Introduction

Rivers play a vital role in human development and are an important natural resource. Ever since the beginning of the earliest human civilizations, human has been using the river environment for a variety of applications, and most of the earliest human settlements occurred along the floodplains of rivers (Garzanti et al. 2015). The periodic flood of the river causes the deposition of the eroded materials as alluvium in low-lying areas (i.e., floodplains). This alluvium then serves as the parent material for the soils that form in those floodplains. Thus, floodplains provide important resources and values that are useful to humankind via direct utility value for agriculture and indirect utility value, such as groundwater supply, nutrient retention, and toxicant retention. One classical illustration of this is the Nile, which is one of the longest rivers in the world and the birthplace of ancient Egyptian civilizations. The Nile floodplain is formed by annual deposits of silt brought down from the Abyssinian highlands by the Blue Nile and the Atbara. River regulation, via High Dam construction at Aswan, has stopped this yearly sediment influx, and the floodplain is now dissected by a network of irrigation canals.

In general, a floodplain is defined by fine-grained alluvium (silt and clay) expressed by suspension from the source location in an upstream river basin. The mineralogy, major elements, and trace element geochemistry of alluvium sediments could represent the source area’s composition and provide useful information on source rocks and formation conditions like weathering (Asadi et al. 2013; Ahmad et al. 2014). Ineralogically, the heavy mineral assemblage of the floodplain deposits provided information about the source area (Omer 1996). Trace elements (e.g., La, Th, Zr, and Sc) are commonly used to study sediment source areas due to their relative low mobility during sedimentary transportation and deposition (Cullers et al. 1979). So that, the mineralogy, major, and trace element geochemistry of sedimentary rocks have been used to determine sedimentary rock source area (Prego et al. 2012), weathering intensity (Ali et al. 2014), and interpert the depositional environment (Verma and Armstrong-Altrin 2013a, b).

The River Nile has been studied by many authors since it is one of the most important river systems in the world (e.g., Hassan 1976; Said 1981; Butzer 1997; Krom et al. 2002; Woodward et al. 2007; Woodward et al. 2015; Macklin et al., 2015; Hassan et al. 2017; Pennington et al. 2017; Hamdan et al. 2019; Zaki et al. 2021; Woodward et al. 2022; Nicoll 2020; Metwaly 2021; Rezk et al. 2022; Abu Seif et al. 2022; Embaby et al. 2023). Previous researchers have studied regional patterns, geomorphological features, sediment budget, erosion patterns, and petrographic and geochemical characteristics. The geochemical and mineralogical composition and characteristics of the Nile floodplain sediments in the Sohag area are poorly understood, despite their importance as proxies for paleoclimate conditions, provenance analysis, depositional conditions, and related diagensis characteristics over time. Consequently, and according to the obtained geochemical data, floodplain geochemistry can also be used in monitoring environmental changes and predicting any potential environmental threats, e.g., desertification and pollution phenomena. The present work aims to study the mineralogy and geochemistry of the modern floodplain Nile sediments in the Sohag area to determine their provenances, climatic conditions during deposition, and weathering influence. Moreover, sediment maturity, provenance, paleo-environmental conditions, paleo-oxygenation conditions, tectonic influence, geochemistry, and source-area weathering were investigated. It also aims to understand their environmental perspective and highlight the main environmental application of the obtained results.

Geological setting

The Sohag sector is occurring in Upper Egypt, occupying an area of about 6,546 km2, between latitudes 26° 7′ 00″ to 26° 57′ 10″ N and longitudes 31° 20′ 00″ to 31° 14′ 10″ E, around the River Nile. The study area is located in Upper Egypt, which is characterized by hot and mild weather with low rainfall in summer and winter, respectively, like most arid regions of North Africa (Fig. 1).

Fig. 1
figure 1

Mean daily maximum and minimum temperature from January to December, Sohag, Upper Egypt, Egypt (Allmetsat 2008)

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The sequence of exposed sedimentary rocks in the Sohag area is composed mainly of older Thebes (Lower Eocene) to younger flood plains (Holocene), as shown in Table 1. Such a wide range of sedimentary sequences in the Nile basin archives and provides information about Pleistocene and Holocene environments. The geological map is shown in Fig. 2, which clearly shows the course of the Nile River along with the major lithologies of the study area and the site samples.

Table 1 Main geological units in Sohag area
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Fig. 2
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Simplified geological map of the study area showing surface sediment sampling stations and the main rock unit outcrops

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Said (1981) stated that the Nile River passes through five stages during its evolution within the Egyptian country. These are, from oldest to youngest: Eonile, Paleonile, Protonile, Prenile, and Neonile.

