A multidisciplinary biofacies characterisation of the Late Triassic (late Carnian–Rhaetian) Kapp Toscana Group on Hopen, Arctic Norway

Abstract

A multidisciplinary study of the Kapp Toscana Group (De Geerdalen, Flatsalen and Svenskøya formations) on Hopen, Svalbard, provides an enhanced palaeoenvironmental interpretation for the Upper Triassic succession on the island. The biofacies of the formations were characterised using a combination of palynological, palynofacies and micropalaeontological analyses. Micropalaeontological, palynofacies and δ 13Corg data are presented from Hopen for the first time. Six distinct biofacies assemblages were recognised: (I) Lower undifferentiated De Geerdalen Formation, characterised by a dominance of fern spores, and low abundance assemblages of foraminifera and ostracods, interpreted to reflect deposition in a deltaic environment during maximum marine regression; (II) Upper De Geerdalen Formation, Hopen Member, rich in bisaccate gymnosperm pollen and the alga Plaesiodictyon mosellaneum, consistent with deposition in a brackish marginal marine setting; (III) Lower Flatsalen Formation, characterised by microforaminiferal linings, marine phytoplankton and super-abundant agglutinated foraminifera, considered to reflect deposition in a shallow marine environment; (IV) Middle Flatsalen Formation, dominated by dinoflagellate cysts, radiolaria and ostracods, indicating deposition in a relatively distal, dysoxic–anoxic marine environment (a maximum flooding surface is inferred based on the acme of radiolarians and dominance of dinoflagellate cysts); (V) Upper Flatsalen Formation, corresponding to a decrease in marine palynomorphs, absence of radiolaria, agglutinated foraminifera and ostracods, and an increase in terrestrial organic matter; and (VI) Svenskøya Formation, characterised by a dominance of terrestrial palynomorphs and deposited in a fluvio-deltaic environment. The biofacies units are integrated with the established litho-, chrono- and palynostratigraphic framework for the island and contribute to an enhanced palaeogeographic understanding of the Barents Sea region during the Late Triassic.