Geomagnetic polarity and carbon isotopic stratigraphic assessment of the late Carnian -earliest Norian in Svalbard : evidence for a major hiatus and improved Boreal to Tethyan correlation

Hounslow, Mark W and Harris, Samuel and Karloukovski, Vassil and Mørk, Atle (2022) Geomagnetic polarity and carbon isotopic stratigraphic assessment of the late Carnian -earliest Norian in Svalbard : evidence for a major hiatus and improved Boreal to Tethyan correlation. Norwegian Journal of Geology, 102: 4. ISSN 0801-4736

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Abstract

Combining magnetostratigraphy and organic carbon isotopic changes has allowed a more precise position to be determined for the base of the Norian in Svalbard successions. A magnetostratigraphy is constructed from two sections (Binnedalen, Nørdstefjellet) from the northern end of Hopen Island (southern Svalbard archipelago), from the De Geerdalen Formation and the lowest part of the Flatsalen Formation. A magnetostratigraphy is also determined from the upper part of the De Geerdalen Formation on Wilhelmøya (eastern Svalbard). On Hopen a composite magnetostratigraphy tied to the Binnedalen section was constructed using correlation based on detailed photographs and logs of the adjacent cliffs. The palaeomagnetic data shows a strong Brunhes overprint, but mean palaeomagnetic directions pass the reversal test and are consistent with other Triassic virtual geomagnetic palaeopole data from Svalbard. The palaeomagnetic signal is carried by magnetite. Organic carbon isotope data identifies three negative excursions in the Hopen succession— below the Hopen Member, within the upper Hopen Member and at the De Geerdalen –- Flatsalen formation boundary. The carbon isotope variations are correlated to Tuvalian (late Carnian) excursions seen in lower paleolatitude sections. The magnetostratigraphy of the Isfjorden Member from Wilhelmøya and central Spitsbergen are similar, and when integrated with the carbon isotope stratigraphy suggests that the Isfjorden Member is not equivalent to the units of the De Geerdalen Formation exposed on northern Hopen, but is older. These relationships suggest the sequence boundary at the base of the Wilhelmøya Subgroup probably cuts down into mid Tuvalian age strata of the De Geerdalen Formation in Spitsbergen and Wilhelmøya, but only into the latest Tuvalian strata on Hopen. A revised Tuvalian geomagnetic polarity scale is also proposed, linked to the carbon isotope excursions.