macrinite, micrinite, and related inertinite macerals in coal.