赣北鄱阳湖地区土塘剖面第四纪红土地球化学特征及古气候意义

摘要

赣北鄱阳湖地区土塘剖面发育第四纪红土，自下而上可分为强网纹红土层、弱网纹红土层、微网纹红土层、均质红土层和下蜀黄土层。基于常量元素、粒度分析数据以及前人年代框架，初探土塘剖面化学风化特征及其古气候意义。（1）土塘剖面粒度组分均一，常量元素含量相近，风化淋溶强烈。（2）土塘剖面各地层间化学风化强度存在差异：下蜀黄土层为初期的去 Na、Ca 阶段；均质红土层为中期的去 K 阶段；微网纹红土层由去 K 阶段向去 Si 阶段过渡；网纹红土层已完全进入晚期去 Si 阶段。剖面常量元素的相对迁移能力为：Na2 O＞MnO2＞CaO＞P 2 O5＞MgO＞K2 O＞SiO2＞Al2 O3＞TiO2＞Fe 2 O3。（3）中更新世以来赣北鄱阳湖地区气候总体上由暖湿趋于干冷，期间伴随多个明显的干湿旋回佐证强烈的淋溶与干湿交替作用是网纹红土发育的重要驱动因子。%The Quaternary laterite was developed in the Tutang section in Poyang Lake region, northern Jiangxi Province,and it was divided into four layers from bottom to top,including the highly de_veloped vermicular laterite layer,the weakly developed vermicular laterite layer,the very weakly devel_oped vermicular laterite layer,the homogenous laterite layer and the Xiashu loess layer.The geochemical characteristics and palaeoclimate of Tutang section was analyzed based on the major element,grain size and chronological data from former researchers,and the conclusions were drawn as follows:(1 ) All lay_ers of Tutang section are quite coincident in particle size and geochemical characteristics,and they all ex_perienced an intense chemical weathering process.(2) As for the degree of weathering,the Xiashu loess is in the primary stage by leaching Ca and Na;the homogenous laterite almost reaches the secondary stage by leaching K;the very weakly developed vermicular laterite almost finishes the secondary stage by leac_hing K,and begins to leach Si;the vermicular laterite has been in the late stage by leaching Si.In terms of migration ability,the major elements are ranked as follows:Na2 O>MnO2 >CaO>P 2 O5 >MgO>K2 O>SiO2>Al2 O3 >TiO2 >Fe 2 O3 .(3) The climate of the Poyang Lake region in northern Jiangxi Province since the Middle Pleistocene changed from warm_wet to cool_dry generally,and the alternate dry and wet fluctua_tions were oprious,which suggested that the strong eluviation and alternate dry and wet fluctuations are the important driving factors to form the vermicular laterite.