The eastern area of the river in the Sohag area is predominately covered by N, NE, E-W, NNE, and NW fractures and lineaments. However, the area west of Sohag only has NW, WNW, and NE-trending lineaments and fractures; the majority of them exhibit significant normal fault displacement, and the intersections of these faults created NW and NE-trending grabens before Pre-Eonile and Eonile sedimentation. This could point to the Red Sea's rift-flank uplift's minimizing westward influence. According to Khalil and McClay (2002), these fractures and fault trends are thought to be related to the N-S and N60E regional expansion linked to the Red Sea rifting that began in the late Eocene–early Oligocene. However, tectonics also had a significant impact on the synchronous Pre-Eonile deposits found within the NW grabens. This is demonstrated by the prevalence of softsediment deformational characteristics, which have a stratiform position here. These features include truncated beds and several tiny synsedimentary faults. While the course of the Nile itself was controlled by NW and NE-trending faults during that time, the Pre-Eonile, Eonile, and Protonile sediments in the study area are defined by NW and NE-trending fault segments, suggesting that these faults play a role in controlling the distribution of these sediments.

Field observations show that several localities along both banks of the Nile Valley in the study Sohag area belong to the Pleistocene deposits. Omer (1996) and Omer and Issawi (1998) differentiated these Pleistocene sediments into four compositionally distinctive units (Qena, Kom Ombo, Ghawanim, and Dandara formations), reflecting their source rock composition in the hinterlands. Sediments of Ethiopian derivation (Ghawanim and Dandara Formations) contain abundant ferromagnesian minerals (augite and hornblende). The Qena Formation is represented by sands and gravels without igneous and metamorphic rock fragments, which reflects their derivation from the Mesozoic sandy sediments (Nubia sequence) widely covering the basement rocks in the Eastern Desert. The Kom Ombo Formation is formed from sands and gravels, including abundant igneous and metamorphic rock fragments derived from basement rocks in the Eastern Desert. The Ghawanim Formation comprises sands and gravels, including abundant basement rock fragments, and shows the first occurrence of Ethiopian heavy minerals such as augite and hornblende.

The Ethiopian lands represent an important source area, stated for the first time, in the provenance of the Nile sediments, as the water of the Egyptian Nile River comes from Ethiopian highlands (Omer 1996, and references therein, op. cit.). Sandy sediments and basement rock fragments were supplied from active wadis in the Eastern Desert. As a result, the sediments of the Qena and Kom Ombo formations are characterized by their poverty in the Ethiopian heavy mineral suite compared with the Ghawanim one, which shows mixed sources. At the present time, the major discharge to the Nile is from the Ethiopian tributaries. This present hydrographic system of the Nile seems to have been formed by the end of the middle Pleistocene. The late Pleistocene sediments around the Nile Valley belong to deposits of the Neonile episode, whereas the Holocene is represented by deposits of the Nile floodplain. In this study, we will refer to the Nile floodplain sediments of the Holocene episode exposed at the study area as the Modern Floodplain Sediments (MFS), which will be used for Nile sediments that were deposited in Egypt by the modern Nile system.

Materials and methods

It is crucial to sample and examine the sediments in the Sohag area’s Nile floodplain because little is known about them. As a result, samples have been gathered and standard analytical techniques (i.e., textural analysis), geochemical analysis (i.e., major and trace element contents using XRF technique), and mineralogical analysis (i.e., Philips X-ray diffractometer technique), have been employed to monitor environmental changes and forecast any potential environmental threats, such as desertification and pollution phenomena in this area, as well as to infer the paleoclimate conditions, provenance analysis, depositional conditions, and related diagenesis characteristics over time. A detailed description of these methods includes the following:

Sediment sampling and size separation

A systematic sampling protocol was used to cover the study area. A total of 35 composite bulk samples (< 2 mm) from surface modern floodplain sediments were collected at a depth of about 10–20 cm. Samples were collected using an auger sampler and placed in polyethylene bags. The collected samples covered both sides of the Nile course.

Analytical method and grain-size analysis

Sediment preparation and chemical analysis were carried out by the AEGL lab at Sohag University according to the described referenced methods, but may be slight modifications have been made according to the need and lab conditions. The textural analysis was performed based on the method described by the USDA (1996). Based on particle size (sand, silt, and clay), categories are classified and graphically computed after Shepard (1954).

Mineralogical studies

In the present study, three composite samples, which represent the most texture categories, were selected for identification of bulk mineral composition. Mineralogical studies of the sediments done by Philips X-ray diffractometer technique for random powder slides, its operated condation (45 kV/35 mA), Ni-filtered CuK α radiation, and an automatic slit Semi-quantitative identification of mineral phases is done according to the method after Schultz (1964).

Geochemical studies

Major and trace element contents are measured in 35 samples from the bulk sediment (< 2 mm). Sample dissolution procedure for major and trace element determination follows the methods described by Shapiro and Brannock (1962). The major and minor oxides and 15 trace elements shown in Table 3 were determined using the XRF technique on the whole rock samples. The accuracy of the analyses was reviewed by analyzing reference samples from Green River Shale (SGR-1) and Granite (GS-N).

The importance of this step is to check the homogeneity of samples (Taylor and McLennan, I985; McLennan 1989; Dupre et al. 1996; Nath et al. 2000). Element contents are normalized to values of Average Shale (Av.Sh.) after Turekian and Wedepohl (1961) and Upper Continental Crust (UCC) after Taylor and McLennan (1985), as presented in Table 2.

