Soil evolution over the Quaternary period in a semiarid climate (Segre river terraces,northeast Spain) |
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| Authors: | David Badía Clara Martí Elena Palacio Carlos Sancho Rosa M Poch |
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| Institution: | 1. High School of Agricultural Engineering, University of Zaragoza, Crtra. Cuarte s/n 22071HUESCA, Spain;2. Faculty of Geology, University of Zaragoza c/Pedro Cerbuna 12, 50009 ZARAGOZA, Spain;3. Higher Technical School of Agrarian Engineering, University of Lleida, Av. Alcalde Rovira Roure, 191. 25198 LLEIDA, Spain |
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| Abstract: | A macro- and micromorphologic study was done on the soils from a stepped sequence of seven dated fluvial terraces in the lower Segre river valley (Lleida, northeast Spain) under a present-day semiarid Mediterranean climate. The soils have evolved from the Holocene through the early Pleistocene, providing an excellent morphostratigraphic framework for evaluating time-dependent factors influencing soil formation in a dry and calcareous environment. Throughout the chronosequence, some properties are regularly age-related specially carbonatation in subsurface horizons. The carbonates occur mainly as micrite, and although microsparite and sparite also appear in the oldest soils, they are replaced by fine-grained calcite by dissolution–reprecipitation processes (micritization process), which is active at present. Some pedological paleofeatures as the presence of sparite and recarbonated argillans in oldest terrace can be interpreted as the reflex of climatic changes during the Quaternary. In spite of this climate variability, the soils display progressive and systematic patterns of carbonate accumulation: on the lowest terraces, the soils do not yet have secondary carbonates but in the beginning Late Pleistocene calcic horizons, with carbonate pendents, are developed; these pendents increase its thickness with age although pendent growth rates decreases from Late Pleistocene to Middle Pleistocene. In the middle of the Late Pleistocene, calcic horizons evolved to petrocalcic horizons, which increase its thickness in the Middle and specially in Early Pleistocene. The presence of calcic and petrocalcic horizons is the primary basis for soil classification. This criterion is applicable not only to the soils of the lower Segre river basin, but also to many soils throughout the semiarid Mediterranean region. |
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| Keywords: | Soil chronosequence Carbonates Pendents Micromorphology Soil classification Cinca-Segre confluence |
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