Multi-wavelength synchrotron radiation XRF determination of U and Th in sedimentary cores from Lake Baikal

A new technique for the determination of uranium and thorium in lacustrine sediments is based on non-destructive synchrotron radiation X-ray fluoresce nce analysis (SR-XRF) of sediment samples using monochromatic beams of diff erent energies as excitation sources, with the recording and subsequent ite rative processing of the X-ray fluorescence spectra. The technique has a mu ltielement capability and enables fast, simultaneous analysis of a few tens of elements. The proposed SR-XRF technique was tested against INAA and ICP -MS methods and showed a number of advantages with a generally good correla tion of results by the three methods. Uranium and Th profiles have been mea sured at a time resolution of 2 kyr in a drill core (BDP-96) from Lake Baik al bottom sediments deposited between 780 and 40 kyr BP. During this time s pan, peaks in the U and U/Th concentration marked "warm" climates. Oscillat ions of U and U/Th in Baikal bottom sediments during the Brunhes chron refl ect climate-induced global change in the volume of polar ice, controlled by long-term cyclicity of the Earth's orbital parameters. The response of the se "warm" periods is similar to that observed earlier in shorter cores that span the two last interglacials (220-0 kyr BP).