Geochemical consequences of intense pulse-like degassing during the onset of the Central Atlantic Magmatic Province
Résumé
The Triassic–Jurassic boundary (TJB) ismarked by one of the five largestmass extinctions of the Phanerozoic and
the eruption of a large igneous province: the Central AtlanticMagmatic 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. Herewe use the numerical model GEOCLIMto 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-termpeaks (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‰. 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 biogenicmethane release. Finally, themodel predicts a succession
of short-term CO2 rises, with an amplitude in close agreement with available proxy-based reconstructions.