Petrographic studies through thin sections and mineralogy using XRD spectra of the Babouri-Figuil Basin sediments shows numerous contacts between grains and mineralogy which slightly vary in the four sampling areas.

Major element geochemistry enabled the characterization of the different sources of terrigenous detrital input in the Babouri-Figuil formations and to evaluate the intensity of the chemical weathering. Associated with mineralogy, this has permitted the reconstruction of the paleoconditions which prevailed during diagenesis.

Concentrations of major elements of sample sediments from the studied basin are listed in Table 1. The major oxides selected for the present course included SiO₂, Al₂O₃, Fe₂O₃, in Table 1. The major oxides selected for the present study included SiO₂, Al₂O₃, Fe₂O₃, MgO, CaO, Na₂O, K₂O, TiO₂, P₂O₅ and MnO. These element oxides have highest concentrations in the samples located in the SL outcrop. The concentration of element oxides are: 47.49 wt% to 90.79 wt% for SiO₂ and 2.92 wt% to 23.18 wt% for Al₂O₃. Iron oxide (Fe₂O₃) is more represented in the SL outcrop sediments and varies from 0.2 wt% to 6.22 wt% in the basin. Concentrations in alkali and alkaline earth are considerably represented (>3% average) in the basin sediments. Other element oxides have concentrations < 1 wt% in almost all sediment samples from the Babouri-Figuil Basin. Major elements

CIA (%) = [Al₂O₃/(Al₂O₃ + CaO* + Na₂O + K₂O)] × 100. ICV = (Fe₂O₃ +K₂O +Na₂O +CaO + MgO + TiO₂)/Al₂O₃.

(Al₂O₃, Na₂O, CaO) have been correlated with silica. It appears from these correlations that the elements tend to group together on the same point. Thus, silica shows that samples belong to the same domain. Hence, it can be considered that the source of sediment input from the basin is the same. Contents in K₂O compared to Na₂O are very low except for few samples. This indicates that the sediments from the Babouri-Figuil Basin are richer in sodium than in potassium. This evidence presents the abundance of plagioclases alongside feldspars. Contents in MgO and CaO are relatively high (>3%).

In the present study, chemical weathering index (CIA) and index of compositional variability (ICV) have been calculated to determine the degree of weathering of the source area (Table 1; Figure 4). The CIA values of the sediments of Babouri-Figuil range from 30.92% to 95.08%. However, the values of ICV vary between 0.41 and 1.79. Almost all samples from SL and MF have ICV < 1, whereas almost all samples from ML and MT are >1.

The petrographic and geochemical study of the sediments of the Babouri-Figuil

Basin shows numerous contacts between grains. These types of contacts form under the effect of pressure-dissolution [14], by selective dissolution at the contact points of the particles subjected to significant stress. The formation of stylolites in these sediments is a consequence of pressure-dissolution [15]. It also accounts for the formation of overgrowths, which is a feeding phenomenon of the quartz grains (Figure 2(a) and Figure 2(c)). Thus, microstylolites and stylolites are formed in function of the size of the amplitude of the observed gear surface [16]. Mechanical-chemical compaction is marked by the reduction of the total volume of the rock. This is due to the dissolution of grains at their point of contact under the effect of stress. It is when Type I syntaxial cement is lacking that Type II syntaxial cement is in direct contact with the grains [17]. Cementing is therefore, the occlusion of the intergranular volume by precipitation of authentic minerals marked by induration and/or lithification of the sediment. It is a phenomenon observed in Babouri-Figuil sandstones with the presence of iron oxides (hematite), silica and calcite, as cement around the detrital grains.

Pressure-dissolution of the basin rocks is a deformation mechanism of the basin, and its importance is demonstrated in the compaction of the sandstones during diagenesis. The sediments (sandstones) of the basin show a dissolution of grains of low stability, namely potassium feldspars and mica, followed by the precipitation of kaolinite and/or silica leading, to the creation of secondary porosity. Corrosion dissolution of quartz grains is also observed in thin portions. The overgrowth of silica above detrital quartz grains indicates the presence of silica resulting from the dissolution of feldspars and/or quartz (Figure 2(a)). A typological duality of alteration is observed on the minerals of this basin. There is a centripetal alteration (Figure 2(d)) which would be indicative of a loss of magnesium, silicification and ferruginization of the minerals during alteration. This could be justified by a relative accumulation of iron at the edge of the void on one hand and a centrifugal alteration, which begins from the core of the mineral [18], and makes the mineral black from the interior to the edges on the thin blades observed, on the other hand.

