Paper No. 11
Presentation Time: 11:00 AM


BACHAN, Aviv, Department of Geosciences, The Pennsylvania State University, 510 Deike Building, University Park, PA 16802 and PAYNE, Jonathan L., Department of Geological Sciences, Stanford University, 450 Serra Mall, Building 320, Stanford, CA 94305,

The end-Triassic mass extinction is associated with a short-lived negative excursion in δ13C of carbonate rocks and organic matter, followed by a more protracted positive δ13C excursion. Previous modeling efforts have focused on the negative δ13C excursion, but the positive δ13C excursion has not been dealt with quantitatively. Moreover, up to now no attempts have been made to address the likely behavior of other isotope systems (δ34S, δ44Ca) across the boundary.

Here we utilize a multi-element box model (CCaPS: carbon, calcium, phosphate, and sulfate) to explore the fit between hypothesized scenarios for perturbations to the global carbon cycle and observed isotope proxy data. We perturb the model with carbon inputs representing pulses of carbon from volcanic and sedimentary reservoirs. We find that on the most isotopically depleted end (e.g. methane), the amount of carbon required to match the magnitude of the negative excursion in δ13C is insufficient to produce the subsequent positive δ13C excursion, except under the most extreme parameterizations of C:P burial ratios. Rapid release of a larger amount of more isotopically enriched carbon (coal, volcanic) replicates both the negative and positive excursions within more plausible parameterizations of C:P burial ratios. Under all model scenarios, the elevated burial of organic carbon leading to the positive δ13C excursion is associated with increased burial of sulfide, causing a coincident positive excursion in δ34S of seawater sulfate. Under the scenario most similar to observed data, the model further predicts a rapid and temporary increase in pCO2 coincident with the volatile release, as well as a temporary decrease in carbonate saturation. The decline in carbonate saturation is predicted to be associated with a negative excursion in δ44Ca, whose magnitude is dependent on model parameterization. The release of volatiles during the emplacement of the Central Atlantic Magmatic Province is widely hypothesized as the driver of the environmental perturbation. The CCaPS model suggests that carbon release can account for existing isotope data, and provides additional constraints on changes in ocean chemistry which may have accompanied the biotic catastrophe.