ENVIRONMENTAL CHANGES AT THE KT BOUNDARY: A GEOCHEMICAL NUMERICAL APPROACH

The cause(s) of Cretaceous/Tertiary (K/T) mass extinction event is a matter of debate since three decades and remains not fully understood yet. A first scenario connects the KT crisis with the impact of an asteroid in Yucatan while the second scenario evokes the emplacement of the Deccan traps in India 66 Ma ago as the real cause for the K-T mass extinction, a hypothesis supported by the fact that every mass extinction, since the Devonian, occurred during the emplacement of large basaltic provinces. Up to now the consequences of bolide impact and volcanism have been poorly quantified. In this study, to improve our understanding the environmental changes that occurred during the K/T boundary, we used a biogeochemical model to investigate theses two scenarios and quantify how sulfur dioxide (SO₂) and carbon dioxide (CO₂), released within the atmosphere, destabilized the global climate-carbon cycle system. Pierrazo et al. (1998) estimated that the extraterrestrial bolide lead to the instantaneously injected from 880 Gt to 2,960 Gt of CO₂ and from 150 to 460 Gt of SO₂. Self et al. (2006, 2008) and Chenet et al (2009) suggested that the emplacement of the Deccan traps released from 15,000 Gt to 35,000 Gt of CO₂ and from 6,800 Gt of 17,000 Gt of SO₂ over a nearly 400 kyr-long period. To decipher and quantify the environmental consequences of both events, we tested different scenarios: a pulse-like magmatic degassing scenario in absence of impact, a bolide impact in absence of volcanism, and a combination of pulse-like magmatic degassing scenarios and bolide impact.