Palynology and geochemistry of sediments in the tidally influenced lower Fraser River, British Columbia

In the tidally influenced Fraser River and adjacent Strait of Georgia (SoG), Canada, palynological and carbon isotope (δ13Corg) signatures of channel-margin sediments are compared to environmental parameters (e.g., substrate grain size, water salinity) in order to establish how these vary across the tidal-fluvial transition. Palynological assemblages in both the Fraser River and SoG (delta front and prodelta) are dominated by tree pollen, which comprises between 85% and 95% of all assemblages. Relative abundances of marine dinocysts are markedly low, and the maximum abundance of dinocysts is 6.8% or 1,023 cysts g-1 of sediment in samples recovered from the prodelta. Dinocyst abundances do not exceed 2% of the total palynological assemblage in the Fraser River, and the number and diversity of dinocysts gradually decreases landward. Organic carbon-13 enrichment values range from -26.55‰ in sediments deposited in the freshwater-tidal reach of the Fraser River, to -21.08‰ in prodeltaic sediments. The δ13Corg and palynological signatures of river, delta front, and prodelta sediments indicate a dominance of terrestrially sourced organic matter regardless of brackish-water and tidal influence on sediment deposition.