THE K–PG BOUNDARY: HOW GEOLOGICAL EVENTS LEAD TO COLLAPSE OF MARINE BIODIVERSITY

The cause(s) of Cretaceous/Paleogene (K–Pg) mass extinction event is a matter of debate since three decades. A first scenario connects the K–Pg crisis with the Chicxulub impact while the second scenario evokes the emplacement of the Deccan traps in India as the cause for the K–Pg  biodiversity collapse. Pierazzo et al. (1998) estimated that the extraterrestrial bolide lead to an instantaneously CO₂ degassing ranging from 880 Gt to 2,960 Gt into the atmosphere, together with a massive release of SO₂ ranging from 150 to 460 Gt_.. Self et al. (2006, 2008) and Chenet et al. (2009) suggested that the emplacement of the Deccan traps released 15,000 Gt to 35,000 Gt of CO₂ and 6,800 Gt to 17,000 Gt of SO₂ over a 250 kyr-long period (Schoene et al., 2015). To decipher and quantify the long term environmental consequences of both events, we tested different scenarios: a pulse-like magmatic degassing, a bolide impact, and a combination of both. To understand the environmental changes and quantify biodiversity responses, we improve GEOCLIM, a coupled climate-carbon numerical model, by implementing an biodiversity model in which marine species are described by specific death/born rates, sensitivity to abiotic factors (temperature, pH, dissolved O₂, calcite saturation state) and feeding relationships, each of these characteristics is assigned randomly. Preliminary simulations accounting for the eruption of the Deccan traps show that successive cooling events (S-aerosols effect) combined with a progressive acidification of surface water (caused by CO₂ and SO₂ injections) cause a major collapse of the marine biomass. In addition to a collapse by one order of magnitude of the marine productivity, our experiments show that most of the equatorial species, less tolerant to cooling events, disappear from low latitudes zones with a response depending on the degassing scenario. According to our study the post crisis recovery occurs in a context of post-eruption warming, which increases the continental weathering. This enhanced input of nutriments and alkalinity quickly restore conditions for a very efficient primary productivity. Additional simulations in which Chicxulub impact, different community structures (regional versus global extent of species…) and processes leading to post crisis biodiversity recovery will be discussed