Hydroxy-interlayered minerals in the Holocene paleosol on the southernmost Loess Plateau, China

• Published in: Applied clay science Vol. 153; pp. 70 - 77
• Main Authors: Huang, Chuan-Qin, Wang, Mi-Nan, Tan, Wen-Feng, Wang, Ming-Kuang, Koopal, Luuk K.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.03.2018
• Subjects: Chinese Loess Plateau; Clay minerals; Holocene paleosol; Hydroxy-interlayered minerals; Hydroxy-interlayered vermiculite; Chinese Loess Plateau; Clay minerals; Hydroxy-interlayered minerals; Hydroxy-interlayered vermiculite; Holocene paleosol
• ISSN: 0169-1317; 1872-9053
• DOI: 10.1016/j.clay.2017.12.007

The presence and formation of hydroxy-interlayered minerals in the Holocene paleosol at the Wugong profile on the southernmost Chinese Loess Plateau were investigated by examining the <1μm and 1–2μm clay fractions of the 50–150cm horizon by Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). Prior to the analyses free Al and Fe phases were removed by dithionite-citric-bicarbonate (DCB) extraction. XRD patterns were obtained with air-dried, Mg-saturated, Mg-saturated with glycerol solvation (Mg-glycerol) and K-saturated and heated at 110, 250, 350, 450 and 550°C samples both before and after hydroxy-interlayered materials removal by sodium citrate extraction. The absorption bands at 3699 and 3430cm−1 in the FTIR spectra of both sub-fractions indicated the presence of hydroxy-interlayered minerals. The K-saturated and heated XRD patterns confirmed this by the progressive collapse of the 1.4nm reflection to a 1.0nm reflection. After removal of the hydroxy-interlayered materials no obvious increase of the relative XRD intensity of the 1.8nm reflection in Mg-glycerol pattern was observed and the 1.4nm reflection exhibited a stronger collapse to 1.0nm after K-saturation and increasing temperature treatment. This indicated that the hydroxy-interlayered minerals in the Holocene paleosol were mainly composed of hydroxyl-interlayer vermiculite. The hydroxyl-interlayer vermiculite was formed by the polymerization of Al/Fe-hydroxy materials within the interlayer space of vermiculite. Shoulder-like reflection at 1.2nm in the K-550°C pattern of the 1–2μm fraction indicated a higher degree of Al/Fe-hydroxylation in the coarse fraction than in the fine fraction, which was consistent with the lower extractable Al and Fe in the coarse fraction. The reflection at 1.38nm in the K-550°C pattern could be interpreted as pedogenic chlorite. Thus, transformation of vermiculite into hydroxy-interlayered vermiculite and finally into a chlorite-like mineral (pedogenic chlorite) has occurred in the Holocene paleosol on the southernmost Chinese Loess Plateau. •Hydroxy-interlayered minerals in the Holocene paleosol on the southernmost CLP was examined.•HIMs was composed of hydroxy-interlayered vermiculite (HIV).•HIV with higher Al/Fe-hydroxylation was enriched in coarser clay fraction.•Changing of vermiculite into HIV and finally into pedogenic chlorite was suggested.