江汉盆地沉积物微量元素特征与长江上游水系拓展

江汉盆地是长江出三峡后第一个大型卸载区,近2.77 Ma以来堆积了近300 m的碎屑沉积物,主要由河流相和湖沼相组成,形成了多个沉积旋回。选择江汉盆地中心位置的ZL钻孔,利用ICP-MS方法,展开微量元素组成分析,研究了新近纪以来江汉盆地沉积物物源的变化。结果表明,上新世以来微量元素化学组成的离散程度逐渐减小,且趋近上部陆壳平均值,可能反映了物源供应区范围的扩展过程。1.25 Ma B.P.以来,多种微量元素含量及Th/Sc、Co/Th、La/Sc、Cr/Cu等比值变化很小,显示长江可能形成于1.25 Ma B.P.以后。

Trace element characteristics of sediments in Jianghan Basin:Implications for expansion of the upper reaches of the Yangtze River

The Jianghan Basin is the largest basin after the Yangtze River flows through the Three Gorges.Sediments of more than 300 m thick have been deposited in the basin since 2.77 Ma B.P.They are mainly composed of fluvial and lacustrine deposits.Meanwhile,there are also several sedimentary cycles.In order to find out the provenance change of the sediments,the authors studied the trace elements in the samples collected from ZL borehole by using the ICP-MS.The dispersion extent of the trace element compositions of these samples has become less with the decrease of the depth since Pliocene,and tended to be close to the mean value of the upper crust.This suggests that the drainage area has become larger.Values of ∑REE,Y,Th,U and ratios of Th/Sc,Co/Th,La/Sc,Cr/Cu become smaller,suggesting that modern Yangtze River was probably formed after 1.25 Ma B.P.