Upper Cretaceous Dinocyst Assemblages from Ellef Ringnes Island, Nunavut: Paleoecological changes within the Boreal Sea

Ellef Ringnes Island, in the Canadian High Arctic, preserves the sedimentary and paleoenvironmental history of the Cretaceous phase of the Sverdrup Basin. The study of dinoflagellate cysts (dinocysts) of the Late Cretaceous Kanguk Formation in combination with other fossil indicators, organic geochemistry and detailed correlation to global sea-level fluctuations provides the first stratigraphic framework for the undivided thick shaly Kanguk Formation. A new dinocyst range chart is developed consisting of mainly cosmopolitan species with a more tolerant temperature range that have invaded the Boreal realm. Extremely rich assemblages in the Boreal Sea resulted from the Cretaceous high sea level flooding terrestrial regions and delivering high supply of nutrients to shallow marine settings where plankton flourished. Ratios between benthic and pelagic dinocysts throughout the Kanguk Formation show a striking correlation to transgressive/regressive phases that are linked to global sea level. Their preservation was generally enhanced by anoxic bottom water conditions and expanded oxygen minimum zones as a result of high organic matter supply. Dinocyst radiation events took place during the late Turonian and late Santonian at times of low global sea level with incoming species preferring a shelf setting. This study demonstrates that dinocysts add a valuable proxy to depositional interpretations of the complex Cretaceous ecosystem of the Boreal Sea.