# REE Geochemistry of Euphrates River, Turkey

Authors: Leyla Kalender; Gamze Aytimur
Journal: Journal of Chemistry
 (2016)

---

## Abstract

The study area is located on the Euphrates River at 38°41°32.48′′N–38°14′24.10′′N latitude and 39°56′4.59′′E–39°8°13.41′′E longitude. The Euphrates is the longest river in Western Asia. The lithological units observed from the bottom to the top are Permo-Triassic Keban Metamorphites, Late Cretaceous Kömürhan Ophiolites, Upper Cretaceous Elazığ Magmatic Complex, Middle Eocene Maden Complex and Kırkgeçit Formation, Upper Pliocene and Lower Eocene Seske Formation and Upper Miocene, Pliocene Karabakır and Çaybağı Formations, Palu Formation, and Holocene Euphrates River sediments. The geochemical studies show that87Sr/86Sr and 143Nd/144Nd isotopic compositions in the Euphrates River bank sediments are 0.7053, 0.7048, and 0.7057 and 0.512654, 0.512836, and 0.512775, respectively. These values indicate mixing of both carbonate-rich shallow marine sediment and felsic-mafic rocks from Elazığ Magmatic Complex into the stream sediments. The positive ε
N
d
(
0
) values (0.35, 3.9, and 2.7) are higher downstream in the studied sediments due to weathering of the mafic volcanic rocks. The chondrite, NAS, and UCC normalized patterns show that the REE compositions of the Euphrates River sediments are higher than chondrite composition but close to NAS and UCC. The river sediments in the tectonic zone and the weathered granodioritic rocks of the Elazığ Magmatic complex affect upstream water compositions.


---

## Body

## 1. Introduction

A number of researchers have studied Nd-Sr isotopic and trace element geochemistry of river sediments and soils as tracers of clastic sources. The geochemical characterizations and Sr-Nd isotopic fingerprinting of sediments in any fluvial system can be done using radiogenic isotopic compositions [1–5]. Rare earth elements (REEs) compositions have been studied in stream sediments [6–8] and in chemical weathering of drainage systems [9–12]. A number of researchers have studied REE composition of both river sediments and river water and discovered that heavy REE concentration is higher in the river sediments than in suspended matter in river water. They also indicated that shale, Upper Continental Crust, and chondrite normalized REE patterns showed that chemical weathering from source rocks in the continental crust, erosion, and terrigenous fluviatile sediment sources can be distinguished using the REE compositions of rivers [13–18]. Leybourne et al. [19] indicated that Ce and Eu can be redox sensitive and attributed to determination of redox conditions. Yang et al. [8] stated that source rock composition is a more important factor affecting REE composition than weathering processes. There are fewer studies on the Euphrates River. Kalender and Bölücek [20] studied the stream sediments in the north Keban Dam Lake in the Eastern Anatolian district and demonstrated that more REEs are transported with Fe and Mn rich oxides and fine size fraction sediments (e.g., clay minerals) via adsorption. Kalender and Çiçek Uçar [21] indicated that the calculated enrichment factor values of the heavy REE are more than those of light REE in the Geli stream sediments. Geli stream is a tributary of the Euphrates River. Rivers carry the weathered rock products from the continents to the dam lakes, natural lakes, and the sea. Thus, this study focuses on the REE concentrations in river bank sediments from the initial point of the Euphrates River (10 kilometers upstream of Keban Dam) to Karakaya Dam Lake. In order to evaluate distribution of REE along the flowing direction of the Euphrates River, the sediment sources and lithological controls were identified using Upper Continental Crust (UCC), North American Shale (NAS), and Chondrite (Ch) normalized REE patterns (all average values taken from [8, 22–25]). Goldstein and Jacobsen [13] studied REE compositions in river water, and major rivers have LREE enriched patterns relative to the NAS, and negative Ce anomalies occur at high pH. This paper firstly presents REE concentrations and includes source rock composition of the Euphrates River sediments and waters.


## 2. Geology

The Euphrates River is located in the Eastern Anatolian district in Turkey and is located on the active tectonic zone of the East Anatolian fault zone. The East Anatolian fault zone is seismically one of the most active regions in the world and is located within the Mediterranean Earthquake Zone, which is a complicated deformation area that was formed by the continental collision between the African-Arabian and Eurasian continents. These deformations involve thrust faults, suture zones, and active strike slip and normal faults, as well as basin formations arising from these faults. The Euphrates River is located on the East Anatolian fault zone and is formed by the mixing of the Karasu River and Murat River 10 kilometers upstream of the Keban Dam. According to Frenken [27], the Euphrates River length is 1100 km from Palu to the Red Sea (Figures 1(a) and 1(b)). The studied sediments were sampled along approximately 50 kilometers of the Euphrates River length. The main stratigraphic units found in the Euphrates River basin range from the Permo-Triassic Keban Metamorphites to Plio-Quaternary Palu Formation (Figure 1(b)). The Keban Metamorphites outcrop on both right and left banks of the Euphrates River. Considering the regional scale, the Keban Metamorphites are represented by marble, recrystallized limestone, calc-schist, metaconglomerate, and calc-phyllite in the study area [28]. Additionally, in the study area, the Upper Cretaceous Elazığ Magmatic Complex consists of volcanic rocks (basalt, andesite, pillow lava, dacite, and volcanic breccia), subvolcanic rocks (aplite, microdiorite, and dolerite), and plutonic rocks (diorite, tonalite, granodiorite, granite, and monzonite). The magmatic rocks are overlain by recrystallized limestone of the Permo-Triassic Keban Metamorphites [29]. The Late Cretaceous Kömürhan Ophiolites are part of the southeast Anatolian ophiolite belt which are formed in a suprasubduction zone within the southern Neo-Tethys [30]. The Kömürhan Ophiolites consist of dunite, layered and isotropic gabbros, plagiogranite, sheet dyke complex, andesitic and basaltic rocks, and volcanosedimentary rocks. The unit is observed in the Karakaya Dam Lake area (Figure 1(b)). Upper Paleocene and Lower Eocene massive limestones are named the Seske Formation which is characterized by interbedded clastic and carbonate rocks. The stratigraphic position of the Seske Formation indicates the extent of how Neo-Tethys was controlled by the tectonic and topographic features of the region during the Eocene [31, 32]. The Seske Formation is observed along the Karakaya Dam Lake (Figure 1(b)). Middle Eocene Maden Complex is composed of basaltic and andesitic rocks and limestone, conglomerates, sandstones, and mudrocks (marl) [29, 33–35]. Middle Eocene Kırkgeçit Formation consists of marine conglomerates, marls, and limestone from the bottom to the top [36]. The Alibonca Formation was deposited after closure of the Neo-Tethys Ocean in Mesozoic time. The unit is composed of sandy limestone and marls which are observed in the Keban Dam Lake area [37] (Figure 1(b)). Upper Miocene-Pliocene Karabakır and Çaybağı Formations consist of sandstone, mudrock, marls, tuff, and basaltic rocks [36]. The units are observed in the northeast of the Keban Dam Lake (Figure 1(b)). The Çaybağı Formation is named by Türkmen [38] at the Çaybağı township in the east of Elazığ. Pliocene-Quaternary units are named the Palu Formation by Kerey and Türkmen [39]. The units consist of quaternary alluvial and fluvial deposits along the level bank of the Murat River which is the initial point of the Euphrates River (Figures 1(a) and 1(b)).Figure 1
(a) Location map. (b) Geology map of the Euphrates River and the sampling sites (from 1 to 90, the geology map was modified from Herece et al. [26]).
(a)
(b)


