Large tonnages of clay materials are used in the ceramics industry in the form of common bricks, structural bricks, refractories, pottery products, stonewares, sanitary wares and roofing tiles (Murray, Reference Murray and Carr1994, Reference Murray2007; Harvey & Lagaly, Reference Harvey, Lagaly, Bergaya, Theng and Lagaly2006; Reeves et al., Reference Reeves, Sims and Cripps2006; Keith & Murray, Reference Keith, Murray, Kogel, Trivedi, Barker and Krukowski2009; Petrick et al., Reference Petrick, Diedel, Peuker, Dieterle, Kuch, Kaden, Krolla-Sidenstein, Schuhmann and Emmerich2011; Mukherjee, Reference Mukherjee2013). The mineralogical and chemical compositions and the grain-size distributions of clays determine their engineering properties (Harvey & Lagaly, Reference Harvey, Lagaly, Bergaya, Theng and Lagaly2006; Keith & Murray, Reference Keith, Murray, Kogel, Trivedi, Barker and Krukowski2009). Due to their plasticity, clay materials may be worked into many shapes, dried and fired to produce products with high levels of hardness (Murray, Reference Murray and Carr1994).
Morocco is one of the main producing and consuming countries of clayey building materials. In particular, the Rif area (northern Morocco) contains large amounts of clays of Neogene age (El Ouahabi, Reference El Ouahabi2013; Mesrar et al., Reference Mesrar, Akdim, Akhrif, Lakrim, El Aroussi, Chaouni and Jabrane2013; El Ouahabi et al., Reference El Ouahabi, Daoudi, De Vleeschouwer, Bindler and Fagel2014a, Reference El Ouahabi, Daoudi and Fagel2014b). These clayey materials have drawn substantial attention over recent years.
In northwest Morocco (Tetouan area), sandy marls of Late Pliocene age contained large amounts of illite/muscovite (43–57%) and clay minerals (30%). The clay fraction consists mostly of illite (88%). These marls have been characterized as silty clays (92% of 2–20 µm fraction) with low to medium plasticity, and they are suitable for structural clay products (El Ouahabi et al., Reference El Ouahabi, Daoudi, De Vleeschouwer, Bindler and Fagel2014a, Reference El Ouahabi, Daoudi and Fagel2014b).
In the Tangier region (northwest Morocco), Pliocene silty clays with variable mineralogical compositions are present. The total clay minerals and quartz contents are 24–48% and 29–61%, respectively, and the clay fraction is dominated by illite (56–82%). These marls are silty clays (70–88% of 2–20 µm fraction) with medium plasticity, and they are suitable for clay roofing tiles and structural clay products (El Ouahabi et al., Reference El Ouahabi, Daoudi and Fagel2014b).
In central northern Morocco (Meknes region), Miocene homogeneous yellow sandy marls are present in the Saïs Basin, consisting of clay minerals (27–45%), quartz (19–27%) and calcite (20–28%). Illite (45–58%) dominates, with variable amounts of smectite. These marls are therefore illitic, very plastic and suitable for structural clay products (El Ouahabi et al., Reference El Ouahabi, Daoudi, De Vleeschouwer, Bindler and Fagel2014a, Reference El Ouahabi, Daoudi and Fagel2014b). In the Fez region (central northern Morocco), Miocene silty grey marls containing 23–37% of total clay are also illitic (37–46% illite) and have medium to high plasticity. Both the Miocene marls from the Meknes region and the Fez marls are suitable for structural clay products (Mesrar et al., Reference Mesrar, Akdim, Akhrif, Lakrim, El Aroussi, Chaouni and Jabrane2013). Furthermore, the Miocene marls from the Taza region (central northern Morocco) have a similar composition consisting of quartz, calcite, dolomite, illite and kaolinite (Mesrar et al., Reference Mesrar, Lakrim, Akdim, Benamar, Es-Sbai and Jabrane2017).
