Initial Reports of the Deep Sea Drilling Project - Volume 18

This volume covers Leg 18 of the cruises of the Drilling Vessel Glomar Challenger. Leg 18 originated in Honolulu, Hawaii, on 29 May, 1971, and terminated in Kodiak, Alaska, on 20 July. Along the route, 15 holes were drilled at 11 sites, recovering a total of 1215 meters of sedimentary and volcanic rock cores. Drilling was conducted in three geographical regions in the northeast Pacific Ocean, viz., the region between the Murray and Molaki fracture zones, Cape Mendocino off northern California, Oregon, and British Columbia margins, and in the Gulf of Alaska off Kodiak Island. Some objectives were outlined by the Pacific Advisory Panel for Leg 18 in the northeastern Pacific Ocean. The primary scientific goal was to study the presumed subduction zones on both sides of the actively spreading Gorda, Juan de Fuca, and Explorer ridges. This could be done by comparing sediment samples of continental margin off Oregon and Kodiak Island with samples of the adjacent trench and abyssal plain to see if oceanic material is incorporated into these continental margins. Other objectives were to determine the provenance and nature of lithologies in upper Delgada Fan so that provenance might be related to the lateral displacement along the San Andreas Fault, and, to determine the nature of the underlying acoustic basement which is postulated to be Franciscan in character. Because of unforeseen geology we failed to drill Delgada Fan, but the hole established a well-documented biostratigraphic column for the northeastern Pacific Ocean, particularly in the middle- and high-latitude regions which was another objective. Finally, the panel suggested a site to determine the nature of the sediments and acoustic basement of Paul Revere Ridge, which is situated at the triple junction of the Juan de Fuca, American, and Pacific plates.