Soil evolution along a toposequence on glacial and periglacial materials in the pyrenees range

Abstract

Data from eight selected soils located in the La Cerdanya basin (Catalan Pyrenees, Spain) are presented in this study in order to elucidate soil forming processes throughout the Quaternary on glacial and periglacial deposits, at altitudes -between 1130 and 2390m. The soils are classified as Umbrisols, Podzols, Arenosols, Regosols, and Luvisols (FAO/ISRIC/IUSS 2006) and Dystrocryepts, Dystrudepts, Fragiorthods, Udalfs (Pale-, Fragi- and Haplo-) and Ustorthents (Soil Survey Staff 1999). The present moisture and temperature regimes are ustic and mesic in the low altitude soils and udic and frigid/cryic in the high altitude soils. The parent materials of the soils are silicate rock end deposits and consist of lateral moraine tills, slope deposits affected by present-day periglacial processes and fluvio-glacial materials at the bottom of the sequence. The soil forming processes in the area relate to the climate changes during the Pleistocene and Holocene, lithology, altitude, and local hydrological conditions. They consist of in-situ deep weathering of granites, organic matter accumulation, fragipan and clay formations, illuviation, and podzolization. The soils have morphological evidences of the past permafrost of the glacial periods, such as the silt and fine sand cappings, lamellar Bt horizons, vesicular structures, and abundant redoximorphic features, which are inherited from moister conditions, probably during the wet interglacial periods. The clay minerals of the soils are mainly illitic, with some kaolinite and smectite in the valley bottom. Chlorite is the dominant clay mineral at higher altitudes (due to mica weathering), whereas hydromica, kaolinite, and halloysite were found in the lower altitudes, due to feldspar weathering. The high mineral weathering and clay illuviation in soils of the lower altitudes indicate that the degree of erosion of the upslope soils have probably been very intense. On upslope soils, the accumulation of organic matter, with clay minerals formation and podzolisation have lead to the development of umbric, cambic, and spodic horizons, whose formation are probably still active at present. © 2008 Springer-Verlag Berlin Heidelberg.