Modeling the consequences on late Triassic environment of intense pulse-like degassing during the Central Atlantic Magmatic Province using the GEOCLIM model
1Institut français du pétrole, 1 & 4 rue Bois-Préau, 92 Rueil-Malmaison, France
2Institut de Physique du Globe, UMR7154, Sorbonne Paris Cité, 1 rue Jussieu, 75238 Paris cedex 05, France
3Laboratoires des Sciences du Climat de l'Environnement, CNRS-CEA, CEA Saclay, Orme des merisiers, Bât. 701, 91191 Gif-sur-Yvette cedex, France
4UFR des Sciences de la Terre, de l'Environnement et des Planètes, Université Paris 7, Sorbonne Paris Cité, 35 rue Hélène Brion, 75205 Paris cedex 13, France
5Géosciences Environnement Toulouse, CNRS-Université de Toulouse III, 14 avenue E. Belin, 31400 Toulouse, France
Abstract. The Triassic-Jurassic boundary (TJB) is associated with one of the five largest mass extinctions of the Phanerozoic. A deep carbon cycle perturbation and a carbonate production crisis are observed during the late Triassic. The Central Atlantic Magmatic Province (CAMP), one of the most important large igneous provinces of the Phanerozoic, emplaced at the TJB. To understand the carbon cycle perturbations observed at the TJB, we investigate the consequences of CO2 degassing associated to the CAMP emplacement on atmospheric and oceanic carbon cycle. The CO2 input within the atmosphere due to volcanism has been modeled using a global biogeochemical cycle box model (COMBINE) coupled with a climate model (FOAM). Weathering fluxes and CO2 equilibrium are constrained by the Rhaetian paleogeography and different scenarios of the CAMP emplacement are modeled. The study focuses (1) on the geological record and the carbonate productions crisis and (2) on the sedimentary carbon isotope record. For point (1), comparison of different modeling scenarios shows that a Gaussian CO2 emission distribution over the duration of the main activity phase of the CAMP fails in reproducing any of the geological observations, mainly the carbonate production crisis observed in the late Rhaetian sediments. Contrastingly, intense degassing peaks lead to successive decrease in carbonate production as observed in the geological record. For point (2), the perturbations of carbon cycle due to the degassing of CO2 with a mantellic carbon isotopic composition of −5‰ do not reproduce the intensity of the observed carbon isotope excursions. This was achieved in our model by assuming a mantellic carbon isotopic composition of −20‰. Even if this hypothesis requires further investigations, such low values may be associated to degassing of carbon from pools of light isotopic carbon located at the transition zone (Cartigny, 2010), possibly linked to setting of large igneous provinces (LIP's). Breakdown of biological primary productivity can also partially account for the sedimentary carbon isotope excursions and for the observed increase of atmospheric pCO2.