TECHNO encrustation description and analysis

The distribution of radioactivities in a large polymetallic encrustation (TECHNO) sampled from the Pacific sea floor has been studied in great detail. The study includes measurements of the long-lived U and Th decay series isotopes, alpha-particle tracks and SUP-10 Be and SUP-26 Al (Results on the latter two cosmonuclides have been reported by Guichard, Reyss and Yokoyama, 1978). The data are discussed in terms of their implication on age dating of the sample. Two interpretations of the data are presented leading to vastly different time scales for the formation of the sample. Here the opinion is divided among the authorship. One group, as well as Guichard et al (1978), favours the million-years scale and the other favors scale measured in thousands of years. The principal pros-and-cons aspects of the two views are mentioned.

(Table 1, page 24), Geochemical cmposition of nodules and crust from the Indain Ocean recovered from R/V Marion Dufresne expeditions

Mineralogical analysis of manganese nodules and crusts collected from Indian ocean aboard Marion Dufresne points to a depth and regional control upon the manganese oxide association: vernadite - birnessite and vernadite - todorokite. Moreover, progressive changes in the vernadite/birnessite ratio as a function of time is clearly seen. Magnetite and titano-magnetite in quantities similar to those of framboidal pyrite in manganese nodules are outlined for the first time. Study of the distribution of metals (Mn, Fe, Ni, Cu, Co) shows a strong latitudinal and regional dependence that may be connected to high productivity zones and to bottom water properties. The problem of mineralogical control on the chemical composition is approached. Finally, it results that any interpretations taking into account all these data haveway to give to the variability of sea-water properties (pH, oxygenation, motions) the prominent control upon manganese nodules composition.

Structure and chemistry of TECHNO encrustations

Using as a starting point the results giving 'traditional' growth rates as determined by the decrease of radioelements (part I) and the hypothesis of rapid formation, the different mineralogical, structure and chemical characteristics of the sample have been studied to try to understand the possible mode of formation of this encrustation. A rapid formation would account for (1) the very peculiar structure of the sample composed of oriented botryoids and the bundle-like structure of the outermost oxide layer; (2) the fact that this sample represents a substitution of a preexisting hyaloclastite; (3) the different chemical gradients, mainly iron, thorium and uranium; (4) the fact that this sample which cannot have been maintained at the sediment-water interface by bioturbation is not covered by a great thickness of sediments. On the other hand, an unsolved problem remains: Why different radionuclides used for dating give growth rates of the same order of magnitude and different 'exposition ages'.