Thermal Transformations of Chernozem-like Soil Samples During Laboratory Heating and Their Implications for Revealing Degree of Soil Maturity
Abstract
Complicated shapes of thermomagnetic curves representing temperature dependence of magnetic susceptibility k(T) are quite usual in many rock magnetic studies on soils and sediments. They, however, can give also useful information about the kinetics of mineral alteration and provide an additional tool for characterization of the initial material. Experimental data obtained for a collection of Chernozem-like soils from Bulgaria using partial k(T) heating - cooling curves are used to deduce the type, grain size and stability of the pedogenic minerals. Appearance of new magnetite phase as a result of heating, which gives several-fold increase in the room temperature susceptibility values is represented by the ratio Kcool/Kinit and gives valuable information about the origin of the newly created phase on heating. The observed linear relationship between the ratio Kcool/Kinit and the relative amount of oxalate-soluble iron (Feo) suggests that thermal transformation of amorphous Fe-containing phases are responsible for the increase of the signal after cooling. Temperature dependence of the exact position of a kink on the cooling branch of k(T) partial curves is supposed to be due to thermal ordering of lattice defects, substitutions and vacancies in the structure of newly created magnetic phase. Differences in microenvironmental conditions in different genetic soil horizons (soil pH, clay content, organic matter, permeability) are present, while parent material is the same. Variation in the values of the ratio Kcool/Kinit, accompanied by similar shapes of thermomagnetic curves suggest that one and the same mechanism operates in all samples, only the relative amount of organic matter decreases with depth and thus determines the rate of Fe3+ reduction necessary for magnetite formation.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2009
- Bibcode:
- 2009AGUSMGP34A..07J
- Keywords:
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- 1512 Environmental magnetism;
- 1519 Magnetic mineralogy and petrology;
- 1540 Rock and mineral magnetism