28 November 1973 Marine Studies Group Meeting

Modern developments in the study of deep-sea sedimentation

Metalliferous sediments from the eastern Pacific D. S. Cronan, Imperial College, London.

Metalliferous sediments associated with the generation of new ocean floor at active spreading centres are known from both mid-ocean ridge crests, and from just above basement on the ridge flanks. The latter are thought to have been formed at the ridge crests and to have moved to their present positions as a result of sea-floor spreading. These sediments are best developed on the East Pacific Rise, where they consist of iron and manganese rich deposits containing relatively high concentrations of Cu, Ni, Pb and Zn, together with several other elements.

The origin of these deposits has been variously ascribed to deep seated hydrothermal activity, seawater leaching of freshly extruded basalt, submarine weathering, bacterial action, and slow precipitation from seawater. However, studies on the partition of enriched elements between the principal phases present in the deposits using selective leaching techniques indicated that the bulk of the iron and manganese are in different phases, and thus could be derived from different sources. The variable distribution of Ni, Co, Pb and Zn between the principal phases of the deposits could reflect differing sources for these elements also.

Magnetic properties of deep-sea sediments—recent results from Arabian Sea and Mediterranean cores N. Hamilton, Department of Geology, University of Southampton

Direct application of magnetic investigations as a technique for understanding aspects of deep-sea sedimentation has to date only

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