Smithian and Spathian palaeontological records of the Vikinghøgda Formation in Central Spitsbergen

Abstract

Vertebrate and invertebrate fossils from the Smithian (Early Triassic) to the Early-Middle Triassic boundary interval of Svalbard, Arctic Norway have been known for a long time, but have rarely been extensively collected with precise stratigraphical control. We describe new bulk collections from precisely measured sections in the Vikinghøgda Formation in Central Spitsbergen. Accompanying geochemical data provide further constraints on the changes in palaeoenvironments. Species richness of both benthos and nekton remains low throughout the studied interval but reduces to a minimum in the early Spathian, i.e. in the wake of the late Smithian extinction and a probable associated short ice age that straddled the Smithian–Spathian boundary as manifested by a global hiatus in continental shelves. The faunal stratigraphical succession and geochemical data series indicate a regression event in the late Smithian followed by deepening sea level in the early Spathian. This is consistent with a global cooling phase in the late late Smithian that has been previously interpreted as a likely glacio-eustatic episode. The lowermost Spathian is marked by near-absence of benthos, compatible with increased water depth but also possibly linked to the aftermath of the Smithian-Spathian extinction. The lateral expansion of another and younger gap (‘the Marmierfjellet hiatus’ of early or middle Spathian age) is here interpreted as an off-shore condensation horizon generated by the probably highest sea-level stand recorded in the Spathian of Spitsbergen. These hiatuses of opposite origin, as well as the acute selective preservation linked with the low carbonate content of the studied series, have to be factored out as biases when estimating species richness and interpreting palaeo-ecological changes. The study also identifies Early Triassic fossil taxa new to Spitsbergen, in particular Peribositria sibirica and bakevellid bivalves. The orthoceratoids are reviewed, and two distinct taxa are identified at different stratigraphical levels.

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