PALYNOLOGY, PETROLOGY AND GEOCHEMISTRY OF THE SPRINGFIELD COAL BED IN PROXIMITY TO A PALEOCHANNEL, EASTERN INTERIOR (ILLINOIS) BASIN, USA

The Springfield coal is late Middle Pennsylvanian (Desmoinesian) in age, and is equivalent with Asturian age strata in western Europe. This study documents changes in palynologic, petrographic and geochemical composition in an area where the Springfield coal is influenced by the Galatia paleochannel system in the Illinois Basin. The channel represents the course of a river that flowed through the swamp as peat accumulated. Within the channel, fine-grained clastics take the place of peat. Along its margins, peat intergrades with claystone and siltstone.

The outermost effect of the channel is the appearance of a siltstone layer, which splits the Springfield coal into a lower and upper bench. Despite the parting, the two coal benches are moderate in ash (avg. 9.8 %) and sulfur (avg. 2.7 %). Both coal benches acquire additional partings, and increase in ash (avg. 26.2 %) closer to the channel margin. Sulfur, which is very uniform (3 - 4 %) in areas not influenced by the channel, is more variable (<1 to >3 %) along the channel margins.

Coal and siltstone layers along the channel margin are dominated by arborescent lycopsid spores (avg. 65.1 %), with subdominant tree fern spore taxa (avg. 25 %). Layers more distal to the channel, but still influenced by it, have a more equant distribution of arborescent lycopsid (avg. 40.9 %) and tree fern (avg. 47.8 %) spores. Layers near the channel margin contain elevated percentages of Lycospora micropapillata and L. orbicula (produced by Paralycopodites). In contrast, layers more distal to the paleochannel contain abundant Lycospora granulata (produced by Lepidophloios). Thymospora pseudothiessenii, which is rare close to the channel, is the dominant tree fern spore in areas unaffected by the channel.

Roof shale macrofloras close to the channel are dominated by one species of pteridosperm, Neuropteris flexuosa. Moving away from the channel, tree ferns, lycopsids, and locally a mixture of pteridosperms, dominate the macroflora. Channel margin samples are dominated by vitrinite (avg. 80.4 %, mmf), with correspondingly low percentages of liptinite (avg. 9.3 %, mmf) and inertinite (avg. 10.3 %, mmf). Areas removed from the channel are similar in composition, with high percentages of vitrinite (avg. 78.1 %, mmf) and low percentages of liptinite (7.9 %, mmf) and inertinite (avg. 14.0 %, mmf).