Reassessment of the evidence for primary fusinite and degradofusinite

Abstract

Insight into the origin of fusinite was gained using Late Carboniferous polished coal balls (permineralized peat) from the New Castle coal bed (Alabama, U.S.A.), the Union coal bed, (Lancashire, England) and the Calhoun coal bed (Illinois, U.S.A.). Two types of fusinite were studied; primary fusinite (fusinite formed without undergoing charring or oxidation) and degradofusinite (fusinite formed due to decay or degradation). Evidence for primary fusinite in vascular plants previously relied on color in coal-ball thin sections for maceral identification. Color is shown to be an unreliable guide to maceral identity in coal-ball thin sections. Other evidence for primary fusinite from vascular plants is scant. Abundant fungi with vitrinitic reflectivity were found in coal balls whereas none with fusinitic reflectivity were found. Although genuine fungal sclerotinite does exist, the occurrence of fungal sclerotinite does not prove that fungal sclerotinite is primary fusinite but only that fungi can be fusinitized. Both lycopod periderm with fungal-decay features and coprolites have vitrinitic reflectivity in coal balls. These tissues should have had fusinitic reflectivity if decay or degradation results in fusinitization. These results, therefore, cast doubt on the existence of degradofusinite. Charcoal and decayed tissues show features that may allow them to be distinguished in some cases. In charcoal, the secondary cell walls of adjacent cells together with the middle lamellae are usually fused into a single homogeneous unit. In decayed tissues, the middle lamellae is preferentially decayed which can result in the separation of adjacent cells. Some prominent illustrations of degradofusinite show fusion of the cell walls of adjacent cells indicating an origin by charring. This indicates that presently accepted criteria for recognizing degradofusinite are inadequate even if degradofusinite does exist. Some evidence for degradofusinite does exist but the key illustration, as published (Teichmüller, 1950, 1989), does not demonstrate the existence of degradofusinite.