海南岛北部玄武岩区土壤母质均一性及相对年龄判定

【目的】时间序列法是定量研究土壤发生过程、演变速率及其变化阈值的重要手段，构建可靠的土壤时间序列需对土壤母质均一性和相对年龄进行判定。【方法】以海南岛北部不同喷发期玄武岩发育土壤所构成的成土时间序列（0.09、0.146、0.64、1.12、1.81、2.30 Ma B. P.）为对象，利用各种土壤属性参数（包括剖面形态、颗粒组成、稳定元素含量、风化发育指数和元素变化率等）对该时间序列母质均一性和土壤相对年龄进行判定。【结果】各剖面颜色、质地、结构等形态总体呈均一、渐变的特征，去除黏粒后的粗粉粒含量、稳定元素Ti/Zr比值在剖面内和剖面间变化均较小，表明时间序列土壤的起源母质相同。随着成土年龄的增加，黏粒含量和剖面发育指数呈线性增加的趋势，土壤风化强度指标（B指数、CIW指数、CIA指数和ba值）服从对数函数变化规律，在土壤相对年龄的判定中具有较好的指示意义。【结论】研究区土壤母质来源相同，土壤相对年龄可通过相关土壤属性体现出来，为定量研究土壤发生阈值奠定了基础。

Parent Material Uniformity and Relative Age Identification of Soil Chronosequence Derived from Basalt in Northern Hainan Island

  Objective  Soil chronosequence is a valuable tool for investigating the processes, rates and thresholds of pedogenesis. In order to establish reliable soil chronosequence, it is necessary to identify the soil parent material uniformity and its relative age.  Method  A soil chronosequence (0.09, 0.146, 0.64, 1.12, 1.81, 2.30 Ma B. P.) derived from basalt in northern Hainan Island was selected to identify the soil parent material uniformity and its relative age by using various soil attribute parameters, including profile morphology, particle compositions, stable elements, soil development index and element mobility.  Result  Results showed that the morphological characteristics of soil profile, such as soil color, texture, and structure exhibited uniform and gradual characteristics. Clay-free coarse silt and Ti/Zr ratio had a low variation coefficient either between soil horizons or among different profiles, suggesting the studied soils derived from a relatively homogeneous parent material. With the increase of soil weathering age, soil clay and profile development index (PDI) showed a linear increasing trend, and the weathering index (B value, chemical weathering index (CIW), chemical alteration index (CIA), as well as ba value) all showed a logarithmic change trend, indicating that these parameters could be used for identifying soil relative age.  Conclusion  The conclusion indicated that all soil profiles in the studied region derived from the same parent material, and soil relative age is consistent with the time gradient, providing a prerequisite for the quantitative study of pedogenic thresholds.