# Mineralogical evolution of certain Saharan soils of Algeria (case of Ziban soils and the Oued Righ valley)

Belkacem Boumaraf, Inesse Saadi, Alexandra Guillaneuf, Samiha Laouar, Karima Belaich, N Mebref, Abdelfatteh Abid, S Hassina

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Belkacem Boumaraf, Inesse Saadi, Alexandra Guillaneuf, Samiha Laouar, Karima Belaich, et al. Mineralogical evolution of certain Saharan soils of Algeria (case of Ziban soils and the Oued Righ valley). IOP Conference Series: Earth and Environmental Science, 2025, 1455, 10.1088/1755-1315/1455/1/012003. [https://doi.org/10.4208/epsl.2025.1455.1.012003]

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Mineralogical evolution of certain Saharan soils of Algeria (case of Ziban soils and the Oued Righ valley)

To cite this article: B Boumaraf et al 2025 IOP Conf. Ser.: Earth Environ. Sci. 1455 012003

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# Mineralogical evolution of certain Saharan soils of Algeria (case of Ziban soils and the Oued Righ valley)

Boumaraf B\*<fnref n="1" />, Saadi I<fnref n="1" />, Guillaneuf A<fnref n="2" />, Laouar S<fnref n="3" />, Belaich K<fnref n="3" />, Mebref N<fnref n="3" />, Abid A<fnref n="4" /> and Hassina S<fnref n="5" />

**Abstract.** Our study area is located in the northeastern part of the Algerian Sahara, specifically in the Ziban and Oued Righ Valley regions. These lands are poorly understood from a pedogenetic perspective. This study represents an initial approach, combining both morphological and mineralogical analyses of recent and current soil covers. The interpretation of these data provides valuable insights for selecting targeted crops based on the type and significance of the edaphic constraints. Pedological analyses of the different morphological levels previously identified, combined with the results of mineralogical and microscopic investigations using X-Ray diffraction analyses, have demonstrated the role of inheritance and the aggradation of secondary minerals. These processes are predominant, with the exception of Attapulgite a fibrous mineral detected in some soil profiles which may result from neoformation. Additionally, at all levels, lateral inputs of sulfates from the closed depressions have contributed to the neoformation of gypsum. Microscopic examination revealed that gypsum invades, disrupts, and impedes the development of some secondary minerals. This phenomenon is attributed to the crystallization pressure of gypsum. This knowledge enhances our understanding of the dynamics governing soil formation and structural stability in these regions.

## 1. Introduction

The nature of soils depends primarily on pedogenesis and pedoclimatic conditions. A comprehensive study of soils from two Saharan regions the Ziban and the Oued Righ Valley was conducted to understand the evolution of these soils in relation to both ancient and current environments. This research integrated morpho-pedological and mineralogical approaches and is innovative in these climatic zones. It involved identifying the mineralogical signatures within the landscape and their distribution across different morphological positions. Morphopedological studies contribute significantly to the interpretation and characterization of polyphase soils, including those associated with the oldest formations. Additionally, they help determine agronomic properties of soils. In these soils, the gypsum crusts remarkable for their decametric or even metric thicknesses represent a major constraint that hinders the agricultural development of these areas.

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<footnote n="1">¹ University Mohamed Khider of Biskra, PIARA, Biskra, Algeria</footnote>

<footnote n="2">² University of Reims Champagne-Ardenne, UR3795 GEGENA, Reims, France</footnote>

<footnote n="3">³ University Mohamed Khider of Biskra, Algeria</footnote>

<footnote n="4">⁴ National institute of agronomic research Institution, Touggourt., Algeria</footnote>

<footnote n="5">⁵ Agricultural departmental services, Biskra, Algeria</footnote>

<footnote>*E-mail: belkacem.boumaraf@univ-biskra.dz</footnote>
Soil properties and more particularly the clay content and the different types of clays present are essential for determining the fertility of agricultural soils because they increase the water retention of soils [1], allow the formation of clay-oil complexes, promote the structuring of soils and allow the adsorption of nutrients. Moreover, interactions of cationic exchanges between organic and mineral matter, that defines the level of fertility in a soil, are defined largely by the type of secondary minerals, particularly the different type of clays, existing especially for Saharan soils where biological activity is low.

The objective of this study is, firstly, to define the geochemical processes that led to the presence of secondary minerals in the two Saharan zones studied in relation to their geomorphological position in order to, secondly, determine their agronomic potential and the crops that can be grown there.

