The gypsum in the soils of Ziban, Algerian Northern Sahara

Agrarian Academic Journal

agrariacad.com

doi: 10.32406/v6n5/2023/76-88/agrariacad

 

The gypsum in the soils of Ziban, Algerian Northern Sahara. O gesso nos solos de Ziban, Saara Norte da Argélia.

 

Belkacem Boumaraf¹, Ines Saadi²

 

^1- Laboratory of Promoting Innovation in Agriculture in Arid Regions, University of Mohamed Kheider, Biskra, Algeria. E-mail: belkacem.boumaraf@univ-biskra.dz

^2- Laboratory of Promoting Innovation in Agriculture in Arid Regions, University of Mohamed Kheider, Biskra, Algeria. E-mail: inesse.saadi@univ-biskra.dz

 

Abstract

 

Gypsum is the most abundant mineral in the soils of arid regions, it forms when the concentrations of Ca⁺² and SO^4-2 are considerable in the soil and has an enormous influence on their physico-chemical properties. Several representative profiles on a sequence in the Ziban region (northeast of Algeria) were studied. The results obtained indicate that several forms of gypsum are distributed according to the physico-chemical characteristics of the soils. The formation of gypsum is geological in the upper levels and of neoformation in the lower part of the plain towards the depression of Oumach this is due to the proximity of the water table.

Keywords: Gypsum. Salinity. Arid soils. Sahara. Groundwater.

 

 

Resumo

 

O gesso é o mineral mais abundante nos solos das regiões áridas, forma-se quando as concentrações de Ca⁺² e SO^4-2 são consideráveis no solo e tem enorme influência nas suas propriedades físico-químicas. Vários perfis representativos em uma sequência na região de Ziban (nordeste da Argélia) foram estudados. Os resultados obtidos indicam que diversas formas de gesso se distribuem de acordo com as características físico-químicas dos solos. A formação de gipsita é geológica nos níveis superiores e de neoformação na parte inferior da planície em direcção à depressão de Oumach isto deve-se à proximidade do lençol freático.

Palavras-chave: Gesso. Salinidade. Solos áridos. Saara. Águas subterrâneas.

 

 

Introduction

 

These soils cover approximately 11,000 km² in the Maghreb, in Algeria they occupy 7966.3 km² representing nearly 10% of the world’s gypsum soils (FAO, 1990).

It should be noted that gypsum can be observed in the soils of humid regions but generally at low levels because it is considered an ephemeral element (HERRERO; PORTA, 2000). On the other hand, in arid and semi-arid regions, it would be permanent by being located at different levels of the landscape or in different parts of the soil profile (POUGET, 1980; HALITIM; ROBERT, 1987).

Arid zones are characterized by the presence of gypsum, limestone and soluble salts of very variable forms. Gypsum can accumulate in the soil when evapotranspiration exceeds precipitation. However, when gypsum particles are present in the soil, their type, quantity and degree of crystallization, these factors have a profound impact on the physical and physicochemical properties of the soil as a plant growth medium (FEDOROFF; COURTY, 1989).

The formation of gypsum is generally associated with gypsiferous rocks and sediments of different origins (HASHEMI et al., 2011). Present in small quantities, gypsum has a positive effect on the properties of the soil and can play a role as an amendment and fertilizer because it provides Ca⁺⁺ and SO⁴ ions – necessary for plant growth. On the other hand, at high levels, it affects the behavior and functioning of soils and plants (POUGET, 1995).

It is essential for us to recall that the genetic characterization of soils in the Saharan context leads the pedologist to a systematic knowledge of the geomorphological framework in which these soils fit; it is now established that it cannot be explained from isolated manner, depending only on the vertical migrations of the mineral matter, on their interdependence with those which surround them, especially since the notion of topo-sequence results from this consideration based on topographical considerations alone. Our study comes in order to identify for each morphological unit the type(s) of gypsum accumulations present in order to establish the existence or not of a genetic link between the soils in each morphological level or from one level to another.

