Abstract

Heavy mineral analysis of the rivers of Oregon and northern California has been used to outline four major sources of sediments on the Oregon continental shelf. These sources include the Columbia River Basin, the Oregon Coast Range, the Klamath-Siskiyou Mountains, and terrace deposits along the central Oregon coast. Dispersal patterns of sand-size sediments show that the dominant direction of littoral transport has been to the north at least during the past 18,000 years. Sands were transported 170 miles to the north on the continental shelf during the end of the Late Wisconsin regression and the beginning of the Early Holocene transgression. The observed dispersal patterns of heavy minerals may be indicative of more efficient littoral processes during the last major sea level lowering. Reduction of sand supply to the littoral zone and natural obstacles, such as erosionally resistant headlands, to the littoral transport of sand have apparently limited the northward transport of sand during the past 3,000 years.

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