The Neogene deposits from northeast Morocco have been the subject of geological, sedimentological, palaeontological and structural studies (Guillemin & Houzay, Reference Guillemin and Houzay1982; Frizon de Lamotte & Leikine, Reference Frizon de Lamotte and Leikine1985; Essafi, Reference Essafi1986; Asebriy et al., Reference Asebriy, Bourgois, Cherkaoui and Azdimousa1993; Azdimousa & Bourgois, Reference Azdimousa and Bourgois1993; Abdellah, Reference Abdellah1997; Cunningham et al., Reference Cunningham, Benson, Rakic-El Bied and McKenna1997; El Bakkali et al., Reference El Bakkali, Bourdier and Gourgaud1998a, Reference El Bakkali, Gourgaud, Bourdier, Bellon and Gundogdu1998b; Cunningham & Collins, Reference Cunningham and Collins2002; Azdimousa et al., Reference Azdimousa, Poupeau, Rezqi, Asebriy, Bourgois and Aït Brahim2006; Münch et al., Reference Münch, Cornée, Féraud, Martin, Ferrandini, Garcia, Conesa, Roger and Moullade2006; van Assen et al., Reference Van Assen, Kuiper, Barhoun, Krijgsman and Sierro2006; Chalouan et al., Reference Chalouan, Michard, Kadiri, Negro, Lamotte, Soto, Saddiqi, Michard, Saddiqi, Chalouan and Frizon de Lamotte2008; Achalhi, Reference Achalhi2016; Achalhi et al., Reference Achalhi, Münch, Cornée, Azdimousa, Melinte-Dobrinescu, Quillévéré, Drinia, Fauquette, Jiménez-Moreno, Merzeraud, Moussa, El Kharim and Feddi2016; Cornée et al., Reference Cornée, Münch, Achalhi, Merzeraud, Azdimousa, Quillévéré, Melinte-Dobrinescu, Chaix, Moussa, Lofi, Séranne and Moissette2016; Nasri et al., Reference Nasri, Elhammouti, Azdimousa, Achalhi and Bengamra2016). However, there have been no studies on the Neogene marls in the area because of the inaccessibility of this mountainous region. This problem has recently been resolved thanks to the construction of the coastal road connecting eastern (Saïdia) and western (Tangier) regions of Morocco. Within this context, the current study aims to characterize the clayey materials from the lower part of the Kert Basin (northeast Rif) and to evaluate their suitability for ceramic production. The potential of the Neogene marls for ceramic applications will be evaluated based on their chemical properties (Fe2O3 content), clay and carbonate mineralogy, particle size and plasticity (Dondi et al., Reference Dondi, Raimondo and Zanelli2014). For this purpose, two geological cross-sections were studied on both banks of the Kert River.
Geological setting
The geological history of the Rif area began in the Late Cretaceous at the time of the closure of the Tethys oceanic domain (Michard et al., Reference Michard, Chalouan, Feinberg, Goffé and Montigny2002). Two periods of relatively rapid convergence occurred during the Late Cretaceous and Eocene–Oligocene, alternated with periods of slower convergence during the Palaeocene and since the Early Miocene (Rosenbaum et al., Reference Rosenbaum, Lister and Duboz2002). Since the Middle Miocene, an east to west extension (Negro et al., Reference Negro, de Sigoyer, Goffé, Saddiqi and Villa2008) led to the formation of the Neogene post-nappes basins in the Rif area during the Tortonian, including the Kert Basin (Guillemin & Houzay, Reference Guillemin and Houzay1982; Achalhi, Reference Achalhi2016; Achalhi et al., Reference Achalhi, Münch, Cornée, Azdimousa, Melinte-Dobrinescu, Quillévéré, Drinia, Fauquette, Jiménez-Moreno, Merzeraud, Moussa, El Kharim and Feddi2016). Since the Late Tortonian, a strong convergence associated with intense volcanism in the eastern Rif area (Azdimousa et al., Reference Azdimousa, Jabaloy, Asebriy, Booth-Rea, Gonzalez-Lodeiro and Bourgois2007) led Africa to move to the northwest (Guillemin & Houzay, Reference Guillemin and Houzay1982; Mazzoli & Helman, Reference Mazzoli and Helman1994). Consequently, the Kert Basin, as with other Neogene basins of the region, was exposed to abundant marly sedimentation during the Miocene.
The Kert Basin is divided into two parts (Guillemin & Houzay, Reference Guillemin and Houzay1982): (1) the lower Kert is located in the western part of the Melilla-Nador Basin and continues to the Beni Saïd Mountain; and (2) the upper Kert extends from the Beni Bou Ifour massif in the East to the Tizi Ouzbar schist (west of Midar) in the west. The latter is limited to the northwest by the Bou Ziza volcano and to the northeast by the Gourougou volcano (Fig. 1).
Study area location in a geological map of north-eastern Rif (Morocco) (modified from Jabaloy-Sánchez et al., Reference Jabaloy-Sánchez, Azdimousa, Booth-Rea, Asebriy, Vázquez-Vílchez, Martínez-Martínez and Gabites2015).
