[B-CG06] Decoding the history of Earth: From Hadean to the present

[BCG06-23] Drivers of the K-Pg mass extinction: impact and volcanism interaction

*Kunio Kaiho¹, Jeroen E. Sonke², Akane Yamakawa³, David Jones⁴, Satoshi Takahashi⁵, Masanobu Yamamoto⁶, Naga Oshima⁷, Laure Laffont², Stephen E. Grasbyi⁸ (1.Tohoku University, 2.Université Paul Sabatier Toulouse 3, 3.National Institute for Environmental Studies, 4.Amherst College, 5.Nagoya University, 6.Hokkaido University, 7.Meteorological Research Institute, 8.University of Calgary)

Keywords:Cretaceous-Paleogene boundary mass extinction, Climate change, mercury isotopes, meteorite impact, volcanism, organic molecule indicators

This study provides novel insights into the mechanisms driving the Cretaceous-Paleogene (K-Pg) mass extinction. Key findings include: (i) Spikes in iridium (Ir) and mercury (Hg) within K-Pg layers, with elevated Hg/Ir ratios compared to chondritic values at both proximal (near the impact site) and distal locations, suggest a simultaneous bolide impact and Deccan Trap volcanism. (ii) Strong correlations between δ²⁰²Hg, the coronene index, and Δ¹⁹⁹Hg in proximal samples introduce a new method for distinguishing volcanic emissions from impact-related sources. (iii) Similarities in volcanic δ²⁰²Hg and Δ¹⁹⁹Hg in high-Hg pre- and post-impact sediments, alongside medium to high coronene levels, indicate that Hg originated primarily from Deccan Traps eruptions rather than background volcanic activity. (iv) Near-zero Δ¹⁹⁹Hg values at the top of impact turbidites at the proximal site suggest local darkness caused by the ejecta cloud. (v) The largest volcanic plume eruptions, likely from the Deccan Traps, occurred approximately one year after the Chicxulub impact. (vi) These dual events coincided with terrestrial plant devastation, severe soil erosion, and the extinction of surface-dwelling planktonic foraminifera. (vii) Climate models incorporating target rock soot followed by volcanic SO₂ emissions predict prolonged sunlight reduction and global cooling. (viii) TEX₈₆^H data indicate post-impact warming, correlating with the extinction of deep-sea planktonic foraminifera. These findings suggest that the Chicxulub asteroid impact, combined with Deccan Trap SO₂ emissions, triggered an initial phase of cooling and environmental collapse, leading to the extinction of surface-dwelling planktonic foraminifera, followed by deep-sea foraminiferal extinction due to subsequent global warming.