Geochemistry of Radioactive Elements in the 



Ocean and the Chronology of Deep-Sea 



Sediments 



EDGARD E. PICCIOTTO 



Laboratoire de Physique Nucleaire, Universite Libre de Bnixelles, Brussels, Belgium 



MODERN techniques make it possible to obtain cores of sediment 

 of from 10 to 20 m in length from the ocean bottom. Owing to the 

 slow and continual sedimentation present in deep oceans, these 

 columns generally represent complete archives of the Pleistocene 

 era (approximately a million years). In ocean zones of very slow 

 or discontinuous sedimentation, these columns may penetrate 

 even into Tertiary sediments of several tens of millions of years 

 of age. 



During this Congress, several speakers, among them Dr. Gustaf 

 Arrhenius, have emphasized the large quantity of important 

 information to be gained from a study of such sediments. Some 

 examples of this information would include: climatic variations 

 deduced from paleontological studies (Foraminifera, Radiolaria) 

 or by Urey's isotopic oxygen method; the rate of sedimentation 

 in the ocean deeps; the oceanic biological productivity; polar 

 drift; volcanic activity on the earth surface; variations in the 

 chemical composition of the ocean; variations in oceanic circu- 

 lation; variations in the flux of cosmic radiation; and the rate of 

 accumulation of micrometeorites and cosmic dust. In all these 

 cases, one particular problem arises, that of fixing a time scale, in 

 order to date in an absolute manner the observed phenomena. 



Admittedly, the only valid methods of chronology of geological 

 phenomena at present are those based on radioactive disinte- 

 gration. These methods have proved their worth in the field of 

 classical geology, and especially in the geology of the pre-Cambrian 



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