陕西周原地区全新世黄土-古土壤序列风化程度研究

Study on Weathering Degree of Holocene Loess-paleosol Sequence in the Zhouyuan Region,Shaanxi Province

通过对周原LC全新世黄土-古土壤剖面的元素含量分布及其化学风化程度和元素迁移特征的研究。结果发现:古土壤S0的CIA和Rb/Sr值高于黄土L0,Na/K比低于黄土L0,指示其风化程度强于黄土L0,形成时期气候比黄土堆积时期温暖湿润;黄土风化成壤过程中,Si,K和Fe相对富集,而Ca,Na,Mg和Ti则迁移淋失,呈现Ca>Na>Mg>Ti>Al>Si>K>Fe的迁移序列;全新世剖面化学风化程度处于脱Na和Ca阶段或早期去K阶段。

In this paper,the chemical weathering intensity and the element migration features of the LC loess-paleosol profile in the Zhouyuan region are studied in detail after analyzing the elements and their variation with XRF.Research results show that CIA value and Rb/Sr and Na/K ratios were obviously different in paleosol and loess layers.The CIA value and Rb/Sr ratio were high in paleosol layer（S0） but low in loess layer（L0）,while Na/K ratio was lower in paleosol than in loess,revealing that chemical weathering of paleosol（S0） was more intensive than that of loess（L0）.The chemical weathering difference between paleosol（S0） and loess（L0） was mainly caused by the distinction of climate conditions.The stronger chemical weathering in paleosol reflects that the climate was warm and humid with high eluviation during the paleosol formation.A relative enrichment of Si,K and Fe occurred during the loess formation,while Ca,Na,Mg and Ti were migrated and leached during the chemical weathering process.The migration capability of elements was in an order of Ca Na Mg Ti Al Si K Fe.Through the research of the activities of elements in the LC profile,it was found that Holocene loess in the LC profile experienced the primary process of chemical weathering characterized by leaching of Ca and Na,or just reached the secondary process characterized by leaching of K.