## 3. Analytical Methods

### 3.1. Climatic Information

Maximum flows of the Euphrates River occurred from February through April, whereas minimum flows occurred from August through October. The annual mean rainfall during that period was 372 mm, and the air temperature varied between 15.21°C (Elazığ) and 16.31°C (Malatya) with the highest and the lowest temperature of 34°C and minus 10, respectively, between 1992 and 2001. The continental climate of the Euphrates Basin is a subtropical plateau climate (data was taken from reports by the Elazığ Meteorology Department). The Euphrates River sediment samples were collected in September, the period of minimum flow of the Euphrates River water. It is also good to take into consideration the effect on chemical compositions of the river bed sediment of processes erosion of the earth’s surface. The sediment samples were taken from locations close to the center of the river bed in consideration of the erosional process and chemical composition of the river bed sediments.


### 3.2. Sampling Sites

In this study, directing studies could not be performed in advance of the development of sample taking methods and suitable particle size and chemical analysis methods. Ninety river sediments and water samples were taken from the right side of the river bed along the direction of the river water flow because it is suitable for sampling of river bed morphology (Figure1(b)).


### 3.3. Sample Preparing for Analysis

The samples were taken in September, when the water flow rate was low. In order to prevent the existence of particles in the sediment samples that were too large, the samples were sifted through sieve with hole diameter of 2 mm (BS10 mesh) so as to obtain the suitable particle sizes. 2 Kg of the river sediment samples was taken at 250–500 m intervals along the Euphrates River (from 10 kilometers upstream of the Keban Dam to Karakaya Dam, 50 kilometers) and placed into plastic bags, numbered, and dried at room temperature. After drying, the samples were sifted to different sieve dimensions in order to determine the particle size fractions suitable for analysis (−200 mesh). In the study of some metals and REE concentrations in sediments, many researchers prefer the grain size of fine-medium sand to silt (−74μm) as it shows very high concentrations, higher than −80 mesh (−180 μm) [8, 21, 40, 41]. In order to minimize the grain size dependencies of heavy metals, concentrations of −75 μm fraction, representing medium fine sand to silt, were used in the present study. Mechanical wet sieving was performed to separate the −74 μm sediment fraction from the bulk samples. Fifteen to twenty grams of each sample was freeze dried for 8 and 9 hours. The sieved fractions were placed in clean porcelain bowls and dried at room temperature.


### 3.4. Chemical Analysis

Elazığ Magmatic Complex includes zirconium- and titanium-bearing minerals [30]. As commonly known, zirconium- and titanium-bearing minerals contain amounts of REE. This method was preferred due to its convenience for the decomposition of the silicate minerals using HF. HF is an efficient disintegration agent used for the decomposition of zirconium silicate and apatite source from granitoids in nature. This decomposition method causes the loss of silica as SiF4 and a part of titanium as TiF4. Bulk samples were ground and sieved through 200-mesh (about 0.074 mm pore size) stainless steel sieve for chemical analysis. 0.5 g of each sediment sample was leached with 90 mL HCl-HNO3-HF at 95°C for 1 hour, diluted to 150 mL, and then analyzed by ICP-OES. The extraction method used by Saito et al. [42] was used to obtain the maximum REE concentration at 9.95 mL 0.01–1 m nitric acid aqueous solution (pH < 4). Standard DS5 was used for the sediment analyses. The sediment samples were analyzed for REE in Acme Analytical Laboratories Ltd., Canada, by Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES). The river water samples have less than 0.1% total dissolved solids, and these analyses were used by ICP-OES at Bureau Veritas environmental lab, Maxxam Analytics. The isotopic measurements were made at the Middle East Technical University (Ankara, Turkey) following the protocol of Köksal and Göncüoğlu [43]. TLM-ARG-RIL-02 methods were adopted. An 80 mg aliquot was taken for analysis of Sr and Nd isotope ratios. The samples were dissolved in beakers in a 4 mL 52% HF at 160°C on the hotplate along four days. The samples were dried on the hotplate using 2.5 N HCl and 2 mL bis(ethylhexyl) phosphate using Bio-Rad AG50 W-X8, 100–200 mesh, and chemical seperation of Sr ionic chromatographic columns was prepared. After chemical separation of Sr, REE fractionation was collected using 6 N HCl. Sr isotopes were measured using a single Ta-activator with Re filament and 0.005 N H3PO4 [44]. 87Sr/86Sr ratios were corrected for mass fractionation by normalizing to 86Sr/88Sr = 0.1194, and strontium standard (NBS 987) was measured more than 2 times. The chemical separation of Nd from REE was made in a teflon column using 0.22 N HCl and 2 mL bis(ethylhexyl) phosphate. 143Nd/144Nd data were normalized by 146Nd/144Nd = 0.7219, and neodymium standard (0.511848
±
5) was measured more than 2 times.


