RESTORATION OF BENTHIC MARINE ECOSYSTEMS DURING THE EARLY AND MIDDLE TRIASSIC IN WESTERN PALEOTETHYAN RAMP SETTINGS

The recovery of the benthos following the late Permian mass extinction event is often described as occurring in the Middle Triassic associated with the return of Early Triassic Lazarus taxa, increased body sizes, platform margin metazoan reefs and increased tiering. Most quantitative paleoecological studies, however, are limited to the Early Triassic and the timing of the final phase of recovery is rarely quantified. Here, multivariate analyses are used to investigate the temporal and environmental distribution of benthic invertebrates from the Middle Triassic succession of the Mecsek Mountains, Hungary, which was deposited in a mixed siliciclastic-carbonate ramp setting on the northwestern margin of the Paleotethys Ocean. This new data is combined with the previously studied Lower Triassic succession of the Aggtelek Karst, Hungary, which records deposition in comparable facies and in the same region.

Here, we show that the Middle Triassic benthic fauna can be characterised by three distinct ecological states. The first two representing mollusc-dominated communities comparable to assemblages from the Spathian. The third ecological state occurs in the Pelsonian Binodosus Zone, and has a more ‘Palaeozoic’ structure with sessile brachiopods dominating assemblages. Similarly, other described upper Anisian and Ladinian assemblages from China and Canada, respectively, are dominated by brachiopods for the first time after the extinction. The return of community-level characteristics to pre-extinction levels and the diversification of invertebrates suggests that the final stages of recovery and the radiation of the benthos in ramp settings following the late Permian mass extinction occurred in the Pelsonian, ~8 million years after the extinction event.