Abstract
The upper reaches of the Segre river, flowing through the Pyrenees, offers a variety of geomorphic surfaces that allow us to study soil chronosequences. The objective of this work is to widen the knowledge about the main characteristics and formation processes of some benchmark soils developed on fluvio-glacial, alluvial-fan and terrace materials of Pleistocene and Holocene age related to the Segre river, either siliceous or carbonatic. This knowledge will allow us to identify soil forming processes, commonly found in Mediterranean environments such as carbonate redistribution, clay formation and mobilization and rubefaction, all as functions of parent material and age. Five profiles, ranging from the Lower Pleistocene to the Holocene were classified according to Soil Taxonomy/WRB. The Montferrer profile (Calcic Palexeralf /Calcic Cutanic Luvisol (Chromic) is a deep, partly decarbonated soil, with calcium carbonate accumulation in depth covering glacial features. The Torre del Remei profile (Typic Paleustalf /Cutanic Luvisol) developed on silicic moraines and shows an extreme clay formation and illuviation. The Alp (Typic Haplustalf /Cutanic Luvisol) and Tartera (Petric Calciustept /Petric Calcisol) soils are developed on alluvial fans with calcium carbonate sources. The former is partly decarbonated, whilst the latter is rubefacted on top and shows speleothem-like carbonate pendants with superposition of clay illuviation. The youngest profile, Abellerols, (Typic Calciustept /Typic Calcisol) shows only a partial decarbonation and calcite accumulation at depth. The results show that soil development is determined by the age of the surface and the source of calcite, either in the parent rock or brought by subsurface flow: clay illuviation is extreme in absence of it. Special morphologies of carbonate pendants are indicators of environmental conditions. The coexistence of clay coatings and secondary calcite can be explained by recarbonatation or by spatial differentiation of soil environments in the profile. One of the implications of this research is the inconsistence of using soil development indices based on morphological indicators when soils are formed on different parent materials and are subjected to different geomorphic dynamics.
Highlights
In Mediterranean environments leaching and accumulation of carbonates, clay illuviation and rubefaction are some of the most common morphological soil features which have been widely reported (Yaalon 1997; Torrent and Barrón 2003; Verheye and De la Rosa 2006)
The objective of this work is to assess the main characteristics and formation processes of some benchmark soils developed on fluvioglacial, alluvial-fan and terrace materials of Pleistocene to Holocene ages related to the Segre river catchment: either siliceous or carbonatic
In three of the studied soils (Montferrer, Tartera, Abellerols) clay illuviation occurred with carbonate accumulation, either before or after
Summary
In Mediterranean environments leaching and accumulation of carbonates, clay illuviation and rubefaction are some of the most common morphological soil features which have been widely reported (Yaalon 1997; Torrent and Barrón 2003; Verheye and De la Rosa 2006). Other authors point out that the red phase corresponds to a climax development, but that as soon as environmental conditions are no longer favourable, this phase is not reached (Verheye and De la Rosa 2006). In this sense, either the soil redness Either the soil redness (eg. Torrent and Barrón 2003) or micromorphological (eg. Dorronsoro 1994) indices have been used as age indicators
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