## 3.1. Climatic Information

Maximum flows of the Euphrates River occurred from February through April, whereas minimum flows occurred from August through October. The annual mean rainfall during that period was 372 mm, and the air temperature varied between 15.21°C (Elazığ) and 16.31°C (Malatya) with the highest and the lowest temperature of 34°C and minus 10, respectively, between 1992 and 2001. The continental climate of the Euphrates Basin is a subtropical plateau climate (data was taken from reports by the Elazığ Meteorology Department). The Euphrates River sediment samples were collected in September, the period of minimum flow of the Euphrates River water. It is also good to take into consideration the effect on chemical compositions of the river bed sediment of processes erosion of the earth’s surface. The sediment samples were taken from locations close to the center of the river bed in consideration of the erosional process and chemical composition of the river bed sediments.


## 3.2. Sampling Sites

In this study, directing studies could not be performed in advance of the development of sample taking methods and suitable particle size and chemical analysis methods. Ninety river sediments and water samples were taken from the right side of the river bed along the direction of the river water flow because it is suitable for sampling of river bed morphology (Figure1(b)).


## 3.3. Sample Preparing for Analysis

The samples were taken in September, when the water flow rate was low. In order to prevent the existence of particles in the sediment samples that were too large, the samples were sifted through sieve with hole diameter of 2 mm (BS10 mesh) so as to obtain the suitable particle sizes. 2 Kg of the river sediment samples was taken at 250–500 m intervals along the Euphrates River (from 10 kilometers upstream of the Keban Dam to Karakaya Dam, 50 kilometers) and placed into plastic bags, numbered, and dried at room temperature. After drying, the samples were sifted to different sieve dimensions in order to determine the particle size fractions suitable for analysis (−200 mesh). In the study of some metals and REE concentrations in sediments, many researchers prefer the grain size of fine-medium sand to silt (−74μm) as it shows very high concentrations, higher than −80 mesh (−180 μm) [8, 21, 40, 41]. In order to minimize the grain size dependencies of heavy metals, concentrations of −75 μm fraction, representing medium fine sand to silt, were used in the present study. Mechanical wet sieving was performed to separate the −74 μm sediment fraction from the bulk samples. Fifteen to twenty grams of each sample was freeze dried for 8 and 9 hours. The sieved fractions were placed in clean porcelain bowls and dried at room temperature.


## 3.4. Chemical Analysis

Elazığ Magmatic Complex includes zirconium- and titanium-bearing minerals [30]. As commonly known, zirconium- and titanium-bearing minerals contain amounts of REE. This method was preferred due to its convenience for the decomposition of the silicate minerals using HF. HF is an efficient disintegration agent used for the decomposition of zirconium silicate and apatite source from granitoids in nature. This decomposition method causes the loss of silica as SiF4 and a part of titanium as TiF4. Bulk samples were ground and sieved through 200-mesh (about 0.074 mm pore size) stainless steel sieve for chemical analysis. 0.5 g of each sediment sample was leached with 90 mL HCl-HNO3-HF at 95°C for 1 hour, diluted to 150 mL, and then analyzed by ICP-OES. The extraction method used by Saito et al. [42] was used to obtain the maximum REE concentration at 9.95 mL 0.01–1 m nitric acid aqueous solution (pH < 4). Standard DS5 was used for the sediment analyses. The sediment samples were analyzed for REE in Acme Analytical Laboratories Ltd., Canada, by Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES). The river water samples have less than 0.1% total dissolved solids, and these analyses were used by ICP-OES at Bureau Veritas environmental lab, Maxxam Analytics. The isotopic measurements were made at the Middle East Technical University (Ankara, Turkey) following the protocol of Köksal and Göncüoğlu [43]. TLM-ARG-RIL-02 methods were adopted. An 80 mg aliquot was taken for analysis of Sr and Nd isotope ratios. The samples were dissolved in beakers in a 4 mL 52% HF at 160°C on the hotplate along four days. The samples were dried on the hotplate using 2.5 N HCl and 2 mL bis(ethylhexyl) phosphate using Bio-Rad AG50 W-X8, 100–200 mesh, and chemical seperation of Sr ionic chromatographic columns was prepared. After chemical separation of Sr, REE fractionation was collected using 6 N HCl. Sr isotopes were measured using a single Ta-activator with Re filament and 0.005 N H3PO4 [44]. 87Sr/86Sr ratios were corrected for mass fractionation by normalizing to 86Sr/88Sr = 0.1194, and strontium standard (NBS 987) was measured more than 2 times. The chemical separation of Nd from REE was made in a teflon column using 0.22 N HCl and 2 mL bis(ethylhexyl) phosphate. 143Nd/144Nd data were normalized by 146Nd/144Nd = 0.7219, and neodymium standard (0.511848
±
5) was measured more than 2 times.


