赣北鄱阳湖地区第四纪黄土的粒度特征及环境意义

Grain-size characteristics of Quaternary sediments and its implication in the Poyang Lake region,northern Jiangxi

对长江中游南岸鄱阳湖东侧砂山下风向的太平关黄土剖面进行了粒度测试分析,与南京下蜀黄土、巫山黄土和长江河流沉积物进行了对比。结果表明:1)太平关剖面粉砂(5-50μm)含量达到了50%以上,粘土次之,砂的含量略大,但不足10%,风成"基本粒组"比重较大。太平关剖面的粒度参数与风成黄土的典型剖面基本一致,而和长江河流沉积物差别明显,表明太平关剖面的风成属性;2)结合区域的气候特征及其粉尘动力学原理,太平关剖面不可能与北方黄土一样来自于西北荒漠、戈壁,而是在冰期的裸露的长江河漫滩、谷地伴随着强大的冬季风经过重力分选近距离搬运的结果;3)粒度组分深度变化揭示多旋回的黄土-古土壤特征,黄土对应的粘土组分含量较大,粉砂和砂的含量较小,古土壤层位对应的粘土组分含量较小,粉砂和砂的含量较大,这种"沉积-成土"的韵律性变化佐证了更新世以来的冷暖气候波动。

The grain size of Taiping Guan loess profile, where is at east of South Poyang lake in the middle reach of Yangtze river, was tested and analyzed, and compared with the Nanjing Xiashu loess, Wushan loess and angtze river sediments. The results show that： l ） The Taiping Guan profile silt （5 -50 microns） content reaches more than 50% , clay content is slightly lower and sand content is slightly larger but less than 10% ; the wind sand takes a larger proportion in the basic particle groups. The grain parameters of the Taiping Guan profile are basically identical with the typical eolian loess profile, and is obviously different with the Yangtze river sediment, which reveals the Aeolian properties of the Taiping Guan profile. 2） Combined with the regional climate characteristics and its dust dynamics, Taiping Guan profile sediment may not like the northern loess from northwest desert and gobi, but was the results of the gravity separation and close transportation from the bare Yangtze river floodplain and valley during the ice ages with strong winter wind. 3 ） Depth changes of grain size composition reveals that the polycyclic characteristics of loess -paleosot.