This paper describes the taxonomy, biostratigraphy and geographic occurrence within the Canadian Boreal Region of an Upper Jurassic-lowermost (Oxfordian-Berriasian) Cretaceous/dinoflagellate cyst assemblage . This association, termed the Borealis Assemblage is intermediate in age between assemblages described by Johnson and Hills (1973) from older Jurassic rocks and those present in the later Early Cretaceous in these regions. Data has been drawn from three surface and four subsurface (well) sections from the northern Interior Plains-Richardson Mountains regions and from four seismic shotpoint locations and seven subsurface (well) sections in the Arctic Islands (Sverdrup Basin). The ranges of the new taxa have been determined from comparison with published macrofaunal zonal schemes and from published ranges of selected spore, pollen and dinoflagellate taxa. Five new dinoflagellate cyst taxa are described: Psaligonyaulax dualis; Pareodinia capillosa; Pareodinia borealis; Horologinella spinosigibberosa; and Lanterna saturnalis. One other species, Gonyaulacysi;a sp. cf. G. cladophora (Deflandre) Dodekova is also associated with the Borealis Assemblage.