Initial Reports of the Deep Sea Drilling Project - Volume 64

This volume covers Leg 64 of the cruises of the Drilling Vessel Glomar Challenger. Deep Sea Drilling Project (DSDP) Legs 64 and 65 were planned as a coordinated drilling investigation of the Gulf of California. The primary goals of Leg 64 were to investigate the early evolution of a passive continental margin and to study hydrothermal systems in the Guaymas Basin. During DSDP Leg 64 the Glomar Challenger drilled a total of 3462 meters at eight sites (474-481) in the Gulf of California region. The Glomar Challenger departed Mazatlán, Mexico in December 1978 and returned to Long Beach, California in January 1979. The Gulf of California presented a singular example of tectonics and sedimentation in a very young ocean, being formed by translation and oblique rifting. The sedimentation of the region is hemipelagic, rapid, and largely dominated by siliceous microfossils. The objectives were defined by the IPOD Passive Continental Margin Panel and the IPOD Gulf of California Working Group. Three main regions, each with particular problems, were examined and these also form the organizational basis of this volume. Briefly, these are 1) Sites 474, 475, and 476. A transect from oceanic crust to continental crust at the southern tip of Baja California in order to define passive-margin subsidence during the early post-rifting phase. 2) Sites 477, 478, and 481. An investigation of the nature of young ocean crust in the Guaymas Basin, where high accumulation rates are common and variable high heat flow indicates active rifting and hydrothermal activity. 3) Sites 479 and 480. Drilling on the Guaymas Basin Slope above the proto-Gulf sequences. Interest focused on the paleoceanography of laminated, homogeneous diatom-rich, anoxic sediments within the zone of low oxygen.