张家界地区风化壳的性质与夷平面形成环境

Characteristics of Weathering Crust and Formation Environment of Planation Surface in Zhangjiajie

通过野外考察、室内测试分析及区域对比,对张家界地区风化壳的性质与夷平面的形成环境进行探讨。地貌学、古岩溶、风化壳等特征综合验证了张家界地区夷平面的存在;风化壳化学特征及区域对比表明,夷平面形成于湿热的晚第三纪,其后形成剥夷面。夷平面上风化壳分层明显,自上而下分为腐殖土层、残积层、半风化基岩层和基岩层;化学分析表明风化壳具有粘土含量高、富铝化程度低的特点,湿热的夷平面环境使风化壳脱硅富铁铝作用较弱,形成硅铝风化壳。综合区域对比可知,张家界地区海拔为1 100~1 300 m的一级夷平面形成于晚第三纪湿热的环境;低于夷平面的砂岩平台组成剥夷面（800~950 m）,大约形成于晚上新世到早更新世之间。

This paper characterized the weathering crust and planation surface in Zhangjiajie based on the field investigation,geochemical analysis,and regional comparison.It is indicated that the planation surface formed in humid environment of Late Tertiary Period,followed by the occurrence of erosional surface.Structures of weathering crusts from the planation surface are clear,showing artificial soil,residual layer,semi-weathered rock and rock downward.The weathering crust is dominated by high silicon and low aluminum,suggesting the moist and hot environment.On the regional scale,the planation surface in Zhangjiajie at the altitude of 1,100-1,300 m occurred in humid environment of Late Tertiary Period,whilst the lower erosional surface（800-950 m） appeared between the Late Pliocene and Early Pleistocene.