【作者】 管东升；

【导师】 潘保田； 管清玉；

【作者基本信息】 兰州大学 ， 第四纪地质， 2012， 硕士

【摘要】 云南巧家县所在的金沙江谷地北岸的黄土状沉积物是金沙江河谷中发现的沉积连续、厚度较大的风尘堆积序列。它不仅为探讨金沙江“干热河谷”的形成、演化及中国西南部古大气环流演化过程和机理提供了理想的地质材料,也为研究西南季风演化及其与青藏高原隆升的关系提供了重要信息和启示。本文通过对金沙江河谷黄土状沉积物(主要为华弹剖面)的系统粒度分析,并与金沙江河流相堆积物、典型的黄土高原第四纪黄土(陇西黄土、沙沟黄土)粒度特征作对比。我们发现无论是粒度频率曲线、粒度结构散点图、C-M图、三角图,还是粒度指数特征与矢量分析图,金沙江河谷黄土状沉积物与第四纪典型风成黄土非常相似,但与金沙江河谷河流相沉积物有明显的差异。由此我们认为金沙江河谷黄土状沉积物与黄土高原第四纪黄土一样,也是风成沉积。进一步的研究发现,金沙江河谷黄土状沉积物与该区域的静水沉积物、河漫滩相砂在地球化学特征上也非常相似,指示该类黄土状沉积物源于金沙江河谷中的静水沉积物与河漫滩相砂,为近源沉积。金沙江河谷中局地山谷风环流(尤其是冬、春季节的谷风)可能是该地区的黄土状沉积物主要搬运动力。华弹剖面古地磁测试结果表明了剖面中没有出现B/M界限,说明黄土状沉积物沉积晚于0.78Ma BP。华弹剖面5m和9m处的光释光年龄分别为81.234±8.24ka BP、122.71±8.12ka BP,据此我们推断黄土状沉积物剖面的底界年龄约为373.47±±8.18ka BP。这暗示了有利于黄土堆积的森林草原环境出现于最近400ka BP,金沙江河谷的干热环境也形成于此时。通过黄土状沉积物剖面主要氧化物的含量变化,华弹剖面与静水沉积物、沙沟黄土主要元素的对比以及CIA指数、A-CN-K图的比较,我们发现在华弹地区黄土状沉积物中,Ca、Mg、Na元素的流失主要在黄土状沉积物风化过程中。粒度变化曲线及地球化学元素变化曲线指示金沙江黄土状沉积物在沉积过程中基本上受冰期-间冰期旋回控制,但在更小的尺度上具有区域独特性,推测这与此地区独特的地形气候相关。此外,金沙江河谷在0.15Ma BP左右金沙谷谷风风力加强,0.12Ma BP左右金沙江气候变得温湿。更多还原

【Abstract】 The loess-like sediment in Jinsha River provides an ideal geological materials for researching the palaeoclimate of southwest China, because it is a thick and successively aeolian deposition. It also provides an important information for studying the relationship between the mosoon and the uplift of Tibetan Plateau, the formation and evolution of "dry-hot vally" in Jinsha River, as well as the interaction between the mode of atmosphric circulation of westsouth Tibetan Plateau and the climate change of surrounding regions.In this study, the grain-size features of the Loess-like sediment which is widely distributed on the terraces and high lands of the Jinsha River valley in Yunnan Province are compared with the typical Quaternary loess(Longxi section and Shagou section) and representative Jinsha River fluvial samples. The results indicate that the grain-size distribution pattern of the Loess-like sediment display a bimodal or polymodal distribution, with the silty fraction being dominant, and is essentially similar to that of Quaternary Loess. In grain-size distribution plots, C-M plots, triangular plots, or grain-size parameters and vector analysis,the Loess-like sediment is also similar to that of Quaternary Loess, but greatly differs from the fluvial sediments. So we can conclude that the Loess-like sediment is of aeolian origin. The geochemical characterization of Loess-like sediment is similar to that of dammed lake sediment and fluvial sediment in the same area, which is significantly different from the typical loess in northwest China, it shows that the Loess-like sediment originated from near material. The valley wind provids the force for tansportion of the loess-like sediment.Result of paleomagnetic stratigraphy research indicates that B/M boundary is not appeared in Huatan profile, so the age of the HuaTan loess is younger than0.78MaBP. The age of loess-like sediment at5m and9m in Huatan profile by OSL are81.23±8.24ka BP、122.71±8.12ka BP. Based on average sedimentation the age of the base of Huatan loess-like sediment is373.47±8.18ka BP. It indicates that the time of grassland and forest steppe appeared at recently400ka BP and the "dry-valley" formed at the same time.From comparing the main oxide content, the main element comparision of loess-like sediment and dammed lake sediment, the main element comparision of loess-like sediment and Shagou loess, CIA,A-CN-K, we can conclude that Ca,Mg,Na is lost during the chemical weather. The curves of grain-size and geochemical characterization indicate that the process of loess-like sediment deposition is controlled by glacial-interglacial cycle, and the loess-like sediment has special feature in smaller time scale. The valley wind of Jinsha jiang River became stronger at0.15Ma BP, and the environment bcame warm and wet at0.12Ma BP.更多还原