| Summary: | A regional survey of the sedimentology, geochemistry and mineralogy of the Pleistocene and Holocene deep-sea sediments from the Juan de Fuca Ridge between 47°00' and 48°15' North latitude and the adjacent Cascadia Plain indicates a mainly terrigenous, turbiditic source for most sediments in the area, with some admixture of biogenic material (mainly planktonic debris) throughout. Small hydrogenous and hydrothermal components may also be present. Sedimentation rates during the Pleistocene of about 100 cm/1000 yr are indicated for the Ridge area. Excess MnO in the oxidised upper few cm of sediment is ascribed to diagenetic remobilization.
Systematic variations in the SiO₂, Al₂O₃ and CaO content of the sediments appear to reflect a transition from a dominantly turbiditic sedimentary regime during the late Pleistocene, to a hemipelagic Holocene regime in the uppermost 50 cm of sediment.
Extensive deposits of metalliferous sediments with a significant hydrothermal component, such as have been reported from the East Pacific . Rise and other parts of the Pacific Ocean, appear to be absent from the area, due probably to extensive dilution by sediments of terrigenous origin. === Science, Faculty of === Earth, Ocean and Atmospheric Sciences, Department of === Graduate
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