The Neogene of the Kert Basin is characterized by a basal conglomerate located on westward side of the Beni Saïd (Guillemin & Houzay, Reference Guillemin and Houzay1982; Essafi, Reference Essafi1986) and Zeghanghane mountains, suggesting a deepening due to the occurrence of syn-sedimentary faults affecting the thickness of the series towards the west of the basin (Essafi, Reference Essafi1986; Abdellah, Reference Abdellah1997). Marls interstratified with layers of rhyolitic tuffs–cinerites were deposited above the conglomerate in a deep Messinian sea (Essafi, Reference Essafi1986). In the lower Kert area, the post-nappe series are Messinian with a clearly transgressive behaviour immersing the Beni Saïd Mountain (eastern Temsamane), setting up a marly sedimentation, which was initiated with detrital conglomerate and sandstone, overlying the Beni Saïd Mountain in the west of the basin. Then, the facies becomes marly, with cinerite intercalations due to the Messinian volcanic activity, from the bottom of the mountain southwest of the Melilla Basin (Guillemin & Houzay, Reference Guillemin and Houzay1982). Interbedded pyroclastic levels (tuffs and cinerites) in the Messinian marls could be used for stratigraphic correlations because of their substantial extent (Abdellah, Reference Abdellah1997). 40Ar/39Ar dating has assigned a date of 6.9 ± 0.02 Ma to the basal level of the Izaroren cross-section (Cunningham et al., Reference Cunningham, Benson, Rakic-El Bied and McKenna1997; van Assen et al., Reference Van Assen, Kuiper, Barhoun, Krijgsman and Sierro2006). The end of open marine deposition occurred prior to 6 Ma (van Assen et al., Reference Van Assen, Kuiper, Barhoun, Krijgsman and Sierro2006), confirming the Messinian age of marls from the lower Kert area. Similar to the neighbouring sedimentary basins, the Late Messinian regression is recorded in the Kert Basin (Guillemin & Houzay, Reference Guillemin and Houzay1982).
Materials and methods
Materials
Sampling was carried out in the Messinian marly sediments of the lower Kert area along two cross-sections; Izaroren and Afza, located on either sides of the Wadi Kert mouth (Fig. 1). The thickness of each section exceeds 100 m. A total of five marly samples, labelled Izar 1, Izar 3, Izar 4, Izar 5 and Izar 6, were sampled from the Izaroren profile (east of the Wadi Kert) (Fig. 2). A total of four samples were also taken from the Afza cross-section (west of the Wadi Kert), labelled Af 1, Af 3, Af 4 and Af 5 (Fig. 3). The sampling locations have been chosen in marly facies away from trees, shrubs and anthropogenic influences. The sampling was performed by digging deep into the formation after removing the altered surface and then sampling a sufficient amount of material. In addition to correlating the two profiles, three more samples were taken from tuff levels: Izar 2 from the Izaroren cross-section and Af 2 and Af 6 from the Afza cross-section.
Lithological description of the Izaroren profile and corresponding photograph illustrating the studied facies. *Messinian age after Cunningham et al. (Reference Cunningham, Benson, Rakic-El Bied and McKenna1997) and van Assen et al. (Reference Van Assen, Kuiper, Barhoun, Krijgsman and Sierro2006).
Lithological description of the Afza profile and photograph illustrating the facies studied.
Experimental methods
The collected samples were subjected to mineralogical and geochemical analyses to estimate the bulk and clay mineralogical composition and to determine the main major chemical elemental composition. The CaCO3 content was determined with calcimetry; grain-size analyses were performed on the <2 µm, 2–20 µm and >20 µm fractions and the sedimentological fractions (<4 µm, 4–63 µm and 63 μm–2 mm) according to the Wentworth scale (Wentworth, Reference Wentworth1922). The Atterberg limits and methylene blue values enable the determination of the marl plasticity, extrusion capacity and specific surface area (SSA).
Mineralogical and chemical analysis
The bulk samples were dried, ground with a pestle and mortar and placed into a sample holder to limit preferential orientation (Moore & Reynolds, Reference Moore and Reynolds1997; Boski et al., Reference Boski, Pessoa, Pedro, Thorez, Dias and Hall1998; Fagel et al., Reference Fagel, Boski, Likhoshway and Oberhaensli2003). The mineralogical composition was determined with X-ray diffraction (XRD) using an XPERT-PRO diffractometer with Cu-Kα radiation (λ = 1.5418 Å) at the National Center for Scientific and Technical Research – Technical Support Unit for Scientific Research (UATRS-CNRST, Rabat, Morocco). The X-ray traces were analysed using X'Pert HighScore Plus software and the PDF-2 database. Semi-quantitative estimation of mineralogical phases was obtained by multiplying the measured intensity of specific reflections by corrective factors to obtain the amount of each mineral (Cook et al., Reference Cook, Johnson, Matti and Zemmels1975; Boski et al., Reference Boski, Pessoa, Pedro, Thorez, Dias and Hall1998; Fagel et al., Reference Fagel, Boski, Likhoshway and Oberhaensli2003).