Table 2 Major oxides (%)composition of the studied modern floodplain sediments along with that of average shale composition
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Results

Grain size distribution (Texture)

The obtained grain size analysis shows that silt > clay > sand. The silt size ranges between 24 and 75% (mean = 60%, sd. = 13); the clay size varies from 9 to 45% (mean = 20, sd. = 8); and the sand size ranges from 4 to 61% (mean = 20%, sd. = 11). Based on sand, silt, and clay percentages, it can be deduced that the MFS sediments are both clayey and sandy silt (Fig. 2; Shepard 1954) (Fig. 3).

Fig. 3
figure 3

Classification of the studied surface soil according to their grain size after Shepard (1954). sC sandy silt, zC silty sand, cS clayey sand, cZ  clayey silt, SZC  Sand silty clay, zS silty sand, sZ sandy silt, C clay, S sand, Z silt

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Bulk mineralogy of MFS samples

Mineral contents of the sediments can be used as a guide to trace the parent rocks of the sediment and can provide useful information about weathering conditions. The occurrence and absence of some mineral contents in the sediments are used to evaluate the resistance of minerals during the weathering processes.

The results of the analysis of non-oriented slides for bulk mineralogy are illustrated in Table 3 and Fig. 4, which show that the most common minerals in the examined samples are quartz (28.63–39.87%), clay minerals (20.51–28.56%), feldspars (10.00–11.49%), and mica (1.09–7.73%), as classic siliciclastic particles occur in smaller amounts. Other less abundant minerals are amphiboles (3.50–6.92%), pyroxene (3.89–5.82%), magnetite (2.55–4.88%), epidote (2.23–3.07%), goethite (1.21–2.88%), zircon (0.25–0.76%), apatite (0.42–0.52%), garnet (0.18–0.31%), and rutile (0.12–0.37%). Calcite (0.98–5.50%), gypsum (1.08–3.45%), and halite (0.59%) indicate they may have different mixed sources.

Table 3 Mineralogical composition of the Nile sediment and soil samples as analyzed by the Rietveld method
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Fig. 4
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Main mineral (in wt. %) contents of floodplain sediments

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Geochemistry

The geochemical analysis of MFS is shown in Tables 2 and 4. The element concentration is compared to the average shale (A.Sh.) of Turekian and Wedepohl (1961) and the upper continental crust (UCC) of Taylor and McLennan (1985) (Figs. 5 and 6).

Table 4 A correlation matrix for major and trace elements; Upper right panel: correlation coefficients. Lower left panel: significant levels of the pairwise linear regression:  − or + significant at 0.01 level, − − or +  + significant at the 0.05 level and − − − or +  +  + significant at 0.001 level
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Fig. 5
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Bar chart shows the relative standard deviation (RSD%) values of the studied variables in the observed surface soil sediments

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Fig. 6
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Boxplot graphs showing the summary of geochemical data for MFS deposits of Major oxides (A), and Trace elements (B)

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Major element geochemistry

The average content of SiO2, Al2O3, Fe2O3, CaO, MgO, Na2O, K2O, TiO2, and MnO in the studied sediments was 56.65, 16.50, 5.47, 3.46, 2.99, 1.39, 1.93, 1.74, and 0.11%, respectively (Table 2). Si is the common constituent of the present MFS samples. It varies from 49.72% (clayey silt class) to 64.41% (sandy silt class), with an average of 56.65%, neatly similar to the average shales of Turekian and Wedepohl (1961) (Fig. 6A). The dominant Si may be due to the prevailing quartz; this is in accordance with the bulk mineralogy findings. SiO2 is positively correlated with the sand fraction and negatively correlated with the mud fraction, indicating that SiO2 increases with increasing particle size. The relation refers to a higher content of quartz in the coarser classes (e.g., Sandy silt class) and a lower content of feldspars.

SiO2 is negatively correlated with most major oxides (Fig. 7A), referring to most of the silica seized in quartz grains (Kampunzu et al. 2005; Deru et al. 2007). The significant negative correlation with Al2O3 characterized the mixing between the siliceous fraction (quartz grains) and the aluminous fraction (Abou El-Anwar and Samy 2013). Al2O3 follows SiO2 in occurances (average = 15.50). Its concentration is, to some extent, higher than that of UCC and Av.Sh (Fig. 6A). The dominance of alumina is due to the clayey-silty nature of the samples. The content of Fe2O3 is high (average 5.47) as compared with UCC. This abundance reflects the occurrence of iron and iron hydroxide minerals. The low amount of K2O (1.93) is due to its mobilization during effective weathering (Cullers 1988). The high content of TiO2 in the MFS’s may be explained mineralogically as due to the presence of rutile and ferromagnesian minerals (see Fig. 4). The positive correlation of TiO2 with several major oxides (e.g., Fe2O3, MgO, and MnO) reflects their association with rutile and ferromagnesian minerals (Table 4).

