Disequilibrium of Uranium, Thorium and Radium Isotopes in Pliocenic Clays

Disequilibrium conditions for U and Th radioactive series were found in two clayey formations from pliocenic italian basins. The disequilibria confirm the open condition of these systems during the last 350 kyrs. Mobility of radionuclides is driven by diffusion of recoil products into interstitial waters. The sediments display differential granulometric features within the clay formations causing preferential adsorption and accumulation of radionuclides. This mobility is effective only on micro and mesoscopic scale. © 1992, R. Oldenbourg Verlag