Oriented preparations were obtained on the <2 µm fraction of the marly samples using the glass slide method (Moore & Reynolds, Reference Moore and Reynolds1997). The clay fraction was obtained by suspension of ~1 g of dried bulk sediment previously sieved at 63 µm in distilled water. The carbonate minerals were dissolved with 0.1 mol L–1 HCl and subsequently washed with distilled water, and the supernatant was removed by centrifugation. The <2 µm fraction was separated by settling following Stokes’ law (AFNOR, 1992; Moore & Reynolds, Reference Moore and Reynolds1997). The first centimetre of the suspension was placed on a glass slide and dried overnight at room temperature. The XRD clay analyses included three different preparations, namely air dried (AD), after solvation with ethylene glycol for 24 h (EG) and after heating at 500°C for 4 h (500°C) (Moore & Reynolds, Reference Moore and Reynolds1997). This last treatment enables us to characterize some hydrated minerals and to distinguish kaolinite and chlorite. Semi-quantitative estimations of the main clay phases were obtained from the measured intensity of a diagnostic peak multiplied by correction factors (Biscaye, Reference Biscaye1965; Cook et al., Reference Cook, Johnson, Matti and Zemmels1975; Fagel et al., Reference Fagel, Boski, Likhoshway and Oberhaensli2003, Reference Fagel, Thamó-Bózsó and Heim2007; Nkalih Mefire et al., Reference Nkalih Mefire, Yongue Fouateu, Njoya, Mache, Pilate, Hatert and Fagel2018) (Figs 4 & 5).
XRD traces of non-oriented powders of the Izar 5 and Af 3 samples: M-L = mixed layer; Ch = chlorite; I = illite; K = kaolinite; Tc = total clay; Q = quartz; C = calcite; Pl = plagioclase; D = dolomite.
XRD traces of the oriented Izar 5 and Af 3 samples: M-L = mixed layer; Ch = chlorite; I = illite; K = kaolinite.
Chemical analysis of the major elements was performed on a wavelength-dispersive Axios X-ray fluorescence spectrometer (WDS-XRF) at the UATRS-CNRST. The results were expressed as mass percentage of oxides. Loss on ignition (LOI) values were obtained by heating the samples at 1000°C for 2 h under oxidizing conditions.
The CaCO3 content was measured using a Bernard calcimeter based on the volume of CO2 evolved according to the French Standard NF P 94-048 (AFNOR, 1996).
Physical and textural analyses
Particle-size distribution was obtained by wet sieving of the samples through an 80 µm sieve. The <80 µm particles were then suspended in water mixed with sodium hexametaphosphate and shaken to avoid agglomeration of clay particles according to the French Standard NF P 94-057 (AFNOR, 1992). The evolution over time of the solution density was measured using the hydrometer method. The maximum diameter and the mass percentage of sedimented particles were calculated based on the measured densities.
The Atterberg limits (i.e. liquid limit (LL), plastic limit (PL) and plasticity index (PI)) were determined using the Casagrande method according to the French Standard NF P 94-051 (AFNOR, 1993). The amount of methylene blue adsorbed by the clay sample was used to determine the cation-exchange capacity (CEC) and the SSA according to the French Standard NF P 94-068 (AFNOR, 1998) using the following equation (AFNOR, 1998):
$${\rm SSA} = {\rm MBV}\lpar {C_{{\rm MB}} \times \hbox{N}_{{\rm av}} \times A_{{\rm MB}}/1000M_{{\rm MB}}} \rpar $$
$${\rm MBV} = V_{{\rm MB}} \times C_{{\rm MB}} \times {\rm} 100/w_0$$where C MB is the concentration of methylene blue solution (10 g L–1), Nav is Avogadro's number (6.02 × 1023), A MB is the area covered by one methylene blue molecule (130 Å2), M MB is the molar mass of methylene blue (319.85 g mol–1), MBV is the methylene blue value (g 100 g–1 of sample), V MB is the volume of methylene blue solution injected into the soil solution (mL) and w 0 is the dry weight of the sample used (g).
Results
Lithological description
The Izaroren profile begins with a grey marl >10 m thick and devoid of visible fossils. The marl is overlain by a whitish rhyolitic tuff layer 8 m thick and rich in quartz and feldspars (El Bakkali et al., Reference El Bakkali, Bourdier and Gourgaud1998a). The series continues with an ~80 m-thick greyish marl layer without visible macrofossils, which becomes gypsiferous at the top (Fig. 2). The profile ends with a succession of 6.5 m-thick indurated sandstone marl and 15–20 m-thick greenish marly layers with some ferruginous features, probably reflecting the beginning of the Late Messinian regression.
