Extent, duration, and nature of the Permian-Triassic superanoxic event

Abstract

The widespread development of anoxic and dysoxic deposition in marine settings occurred during the Permian-Triassic (P-Tr) transition interval. Facies varied according to paleobathymetry and paleolatitude. Thus, dark gray, uranium-enriched shales characterize deeper shelf locations over wide areas of northern Boreal seas, whereas the oceanic record consists of condensed, organic-rich, black shales. Finely laminated, pyrite-rich, micritic mudstones occur in equatorial Tethyan sections. Contemporaneous dolomitization in many shallow-marine settings provides further indirect evidence for widespread P-Tr anoxia. Similarly, common reports of unusual stromatolites in the earliest Triassic Griesbachian Stage could reflect the widespread occurrence of direct calcite precipitation from carbonate-saturated anoxic bottom waters. Oxygen-poor conditions are first recorded from the Late Permian, deep-water, accreted oceanic terranes of Japan. Such conditions vastly increased in extent in the interval between the latest Permian and the late Griesbachian, when dysaerobic facies developed in all but the shallowest of marine settings. The Panthalassa ocean was probably truly euxinic in this interval. Anoxia was never so extensive or so intense after this interval, and the superanoxic event ceased abruptly in equatorial Tethyan latitudes in the latest Griesbachian. Elsewhere, anoxia persisted at least into the Dienerian Stage in the Perigondwanan shelf sections of the Neo-Tethys, and deep-water anoxia may have persisted in Panthalassa until the middle Triassic.

The Phanerozoic δ88/86Sr record of seawater: New constraints on past changes in oceanic carbonate fluxes

“…8). The suggested low seawater sulfate concentrations of about 1 to 4 mmol/l (Luo et al, 2010), relatively high δ 34 S CAS signatures of more than 30 ‰ (Kampschulte and Strauss, 2004), the occurrence of pyrite in P/T sediments (Wignall and Twitchett, 2002) as a consequence of high BSR rates, and short term distribution patterns of redox-sensitive U (δ 238 U) and Mo isotopes in coeval sediments (Brennecka et al, 2011;Zhou et al, 2009) are also consistent with such a scenario. Accordingly, we argue that the massive carbonate formation suggested by our δ 88/86 Sr sw record and related model results was sustained and possibly triggered by BSR, producing large amounts of alkalinity in anoxic waters and sediments.…”

“…This hypothesis could also explain the inorganic precipitation of sea-floor CaCO 3 cements that are observed in Late Permian reef complexes and Early Triassic carbonate platforms and pelagic plateaus (Grotzinger and Knoll, 1995;Kershaw et al, 2011;Knoll et al, 1996;Riding and Liang, 2005;Woods et al, 1999). The long lasting anoxic conditions may have been supported and amplified by a combination of additional factors, such as global warming (Wignall and Twitchett, 2002), a stagnant and stratified ocean (Knoll et al, 1996), and long term high nutrient fluxes to the oceans from the weathering of coal-swamp deposits ( Fig. 8; Berner and Canfield, 1989).…”

High-resolution carbon isotope changes in the Permian–Triassic boundary interval, Chongqing, South China; implications for control and growth of earliest Triassic microbialites

“…Although oxygen-poor conditions were widespread (Wignall and Twitchett, 2002), microbialites did not form everywhere, probably because in those places the supersaturation was not high enough. Ostracod data from Laolongdong (CrasquinSoleau and Kershaw 2005) show low oxygen levels within the microbialite, consistent with the interpretation by Kershaw et al (2007).…”

“…Thus the elevated δ 13 C CARB values through the late Permian (Fig. 3) could reflect a stratified ocean where isotopically light carbon was stored in the deep ocean in stagnant conditions (Isozaki, 1997;Wignall and Twitchett, 2002), particularly in Tethys. If the ocean overturned, then return (by upwelling) of isotopically light carbon to surface waters could dominate the observed fall in δ 13 C CARB .…”

“…Following arguments arising from study of sulphur isotopes mentioned above, there is ample evidence that many earliest Triassic microbialites grew in a regime of poor oxygenation in shallow waters (Wignall and Twitchett, 2002), applicable to Laolongdong, but there are also sites with poor oxygenation (Wignall and Twitchett, 2002) that lack microbialites. Furthermore, Kozur (2007, p. 173) gave a general statement to note that ostracods, of types typical of oxygenated water, occur in the Abadeh section, Iran.…”