## 4. Results

### 4.1. Nd-Sr Isotope Compositions of the Euphrates River Sediments

REE concentrations of the Euphrates River sediments from Keban Dam to Karakaya Dam are presented in Table1. The result of isotopic composition of the studied sediments and those from different origin, summarized statistical values, and REE compositions of the Mississippi and Amazon River sediments are presented in Table 1. The 75 μm (200 mesh) size fraction from the Euphrates River sediment samples (A43, A61, and A89) was analyzed for 87Sr/86Sr and 143Nd/144Nd ratios (Figure 2 and Table 1). The study shows that 87Sr/86Sr and 143Nd/144Nd isotopic compositions have range of 0.7053, 0.7048, and 0.7057 and 0.512654, 0.512836, and 0.512775, respectively. ε
N
d
(
0
) values were calculated using(1)
ε
Nd
0
=
Nd
143
/
Nd
144
Measured
0.512636
-
1
×
10
4 (see [48, 49]).Table 1
Summary statistical values of REE from Euphrates River sediments. Density values (g/cm3) taken from Gupta and Krishnamurthy [45]. ∗Sediments from Sholkovitz [46]. Calculated εNd and 1000/Sr data from Martin and McCulloch [4]; ∗
∗Burke et al. [1]; ∗
∗
∗Bussy [2]; ∗
∗
∗
∗Akgül et al. [47], +Mensel et al. [48].
(a)
LREE
N
=
90
Density
Max./min. values
Euphrates River (ppm)
∗Mississippi River
∗Amazon River
HREE
N
=
90
Density
Max./min. values
Euphrates River (ppm)
∗Mississippi River
∗Amazon River
La
6.14
3.4/15.9
8.57
60.8
349
Tb
8.23
0.18/0.47
0.33
—
—
Ce
8.16
7.5/34.4
18.11
125.4
707
Dy
8.55
0.63/3.12
2.17
7.46
39.7
Pr
6.77
0.88/4.46
2.22
—
—
Ho
8.79
0.17/0.63
0.43
—
—
Nd
7.00
5.39/12.1
7.70
56.4
355
Er
9.06
0.43/1.67
1.20
4.94
21.7
Sm
7.52
0.82/4.05
2.14
—
—
Tm
9.32
0.05/0.28
0.17
—
—
Eu
5.24
0.23/0.82
0.57
2.11
10.9
Yb
6.96
0.29/1.59
1.11
3.94
20.5
Gd
7.90
0.44/3.65
2.20
9.86
46.3
Lu
9.84
0.02/0.23
0.15
0.47
3.02
Mean
5.93
—
—
Mean
0.79
—
—
St. deviation
6.18
—
—
St. deviation
0.74
—
—
(b)
The result of isotopic composition of the studied sediments and some examples in the world
Sample code
143Nd/144Nd
87Sr/86Sr
εNd (0)
1000/Sr
A43
0.512654
0.7053
0.35
16.1
A61
0.512836
0.7048
3.9
13.74
A89
0.512775
0.7057
2.7
13.17
Basaltic soil+
0.511783
0.705603
2.26
3.9
Metased. soil+
0.512501
0.709646
−2.67
6.57
Metagreywackes+
0.512847
0.705374
4.08
2.49
Sediments+
0.512805
0.704583
3.26
4.0
∗
∗Jurassic-Cretaceous sediments
—
0.707–0.708
—
—
∗
∗
∗Arve River sediments
—
0.728
—
Related to Mont-Blanc granite
0.704
—
Carbonate-rich rocks
∗
∗
∗
∗Elazığ Magmatites Upper Cretaceous
0.512414–0.512851
0.706022–0.708451
7.5
Diorites and granites
—
3.5
—Figure 2
Distribution of REE and the determined sample sites (A43, A61, and A89) for87Sr/86Sr and 143Nd/144Nd isotopic analysis from the Euphrates River sediments.The calculatedε
N
d
(
0
) values have range of 0.35, 3.9, and 2.7. Table 1 shows the result of the radiogenic isotope compositions in the Euphrates River sediments, 87Sr/86Sr and 143Nd/144Nd, and calculated ε
N
d
(
0
) data of the sediments from different origins. The isotope compositions ratios of 143Nd/144Nd and 87Sr/86Sr in the Euphrates River sediments suggest that the REE pattern of river sediments changes systematically with the compositions of the rocks in the drainage area. The range of 87Sr/86Sr ratios found in the Euphrates River sediments may be explained using metagreywackes and sediments (0.705374, 0.704835, and 0.704583, resp.) according to Table 1. The calculated 1000/Sr ratios are 16.1 (A43), 13.17 (A61), and 13.74 (A89), and Nd values are 5.98 (A43), 6.45 (A61), and 8.40 (A89) ppm, while La concentrations are 9.8 (A43), 7.8 (A61), and 4.5 (A89) ppm. The comparison with 1000/Sr and La values indicated that the weathering of felsic igneous rocks decreases downstream of the Euphrates River, while it increases in the mafic igneous rocks.


### 4.2. REE Results of the Euphrates River Sediments

Large variations are observed in the distribution of the REE in the Euphrates River sediments (Table1). La concentrations range from 3.4 to 15.9 ppm, while Lu concentrations range from 0.02 to 0.23 ppm. The concentrations of the light REE are 7.5 times higher than heavy REE concentrations. Ce concentrations range from 7.5 to 34.4 ppm. Figure 2 plots indicate that the concentrations of La and Ce are the highest along the flowing direction of the Euphrates River. The concentrations of the REE at the A37 sample site decrease because of the next thrust zone. Thus, the circulation of mixing waters possibly influenced the concentrations of REE in the studied river sediments. The REE plots for the Euphrates River sediments in this study exhibit a small degree of variation. The abundance of the REE in the river sediments is probably due to the mineralogic characterizations of the regional rocks. Figure 2 plots can be explained to mean that the variations of the light REE along the flowing direction are higher until A51 sample site, except for A34, A35, A36, and A37 sites. The heavy REE concentrations increase from A51 sample site to A90 because of the mineralogic characterizations of mafic volcanic and metaophiolitic rocks.


