The Palaeoecological and Industrial Significance of Inertinite (Charcoal) in Late Permian Coals from the Kuznetsk Basin, Russia

Thirteen Late Permian subbituminous coal seams (numbered 68-94) were sampled from the Kuznetsk Basin, Russia. The coals formed in extensive long-lived peat-forming (mire) environments on floodplains as part of a fluvial system (Davies et al., 2010). Fossil plants (permineralised, charcoalified or impressions) show characteristics consistent with cordaitaleans, which were the dominant peat-forming plants in Angara during the Permian.

Crushed coal samples show temporal variation in inertinite (charcoal content) from 7.1% - 50.2%, with a high overall mean of 28.3%. More detailed petrographic work was carried out on five in situ coal pillars (seams 78, 88 and 91) where inertinite distribution was used to interpret palaeowildfire occurrence and type as well as providing an approach to calculating fire return intervals (FRI) in deep time. In situ pillars are essential for this type of research as they retain the original spatial and temporal variation in inertinite distribution. Inertinite is present in all lithotype units (up to 61% mineral matter free basis). The coal pillars show comparable wildfire histories despite differences in environments of deposition. In addition, FRI may have been more frequent in the Permian than in modern peat-forming environments.

Quantitative reflectance of macroscopic and microscopic (inertodetrinite) charcoal in coal pillars has revealed that both size fractions are within the temperature range of modern low temperature surface fires. However, a small amount of the charcoal reflectance values are >4%Ro and may in fact represent charcoal derived from high temperature crown fires. This demonstrates the importance of reflectance measurements of both macro- and microscopic charcoal in interpretation of palaeowildfire type.

Despite inertinite contents of up to 61% in these Permian coals, neither inertinite content nor distribution strongly affects the characterisation (proximate and ultimate) properties of the coal as a whole. However, coals with high inertinite contents (>30%) do produce denser chars and show poorer burnout during pilot-scale Drop Tube Furnace (DTF) combustion experiments.