Aeolian Sand Deposit Assessment in an Arid Area, Case Study: The Region of Ksour Mountains (SW of Algeria)

The phenomenon of aeolian sand deposit constitutes a major problem in the region of Ksour Mountains in Algeria, which causes serious social and economic problems. To assess the textural properties of sands, and to investigate the origin of aeolian sand deposit in the study area, eleven (11) samples were collected from the sands of Ain Sefra. Then the granulometry, calcimetry and morphoscopy of the samples were studied. Granulometric testing of samples from 11 locations showed that sand size was very ne to ne grained, with a mean grain value of 226.5 μm. It sort ranged from 1.22 to 1.90, indicating well sorting the sands and skewness values ranging from-0.4 to 0.66, being mainly negative with an average of -0.06, indicating symmetrical to ne skewed values. The values of kurtosis ranges from 0.79 to 1.5, with an average of 0.93, where 64 percent of samples are Mesokurtotic and 36 percent of samples are Platikurtotic. Calcimetric results show a very low percentage of carbonate, which ranges from 1.85 % to 7.4 % and illustrate a very low content of ne fraction and organic matter. The preliminary examinations of the sands in our study area by morphoscopy showed that 73 percent of sand are in RM category, 19 percent in the rounded and shiny (EL) category. In comparison, 08 percent are represented by the fresh and angular (NU) category. The outcome of various experimentation led to the conclusion that the aeolian sand deposit in the study area, are linked to the wind transport from the Moroccan territory such as Chott Tigri, Oued Maader, the corridor between Figuig, Bouarfa and Massa Daraa, which are the dominant sources of sands in the region of the study area. Therefore, the study better understands the origin of sands and their characteristics in this part of the Ksour Mountains.


Introduction
With an increasing danger of aeolian sand migrations from different sources, it is essential to bear in mind how the present sands environment is emerging under human and natural pressures. Aeolian sands have been studied in various elds in the earth and sciences. Early scienti c works on the geological origin of aeolian sands have been reported, referring to their physical, chemical, mineralogical, and morphological features. Blake (1855) was one of the rst to notice the extensive development of wind erosion forms in the Sahara, and von Richthofen (1882) identi ed the fundamental aeolian origin of the huge loess deposits that cover much of northern side of China. Then, there was a surge in interest in aeolian processes in the late nineteenth century and the twentieth century, and some very descriptive references were produced (Beadnell, 1909;McKee, 1979;Pease et al., 1999;Zhu, 1985). Recently, a diversity of research on aeolian sands characterization, the same as approaches to reduce its movement, has been published worldwide (Baratoux et  In Algeria, sand dunes serve as one of the country's most prominent geomorphological features in the Sahara, where roughly 20 million hectares are threatened by wind erosion. Algeria's arid regions are known for their fragile ecosystems. They are the main areas affected by Aeolian sand deposits (Nedjraoui & Bédrani, 2008). The arid and steppe areas, constantly affected by the winds, are located in the southwestern part of Algeria and the Saharian Atlas. In this region, there are sandy currents formed by long bands of dunes that are oriented from the southwest (SW) to the northeast (NE) (Nedjraoui & Bédrani, 2008). Aeolian sand migrations do not proceed from a continuous and single movement to the nal deposition zone in arid environments. These sandy migrations act by continuously recycling the sand passing through the wadis, spread by the latter at the outlet of a plain, picked up by the wind before accumulating again (Benazzouz, 2003). The wind is the focal component responsible for the transport and deposition of sand sediments and landform modeling (Abuzaid et al., 2021; Mainguet, 2012). Speed, direction, magnitude and frequency are the main elements of wind that de ne its e ciency. However, only strong winds that reach the threshold speed can have erosive activity. Three sands types are distinguished, autochthonous and allochthonous, which provide information about past environmental change in the surrounding watershed. Depending on their importance, these types are either transitional or form dunes. A few studies have been reported recently to assess aeolian sands deposit in Algeria. Benazzouz (2003) studied the aeolian sands mineralogy in the Zibans range in the south of Algeria. Boureboune and Benazzouz (2009) carefully designed to combat the deserti cation in Zibans and Hodna basin in Algeria. Boulghobra (2016) used satellite imagery and climatic data to assess the aeolian sand deposit in the region of In-Salah in the south of Algeria. Boulghobra et al. (2016) investigated the aeolian risk in the Touggourt region situated in the south of Algeria. Bouarfa and Bellal (2018) investigated the concentration of sand buildup beneath Algeria's western mountain foothills between 1985 and 2015. All this previous research provided in Algeria, focused mostly on the desert domain, with no studies have been conducted to determine the Aeolian sand deposits in our study area. This research aims to learn more about the textural properties of sand dunes in the region of Ksour Mountains and particularly the region of Ain Sefra and to investigate the source of aeolian sand deposits in this part of Ksour Mountains. This research could help us better understand the factors that in uence the shape and size of dunes and the methods in which eolian sand bodies accumulate.