 

Material and methods

 

1. Geographie of the ziban región

 

The region of Ziban is located in southeastern Algeria at 425 Km of the capital (Algiers) (Figure 1). It is bounded in the north by the Saharan Atlas, which represents a SW – NE directional relief. It extends to the Chott Melghir area in the southeast and to the Eastern erg in the southwest. Biskra region constitutes a transition zone between two different morpho-structural domains, the folded domains in the north and the flat and desert expanses of the Sahara in the south (Figure 2).

Vast of more than 400,000 km² which rises slowly towards 200-300 m altitude on the slightly inclined plateaus of M’Zab to the west, Tademait  and Hamada of Tinghert to the south and the Tunisian Dahar to the East. To the north, the Ranges of Aures and Nemenchas dominate this basin. It is a Cretaceous halo that constitutes the plateaus that surround the central depression. Tertiary and Quaternary formations occupy the central part (Gouscov, 1964) (Figure 3).

 

Figure 1 – The geographic location of the region of Ziban.

 

Figure 2 – Geological levelling to northern Sahara. (Boudibi, 2021).

 

Figure 3 – Hydrogeological cross sections (extracted from the hydrogeological map of Biskra). (Boudibi, 2021).

 

2. Climate of the Ziban region

 

The dry period extends throughout the year. The average annual rainfall is 66.44 mm (period 2003-2023).The driest months remain June, July and August with an average of 1 mm of rain. The wettest month is January with a maximum of 17.23 mm. The average annual temperature is 22.37°C with the highest temperatures during the month of July with an average of 34.33°C.The lowest temperatures are recorded during the month of January (10.79°C on average). During the period from April to July, the winds of the sirocco blow very strong (ONMT, 2023).

 

3. Geomorphological mapping

 

3-1. Field prospecting methods

 

After a general reconnaissance of the region of the Ziban, executed thanks to the basic documents, topographical, geological maps (Castany, 1952) and satellite images (Digital Elevation Model (DTM)). It is in its northern part that we concentrated the land prospections, because it offered from the plateau of Still to the bottom of the Chott Oumach many forms of land that suggested a distribution of soil varied and numerous.

 

3-2. Geomorphological mapping

 

The geomorphological study is based on a methodical cartographic survey (Gueremy; MARRE, 1996; Marre, 2007). It showed the existence of five geomorphological levels tiered with the bottom of the Chott Oumach and four glacis (Figure 4).

 

a) The bottom of the Sebkha d’Oumache, the level N° 0

b) The lower glaze of level N° 1

c) The average glaze of level N° 2

d) The high glaze of level N° 3

e) The very high glaze level N° 4

 

Figure 4 – Geomorphological map of the area.

 

4. Soil samplingandanalysis methods

 

The collection of soil samples is carried out according to the levels géomorphologique the swallow towards the lover we have respectively four levels 1, 2, 3 and 4 (Figure 4) the zero level could not be taken into consideration; It coincides with the level of the large chotts and the almost permanent presence of the salt table.

For each level studied, nearly 24 surveys are carried out, and at least three soil profiles representative measures were analyzed. Each level studied is represented by its typical soil profile. With four representative profiles described and analysed. Soil analyses are carried out on clay content, total limestone, pH (1/2.5), electrical conductivity (EC 1/5), CEC, gypsum and finally analyses and mineralogical treatments which were carried out with an X-ray diffractometer at the geology laboratory of the University of Reims (France).

 

Results and discussion

 

a) The bottom of the Oumach Chott, the level N° 0

 

This level corresponds to the current decantation basin with pseudogley soils. Covered with characteristic white salt, (the great chott) with an almost absolute absence of vegetation (Figure 5). It offers a remarkably flat topography. (Altitude from -10 to -35m) Characterized by a carpet of whitish saline crystals, of different types, (sulphated and chlorinated). In some places, on the surface, becomes by its consistency a crust viscous and crisp (BrierE, 2000).

 

Figure 5 – The Oumach chott (Boumaraf, 2014).

 

b) The lower glaze of level N° 1

 

Perceptible by a passage towards a higher threshold, with a transition sometimes not very obvious, an extremely short concavity, and where the density of the halophyte plants become more numerous. Implanted in silts saturated by the salts, and which marks the passage to the chott. It is characterized by silty-sandy loam soils. This is the fringe of the big chott.

