Fossil Vegetational Transect from Below the Colchester Coal to the Roof of the Cardiff (Survant) Coal (Desmoinesian, Upper Middle Pennsylvanian), Illinois Basin

Abstract

Four collections of Middle Pennsylvanian plant fossils create an opportunity to examine a transect from below the Colchester Coal through the roof shale of the Cardiff (Survant) Coal of the Illinois Basin. The collections come from the Colchester Coal seat earth, the Colchester Coal roof shale (two collections), and the roof shale of the Cardiff Coal. The Colchester Coal is one of the most widespread coals in the American Pennsylvanian, extending from the Appalachian Basin (Lower Kittanning Coal) to the Midcontinent Region (Whitebreast and Croweburg coals). The Colchester Coal has been made famous by the fossilized plants and soft-bodied animals preserved in a facies of its roof shale, the Francis Creek Shale, host of the Mazon Creek biota. The collections reported here are much smaller than the Mazon Creek flora, and so represent local assemblages. The collection from the Cardiff Coal, which is no longer mined, is the first report of a flora associated with that coal bed. The three roof shale floras, collected in 1906, are small and likely were collected from the surface area at the mine tipple. They appear to represent the flora preserved close to the coal-bed surface and thus capture the final flora of the peat swamp. Accordingly, they represent the early phases of transition from a humid to a subhumid climate at the time of glacial melting and sea-level rise. Similarly, the Colchester Coal seat-earth collection likely represents a local landscape preserved during the time of climate change from a wet sub-humid to a humid climate, just preceding the onset of peat formation.