### 4.3. REE Results of the Euphrates River Water

REE concentrations of the Euphrates River waters are presented in Table3. The Amazon, Indus, Mississippi, and Ohio Rivers water data from Goldstein and Jacobsen [13] are also presented in Table 3. La concentrations have range from 0.02 to 2.63 ppb, and Ce concentrations have range from 0.12 to 5.43 ppb. The highest Ce and La values in the water samples are observed at the A34 site, and Pr, Sm, Gd, Dy, Er, and Yb have the highest values, 0.07, 0.07, 0.07, 0.06, 0.03, and 0.03 ppb, respectively, at the same site. However, the lowest Ce and La concentrations in the studied sediments were observed at the same site. The results indicate that the circulation of mixing water along the tectonic zones can be a much more important factor on the absolute abundance of the REE in river sediments than weathering of the regional rocks.


## 4.1. Nd-Sr Isotope Compositions of the Euphrates River Sediments

REE concentrations of the Euphrates River sediments from Keban Dam to Karakaya Dam are presented in Table1. The result of isotopic composition of the studied sediments and those from different origin, summarized statistical values, and REE compositions of the Mississippi and Amazon River sediments are presented in Table 1. The 75 μm (200 mesh) size fraction from the Euphrates River sediment samples (A43, A61, and A89) was analyzed for 87Sr/86Sr and 143Nd/144Nd ratios (Figure 2 and Table 1). The study shows that 87Sr/86Sr and 143Nd/144Nd isotopic compositions have range of 0.7053, 0.7048, and 0.7057 and 0.512654, 0.512836, and 0.512775, respectively. ε
N
d
(
0
) values were calculated using(1)
ε
Nd
0
=
Nd
143
/
Nd
144
Measured
0.512636
-
1
×
10
4 (see [48, 49]).Table 1
Summary statistical values of REE from Euphrates River sediments. Density values (g/cm3) taken from Gupta and Krishnamurthy [45]. ∗Sediments from Sholkovitz [46]. Calculated εNd and 1000/Sr data from Martin and McCulloch [4]; ∗
∗Burke et al. [1]; ∗
∗
∗Bussy [2]; ∗
∗
∗
∗Akgül et al. [47], +Mensel et al. [48].
(a)
LREE
N
=
90
Density
Max./min. values
Euphrates River (ppm)
∗Mississippi River
∗Amazon River
HREE
N
=
90
Density
Max./min. values
Euphrates River (ppm)
∗Mississippi River
∗Amazon River
La
6.14
3.4/15.9
8.57
60.8
349
Tb
8.23
0.18/0.47
0.33
—
—
Ce
8.16
7.5/34.4
18.11
125.4
707
Dy
8.55
0.63/3.12
2.17
7.46
39.7
Pr
6.77
0.88/4.46
2.22
—
—
Ho
8.79
0.17/0.63
0.43
—
—
Nd
7.00
5.39/12.1
7.70
56.4
355
Er
9.06
0.43/1.67
1.20
4.94
21.7
Sm
7.52
0.82/4.05
2.14
—
—
Tm
9.32
0.05/0.28
0.17
—
—
Eu
5.24
0.23/0.82
0.57
2.11
10.9
Yb
6.96
0.29/1.59
1.11
3.94
20.5
Gd
7.90
0.44/3.65
2.20
9.86
46.3
Lu
9.84
0.02/0.23
0.15
0.47
3.02
Mean
5.93
—
—
Mean
0.79
—
—
St. deviation
6.18
—
—
St. deviation
0.74
—
—
(b)
The result of isotopic composition of the studied sediments and some examples in the world
Sample code
143Nd/144Nd
87Sr/86Sr
εNd (0)
1000/Sr
A43
0.512654
0.7053
0.35
16.1
A61
0.512836
0.7048
3.9
13.74
A89
0.512775
0.7057
2.7
13.17
Basaltic soil+
0.511783
0.705603
2.26
3.9
Metased. soil+
0.512501
0.709646
−2.67
6.57
Metagreywackes+
0.512847
0.705374
4.08
2.49
Sediments+
0.512805
0.704583
3.26
4.0
∗
∗Jurassic-Cretaceous sediments
—
0.707–0.708
—
—
∗
∗
∗Arve River sediments
—
0.728
—
Related to Mont-Blanc granite
0.704
—
Carbonate-rich rocks
∗
∗
∗
∗Elazığ Magmatites Upper Cretaceous
0.512414–0.512851
0.706022–0.708451
7.5
Diorites and granites
—
3.5
—Figure 2
Distribution of REE and the determined sample sites (A43, A61, and A89) for87Sr/86Sr and 143Nd/144Nd isotopic analysis from the Euphrates River sediments.The calculatedε
N
d
(
0
) values have range of 0.35, 3.9, and 2.7. Table 1 shows the result of the radiogenic isotope compositions in the Euphrates River sediments, 87Sr/86Sr and 143Nd/144Nd, and calculated ε
N
d
(
0
) data of the sediments from different origins. The isotope compositions ratios of 143Nd/144Nd and 87Sr/86Sr in the Euphrates River sediments suggest that the REE pattern of river sediments changes systematically with the compositions of the rocks in the drainage area. The range of 87Sr/86Sr ratios found in the Euphrates River sediments may be explained using metagreywackes and sediments (0.705374, 0.704835, and 0.704583, resp.) according to Table 1. The calculated 1000/Sr ratios are 16.1 (A43), 13.17 (A61), and 13.74 (A89), and Nd values are 5.98 (A43), 6.45 (A61), and 8.40 (A89) ppm, while La concentrations are 9.8 (A43), 7.8 (A61), and 4.5 (A89) ppm. The comparison with 1000/Sr and La values indicated that the weathering of felsic igneous rocks decreases downstream of the Euphrates River, while it increases in the mafic igneous rocks.


