Org. Geochem. Vol. 5, No. 4, pp. 227-239, 1984 0146-6380/84 $3.00+0.00 Printed in Great Britain Pergamon Press Ltd Coalification of organic matter in coal balls of the Pennsylvanian (upper Carboniferous) of the Illinois Basin, United States PAUL C. LYONS, CAROLYN L. THOMPSON*, PATRICK G. HATCHER, FLOYD W. BROWN U.S. Geological Survey, 956 National Center, Reston, VA 22092, U.S.A. MICHAEL A. MILLAY Department of Botany, University of Maryland, College Park, MD 20742, U.S.A. NIKOLAUS SZEVERENYI and GARY E. MACIEL Colorado State University, Fort Collins, CO 80523, U.S.A. (Received 12 October 1983; accepted 25 October 1983) Abstract--An evaluation was made of the degree of coalification of two coal balls from the Illinois Basin of the Pennsylvanian (upper Carboniferous) of the United States. Previous interpretations are mainly misleading and contradictory, primarily because of the assumption that the brown color and exceptional cellular and subcellular preservation typical of American coal balls imply chemical preservation of cellulose and lignin, the primary components of peat. Xylem tissue from a medullosan seed fern contained in a coal ball and the coal attached to the coal ball from the Calhoun coal bed, Mattoon Formation, Illinois, was analyzed by elemental, petrographic, and nuclear magnetic resonance (NMR) techniques to determine the degree of coalification. The NMR and elemental data indicate the lack of celluloseand iignin and a probable rank of high-volatile C bituminous coal. These data corroborate data for a coal ball from the Herrin (No. 6) coal bed (Carbondale Formation, Middle Pennsylvanian) and support our hypothesis that the organic matter in coal balls of the Pennsylvanian strata of the United States is coalified to about the same degree as the surrounding coal. Data presented show a range of lower reflectances for xylem tissue and vitrinite in the analyzed coal balls compared with vitrinite in the attached coal. The data reported indicate that physical preservation of organic matter in coal balls does not imply chemical preservation. Also our study supports the hypothesis that compactional (static load) pressure is not a prerequisite for coalification up to a rank of high-volatile C bituminous coal. A whole-rock analysis of the Calhoun coal ball indicates a similarity to other carbonate coal balls from the United States. It consists primarily of calcium carbonate and 1-2~ organic matter; silica and alumina together make up less than 0.5~o, indicating the lack of minerals such as quartz and clays. INTRODUCTION Coal balls are permineralized concretions of some of the peat that ultimately was coalified to form coal beds (Mamay and Yochelson, 1962). They have been used extensively in anatomical and morphological studies of American Carboniferous floras (Andrews, 1951; Phillips, 1980) and have also been used in studies of the plant communities and paleoecology of coal-forming swamps of the Carboniferous (Phillips, 1980). However, the chemical composition of the organic matter in coal balls has not been extensively studied. In order to determine the chemical composition of coal ball plant tissue and its degree of coalification, we studied a carbonate coal ball containing part of medullosan seed fern from the Herrin (Nol 6) coal bed (Carbondale Formation, Middle Pennsylvanian) of Illinois (Eastern Interior coal region). We found by elemental, chemical, and nuclear magnetic reso- *Present address: CONOCO, Inc. P.O. Box 1267, Ponca City, OK 74601, U.S.A. nance (NMR) techniques, using pure cellulose and lignin for comparison, that cellulose and lignin were not preserved, which confirmed the data of Darrah (1941) on pyritic coal balls from the Western Interior coal region; we also found that the degree of coalification of the organic matter, as compared with coalified logs and coals of different rank, was about the same as that of the surrounding coal; that is, a rank equivalent to about that of a high-volatile C bituminous coal (Hatcher et al., 1982b). Thus, a working hypothesis was developed that woody plant tissues in coal balls from the Illinois basin, and possibly from other Pennsylvanian basins of the United States, are coalified to about the same degree as the surrounding coal. To test this hypothesis, a second coal ball of a medullosan seed fern from a stratigraphicaily higher horizon, the Calhoun coal bed of Illinois (Fig. 2; Mattoon Formation of Kosanke et aL, 1960; Upper Pennsylvanian), was studied by similar techniques. Most coal balls in the United States have been collected from this basin. The present study does not include analysis of Devonian and Mississippian pyri- 227