This study provides a lateglacial paleofire record for Michigan which will help to reconstruct the larger geographic pattern of fire during lateglacial time, as very few charcoal studies have been carried out for the Midwest. This work will be integrated into the Global Charcoal Database at the World Data Center for Paleoclimatology for future studies relating to fire patterns and regions, and vegetation and climate change.
This study was initially designed to test the biomass burning aspect at 12,900 BP of the Firestone et al. (2007) extraterrestrial impact hypothesis. Four lakes near Flint Michigan were sampled because of their proximity to the Gainey Paleoindian site featured in the Firestone et al. (2007) paper. Charcoal was quantified in these four lakes to develop a multi-site lateglacial fire record for the Midwest. The results show contemporaneous fire not only at 12,900 BP but multiple times between 14,500 and 12,900 BP. This synchronicity of the fires between 14,500 and 12,900 BP suggests some as-yet-indeterminate large-scale natural cause, or causes. From 12,900 BP on into the Holocene, the pattern changes. Fires are continuous with high charcoal peaks at Swift Lake, continuous at Slack Lake but with slightly lower charcoal peaks compared to Swift, and having much lower peaks at Lake Sixteen and Big Fish Lake (charcoal is present but at very low levels). This pattern is interpreted to be a result of the distance from the Paleoindian site. Swift and Slack Lakes are each less than one km from the Gainey site, while the other two lakes are 30 km and 16 km away from it. The disparity of the amplitude of the signals in the fire patterns between the two pair of lakes from 12,900 BP forward in time suggests Paleoindian origin for fire.
Additional radiocarbon dates are needed to refine the chronology of the timeline and gain a better understanding of the sedimentation rate. More charcoal research should be conducted on lakes across a larger region, for the interval from the Last Glacial Maximum into the Holocene.