Abstract

The Fraser Delta is a Holocene feature with complex surficial geology that has built into the deep (> 300 m) water of the Strait of Georgia on Canada's west coast. We used high-resolution marine geophysical data, core lithofacies, and fallout stratigraphy to examine modern sedimentation rates on the delta slope and prodelta. Modern sedimentation rates, measured by the peak and onset of 137 Cs in cores, are in excess of 13 cm yr (super -1) near the mouth of the main fluvial distributary but drop to less than 3 cm yr (super -1) farther than 4 km offshore. Asymmetry to the pattern of sedimentation rates reflects both the prevailing oceanographic circulation and human influence. The map of modern sedimentation provides a synoptic view of this deltaic system that is of value to understanding older deltaic systems as well as the modern offshore environments on this populous and heavily used delta. In attempting to estimate the annual sediment discharge of the river from our sedimentation-rate map, we were able to account for slightly less than 40% of the measured river discharge. Our inability to adequately characterize the deposition and resedimentation of the sand fraction is probably responsible for most of the discrepancy.

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