## 2. Materials and methods

### 2.1 Geography and geology of the Study regions

The Oued Righ Valley and the Ziban are located in the northeastern Algerian Sahara, along the vast eastern Erg and south of the Aures and Massif. The Oued Righ Valley forms a broad, flat trough 15 to 30 km wide, stretching approximately 150 km along a south-to-north axis between latitudes 32° 45′-34° 30' and longitudes 5° 45′-6° 15' East. These regions are part of a larger geographic unit known called the Bas Sahara, a vast basin covering more than 400,000 km².

The basin gently rises to an altitude of 200–300 meters, bordered by the slightly inclined plateaus of M'Zab to the west, Tademait and the Hamada of Tinghert to the south, and the Tunisian Dahar to the east. To the north, the Aures and Nemencha ranges dominate the landscape. The surrounding plateaus are primarily composed of Cretaceous-age formations, while the central depression contains Tertiary and Quaternary formations [2], [3] and [4] (Figure 1).

<figure><img src="image_5.png" /><figcaption>**Figure 1:** Hydrogeological section of the Lower Sahara [5].</figcaption></figure>
## 2.2 Prospecting and sampling

Soil samples were collected based on geomorphological levels previously identified [6]. In the Ziban region, five levels were identified: 0, 1, 2, 3, and 4 [3] (Figure 2). The level 0, was not sampled because it corresponds to the level of the Chotts Oumach, where the surface layer is almost permanently covered by salt et where agronomic potential is zero.

A similar approach was applied in the Oued Righ Valley, where 5 morphopedological levels were identified (Figure 3). Level 0, corresponding to the Sebkha of Merouane, was not sampled for the same reasons as in the Ziban region.

For each studied level, 15 soil samples were collected, allowing us to define a typical profile for each level. Pedological analyses were performed to measure clay content, total limestone content via calcimetry, pH (1:2.5), electrical conductivity (EC 1:5), cation exchange capacity (CEC) using the Bower method [7] gypsum content using the Coutinet method [8], and finally, the different types of clay present using X-ray diffraction analysis on the fraction less than 2 microns.

<figure><img src="image_6.png" /><figcaption>**Figure 2:** Morphopedological section of the Ziban region</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>**Figure 3:** Morphopedological section of the Oued Righ region</figcaption></figure>
## 3. Results and discussion

### 3.1 Levels 1 and 2

The results obtained from the higher levels of the two study zones (Table 1) revealed a fairly stable alkaline pH with values between 7.8 and 8.2, a high EC for all horizons studied, and a strong presence of gypsum with contents ranging from 38.6% to 66.9%. This phenomenon is linked to the proximity of a shallow water table, approximately 60 cm, with a high EC due a high salt content [9]. In contrast, CaCO₃ is present only in small quantities across these levels (1.7% to 2.6%) and remains significantly less abundant compared to gypsum.

In level 1 and 2, various forms of gypsum accumulations can be observed, both micro and macroscopic (e.g., powdery, lenticular, acicular, and sand roses). These formations result from active fluctuations in the water table. Additionally, a significant spatial variation in the saline profile is noticeable in the collected samples, primarily due to the vertical position of the gypsum crust. This crust has a relatively manageable thickness for potential excavation, particularly for planting date palms.

