九江下蜀黄土和红土的化学风化特征

南方下蜀黄土和红土为研究亚热带地区的古风化强度提供了良好的地质记录。对九江两个下蜀黄土和红土剖面(JJ3和JJ4)的色度、磁化率和常量元素组成进行了研究。JJ3和JJ4剖面沉积物的磁化率和红度(a*)变化趋势较一致。与上地壳相比,九江下蜀黄土与红土的Ca、Na重度亏损,K轻度亏损。九江下蜀黄土的CIA值小于80,而红土的CIA值大于80。Rb/Sr比值和CIA值显著正相关(R2为0.95),二者可有效指示下蜀黄土和红土的化学风化程度。

Chemical Weathering of Xiashu Loess and Red Earth in Jiujiang, Jiangxi Province

Xiashu loess and red earth in southern China provide valuable records for investigating the strength of chemical weathering during the Quaternary in subtropical zone. Here we investigate the reflectance, magnetic susceptibility and major elements of two Xiashu loess and red earth sections (JJ3 and JJ4) from Jiujiang, Jiangxi Province. Magnetic susceptibility and redness (a*) are good proxies for stratigraphic correlation of Xiashu loess and red earth in the space. Compared to average compositions of the upper continental crust (UCC), Ca and Na of Xiashu loess and red earth in JJ3 and JJ4 sections are seriously depleted, and K is slightly depleted. Values of chemical index of alteration (CIA) of Xiashu loess in JJ3 and JJ4 sections are less than 80, but CIA values of red earth are greater than 80, indicating that red earth suffered stronger chemical weathering than Xiashu loess in Jiujiang. Rb/Sr ratio is significantly positively correlated with CIA values (R2 = 0.95). Both CIA values and Rb/Sr ratio can effectively indicate the chemical weathering of Xiashu loess and red earth in Jiujiang.