چكيده لاتين :
Introduction
Rafsanjan plain, being about 4000 Km2 in area is located at the southeast of central Iran in a tectonic depression trending NW-SE. Due to the erosion of Sarcheshmeh and Davaran mountains (respectively at the south and north of the plain), sediments carried by floods to this depression have created bahadas comprised of alluvial fans at the north and south of the plain. At the central part, where the floods cease, a clay flat playa is present. Aeolian landforms lie mainly at the surface of both northern bahada and the central playa.
Methodology
In order to identify and map the aeolian geomorphological units, using the so-called 1:20000 aerial photos, a print laydown was prepared. Afterwards, the aeolian geomorphological units were identified and separated. Finally, the units were ground checked. Also, several samples were taken across the plain from aeolian sands, and were analyzed from roundness, transparency, mineralogy and granolometry aspects.
Results and Discussion
Analysis of the samples of sand revealed that the basal parts of huge alluvial fans located at the southern parts of the plain are the main source area of sands. Morphology of sand dunes attests to this conclusion. So, alluvial sands at the basal parts of these fans are transported by the dominant winds which blow from southeast. The sands, after traversing the central playa, are mainly deposited at the northern foothills, although several types of migrating dunes are observed in central as well as southern parts of the plain.
The dunes are named based on the nomenclature proposed by Pye and Tsoar (1990) in which they are firstly classified into simple, compound and complex ones. The simple dunes include topographic, authogenic and phytogenic varieties. The topographic dunes which form as a result of the influence of topographic obstacles include echodunes, climbing, falling and lee dunes, most of them lie adjacent to the Davaran Mountain or even over its foot slopes. The autogenic dunes in this plain include barchanoids, seifs, domedunes and a stardune. Sand sheet and zibar unites also belong to this group.
The phytogenic dunes identified in this plain include parabolics, nebkhas and vegetated linear dunes. They occupy a considerable part of the plain. Obviously, some of identified dunes are too limited in area to be mapped. Also, in some instances, there is more than one type of dune in a mapped unit.
In all, the mapped aeolian geomorphological units include desert pavement (55 Km2 in extent and overwhelmingly over the southern alluvial fans). Source areas (predominantly over the distal parts of the southern alluvial fans), yardangs (at the central part and near Koshkuieh in southwest), zibars (145 Km2 area at southeast and southwest), sand sheets (in a 45 Km2 area), barchans (in a 25 Km2 area at the central part), seif- barchans (comprising nonsymmetrical barchans and seifs in an area 250 Km2 at northwest), seifs and linear vegetational dunes (in a small area at nourthwest), nebkhas and coppices (which include accumulation around tamarix trees in the west), dome dunes (as a small unit in the east), parabolics (in the eastern and north-central parts of the plain covering 150 Km2 ) and parabolic – seif unit (comprised of parabolics with seifs at their nose). It is worth noting that yardangs are formed over a part of the clay flat which is uplifted by an active fault and have been eroded by the sands shifting towards northeast. The yardangs are located between the corridors formed by the erosion of these playa clays.
Conclusion
According to the studies undertaken in the Rafsanjan plain, the southern huge alluvial fans act as the main source of sand and, dominant winds which blow from southwest, they have traversed the central part and predominately accumulated at the north and northeast of the plain. During transportation, the sands have accumulated as a result of topographic or vegetational barriers. In some parts, nondominant winds have played a role. Drifting sands have also invaded the Davaran Mountain and create climbing, lee and echo dunes there. The total area of surfaces in this plain is about 1060 Km2 and several aeolian geomorphological units; including desert pavement, source areas, yardangs, zibars, sand sheets, barkhans, seif- barchans, seif- linears, barchans- coppices, domes and parabolics were identified and mapped.