The shape of the gypsum in this level is powdery characterized by Watson (1985) as an unconsolidated surface (> 2 mm) gypsum deposit, which can be accentuated by the proximity of a saline solution from the water table, due to fractures generated in the structure when it is desiccated during dry periods. The rate of gypsum, which is lower in surface area than in depth, remains high (between 34.88% and 66.4%). However, according to Timpson et al. (1986), the precipitation of the salts occurs in a vertical sequence from the level of the water table to the surface in the following order: CaCo³-CaSO⁴-NaCl-MgSO⁴-MgCl²-CaCl² (Figure 6). This can be explained by the high electrical conductivity at the surface which causes the partial dissolution of the gypsum crystals.

 

Figure 6 – Precipitation of soluble salts from a loaded slick. (Timpson et al., 1986).

 

The Cl- / SO⁴– ratio is sometimes greater than 2, which reflects the high mobility of the Cl- ion relative to SO⁴– especially when the groundwater geochemical facies are of the sulphated chloride type (Boumaraf, 2014). The presence of gypsum gives low Cl- / SO⁴– ratios because of the dissolution of this salt under such circumstances of ionic concentration in the aqueous extract (electrical conductivity between 8.2 and 18.12 dS / cm).

 

c) The average glaze of level N° 2

 

This level appears a few meters nested with the previous one. It presents itself like a huge glacis, with very weak slope. It is characterized by gypsum accumulation soils, is characterized by gypseous crusts and encrouting at varying depths. Invaded by the nebkas who find there favorable conditions for their formation, (the proximity of the water table) and confers on the general landscape a bumpy appearance. The surface of this level has a greater surface area than that of the boundary levels.

In this level, the general structure of the soils is loose with a sandy to loamy texture. The pedogenetic evolution of these soils is globally weak. This character is due to climatic conditions that cause wind deflation. The landscape is invaded by nebkas. The grounds are covered with a more or less important wind veil which limits their evolution. This veil is made of sand grains, which are associated with many very fine forms of gypsum crystals (Figure 6).

According to Wang (1998), crystal formation is large when the Ca⁺⁺ content in the soil solution is greater than 10-3 mol / l. However, the accuracy of the localization of the various forms is unknown because they are subject to continuous solubilization and crystallization phenomena which are caused by the highly contrasted seasonal variation of the water table level (dominance of the per-assensum or per-descalum movements) and also the ionic nature of it.

He microscopic observations of the samples collected in the field we could distinguish on the surface of lenticular crystal forms and very rarely acicular. In depths, they are sub-angular to ovoid in shape (Figure 7).

 

Figure 7 – Strong presence of gypsum associated with the grains of the covering sands, profile: c2, horizon (0 – 45cm). Photos: Boumaraf, 2014.

 

We could observe in the horizons of the profile nodules of various sizes (between 2 and 20 cm) and dense. Sometimes they are confused with reddish-yellow sands. More deeply we observe crusts that overcome gypsum crusts. In this case, the lamellar structural tendency of encrusting does not seem sufficient to distinguish them from each other.

According to Halitim and Robert (1987), the hardening of the gypsum encrustation is due to the interpenetrating coating of gypsum crystals without the intervention of cement, where the various constituents of the soils (quartz, clay, limestone) are trapped in a sort framing formed from gypsum lenses bonded together with other smaller size crystals.

The content of the gypsum in the profiles represents, in this level, varied values between (21.2 and 74.3%). On the other hand, total limestone has obviously very low values in all treated samples According to Vieillefon (1976), gypsum and limestone in the soil are not independent of each other. When the amount of limestone decreases, that of gypsum increases. Halitim et al. (1987) shows that gypsum invades, destroys and blocks the evolution of limestone accumulations. They think that this phenomenon is due to the crystallization pressure of gypsum (1100 kg / cm²) which destroys limestone individualizations as a result of the continuous arrival of sulphate solutions and their precipitation (Figure 8 and 9).

 

Figure 8 – Crystals of calcite agglutinated by gypsum. Photo: Boumaraf, 2014.

 

Figure 9 – Quartz crystals agglutinated with gypsum (G) (X10). Photo: Boumaraf, 2014.

