黄土高原黄土和红粘土^(10)Be地球化学特征  

GEOCHEMISTRY OF COSMOGENIC ^(10)Be IN LOESS-PALEOSOL SEQUENCES AND RED CLAY IN THE LOESS PLATEAU

作　　者：顾兆炎[1] D.Lal 郭正堂[1] 刘东生[1] J.Southon M.W.Caffee 

机构地区：[1]中国科学院地质与地球物理研究所,北京100029 [2]美国斯克里普斯海洋研究所,拉荷亚ca92093 [3]美国劳伦斯利物茂国家实验室加速器质谱中心,利物茂ca94551

出　　处：《第四纪研究》2000年第5期409-422,共14页Quaternary Sciences

基　　金：国家自然科学基金!49773184

摘　　要：充分认识元素和同位素在不同环境条件下的地球化学行为，是运用元素和同位素示踪环境变化的前提。对来自于黄土高原的黄土、古土壤和红粘土样品的宇宙成因核素10Be测量和化学成分分析，以及各种化学淋溶实验表明：10Be主要以吸附状态赋存于粉尘沉积物粘粒矿物的表面，部分已结合进自生的粘土矿物中；在粉尘沉积物风化过程中10BC与9Be和Al的活动性相似，基本没有发生迁移，其原因是连续沉积的粉尘含有大量的碱性物质，阻止了10Be的解吸附和淋滤；沉积和风化作用导致了10Be浓度与化学指标在黄土－古土壤和红粘土剖面中的协同变化。The cosmogenic radionuclide 10Be (half-life = 1.5Ma) has generated much interest because of its potential as a tracer in the environment and applications to the Earth sciences. Several studies of 10Be in Chinese loess have been made to reconstruct the histories of climate and weathering on the Loess Plateau. Nevertheless, 10Be geochemical behavior, especially the mobility in wind-blown dust sequences during weathering, needs to be more fully understood for its applications in sedimentology,pedology, paleoclimatology, and chronology. In this paper, measurements of 10Be,9 Be, and major elements in different grain size fractions, in selective chemically leached frachons, and in bulk samples from some sections of loess-paleosols and red clay in the Loess Plateau were conducted using the AMS (accelerator mass spectrometer), XRF and ICP-MS. The obtained data provide a clear picture on geochemistry of 10Be in the dust deposits, which extend the earlier understandings.Similar to the 9Be distribuhon pattern over different grain size frachons, 10Be concentration increases with the decrease in particale size of the loess and paleosol samples. The amount of 10Be in the < 4μm grain size fraction is more than 60% of total, indicating that most of 10Be is carried by clay minerals. Since dust sediments have an appreciable endowment of 10Be from the source regions, concentrations of 10Be in loess, paleosols and red clay would depend on the dust grain size.We observed that although 10Be concentrahons in the > 4μm gtain size fractions inboth the loess and paleosol samples are similar, the 10Be frachons in the < 4μm size frachons are much higher in the paleosol samples, suggesting that most of 10Be in loess was absorbed on the surface of mineral panicles, while an appreciable amount of 10Be in paleosol and red clay was incorporated in authigenic clay minerals formed in-sita during weathering of the dust. This conclusion is also supported by several leaching experiments showing that 10Be is leached from the loess samples easier th

关 键 词：黄土 红粘土 黄土高原 铍同位素 地球化学 

分 类 号：P642.13[天文地球—工程地质学] P595[天文地球—地质矿产勘探]