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Biomagnetostratigraphy of the Vikinghøgda Formation, Svalbard (Arctic Norway), and the geomagnetic polarity timescale for the Lower Triassic

Mark W. Hounslow^1,, Clare Peters², Atle Mørk³, Wolfgang Weitschat⁴ and Jorunn Os Vigran⁵

¹ Center for Environmental Magnetism and Palaeomagnetism (CEMP), Geography Department, Lancaster University, Bailrigg, Lancaster LA1 4YB, UK
² School of Geography and Geosciences, Irvine Building, University of Saint Andrews, North Street, St. Andrews, KY16 9AL Fife, Scotland, UK
³ SINTEF Petroleum Research, NO-7465 Trondheim, and Department of Geology and Mineral Resources Engineering, Norwegian University of Science and Technology, NO-7491, Trondheim, Norway
⁴ Geologisch-Paläontologishes Institut und Museum, Universität Hamburg, Bundesstraβe 55, 20146 Hamburg, Germany
⁵ Mellomila 2, NO-7018 Trondheim, Norway

Correspondence: E-mail: m.Hounslow{at}lancs.ac.uk

A biomagnetostratigraphy for the Lower Triassic is constructed, using the ammonoid biostratigraphy from Arctic Boreal successions. Combined thermal and alternating field demagnetization determines the Triassic magnetic field polarity in 86% of specimens, with 36% showing linear trajectory line fits and the remainder showing great-circle trends toward the characteristic magnetization. Mean pole directions for the Deltadalen ( = 50°, = 159°, dp/dm = 3.9°/5.1°), Lusitaniadalen ( = 56°, = 163°, dp/dm = 4.4°/5.4°), and Vendomdalen ( = 57°, = 143°, dp/dm = 4.4°/5.4°) members fall close to the European Lower Triassic apparent polar wander path. Mean directions for two of these member-means pass the reversal test. The remanence is predominantly carried by magnetite. The polarity stratigraphy, when integrated with the ammonoid and meager conodont data, is similar to that determined from successions in the Sverdrup Basin (Canada). The Permian-Triassic boundary post-dates a pronounced palynofloral turnover and predates a short duration reverse magnetozone (LT1n.1r). In the correlated Shangsi section (in South China), LT1n.1r occurs after the first appearance datum (FAD) of H. parvus, but in the Arctic is within the Otoceras boreale Zone. The late Griesbachian to early Smithian is mostly reverse polarity, with three normal-polarity intervals, overlain by mid and late Smithian normal polarity. The Spathian contains four reverse-polarity intervals, the oldest one within the early Spathian with the remainder in the late Spathian. The transition into the Anisian is within the uppermost reverse magnetozone, a feature documented in other sections of this age. The polarity pattern is correlated to other marine sections, indicating the robustness of the biomagneto-stratigraphic composite and its utility in calibrating Lower Triassic time.

Key Words: boreal • ammonoids • geochronology • magnetostratigraphy • Permian-Triassic boundary • Svalbard