Geographical context
The Ain Sefra is part of the Ksοur Mountains, and it covers about 3851 Km2. It is situated in the southwest of Algeria, it's limited to the north by Chott-Chergui and Chott-Gharbi watersheds, to the west by Morocco, to the south by the region of Bechar, and to the east by El-Bayadh ( days is 55 days, and the annual average temperature is 17.79°C. The south sector and west-southwest winds are effective and able to cause movement of sands according to the annual wind rose, where the more frequent winds are between 4 and 6 m/s. Furthermore, according to the effective wind threshold speed, sand movement quantity is between 23.03 and 15,224 m3/m/year. The soils are shallow and less fertile, with an organic matter level that does not exceed 3 percent (Aidoud & Touffet, 1996). From a geological standpoint, the geological series of the region range from the Triassic to the recent Quaternary, and the geological facies that dominate the region are Jurassic and Pliocene sandstones and limestones (Derdour et al., 2021). The analysis of the land use revealed that the forests represent 7.05 percent of the surface of the study area, the rocky outcrops represent 15.06 percent, the very degraded ranges represent 24.06 percent, the steppe ranges represent 29.14 percent, the wind accumulations represent about 17.94 percent, and the sand dunes represent only 6.74 percent (Derdour et al., 2018). The region of Ain Sefra suffers from serious environmental problems linked to wind erosion and dune migration which further accelerate the process of deserti cation (Fig. 2).

Data acquisition.
In our study area, eleven (11) samples were collected for granulometry, calcimetry, and morphoscopy analyses to cover all the watershed (E01-E02-E03 E04 -E05-E06-E07-E08-E09-E10-E11), as shown in Table 1 and Fig. 3. In fact, on each side, the most representative dunes were the subject of sand samples (500 g) taken from their crest. And on a dune of each site, we sampled on the right and left toes, on the middle of the right and left anks (Fig. 4), on sand accumulations, and on the sands inside the city of Ain Sefra. All Samples of sands were taken simultaneously with wind measurements made at the same height as the samples. It is to nd a correlation between the particle size of the moving sand and the wind speed and compare them to the sand taken in this position.

Granulometric analysis
For this research, the granulometric examination was carried out according to the classical method described by Berthois (1959) and Verger (1963) in relation to the AFNOR standards (AFNOR, 2018). The samples were rinsed, dried in an oven, weighed, and sieved on a column of twelve sieves with mesh sizes ranging from 500 m to 0.63 m for twenty minutes. The purpose is to create particle size curves (frequency, cumulative) and calculate particle size characteristics that provide information on the degree of sediment categorization, such as mean, sorting (standard deviation), skewness, Kurtosis and standard deviation. These parameters can be calculated by using the software of GRADISTAT developed by Blott and Pye (2001). The semilogarithmic particle size curves' form enables for the identi cation of  Table 2. Show the size scale adopted in the GRADISTAT program, used in the discussion section. Table 2 Size scale adopted in the GRADISTAT software, adapted form Udden (1914) and Wentworth (1922

The morphoscopic determination
Morphoscopy, which was determined by Ribault (1975), as being "the statistical determination of the different types of quartz in sandy deposits", the proportions of each type and the variations of these proportions during transport. Then during these counts, the most representative particles were selected to be observed with a Scanning Electron Microscope (SEM). The morphoscopic assessment of the sand grains in this zone also provides information on their deposit habitats, transport conditions, and environmental effect. The analyzes were carried out in the Scienti c and Technical Research Center on Arid Regions (CRSTRA).