 

Generally the structure is finer in depth. However, sometimes it becomes massive, with the presence of a gypsum crust of light yellow to tanned brown.

 

d) The high glaze of level N° 3

 

These are spreading glazes defined by inclined surfaces. A slope varying from 5% to 15% downstream, with a reduced spatial extension, and very variable compared to the previous level. The piedmont becomes slightly concave offering the appearance of a perched formation. The hydrographic network and more pronounced upstream by deep ravine from 20 to 40cm, and downstream of rare channels. On the surface, we observe very regularly, thick gypseous crusts, probably of Villafranchian epoch developed on Miopliocene materials (Ballais, 2010).

The soils are generally little evolved because of the discontent, at varying depths, crusts, gypsum crusts and conglomeratic elements (Figure 10). On the whole of this level, the gypseous crusts are exposed on the surface downstream. The percentage of gypsum varies between 25.6 and 72.2% (Figure 10).

Conrad estimates, in 1969, that this type of formation is due to a circulation of water on the old deposits of Piedmont. During the regressive periods of the climate, the Quaternary. Other authors consider these slopes as relic terraces reworked by a dynamic slope with old colluvial deposits resting on a marly and gypsum waterproof bedrock. They take their spatial evolution only to the decrease of the runoff and not of the sulphate precipitation caused by the fluctuation of a charged sheet.

 

Figure 10 – State of level 3 surface. Photo: BOUMARAF, 2014.

 

The lacustrine deposits of the early Upper Quaternary Pliocene (Mio-Pliocene of some authors) (Nesson, 1971), consist of more or less gypseous clays without coarse inputs. The Middle Pleistocene deposits are only coarse on the north shore of the Chott Oumach, proof of the increased contribution by the wadis which come down from the Saharan Atlas and which transport today only silt, whereas on the southern and western banks are observed only rare sandy beaches.

Calcium carbonate and soil gypsum are not independent of each other: when the calcium carbonate content decreases that of the gypsum increases. According to Boyadgiev (1974) and Vieillefon (1976), the link between limestone and gypsum depends on their form of accumulation and the level of soluble salts. The more their structure is fine and powdery in a salty environment the more the ratio is significant. Gold this is not the case here, except in the case of the profile b3 with the subterranean horizon (45-110 cm) where the rate of clay is 27.2%.

Gypsum particles have no negative charges and therefore the exchange capacity of gypsum soils is expected to decrease as the gypsum content increases, especially in low organic matter soil. The CEC varies between 2.4 and 12.1 Cmol / kg.

 

e) The very high glaze level N° 4

 

This level is represented by an immense glacis, dominating the northern part of the valley by a steepness of several tens of meters. These formations present at the top ribbon film crusts (Figure 11 and 12) consisting of friable clusters and nodules glued to a hard layer gypso-limestone. At its base a marly consolidated substrate. The crusts and encrouting, with a glassy structure, follow the topography. Surface debris is observed in gaps of variable size. Covered by a sandy veil and a loose vegetal cover composed of xerophytes rarely reaching 50cm. This level carries some traces of flow reduced to ravines of a few tens of centimeters.

 

Figure 11 – The very high glaze level. BOUMARAF et al., 2016.

 

Figure 12 – Laminated morphology of level 4 crusts and encrustations.

 

However, this gypseous crust covers almost all level 4, sometimes it is dislocated in some places., Fragmented and remodeled during paleoclimates According to the PNUD, (1971) this formation can be related to the Villafranchian. However, it should be emphasized that the gypsum horizons develop even on the dunes where there is no groundwater or sheet flow (MATHIEU; THOREZ, 1976) as a result of lateral inflow caused by the wind. Currently all these formations outcrop in this level are covered with fine sand of aeolian contribution and on the piedmont and the embankment of this formation.

 

Sequential morpho-pedological analysis

 

From the elements collected through the geomorphological and pedological studies, the characteristic genetic traits of soils in our study area are spread over two distinct territories. The former is not subject to the current influence of the water table. The second, situated below the first towards the sebkha is, or on the contrary, under the continual influence of this sheet and of these saline accumulations that it generates this sheet (Figure 13). Its effects are accentuated by the absence of a vegetal cover especially at the level of sebkhas (Level 0) where the entrainment of the salty particles windable causes a secondary salinization on the surfaces studied and even beyond. This explains the presence of gypsum crusts and other forms of gypsum depending on the nature of the existing soil at the upper levels. The current effect of the water table is non-existent.

