Evolution of natural radioactivity of Cainozoic deposits in Byelorussia and a problem of determining the neogenic-pleistocenic boundary

The distribution of natural radioactivity in Cainozoic deposits of Byelorussia has been considered to study the possibility of using natural radioactivity to single out the pliocen-pleistocenic boundary. Three types of radioactivity (α,β,γ) have been investigated. It should be noted that the expression of total radioactivity in the uranium equivalent gives different results depending on the measuring method. The total radioactivity of deposit rocks on β-and γ-radiation is principally due to kalium and thorium, and α-activity to radium and uranium. Radioactivity depends also on the mechanical composition of rocks; its values in loams have been analyzed. The investigated samples as a whole are characterized by low natural radioactivity (the mean activities for loams are: α=127; β=0.90; γ--1.03% of equivalent uranium) on the background of which separate regions of the increased radioactivity, being of interest, are singled out. The highest α-and γ- activities are found in the South Byelorussia in the upper miocenic loams. in the same rocks, the general uranium content was determined by the photocalorimetric method. They contain from 2.6 to 5.4x10-4% of uranium, which is 1.5 times as high as the Clark value. To evaluate the dose of γ-radiation obtained by the organisms who lived in the Cainozoi the samples of the highest activity were recalculated. On the basis of the investigation performed it can be supposed that the increase in natural radioactivity of the medium in the upper Miocene could have the most significant effect on living organisms