藏北高原安多地区高山草甸土的母质成因及其成土模式

Origin of Parent Materials and Pedogensis for Alpine Meadow Soils in Amdo,Northern Tibetan Plateau

基于对藏北高原安多地区高山草甸土的粒度组成及理化性质的研究,探讨了该地区高山草甸土的母质成因及成土模式。分析结果表明,安多地区高山草甸土的粒度分布以20μm为界线呈双峰态分布。主峰峰值粒径在90μm左右,较细峰呈宽阔细尾分布,峰值粒径在3～6μm之间。高山草甸土的各粒级组成(<2μm、2～20μm、20～300μm、300～2 000μm)沿剖面变化很小。高山草甸土主要由极细砂组成(50～125μm),平均粒径集中在60～90μm,明显比黄土高原黄土、川西黄土、成都粘土的粗。高山草甸土粒度分布特征与土壤底部的薄层粗骨性残留古风化层相比存在显著差别,而与该区域河谷沉积、风尘沉积具有相似的特征。总之,各实验数据指示,安多地区高山草甸土具有土层厚、质地均匀、无砾石和层理不发育的特点,与基岩原地风化形成的高山草甸土存在明显差别,其成土母质来源于风尘沉积。该区高山草甸土成土过程符合风尘"加积型"土壤发育模式,而风尘沉积在高山草甸土的形成和发育过程中发挥了重要的作用。

In order to understand the pedogenisis process of alpine meadow soil in Amdo area, northern Tibetan Plat- eau,we investigated the granulometric composition and physico-ehemieal properties of alpine meadow soils from eight soil profiles. The results indicate that alpine meadow soils show bimodal distribution patterns with dividing point as about 20 μm. The main peak values are 90 μm, while the second peaks exhibit broad tail with the peak values 3 -6 μm. The compositions of various grain size fractions （ 〈2 μm,2 -20 μm,20 -300 μm,300 -2 000 μm） change a little with depth at the soil profiles. The alpine meadow soils mainly consist of very fine sand with mean grain size 60 -90 μm. Compared to the loess from Chinese Loess Plateau and eastern Tibetan Plateau, and the Chengdu Clay in the Sichuan Basin, the alpine meadow soils are coarser. Generally, alpine meadow soils in the present study presented a thick layer, homogeneous structure, without gravels, a complete lack of visible bedding, and a clear transition with underlying relics of paleo-weathering crust. Therefore, we propose that the parent materi- als of alpine meadow soils in Amdo region are aeolian deposits. The aeolian dust aggradation plays an important role in the pedogenesis process of the alpine meadow soils.