Fig. 7
figure 7

Harker variation diagram of major (A) and trace elements (B) for MFP sediments. Note that for most elements the variation in elemental abundance is simply related to dilution effect of SiO2. Na2O, K2O, Ba and Sr show linear trend suggesting that feldspar are present in sand size fraction

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In addition, Ti tends to be incorporated within the crystal lattice of clay minerals, where it substitutes for Fe+3 and Al+3 as TiO2 is positively correlated with Al2O3 (r = 0.8263). The relative enrichment of P2O5 (average 0.25%) may be related to the presence of detrital apatite in the sediments and the effects of cultivation and farming practices in the study area. Phosphorus addition to floodplain sediments through fertilizer in the form of calcium phosphate may also be considered an influencing factor in this environment, as indicated by the positive relationship with several minor elements (e.g., Cd, Pb, Cu, V, Ni, and Cr). The MFS’s are enriched in calcium and magnesium.

The concentration of CaO varies between 1.60 and 6.09% (Avg. 3.46), while the concentration of MgO varies between 2.50 and 3.82%. These two oxides are more mobile and easily soluble, and hence they vary depending on the geology of the drainage basin. Ca has a good correlation with Mg (0.3772). The CaO content of the analyzed bulk samples is negatively correlated with silica and alumina (r = − 0.6906 and − 0.7466, respectively), indicating that most of the CaO is controlled by components other than alumina silicate minerals such as gypsum and calcite. Also, it shows a positive correlation with P2O5 (r = 0.7071), which reveals that apatite has an effect on calcium distribution. MgO has a positive relationship with Fe2O3, MnO, and TiO2 (r = 0.3421, 0.3772, and 0.3143, respectively), which reveals that the ferromagnesian minerals have a strong effect on MgO. The negative correlation between MgO and Al2O3 may be due to the concentration of Al2O3 in the silicates and clay minerals.

Trace elements geochemistry

Trace elements concentration in sediments is mainly driven by the weathering of bedrock and catchment areas (Yang and Rose 2005). Table 5 demonstrates the content of trace elements from the MFS sediments and is illustrated by a spidergram normalized to Av.Sh and UCC (Fig. 8).

Table 5 Trace element (ppm) composition of the studied modern floodplain sediments along with that of average shale composition
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Fig. 8
figure 8

Elemental composition of MFP sediments, normalized to average shale (Av.Sh., Turekian and Wedepohl 1961) and the upper continental crust (UCC; Taylor and McLennan 1985a, b)

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The MFS sediments are enriched in HFSE like Zr and Ti. Zr and Ti are commonly formed from melts during magma fractional and crystallization (Feng and Kerrich 1990), resulting in their concentration in felsic rocks. The MFS sediments exhibit a considerable enrichment of Zr and Ti in comparison to Av.Sh and UCC. Zr and Ti are positively correlated (r = 0.6914), which suggests that their relationship is strongly doomed by the heavy mineral phase (zircon and rutile).

The LILE trace elements such as Rb, Th, and Ba show low concentrations (Fig. 6B), Ba (331–467 ppm), and Rb (3–71 ppm). These elements are set mainly in K-feldspars and sheet silicates in the parent rocks. Their lower content relative to Av.Sh. as well as to UCC (Fig. 7), may indicate an intensive weathering process. Th (7–13 ppm) is also showing depletion with respect to Av.Sh (12 ppm) and UCC (10.7 ppm). Sr (178–651 ppm) is enriched when compared with Av.Sh. and UCC. Sr content in MFP sediments is positively correlated with CaO (r = 0.1759); this behavior indicates the contribution of carbonate minerals to their concentrations, as supported by the mineralogical findings (Fig. 4). The concentration of TTE elements such as Cu, Cr, V,Co, Zn, and Sc is mostly high compared to those of Av.Sh and UCC. The correlation between Al2O3 and V, Sc, and Cr for the MFS (r = 0.57, 0.75, and 0.69, respectively) shows that they may be partly related to phyllosilicates (López et al. 2005; Armstrong-Altrin et al. 2014). All transition elements from the study area show good inter-elemental correlations. (e.g., Fe-V = 0.59; Fe-Ni = 0.78; V-Zn = 0.58; Co-Ni = 0.82 Fig. 7B). These elements are likely to be present together in the hydroxide coatings on sediment grains.

The contents of ferromagnesian elements such as Co, Cr, Cu, Ni, V, and Zn in MFS samples show high concentration levels, averaging 28.68, 121.30, 61.27, 55.67, 339.44, and 156.23 ppm, respectively, relative to the values of UCC and Av. Sh (Fig. 7). The basic igneous rocks contain high concentrations of Ferromagnesium, such as Co, Ni, and V (Hiss 1960; Maitre 2002). Also, Cu, Zn, and Cr are mainly related to the weathering of mafic rocks (Gough et al. 1989; Gasser and Dahlgren 1994). The high concentration of these elements in the present MFS suggests that the origin of these elements was mainly lithological and originated in the Ethiopian Highlands. This supposition is supported by the mineralogical studies (the abundance of Ferromagnesium, amphiboles, pyroxene, and epidote).

