Maastrichtian Coals from Nigeria: Implications for the Formation of the Inertinite Macerals, with Particular Attention to Macrinite

Subbituminous to high volatile C bituminous Maastrichtian coal samples from the Enugu and Okaba Odagbo coal fields, Anambra Basin, and the Orukpa coal field, Benue Trough, Nigeria, were collected for the U.S. Geological Survey's World Coal Quality Inventory. The University of Kentucky Center for Applied Energy Research conducted petrographic analysis on the 16 samples. The samples show wide variation in the maceral percentages, ranging from 34 to 82 % huminite/vitrinite and from 7.6 to 31% fusinite + semifusinite + inertodetrinite.

The inertinite group contains relatively abundant fusinite and semifusinite, with lesser amounts of inertodetrinite; but also has secretinite, micrinite, macrinite, and funginite. The fusinite + semifusinite and each of the other inertinite maceral varieties can possibly have distinct origins, rather than the commonly attributed origin from fire. In particular macrinite, often a rare maceral, is present in amounts up to 3.8% in this set of Cretaceous coals. Macrinite can be associated with funginite in these coals, as well as in other coals we have examined. A causal association between the two macerals is debatable, but other researchers have suggested that there could be a genetic connection. Fungal degradation of woody and other material is a plausible origin for the amorphous to (marginally) detrital structure found in the associated macrinite.