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对汉江上游流域进行了深入的地层学及地貌学调查,在郧县河段河流一级阶地上覆黄土-古土壤沉积剖面中发现了典型的古洪水沉积层。对其进行了系统采样和粒度分析,结果表明,古洪水沉积层的粒度在空间上有明显的变化。水平方向上,相同层位的粒度自然分布曲线、概率累积曲线和平均粒径基本相同;垂直方向上,从上向下粒度自然分布曲线、概率累积曲线和平均粒径明显不同,粒径逐渐变细。水平方向上的粒度特征说明,古洪水同层位的样品可以相互替代;垂直方向上的变化与前人在泾河以及渭河流域等地研究发现的古洪水沉积层呈从下向上逐渐变细的沉积模式不同,说明古洪水沉积层的沉积模式并非只有一种,而是存在多种沉积模式,这种变化可能与洪水过程有关。
The stratigraphy and geomorphology of the upper reaches of the Hanjiang River have been investigated. Typical paleo-flood sediments have been found in the loess-paleosol depositional sections of the first terrace of the Yunxian River. The systematic sampling and particle size analysis were carried out. The results show that the grain size of the paleo-flood sediments has obvious spatial variation. In the horizontal direction, the natural distribution curve of the particle size of the same horizon, the probability cumulative curve and the average particle diameter are basically the same; in the vertical direction, the natural distribution curve of the particle size from the top to the bottom, the probability cumulative curve and the average particle diameter are obviously different, fine. The grain size features in the horizontal direction show that the samples from the same flood plain can be replaced by each other. The changes in the vertical direction are similar to those of previous flood sediments in the Jinghe and Weihe River basins, Different sedimentary models suggest that there are not only one sedimentary model of paleo-flood sediment but rather a variety of sedimentary models, which may be related to the flood process.