Review and update on the applications of inertinite macerals in coal geology, paleoclimatology, and paleoecology

Inertinite is a coal component group recognized under microscope. The origin, formation, and applications of inertinite continue to be debated. Many important achievements have been reported in the recent years. The most important advance is that the presence of inertinite macerals has been used as the most critical evidence of paleowildfires. However, the origin of some micrinite has been recognized as liptinitic/huminitic or as kaolinite, and even as voids. Some secretinite and funginite can be formed by microbial and fungal oxidation. Some researchers questioned the validity of using the maceral (including inertinite) ratios to indicate the depositional environment and appealed to stop using maceral parameters (including inertinite) to explain peat-forming environments and vegetation. Because the proven inertinite macerals formed by organic matter degradation comprised only a small part of all inertinite groups, most inertinite macerals can be used as evidence of paleowildfires, and the inertinite macerals may be used to estimate the wildfire type. The inertinite reflectance values may be used to estimate the wildfire temperature, and the oxygen level can be estimated by the inertinite contents. Furthermore, the relationship between inertinite and other wildfire evidences, e.g., char, charcoal, soot, and fusain, has also been clarified.