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《Marine Geology & Quaternary Geology》 2002-03
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PRETREATMENT METHODS AND THEIR INFLUENCES ON GRAIN-SIZE MEASUREMENT OF AEOLIAN "RED CLAY" IN NORTH CHINA

LU Hua yu, MIAO Xiao dong, SUN You bin (State Key Laboratory of Loess and Quaternary Geology,Institute of Earth Environment,Chinese Academy of Sciences,Xi'an 710075,China)  
The "Red Clay",which is underlying Quaternary loess paleosol deposit,is regarded as a good proxy record of climate and environment changes in late Miocene and Pliocene in North China.And,its grain size distribution is widely employed to reconstruct palaeoclimate as well as palaeoenvironment.However,pretreated methods for the grain size measurement are various in laboratories,the pretreated procedures have certainly influenced results of grain size distribution,and therefore cause controversy over the palaeoclimatic and palaeoenvironmental interpretations.Here,we choose 30 "Red Clay" samples from three representative sections which are located at a transaction from north to south in the Loess Plateau,and each sample is pretreated in six different ways and the samples are measured in a laser particle analyzer.Results show that there exist great differences in grain size distribution of one sample pretreated in the ways:differences of the size index such as Mean can be 20 times fluctuation.We meanwhile examine influences of each step on the grain size measurement,and a pretreatment method is strongly recommended.By this method,the calcium carbonate,organic matter and part of the secondary ferruginous mineral are removed,and the chemical dispersion matter((NaPO 3) 6)as well as the ultrasonic machine are employed in order to completely disperse the particles.We also prove that chemically extracted quartz from the "Red Clay" is coarser in grain size than that of the bulk samples.This results from the removing of the secondary minerals.This may bring further question if the chemically extracted quartz is a good proxy index although it is insensitive to weathering after deposit.
【Fund】: 国家自然科学基金资助项目 (4 990 2 0 0 9) ;; 中国科学院知识创新工程重大项目 (KZCX1-10 -0 1和 KZCX2 -SW-118)
【CateGory Index】: P642.1
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