Early Cretaceous palaeoceanography of the Greenland–Norwegian Seaway evidenced by calcareous nannofossils

Reconstructions of the palaeoclimate of the Early Cretaceous are controversial, varying from a warm-temperate greenhouse world to icehouse conditions. We studied calcareous nannofossil assemblages of sediments from North-East Greenland (Wollaston Forland and Kuhn Ø) of Late Ryazanian–Barremian age in order to better understand the palaeoclimate and palaeoceanography of the high latitudes. The calcareous nannofossil assemblages are characterized by abundant Crucibiscutum spp. and Watznaueria spp., Biscutum constans and other Boreal taxa. They show also influxes of Tethyan and low to mid latitudinal taxa like nannoconids (e.g. Nannoconus bermudezii, Nannoconus dolomiticus, Nannoconus steinmannii), pentaliths (Micrantholithus hoschulzii, Micrantholithus obtusus), conuspheres, Speetonia colligata and Cruciellipsis cuvillieri in the Upper Ryazanian and Lower Hauterivian. Reconstructed surface water conditions, indicated by fluctuations in the assemblage compositions, suggest cool conditions for the Late Ryazanian, a cold climate for the Valanginian, and warm climatic conditions for the Hauterivian–Barremian. High meridonial temperature gradients and cool–cold climatic conditions in the high latitudes caused supposedly the formation of deep water in the South Anyui Gulf in the Late Ryazanian–Valanginian. Palaeoceanographic changes, reflected in a counter-balanced ocean current system in the Greenland–Norwegian Seaway, allowed Tethyan biota to spread as far north as North-East Greenland during the Late Ryazanian.