Geochemical consequences of intense pulse-like degassing during the onset of the Central Atlantic Magmatic Province

The Triassic-Jurassic boundary (TJB) is marked by one of the five largest mass extinctions of the Phanerozoic and the eruption of a large igneous province: the Central Atlantic Magmatic Province (CAMP). The TJB is characterized by a carbonate production crisis, by negative excursions in the carbon isotopic ratio of buried organic matter, and by successive peaks in atmospheric CO2. Here we use the numerical model GEOCLIM to explore the possible connections between the CAMP emplacement and the observed carbon cycle perturbations. Different degassing scenarios linked to the CAMP eruption are explored. We show that the emission of realistic amounts of CO2 that follow a geologically constrained degassing scenario as short-term peaks (less than 10 ka) leads to successive decrease in carbonate production, as observed in the geological record. We also calculate the evolution of carbon isotopes and show that our model reproduces the amplitude of the isotopic excursion with a volcanic degassing of CO2 characterized by a carbon isotopic composition of -20 parts per thousand. Such low values could be associated to carbon pools of light isotopic composition located at the transition zone [Cartigny, P.2010, Earth and Planetary Science Letters, v. 296, p. 329-339] and not necessarily to biogenic methane release. Finally, the model predicts a succession of short-term CO2 rises, with an amplitude in close agreement with available proxy-based reconstructions. (C) 2015 Elsevier B.V. All rights reserved.