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The geochemistry and diatom assemblages of varved sediments from Saanich Inlet, B.C. Powys, Richard I. L.


Varved, anoxic sediments in Saanich Inlet, British Columbia, are formed by the annual cycle of summer deposition of diatom frustules and winter inputs of terrigenous material derived from land runoff. The objective of this study was to sample the varve record in order to develop a palaeoceanographic history of the Inlet. Box-cores of varved sediments were collected from Finlayson Arm, Saanich Inlet. The cores were quick, frozen upon recovery, to preserve the laminae, were subsequently sectioned and X-radiographs of the sections prepared. The varves were individually sampled and analysed for their diatom assemblages together with carbon, carbonate, major and minor element concentrations and ²¹⁰Pb activity. The chronology of a representative core determined by ²¹⁰Pb was inconsistent with that determined by varve counting. The geochemical data indicated that the upper 15cm of the core had a distinct elemental composition and a lower porosity that indicated a changed sedimentation rate. It also appeared that around 20 years of sediment had been lost from the core-top. The upper sediment contains a carbonate increase linked to a dust dump from a local cement plant which occurred between 1960-1963. In the lower section of the core, both the diatom and the geochemical data indicate seasonal variation expected from the formation of annual varves. However, a well constrained chronology cannot be obtained for this core because of the non-steady state sedimentation. This makes the interpretation of inter-varve variations in the light of regional climatic records impossible. Nevertheless, a change in production on a cycle of approximately 10-15 years is evident and this study provides conclusions that will be useful to future palaeoceanographic investigations on longer cores from a part of the Inlet where sedimentation is more constant.

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