Clay Illuviation in a Holocene Palaeosol -Sequence in the Chinese Loess Plateau

Abstract

The loess-palaeosol sequence on the Loess Plateau of China has been subjected to sophistic genetic processes such as dust accumulation, soil erosion, deposition and soil formation. These processes should be carefully distinguished when we clarify the soil genesis and classification, and interpret physical and chemical indicators to evaluate the bio-climate changes. Heavy minerals, pollen, and soil properties were studied in a typical Holocene loess profile in the north of the Loess Plateau, consisting of a palaeosol underlain by the Malan loess (late Pleistocene) and overlain by modern loess. The palaeosols, which were developed during ca. 8800–4400 $¹⁴$C years BP., consists of an upper humus-rich AB horizon over a clay-rich Bt horizon. The highest content of clay coatings was about 7.9% (by area percentage) appears at a depth of 140cm, the lower part of the clay-rich horizon. The humus-rich horizon at a depth of 80cm was intensely weathered in terms of heavy mineral analysis, and the higher pollen content and diversity also indicate a stronger weathering bioclimatic environment at that time. The Calcitic layer overlying the clay coating suggested that the carbonate material was derived from the overlying modern loess. This phenomenon may imply that the clay translocation could occur within 60cm, indicating a strong eluviation-illuviation process that took place during the development of the palaeosol. The results give valuable information on the genesis of the profile and classification of the palaeosol, and for the interpretation of the proxy indicators of bio-climate changes.