 

Figure 13 – Spatial distribution of the main pedogenetic mechanisms of gypsum formation in the Ziban Region.

 

Conclusion

 

All the factors which govern the formation and evolution of soils in the Ziban region induce a double differentiation in the vertical organization of the profiles and in the lateral distribution. By analyzing variations in analytical and morphological results obtained from the sebkhas, our landscape is part of a region which evolves within the framework of the endorheic system. This cartographic approach allowed us to collect a large number of observations by carefully studying the relationships that exist between the different soil profiles that follow one another along the slope. The relative importance of these two modes of differentiation depends on the preferential orientation (vertical or oblique) of the transfers of water, solutes and particles. The study of morphological and chemical characteristics makes it possible to discern which factors played the most determining role in the formation and distribution of soils. We note that either one factor has always taken precedence over the others, or that the action of a factor has been exerted over a longer period, or even that the major features of inherited actions are remained clearly visible.

The results obtained indicate that the lenticular form of gypsum is the most abundant in the different horizons of the profiles studied while there are other forms of gypsum were averagely found in the soils, such as the prismatic, acicular, columnar form, and ovoid in the upper and intermediate levels, the latter we see the effect of the tablecloth where we noted the presence of crust and consolidated encrustation of the gypsum whose formation and subsequent to the formation of this glacis. For the zone of chott d’Oumache it is the gypsum in powder form on the surface which dominates.

 

Conflicts of interest

 

There were no conflicts of interest for the authors.

 

Authors’ contribution

 

Boumaraf Belkacem – field prospecting and analysis of samples interpretation of work; Saadi Ines – microscopic analyzes, correction and revision.

 

Acknowledgment

 

We would like to thank our colleagues from the Laboratory of Ecosystems Diversity and Agricultural Production Systems Dynamics in Arid Zones (DEDSPAZA) at the University of Biskra, Algeria, for allowing me to finalize the soil analyzes.

 

Bibliographical references

 

BALLAIS, J. L. Des oueds mythiques aux rivières artificielles: l’hydrographie du Bas-Sahara algérien. Physio Geo, v. 4, p. 101-127, 2010. https://doi.org/10.4000/physio-geo.1173

Boudibi, S. Modeling the Impact of Irrigation Water Quality on Soil Salinization in an Arid Region, Case of Biskra. 148p. Thesis (Doctorat). Department of Agronomic Sciences,  University of Biskra, Biskra, Algeria, 2021. https://doi.org/10.13140/RG.2.2.12406.93768

BOUMARAF, B.; Bensaid, R.; Marre, A. The spatial apportionment pedogenetiques soils processes in wadi righ (north eastern Sahara) vallee a mineralogique approach. Annals of the University of Oradea, Geography Series / Analele Universitatii din Oradea, Seria Geografie, n. 1, p. 55-58, 2014. https://geografie-uoradea.ro/Reviste/Anale/Art/2014-1/AUOG_648_Boumaraf.pdf

BOUMARAF, B.; MARRE, A.; Saadi, I. Geomorphological mapping of a Saharan region, the still lands north east Sahara. Annals of the University of Oradea, Geography Series / Analele Universitatii din Oradea, Seria Geografie, n. 2, p. 153-158, 2016. https://geografie-uoradea.ro/Reviste/Anale/Art/2016-2/4.AUOG_712_Boumaraf.pdf

BOYADGIEV, G. Les sols du Hodna. UNPD/FAO. Rome Rapport Technique, n. 5, 1974, 141p.

BRIERE, P. P. Playa, playa lake, sabkha: proposed definitions for old terms. Journal of Arid Environments, v. 45, n. 1, p. 1-7, 2000. https://doi.org/10.1006/jare.2000.0633

CASTANY, G. Carte géologique: feuille Sud 1/500000. Ed Institut géographique national. Sous la direction de M Solignac, 1952.

