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Patterns of sedimentation in Queen Charlotte Sound, British Columbia Luternauer, John Leland

Abstract

This study is concerned with the geomorphology and sediment dispersal in Queen Charlotte Sound, a 20,000 sq. km. continental shelf area off the British Columbia mainland between Vancouver Island and Queen Charlotte Islands. Field work involved collection of: a) 357 bottom samples, b) 5 gravity cores and c) 12 series of bottom photographs. Selected continuous seismic profiles obtained prior to initiation of the study are also included. Laboratory procedures included a) analysis of sediment texture, b) determination of heavy mineral, clay group, organic C, CaCO₃, glauconite pellet and iron-stained sand content in samples, c) examination of Sound-floor bedforms and d) creation of a detailed bathymetric map. Principal physiographic features on the shelf are broad troughs and banks. Troughs generally extend from the mainland to the shelf edge (at approximately 300 metres) and appear to have been at least partly excavated by glaciers which left several characteristic deposits upon their retreat. Net sediment accumulation is occurring in the troughs mainly below 160 metres. Banks appear to be massive drift deposits which are being planed to depths as great as 130 metres below present sea-level. River erosion probably has incised at least one bank's margin at a time when sea-level stood lower. Mud derived from glacial meltwater and discharged during the summer from the mainland into the southeastern Sound probably is a) mostly deposited relatively close inshore, b) the principal sediment presently contributed to the Sound and c) the coarsest sediment now contributed to the Sound. Sedimentation rates on the outer shelf are very low probably because most sediment not deposited inshore is transported beyond the shelf in the less saline surface water. Fine sand is swept both northerly and southerly across bank tops by tidal currents.

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