Distribution of surficial sediments of the central and southern Strait of Georgia, British Columbia

Abstract

The Strait of Georgia is a long, narrow, semi-enclosed basin with a restricted circulation and a single sediment source, the Fraser River, providing practically all the sediment now being deposited in the Strait. This river is building a delta into the Strait from the east side near the south end. Ridges of Pleistocene deposits within the Strait and Pleistocene material around the margins, like bedrock exposures, provide local sources of sediment of only minor importance.Sandy sediments are concentrated in the vicinity of the delta, and in the southern and southeastern parts of the Strait. Mean grain size decreases from the delta toward the northwest along the axis of the Strait, and basinwards from the margins. Silts and clays are deposited in deep water west and north of the delta front. Bedrock or poorly sorted sediments containing gravel occur near tidal passes, on the Vancouver Island shelf area, on ridge tops within the Strait, and with sandy sediments at the southeastern end of the study area. The Pleistocene ridges are areas of nondeposition, having at most a thin veneer of modern mud on their crests and upper flanks.