Laboratory analyses
The calcimetric study reveals the selective calcium loss from an impure parent limestone (Derdour et al., 2020). Eleven samples from the commune of Ain Sefra were calcimetrically analyzed (   Table 4, the analysis of the composition of the sandy material within the dune system of Ksour Mountains shows a very low content of ne fraction and organic matter (silt, clay and organic matter). However, this overall trend is interrupted in places. It may be related to the presence or absence of plant cover capable of providing organic matter and subsequently increasing the percentage of the ne fraction. The cumulative semi-logarithmic curves of the sands samples taken from our study presented in Fig. 5 show a sigmoidal (hyperbolic) type pattern. The curves have the shape of a "S "more or less spreading which indicates ne sands, which means that the sands are stretched, well classi ed with a well-developed rectilinear sector in its middle part more and more towards the east. This facies also indicates that the sands were transported in a more or less disturbed environment with ne particle evacuation.  (Fig. 6-A). The mean values range from 201.5 to 245.5, with an average of 226.5 which shows that the samples mostly belong to ne sands. These results are comparable with those given by the median. We noted that this average, in general, tends to decrease according to the position of the samples ( Table 6). The measures of the sorting (Standard deviation) or uniformity of the grains indicating energy conditions that prevailed during transport and deposition. It ranges from 1.22 to 1.90, with an average of 1.31 (Fig. 6-B). This indicates the well-sorting of the sediments, according to the classi cation of Folk and Ward (1957). The majority of samples (08 samples) are very well sorted, representing smooth and stable currents, followed by moderately sorted species of 03 samples (E05, E07, E011) which can be attributed to slight variability in current velocity. The Skewness measures the degree of asymmetry in the frequency curves regarding the predominance of grains fractions. The kurtosis values range from 0.79 to 1.5, with an average of 0.93. Where 64 percent of samples are Mesokurtotic and 36 percent are Platikurtotic (Fig. 6-C). The skewness value in our samples ranges from -0.4 to 0.66, with an average of -0.06, ranging from near symmetrical to strongly ne skewed. According to the classi cation of Folk and Ward (1957), we remark that most of the samples are symmetrical, and the rest are coarse skewed and very ne skewed ( Fig. 6-D). It shows the symmetry of the curves in the part of the dune system. It explains that the deposition of sediments takes place suddenly and without subsequent reworking by excess load and / or by a decrease in the competence of the carrier current. While in the other parts, the curves show an asymmetry towards the ne elements, with a negative asymmetry, which means that the sediments are deposited in a turbulent medium which deprives them of the ne elements which ll the void left between the coarse elements after disposal is the process of de ation, the main driving force behind aeolian sands deposits.  Morphoscopic analysis of the quartz particles in sediments from the Ksour Mountains identi ed several forms, including fresh and angular (NU), round mat (RM), and rounded and shiny (EL) quartz grains. The fresh and angular (NU) shape of the grains could result from low transport. The presence of round mat (RM) grains suggests the impact of aeolian transport. The rounded and shiny (EL) grains indicate the long aquatic mechanical mixing probably of hydrological origin. Fig. 7 shows the Scanning Electron Microscopy (SEM) observation of sands of the study area. The preliminary examinations of the sands in our study area showed that 73 percent of sand are in RM category, i.e. round mat grains are frosted and rounded by aeolian transport and it has a high carbonate content 47 percent CaCo3 and a low percentage in organic matter, silt and clay, from a dynamic point of view, that the wind transport is done mainly by saltation and affects 98 percent of the sand grains, while the deposit is dune. Otherwise, the rounded and shiny (EL) category represents about 19 percent of samples, while 08 percent are represented by the fresh and angular (NU) category, which have undergone low transport. The morphoscopic study of the sands of the research area asserts that the grains of the sands in our study area are blunt and shiny grains with a dominance of rounded edges, and can sometimes acquire the shape of almost perfect spheres. Their surface appearance is always very polished, shiny, gleaming under the light of the binocular magnifying glass. They are characterized by long transports due to an allochthonous origin, with a very high probability. According to Bouarfa and Bellal (2018), the primary winds are from the south and north, with the east and west coming in second and third, from the unidirectional sandy transport regime.
Only the winds from the South and WSW sectors are effective and the most frequent, they are capable of generating a sandy displacement.
On the other hand, outside the region we can count outcrops and source areas providing allochthonous sand. Therefore, we suggest that other reservoirs supplying the sands containing large quantities of sand are located on Moroccan territory such as Chott Tigri, Oued Maader, the corridor between Figuig, Bouarfa and Massa Daraa, are the dominant sources of sands in the region of Ksour Mountains. Chott El Gharbi as example covers an area of more than 140,000 ha, and a large part of its supply comes exclusively from Moroccan territory. The entire transit corridor connecting the two Chotts (El Gharbi and Ehergui) is covered by a sandy veil about thirty kilometers wide which gives us very explicit information on the passage taken by the sand during its transfer from the South-West (Chott El Gharbi) to the North-East (Chott EChergui).

Conclusions
The region of Ksour Mountains is suffering in many localities from signi cant aeolian sand deposit problems, which result from the severity of climatic and soil conditions, and the non-rational usage of natural resources constitutes the most spectacular deserti cation phenomenon. The comprehension of the sand deposit phenomenon was achievable by the combined effect of geological, climatic, edaphic and geomorphological factors. The regional wind transport process plan is sand between source zones and deposit zones. The wind remains the primary element responsible for modeling the landform where the wind regime, including direction, magnitude, and frequency, identi es shape, migration, dynamics, and accumulation of dunes of sands. Granulometric testing of samples from 11 locations showed that sand size was mainly very ne to ne grained, with mean grain value of 226.5 µm, sorting ranged from 1. Calcimetric results show a very low carbonate percentage, ranging from 1.85 percent to 7.4 percent, and illustrate a very low ne fraction content and organic matter. The preliminary examinations of the sands in our study area by morphoscopy showed that 73 percent of sand are in RM category, 19 percent in the rounded and shiny (EL) category. In comparison, 08 percent are represented by the fresh and angular (NU) category. The sands of our study area are characterized by long transports due to an allochthonous origin from Moroccan territory, with a very high probability. Despite the success demonstrated, a signi cant limitation is the lack of prior research studies on the topic in the Moroccan side. Further work to improve on these new developments is suggested. However, selecting the best aeolian sand stabilization method looks to be a di cult process that necessitates a thorough experimental investigation involving a variety of additives as well as other signi cant variables such as agent quantities and aging duration. Problems caused by wind-blown sands in Ain Sefra city. Positions of the samples in the dunes of Ain Sefra.
Page 16/18 Figure 5 Cumulative curves of samples of sands in the study area.

Figure 6
Histograms of all samples plotted with the respect to statistical parameters calculated by the GRADISTAT program: A-Median, B-Sorting, C-Kurtosis, D-Skewness.