晋南全新世黄土剖面常量元素地球化学特征及其古环境意义

Geochemical characteristics of major elements and its paleoenvironmental significance of Holocene loess profile in southern Shanxi, China

通过对晋南地区中梁铁厂全新世黄土剖面常量元素含量分析和粒度、磁化率及光释光年代测定,探讨全新世以来该剖面的化学风化特征及其古环境意义。剖面沉积物的Al2O3、TFe2O3、K2O含量变化趋势基本一致,三者含量在古土壤层中较高,代表气候暖湿;剖面常量元素含量与UCC对比具有富Ca而贫Na、K的特征;剖面总体处于低等化学风化强度,介于陕西扶风和宁夏彭阳的剖面之间,其中古土壤层处于中等风化强度,Ca、Na大量淋失。常量元素地球化学特征指示该区全新世以来气候经历了"气候回暖→温暖湿润→气候转凉→持续干凉"的转化过程。1.2-2.5 ka BP期间区域地表流水作用较强,导致了Ca的相对淋失。

Based on the analysis of major elements, magnetic susceptibility, grain size and optically stimulated luminescence （OSL） dating of samples from the Zhongliangtiechang （ZLTC） profile in southern Shanxi Province, China, using comprehensive approaches such as Chemical Index of Alteration （CIA）, loss and accumulation of major elements relative to UCC, A-CN-K diagram, the geochemical characteristics and its paleoenvironmental significance are discussed. The results show that the chemical compounds consist mainly of SIO2, A1203, CaO and TFe203. The curves of A1203, TFe203 and K20 have the same trend, and the three elements come out top in paleosol layer when the climate is warm-wet. Ca enriches while Na and K decrease in ZLTC profile relative to UCC, which possibly represents the characteristics of loess in the source region. The climate is the main factor which influences the feldspar weathering process, and the feldspar weathering is mostly showing up to plagioclase feldspar weathering. The profile is in low weathering intensity as a whole, which lies between profiles in Fufeng of Shanxi and Pengyang of Ningxia; the sequence is in accordance with recent climate conditions in the three regions. The paleosol layer is in medium weathering intensity, in which Ca and Na leached greatly; while the loess layer is in low weathering intensity. Geochemical characteristics of major elements indicate that the climate ＂cool-dry （9.6-10.5 ka BP）-〉 warm-wet （4.9-9.5 ka BP）-〉 warm-dry （2.5-4.9 ka BP） -〉 cool-dry （since 2.5 ka BP）＂. During 1.2-2.5 ka BP, the content of particles with grain size above 100 μm is the highest, the deposition rate is high, and Ca leaches relatively, which represents the sheet erosion is strong at that time.