A new investigation into the so-called "Carnian Crisis", conducted by a team led by Alexander Lukeneder, a paleontologist at the Natural History Museum of Vienna, reveals astounding events surrounding global climate change during the Triassic period.

The study, published in Scientific Reports, reveals astonishing details about how the global climate changed 233 million years ago, leading to a massive extinction in the seas of the Mesozoic era.

The global “Carnian Crisis”, which lasted for two million years (from 234 to 232 million years ago), left its mark on the rocks of the Reiflinger Basin near Lunz am See. Massive volcanism in Canada and the northern United States triggered the formation of a basalt layer over a thousand meters thick. These volcanic eruptions released enormous amounts of CO2 into the atmosphere, drastically altering the climate.

The late Triassic was characterized by a greenhouse climate with monsoonal precipitation, increasing the influx of mud into the Tethys Ocean. Reefs were smothered, carbonate platforms died, and oxygen became scarce on the seafloor, creating dead zones.

Reiflinger Basin
Reiflinger Basin. Credit: A. Lukeneder / NHM Wien

Under these conditions, deposits with incredibly well-preserved fossils were formed, including ammonites, squids, mussels, snails, crabs, marine isopods, and bristle worms. Among the exceptional fossils are flying fish, the coelacanth Coelocanthus, and the lungfish Tellerodus.

The sea of the Reiflinger Basin was surrounded by islands with the first coniferous forests like Voltzia, which grew in warm and humid conditions. The proximity to freshwater is confirmed by alluvial remains of terrestrial plants and numerous findings of crustaceans from the genus Euestheria. The “Carnian Crisis” is observed in a narrow geological strip in Austria, extending from Mödling in Lower Austria to northern Styria near Großreifling.

The research has allowed exploration of the late Triassic environment and a better understanding of the environmental conditions, food chains, and predator-prey relationships of the time. The food chain began with tiny crustaceans, followed by small fish and predatory squids, and culminated with ammonites preyed upon by larger predatory fish. Ichthyosaurs were the top predators in this ecosystem.

Food Chains in the Reiflinger Basin
Food Chains in the Reiflinger Basin. Credit: A. Lukender / NHM Wien

The international team, led by Alexander Lukeneder and composed of experts from various institutions, conducted extensive rock and fossil analysis using advanced methods. Macrofossils like ammonites, squids, and fish, as well as representatives of the flora, were studied.

Pollen associations and their changes during the “Carnian Crisis” were also analyzed. These studies show a shift from marine conditions to freshwater influences, with an increase in alluvial plains and marshes with pioneer vegetation.

Thanks to microfossils and geochemical and geophysical analyses, a detailed picture of the environment 233 million years ago in the Austrian limestone Alps has been obtained. The revised identification of ammonites and the analysis of tiny fish teeth allow precise age classification. The rock sequences of the limestone Alps are comparable to deposits of the same era throughout the Tethys region.

Rock with ammonites, conodonts and pollen
Rock with ammonites, conodonts and pollen. Credit: A. Lukeneder / NHM Wien

Volcanism caused a strong emission of CO2, altering the global carbon isotope composition, and this chemical footprint is detected in rocks near Lunz am See. Geophysical measurements show an increase in radiant particles and magnetizable minerals during the “Carnian Crisis”, as well as a change in the composition of clay minerals.

These conditions reflect a greater input of organic residues and weathering products of terrestrial plants due to increased precipitation.

The research, funded by various institutions, has revealed how material washed in from land permanently altered the water chemistry, creating hostile and oxygen-poor conditions on the seafloor. This study offers a deep understanding of how one of the greatest environmental disasters in Earth’s history affected the ecosystem and left its mark in the Austrian rocks.


Sources

Naturhistorisches Museum Wien | Lukeneder, A., Lukeneder, P., Sachsenhofer, R.F. et al. Multi-proxy record of the Austrian Upper Triassic Polzberg Konservat-Lagerstätte in light of the Carnian Pluvial Episode. Sci Rep 14, 11194 (2024). doi.org/10.1038/s41598–024–60591–9


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