The turnover of land plants in Europe at the boundary of the Triassic and Jurassic periods, 200 million years ago, was driven by environmental changes triggered by massive volcanic activity, according to a new study published online today (13 July) in Nature Geoscience. The study is titled 'Floral changes across the Triassic/Jurassic boundary linked to flood basalt volcanism.'
One of the five largest extinctions occurred at the boundary of the Triassic and Jurassic periods, some 201.6 million years ago. The loss of marine biodiversity at the time has been linked to extreme greenhouse warming, triggered by the release of carbon dioxide from flood basalt volcanism in the central Atlantic Ocean. In contrast, the biotic turnover in terrestrial ecosystems is not well understood, and cannot be readily reconciled with the effects of massive volcanism.
Bas van de Schootbrugge of the Institute of Geosciences, Goethe University Frankfurt and colleagues used three drill cores from Germany and Sweden to reconstruct the changes in the environment. They found that gymnosperm forests in NW Europe were transiently replaced by fern and fern-associated vegetation, a pioneer assemblage commonly found in disturbed ecosystems. The Triassic-Jurassic boundary is also marked by an enrichment of polycyclic aromatic hydrocarbons, which, in the absence of charcoal peaks, they interpret as an indication of incomplete combustion of organic matter by ascending flood basalt lava.
They concluded that the terrestrial vegetation shift was so severe and wide ranging that it is unlikely to have been triggered by greenhouse warming alone. Instead, the authors suggest that the release of pollutants such as sulphur dioxide and toxic compounds such as the polycyclic aromatic hydrocarbons may have contributed to the extinction.