The Afza profile is significantly affected by normal faults, attesting to the Messinian syn-sedimentary subsidence (Fig. 3). At the base, similar to the Izaroren profile, a 10 m-thick greenish marly layer with some yellowish patches occurs. It is topped by a whitish 2 m thick tuff layer. The succession of at least two grey marly layers with red ferruginous features (12–15 m) alternates with two conglomeratic banks of sandy breccias (5–7 m) and is affected by normal faults. This alternation is overlain by a sandbar ~4 m thick with bioturbations and ferruginous features on its upper surface. The series continues with a green plastic marly sediment 45 m thick, topped by a slightly altered white volcanic tuff of ~12 m thick.
Marl characteristics
The marls consist mainly of quartz (12–25 wt.%), total clay (38–58 wt.%) and calcite (13–32 wt.%), associated with minor amounts of feldspars (3–15 wt.%) and dolomite (1–5 wt.%) and traces of siderite (0–1 wt.%) and rhodochrosite (0–2 wt.%) (Table 1). Cristobalite occurs only in Izar 6 (22 wt.%) and Af 5 (6 wt.%). The amount of quartz was slightly smaller in Izaroren marly samples (12–18 wt.%) than in Afza samples (22–25 wt.%). Conversely, the total clay amount is greater in the Izaroren (39–58 wt.%) than in the Afza profile (38–46 wt.%). The clay fraction (<2 µm) varies considerably in the two profiles: it consists of illite (28–46 wt.%), kaolinite (2–27 wt.%) and illite-vermiculite mixed layers of 10–14 Å (26–48 wt.%). The chlorite content varies between 11 and 29 wt.%, but chlorite is absent in the uppermost samples of the Izaroren and Afza profiles (samples Izar 6 and Af 5).
Bulk and clay mineralogy (wt.%) of the studied samples.
Qz = quartz; K-F = K-feldspar; Pl = plagioclase; Cc = calcite; Do = dolomite; Sid = siderite; Cris = cristobalite; Rhod = rhodochrosite; Amp = amphibole; I = illite; K = kaolinite; Ch = chlorite.
The chemical composition of the studied marly samples (Table 2) showed that the main oxides are SiO2 (38.3–54.8 wt.%), Al2O3 (8.5–13.1 wt.%), Fe2O3 (9.1–16.6 wt.%) and CaO (6.6–9.2 wt.%). TiO2 (0.37–0.65 wt.%), MgO (1.75–2.98 wt.%), K2O (1.09–1.67 wt.%), Na2O (1.04–4.28 wt.%), SO3 (0.30–1.10 wt.%), MnO2 (0.29–0.51 wt.%) and P2O5 (0.15–0.20 wt.%) are present in small amounts. The LOI values vary between 11.37 and 16.85 wt.%, mainly due to the variable amounts of carbonates and clay minerals. The amounts of carbonates (Table 3) vary between 13.0 and 20.4 wt.%, which is typical of marly facies.
Chemical compositions (wt.%) of the samples studied.
a Data in ppm.
Carbonate content, grain size, Atterberg limits and SSA results of the marly samples studied.
The thermogravimetric/differential thermal analysis curves of the Izaroren 4 marl are shown in Fig. 6. The curves display four endothermic and two exothermic peaks. The first endothermic peak at ~100°C is associated with loss of weight of 3.6 wt.% due to the removal of physisorbed water. The exothermic peak at ~160°C is attributed to oxidation of organic matter. The second endothermic peak at ~550°C is associated with a relatively large weight loss of 5.86 wt.% and is assigned to dehydroxylation of kaolinite into metakaolinite (Brindley & Nakahira, Reference Brindley and Nakahira1959; Shvarzman et al., Reference Shvarzman, Kovler, Grader and Shter2003). The third and fourth endothermic peaks at ~730°C and ~850°C are associated with moderate weight loss (5.1 wt.%) due to the decomposition of dolomite and calcite (Alvares et al., Reference Alvares, Navarro and Garcia Casado2000). The small exothermic event at ~900°C associated with a small weight loss of 0.6 wt.% is related to crystallization of intermediate Ca-silicates phases and most probably the inception of aluminosilicates (spinel) formation (Trindade et al., Reference Trindade, Dias, Coroado and Rocha2009; El Ouahabi et al., Reference El Ouahabi, Daoudi, Hatert and Fagel2015; Milošević & Logar, Reference Milošević and Logar2017).
Thermogravimetric analysis (TGA)/differential thermal analysis (DTA) curves of the Izar 4 sample.
