Mineralogical and pedogenetic evidence for palaeoenvironmental variations during the Holocene on the Loess Plateau, China

Clay minerals in soils reflect successive stages of mineralogical evolution, which depend on the environmental conditions that have prevailed during pedogenesis. The objective of this research was to document the mineralogy of the clay fractions (<2 mu m) of three Holocene loess-paleosol sections on the Chinese Loess Plateau (CLP) and to deduce the climatic and pedogenetic differences at the three sites. The three sections were located at Ansai. Luochuan and Wugong in a north-south transect of the CLP and dated from the late period of Late Pleistocene (0-23,860 +/- 90 year B.P.). In general, the mineralogy of loess and paleosol was similar over the CLP. However, the pedogenesis and mineralogy of the profiles in the three sections showed significant temporal and spatial variations along the climate gradient. In Ansai the Holocene loess was preserved in thick eolian deposits and relatively homogeneous as far as grain size distribution and clay mineralogy. The clay composition as a function of depth did not vary significantly, which coincided with coarse grains and constant CaCO3 contents. In Wugong the mineral weathering and pedogenesis have resulted in a prominent increase of vermiculite in the paleosol with more clay and intensive decalcification. In general, a subtle decrease of kaolinite and smectite in paleosol occurred in southward direction. It can be concluded that pedogenesis and mineral weathering progressively weakened in going from south to north across the Loess Plateau, which signified a weaker influence of the humid and temperate summer monsoon in the north during the Holocene. In other words, the climatic changes during Holocene were not uniform across the CLP. The weak weathering and pedogenesis in Ansai indicate a stable and dry climate and pedogenic environment over the last 11,500 years around Ansai. (C) 2012 Elsevier B.V. All rights reserved.