Marine shelf to paralic biofacies of Upper Triassic to Lower Jurassic deposits in Spitsbergen

The Upper Triassic to Lower Jurassic Kapp Toscana Group of Spitsbergen consists of mudstones, sandstones and shales deposited in offshore marine to paralic conditions in an extensive shelf embayment. The study focuses on microfossil-based biofacies features (mainly foraminifera, but also palynomorphs) combined with sedimentary and selected geochemical data, in relation to transgressive–regressive developments. The analysed material includes field logs and sediment samples originating from the Juvdalskampen section, central Spitsbergen. nthic foraminiferal succession reveals three principal associations: 1) assemblages of mixed agglutinated and calcareous components, typified by medium to high diversities, indicating offshore shelf conditions; 2) assemblages consisting dominantly or entirely of agglutinated forms with low diversity, attributed to hyposaline conditions; 3) highly impoverished agglutinated assemblages or barren samples suggesting extremely brackish to freshwater environments. The marine influence is highest in the lower and upper parts, and lowest in the middle part of the Kapp Toscana Group, as indicated both by foraminiferal and palynomorph proxies. The potential of the boron concentration as a salinity indicator is demonstrated by its co-variance with biofacies features: the boron content increases with increasing salinity. pp Toscana Group consists of two depositional sequences. The Storfjorden sequence (Carnian to Early Norian) starts with a transgressive systems tract formed in offshore shelf conditions with normal marine salinity and terminates at the maximum flooding event, which is succeeded by a highstand systems tract deposited in paralic (hyposaline to freshwater), prodelta to delta plain environments. The overlying Wilhelmøya sequence (Middle Norian to Bajocian) is punctuated by several hiatuses, and was deposited in hyposaline waters on a sediment-starved, prodelta shelf platform.