## 4.2. REE Results of the Euphrates River Sediments

Large variations are observed in the distribution of the REE in the Euphrates River sediments (Table1). La concentrations range from 3.4 to 15.9 ppm, while Lu concentrations range from 0.02 to 0.23 ppm. The concentrations of the light REE are 7.5 times higher than heavy REE concentrations. Ce concentrations range from 7.5 to 34.4 ppm. Figure 2 plots indicate that the concentrations of La and Ce are the highest along the flowing direction of the Euphrates River. The concentrations of the REE at the A37 sample site decrease because of the next thrust zone. Thus, the circulation of mixing waters possibly influenced the concentrations of REE in the studied river sediments. The REE plots for the Euphrates River sediments in this study exhibit a small degree of variation. The abundance of the REE in the river sediments is probably due to the mineralogic characterizations of the regional rocks. Figure 2 plots can be explained to mean that the variations of the light REE along the flowing direction are higher until A51 sample site, except for A34, A35, A36, and A37 sites. The heavy REE concentrations increase from A51 sample site to A90 because of the mineralogic characterizations of mafic volcanic and metaophiolitic rocks.


## 4.3. REE Results of the Euphrates River Water

REE concentrations of the Euphrates River waters are presented in Table3. The Amazon, Indus, Mississippi, and Ohio Rivers water data from Goldstein and Jacobsen [13] are also presented in Table 3. La concentrations have range from 0.02 to 2.63 ppb, and Ce concentrations have range from 0.12 to 5.43 ppb. The highest Ce and La values in the water samples are observed at the A34 site, and Pr, Sm, Gd, Dy, Er, and Yb have the highest values, 0.07, 0.07, 0.07, 0.06, 0.03, and 0.03 ppb, respectively, at the same site. However, the lowest Ce and La concentrations in the studied sediments were observed at the same site. The results indicate that the circulation of mixing water along the tectonic zones can be a much more important factor on the absolute abundance of the REE in river sediments than weathering of the regional rocks.


