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The AAPG/Datapages Combined Publications Database
Five holes were drilled several hundred kilometers offshore near the Mendocino and Pioneer fracture zones. Situated in 3,200-4,200-m water depths, these holes penetrate most or all of the stratigraphic column present at each site. They provide pertinent geologic data concerning the age of the oceanic crust and demonstrate 200-1,200-km offset across the fracture zones in that region. The deposits range in age from Pleistocene through late Oligocene. Their rates of deposition range from 0.1 to 56.0 + cm/1,000 years. Most are of terrigenous origin, although thin pelagic intervals are present in two holes. Such sedimentation agents as biogenous productivity, tropospheric transport, bottom currents, grain-by-grain settling, and turbidity currents have contributed to the sedime t accumulations. Two of the holes that are only 20 km apart are lithologically similar. Each of the other holes has distinctive lithologic characteristics and thereby reflects variations in the contributions made by the different sedimentation agents. Several holes contain intervals of porous sand as well as organic-rich mud.
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