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.