Depositional environment, ichnological features and oxygenation of Permian to earliest Triassic marine sediments in central Spitsbergen, Svalbard

Abstract

Late Early Permian–lowermost Triassic carbonate, siliceous (spiculites) and clastic marine sediments in the Marmierfjellet area (Isfjorden, central Spitsbergen) contain a relatively diverse and abundant trace fossil assemblage providing important information about the depositional processes. The Vøringen Member (Late Artinskian–Kungurian) of the Kapp Starostin Formation (Late Artinskian–? Changhsingian) contains trace fossils (Nereites, Phycosiphon, Zoophycos and Arenicolites—common in tempestites) typical of the proximal–archetypal Cruziana ichnofacies, which indicates lower shoreface. Nereites, Phycosiphon and Zoophycos, accompanied by other rare trace fossils, characterize the Svenskegga and Hovtinden members of the Kapp Starostin Formation. They are interpreted as the distal Cruziana ichnofacies, possibly transitional to the Zoophycos ichnofacies typical of the lower offshore zone. However, the sporadic occurrences of Arenicolites and Macaronichnus can point to episodic shallowing to upper offshore–lower shoreface. The lowest part of the Triassic Vikinghøgda Formation (Induan–Olenekian) contains a very low-diverse ichnoassemblage composed of a few simple and branched forms ascribed to the impoverished Cruziana ichnofacies (lower to upper offshore environment), which is attributed to the early recovery stage after the Permian–Triassic extinction. The trace fossils and loss of primary sedimentary structures caused by intense bioturbation throughout most of the section point to generally oxygenated pore waters on the sea floor. However, some horizons, especially laminated black shales, display reduced or no bioturbational activity. These horizons also show high V/(V+Ni) ratios, which indicate oxygen-depleted sediments with periods of anoxic conditions. A remarkable black shale unit deposited under anoxic and sulphidic conditions occurs at the Permian–Triassic transition.

• Trace fossils
• Permian–Triassic boundary
• palynology
• spiculites
• trace elements
• anoxicity

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Acknowledgements

Fieldwork in Svalbard was funded by the Norwegian Research Council and the University of Tromsø (NMH). AU received additional support from the Jagiellonian University (DS funds). SAG received funding from the Arctic Petroleum Exploration project (Research Centre for Arctic Petroleum Exploration) which is funded by the Research Council of Norway (grant no. 228107). We gratefully thank Jan Kresten Nielsen for fruitful discussions and Jan Ove Ebbestad for commenting on an earlier draft of the manuscript. Some of the figures were drawn by Jan Petter Holm. We are indebted to Kenneth Andre Evison and Nils Andreas Hanken for field assistance. The paper benefitted from critical review by Francisco Javier Rodríguez-Tovar (Granada) and Paul Wignall (Leeds).

Notes

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