Lower Cretaceous (upper Ryazanian-Hauterivian) chronostratigraphy of high latitudes (North-East Greenland)

Calcareous nannofossils of Lower Cretaceous sediments from four sections of the Wollaston Forland and Kuhn Ø, North-East Greenland, have been examined. Sediments of Ryazanian-Hauterivian age were deposited in North-East Greenland following a major Late Jurassic-earliest Cretaceous rifting event. The upper Ryazanian-Hauterivian marine post-rift sediments consist of fossiliferous calcareous mudstones 27-40m thick, assigned to the Albrechts Bugt and Rødryggen members. These calcareous mudstones rest unconformably on dark Jurassic mudstones and are overlain by dark Barremian mudstones. The biodiversity of the calcareous nannofossil assemblages from North-East Greenland is lower than contemporaneous Tethyan assemblages of lower latitudes. Well-preserved assemblages consist of common Watznaueria spp., Crucibiscutum spp., Biscutum constans and other taxa. Integrated calcareous nannofossil and ammonite data form the basis of a biostratigraphic zonation scheme for the Boreal-Arctic Province of the Boreal Realm and this is correlated with existing Boreal zonation schemes. Important calcareous nannofossil marker species include Sollasites arcuatus, Crucibiscutum ryazanicum, Kokia borealis, Nannoconus oviformis, Triquetrorhabdulus shetlandensis, Micrantholithus speetonensis, Eiffellithus striatus, Tegumentum octiformis, Perissocyclus plethotretus, Tegulalithus septentrionalis, and Clepsilithus maculosus. This study shows that the existing calcareous nannofossil zonation schemes are applicable in the Boreal-Arctic Province. The occurrence of diverse and well-preserved calcareous nannofossil assemblages in North-East Greenland at a higher latitude than their typical known area of distribution marks a significant change in their biogeographic distribution pattern during the Early Cretaceous.