Manganese nodules dating

Burnett W. C. and Morgenstein M. (1976) Growth rates of Pacific manganese nodules as deduced by uranium-series and hydration-rind dating techniques. Earth Planet. Sci. Lett. 33, 208-218. 

Deep-sea Mn nodnles and crusts are amongst the slowest growing minerals on Earth (Manheim 1986). They have a minimum growth rate of 0.8 mm Ma (Puteanus and Halbach 1988) which is eqnivalent to the formation of about one unit cell every year. Shallow-water concretions grow about 10 times faster. Several methods have been used to date deep-sea manganese nodules and crusts (Ku 1977 Mangini 1988). 

The Th/ Th and Pa/ Th methods were the first radiometric methods to be used for dating of manganese nodules but their application was limited because of the short half lives of Th and Pa. In spite of the limitation of working with samples from the uppermost 1-2 mm of the sample, high resolution studies of nodules have been achieved using this method. For example, Eisenhaueret al. (1992) analyzed 69 samples to a depth of 1.4 mm with a resolution of 0.02 nun in the VA 13/2 Mn crast sample (see section... 

Radiometric dating has revealed wide variations (by four orders of magnitude) for the growth rates of marine manganese deposits Co-rich Mn cmsts (0.8 mm Ma Puteanus and Halbach 1988), deep-sea manganese nodules on red clay substrates (1-2 mm Ma Hu and Ku 1984), deep-sea manganese nodules on siliceous ooze substrates (3 -8 mm Ma" Hu and Ku... 

A limited amount of work has been done on the dating of shallow-water nodules, which, because of diagenetic remobihzation of manganese within the sediment column, generally form more rapidly than deep-ocean deposits. Unlike deep-water nodules, the rapidly growing shallow-water nodules do not contain excess °Th or Pa but instead contain, initially, quantities of °Th and Pa that are less than their equilibrium... 

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