The end-Triassic mass extinction event is estimated to have caused the disappearance of several marine families (23%) and genera (50%) on a global scale (Hallam and Wignall, 1999; van de Schootbrugge et al. 2007). In the terrestrial realm regional to supraregional losses of vertebrate families (up to 42%) and plant species (up to 95%) have been recorded (McElwain et al, 1999, 2007; Olsen et al., 2002; Whiteside et al., 2007). The event is temporally linked to the flood basalt volcanism of the Central Atlantic Magmatic Province (CAMP)(Schoene et al. 2010) and major perturbations in the carbon cycle recorded in stable carbon isotope records globally are generally attributed to the effects of outgassing of ¹²C-enriched CO₂ from this large igneous province (Hesselbo et al., 2002).

High resolution palynological and bulk organic C-isotope data from Triassic–Jurassic (T/J) successions in Denmark and Sweden provide evidence of major and partly coeval shifts in the marine and terrestrial palynofloras. The demise of typical Rhaetian dinoflagellate cysts and the temporary disappearance of these phytoplankton appear to coincide with an interval indicating terrestrial deforestation marked by a major decline in pollen from conifers, cycads and ginkgos. Instead high abundances of fern spores, the enigmatic pollen Ricciisporites tuberculatus and sphaeromorphs totally dominate the assemblages. Additional significant features of this interval within the basin, include increased erosion and reworking, changes in fluvial style and temporary loss of peat-forming vegetation.

Many of the changes recorded in the T/J-boundary succession of the Danish Basin can be attributed to outgassing of SO₂ from the CAMP, and subsequent acid rain and acid deposition (van de Schootbrugge et al. 2009). However, the high abundance of sphaeromorphs within the end-Triassic event interval of the Danish Basin remains enigmatic. There are two working hypotheses for the mass occurrence of these sphaeromorphs: 1) They are in situ and represent a prasinophycean algal bloom. 2) They are reworked and represent a phase of increased weathering and erosion. The possible causes, consequences, as well as palaeoecological significance of these two hypotheses on the interpretation of the end-Triassic event will be discussed.

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McElwain, J.C., Beerling, D.J. and Woodward, F.I. (1999). Fossil plants and global warming at the Triassic-Jurassic boundary. Science 285, 1386-1390.

McElwain, J.C., Popa, M.E., Hesselbo, S.P., Haworth, M. and Surlyk, F. (2007). Macroecological responses of terrestrial vegetation to climate and atmospheric change across the Triassic/Jurassic boundary in East Greenland. Paleobiology 33, 547-573.

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Schoene, B., Guex, J., Bartolini, A., Schaltegger, U. and Blackburn, T.J. (2010). Correlating the end-Triassic mass extinction and flood basalt volcanism at the 100 ka level. Geology 38, 387-390.

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