Late Quaternary benthic foraminiferal biofacies and paleoceanography of Queen Charlotte Sound and southern Hecate Strait, British Columbia

Abstract

Analysis of Late Quaternary benthic foraminifera in cores from Queen Charlotte Sound and Hecate Strait yields new information on the paleoceanographic history of the region. Q-mode cluster analysis grouped samples into seven associations reflecting benthic foraminiferal biofacies: the Gyroidina-Bolivina Biofacies and Gyroid­ ina-Seabrookia Biofacies are relict lower to middle bathyal faunas introduced to shallower depths when cooler water masses influenced the area; the Cribroel­ phidium Biofacies, I slandiella Biofacies, Epistominella Biofacies, and Bucella Biofacies are similar to each other in faunal makeup and characterize varying depositional conditions at neritic depths; the Lobatuln-Gavelinopsis Biofacies characterizes shallow, high energy, shelly banks. Repetition of many of these biofacies in the cores indicates an overall instability, or cyclic nature, of the water masses affecting the region through the Late Qua­ ternary. A gradual increase in the proportion of Buliminelln elegantissima, a foraminifer associated with terriginous plant debris suggests a gradual decrease in sea level dur­ ing deposition of the Bl lithologic unit (~= 12,000 years BP in the cores presented here) deposited at most sites. A population maximum of Buliminella elegantissima in diachronous lag deposits of the B2 lithologic unit (=11,600-10,000 years BP) indicates a maximum low­ stand. The almost complete absence of this species in superjacent B3 lithologic unit sediments indicates subse­ quent rapid subsidence and termination of terrestrial organic input, probably due to the collapse of the Fraser Glaciation forebulge. Deposition of the B3 unit had ter­ minated everywhere in the region by =9,000 years BP. A Cassidulina reniforme population maximum occurs in sediments dated between about 10,100 and 11,300 years B.P. The presence of high proportions of this species, associated with very cold water (glacial or near-glacial) regimes, indicates a brief interval of cooler conditions during deglaciation, isochronous with the Younger Dryas event of Europe and eastern North America. This suggests that this event is not restricted to the North Atlantic but represents a much more widespread phe­ nomenon.