Recent Marine Sediments in Saanich Inlet, a Stagnant Marine Basin

Saanich Inlet, a fjord on the eastern side of Vancouver Island, has H2Sin the bottom waters during most of the year. Recent marine sediments in the inlet include three distinctly different types. Black, fine-grained, varved clayey silts containing H2Sand large amounts of diatom frustules and carbonaceous organic materials occur in the central part of the inlet. Olive-gray silts with moderate concentrations of organic materials and reducing capacities occur on the sill at the entrance to the inlet. The nearshore sands and gravels have low organic contents and low reducing capacity. Carbonate-rich sediments occur near a limestone quarry and cement factory. A carbon-nitrogen ratio of 7 is typical of the sediments in the inlet. Five sources of sediment can be distinguished: (1) carbonaceous and siliceous organic matter from marine organisms, principally planktonic diatoms, (2) suspended sediment in low-salinity water brought from the Fraser and Cowichan rivers, (3) material eroded from adjacent shorelines, (4) streams discharging into the inlet, and (5) the cement plant and limestone quarry at Bamberton. The varved sediments in the central basin consist of olive-gray laminae, apparently formed during the peak diatom production in spring or summer and olive-black laminae, containing larger mounts of terrigenous sediment, probably formed during the autumn winter. Zones of nonlaminated sediment may be formed by terrigenous material or by the disruption of the laminated sediment by other physical processes. No evidence of burrowing organisms has been detected. Four to 6mm of wet sediment are deposited each year in the southern portion of the inlet. If this rate is typical of the basin as a whole, approximately 105metric tons of sediment are deposited each year. At least 25-35% of this sediment is derived from marine organisms.