Dinoflagellate cysts from the upper Campanian (Upper Cretaceous) of Hornby Island, British Columbia, Canada, with implications for Nanaimo Group biostratigraphy and paleoenvironmental reconstructions

Abstract

Abstract Thirty mudstone samples from coastal exposures of the Northumberland Formation on Hornby Island, British Columbia, Canada, yielded diverse dinoflagellate cyst and terrestrial sporomorph assemblages. A late Campanian age for the formation has been well defined through magnetostratigraphy, macrofossil biostratigraphy, and geochemical studies of the Hornby Island section. Dinoflagellate cyst taxa corresponding to 61 genera are exceptionally well preserved and include specimens referable to at least 68 formally established species. The earliest occurrences of Canninginopsis maastrichtiensis, Druggidium cf. discretum, Phanerodinium belgicum, Renidinium cf. vitilaire, Senegalinium simplex, Spiniferella cornuta, and Xenicodinium delicatum sensu Slimani et al. are reported along with the most recent occurrence of Senoniasphaera protrusa, extending their stratigraphic ranges into the upper Campanian. The palynomorph assemblages support a late Campanian age. Two dinoflagellate cyst ecozones are recognized (ecozone 1 and ecozone 2). Assemblages suggest sediment deposition in an inner shelf environment with moderate to high nutrient input and primary productivity.