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Liu Jihua Liang Hongfeng Yao De Gao Xiangping(Institute of Marine Geology,MGMR,Qingdao,266071,China)  
deep-sea sediment samples were collected in CC area by R/V“Haiyang Ⅳ” in northern East Pacific Ocean during 1987-1989.U contents in samples are detected by INNA method Based on the smear slide detection,the sediments are divided into four types:zeolitic clay siliceous clay,siliceous ooze and calcareous siliceous clay. U contents are different in these sediment types and are,on the arerage,2.16×10 ̄(-6) in zeolitic clay,1.95×10 ̄(-6) in siliceous clay,1.65×10 ̄(-6) in siliceous ooze and 1.59×10 ̄(-6) in calcareous-siliceous clay.In the same type of sediments,U has a higher variation coefficient than any other elements,indicating that U is dispersive in deep-sea sediments. The tendency of regional distribution is that U is higher in content in the northern part than in the south, which is similar to Corg and opposite to CaCO_3.Compared with sediments from shelf and enclosed or semi-enclosed sea, deep-sea sediments have the lowest U contents. This fact shows U is in depletion in deep sediments. It is the feature of crystal chemistry of U,Th and the sources of deep-sea sediments that decides the U in deep-sea sediments to have two main sources:sea water and continent.Authigenic clay minerals such assmectite and organic materials absorb U from sea water while terrigenous clay mineralskeep U from land. High Eh and lower Corg and components associated with biogenicfragments as SiO_2,CaCO_3 and P_2O_5 all dilute U contents and make U depleted.Anotherimportant feature is that Th/U ratios are high in deep-sea sediments,which reflects astrong differentiation in CC area.
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