ENVIRONMENTAL CONTROLS ON THE RECOVERY OF BENTHIC INVERTEBRATE COMMUNITIES IN THE WAKE OF THE LATE PERMIAN MASS EXTINCTION

Climate warming during the late Permian is associated with the most severe mass extinction event of the Phanerozoic, and the expansion of hypoxic and anoxic conditions in shallow shelf settings. It has been hypothesised that wave aeration provided an oxygenated ‘habitable zone’ in the shallowest environments that allowed some survival and a rapid recovery of benthic invertebrates during the Early Triassic. Here, we use multivariate analyses to investigate the temporal and environmental distribution of benthic invertebrates from the Lower Triassic succession of the Aggtelek Karst, Hungary, which was deposited in a mixed siliciclastic-carbonate ramp setting on the northwestern margin of the Paleotethys Ocean. Nearshore settings recorded in the Griesbachian, Dienerian, Smithian and Spathian are characterised by taxonomically homogenous assemblages of low diversity and low evenness. Ecological and taxonomic recovery in this environmental setting was hampered by persistent environmental stress, attributed to increased runoff that resulted in large salinity fluctuations, increased sedimentation rates and eutrophication leading to an environment only favourable for opportunistic taxa. In contrast, facies representing shoal and mid-ramp settings further offshore are characterised by assemblages with high diversity and functional complexity, including the presence of both erect and deep-infaunal tier taxa. Prior to the upper Spathian, Tirolites carniolicus Zone, the shelly fossils and trace fossils are limited to - facies that were deposited under wave activity, which supports the ‘habitable zone’ hypothesis. In the Tirolites carniolicus Zone itself, however, the oxygen minimum zone apparently retreated offshore and the habitable deeper shelf settings became rapidly colonised by shallow-water taxa, and these facies record the highest levels of diversity and bioturbation.