中文摘要：

第四纪红土广泛分布于中国长江中下游地区，是反映中国南方第四纪古环境的重要载体。基于安徽郎溪县十字镇一处典型黄棕色土-网纹红土剖面的155个样品的粒度分析，并结合磁化率、色度和漫反射光谱数据，再结合前人年代地层学和磁性地层学的研究，将郎溪十字镇剖面与长江中下游地区广泛分布的下蜀黄土进行对比，旨在探索该剖面红土的物源。并且对上部黄棕色土和下部埋藏红土的风化程度进行比较，进而揭示从网纹红土到黄棕色土的转变反映出的古气候古环境变化信息。结果表明：1）样品均不含〉2mm的砾石，砂质量分数较少，以“风尘基本粒组”（10～50gm）为优势粒级，其次为黏粒（〈2μm），粒度组成特征反映了明显的风成特性；粒度频率曲线和粒度参数对比分析表明，网纹红土平均粒径较上覆黄棕色土细，细粉砂（2～10μm）和黏粒（〈2μm）更加集中，说明网纹红土沉积后经历了更强的风化成土过程；2）磁化率、色度和漫反射光谱数据分析表明，网纹红土较上覆黄棕色土含有更多的赤铁矿和针铁矿。这是因为网纹红土形成于中国南方一个极端湿润期，高温高湿的还原环境导致强磁性的亚铁磁性矿物部分被溶解转化为弱磁性矿物（如赤铁矿和针铁矿）；3）郎溪十字镇剖面磁化率值与黏粒（〈21μm）质量分数具有很好的可比性，呈明显负相关关系，说明郎溪十字镇剖面的磁化率值具有指示风化作用强度的意义。郎溪十字镇剖面从上部黄棕色土到下部网纹红土的各项理化指标都具有非常明显的变化，可能反映了中国南方一次重大的气候转型事件，可以被视为长江中、下游地区对中更新世全球性重大气候变化的响应。

英文摘要：

The Quaternary red soil is widely distributed in the middle and lower reaches of the Yangtze River, and also an important medium reflecting the Quaternary paleo-environment in southern China. The soil profile, located in Shizi town of Langxi County, Anhui Province, has a special double-layer structure with Yellow-brown Earth overlaying the reticulate red clay. Based on the analysis of particle-size, soil magnetism, color index and diffuse reflectance spectra of the 155 samples, combining with the research methods of Chronostratigraphy and Magnetic stratigraphy, comparing the study profile with that of Xiashu loess in the middle and lower reaches of the Yangtze River, this paper aims to explore the material source of the profile. We also compare double-layer structure with Yellow-brown Earth overlaying the reticulate red clay, in order to reveal the implications of paleo-climate and paleo-environmental change about the transition of the double-layer structure. The results show that： 1） The studied profile of the section contains no gravel （〉2 mm）, low content of sand （〉 63μm）, and aeolian particle （10-50 μm） is the major type of particle in all samples, clay （〈2 μm） is the second major type. All the above conditions reflect the aeolian characteristics of the studied profile. Generally speaking, the grain-size frequency curves of the reticular red clay horizons show the double-peak mode-the 10-50 μm particle group is ＂the dominated mode＂ and the one less than 2 μm is ＂the secondary mode＂ or ＂the dominated mode＂ of some samples. As compared with the Yellow-brown Earth range in the upper part, the underlying reticular red clay range is finer in particle-size and more intensively weathered. 2） The results of soil magnetism, color index and diffuse reflectance spectra for the Yellow-brown Earth range and the reticular red clay range samples in Langxi shows that the reticular red clay range has more hematite and goethite than the Yellow-brown Earth range. This is because the