AN EFFECTIVE CLEANING METHOD FOR PRODUCING PURE DIATOM SAMPLES FROM LAKE SEDIMENTS

As an important component of lake sediments,diatom is of great value for reconstructing paleoclimate and paleoenvironment.However,it is very difficult to get high-purity diatom samples from lake sediments.Nowadays,available clean-up methods work best only for sediments with 20% diatom content,thus its application is very limited.Based on repeated experiments of various cleaning procedures and observation in light microscope,a continuous five-stage cleaning method is established,including organic matter and carbonate removal by HCl-H2O2,coarse detrital minerals removal by sieving,clay removal by differential settling,diatom purification by heavy liquid floatation and impure material removal by sieving.The five-stage cleaning method is successfully used to produce diatom samples with 90 diatom content from lake sediments with 7% diatom content.This new procedure provides a good approach to study the silicon and oxygen isotope in diatom.It is necessary to observe and compare repeatedly the distribution characteristics of diatom and non-diatom materials in sediments via light microscope so as to choose appropriate separation procedure and to establish effective cleaning method.