Palynofloral associations before and after the Permian–Triassic mass extinction, Kap Stosch, East Greenland

Abstract

The Permian–Triassic boundary (PTB) interval is known to document a major biodiversity crisis in the history of
life. It is generally accepted that this crisis had a significant impact on marine invertebrates. The consequences
for terrestrial ecosystems are still controversially discussed. Based on palynological analysis we present a high
time resolution microfloral succession of the expanded Late Permian (Wuchiapingian)–Early Triassic (Dienerian)
section from Kap Stosch, East Greenland. The quantitative distribution of palynomorphs (range charts and relative
abundance data) allows for the differentiation of six distinct palynofloral associations. Ammonoids and
conodonts provide independent age control for these assemblages. The Wuchiapingian association I, documented
from the Ravnefjeld Formation, shows a typical Late Permian assemblage dominated by bisaccate and
monosaccate pollen grains and Vittatina spp. It is separated from association II, present in the basal part of the
Wordie Creek Formation, by an important hiatus. This association of Changhsingian or earliest Griesbachian age
is characterised by the common occurrence of Ephedripites spp. and reduced abundance and diversity of Vittatina
spp. Association III, dated as Griesbachian by the presence of ammonoids, is marked by high relative abundances
of taeniate bisaccate pollen grains and high spore diversity. A distinct floral break occurs between the gymnosperm
dominated Permian and Griesbachian floras and the lycopsid spore dominated Dienerian associations
IV–VI. Ammonoid occurrences verify a Dienerian age for the latter associations. Association V is marked by the
absence of non-taeniate bisaccate, striate monosaccate pollen grains, and Vittatina spp. Aratrisporites spp. a typical
Triassic lycopsid spore occur consistently from this level onwards. Association VI is characterised by
highest lycopsid spore abundances. Cluster analysis demonstrates that Griesbachian assemblages (associations
II?–III) are similar to Permian ones and clearly differ from Dienerian assemblages confirming a major floral turnover
near the Griesbachian–Dienerian boundary. In contrast to the commonly advocated idea of a profound
effect of the PTB crisis on terrestrial ecosystem, the present data set shows no major effect of the PTB event on
floral diversity. Strikingly, considering species numbers alone, the major floral event at the Griesbachian–Dienerian boundary is also indistinct, but sticks out from abundance data, emphasising the necessity to consider both species ranges and abundances data to characterise terrestrial ecosystem dynamics in critical time intervals. Generally we note a gradual disappearance of Permian floral elements such as Vittatina spp., Weylandites spp. or Florinites spp. and a gradual appearance and diversification of typical Triassic spores such Aratrisporites spp. and Densoisporites nejburgii.