Mineral magnetic properties of a weathering sequence of soils derived from basalt in Eastern China

The magnetic properties and magnetic mineralogy of a weathering sequence of soils developed on basalt parent material from eastern China, were studied by rock magnetism, X-ray diffraction and soil chemical analyses to establish the connection between mineral magnetic properties and pedogenic development in a subtropical region. The magnetic susceptibility of soils formed on basalt varied greatly and did not increase with the degree of pedogenic development. The frequency-dependent susceptibility (chi fd) values of soils ranged from 1.0 to 11.1% and increased with the pedogenic development. Highly significant linear relationship was found between the frequency-dependent susceptibility and the Fed content (R-2=0.683) and Fe-d/Fe-t ratio (R-2=0.780) in soils, indicating that pedogenic SP ferrimagnetic grains were associated with enrichment of the secondary iron oxide minerals in the weathering process of soil. Rock magnetism analysis showed that the major magnetic carriers in the weakly weathered soil profiles are magnetite and/or maghemite, and the highly developed soil profiles are generally enriched in magnetite/maghemite grains of pedogenic origin and the magnetically hard haematite, indicating that the magnetic component was transformed from a ferrimagnetic phase (magnetite) to antiferromagnetic phase (hematite) during pedogenic development. Results indicated that some of the magnetic parameters of soils, in this case chi fd, can be useful for pedogenic comparisons and age correlations in the weathering sequence of soil. It is thus suggested that multiparameter rock magnetic investigations represent a more powerful approach for pedogenesis. (C) 2007 Elsevier B.V. All rights reserved.