Protactinium, thorium isotopes and uranium in present sediments of the Black sea

16 surface samples of the Black sea deposits has been analyzed radiochemically. The analysis gave data on the 231Pa content, whose concentration varies within the limits (0.26-1.13) 10-12 g/g. It has been shown that more than 80% 231Pa and 230Th penetrate from terrigeneous materials. The study of distribution of authigenic forms of 230Th and 231Pa in the deposits has shown that the behaviour of these isotopes under conditions of the Black Sea basin is identical. The determining effect of terrigeneous introduction of 231Pa and 230Th on the formation of the general contents of these isotopes in the Black Sea deposits makes impossible the application of the ionic-protactinium method for determination of their age. The rate of the deposit accumulation at present time calculated on the basis of the data on 230Th content in surface samples is about 10 cm/103 years