Continental source area contributions to fine-grained sediments on the Oregon and Washington continental slope

Abstract

Summary Chemical and quantitative mineral abundance data for the 2–20 μm fraction of 78 samples from the Oregon-Washington continental slope have been modelled using linear programming to estimate sediment contributions from continental source areas and evaluate the effects of mixing material derived from these sources on the formation of hemipelagic sediments. The mineral data distinguish three source areas, while the chemical data define only two. Results from the two data sets indicate similar patterns and magnitudes of source area influence on the continental margin. The contributions are used to construct a sediment budget for 2–20 μm-sized sediments on the continental slope. The slope sediments contain approximately 47% Columbia River, 32% Klamath Mountain, and 21% California Coast Range material. Approximately 25–50% of the Columbia River, 29–46% of the Klamath Mountain, and 7–12% of the California Coast Range annual suspended sediment input is retained on the slope, indicating that the slope acts as a more effective trap of 2–20 μm material from proximal than distal source areas. This study also demonstrates the importance of multiple sediment sources and sediment mixing in the formation of hemipelagic sediments on a continental margin.