甘肃西峰晚第三纪红粘土的化学组成及化学风化特征

通过对甘肃西峰红粘土样品的地球化学研究,发现其碳酸盐含量较高,而Si、Al、Fe等元素含量相对较低。为消除碳酸盐的影响,样品经酸溶处理后其化学组成十分均一,反映物质来源的一致性。稀土元素以及微量元素分布形式揭示出红粘土与第四纪黄土-古土壤风成成因的相似性。研究表明,红粘土的化学风化尚处于脱Ca、Na为主的早期阶段;CIA值和酸不溶物中的Na/K比及Rb/Sr比参数一致地指示了红粘土化学风化程度高于第四纪的黄土和古土壤,反映出晚第三纪以来黄土高原的气候由相对温暖湿润向第四纪逐渐变干变冷演化的总趋势。 

CHEMICAL COMPOSITION AND CHARACTERIZATION OF CHEMICAL WEATHERING OF LATE TERTIARY RED CLAY IN XIFENG,GANSU PROVINCE

Geochemical studies have been conducted on the red clay samples from Xifeng,Gansu Province,China.Results show that these samples are enriched in carbonate and depleted in other elements such as Si,Al,and Fe.To eliminate the effect of the carbonate fraction,five samples were leached by 1mol/L acetic acid.It can be found that the acid-insoluble fractions of the samples have similar compositions,indicating same sources.The distribution patterns of rare earth elements and trace elements indicate the similarity of eolian origin between the red clay and Quaternary loess and paleosols.Further investigations show that the red clay experinece the incipient stage of chemical weathering characterized by removal of Na and Ca.Several geochemical parameters such as CIA values,Na/K and Rb/Sr ratios in the acid insoluble fractions reveal that the red clay has undergone more intense chemical weathering than loess and paleosols,suggesting that the paleoclimate on the Loess Plateau has evolved from warm and moist conditions during Late Tertiary to dry and cold conditions during Quaternary.