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The AAPG/Datapages Combined Publications Database

CSPG Special Publications

Abstract


Pangea: Global Environments and Resources — Memoir 17, 1994
Pages 797-804
Boundaries

The Earliest Triassic as an Anoxic Event, and Its Relationship to the End-Palaeozoic Mass Extinction

A. Hallam

Abstract

Two independent geochemical criteria, cerium anomalies and carbon/sulphur ratios, suggest a condition of widespread oceanic anoxia at the start of the Triassic. This is supported by the occurrence of extensive anaerobic and dysaerobic facies and the absence of reef and associated high diversity benthic communities. These general conclusions are tested by detailed facies and sequence stratigraphic analysis of key sections across the Permian-Triassic boundary in the former Palaeotethys region, in Italy, Pakistan and China. The results suggest that the youngest Permian faunas became extinct as a consequence of the extensive spread of anoxic waters into epicontinental seas associated with a striking marine transgression at the beginning of the Triassic. Carbon isotope data from both carbonate and organic carbon suggest that there was a sharp drop in marine organic productivity at the P-T boundary, so that, unlike other oceanic anoxic events, there is a negative shift of δ13C.

There was a delayed recovery to the mass extinction event, with reef communities and Lazarus taxa returning in the Middle Triassic, indicating that a greater number of taxa survived in Early Triassic refugia than commonly supposed. Comparisons are made with other mass extinction events, suggesting that the Permian-Triassic event was not unique in its likely causation, being merely a consequence of events on a larger scale than the others.


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