THE K–PG BOUNDARY: GEOLOGICAL EVENTS, MARINE ACIDIFICATION AND COLLAPSE OF PRIMARY PRODUCERS

The Cretaceous/Paleogene (K–Pg) boundary is the best-documented mass extinction event and calcareous nannoplankton (1-20μm of size) provide the most striking evidence of the biotic losses, of 131 late Maastrichtian species only 10-12 survived into the Danian (Bown, 2004). The severity of extinctions among pelagic calcifying species compared to noncalcacereous taxa (~50% siliceous diatoms, Macleod et al, 1997) or noncalcifying phytoplankton (Medelin et al, 2008) has suggested that a massive acidification occurred during the K-Pg boundary (Keller, 2014, Tyrrell et al, 2015). For deciphering mechanisms able to generate such event, we revisited this issue with a more complete scenario where the emplacement of the Deccan traps is combined with Chicxulub impact. In addition to rocks vaporization during the impact, we included a massive release of carbon and sulfur during the emplacement of the Deccan traps over a 250 kyr-long period (Self et al. (2006, 2008, Chenet et al., 2009, Schoene et al., 2015). Using an up-to-date biogeochemical model (GEOCLIM), different simulations were conducted to quantify the effects of seawater acidification on primary productivity, biomass and biodiversity thoughout K-Pg boundary. We then compared model outputs with available geochemical and palaeontological data.