黄土高原南缘风尘堆积与现代土壤发育的关系研究

Relation Between Eolian Accumulation and Modern Soil Development in the Southern Part of the Loess Plateau

通过对陕西关中地区JYC剖面不同层微形态的观察和定量分析,发现原生不稳定矿物急剧减少、粗颗粒磨圆度、球度、定向性高和含较多侵入物是耕作层的典型特征;针状方解石微晶大量出现在犁底层,指示一种较短期的相对稳定的较干旱环境;相似性系数暗示古土壤S0以上部分具有风积物主要特征,其中0～40cm是2000年以来人类不断施加黄土性质土粪、农业耕作和粉尘降落的综合产物,40～75cm主要是自然风尘堆积的产物。

A soil profile at the LGT site in the western part of the Guanzhong Basin was studied to illustrate soil-forming process and micromorphological features of modern soil. Micromorphology of the thin sections is observed under a petrographic microscope and its image is quantificationally measured by LEICAL Qwin software. Results show that the minerals assemblage of every horizon is very similar, which is mainly composed of Q and Pl. Difference of C/F15μm ratio, mineral content and coarse features is obvious. Coarse grain of the Ap horizon is characterized by higher roundness （1. 636-1. 818）, lower aspect ratio （1. 861-1. 909）, small size （35-41 μm） and some intrusive mass. Shape of coarse grain in BC horizon is characterized by lower roundness （1. 898-1. 982） , higher aspect ratio （2. 215-2. 312） and big size （42-47μm）. BC horizon is characterized by abundant secondary-calcite quantity and slight amount unstable primary minerals such as Cc and Hb and Bi. Pedofeatures mainly consist of clay and calcite and amorphous Fe. Ap horizon is characterized by abundant secondary-carbonate and earthworm excrement and slight amount residual clay. Abundant needle-shaped secondary calcite minicrystal is observed in the Ap2 horizon. There are little secondary clay and various secondary calcites in BC horizon. Comparability coefficient, between modern soil and Malan loess L1. is 0. 8105-0. 8951 in Ap horizon and 0. 9051-0. 9352 in BC horizon, respectively. All the results in this study suggest that Earth-cumulic Orthic Anthrosols consists of both upper Ap horizon （0-40cm）, which indicated that loess dung and eolian dust deposition and cultivation occur simultaneously in the process of Ap horizon-formation since 2000 years, and lower BC horizon（40-75cm）, which is aeolian sedimentation in relative aridity period during late Holocene. Abundant needle shaped calcite suggested short-term stable and dry environment.