<table><caption>**Table 1.** analytical and mineralogical results of the two study areas (EC: electrical conductivity, Chlor: chlorite, Kaol: kaolinite, Atta: attapulgite, Hall: halloysite)</caption><thead><tr><th rowspan="2">Profiles</th><th rowspan="2">Depth<br>cm</th><th rowspan="2">EC<br>dS/cm²</th><th rowspan="2">pH</th><th rowspan="2">Gypsum<br>%</th><th rowspan="2">CaCO₃<br>‰</th><th colspan="4">Fraction &lt; 2µm</th></tr><tr><th>Chlor</th><th>Illite</th><th>Kaol</th><th>Atta</th><th>Hall</th></tr></thead><tbody><tr><td colspan="10" style="text-align:center; font-weight:bold;">Ziban Region</td></tr><tr><td>Level 1</td><td>2--30</td><td>5.4</td><td>8.2</td><td>44.2</td><td>2.6</td><td>++</td><td>+++</td><td>+</td><td></td></tr><tr><td>Level 2</td><td>2-25</td><td>3.8</td><td>7.9</td><td>38.6</td><td>1.8</td><td>++</td><td>++++</td><td>++</td><td>++</td></tr><tr><td></td><td>25-55</td><td>3.4</td><td>7.8</td><td>43.1</td><td>1.7</td><td>+++</td><td>++++</td><td>++</td><td>+++</td></tr><tr><td>Level 3</td><td>15-45</td><td>3.2</td><td>7.9</td><td>35.8</td><td>1.5</td><td>++</td><td>++++</td><td>+</td><td>+++</td></tr><tr><td>Level 4</td><td>2-15</td><td>4.6</td><td>7.8</td><td>38.55</td><td>2.8</td><td>+++</td><td>+++</td><td>+++</td><td>++</td></tr><tr><td></td><td>15-33</td><td>4.0</td><td>7.9</td><td>65.4</td><td>1.3</td><td>+++</td><td>++++</td><td>+++</td><td>++</td></tr><tr><td></td><td>33-75</td><td>4.2</td><td>8.1</td><td>42.2</td><td>2.1</td><td>+++</td><td>++++</td><td>+++</td><td>++</td></tr><tr><td colspan="10" style="text-align:center; font-weight:bold;">Oued Righ Region</td></tr><tr><td>Level 1</td><td>2--15</td><td>5.2</td><td>8.1</td><td>41.6</td><td>2.2</td><td>++</td><td>+++</td><td>++</td><td></td></tr><tr><td></td><td>15-35</td><td>4.2</td><td>7.8</td><td>51.6</td><td>1.6</td><td>+++</td><td>++++</td><td>+</td><td>++</td></tr><tr><td>Level 2</td><td>2-25</td><td>4.8</td><td>7.9</td><td>34.5</td><td>2.6</td><td>++</td><td>++++</td><td>++</td><td>++</td></tr><tr><td></td><td>25-60</td><td>3.1</td><td>7.9</td><td>66.9</td><td>1.8</td><td>+++</td><td>+++</td><td>+</td><td>+++</td></tr><tr><td></td><td>60-110</td><td>5.1</td><td>7.8</td><td>49.84</td><td>1.8</td><td>+++</td><td>+++</td><td>+++</td><td>++</td></tr><tr><td>Level 3</td><td>30-80</td><td>5.8</td><td>8.0</td><td>21.2</td><td>10.2</td><td>+++</td><td>+++</td><td>+++</td><td>++</td></tr><tr><td></td><td>80-120</td><td>5.3</td><td>8.1</td><td>58.1</td><td>2.2</td><td>++</td><td>-</td><td>-</td><td>++</td></tr><tr><td>Level 4</td><td>25-110</td><td>4.8</td><td>7.9</td><td>68.6</td><td>1.8</td><td>+++</td><td>+++</td><td>+++</td><td>+++</td></tr></tbody></table>

-: Trace, +: very weak, ++: weak, +++: medium, +++++: abundant
According to local stratigraphic analyses of the lower Sahara, attapulgite should be absent in these levels, due to geochemical instability, which is unfavorable for its neoformation. As suggested by [10], the absence of attapulgite in the Chott and Sebkha zones of El Hodna could be attributed to a lack of high concentrations of soluble salts, a key factor in the genesis of this fibrous mineral in such regions [11]. In semi-arid climates, the disappearance of attapulgite in certain horizons is associated with very low or absent limestone content and increased soil moisture. Furthermore, studies [12] have highlighted the vulnerability and absence of attapulgite in subhumid and humid regions. It remains uncertain whether the quasi-structural permeability of this level contributes to the potential destruction of attapulgite; however, its absence is consistently noted in the epipedon.

Kaolinite (7.2 Å) (spacing between reticular planes in minerals) is also present in this profile, albeit at low intensities, as its primary diffraction peak is masked by the very intense gypsum peak (7.56 Å) in X-ray diffractograms. Kaolinite is typically formed in environments characterized by significant leaching and desaturation, where aluminum silicates are abundant, supporting its neoformation. However, the saline profile at this level does not exhibit such a pattern (hyperpedonian); instead, the kaolinite present appears to be inherited. Once introduced into this environment, kaolinite remains the most stable phyllosilicate mineral.

