The Determination of the Sedimentologic and Geomorphologic Parameters of Sand Dunes of Qom Tapeh Using Geological and Meteorological Data, Northwest of Tabriz (Sufian)

Qum Tapeh dunes are wind sand dunes that are located between longitude of 46 ° 1' to 46 ° 2 ' east and latitude of 38 ° 14' to 38 ° 15 ' north. These dunes, covering an area of about 6 km2, are located in the northwest of Tabriz and southeast of Sufian. Sedimentary rocks including sandstone, dolomite, and limestone are the most common rocks in the area. Generally, from the Neogene to the present day, the physical and chemical weathering of sedimentary rocks – mainly clastic ones – has provided detrital particles such as gravel, sand, and shale and chemical deposits such as limestone, gypsum, and salt in this region. Rapid winds in east-west direction and vice versa play an important role in sorting and distribution of the sediment particles. The sustainability of winds with constant energy has been associated with the transportation of fine particles; moreover, the accumulation of coarser particles would result in the development of sand dunes.

In this research, the systematic sampling was first carried out for the granulometric analysis of sediment, investigating its constituents, and the recognition of the transportation agent.

Granulometry was performed by using a dry sieving method, with a sieve distance of 0.5 phi to silt (4 phi) by Carver (1971) method, Accordingly, the particles size in sediments of Qum Tapeh sand dunes was determined in the range of coarse sand to silt and clay. The results showed that the particles’ diameter in the sand dunes varied from 0.25 to 0.0039 mm (i.e., size of sand to silt and clay). The average sorting index was 0.321phi, which indicated that the sediments were well-sorted. The mean skewness was +0.357, which meant that the particles were fine skewed, and that the most important mechanism for transportation of these sediments was saltation. Also, the average kurtosis index was 1.726, which meant that they were very leptokurtic. The unimodality of the sediments also enhanced their sorting. Fine particle size, good sorting, and positive skewness indicated the effective role of wind in the transportation and distribution of sediment particles in the area. Comparing the kurtosis index and the sorting may lead to the conclusion that the more their kurtosis, the better their sorting. The petrography study showed that siltstone was the most important rock fragment in wind sediments of Qum Tapeh. The main constituents were clastics with very small amounts of carbonates, of which quartz was the most abundant (65%) mineral found in these sediments. The size of quartz in the sediments varied from silt to very coarse sand, and it often showed undulose extinction. In some monocrystalline quartz grains, there were some types of inclusions that were mostly zircon and muscovite. Monocrystalline quartz grains were mainly composed of plutonic and sedimentary quartz. The higher percent of monocrystalline quartz in comparison with polycrystalline quartz, as well as the presence of quartz grains with overgrowth cement indicated long-term transport and recycling of sediments in the area.   The amount of feldspar in the sediments was 23%, which suggested that the potassium feldspars were more abundant than plagioclase. In terms of geomorphology, the sediments of this area were divided into categories of floating sand, shelter sand, and sand dunes. Also, the most important sand dunes were formed as longitudinal dunes. The direction of wind in the formation of these dunes was not clear, but it may have been in two directions.