The petrographic and geochemical characteristics of the sedimentary rocks of the Babouri-Figuil Basin indicate that the figurative elements could come from the dismantling of granitic bedrock. The ratio Al₂O₃/TiO₂ ranges from 2.00 to 36.21. This ratio is relatively high, and is associated with the geochemical classification according to Herron [19]. It reveals that the samples analyzed are mostly wacke (Figure 5), indicating a more continental source [20] of sediments of the Babouri-Figuil Basin. Similarly, the diagram in Figure 6, based on Suttner and Dutta [21], indicates that sediments form the Babouri-Figuil Basin were mostly deposited in a semi-arid and arid environment, which is justified by the presence of the hard-grounds and numerous desiccation cracks observed in the basin. They are associated with an arid environment. Also the discrimination functional diagram of the original signatures of the sandstone-mudstone suites using the following major element ratios after Roser and Korsch [22]: Discrimination function 1 = 30.638TiO₂/Al₂O₃ − 12.541Fe₂O₃(total)/Al₂O₃ + 7.329MgO/Al₂O₃ + 12.031Na₂O/Al₂O₃ + 35.402K₂O/Al₂O₃ − 6.382; Discrimination function 2 = 56.500TiO₂/Al₂O₃ − 10.879Fe₂O₃(total)/Al₂O₃ + 30.875MgO/Al₂O₃ − 5.404Na₂O/ Al₂O₃ + 11.112 K₂O/Al₂O₃ − 3.89. It shows that most of the sediments derived from felsic igneous rocks, quartz sedimentary rocks, mafic igneous rocks and occasionally intermediate igneous origin (Figure 7). This could be linked to the mineralogy of the studied sediments and the surrounding rocks made-up of leucocratic granites and syenites and occasionally the gneissic formations.

The degree of chemical weathering of source rocks and the maturity of sediments are measured by determining the CIA, ICV, and also through the mineralogy. These indices correspond to the sum of the weathering processes that affected these materials from the sedimentation media (supergenic weathering processes) and during burial (diagenetic and/or hydrothermal weathering processes). Mineralogical features from the studied sediments revealed presence of clay minerals and high content in iron oxide coatings, which may result from diagenetic processes or from intense weathering in the source area. The presence of kaolinite and montmorillonite suggests chemical weathering of feldspars, which is the mineral phase from the granitic and gneissic source area. In the Babouri-Fifuil basin, the chemical weathering index varies between 30.92% and 95.07%. These observations indicate that the elements shown also come from the dismantling of volcanic bedrock as well as from the granitic massif. The SiO₂/Al₂O₃ ratio in the Babouri-Figuil Basin is average (22.10%). The variation in CIA values and SiO₂/Al₂O₃ reflects the variation in the proportion of feldspars and different clay minerals in these sediments [23]. It is therefore high in samples where feldspars are in low proportion or absent (SL, MF). This comparison with the low feldspar rate is the result of intense chemical alteration in the basin.

Moreover, chemical index such as CIA values are well correlated in these sediments (Figure 4), exhibiting low to high chemical weathering (Table 1). The above correlations suggest that weathering can be significantly influenced by the grains size of the sediment [24]. Variation in values of chemical indices values of the studied sediments can be attributed to the variation in the composition of source rocks. Titanium oxide (TiO₂) shows a positive correlation with Al₂O₃ (Figure 6) in general, and illustrates an accumulation of immobile elements. This accumulation coupled with the high CIA values indicates considerable chemical alteration of the terrigenous detrital materials [3] [25] [26]. For sediments from the Babouri-Figuil Basin, ICV > 1 suggests compositionally immature sediment and ICV < 1 suggests compositionally mature sediment [27]. From the ICV calculation and the ICV versus CIA diagram proposed by Coxet al. [27], almost all sediments from MT and ML are immature, and a low or weak weathering character of these sediments is confirmed. Contrarily, sediments from SL and MF are generally mature with intense weathering except for two samples (Figure 4).