Soil evolution over the Quaternary period in a Mediterranean climate (SE Spain)

Palaeosols in the Granada Basin (SE Spain) have been studied in two different situations: surface soils on geomorphically stable surfaces since the Early Pleistocene with younger pedogenic overprinting and buried soils on unstable surfaces from the Middle –Late Pleistocene on which successive erosional – depositional episodes have alternated with pedogenic episodes. For each soil clay and iron accumulation indices, the Fet + Al t /Si t ratio, clay mineralogy and micromorphological features were used to estimate the degree of soil development. From the Early to the early Late Pleistocene, the main pedogenic processes were the leaching of carbonates, weathering, illuviation and rubification, which resulted in Bt horizons with red colours, clay texture, clay coatings and kaolinite neoformation. The degree of weathering and the development of these Bt horizons varied over time, and the soils that formed on the surfaces from the Early Pleistocene show strongest weathering and development. However, after their formation, there were periods in which they were partially truncated and recalcified, resulting in polygenetic soils. The different degrees of development of the buried soils during the last 474,000 years indicate that the wettest warm period was stage 7 and the driest, stage 5. Stages 9 and 11 must have had climates with intermediate wetness. Since the clay accumulation and iron oxide accumulation indices, the differences in Fet + Al t /Si t ratio between Bt and C horizons, the extent of kaolinite neoformation and the micromorphological features of the soils formed during stage 7 are all similar to the surface soils that formed on Early Pleistocene deposits, these features cannot be used to date surfaces older than 242,000 BP. By contrast, the soils that formed during stage 7 and later periods show different extents of development and thus can be used for the approximate dating of landforms.