On the timing of palaeoenvironmental changes at the Permo‐Triassic (P/TR) boundary using conodont biostratigraphy

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Abstract
Four conodont zones can be recognised during the Permo‐Triassic (P/Tr) boundary interval; in ascending order, the Hindeodus latidentatus, H. parvus, Isarcicella isarcica and Clarkina carinata Zones. These zones have been recognised in southern and equatorial palaeolatitudes and initial results suggest that they may also be applied in high northern palaeolatitudes. By using this conodont zonation it is therefore possible to assess the global palaeoenvironmental changes associated with the P/Tr mass extinction. Many shallow shelf sections have an unconformity at the base of the latidentatus Zone which may correspond to the well known but over‐stated P/Tr regression. The succeeding latidentatustocarinata interval saw continuous deepening in most sections. Shallow marine facies are well developed in the latidentatus Zone and they contain a diverse array of typical Late Permian taxa, only in basinal locations are dysaerobic/anaerobic strata locally developed (e.g. South China, Kashmir). Anoxic deposition became spectacularly widespread in the parvus Zome in both shallow and deep water areas (e.g. the Dolomites and Sicily respectively). This level also corresponds to the main mass extinction and by the base of the parvus Zone the extinction event was to all intents over. The exception is provided by the southern latitude sections of the Salt Range, Pakistan where Permian benthic taxa persisted until the carinata Zone. It can be no coincidence that the demise of these holdover taxa is marked by the first development of dysaerobic strata in the region.