ALBERT

Description: The chemical and mineralogical composition of pelagic sediments from the East Pacific Ocean has been determined with the aim of defining the ultimate sources and the mechanisms of formation of the solid phases. The distribution of elements between sea-water, the pore solution and the various solid components of the sediments permits interpretations of the variations in time and space of the gross chemical composition of pelagic clays. For example, manganese, present in sea-water in a divalent form, is apparently oxidized at the sediment-water interface to tetravalent species which subsequently become a part of the group of ferromanganese oxide minerals which are found in the marine environment. It is suggested the rate of manganese accumulation in sediments is some function of the length of time the sediment surface is in contact with sea-water. The contribution of chemical species from the different geospheres is considered. The quantitative importance of pelagic clays in the major sedimentary cycle is studied on the basis of the distribution of the weathered igneous rock products between continental and pelagic deposits and sea-water. These analyses of a wide variety of pelagic clays allow a reformulation of the geochemical balance and it is concluded that pelagic clays account for approximately 13 per cent of the total mass of sediments produced over geologic time.

Description: Attempts to classify pelagic sediments have been based either on appearance and composition, or on the ultimate origin of the components. In particular it appears feasible to distinguish minerals which crystallized in sea-water from those which formed in magmas, in hydrothermal solution, or by weathering under acidic conditions. It is the case of iron and manganese oxide mineral aggregates which constitute one of the major types of rock encountered on the ocean floor; according to Menard (unpublished) about 10% of the pelagic area of the Pacific is covered by such nodules. The nodules consist of intimately intergrown crystallites of different minerals among those identified, besides detrital minerals and organic matter, are opal, goethite, rutile, anatase, barite, nontronite, and at least three manganese oxide minerals of major importance. Arrhenius and Korkisch (1959) have attempted to separate from each other the different minerals constituting the nodules, in order to establish the details of their structure and the localization of the heavy metal ions. The results demonstrate (Table II) that copper and nickel are concentrated in the manganese oxide phases concentrated in the reducible fraction. Cobalt, part of the nickel and most of the chromium are distributed between these and the acid-soluble group of the non-manganese minerals, dominated by goethite and disordered FeOOH.

Description: The origin of authigenic minerals on the ocean floor has been extensively discussed in the past with emphasis on two major processes; precipitation from solutions originating from submarine eruptions, and slow precipitation from sea water of dissolved elements, originating from weathering of continental rocks. It is concluded that in several marine authigenic mineral systems these processes overlap. A diagnostic principle is suggested, permitting a qualitative or semiquantitative discrimination between marine authigenic minerals crystallized from dissolved species, which have spent a long time in solution on the one hand, and the same minerals generated from solutions, near their source on the other. Extensive data are available for the manganese and iron oxide minerals forming manganese nodules. It is indicated on the basis of their composition and structure that many of the nodules found in the vicinity of the continents are made up essentially of manganese derived from continental weathering. In contrast to this group, all of the nodules found in the Pacific area of submarine vulcanism display the criteria for rapid precipitation near the source of solution. The distribution of barium minerals over the deep ocean floor is discussed.The same diagnostic principle is suggested for application to these solids, in order to discriminate between baryte and harmotome crystallized near the source of barium- rich, acidic vulcanites, and the same minerals formed from continental solution with passage through the biosphere. In the case of the authigenic aluminosilicates it is found that many of the framework elements (Si and particularly Al) have low passage time through solution, and the major fraction of these elements is consequently removed from solution in the vicinity of the eruptive source materials. Extensive modification of the crystal structures, however, takes place over long periods of time, adding particularly cations from sea water, and probably to some extent silica from siliceous fossils, which on their decay on the ocean floor appear to contribute to the silicate framework of growing zeolites. The marked fractionation of the rare earth ions between coexisting phases is pointed out, with discussion of the potential use of this phenomenon to indicate the processes of formation. The use of the hafnium/zirconium ratio as a tracer for the igneous source type is suggested, and the application of ideally imperfect tracers to establish the varying relative importance of volcanic versus halmeic source of marine minerals is discussed in general.

Description: A criterion is suggested for discrimination between ferromanganese oxide minerals, deposited after the introduction of manganese and associated elements in sea water solution at submarine vulcanism, and minerals which are slowly formed from dilute solution, largely of continental origin. The simlultaneous injection of thorium into the ocean by submarine vulcanism is indicated, and its differentiation from continental thorium introduced into the ocean by runoff is discussed.

Description: Manganese nodule samples from the South and North Pacific were selected for the determination of their main and trace constituents. Results obtained by direct atomic-absorption determination of the elements in samples dissolved in 6 M hydrochloric acid (containing 2 % v/v of the hexoneisopropanol-HCl mixture). The following sensitivities for 1 % absorption are obtained: Mn = 0.10 ppm, Cu = 0.12 ppm, Co = 0.22 ppm. and Pb = 0.85 ppm. Uranium cocentration was determined by fluorimetry (Galvanek-Morrison fluorimeter, Mark V (Jarrel-Ash).