Discussions

Floodplain sediments distribution and origin

Texturally, the floodplain sediments have dominant fine-grained sediments composed mostly of a variable amount of sand, silt, and clay (Miall 1996). The texture of floodplain sediment also depends on the type of floodplain, which is variable from river to river, and on the distribution of sediments on the floodplain. Large rivers like the Nile develop wide floodplains with significant varieties of facies (Tunbridge 1981), and the mean size of the bulk MFS is shown to be silt. The distal facies of the Nile stream are more clayey as compared to the proximal facies (Willis et al. 1994). The present distribution of the sand fraction in the floodplain sediments shows a general trend of increasing across the desert side on both sides of the Nile and also adjacent to the Nile stream in certain locations. The increase in sand fraction content across the Nile course is influenced by the effective deposition process. Also, the high content of sand particles close to the desert lands may originate from the near desert area putted by the wind action. According to the diagram of log (Na2O/K2O) vs. log (SiO2/Al2O3) after Pettijohn et al. (1972) (Fig. 9A), the MFS’s are classified mainly as greywacke (Fig. 9B), whereas in the log (Fe2O3/K2O) vs. log (SiO2/Al2O3) diagram of Herron (1988), they were identified as shale. The classification suggests that the MFS’s are immature, which is in agreement with the existence of detrital feldspar and with lower K2O/Na2O ratios than UCC but higher than Av.Sh. The values of the K2O/Al2O3 ratio of the present MFP sediments range from 0.10 to 0.13 (average = 0.12), which indicates the prevalence of clays over K-feldspars and micas (Cox et al. 1995; Moosavirad et al. 2011).

Fig. 9
figure 9

Plots; A log (Na2O/K2O) vs. log (SiO2/Al2O3) after Pettijohn et al. (1972) and B log (Fe2O3/K2O) vs. log (SiO2/Al2O3) from Herron (1988)

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Osman (1996) stated that the Nile sediments are composed of silicats such as quartz, plagioclase, alkali feldspar, non-siliacte magnetite, pyrite, and clay minerals such as smectite, kaolinite, chlorite, and mica. Aboughalma (1999) concluded that the Nile Delta sediment mineralogy consists of plagioclase feldspar and alkali feldspar, calcite, and dolomite. He also stated that Nile Delta sediments are composed of smectite, kaolinite, chlorite with rare mica, and iron minerals represented by hematite, goethite, and lepidocrocite. Those findings are similar to our investigation, but we did not find hematite or lepidocrocite, and we found gypsum and halite. According to the sequence of opaque minerals documented above, there is a spatial separation of assemblages of mineral types that can be used to deduce that two main types of sources are connected to the formation of the presented modern floodplain, i.e., the first heavy mineral assemblage of magnetite, goethite, zircon, epidote, and garnet of fooldplain deposits derived from the basement complex in the Eastern Desert and its surrounding rocks (Zaki et al. 2001), and the second heavy mineral assemblage of goethite, pyroxene, hornblend, and mica of foaldplain deposits derived from the Ethiopian highlands. Calcite, gypsum, and halite minerals can originate from the evaporation of irrigation water from relatively saline groundwater sources in some areas (Ibrahim and Emara 2010).

Geochemistry and source-area weathering

Nesbitt and Yong (1982) used CIA = 100*[(Al2O3)/(Al2O3 + CaO* + Na2O + K2O)] to know the intensity of chemical weathering on source rocks. The CIA also gives useful information about paleoclimate in the source area. Calculated CIA for studied samples (ranges from 50.8 to 74.2 and averaging 62.2) compared with UCC (56.9); they are higher but plotted close to the Av.Sh. composition (Fig. 10). These results show that a mild degree of chemical weathering acts on the source area. The wide value range between samples might be due to differences in supply from pre-existing rocks. Plotted CIA values with a ternary diagram (Nesbitt and Young 1984; Fedo et al. 1996; Fig. 10). The MFS shows a linear trend parallel to the Al2O3– CaO-Na2O (Fig. 8). This plotting also shows that the MFS samples are located around the continental crust (UCC) value and refer to vacillating weathering. This weathering trend indicates the leaching of Na and Ca more than K (Nesbitt and Young 1984) and suggests that the present sediments may have come from more than one source area.

Fig. 10
figure 10

Plotting of Modern floodplain samples on ternary diagram after (Nesbitt & Young 1984)

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Sediment maturity

The index of compositional variation (ICV) = (Fe2O3 + K2O + Na2O + CaO + MgO + MnO)/Al2O3, is determined by the source rocks, the maturity of the sediments, and the dominant climatic conditions (Cox et al. 1995). The ICV average value of the MFS is lower than both reported for the Av.Sh. value (ICV = 1.08) and UCC (ICV = 1.20). This shows that the studied sediments are immature and derived from a source area undergoing moderately weathered intensity. In addition, the low values of ICV range from 0.48 to 1.31, with an average of 0.95 in the present study, show a variation between min. and max., which again supports two different behaviors reflected by the studied sediments. Thus, the studied sediments are mainly composed of clay minerals and contain rock-forming minerals, with a dominance of clay minerals with less k-feldspars and mica (Cox et al. 1995).

