丰宁黄土-古土壤剖面常量元素地球化学特征

丰宁滦河上游的河谷地带有多处黄土堆积，由于该地区黄土分布零星、厚度较小，在以往的研究中却很少引起人们的关注，然而该地区黄土堆积是河北坝上地区环境演化和气候变化的重要地质记录.为了探讨该地区黄土的成因、物源以及化学风化强度，选取代表性的黄土-古土壤剖面77个样品进行了常量元素分析，并与已知典型风成堆积物的地球化学元素特征进行对比.结果表明:(1) 丰宁剖面的主要常量元素(SiO₂、Al₂O₃和Fe₂O₃)之和以及UCC(Upper Continental Crust)标准化曲线均与典型风成堆积物具有较好的相似性, 表明丰宁黄土和古土壤为风成成因；(2) 丰宁黄土处于初等化学风化阶段，古土壤则进入了中等化学风化阶段.与典型风成堆积物相比，化学风化强度序列为:宣城风成红土＞＞西峰红黏土、镇江下蜀土＞丰宁古土壤、洛川古土壤＞洛川黄土＞丰宁黄土；(3) 常量元素迁移特征表明丰宁黄土和古土壤的化学风化已完成了早期去Na、Ca阶段，并进入到了中期去K阶段；(4) 丰宁黄土、古土壤的K₂O/Al₂O₃和Fe₂O₃/Al₂O₃比值与洛川黄土、洛川古土壤、镇江下蜀土、西峰红黏土较为接近，表明这些风成堆积物可能具有相似的源区.而TiO₂/Al₂O₃比值小于其他风成堆积物, 指示丰宁剖面具有其他物源. 

Elemental Composition Features of Loess-Paleosol Profile in Fengning,Hebei Province

The loess deposited in the upper reaches of the Luanhe River valley is an important geological record of past palaeoclimate and palaeoenvironment in the Bashang Plateau of Hebei Province. Due to the scattered distribution and small thickness of the loess in this region, it has attracted little attention in previous studies. In order to discuss the genesis, provenance and chemical weathering intensity of loess in this region, the elemental composition analysis of 77 samples from typical loess-paleosol profile was carried out and compared with known typical aeolian deposits. The results show that: (1) The sum of major elements (SiO₂, Al₂O₃ and Fe₂O₃) and UCC (Upper Continental Crust)-normalized patterns of Fengning profile are similar to those of typical aeolian deposits, indicating that Fengning loess and paleosol were aeolian; (2) Fengning loess underwent weak chemical weathering and paleosol underwent moderate chemical weathering. Compared with the typical aeolian deposits, the sequence of chemical weathering intensity is as follows: Xuancheng aeolian red earth > > Xifeng red clay and Zhenjiang Xiashu loess > Fengning paleosol and Luochuan paleosol > Luochuan loess > Fengning leoss; (3) The migration feature of major elements reveal that Fengning loess and paleosol finished the primary process of chemical weathering characterized by leaching of Ca and Na, and almost reached the secondary process characterized by leaching of K; (4) The scatter diagram of K₂O/Al₂O₃ and Fe₂O₃/Al₂O₃ are similar to that of Luochuan loess, Luochuan paleosol, Zhenjiang Xiashu loess and Xifeng red clay, indicating that these aeolian deposits might have the same source. The ratio of TiO₂/ Al₂O₃ is less than that of other aeolian deposits, indicating that Fengning loess and paleosol have other source.