甘肃临夏北塬黄土剖面地球化学特征

Geochemical Characteristics of Beiyuan Loess Profilein Linxia City, Gansu, China

对１５万年以来甘肃临夏北塬黄土剖面样品的地球化学分析研究表明，该剖面黄土地层中主要化学成分的含量与黄土高原其它地区基本相同．对其中古土壤层氧化物迁移特征的分析表明，元素迁移能力按下列顺序排列：Ｃａ２＋＞Ｍｇ２＋＞Ｆｅ３＋Ｋ＋＞Ｎａ＋＞＋＞Ｓｉ４＋＞Ｆｅ２＋＞Ａｌ３＋．Ｃａ元素及化合物ＣａＣＯ３是黄土、古土壤中的最活跃的组分，可作为反映地球化学特征的标型组分．标型化合物ＣａＣＯ３分布特征与淋溶程度有关，可反映气候的干湿程度．氧化物比值反映黄土、古土壤风化成土作用的程度，与生物气候环境变化有关。

Beiyuan loess profile, located at Beiyuan in north of Linxia City, is situated on the second terrace of Daxiahe River, a tributary of the Yellow River. The profile is 40 m thick covering last 150 Kyr. Geochemical analysis of 72 samples taken from the profile show that the main chemical components of loess are similar to those in other places of Loess Plateau. Studies for chemical element migrating capability present such a sequence as:Ca2+>Mg2+>Fe3+>K+>Na+>Si4+>Fe2+>Al3+. Ca with its chemical compound CaCO3 is the most active composition in loess sediment. It can be taken as a representative of geochemical characteristics of loess deposits. Its distribution is related to the filterdissolving process in the loess, so it can be used to indicate the humidity of paleoclimatology. The ratios of oxides in loess that show weatheringpedogenic degrees are correlated with bioclimatic changes. CaO+MgO/Al2O3 is more sensitive than other index to indicate the environmental changes.