Dinoflagellate cyst-based paleoenvironmental reconstructions and phytoplankton paleoecology across the Cretaceous–Paleogene (K/Pg) boundary interval, Vancouver Island, British Columbia, Canada

Abstract

A conformable K/Pg boundary succession is reported for this first time in North America west of the Rocky Mountains and in the north-eastern Pacific based on biostratigraphic controls, occurring within the upper Maastrichtian–lower Selandian marine sedimentary rocks of the Oyster Bay Formation, Vancouver Island, British Columbia. Approximate placement of the boundary is made possible by a suite of temporally constrained palynological K/Pg interval indicator taxa. The low-diversity, homogenous coastal dinoflagellate cyst assemblages of the Cordosphaeridium, Glaphyrocysta, Hystrichosphaeridium and Spiniferites-dominated uppermost Maastrichtian of the Lynnwood section transition to that of a more intermixed estuarine setting dominated by Areoligera, Exochosphaeridium and Ginginodinium along with peaks of low-salinity tolerant Senegalinium into the Danian–Selandian strata of the Appian Way and Oyster River sections. A marine assemblage turnover in the middle Oyster Bay Formation under conditions of elevated primary productivity and community heterogeneity owing to nutrient-rich waters is observed. Evidence for this interpretation is reinforced by the presence of overall higher cyst concentrations, peridinioid abundance and greater species diversity in association with botanical and shallow marine invertebrate fossil assemblages. The palynological data record probable eustatic regressive and transgressive sequences which illustrate a history of fluctuation between a predominantly coastal and largely estuarine paleoenvironment punctuated by the end-Cretaceous event. The presence of heavily negative δ13Corg values in addition to facies changes throughout the succession support a neritic profile for the Oyster Bay Formation. The palynological assemblages reflect localized paleoenvironmental conditions and climatic changes across the K/Pg boundary consistent with observations from numerous localities across both hemispheres.