Submarine channels in rupert inlet, British Columbia: II. Sediments and sedimentary structures

Abstract

In a previous paper the morphological evolution of submarine channels in the Rupert Inlet mine tailing deposit was traced through a succession of three distinct periods or phases over a five-year period: a meandering channel phase, an apron phase and a rechannelized phase. The distributions of sediment properties including grain size, specific gravity, and Cu and Fe concentrations for these phases are presented here. Copper-rich, coarse-grained deposits were found along channel axes and down the apron flanks. Sandy, fining-upward turbidites in cores from the levees during the meandering channel phase were characterized by higher Cu (and lower Fe) concentrations than the adjacent mud, and had sharp basal contacts sometimes exhibiting flame and load-pocket structures. The average thickness of, and fraction of the sediment column occupied by, turbidites was found to increase with distance downchannel, indicating a downchannel decrease in the importance of continuous (as opposed to surge-type) flow to the channel-building process. Deposition rates, determined from the local time rates of change of tailing deposit thickness, ranged from 0.1 to 4 m yr −1 at the core sites and were used together with the number of coarse-grained turbidites per core to yield a minimum turbidity current surge recurrence interval of 2–5 days during the meandering channel phase.