Title: Anoxia as a cause of the Permian/Triassic mass extinction: facies evidence from northern Italy and the western United States
Abstract: Facies, faunal and geochemical evidence from the Permian/Triassic boundary sediments of the Dolomites and Idaho indicates a major anoxic event in the earliest Triassic. In both regions, the basal beds consist of finely laminated micrites with common syngenetic pyrite. The only fauna consists of occasional bedding plane assemblages of Lingula or Clacaria, a typical lower dysaerobic assemblage. This is a level where previous studies have shown a major negative carbon isotope excursion and a cerium anomaly. In the Dolomites, the pyritic micrite directly overlies strata containing a diverse and typically Permian marine fauna of algae, foraminifers (including fusulinids) and articulate brachiopods, implying an abrupt extinction in contradiction to many previous views. Sequence stratigraphic analysis of the Dolomite boundary sediments reveals a minor sequence boundary in the late Permian followed by extremely rapid transgression leading to the development of the relatively deep water pyritic micrite — a maximum flooding surface at the Permo-Triassic boundary. A further pulsed deepening in the lower Griesbachian, recorded in both the Dolomites and Idaho, lead to the widespread establishment of dysaerobic facies. It is clear that most of the extinctions occurred at the erathem boundary although the subsequent failure of the marine benthos to fill the empty ecospace in the ensuing Griesbachian may have been due to the widespread development of dysaerobic conditions.
Publication Year: 1992
Publication Date: 1992-05-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 440
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