The Hopen Member: A new member of the Triassic De Geerdalen Formation, Svalbard

Hopen is a solitary island of Upper Triassic strata in the south-eastern most corner of the Svalbard archipelago. Outcrop studies throughout the island, supported by palynology, magnetostratigraphy and geological modelling have led to the identification of a new member unit within the upper part of the De Geerdalen Formation, the Hopen Member. Based on the distinctive visual properties of the strata observed in the mountain sides of Hopen, a recorded change in sediment style and an increase in the concentration of marine palynomorphs, the unit is well expressed. The Hopen Member represents an extensive, ~70 m thick succession of marine influenced shale and subordinate sandstones, distinguishing itself from the paralic and non-marine clastic sediment packages of the remaining part of the De Geerdalen Formation. The Hopen Member is traceable throughout the entire island, given its prominent darker colouration due to the lateral extent of its marine mudstones, unlike the bed packages below, which are laterally inextensive and more sandstone rich. Palynological and magnetostratigraphic studies have indicated an age of latest Carnian to earliest Norian for the member. With the age and stratigraphical position of the member being taken into account, it is possible to define this unit as a time equivalent to that of the Isfjorden Member of central Spitsbergen. However, its distinctively different lithological properties call for the creation of a new lithostratigraphic unit as opposed to simple correlation.