CONRAD, G. L’évolution continentale post-hercynienne du Sahara algérien” in Publication C.R.Z.A. Annales de Géographie, t. 81, n. 444, p. 245-248, 1972. https://www.persee.fr/doc/geo_0003-4010_1972_num_81_444_18699_t1_0245_0000_2

FEDOROFF, N.; COURTY, M. A. Indicateurs pedologiques d’aridification; exemples du Sahara. Bulletin de la Société Géologique de France, v. 5, n. 1, p. 43-53, 1989. https://doi.org/10.2113/gssgfbull.V.1.43

GOUSKOV, N. Notice explicative de la carte géologique de Biskra au 1/200000. Publication de la série géologique. Algérie, 1964, 13p.

GUEREMY, P ; MARRE, A. Une nouvelle méthode de cartographie géomorphologique applicable aux aléas naturels. Travaux de l’Institut de Géographie de Reims, n. 93-94, p. 5-40, 1996. https://www.persee.fr/doc/tigr_0048-7163_1996_num_24_93_1333

Halitim, A.; Robert, M. Interactions du gypse avec les autres constituants du sol. Analyse microscopique de sols gypseux en zone aride (Algérie) et études expérimentales. Micromorphologie des sols. Réunion internationale de micromorphologie des sols, 7, p. 179-186, 1987.

Hashemi, S. S.; Baghernejad, M.; Khademi, H. Micromorphology of gypsum crystals in Southern Iranian soils under different moistures regimes. Journal of Agriculture Science Technology, v. 13, n. 2, p. 273-288, 2011. https://doi.org/20.1001.1.16807073.2011.13.2.3.8

HERRERO, J.; PORTA, J. The terminology and the concepts of gypsum-rich soils. Geoderma, v. 96, n.1-2, p. 47-61, 2000. https://doi.org/10.1016/S0016-7061(00)00003-3

MARRE, A. Cartographie géomorphologique et cartographie des risques. Bulletin de l’Association des Géographes Français, n. 1, p. 3-21, 2007. https://doi.org/10.3406/bagf.2007.2537

MATHIEU, L. ; THOREZ, J. Etude détaillée de deux niveaux quaternaires du couloir de Taza Guercif (Maroc Oriental). Annales INA, v. 1, p. 124-138, 1976. http://dspace.ensa.dz/jspui/bitstream/712/1/ia00p155.pdf

NESSON, C. L’évolution des ressources hydrauliques dans les oasis du Bas-Sahara algérien. Service de documentation et de cartographie – géographie, v. 17, 1971, 103p.

ONMT. Office National de la Météorologie. Synthese de Donnees Climatiques, Rapport Polycopie, 2012, 46p.

PNUD. Programme des Nations Unies pour le Développement. Oued Righe, cadre physique, étude des ressources en eau définition du projet, 1971, 119p.

POUGET, M. Gypsosols. Référentiel Pédologique. Paris: Institut National de la Recherche Agronomique, 6ème version, 1995, 332p.

POUGET, M. Les relations sol-végétation dans les steppes sud-algéroises (Algerie). Paris: L’Office de la Recherche Scientifique et Technique Outre-Mer, p. 953-954, 1980.

TIMPSON, M. E.; RICHARDSON, J. L.; KELLER, L. P.; MCCARTHY, G. J. Evaporite mineralogy associated with saline seeps in southwestern North Dakota. Soil Science Society of America Journal, v. 50, n. 2, p. 490-493, 1986. https://doi.org/10.2136/sssaj1986.03615995005000020048x

VIEILLEFON, J. Inventaire critique des sols gypseux en Tunisie: étude préliminaire. Tunis: DRES ORSTOM, 98, 1976, 80p.

WATSON, A. Structure, chemistry and origins of gypsum crusts in southern Tunisia and the central Namib Desert. Sedimentology, v. 32, n. 6, p. 855-875, 1985. https://doi.org/10.1111/j.1365-3091.1985.tb00737.x

 

 

 

Received on August 31, 2023

Returned for adjustments on November 25, 2023

Received with adjustments on December 5, 2023

Accepted on December 6, 2023