| Popis: |
Samples were analyzed from Effingham Inlet, southwestern Vancouver Island, British Columbia, to assess the oceanographic controls on benthic foraminiferal distribution. The resultant proxy data will be used to interpret cores collected throughout the basin, and assess the causes of periodic variation in fish populations over time. Seven foraminiferal assemblages were recognized with the primary controlling factors being oxygen content, and proportion of organic matter in the sediment. The estuarine Buliminella Assemblage characterizes well-oxygenated environments with high levels of terrestrial plant matter. This assemblage disappears when oxygen levels fall beneath suboxic levels of 40 μM/kg. The Buccella Assemblage, dominated in part by attached forms and islandiellids, is typical of well-oxygenated bank environments in the region. The Psammosphaera Assemblage is related to the lower salinity and variable conditions present in the shallow water where it occurs. The Stainforthia-Nonionella Assemblage characterizes one well-oxygenated environment outside the inlet. The Stainforthia-Bolivinellina Assemblage is typical of suboxic/dysoxic conditions (10–40 μM/kg) in the outer basin. The Stainforthia Assemblage is identified from dysoxic environments of deepest parts of the outer basin. A gradation between the Stainforthia-Bolivinellina Assemblage and the Stainforthia Assemblage is significant as a whole range of suboxic/dysoxic/anoxic conditions are detectable, potentially permitting recognition of even subtle variations in paleoceanographic/atmospheric circulation. The Stainforthia-Buccella Assemblage was recovered from the least oxygenated area of Effingham Inlet under fully anoxic (with H2S) conditions, and provides evidence that even the most isolated portions of Effingham Inlet are periodically oxygenated. |
