汉江上游风成谷地黄土的重矿物组成特征及意义

汉江流域位于黄土高原南侧,属中国南北气候的过渡区域,其重矿物组成对区域沉积物物质来源与演化研究具有重要意义。运用强磁选、重液分离法等技术手段将汉江上游谷地黄土沉积物中的重矿物提取出来,在双目显微镜和偏光显微镜下测定其含量和特征。结果表明:(1)汉江黄土重矿物有22种,其中角闪石、磁铁矿、钛铁矿等矿物为优势矿物,占重矿物总量的60%以上;稳定矿物约占重矿物总量的47.95%,是汉江黄土最主要的矿物组合。(2)典型黄土和古土壤中重矿物种类相同,但含量有一定差异,马兰黄土(L1)相较古土壤(S0)不稳定矿物含量较高,稳定矿物含量较低;(3)汉江黄土与北侧黄土高原黄土相比重矿物种类相似,稳定性组合分布一致,但汉江黄土稳定性矿物含量较高,不稳定性矿物含量较低。这些特征说明:(1)汉江上游地区古土壤和黄土物质来源一致,古土壤S0在物质组成上继承了黄土,是黄土高度风化的产物;(2)汉江谷地黄土和黄土高原风成黄土两者的物源区一致,但汉江地区黄土受到较黄土高原地区强的风化成壤作用。

HEAVY MINERAL COMPOSITION CHARACTERISTICS AND SIGNIFICANCE OF LOESS IN THE UPPER HAN JIANG RIVER VALLEY

By the analysis on the heavy mineral in eolian loess in the upper Han Jiang river valley, we get many characteristics of the heavy mineral. There are more than 20 kinds, including opaque minerals such as hornblende, magnetite, ilmenite etc. They are the advantageous minerals, accounting for 60% of all. The stable minerals are 47.95% of the total heavy mineral, which are the main mineral in loess on Hanjiang River. The kinds of heavy minerals in Hanjiang are similar to that in the Loess Plateau. They are resembled to the stability, indicating the same resource between them. However, the content of stable minerals is relatively high and that of instable minerals is relatively low. The reason is that the distance between the Hanjiang River and the main sourced regions are higher than that between Loess Plateau and the sourced regions. It resulted in the difficult reservation of the instable minerals because of the wet climate. The mineral compositions in different stratigraphy of the loess profile in the upper Hanjiang River are same, indicating the same resource in loess and palaeosol in the late Pleistocene, and the composed materials in the S0 succeed to that of L1 and different content between each other. There are higher content of instable minerals in L1 than that of S0 but relatively low in the stable minerals. The surface of the minerals is fresh and clean, and the clay is relatively less than that in palaeosol. The instable minerals were made into clay minerals because of the strongly weathering and pedogenesis during the formation of palaeosol.