POST-GLACIAL PALEOCEANOGRAPHIC HISTORY OF SAANICH INLET, BRITISH COLUMBIA, BASED ON FORAMINIFERAL PROXY DATA

Abstract

Five benthic foraminiferal biofacies characterize the late Pleistocene to Recent succession at ODP Sites 1033B and 1034B (Leg 169S) in Saanich Inlet, southern Vancouver Island, British Columbia. These faunas document three distinct paleoceanographic phases in the evolution of this inlet. From the latest Pleistocene, ~14,000 years BP, to the earliest Holocene, the distribution of benthic foraminifera ( Cribroelphidium excavatum [Biofacies 5]), Islandiella norcrossi [Biofacies 4], and Nonionella stella [Biofacies 3]) in Saanich Inlet was strongly controlled by the influence of cold, low-salinity waters associated with deglaciation. Early Holocene sediments are characterized by Stainforthia feylingi Biofacies 2. Despite a shallower sill depth at the entrance of Saanich than exists today sedimentological and foraminiferal evidence indicate that bottom waters were oxygenated. The foraminiferal fauna indicates that oxygen levels varied from a minimum low oxic (1.5–3 ml/l [67–133 μM]) level early on to suboxic (0.3–1.5 ml/l [13.3–67 μM]) conditions up section where sediments become progressively more laminated. During the early Holocene air temperatures in the region were up to 4°C warmer, and it was much drier than at present. The resultant reduced freshwater flow into the southern Strait of Georgia was conducive to the free exchange of Saanich Inlet bottom waters with those of well-oxygenated Haro Strait. After 7000 years BP the climate in the region cooled and, as the influence of freshwater from Strait of Georgia increased, oxygenation of Saanich bottom waters became a rare occurrence. Finely-laminated sediments characterized mid-Holocene to Recent sediments in the inlet reflecting the development of full anoxic conditions at depth. The Lobatula fletcheri–Buccella frigida Biofacies 1 characterizing this interval is allochthonous and derived by down-slope transport from shallower, more oxygenated regions of Saanich Inlet.