## 5. Discussion

The results suggest that the tectonic zone is an important factor in controlling the abundance of the REE concentrations in the Euphrates River sediments. Moreover, the study indicates that the REE compositions are dependent upon the type (subtropical climatic influences, water circulation, riverbed morphology, and secular variation) of weathered regional rocks. The comparison of87Sr/86Sr compositions of the Euphrates River sediments with those from basaltic soil and metasedimentary soil from Sholkovitz [46] in Table 1 shows that the studied sediments have basaltic and metagreywackes characterization (Figure 3). Bussy [2] obtained 0.728 for 87Sr/86Sr ratio in the Arve River sediments which are related to the Mont-Blanc granites (Table 1). However, this study reveals that 87Sr/86Sr ratio in carbonate-rich rocks is 0.704. The lower 87Sr/86Sr ratios (0.7053, 0.7048, and 0.7057 obtained for the sample sites A43, A61, and A89, resp.) from river sediments in the Keban Dam Lake area, downstream of the contact between the Permo-Triassic shallow marine metasediments and the Upper Cretaceous magmatic crystalline complex of the Elazığ Magmatic Complex, are caused by mixing of the two sources. 143Nd/144Nd isotopic compositions in the studied river sediments determined have range values of 0.512650, 51283640, and 512775 (Table 1), and the values are similar to the composition of metagreywackes. 143Nd/144Nd isotopic composition ratios have range values 0.512414 to 0.512851 for granodiorites in Upper Cretaceous Elazığ Magmatites [47] (Table 1). These comparisons indicate that the weathered felsic igneous rocks in the river sediments are greater at the A43 sample site because of Upper Cretaceous granitic rocks from Elazığ Magmatic Complex than at the A61 and A89 sample sites. These sites have weathered basaltic igneous rocks compositions due to Upper Cretaceous basic volcanic rocks of the Elazığ Magmatic Complex. Figure 3 shows that neodymium isotope ratios in the New England fold belt change from positive ε
N
d
(
0
) values in tertiary basalt to negative values in granitoids and metapelitic rocks [48]. The positive ε
N
d
(
0
) values reflected the contribution of the isotope compositions in the downstream sediments due to weathering of the basic volcanic rocks. Thus, regional and local studies indicate that the Euphrates River sediments have different isotope composition due to mixing of different weathered source rocks (e.g., Permo-Triassic Keban Metamorphites and Upper Cretaceous Elazığ Magmatic Complex, granodioritic and basic volcanic rocks). The Euphrates River sediments have the lowest average REE concentrations, while the Mississippi and Amazon River sediments yield the highest values. Table 1 shows that the average LREE (La, Ce, Nd, Eu, and Gd) and HREE (Dy, Er, Yb, and Lu) compositions of the Euphrates River sediments are lower by 8.33 to 3.63 and 39.52 to 18.34 times compared to the REE compositions of the Mississippi River and Amazon River REE compositions. The researchers indicated that the light and middle REE enrichment in river sediments may be related to apatite-rich rocks [52, 53]. However, Kalender and Çiçek Uçar [21] suggested that the calculated enrichment factor values of the heavy REE are more than those for the light REE in the tributaries of the Euphrates River sediments due to Fe-Mn oxyhydroxide adsorption capacity for HREE linked to the basic volcanic rocks source of HREE. Yang et al. [8] stated that zircon contributes to the bulk HREEs in sediments because of the relatively high abundance of HREEs in zircon. The lithologic units along the Euphrates River bed contribute to the bulk of LREEs concentrations as a result of apatite-rich, zircon-poor Upper Cretaceous granodiorites. La/Yb mean ratio of 7.72 in the studied sediment samples indicated high erosional rate because La may be removed from crustal source via weathering process and this is in agreement with the finding of Obaje et al. [18]. The distribution trend of REE along the flowing direction of the Euphrates River at some of the sample locations A32, A33, A34, A35, and A36 indicates that the thrust zone between Upper Cretaceous Elazığ Magmatic Complex and Permo-Triassic Keban Metamorphites influences the decreasing REE composition in the river sediments due to mixing water circulation. Average LREE concentrations upstream have higher-than-average HREE concentration compared to downstream ones due to the shallow marine metasediments and felsic magmatic rocks (Permo-Triassic Keban Metamorphites, felsic rocks from Upper Cretaceous Elazığ Magmatites) upstream. However, the basic volcanic rocks (Maden Complex and Kömürhan metaophiolites) are observed downstream along the Euphrates River flowing direction. Obaje et al. [18] and Ramesh et al. [54] stated that positive Ce anomalies are related to the formation of Ce4+ and Ce hydroxides and terrigenous input and diagenetic conditions. The positive Ce anomalies may indicate hydromorphic distribution of the REE in river sediments. According to some researchers, Eu anomalies have less contribution from felsic magmatic rock weathering. The negative Eu anomalies (<0.01 detection limit) indicate that the REE compositions in the river sediments more or less contribute to felsic magmatic rock weathering compared with terrigenous input and basic magmatic rock weathering. Lower river flowing velocity may be responsible for REE homogenous REE distribution in agreement with Obaje et al. [18]. The average chondrite normalized values indicate LREE and HREE enrichment, and their summarized statistical values range from 26.77 to 7.35 and 7.23 to 4.68, respectively (Table 2). The chondrite normalized patterns illustrate that the REE composition of the Euphrates River sediments differs from chondrite composition but also the REE enrichment is close to NAS and UCC. The REE normalized values of the Nigerian Gora River from Obaje et al. [18] are shown in Table 3. The Ce/Ch. value is higher (20.15) in the Euphrates River sediments than the Nigerian Gora River sediments (17.96) due to sulfide-rich mineralization in the studied area, especially Keban polymetallic mine deposit. Ramesh et al. [54] revealed that the positive Ce anomalies indicate terrigenous input, depositional environment, and diagenetic conditions due to the formation of Ce4+ and stable Ce hydroxides. According to Nielsen et al. [55], Tl and Ce may be controlled by residual sulfide and clinopyroxene, respectively, during mantle melting due to their highly different ionic charges and radii. Luo et al. [56] indicated that while the adsorption ability of REE decreases on colloidal particles from light (La) to heavy (Lu), the complexes of REE with carbonate increase, and also the larger colloidal particles have stronger ability to adsorb Ce from weathering of granitic rocks. However, both LREE and HREE concentrations are lower than NAS and UCC (Figures 4 and 5). LREE patterns show that Sm and Eu patterns are closer to 1, and Gd pattern is higher than 1 La, Ce, Pr, and Nd (Figures 4(a), 4(b), 4(c), 4(d), 4(e), 4(f), and 4(g)). Gd/Y
b
NAS and UCC ratio >1 indicates that apatite from granodioritic rocks had contributed to the river sediment REE compositions [57–61]. According to Leybourne and Johannesson [60], Eu is mobilized during hydromorphic transport compared to Sm and Gd. However, the study reveals that Sm and Eu are mobilized more compared to Gd. Thus, Gd enrichment was observed in the river sediments. However, HREE patterns enrichment is relative to chondrite but HREE NAS and UCC normalized patterns are observed to be close to 1 (Figures 5(a), 5(b), 5(c), 5(d), 5(e), 5(f), and 5(g)). All of the river sediment REE compositions that display enrichment are relative to chondrite REE composition.Table 2
North American Shale (NAS), upper continental crust (UCC), and chondrite (Ch.) from Yang et al. [8], Condie [22], Taylor et al. [23], and Sholkovitz [50, 51] and normalized REE summary statistical values (ppm) in Euphrates River sediments; ∗Obaje et al. [18].
LREE
Mean
St. dev.
∗Nigerian Gora River
HREE
Mean
St. dev.
∗Nigerian Gora River
La/NAS
0.28
0.08
—
Tb/NAS
0.39
0.11
—
La/UCC
0.29
0.09
—
Tb/UCC
0.52
0.15
—
La/Ch.
26.77
8.08
39.76
Tb/Ch.
6.51
1.85
—
Ce/NAS
0.27
0.09
—
Dy/NAS
0.52
0.13
—
Ce/UCC
0.28
0.09
—
Dy/UCC
0.62
0.15
—
Ce/Ch.
20.12
6.34
17.96
Dy/Ch.
7.23
1.78
—
Pr/NAS
0.29
0.09
—
Ho/NAS
0.42
0.10
—
Pr/UCC
0.31
0.10
—
Ho/UCC
0.53
0.13
—
Pr/Ch.
17.10
5.46
—
Ho/Ch.
5.74
1.41
—
Nd/NAS
0.28
0.06
—
Er/NAS
0.42
0.10
—
Nd/UCC
0.30
0.06
—
Er/UCC
0.52
0.13
—
Nd/Ch.
14.26
2.97
18.96
Er/Ch.
5.73
1.39
—
Sm/NAS
0.38
0.11
—
Tm/NAS
0.35
0.09
—
Sm/UCC
0.48
0.14
—
Tm/UCC
0.51
0.14
—
Sm/Ch.
10.20
3.00
—
Tm/Ch.
5.22
1.41
—
Eu/NAS
0.48
0.12
—
Yb/NAS
0.36
0.09
—
Eu/UCC
0.65
0.17
—
Yb/UCC
0.51
0.12
—
Eu/Ch.
7.70
1.98
404.62
Yb/Ch.
6.18
1.47
25.52
Gd/NAS
0.45
0.12
—
Lu/NAS
0.33
0.09
—
Gd/UCC
0.58
0.16
—
Lu/UCC
0.47
0.12
—
Gd/Ch.
7.35
1.98
58.50
Lu/Ch.
4.68
1.23
—Table 3
REE concentrations in river water in ppb. The Amazon, Indus, Mississippi, and Ohio Rivers data from Goldstein and Jacobsen [13].
LREE
N
=
90
River water
Dissolved load
Euphrates
Amazon
Indus
Mississippi
Ohio
La
0.25
0.074
0.0029
0.020
0.0063
Ce
0.54
0.21
0.0024
0.010
0.010
Pr
0.04
—
—
—
—
Nd
0.18
0.13
0.0032
0.020
0.011
Sm
0.04
0.034
0.00071
0.004
0.0025
Eu
<0.01
0.008
0.00022
0.001
0.0006
Gd
0.04
—
0.050
—
—
Tb
<0.01
—
—
—
—
Dy
0.04
0.031
0.036
0.0075
0.006
Ho
<0.01
—
—
—
—
Er
0.02
0.016
0.017
0.0065
0.005
Tm
<0.01
—
—
—
Yb
0.2
0.015
0.0014
—
0.0036
Lu
<0.01
—
0.0021
—
0.0006Figure 3
Normalized patterns of the LREE average concentrations (N
=
90) of Euphrates River sediments in the NAS, UCC, and Ch. (a) La, (b) Ce, (c) Pr, (d) N
d
∗ (N
=
50), (e) Sm, (f) Eu, and (g) Gd normalized patterns.
(a)
(b)
(c)
(d)
(e)
(f)
(g)Figure 4
Normalized patterns of the HREE average concentrations (N
=
90) of Euphrates River sediments in the NAS, UCC, and Ch. (a) Tb, (b) Dy, (c) Ho, (d) Er, (e) Tm, (f) Yb, and (g) Lu normalized patterns.
(a)
(b)
(c)
(d)
(e)
(f)
(g)Figure 5
Diagram of Nd versus Sr isotopic composition in rock, soil, and sediment samples from Martin and McCulloch [4]. Lines connect rock and soil samples taken from the same locality. Outlined fields show isotopic compositions of the New England granitoids, metapelitic rocks, and metagraywackes from the New England fold belt [49].REE compositions of the Euphrates River water were compared with REE in dissolved load of Amazon, Indus, Mississippi, and Ohio River waters from Goldstein and Jacobsen [13] (Table 3). Figure 6 indicates that the REE compositions of the Euphrates River water are higher than REE compositions in the dissolved load compared of the Amazon, Indus, Mississippi, and Ohio Rivers. However, the REE patterns of the Euphrates River water were similar to REE in dissolved load in the Amazon, Indus, Mississippi, and Ohio River waters. Yb content in the Indus River water is higher while Ce content in the Mississippi River water is lower than in the Euphrates River water. According to Goldstein and Jacobsen [13], high Yb values in suspended materials may be derived from older rocks. Goldberg et al. [62] indicated that Ce depletion in river waters in a high pH environment may be related to the result of preferential removal of Ce4+ onto Fe-Mn oxide coatings of particles. This indicates that suspended materials load in the Euphrates River water is probably more than in the Mississippi, Ohio, and Indus River waters. Ce anomalies are calculated using the following equation:(2)
Ce
∗
=
3
Ce
NAS
2
La
NAS
+
Nd
NAS from [13], where(3)
Ce
∗
=
3
×
0
,
000024
2
×
0.000015
+
0
,
000020
=
1.16
.As shown, positive Ce anomalies (Ce
∗
>
1) support the fact that Ce may be fixed on the clay at pH > 7. Also, the calculated L
a
/
Y
b
N
A
S values in the Euphrates River water and sediment are 0.098 and 0.77. It is apparent that both Euphrates River waters and sediments have heavier REE composition than light REE according to NAS normalized patterns.Figure 6
Distribution of REE in the Euphrates River waters and the Amazon, Indus, Mississippi, and Ohio River waters data from Goldstein and Jacobsen [13].


