Microscopy of sclerotinites in the coal beds of the central part of the Appalachian coal field, U.S.A

Abstract

SUMMARYRodlets from fusain and carbominerite bands or lenses in bituminous coal beds of the central part of the Appalachian coal field in the eastern United States were studied in three dimensions using both light microscopy and scanning‐electron microscopy (SEM). Infrared studies and chemical analyses complemented reflectance measurements. The rodlets are found strati‐graphically from the Pocahontas no. 3 coal bed (Pocahontas Formation, Lower Pennsylvanian or Namurian B & C) to the Washington coal bed (Washington Formation, Lower Permian). The most common rodlets are noncellular, range in diameter from 60 to 440 μm, and, when polished, have the relief and high reflectances typical of the inertinite maceral group. They have characteristic notches, ovoid shapes, distinctive fracture patterns, dense (oxidized) rims, vesicles, cavities and canals, some of which contain minerals (tentatively identified by SEM semiquantitative X‐ray and infrared analyses). Some rodlets show a cellular cast on their longitudinal surfaces. Due to different exposures in variously‐oriented polished sections, this type of rodlet is classified as sclerotinite of the inertinite maceral group. Comparison of the sclerotinites from the central part of the Appalachian coal field with the fusinitized resin rodlets from coal and coal balls of the Illinois basin (Kosanke & Harrison, 1957) and with the ‘sclerotioids’ of the St Rose no. 5 coal of Nova Scotia indicates that they represent the same bodies. All are interpreted to be rodlets of resinous origin belonging to one or more of the genera of medullosan seed ferns of Carboniferous and Permian age. We suggest using the existing terms ‘resino‐sclerotinite’ and ‘fungo‐sclerotinite’ for two distinct maceral varieties of the inertinite maceral group because of their distinguishing properties and their different paleobotanical origins. Two types of cellular rodlets, woody splinters and sclerenchyma strands, are also documented in this study because of their close association with the resino‐sclerotinites of the central part of the Appalachian coal field.