The SiO2/Al2O3 ratio is important in identifying the textural maturity of sedimentary rocks; sediments that show (> 10) refer to high-recycled and more mature sediments (Bakkiaraj et al. 2010; Wang and Zhou 2013). The SiO2/Al2O3 ratios of the studied sediments (2.65–3.84, with an average of 3.46) are low (< 10), referred to as low mature sediments (Table 3).

Provenance and paleo-environmental conditions

The major and trace elements composition of sediments is increasingly used by number of researchers to deduce the sediments provenance (Al-Juboury and Al-Hadidy 2009; Shadan and Hosseini-Barzi 2013; Jafarzadeh et al. 2014), weathering conditions, and sorting (McLennan et al. 1993). The discriminant function diagram proposed by Roser and Korsch (1988) is used to determine the provenance of sedimentary rocks in many studies (e.g., Hofer et al. 2013; Khanchuk et al. 2013; Vdačný et al. 2013). Applying this diagram (Fig. 11) to identifying the provenance of the studied sediments shows that the source of the studied muddy sediments (sand < 15%) is mostly mafic igneous, with a partial contribution from sedimentary provenance, and the coarser ones are derived mainly from mixed sedimentary and felsic igneous rocks (Fig. 11).

Fig. 11
figure 11

Plots of the investigated modern floodplain sediments on the discriminant diagram (after Roser and Korsch 1988). The discriminant functions are: DF1 = − 1.773*TiO2 + 0.607*Al2O3 + 0.76*Fe2O3 (total) − 1.5*MgO + 0.616*CaO + 0.509*Na2O − 1.224*K2O − 9.09. DF2 = 0.445*TiO2 + 0.07*Al2O3 − 0.25*Fe2O3 (total) −  1.142*MgO + 0.438*CaO + 1.475*Na2O + 1.426*K2O − 6.861

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Plotting of CIA against ICV values (Abou El-Anwar and Samy 2013; Saber et al. 2018; Saber 2020; Fig. 12) shows strongly contrasting ICV values, with the fine-grain class plotted close to the basalitic trend while the course-grained class shows a trend from the granitic one towards the blaslitic one. Plotting sediments on the Th vs. Sc diagram (Fig. 13) indicates that rich sediments (sand > 15%) are derived from felsic rocks and muddy sediments (sand < 15%) are derived from mafic sources. Plotting sediments on the La vs. Th diagram (Fig. 14) shows that the sediment is represented by two clusters: sand-rich samples (> 15%) and more muddy samples (< 15%), which indicate two mixed different sources of the studied sediments.

Fig. 12
figure 12

Plotting of the studies sediments in CIA vs. ICV diagram

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Fig. 13
figure 13

Plotting sediments on Th vs. Sc diagram (Taylor and McLennan 1985a, b). Th/Sc = 1 ratio is that of the upper continental crust (data from Taylor and McLennan 1985a, b)

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Fig. 14
figure 14

La vs. Th plot of modern floodplain sediments (Taylor and McLennan 1985a, b). Two distinct clusters showing two different sources and two linear trends suggesting grain size sorting and silica dilution effects on La-Th behavior in throughout the studied samples

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The Th/Sc ratios range from 0.19 to 4.86 with an average of 1.45 and La/Th from 1.44 to 4.38 with an average of 2.91 (Table 4), which also supported the different mixed sources of modern floodplain sediments. Plotting sediments on a Cr/Th vs. Sc/Th discermanation diagram (Taylor and McLennan 1985, Fig. 15) The analyzed sediments are defined as two clusters. On the one hand, the sand-rich samples (> 15%) referred to felsic provenance. On the other hand, the muddy samples (sand < 15%) have a source referred to as mafic provenance. Thus, Fig. 15 proves that the source rocks, a mixed source of the present-day floodplain sediments, are mixed felsic and mafic rocks.

Fig. 15
figure 15

Plot of Cr/Th versus Sc/Th indicating the controls of various source rocks on sediment geochemistry in the studied rivers. The data of UCC are from Rudnick and Gao (2003)

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The Th/Sc versus Zr/Sc diagram of McLennan et al. (1993) shows that modern floodplain sediments represented by two trends are observed: trend 1 (muddy samples) refers to primary source rocks, suggesting homogeneity and minimal influence of sorting by heavy minerals, and trend 2 (coarser samples) refers to sedimentary processes suggesting heavy minerals brought by sediment recycling and sorting (Fig. 16).

Fig. 16
figure 16

Plotting modern floodplain sediments on Th/Sc vs. Zr/Sc f diagram (McLennan et al. 1993), increase going from mafic to felsic source areas, but the coarser samples show anomalous Zr related to recycling of older sediments. Trend 1 represents sediments derived from igneous rocks and are less affected by sedimentary sorting and recycling. Trend 2 represents heavy mineral accumulation by sedimentary sorting and recycling

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Plotting of modern floodplain sediments La-Th-Sc on the discriminate diagram of Bhatia and Crook (1986, Fig. 17A), Cullers (1994). Samples plotted in a narrow region range from typical granitic gneiss rocks for the sand-rich samples (sand > 15%) to metabasic rocks for the muddy samples (sand < 15%), which indicates that the studded sediments were derived from felsic and mafic rocks. Plotting modern floodplain sediments on the V-Ni-Th*10 ternary diagram (Fig. 17B) also indicates that the studied sediments were inherited from mafic and felsic rocks.

