OCCURRENCE AND RECOGNITION OF COPROLITES IN COALS: RESULTS FROM LATE PALAEOZOIC COALS AND EXPERIMENTAL CHARRING

Most, if not all, inertinite in coal is generally considered to represent charcoal (Scott, 2010, Palaeo3, 11-39). However, it has been suggested that coprolites (fossil faecal pellets) in coal can be preserved as a form of macrinite (an inertinite maceral showing high reflectance) that may not have been subjected to fire but results from fungal degradation (Hower et al. 2011 Int J. Coal Geol, 86, 231-240). Plant decomposing arthropods (e.g. mites, colembolla and millipedes) have been recognised in the fossil record since the early Devonian but are particularly abundant in the Carboniferous. The arthropod coprolites can be distinguished by their shape, size, nature of contents and distribution. Permineralized peat, from the Mississippian and Pennsylvanian, often contains abundant coprolites, some of which have erroneously been described as plant organs (such as Heterotheca from the Mississippian). We have studied coprolites in permineralized peats from Britain and North America, using combined transmitted and reflected light on polished blocks and polished thin sections, to help in the interpretation of coprolites in coal (fossil peat). We have also studied the morphology and characteristics of coprolites in late Permian coals from the Kuznestsk Basin, Russia. Charred arthropod faecal pellets also occur in modern litter as well as in a range of fossil charcoal assemblages. We use these, and experimentally charred modern faecal pellets, to assess changes in morphology and reflectance resulting from charring. Our data shows increasing reflectance with increasing temperature of charring. We see no evidence of increasing reflectance without exposure to increasing temperature. The significance of our findings both in the interpretation of the origin of coal macerals and in coal petrographic nomenclature will be addressed. We show that faecal material has varied reflectance depending on whether or not pellets were charred. In coals at least some, perhaps all, charred faecal pellets would be assigned to the maceral macrinite and we see no conclusive evidence that macrinite can be derived by fungal degradation.