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The Vikinghøgda Formation (250 m) is defined with a stratotype in Deltadalen‐Vikinghøgda in central Spitsbergen. The Vikinghøgda Formation replaces the Vardebukta and Sticky Keep Formations of Buchan et al. (1965) and the lower part of the Barentsøya Formation of Lock et al. (1978) as extended geographically by Mørk, Knarud et al. (1982) in central Spitsbergen, Barentsøya and Edgeøya. The formation consists of three member: the Deltadalen Member (composed of mudstones with sandstones and siltstones), the Lusitaniadalen Member (dominated by mudstones with thin siltstone beds and some limestone concretions) and the Vendomdalen Member (composed of dark shales with dolomite interbeds and nodules). The Lusitaniadalen and Vendomdalen members replace the former Sticky Keep Formation/ Member in the siirne areu. The Vikinghøda Formation can be followed through central and eastern Spitsbergen to Barentøya and Edgeøya and includes all sediments between the chert‐rich Kapp Starostin Formation (Permian) and the organic‐rich shales of the Botneheia Formation (Middle Triassic). The subdivision into three members is also reflected in the organic carbon content and palynofacies. Upwards. each succeeding member becomes more distal, organic‐rich and oil‐prone than the one below. The Vikinghøda Formation is well‐dated by six ammonoid zones. although the transitional beds between the Deltadalen and Lusitaniadalen members lack age diagnostic macrofossils. Corresponding palynozonation and magnetustratigraphy have also been determined. The overall stratigraphical development correlates well with other key Triassic areas in the Arctic, although intervals in the late Dienerian and early Smithian may be condensed or missing.

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When moving from west to east across Svalbard, organic geochemical, palynological and sedimentological data from the Middle Triassic dark shales of the Sassendalen Group show an improved quality of hydrocarbon source rock (kerogen type II/III), and an increased abundance of structured algal material, including Tasmanites. Triassic specimens of Tasmanites in palynological residues from Svalbard are generally of small size (<100 mm in diameter). Tasmanites of variable size, and the associated degradation products, occur frequently in Middle Triassic dark shales, and extraordinarily large-sized specimens (phycomata >500 mm in diameter) are recorded in silty shales and siltstones palynologically dated as being of Ladinian-Carnian age. Similar occurrences are also present in deposits of the Norwegian Barents Sea. Our organic geochemical analyses suggest that Tasmanites is a major source for the hydrocarbons encountered in these rocks. Tasmanites algae are also enriched in Ladinian-Norian deposits in Taimyr, Siberia. The development of a marine embayment, the direction of the ocean currents, the supply of clastic material and freshwater, and the palaeolatitude all show similarities to the conditions in the present Mediterranean, and adjacent Atlantic Ocean. Ecological conditions in the water column (light intensity, nutrient supply and temperature) are expected to have been similar, and favoured the growth and accumulation of Tasmanites. The accumulation of monotypic, large Tasmanites cells in silty shales is explained as a result of contemporaneous recirculation and sorting.

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