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我国的黄土-古土壤序列完整地记录了最近2.5Ma东亚古气候的变化,其中的磁化率被证明是指示夏季风环流强弱的一个较好的代用指标.近年来,有关黄土和古土壤中磁化率成因已有多种模式提出,研究工作仍在深入.为此,从地球化学角度出发,在黄土-古土壤剖面中找出分辨率高、指示性强、成因清楚的气候代用指标,对于揭示磁化率的成因和指示古气候的变化均有重要意义.笔者在分析了大量元素之后,选择了Rb和Sr进行深入探讨,取得了较为满意的结果.由于Rb和Sr表生地球化学行为主要受风化成壤作用强度,尤其是土壤湿度控制,因此黄土-古土壤中Rb/Sr比有可能成为揭示黄土高原夏季风变迁历史的又一替代性指标.1 样品的采集与分析样品采自洛川黑木沟剖面,该剖面位于陕西省洛川县城南约5km(35°45′N,109°25′E).采样层位包括全新世黑垆土(S_0)、马兰黄土(L_1)、离石黄土顶部第1层古土壤(S_1)及其下伏黄土(L_2).采样从黑垆土底部开始,采样间距20cm.样品同时进行磁化率测试和Rb和Sr的含量分析.磁化率测量在中国科学院西安黄土与第四纪地质国家重点实验室完成,采用英国Bartington公司制造的MS2磁化率仪进行测试.Rb和Sr含量分析在南京大学现代分析中心进行,采用X射线荧光光谱方法(XRF),其分析误差为±1(×10~(-6)).
The loess-paleosol sequences in China have completely recorded the paleoclimate changes in the recent 2.5 Ma East Asia, of which the magnetic susceptibility has proved to be a good proxy for indicating the strength of the summer monsoon circulation. In recent years, The origin of magnetic susceptibility has been proposed in many ways and the research work is still in progress.For this purpose, from the geochemical point of view, we can find the climate proxy index with high resolution, strong indication and clear cause in the loess-paleosol profile Revealing the cause of magnetic susceptibility and indicating the changes of paleoclimate are of great significance.After analyzing a large number of elements, the author chose Rb and Sr for further discussion and achieved satisfactory results.As the main geochemical behavior of Rb and Sr epigenetic surface Therefore, the ratio of Rb / Sr in loess-paleosol may be another alternative indicator to reveal the history of the summer monsoon over the Loess Plateau.1 The sampling and analysis of samples taken from Los The profile of the Heimugou trench is about 5 km (35 ° 45’N, 109 ° 25’E) south of Luochuan County, Shaanxi Province. The sampling horizon includes Holocene Loess Plateau (L0), Malan Loess Plateau Lishi The top soil layer 1 ancient soil (S_1) and the loess under it (L_2) were sampled from the bottom of black soil with a sampling interval of 20cm.The samples were tested simultaneously for magnetic susceptibility and Rb and Sr content.The magnetic susceptibility measured in China Xi’an Academy of Sciences, Loess and Quaternary Geology State Key Laboratory completed using the British company Bartington MS2 magnetic susceptibility testing .Rb and Sr content analysis conducted at the Modern Analysis Center of Nanjing University, using X-ray fluorescence spectrometry (XRF) The analysis error is ± 1 (× 10 -6)).