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Ultra-shallow-marine anoxia in an Early Triassic shallow-marine clastic ramp (Spitsbergen) and the suppression of benthic radiation

Wignall, Paul B.; BOND, DAVID P. G.; BLOMEIER, DIERK P. G.; Wignall, Paul B.; Bond, David P. G.; Sun, Yadong; Grasby, Stephen E.; Beauchamp, Benoit; Joachimski, Michael M.; Blomeier, Dierk P G

Authors

Paul B. Wignall

DAVID P. G. BOND

DIERK P. G. BLOMEIER

Paul B. Wignall

Yadong Sun

Stephen E. Grasby

Benoit Beauchamp

Michael M. Joachimski

Dierk P G Blomeier



Abstract

Lower 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.

Publication Date Mar 1, 2016
Journal Geological magazine
Print ISSN 0016-7568
Electronic ISSN 1469-5081
Publisher Cambridge University Press (CUP)
Peer Reviewed Peer Reviewed
Volume 153
Issue 2
Pages 316-331
APA6 Citation Wignall, P. B., Bond, D. P. G., Sun, Y., Grasby, S. E., Beauchamp, B., Joachimski, M. M., & Blomeier, D. P. G. (2016). Ultra-shallow-marine anoxia in an Early Triassic shallow-marine clastic ramp (Spitsbergen) and the suppression of benthic radiation. Geological magazine, 153(2), 316-331. https://doi.org/10.1017/s0016756815000588
DOI https://doi.org/10.1017/s0016756815000588
Keywords Anoxia; Triassic; Shallow marine; Spitsbergen; Extinction
Publisher URL http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9987194&fileId=S0016756815000588
Copyright Statement ©2016 University of Hull
Additional Information Author's accepted manuscript of article published in: Geological magazine, 2016, v.153, special issue 2.

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