Fig. 17
figure 17

A Plotting modern floodplain sediments on La-Th-Sc, after Bhatia and Crook (1986). B Plotting modern floodplain sediments on V–Ni–Th*10 diagram (after Bracciali et al. 2007)

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Paleo-oxygenation condition

Ratios such as Ni/Co, Cu/Zn, and V/Cr have been used as a second-hand proxy to assess paleo-redox conditions (Jones and Manning 1994). Many authors use the Ni/Co guide as a redox proffer (Brumsack 2006; Nagarajan et al. 2007; Fathy et al. 2023). Jones and Manning (1994) suggested that Ni/Co values under five referred to aerobic conditions, but values higher than five referred to anoxic environments. In the present study, Ni/Co ratios ranged from 1.59 to 3.66 (Table 4), indicating that the floodplain sediments were formed in a well-oxidized environment. The Cu/Zn ratio has been used as an indicator of redox conditions (Hallberg 1976), where high Cu/Zn values refer to a reducing environment and low Cu/Zn values refer to an oxidizing environment. According to the present results, the low Cu/Zn ratios (min = 0.20 and max = 0.78) in the examined sediments (Table 4) indicate stronger oxidizing conditions.

Tectonic setting and source areas

It is well known that the tectonic setting of sediment source rocks has an important effect on the chemical composition of sedimentary rocks. (Bhatia 1985). Detrital sedimentary rocks extruded from different tectonic settings have different geochemical compositions and characteristics determined by different source rocks (Bhatia 1985; Roser and Korsch 1988). Many discriminant diagrams are frequently used in investigations to determine the tectonic setting of sediment source areas (e.g., Bhatia 1983; Roser and Korsch 1986). For the tectonic distinction of high-silica rocks and low-silica rocks, Verma and Armstrong-Altrin (2013a, b) suggested two novel major-element diagrams based on discriminant functions. The present modern floodplain’s chemical analysis was initially partitioned into high-silica and low-silica by setting the chemical composition to 100% on an anhydrous basis. According to the chemical data plotted by Verma and Armstrong-Altrin (2013a, b) diagrams (Fig. 18A and B), the sediments of high silica are scotered in the collision field, while the low silica samples are located in the continental rift field. Accordingly, the investigated fine-grained modern fooldplain (the sediments of high silica) rich in V and Cr and Sc have passive margin geotectonic setting and their source rocks were originated in a collision tectonic setting. While the coarse-grained sediments (the low silica samples) rich in Th, Sr and Ba their source rocks were originated in a continental rift field tectonic setting, reflect two different tectonic settings and source areas are shared in supplying the sediments to the present basin.

Fig. 18
figure 18

Plotting floodplain sediments on discriminant diagrams of Verma and Armstrong-Altrin (2013a, b). A High-silica and B low-silica clastic sediments of the study area. The subscripts m1 and m2 in DF1 and DF2 are based on loge- and log ratios of major elements.. Arc—island or continental arc; Rift—continental rift; Col—collision. The discriminant functions equations are: 1-For High-silica [(SiO2)adj = N 63%– ≤ 95%]: DF1(Arc–Rift–Col)m1 = − 0.263 * In(TiO2/SiO2)adj) + 0.604 * In(Al2O3/SiO2)adj)–1.725 * In(Fe2O3t/SiO2)adj) + 0.660 * In(MnO/SiO2)adj) + 2.191 * In(MgO/SiO2)adj) + 0.144 * In(CaO/SiO2)adj)–1.304 * In(Na2O/SiO2)adj) + 0.054 * In(K2O/SiO2)adj)–0.330 * In(P2O5/SiO2)adj) + 1.588, DF2(Arc–Rift–Col)m1 = – 1.196 * In(TiO2/SiO2)adj) + 1.604 * In(Al2O3/SiO2)adj) + 0.303 * In(Fe2O3t/SiO2)adj) + 0.436 * In(MnO/SiO2)adj) + 0.838 * In(MgO/SiO2)adj)–0.407 * In(CaO/SiO2)adj) + 1.021 * In(Na2O/SiO2)adj)–1.706 * In(K2O/SiO2)adj)–0.126 * In(P2O5/SiO2)adj)–1.068. 2-For Low-silica [(SiO2)adj = N 35%– ≤ 63%]: DF1(Arc–Rift–Col)m2 = 0.608 * In(TiO2/SiO2)adj)–1.854 * In(Al2O3/SiO2)adj)–0.299 * In(Fe2O3t/SiO2)adj)–0.0550 * In(MnO/SiO2)adj) + 0.120 * In(MgO/SiO2)adj) + 0.149 * In(CaO/SiO2)adj)–1.510 * In(Na2O/SiO2)adj) + 1.941 * In(K2O/SiO2)adj)–0.003 * In(P2O5/SiO2)adj)–0.294, DF2(Arc–Rift–Col)m2 = – 0.554 * In(TiO2/SiO2)adj)–0.995 * In(Al2O3/SiO2)adj) + 1.765 * In(Fe2O3t/SiO2)adj)–1.391 * In(MnO/SiO2)adj)–1.034 * In(MgO/SiO2)adj) + 0.225 * In(CaO/SiO2)adj) + 0.713 * In(Na2O/SiO2)adj)–0.330 * In(K2O/SiO2)adj) + 0.637 * In(P2O5/SiO2)adj)–3.631

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Environmental application of the present work

The present work uses sedimentology, mineralogy, and geochemistry studies of Nile floodplain sediments to provide information, possible interpretations, and their environmental application.

