Fluvial and eolian morphogenesis in south Hodna (Algeria)

Hodna is located in arid region in central Algeria. In this area, wind erosion is very important; it is also crossed by several small water courses. Periodic floods moisten the soil, bring alluvium and contribute to leaching salts. They also enrich the soil with minerals. The main objective of this work is to study the origin of the sediments using quartz grain morphoscopy, to analyse their particle size distribution and their vertical variation in soil profiles. Three profiles, located in agricultural parcels used for several years, were selected. Control samples were taken in adjacent parcels. 23 samples, corresponding to the soil horizons were collected in the field. Statistical analysis of soil samples shows that the sand fraction is important and dominates the particle size distribution of these soils. The increase of the fine fraction (fine silt and clay) coincides with the lower percentage of total sand and vice versa and, limestone changes proportionally with the fine fraction and suggesting its location in this fraction. At depth, the decrease of sands always corresponds to an increase of the fine fraction. This enrichment appears to be located in the median horizons where the textural profile marks a wave showing the highest values. In the surface horizons in agricultural parcels, the fine elements content are always greater than the controls. This is related to the tillage which comes back the fine elements in the surface. The morphoscopic analysis of sands revealed mixed deposits fluvial and wind. The comparison of agricultural parcels and controls indicates a change in the surface horizon due to tillage. This study shows also signs of significant current wind action in surface.