Palaeoecology of the late Permian mass extinction and subsequent recovery
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Climate warming during the latest Permian is associated with the most severe mass extinction event of the Phanerozoic, and the expansion of hypoxic and anoxic conditions into shallow shelf settings. Our understanding of the magnitude, pattern and duration of the extinction event and subsequent recovery remains equivocal. Evidence suggests that the action of waves provided an oxygenated refuge, i.e. ‘habitable zone’, above wave base that may be limited to high latitudes, in association with a faster pace of recovery. In addition, advanced recovery faunas have been documented from the Induan and there is evidence from the pelagic realm that further biotic crises may have delayed the recovery of benthic organisms coinciding with large carbon isotope perturbations at the Lower Triassic sub-stage boundaries. To test these hypotheses, novel palaeoecological data was collected from localities in Hungary, northern Italy, and Svalbard. To understand better the ecological impact of the extinction, a database of all known benthic marine invertebrates from the Permian and Triassic periods was created, with each taxon assigned to a functional group based on their inferred lifestyle. This study found that the skeletal and ichnofaunal assemblages consistent with advanced ecological recovery are limited to settings aerated by wave activity, which supports the habitable zone hypothesis. In the western Palaeotethyan sections it was found that the proximal end of the ‘habitable zone’ was limited by persistent environmental stress attributed to increased runoff that resulted in large salinity fluctuations, increased sedimentation rates and eutrophication creating an environment only favourable for opportunistic taxa. In the Tirolites carniolicus Zone, however, the ‘habitable zone’ expands into more proximal and offshore settings. This is associated with climate cooling in the late Spathian. The data also demonstrate that despite the taxonomic severity of the extinction, only one mode of life went extinct and only one subsequently evolved in the aftermath. Functional diversity was, however, reduced in particular regions and environmental settings, and recovery varied spatially and temporally. In western Palaeotethys, benthic communities record evidence for biotic crises, such as reduced tiering in the Smithian, associated with Early Triassic carbon isotope excursions, but, until the Spathian there was no significant change in the composition of the benthic faunas.
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