Paleoenvironments of the Strait of Georgia, British Columbia during the last deglaciation: microfaunal and microfloral evidence

Abstract

The Strait of Georgia is situated between Vancouver Island and the western Canadian mainland. It was deglaciated quickly, around 12,500 14C yr BP, by in situ downwasting. The subsequent marine invasion has left glacimarine sediments with foraminifers, diatoms and dinocysts characterizing successive paleoenvironments recognizable basinwide. The first paleoenvironment represents near-ice conditions under the influence of the turbid meltwater plume marked by low algal productivity and few foraminifers, mostly Elphidium excavatum. Just off the plume, the second environment shows a peak of Nonionellina labradorica possibly resulting from an observed sudden increase in diatom numbers, mostly ice-dwelling forms implying a long annual sea-ice cover. Further away, Cassidulina reniforme increases, N. labradorica decreases while other calcareous foraminifer species colonize the area; there are fewer ice diatoms, more marine planktonic diatoms and dinocysts become more abundant. Finally, after 12,000 14C yr BP, calcareous foraminifers are gradually replaced because of dissolution of calcium carbonate by a low-diversity arenaceous assemblage. At the same time, abundant planktonic diatoms and dinocysts indicate warmer surface temperature. The succession of fossils and environments compares well with modern, horizontal, off-glacier successions observed in fjords of the European Arctic.