WIDESPREAD WILDFIRES AT THE PALEOCENE EOCENE BOUNDARY: EVIDENCE FROM ABUNDANT CHARCOAL PRESERVED IN THE THICK MARLBORO CLAY

The overall warming trend of the late Paleocene through early Eocene was punctuated by a prominent, short-lived warming event known as the Paleocene-Eocene Thermal Maximum (PETM; ~56 Ma): a 5-8°C global warming associated with a negative carbon isotope excursion (CIE). The PETM was accompanied by the rapid expansion of terrestrial plants and mammals, acceleration of the hydrologic cycle, ocean acidification, and the extinction of 40-60% of deep-sea benthic foraminifera. The backdrop for these climatic and biotic changes is a massive injection of isotopically light carbon into the ocean-atmosphere system, creating a negative δ¹³C excursion in both marine and terrestrial settings. The source and magnitude of the ¹³C-depleted carbon that generated the CIE is still debated. However, the recent discovery of silicate glass impact ejecta (microtektites and microkrystites) in the onset of the CIE indicates that the Paleocene-Eocene (P-E) boundary transition was coincident with an extraterrestrial impact. Here, we present the discovery of charcoal-rich sediments from three Atlantic Coastal Plain paleo-continental shelf sites (Medford, Wilson Lake B, and Millville) where primary impact ejecta was recently identified at the P-E boundary. Peak charcoal abundances occur immediately above the spherule layer and charcoal content decreases upsection. The individual microscopic black carbon shards (~100 μm long) contain 60-85 wt % carbon and show the remains of charred plant features, such as cellular textures and side wall pits. We infer that the thermal anomalies resulting from the impact and ejecta fallout probably ignited widespread wildfires, evidence for which has been documented previously from other P-E sections globally. Post-wildfire changes in soil infiltration dramatically increase runoff and erosion, resulting in substantial soil loss. Burnt terrestrial plant matter and eroded forest soils would have been transported to the shelves in a massive deluge of sediment, and is probably responsible for the thick Marlboro Clay whose base is coincident with the onset of the CIE.