PALEOWILDFIRE IN THE PENNSYLVANIAN: A COAL BALL ANALYSIS APPROACH

The paleobotanical record of the Pennsylvanian equatorial tropics is known for its rich fossil assemblages, many of which provide in situ snapshots of paleo-landscapes. These assemblages often also capture the history of Pennsylvanian wildfire in the form of fusain—fossilized charcoalified materials. This subperiod is known for having increased wildfire activity, potentially related to “hyperoxic” conditions, i.e. atmospheric oxygen levels above the Present Atmospheric Level of ~21%. Hyperoxic wildfire likely acted as one of the agents shaping wetland and seasonally dry ecosystems of Pennsylvanian Euramerica. However, as of now, the behavior of wildfire under hyperoxic conditions in general, and the characteristics of fires in Pennsylvanian landscapes in particular, are at best partially understood.

Our methodology for studying Pennsylvanian wildfire uses a three-faceted approach involving coal ball analysis, experimental combustion, and wildfire simulation. The focus here is on results from the coal ball analysis, in which we utilize a dataset of over 85,000 microscopically analyzed square centimeters of coal ball peels collected from five Pennsylvanian localities in the US Midcontinent and the Southern Appalachian Basin. This dataset includes information on the plant genus, broader taxonomic group, tissue type, plant organ, aerial/subterranean condition, and critically, preservational features such as evidence of fusinization, for each square-centimeter. We analyze the correlation between fusain abundance and factors such as taxonomic composition, diversity-dominance patterns, ecological habits of taxa, and relative abundance of various plant tissues and organs. These analyses allow us to infer landscape-scale characteristics of paleowildfire, including fuel structure & composition; fire size, intensity, and spatial pattern; and the importance of ecosystem composition and structure to fire dynamics.