MULTI-PROXY MODELING OF THE END-TRIASSIC ENVIRONMENTAL PERTURBATION

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.