PALEOECOLOGY OF THE LOWER TRIASSIC SERVINO FORMATION, ITALY

The late Permian mass extinction is the most severe biotic crisis of the Phanerozoic, associated with the expansion of hypoxic and anoxic conditions in shallow shelf settings. It has been hypothesized that wave aeration provided oxygen to the sea floor, creating a ‘habitable zone’ in the shallowest environments that allowed the survival and rapid recovery of benthic invertebrates during the Early Triassic. We test this hypothesis by studying the rock and fossil records of the Servino Formation, Italy. The fossil assemblages from the Servino Formation record low diversity communities comparable to other western Paleotethyan localities that are restricted to the proposed ‘habitable zone’. The lack of recovery prior to the Spathian, i.e. final substage of the Early Triassic, may be due to environmental stress associated with restricted marine conditions and shows that survival and recovery within the proposed ‘habitable zone’ is limited, at least in the Servino Formation. The lower Spathian Myophoria Beds Member record an increase in taxonomic and functional richness, the appearance of stenohaline, erect taxa, as well as a significant turnover and increased heterogeneity in the composition of benthic assemblages within the proposed ‘habitable zone’. Prior to the late Spathian “Upper Member” bioturbation is weakly developed and restricted to only a few thin horizons. In the “Upper Member”, however, the intensity and proportion of bioturbated rock increases, which is attributed to climatic cooling and a reduction in the intensity of climate-induced environmental stressors. The expansion of the ‘habitable zone’ during the late Spathian is now recognised in deep offshore (below wave-base) and nearshore settings of the western Paleotethys and reflects a third phase of recovery of benthic marine ecosystems, approximately 4.5 million years after the extinction event.