The strong presence of illite is likely associated with the high potassium (K+) content in the groundwater (18.11–22.7 ppm) [13]. Conversely, chlorite demonstrates a stronger peak intensity at this level, reflecting the perfect crystallinity of its crystal lattice due to the abundance of basic cations, particularly magnesium (Mg2+), in this environment. Heating and swelling tests with ethylene glycol, performed on samples from level 2 in the Ziban study region (25–55 cm depth), revealed that the clay is more likely a smectite–chlorite interstratification.

## 3.2 Levels 3 and 4

The soils of glacis levels 3 and 4 are shallow and covered with coarse conglomerates. They present significant edaphic constraints for cultivation due to the presence of an almost continuous gypsum crust, either at the surface or at depth. The diffractometric analysis performed on samples from the Ziban and Oued Righ levels 3 and 4 clearly highlights the predominance of gypsum over all primary and secondary minerals, particularly in the deeper horizons of both regions. Compared to the content of gypsum, the content of total limestone is relatively low. When limestone content decreases, gypsum content increases. According to [9], gypsum invades, disrupts, and impedes the development of calcareous accumulations. This phenomenon is attributed to the crystallization pressure of gypsum (1100 kg/cm²), which destroys limestone structures through the continuous arrival of sulfate-rich solutions and their subsequent precipitation.

Fibrous minerals are represented in these levels by attapulgite, which is present across all profiles. Illite and kaolinite are also detected in all profiles from both regions, except in the subsurface horizon of level 3 (Oued Righ Valley) at a depth of 80 to 120 cm, where kaolinite is notably absent.

In the Saharan climatic context, these minerals are inherited. Once present, they may undergo transformations, particularly through aggradation processes. This is especially true for illite, given the high ionic concentration of the soil solution. The simultaneous presence of chlorite or smectite could indicate such evolutionary processes. Attapulgite, often considered a clay mineral formed through neoformation [10], appears in recent formations as an inherited component, likely transported as wind-borne dust [9]. However, the presence of attapulgite at depth and within
crusted horizons, coupled with its absence at the surface, suggests that the crust is rather detrital in origin.

## 4. Conclusions

Based on the mineralogical results from samples collected at various geomorphological levels, the distribution of clay minerals in this landscape appears to be governed mostly by wind activity. In the Oued Righ Valley, attapulgite is transported by wind as dust originating from neighboring desert and sub-desert formations [14]. Its presence in samples from the Erg and its absence in deposits at the summit levels of the sands do not follow a specific subsurface mechanism within intermediate horizons. However, the presence of this fibrous mineral, particularly at depth in levels 3 and 4 of the two regions studied, can be attributed to pedoclimatic conditions favorable for its conservation. Moreover, downstream seasonal fluctuations in the water table level create environments rich in basic ions, providing conditions for the preservation and in some cases, the aggradational transformation of silicate minerals such as illites and chlorites.

Overall, levels 1 and 2 have broader agricultural suitability than the higher levels for two main reasons: the manageable thickness of the gypsum crust and the presence of a lower underlying layer that facilitates the leaching of salt-laden water during cultivation. For levels 3 and 4, their location favors the cultivation of herbaceous plants that do not require deep root development. These lands are more suitable for pastoral use due to an almost continuous gypsum crust in the soil.

## References

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[3] Laour, S, Boumaraf, B, & Saadi, I. 2023. Morpho-pedology Variations in Pre-Saharan Region Case Ziban Soils. Analele Universității din Oradea, Seria: Geografie, 33(1),43-

[4] Boumaraf B., Saadi I, Marre A, Bensaid. B 2016. The Spatial Distribution of Pedogenetics of Soil Processes in the Valley of Oued Righ.Algeria...., International Journal of Advances in Science,

[5] Nesso.C, 1971: L'évolution des ressources hydrauliques dans les Oasis du bas Sahara Algérien. Service de documentation et de cartographie - géographie. Vol 17 103p

[6] Gueremy.P., Marre.A. 1996. Une nouvelle méthode de cartographie géomorphologique applicable aux aléas naturels. Travaux de l'Institut de Géographie de Reims, pp 5-40.

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[8] Coutinet.S, 1965: Méthodes d'analyses utilisables pour les sols salés, calcaires et gypseux, Analyses des eaux. INRA, n°2, Paris, pp 1242-1253

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[14] Callen.RE, 1984. Clay of the Palygorskyte-Sepiolite dispositional environment, age and distrubution. Developments in sedimentology. 37 Elsevier, Amsterdam, pp 1-37.