Rare earth element and clay minerals of paddy soils from the central region of the Mekong River, Laos.

摘要

The rare earth elements (REE) content, particle-size distribution, and clay mineralogical composition were analysed for paddy soils collected from the title area to study the origin and inherent potentiality of these soils. REE as the chondrite-normalized curve or the plot of Ce/Eu against Eu/Sm was useful for grouping soils according to their origins. Soils in the upper area (Luang Prabang Province, ?00-400 m a.s.l.) originated from the composite materials of sediment derived from local granite and limestone and sediment transported by the Mekong River. The predominant clay mineral was mica, and its weathering product, or kaolinite, and the mineralogical composition varied from site to site. The soils were generally characterized by high clay and silt contents. Inherent potentiality was intermediate to high. Soils in the lower area (Vientiane Prefecture and Borikhamxay Province, ?0-150 m a.s.l.) originated from sediment transported by the Mekong River or from sediment derived from local sandstone. The soils originating from the Mekong River sediment were medium-textured and mica-dominated and were at the intermediate level of inherent potentiality. Soil originating from the sediment of local sandstone was coarse-textured and contained mica and kaolinite as the predominant clay minerals. Its inherent potentiality was poor.