The grain-size data showed significant variation along the profiles, implying lateral and vertical variation within the deposit (Table 3). Hence, along the Izaroren section, the grain-size fractions did not show homogeneity (Fig. 7a). Thus, the sand content is 9 wt.% in the Izar 6 sample, but it did not exceed 3 wt.% in the other samples of the Izaroren profile. Nevertheless, the silt content varied considerably (26–75 wt.%) along the profile. The clay fraction varied inversely with the silt fraction from 23 to 71 wt.%.
Particle-size distribution along (a) Izaroren and (b) Afza profiles based on d10, d30, d50, d60, d75 and d90 parameters.
In the Afza section, more regular variations in clay, silt and sand fractions were observed (Fig. 7b). Thus, the sand content increased gradually from the base of the profile (10 wt.%) to the top (18 wt.%). Similarly, the silt content increased from 28 wt.% at the base to 49 wt.% at the top, and from 29 wt.% to 37 wt.% in the middle part of the profile. However, the clay content decreased gradually from the bottom (60 wt.%) to the top (32 wt.%).
The differences in mineralogical and grain-size properties are reflected in the geotechnical data (Table 3). The LL, PL and PI varied from 44% to 72%, from 20% to 45% and from 23% to 45%, respectively. The SSA values varied considerably, from 26.3 to 125.6 m2 g–1.
Discussion
Characterization of Miocene marls
Mineralogical analysis enabled the establishment of a correlation between the lithologies of the two cross-sections. Thus, the two profiles may be subdivided into two parts: (1) grey marl in the lower part; and (2) green marl in the upper part (Fig. 8). In addition, total the clay content varied inversely with the amount of quartz and cristobalite. At the tops of the two profiles, slight decreases in total clay from 43 to 39 wt.% and from 42 to 38 wt.% occurred in the Izaroren and Afza profiles, respectively. These decreases are associated with the appearance of cristobalite (22 and 6 wt.% in the uppermost samples of the Izaroren and Afza profiles, respectively). Likewise, chlorite varied inversely with the abundance of illite and kaolinite and disappeared definitively at the top of the two profiles (Table 1). The late appearance of cristobalite is due to the Messinian volcanism characterizing the eastern Rif, supported by the disappearance of chlorite and the deposition of the tuff overlying the green marl in the Afza profile.
Correlation between the Izaroren and Afza profiles based on pyroclastic layers and mineralogical composition.
These marls are rich in marine, biogenic calcite (planktonic and benthic), which could also have a continental origin. Traces of siderite and rhodochrosite were formed in the sediments during their deposition or shortly thereafter. In fact, they point to reducing or locally oxidizing conditions.
The chemical composition is in accordance with the mineralogical composition of the marls. The high SiO2 content is mainly related to the large amounts of clay minerals and quartz and also the presence of cristobalite in samples Af 5 (SiO2 = 46.37 wt.%) and Izar 6 (SiO2 = 54.80 wt.%). The Al2O3 and CaO contents are mostly associated with total clay and calcite abundance, respectively. The LOI values vary between 11.4 and 16.8 wt.%, which is related to the presence of clay minerals, Fe-oxides, organic matter and carbonates (Milheiro et al., Reference Milheiro, Freire, Silva and Holanda2005; Baccour et al., Reference Baccour, Medhioub, Jamoussi, Mhiri and Daoud2008).
Along the Izaroren profile, samples Izar 1 and Izar 4 are classified as silty clays according to their grain size (Shepard, Reference Shepard1954), whereas the remaining samples (Izar 3, Izar 5 and Izar 6) are classified as clayey silts (Fig. 9). This grain-size variability is mainly due to hydrodynamic fluctuations during sedimentation.
Plot of grain-size results of the samples studied in the Shepard ternary diagram (Shepard, Reference Shepard1954).
Similarly, the uppermost sample of the Afza cross-section (Af 5) was clayey silt, whereas the remaining samples were silty clays (Fig. 9). The progressive evolution of the different particle size fractions with depth is due to the gradual increase in hydrodynamic energy during deposition.
The mineralogical composition of the Messinian marls from the lower Kert area displayed similarities with Neogene marls from the Saïs Basin in the Meknes region of Morocco (El Ouahabi et al., Reference El Ouahabi, Daoudi and Fagel2014b). However, the marls of the lower Kert area contain 10–14 Å illite-vermiculite mixed-layer clays instead of smectite in the Meknes marls. Furthermore, a similar mineralogical composition has been observed for the Algerian Neogene clayey deposits from the Jijel Basin (Baghdad et al., Reference Baghdad, Bouazi, Bouftouha, Bouabsa and Fagel2017), but with a greater amount of kaolinite than the lower Kert marls. Both Neogene marls were used successfully for structural clay products (El Ouahabi et al., Reference El Ouahabi, Daoudi and Fagel2014b; Baghdad et al., Reference Baghdad, Bouazi, Bouftouha, Bouabsa and Fagel2017).
