Abstract
AbstractLower Triassic marine strata in Spitsbergen accumulated on a mid-to-high latitude ramp in which high-energy foreshore and shoreface facies passed offshore into sheet sandstones of probable hyperpycnite origin. More distal facies include siltstones, shales and dolomitic limestones. Carbon isotope chemostratigraphy comparison allows improved age dating of the Boreal sections and shows a significant hiatus in the upper Spathian. Two major deepening events, in earliest Griesbachian and late Smithian time, are separated by shallowing-upwards trends that culminated in the Dienerian and Spathian substages. The redox record, revealed by changes in bioturbation, palaeoecology, pyrite framboid content and trace metal concentrations, shows anoxic phases alternating with intervals of better ventilation. Only Dienerian–early Smithian time witnessed persistent oxygenation that was sufficient to support a diverse benthic community. The most intensely anoxic, usually euxinic, conditions are best developed in offshore settings, but at times euxinia also developed in upper offshore settings where it is even recorded in hyperpycnite and storm-origin sandstone beds: an extraordinary facet of Spitsbergen's record. The euxinic phases do not track relative water depth changes. For example, the continuous shallowing upwards from the Griesbachian to lower Dienerian was witness to several euxinic phases separated by intervals of more oxic, bioturbated sediments. It is likely that the euxinia was controlled by climatic oscillations rather than intra-basinal factors. It remains to be seen if all the anoxic phases found in Spitsbergen are seen elsewhere, although the wide spread of anoxic facies in the Smithian/Spathian boundary interval is clearly a global event.
Highlights
The development and intensification of marine anoxia during the Permian-Triassic is a well-known phenomenon widely regarded as a direct cause of the contemporary mass extinction (e.g. Wignall & Hallam, 1992; Isozaki, 1994; Wignall & Twitchett, 2002; Algeo et al 2008; Bond & Wignall, 2010; Song et al.2014)
At Festningen, the sharp negative excursion close to the base of the Vardebukta Formation is a marker for the Permian/Triassic boundary and this is followed by a rapid rise to heavier values before a slowdown in the trend
Mørk et al (1982) who placed the base of the Tvillingdodden Formation at the base of the Smithian, rather than in the mid Smithian as we suggest here (Fig. 2)
Summary
The development and intensification of marine anoxia during the Permian-Triassic is a well-known phenomenon widely regarded as a direct cause of the contemporary mass extinction (e.g. Wignall & Hallam, 1992; Isozaki, 1994; Wignall & Twitchett, 2002; Algeo et al 2008; Bond & Wignall, 2010; Song et al.2014). The temporal development and intensity of Early Triassic marine anoxia varied considerably with the Smithian/Spathian (S/S) interval being especially noteworthy as an intense phase of oxygen deprivation (Galfetti et al 2007; Wignall et al 2010; Meyer et al 2012; Song et al 2012; Grasby et al 2013; Sun et al 2015). Song et al 2012; Tian et al 2014) and the Sverdrup Basin (Grasby et al 2013), the spatial development of marine anoxia is unconstrained and the context of the events, such as the S/S episode, within the prolonged history of the Early Triassic “superanoxic event”.
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