SEDIMENTS OF WILLAPA SUBMARINE CANYON,
WASHINGTON UNIV SEATTLE
Pagination or Media Count:
A study of Willapa Submarine Canyon, located off the Washington coast, was undertaken in an attempt to define the type, distribution, and rate of deposition of sediment within the canyon. Well sorted sands are common on the continental shelf near the canyon head and green pelagic muds predominate within the canyon. The muds are thinly bedded and cores from the thalweg contain sand layers. Organic- and carbonate-carbon contents of sediments range between 0.2-2.9 and 0.05-1.5 per cent respectively. The clay-sized fraction of the average sediment consists of approximately 20 per cent Fe-chlorite, 30 per cent kaolinite, and 50 per cent illite with minor amounts of montmorillonoids and mixed-layer clays. Analyses of the heavy-mineral and clay-mineral suites show that the Columbia River is the most probable source of sand and mud in the canyon. Rock dredged from the canyon walls contains fossils which suggest Willapa Canyon has formed since early-Pliocene time.