During a cruise (P6603) of the R/V Pillsbury of the University of Miami, several cores were taken from the Cariaco Trench. The concentrations of thorium, protactinium, and uranium have been studied. A layer of oxidized clay is present below a few meters of reduced sediments. Analyses
show high concentration of uranium to be associated with the organic-rich reducing sediments. In one core, a fivefold decrease in uranium content is found in the oxidized layer, whereas the thorium and protactinium remain the same. Aeration of the sediment at the end of the last glaciation
dissolved uranium in the oxidized layer. In the reducing layers, uranium concentrations are higher than in sediments of the open sea.
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