Various erosional forms in marly lands with different physical properties ‎and clay mineral variations in southern Guilan province

Marls are the most talented geological formation of erosion and produce large amount of sediments that annihilate fertile soil and deduct the capacity of dams. Erosion in marls depends on external factors such as distribution of rainfall and internal factors which include soil physical and mineralogical properties. Therefore, the objective of this research was to determine erosion variations because of the changes of physical and mineralogical properties of marls in arid regions of Guilan Province (Gilevan region) located in Northern Iran. The concerned soil physical properties of marly lands were percentage of saturation, surface gravels, sands, silts, clays, fine sands, fine clays, and the level of bulk density, mean weight diameter (MWD) of soil aggregates (dry sieve), liquid limit, plastic limit, activity and ratio of fine clay to total clay. In addition, four samples from Marly soils were prepared for X-ray diffraction analysis. Comparing the average of physical factors with different type of erosion by means of Duncan multiple range test showed that the percentage of clays, fine clays, saturation, and the level of MWD, liquid limit and activity showed significant changes (p<0.05) in some types of erosion, whereas other measured parameters had no significant effect on the form and type of erosion. Furthermore, results of X-ray diffraction showed the presence of smectitic group clay minerals that are dispersive (2:1 clays), in badland and gully areas, while these types of clay minerals were not found in areas with rill and sheet erosion. Hence, with respect to the results of this research, it can be concluded that mineralogical properties such as smectitic clays, as well as some soil physical characteristics such as clay percentage, fine clay and mean weight diameter are the main factors controlling the shape and form of erosion in marly lands of Northern Iran.