SEDIMENTATION-RATES AND PATTERNS ON A DEEP-WATER DELTA (FRASER DELTA,CANADA) - INTEGRATION OF HIGH-RESOLUTION SEISMIC STRATIGRAPHY, CORE LITHOFACIES, AND CS-137 FALLOUT STRATIGRAPHY

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 Nest coast. We used high-resolution marine geophysical dat a, core lithofacies, and fallout stratigraphy to examine modern sedime ntation rates on the delta slope and prodelta, Modern sedimentation ra tes, measured by the peak and onset of Cs-137 in cores, are in excess of 13 cm yr(-1) near the mouth of the main fluvial distributary but dr op to less than 3 cm yr(-1) farther than 4 km offshore. Asymmetry to t he pattern of sedimentation rates reflects both the prevailing oceanog raphic circulation and human influence. The map of modern sedimentatio n provides a synoptic view of this deltaic system that is of value to understanding older deltaic systems as well as the modern offshore env ironments on this populous and heavily used delta. In attempting to es timate the annual sediment discharge of the river from our sedimentati on-rate map, we were able to account for slightly less than 40% of the measured river discharge. Our inability to adequately characterize th e deposition and resedimentation of the sand fraction is probably resp onsible for most of the discrepancy.