Origin and distribution of clay minerals of soils in semi-arid zones: example of Ksob watershed (Western High Atlas, Morocco)

The Ksob basin watershed is located in a region with a semi-arid climate; it is characterized by large area, variable geology and clay mineralogy, variable topography and different types of thin soils. In the aim to determine the origin and distribution of clay mineral of soils of this basin, three types of samples were considered in this study; the parent rock, the different horizon of soils and the recent river deposit. Clay mineralogical composition, particle size distribution, soil texture, carbonate, moisture and organic matter content (SOM), pH and conductivity were measured to identify the soil properties. Chlorite and illite of the studied soils basin were principally inherited from the parent materials, while vermiculite was principally formed in the soil environment. The other phases (dioctahedral smectite, illite-smectite mixed layers, kaolinite and palygorskite) can result from both inheritance and transformation. Ttrioctahedral smectite and palygorskite can also results from neoformation. Carbonate, SOM content and pH of the studied soils vary independently with clay mineralogy. However soils texture, parent rock, topography and climate strongly influence soil clay mineralogy and its evolution.