In terms of desertification,The term “soil desertification” refers to the deterioration of soil in dry, semi-arid, and sub-humid regions as a result of numerous factors, including climatic change and human activity. Soil degradation problems in Egypt prevail, and protection of the current agricultural soils, which are located in the former floodplain and have been subject to many programs for land reclamation by the Egyptian government over the past few decades, has emerged as the most important concern. Egypt is primarily a desert country because more than 97% of its total territory is covered by desert, with the remaining 3% located in the Nile Valley and Delta. The population of this small area is 105 million. This intense population strain exacerbates already existing environmental issues and hastens processes of desertification brought on by either climate or anthropogenic reasons.According to the Egyptian National Action Program to Combat Desertification (UNCCD, 2005), civilization, salt, the use of polluting products, fertilizer products, pesticides, and sand encroachment are the main causes of desertification in Egypt.Ethiopian Highlands are subjected to soil deterioration, including erosion and declining fertility, which is a known issue (e.g., Van de Wauw et al. 2008). According to Alemayehu (2003), 80–85% of Ethiopians are employed in agriculture, and as farming is intensified as a result of factors including population growth and the necessity to enhance food production during droughts, the soil’s quality is deteriorating (Devereux 2000). The three main factors to take into account when analyzing sediments and their effects on the environment are their grain-size distribution, mineralogical composition, and chemical composition.

As a starting point in the current endeavor to clarify the environmental fineness of the Nile floodplain, the grain size distribution, mineralogy composition, and trace metal constituents of the sediments have been examined. The distribution of sand fractions on the Nile floodplain sediments shows a general increase: (1) in the direction of the desert edges on either side of the Nile river; (2) adjacent to the Nile stream in certain locations. The deposition Nile floodplain sediments may have some control over this distribution of increased sand fraction content near the Nile stream. Increases in sand content may be caused by wind action from the nearby desert area.More over, the closure of the Aswan High Dam resulted in a reduction in sediment flows. This is due to the continuous input of dry wadi and eolian dunes, which increased the mixing between fluvial and wind-blown sands. The heavy mineral assemblage of the present Nile floodplain deposits proved the derivation of the floodplain deposits from aeolian sand from the pre-formations forming Pliocene–Pleistocene Nile terraces present around the area of study.

The occurrences of calcite, gypsum, and halite minerals can be used as salinity indicators. These minerals may be formed by the evaporation of irrigation water from relatively saline groundwater sources in some areas, by the relics of inorganic fertilizers distributed on the surface, or by the sand accompanying the winds coming from the near desert areas. The agricultural activities in the Nile River basin influence the floodplain sediments of the Nile valley. The higher Cd and Zn contents could be related to anthropogenic sources. Thus, desertification in the Nile floodplain in the Sohag area may be due to either climatic or human factors such as salinity, pollution, fertilizer use, and sand encroachment.

Conclusions

Sedimentology, mineralogy and geochemistry studies come to the following conclusions.

  • The sediments of the Nile floodplain are composed mainly of silt (26–77%), clay fraction (7–44%), and sand content (3–63%), and their texture is classified as clayey silt.

  • Based on their geochemistry, the sediments are classified as greywacke to shale.

  • Two main heavy mineral assemblages are recognized: the first, represented by magnetite, goethite, zircon, epidote, and garnet, indicates a basement complex in the Eastern Desert and its surrounding rock source; the second, represented by goethite, pyroxene, hornblend, and mica, reflect derivation from the Ethiopian highlands.

  • The Nile sediments are immature and formed due to moderate degree and nonsteady-state chemical weathering in the source area.The sources of present floodplain sediments are different, where fine sediments are mostly derived from mafic igneous rocks with a partial contribution from sedimentary rocks, while the coarser ones are derived mainly from sedimentary rocks with a felsic igneous one.

  • Two different tectonic settings are shared in supplying the sediments to the present basin: the high silica modern fooldplain sediments (coarse-grained) reflect collision tectonic setting source area, and the low silica sediments (fine-grained) reflect continental rift tectonic setting

  • The study found that the studied area’s desertification may be caused by both climate and human reasons, including salinity, fertiliser use, pollution, and sand encroachment.

  • The current results can help decision-makers take the right measures to preserve the region from the dangers of desertification by enacting laws that reduce pollutants and the use of organic fertilizers, as well as finding solutions to sand encroachment. Also the present studies opens the way for future comprehensive studies to compare the present findings with those from other regions to get a more broader perspective on sediment dynamics and their environmental impact.