PIPING IN SEDIMENTARY BASINS IN MURCIA (SPAIN): PRELlMlNARY RESULTS FROM X-RAY DIFFRACTION AND SCANNING ELECTRON MICROSCOPY ANALYSIS

Abstract

Soil erosion by piping is an important process in the morphological development of semi arid sedimentary basins in south east Spain. Pipes occur throughout the territory in varying degrees of evolution. This work presents a brief summary of the terminology of the process, and outlines which areas have been studied in Spain hitherto, which factors are associated in the genesis and development of piping based on previous work, and the most important environmental factors present in the two study areas chosen - the Mula basin and the Mazarron district. Representative samples from three different depths have been studied in both the neogene and quaternary sedimentary environments. The samples have been studied by particle size analysis, X-ray diffraction analysis, and sacanning electron microscopy analysis. The results obtained indicate important differences in porosity, permeability and mineralogy. The proportion of clay is similar, but, nevertheless, the quantities of smectite, illite and chlorite vary substantially between the two deposits. These results, together with the frequency and size of the pores and the grade of cementation between different horizons in the soil profiles, account for the different rates of genesis and evolution of the pipes, which are more active and better developed in the neogene Mula basin. With time their morphologicai o impact is almost identical. The capacity for water movement in the soil at different depths and on the surface, that is the grade of saturation of the soils, favours piping. This is a basic process in the excavation and retreat of many slopes, and also in the routing of surface flow and the formation of gullies.