Stratigraphic relationships and paleoecology of a late-glacial peat bed from the Queen Charlotte Islands, British Columbia

Abstract

The stratigraphic relationships of late-glacial and Holocene sediments exposed in sea cliffs at Cape Ball on the Queen Charlotte Islands are summarized, based on section descriptions and 13 radiocarbon dates on wood, peat, and marine pelecypod shells. One peat bed dated at 12 400 ± 100 years BP (GSC-3112) to 10 200 ± 90 BP (GSC-3159) was investigated for pollen and plant macrofossils. This study extends the late Pleistocene vegetation history of the Queen Charlotte Islands by about 1550 years, and suggests that the record will date back to before 13 700 ± 100 BP (GSC-3222).Four local pollen zones are described from the 70 cm thick peat, beginning with a 7 cm thick herb-dominated zone (CB-1), characterized by up to 60% grass pollen, and including a unique assemblage with abundant Apiaceae, Cyperaceae, Empetrum/Ericaceae, Polemonium, Plantago macrocarpa, Fritillaria, and Ranunculus. A high diversity of other herbs, including subalpine/alpine species and two taxa presently absent from the Charlottes (Armeria maritima and Polemonium caeruleum type), suggests that this zone represents an open floodplain vegetation with no modern analogue. Zone CB-2 (63–45 cm) is dominated by Pinus conforta type pollen (65–70%) and moderate values for fern spores. Zone CB-3 (45–30 cm) shows a rapid rise of Picea pollen from 3 to 39%, followed by a drop to about 12%. Fern spores (20–50%) and Alnus (6%) also reach maximum levels in this zone. Abundant wood fragments and sand inclusions are compatible with an interpretation of a swampy floodplain forest during this interval. The uppermost zone (30–0 cm) exhibits high Pinus contorta (40–60%) and Cyperaceae (12–38%) values, along with a moderate abundance of grasses, ferns, and Apiaceae. Estuarine and marine sediments with pelecypod shells, deposited during a marine transgression, overlie the peat bed.Implications for the controversy over the existence of late Pleistocene refugia in the Charlottes are briefly discussed.