ROCK-MAGNETIC CHARACTERISTICS OF THE RED SOILS IN SOUTHERN CHINA AND THE MAGNETISM FOR ENHANCING MAGNETIC SUSCEPTIBILITY

The Quaternary red clay in southern China is an important media for the study of paleoenvironmental changes. The typical red clay profiles usually consist of homogenous red clay range in the upper part and reticular red clay horizons in the lower part. Based on systematic analysis on rock magnetism,diffuse reflectance spectra and grain size,this paper studied the red clay sections(CS、HN、NC and XY) in southern China. The results of grain size show that the components <2 μm in the homogenous red clay are higher than those in the reticular red clay, indicating that the reticular red clay is a better-developed paleosol unit with stronger chemical weathering than the homogenous red clay. The climate condition during the reticular red clay period was confirmed to be the warmest and wettest. And their magnetic characteristic indicate that the main magnetic minerals of these red soils are magnetite, magnetite, hematite and goethite. However, the proportion of ferromagnetic minerals in the reticular red clay samples are lower than that in the homogenous red clay samples, mainly composed of PSD and MD. With pyogenic developing, the proportion of ferromagnetic component decreases in the reticular red clay while the content of anti-ferromagnetic minerals(mainly hematite) increases. There are amounts of dark brown Fe-Mn film on the cranny surface of the reticular red clay, which indicates where the iron in reticular red clay went to. This phenomenon seems to suggest different pedogenic conditions between reticular red clay and the homogenous red clay. The reticular red clay development in southern China was under more humid condition and pedogenesis actually occurred under waterlogged conditions. So that fine-grained magnetite and magnetite are gradually dissolved, and finally converted into goethite and hematite. Such transformation of magnetic minerals resulted in the lower MS value in the reticular red clay.