中文摘要：

在长江中游地区的湖南和湖北两省,选择宜昌、咸宁、常德、长沙、株洲5个第四纪红土剖面,分析第四纪红土的粒度组成特征,研究红土的成因及南方古环境的演变。结果表明,这些地区第四纪红土的粒度组成呈明显的二元结构：剖面上部（宜昌剖面0～320 cm,咸宁剖面0～220 cm,常德剖面0～270 cm,长沙剖面0～280 cm,株洲剖面0～150 cm）粒度细小而均匀,砂粒含量低,大部分小于1%;粗粉砂（又称风尘＂基本粒组＂）相对富集,平均含量分别为34.38%、32.29%、32.48%、31.69%和31.86%。而且土壤样品粒度频率分布曲线与安徽宣城第四纪红土很相似,与镇江下蜀黄土也有明显继承性。这些特性均反映了剖面上层红土的风成特性。但研究剖面下部红土,粒度组成有明显不同：含有砾石,砂粒含量较高,不同粒度组分垂向变化明显,粒度频率分布曲线与宣城红土和下蜀黄土有显著差异,表现出明显的冲、洪积相特性。第四纪红土的＂二元结构＂,反映了研究区域第四纪古环境的多变性和复杂性：早期红土形成后,因受间冰期湿热气候的影响,多受流水作用改造;而晚期红土更多地受风尘堆积的影响,沉积后虽经过了强烈的原位风化,但仍保留了风尘沉积的特性。

英文摘要：

Particle-size distribution of five typical profiles of Quaternary red clay in Yichang and Xianning,Hubei Province,and Changde,Changsha and Zhuzhou,Hunan Province,the middle reaches of the Yangtze River,was analyzed to study origin of the Quaternary red clay and its implications for evolution of the paleo-environment in South China.Results indicate that all the profiles demonstrate obvious dualistic structure in particle-size composition,e.g.in the upper part of the profile（0～320 cm of the Yichang profile,0～220 cm of the Xianning profile,0～270 cm of the Changde profile,0～280 cm of the Changsha profile,and 0～150 cm of the Zhuzhou profile）,the clay is fine and uniform in particle size and low in content of sands,mostly 1%,and relative high in content of coarse silt or basic component of aeolian dust fraction,accounting for 34.38%,32.29%,32.48%,31.69% and 31.86% on average,respectively.Moreover,the particle-size distribution frequency graphs of the red clay samples are similar to those of the Quaternary red clay in Xuancheng,Anhui Province,and also show some inherited patterns from the Xiashu loess in Zhenjiang,Jiangsu Province.All the above reflect the aeolian characteristics of the red clay in the upper parts.However,the lower parts of the profiles is significantly different from the upper in particle-size composition.They often have gravels and a relatively high content of sands,showing a significant vertical variation of different particle-size fractions along the file.Furthermore,the files are also significantly different from those of the Quaternary red clay in Xuancheng,Anhui Province,and the Xiashu loess in Zhenjiang,Jiangsu Province,in particle-size frequency graph,demonstrating diluvial or alluvial properties.The dualistic structure of the Quaternary red clay in the middle reaches of the Yangtze River manifests variability and complexity of the paleo-environment in the study area.After the red clay formed in the early stage of the Quaternary period,it was often exposed to the impact of intergl