## 6. Conclusions

(1) This paper indicates that a contribution from a third component can change the isotopic composition of the studied sediments: (a) Permo-Triassic carbonate-rich metasediments and (b) felsic magmatic and (c) mafic volcanic rocks from Upper Cretaceous Elazığ Magmatic Complex.(2) The study indicates that the Euphrates River average LREE (La, Ce, Nd, Eu, and Gd) and HREE (Dy, Er, Yb, and Lu) compositions have lower range values from 8.33 to 3.63 and 39.52 to 18.34 times less than Mississippi River REE and Amazon River sediment compositions, respectively.(3) This paper revealed that the Euphrates River has higher LREE than HREE concentrations, and also, in the thrust zone which is close to the Euphrates River bed, there is low REE composition due to fast water circulation.(4) Average LREE concentrations upstream in the Euphrates River are higher than average HREE concentrations downstream due to felsic magmatic rocks.(5) La/Yb ratio (7.72) indicates high erosion rate, and La may have been added from crustal sources via weathering processes.(6) The positive Ce and La anomalies indicate both terrigenous input and contribution of the oxidative compounds from sulfide-rich mineralization in the Euphrates River bed sediments.(7) The chondrite, NAS, and UCC normalized patterns show that the REE compositions of the Euphrates River sediments differ from chondrite but are similar to NAS and UCC.(8) The Sm and Eu patterns are close to 1, and Gd pattern is higher than 1 (>1), and also Gd/Y
b
NAS and UCC ratio greater than 1 indicates that the source of REE may be apatite-rich granodioritic rocks which are from the Elazığ Magmatic Complex. Also, terrigenous sediments and lithological control are more effective on the Euphrates River sediment REE compositions.(9) The Euphrates River waters have the highest composition values for both LREE and HREE in comparison to the other basic river waters (the Amazon, Indus, Ohio, and Mississippi River waters) due to regional felsic and mafic lithological units. Due to circulation of mixing water, REE concentrations increase in the river water but decrease in the river sediments.



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*Source: 1012021-2016-05-23.xml*