The variations in mineralogical and grain-size results mainly affected the geotechnical properties of the clays. The Atterberg limits showed that samples Af 3 and Af 4 were moderately plastic, whereas the remaining samples were highly plastic (Fig. 10).
Plot of studied samples in a plasticity chart (Casagrande, Reference Casagrande1947; Holtz & Kovacs, Reference Holtz and Kovacs1981).
The SSA depends on the abundance and type of clay minerals, the CEC and the grain size of the materials (De Kimpe et al., Reference De Kimpe, Laverdiere and Martel1979; Tiller & Smith, Reference Tiller and Smith1990; Petersen et al., Reference Petersen, Moldrup, Jacobsen and Rolston1996; De Jong, Reference De Jong1999). The SSA values of the lower Kert marls (26.3–125.6 m2 g–1) are considered low, even though they are greater than the Meknes marl values (33.3–37.9 m2 g–1). The lower Kert marls belonged to the SSA intervals of kaolinite (10–30 m2 g–1), illite (70–140 m2 g–1) and chlorite (50–150 m2 g–1), and they were much lower than smectite (700–800 m2 g–1) and vermiculite (760 m2 g–1) (Beaulieu, Reference Beaulieu1979; Mahmoudi et al., Reference Mahmoudi, Bennour, Srasra and Zargouni2017), which is consistent with the mineralogical data.
Suitability for ceramics applications
The suitability of raw clay deposits for ceramics applications is determined by their physical properties, mineralogy and chemistry (El Ouahabi et al., Reference El Ouahabi, Daoudi and Fagel2014b; Lisboa et al., Reference Lisboa, Rocha and de Oliveira2016; Baghdad et al., Reference Baghdad, Bouazi, Bouftouha, Bouabsa and Fagel2017; Kharbish & Farhat, Reference Kharbish and Farhat2017; El Boudour El Idrissi et al., Reference El Boudour El Idrissi, Daoudi, El Ouahabi, Collin and Fagel2018). The bulk mineralogical association of the samples studied and the dominance of illite in their clay fractions classify these marls as common clays (Murray, Reference Murray2007; Keith & Murray, Reference Keith, Murray, Kogel, Trivedi, Barker and Krukowski2009) and endow them with suitable ceramics properties (Ferrari & Gualtieri, Reference Ferrari and Gualtieri2006; Wattanasiriwech et al., Reference Wattanasiriwech, Srijan and Wattanasiriwech2009; Baghdad et al., Reference Baghdad, Bouazi, Bouftouha, Bouabsa and Fagel2017; Mahmoudi et al., Reference Mahmoudi, Bennour, Srasra and Zargouni2017). According to the Strazzera ternary diagram (Strazzera et al., Reference Strazzera, Dondi and Marsigli1997) (Fig. 11), the top sample of the Afza profile (Af 5) is suitable for clay roofing tiles and the remaining samples are suitable within the field of structural clay products, except for the lowermost sample of the Izaroren profile (Izar 1). Samples Af 5, Izar 1 and Izar 6 are extremely plastic. They require some processing, such as the addition of coarse tempering materials (e.g. quartz, feldspar or chamotte), to decrease their plastic behaviour. The remaining samples are moderately to highly plastic marls that are suitable for extrusion (Fig. 12).
Classification of the studied samples based on the Strazzera ternary diagram (Strazzera et al., Reference Strazzera, Dondi and Marsigli1997).
Bain diagram showing the potential moulding of the studied samples (Bain, Reference Bain1986).
According to the Winkler classification scheme (Winkler, Reference Winkler1954) and based on the grain-size results (Fig. 13), the Af 1 and Izar 4 samples are suitable for roofing tiles and masonry bricks and samples Af 3, Af 4, Af 5 and Izar 1 are suitable for hollow products. Nonetheless, sample Izar 1 requires some pre-treatment to make it suitable because of its relatively large proportion of clay fractions. In comparison, Neogene marls from the Jijel Basin (Algeria) plot between the hollow products and roofing tiles/masonry bricks fields (Baghdad et al., Reference Baghdad, Bouazi, Bouftouha, Bouabsa and Fagel2017), while marls from Meknes (Morocco) do not plot in any application domains because of their high silt content (El Ouahabi et al., Reference El Ouahabi, Daoudi and Fagel2014b).
