Dating of Sediments Using Radioisotopic Techniques


Abstract: Dating of lake sediments together with the determination of the distribution of trace elements throughout the depth of sediments, gives us valuable information in the study of the impact of natural and cultural events on the environment. Using ^{210}Pb(t_{1 / 2}=22.3y) a member of the natural radioactive ^{238}U series, it is possible to date sediments within the last 200 years. The fallout nuclide ^{137}Cs(t_{1 / 2}= 30.1y) with its known deposition pattern resulting from extensive testing of nuclear weapons in the atmosphere between 1954-1963 and from the nuclear accident in Chernobyl in 1986 provides a complimentary method of sediment dating. The maxima in fall-out corresponding to the 1963 and 1986 are usually well preserved in sediment horizons and they can be used as time markers. ^{7}Be(t_{1 / 2}=53.3d), a cosmic ray produced nuclide is expected to be present only in the uppermost sediment layers. The presence of ^{7}Be in the sediments ensures complete core recovery. Sediment cores from Lakes Zurich and Constance from the Sea of Marmara, southern Turkey and northen Cyprus were dated using natural ^{210}Pb, fallout ^{137}Cs and cosmic-ray produced ^{7}Be radionuclides.


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