138-7 Destroyer of Micro Worlds: high-resolution forest fire and terrestrial input records across the K-Pg boundary at El Kef

Session: The Cretaceous-Paleogene (K-Pg) Boundary Interval: From Large-Scale Geological Events to Mass Extinction Mechanisms

Presenting Author:

Robert Kelleher

Authors:

Kelleher, Robert¹, French, Katherine L.², van Maldegem, Lennart³, Alegret, Laia⁴, Röhl, Ulla⁵, Jones, Heather⁶, Bralower, Timothy⁷, Negra, Mohamed Hédi⁸, Summons, Roger⁹, Sepúlveda, Julio¹⁰

Abstract:

This study generated high-resolution aromatic and aliphatic biomarker records across the Cretaceous-Paleogene mass extinction from thermally immature cores that were collected as part of the El Kef drilling project (Jones et al., 2024). We reconstructed changes in forest fire intensity and duration as well as terrigenous input along the North African continental margin over the final ~150 kyr of the Maastrichtian, across the K/Pg boundary at 1-cm intervals, and during the first ~2 myr of the Danian recovery period. Our main analytical tools are polycyclic aromatic hydrocarbons (PAHs) for forest fires, complemented by previously published XRF elemental chemistry (Jones et al., 2024) and stable isotope data (Sepúlveda et al., 2019), as well as aliphatic biomarkers to trace changes in terrigenous input and bulk marine productivity. We found no clear evidence for a significant increase in forest fire intensity or duration across the K/Pg boundary near El Kef; however continental weathering and post-depositional degradation may have masked forest fire signals. Significant increases in conifer markers (retene, simonellite, and pimanthrene), coincident with moderate increases in pyrogenic PAH concentrations could indicate increased conifer burning and forest loss related to the asteroid impact; however the alkylated PAH derivative index (APDI) and kinetic vs. thermodynamic isomer records support low-temperature, petrogenic formation (such as found in coals, oils, and/or organic-rich shales), instead of burning, as the dominant sources of PAHs to El Kef over this time span. More clearly, we found evidence for enhanced continental weathering during the first ~80,000 years post-impact, based on selective loss of low molecular weight PAHs as well as XRF elemental data, and an influx of thermally immature organic matter (based on hopanes and steranes), initially coincident with spikes in iridium and other trace metals at the K/Pg boundary. This period of enhanced continental weathering appears to match previous work at the El Kef outcrop (< 50 m from our cores), which suggests increased weathering (Vonhof and Smit, 1989) and ~100 kyr of climate warming (MacLeod et al., 2018). Our study illustrates the complicated picture of forest fires and weathering in the Western Tethys related to the K/Pg event, refines the stratigraphic position of the boundary at El Kef, and presents an unprecedentedly high-resolution record of environmental change across the boundary in North Africa.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8314

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