Soils with gypsum of the central catalan depression. Excursion guide: International Symposium on Soils with Gypsum, Lleida 15-21 September 1996

Abstract

The Central Catalan Depression is the name given to the eastern sector of the Tertiary Ebro sedimentary basin. The geological and climatic characteristics of this region along the Tertiary and Quaternary have been the origin of evaporate formations which are widespread in the Depression. They have given rise lo a wide typology of soils with gypsum, mainly depending on the type of formation -marine or continental and on geomorphological and climatic changes during the Quaternary. Agricultural land use, which exists in Ibis region since (pre)historical times, has also affected soil morphology. The objective of Ibis excursion is lo visit several of these soils, located in the western sector of the Catalan Central Depression, in order to discuss their genesis, relation with the landscape and vegetation, land use and classification. The itinerary of the excursion is displayed in Fig. 1. The excursion is organized visiting three main areas: - An area where gypsum rocks outrop under dryland conditions: Ivorra site, where the soil-Iandscape relationships wilI be discussed in depth. - An area where gypsum soils occur in large alluvial fans under irrigation: Urgell site, where strong differences in soil morphology will be demonstrated. - An area where gypsum soils occur in smaller alluvial fans linked lo the Tertiary gypsum outcrops under dryland conditions: Algerri site, where gypsum accumulations are more indurated and occur in gravelly materials. The methods for soil surveying and field description are based Qn C.B.D.S.A. (1983). The description and references for the physical and chemical analytical methods can be found in Porta el al. (1986) and in Porta el al. (1993). Some adaptations needed for gypseous materials are detailed in Herrero (1991) and Poch (1992). Thin sections are described according lo Bullock el al. (1985), wilh adaplalions and new terms introduced in Spanish by Herrero (1991) and in English by Herrero and Porta (1992) and Sloops & Poch (1994). Regarding lhe specific terms applied lo soils with gypsum, the reader can consult the short note by Herrero (1996) included in the Proceedings of the Symposium. The excursion guide provides general information about the area, as well as detailed information of the sites visited.