Plot of the studied samples in the Winkler ternary diagram (Winkler, Reference Winkler1954).
According to the (Al2O3)–(Fe2O3 + CaO + MgO)–(Na2O + K2O) ternary diagram (Fig. 14) (Fiori et al., Reference Fiori, Fabbri, Donati and Venturi1989), all Afza samples and samples Izar 3 and Izar 4 from the Izaroren marls belong to the red ceramic field. The marls studied are moderately rich in CaO, acting as a fluxing agent (Trindade et al., Reference Trindade, Dias, Coroado and Rocha2009, Reference Trindade, Dias, Coroado and Rocha2010), which allows us to predict the transformation of high-temperature minerals in ceramic products (Trindade et al., Reference Trindade, Dias, Coroado and Rocha2010; El Ouahabi et al., Reference El Ouahabi, Daoudi, Hatert and Fagel2015). The greater amount of Fe2O3 (>5 wt.%) might give all samples a reddish colour after firing (Abajo, Reference Abajo2000; Ngun et al., Reference Ngun, Mohamad, Sulaiman, Okada and Ahmad2011) and so make them inappropriate for fine ceramics without any processing to dilute the Fe2O3 content. Comparable Fe2O3 amounts were also detected in the Neogene marls from Meknes (12.16–16.63 wt.%), making them unsuitable for fine ceramics (El Ouahabi et al., Reference El Ouahabi, Daoudi, De Vleeschouwer, Bindler and Fagel2014a). Considerably lower Fe2O3 contents were detected in the Neogene marls from the Jijel Basin (Algeria) deposits (4.89–8.08 wt.%) (Baghdad et al., Reference Baghdad, Bouazi, Bouftouha, Bouabsa and Fagel2017). Similar Fe2O3 percentages (4.21–8.61 wt.%) with high carbonate contents (20–25 wt.%) were observed in the Tertiary marls from the Bailén area in southern Spain. These marls are suitable for making porous red wall tiles, clinker, vitrified red floor tiles and porous light-coloured wall tiles by pressing (González et al., Reference González, Galán, Miras and Aparicio1998).
Plot of the studied samples in an (Al2O3)–(Fe2O3 + CaO + MgO)–(Na2O + K2O) ternary diagram (Fiori et al., Reference Fiori, Fabbri, Donati and Venturi1989).
In the north-western Mediterranean, Tertiary marls from the Castellon area (Spain) have much lower Fe2O3 contents (3.75–6.10 wt.%), with highly variable amounts of CaCO3 (16–27 wt.%) (Jordán et al., Reference Jordán, Sanfeliu and De la Fuente2001). Similarly, Plio-Pleistocene marls from the Sassuolo district (Italy) show low Fe2O3 contents (4.5–6.0 wt.%), with great variability in terms of carbonate content (15–25 wt.%) and MgO (Dondi, Reference Dondi1999).
Due to the occurrence of sulfate and sodium associated with large amounts of calcium in most of the marls studied (Table 2), efflorescence may occur during firing (González et al., Reference González, Galán and Miras2006; Andres et al., Reference Andres, Díaz, Coz, Abellán and Viguri2009). This phenomenon may be controlled by monitoring the firing parameters, such the rate of heating and the firing temperature (Andres et al., Reference Andres, Díaz, Coz, Abellán and Viguri2009).
Summary and conclusions
The Neogene clayey deposits located on the Kert riverbanks (north-eastern Rif, Morocco) were characterized and their suitability for the manufacture of ceramics was also discussed. The marls mainly consist of quartz, calcite and clay minerals, namely illite, kaolinite, illite-vermiculite mixed layers (10–14 Å) and chlorite. This composition qualified these materials as common clays. The chemical composition of the marls is in agreement with the mineralogical composition. The main oxides were SiO2, Al2O3, Fe2O3 and CaO. The mineralogical and geochemical data confirmed the occurrence of volcanic relicts recorded in the Messinian sedimentary series. The Neogene clay deposits studied were marly silts or silty marls with moderately to highly plastic behaviour.
The marls of the lower Kert are suitable as potential raw materials for the ceramics industry. These marls might be used in the manufacture of structural clay products, especially hollow products, roofing tiles and masonry bricks, except for sample Izar 1, which requires processing to make it suitable for these ceramics types. Some marl samples were appropriate for optimal (Af 3, Af 4 and Izar 4) or acceptable (Af 1, Izar 3 and Izar 5) extrusion. The remaining samples (Af 5, Izar 1 and Izar 6) might require additional treatments or formulations because of their high plasticity. The addition of sand or chamotte is necessary to produce extruded ceramics.
