GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 147-7
Presentation Time: 3:30 PM


FUNG, Megan K.1, SCHALLER, Morgan F.2 and KATZ, Miriam E.2, (1)Department of Earth and Environmental Sciences, California Lutheran University, 60 West Olsen Rd, Thousand Oaks, CA 91360, (2)Department of Earth and Environmental Sciences, Rensselaer Polytechnic Institute, 110 8th St, Troy, NY 12180

Discovery of impact spherules associated with the onset of the Carbon Isotope Excursion (CIE) that marks the Paleocene-Eocene (P-E) boundary (~56 Ma) indicates that the P-E transition was coincident with an extraterrestrial impact. Here, we present a considerable (17-fold) increase in charcoal at four Atlantic Coastal Plain paleo-continental shelf sites (Randall’s Farm, Busch Gardens, Wilson Lake B, South Dover Bridge) located ~300 km apart along a paleodepth gradient. Individual charcoal shards (~100 μm long) show diagnostic charred plant features. Preliminary results reveal important findings: 1) charcoal records from the deeper sites (Wilson Lake, South Dover Bridge) display more defined peaks than the shallower sites (Randall’s Farm, Busch Gardens); and 2) absolute charcoal numbers are highest proximal to the paleo-river systems that dominated the region, and were situated near the present Susquehanna and Potomac Rivers (Randall’s Farm) and are drastically lower at distal Busch Gardens. Differences in charcoal background levels among the sites show that the charcoal distribution is not uniform and is likely influenced by localized effects and proximity to the paleo-Potomac and paleo-Susquehanna Rivers. Significantly, the peak in charcoal abundance occurs immediately above the P-E spherule layer at two sites containing impact ejecta on the Mid Atlantic Coastal Plain (MACP). Furthermore, the carbon isotope ratio of charcoal (δ13Ccharcoal) through the peak shows that it originated from pre-impact vegetation that burned. We consider two scenarios to explain this widespread, synchronous increase in charcoal at the P-E boundary: 1) warming-induced, continental-scale drying; and 2) impact-induced wildfires. Differentiating between these two hypotheses depends critically on the observed sequence of events, which on the western North Atlantic margin is: the impact spherule horizon, followed by the peak in charcoal (derived from vegetation that grew before the CIE and impact), and finally the nadir of the CIE. Regardless of the ignition scenario, a critical finding is that the pre-excursion δ13Ccharcoal remains constant through the CIE onset, requiring a dramatic increase in sedimentation and is most consistent with a rapid (sub-millennial) CIE onset.