The detection of the markedly depleted in U-234 Dictyoneme shale component

Uranium isotope (U-238 and U-234) content was measured in the different chemical fractions of the dictyoneme shale of the phosphoritic Maardu quarry in Estonia. Possible mechanisms of even uranium isotope fractionation are discussed. Grain dimension of a mineral phase considered as thin dispersed uraninite in black shales is evaluated by use of U-234/U-238 isotopic ratios.