Anomalies in global carbon cycling and extinction at the Triassic/Jurassic boundary : evidence from a marine C-isotope record

This study investigates whether the end-Triassic biotic crisis was coupled with a perturbation of the marine C-isotope budget. The marine C-isotope signature serves as a proxy of the marine carbon reservoir and ultimately of the global C cycle. A continuous shallow water marine limestone succession from the Western Southern Alps (Bergamasc Alps, northern Italy) provides information on the end-Triassic biotic crisis and on the evolution of the marine carbon reservoir across the Triassic/ Jurassic (T/J) boundary. The established carbonate C-isotope curve is marked by a negative C-isotope pulse coinciding with the disappearance of the end-Triassic benthic faunal assemblage and a widespread Rhaetian carbonate platform drowning event. The negative spike is followed by a positive C-isotope excursion starting at the palynological T/J transition. The negative Cisotope pulse may have resulted from the sudden release of gas hydrates. The positive isotope excursion records a global change in organic carbon burial rates, probably in response to elevated atmospheric CO2 levels at a time of massive volcanic activity in the Central Atlantic Magmatic Province. High CO2 levels were responsible for the end-Triassic biocalcification crisis, carbonate platform collapse, and, possibly, the sudden release of methane from gas hydrate.