Geochemistry of Major and Trace Elements in Recent Balakian River Sediments, Northern Iraq: Evidence for Provenance and Source Rocks

Abstract


Introduction
The chemical composition of river and stream sediments was used as a mineral deposits prospecting tool (Plant and Hale, 1994) and identical approaches and techniques can be utilized for more environmentally related research (Förstner et al., 1991).The chemical structure of river sediments indicates the geochemistry of bedrock in erosion areas and distinguishes the weathering trend in the catchment region (Sorokina, 2020).River sediment geochemistry has drawn a lot of interest because it reflects the parent rocks, natural processes, and human activities in the watershed.Studies of the 2 chemical element distribution in these sediments also aid in our understanding of these processes (Babu et al., 2021).
In general, the sediments transported and deposited by rivers originate from a variety of sources, including different geological formations that are influenced by a variety of climatic systems and physiographic settings.Thus, the river sediment content is influenced by a number of factors, for instance, lithology, climate, relief, weathering type, diagenesis, and transportation (McLennan et al. 1993;Cox et al. 1995;Dinelli et. al., 2005).Lupker et al. (2016) illustrated that the eroding substrate chemistry determines the elemental composition of river sediments, which is modified by processes such as chemical weathering, cation exchange, and hydrodynamic sorting.As a result, river sediment compositions are being studied to determine the controls on chemical and physical weathering rates (Von Blanckenburg et al., 2012).
The Balakian River (BR) is located in northern Iraq, specifically to the south of the Iraqi-Turkish border.The drainage system of the river flows southeastward through a number of geological formations of sedimentary origin to intersect with the Sidikan River, about 23 km southeast of Mirgasur, and continues toward the southeast until it intersects with the Rawanduz River, about 10 km southwest of Diyana.The exposed formations in the drainage basin were subjected to various geological and tectonic studies to determine the nature of the source rocks and the tectonic setting of the source area.Tobia and Kafy (2016) studied heavy mineral chemistry in recent Balakian River sediments to determine the provenance of these minerals, but these river sediments lack detailed geochemical studies.Therefore, this paper aims to utilize river sediment geochemistry and compares the chemical data results to available geological data in order to evaluate the effects of lithology on sediment composition in order to understand the influence of weathering, provenance, and source area of sediments that are found along the course of the BR.

Location and Geological Setting
The geological map of the studied region is presented in Fig. 1.It appears that the study area is situated in the high folded zone of Iraq's unstable shelf tectonic zone (Jassim, and Goff, 2006).The study area is located in northern Iraq's mountainous region, between latitudes 36⁰40′00″N-36⁰50′20″N and longitudes 44⁰19′30″E-44⁰30′30″E.Where the drainage system of BR runs southeastward from Mergasur Town, about 12 kilometers south of the Iraqi Turkish border, to intersect Rawanduz River, about 10 kilometers southwest of Diyana Town as shown in Fig. 1.BR cuts across a number of different geological formations.The possible stratigraphic sequences that affected the fluvial sediments in the studied area, from the oldest to the youngest, represented by Shiranish and Tanjero formations (Late Campanian) and the Red Bed Series (Late Maastrichtian -Pliocene).
The sedimentary rocks of the Shiranish (Late Campanian -Early Maastrichtian) and Tanjero (Late Campanian -Late Maastrichtian) formations are exposed along the Balakian River, marl and marly limestones compose the majority of the Shiranish Formation, whereas the Tanjero Formation is comprised of sandstones, siltstones, conglomerates, silty marl, silty or sandy organic detrital limestones, and globigerinal marl (Buday, 1980;Jassim and Goff 2006).The Red Bed Series (Late Maastrichtian -Pliocene) consist of clastic rocks represented by chert red layer of claystone, alternation of thick bedded gray sandstone, conglomerate with occasional limestone beds and marl (Al-Barazinjy, 2005).In addition, the Walash and Naopurdan groups are exposed in the northeast part of the river.The Walash Group (Eocene) consists of volcanic rock enclosed in immature sedimentary rocks, which consist of sandstone, siltstones, and mudstones.While the Naopurdan groups (Oligocene) are divided into volcanic and sedimentary units, the former unit comprises andesitic volcanics, which are composed of lavas, tuffaceous slates, agglomerates, and occasional basic pillow lavas, whereas the latter unit comprises grey

Materials and Methods
Sixteen samples of recent stream sediment were collected from the BR, located in the northern part of Iraq in September 2020 (Fig. 1).The sediments were manually sampled, particularly those in contact with running water, with a metal bucket measuring 268.3 cm in diameter.To avoid contamination from riverbank material, sampling were done at a distance from the riverbanks.About 3-4 Kg of sediments were collected from the mainstream to provide enough material in plastic bags for the geochemical analysis.
The studied samples were sun-dried before being finely powdered in an agate mortar.The samples were sieved through a 200 µm sieve and then pressed into 32 mm thick pellets with wax as a blinder.The concentration of the elements were measured by using polarized energy dispersive XRF.USGS standards, GEOL, GBW-7109, and GBW-7309 sediment were similarly compressed into pellets as the samples and used for quality assurance.The Spectro XLAB 2000 PEDXRF spectrometer was used in this study at the Earth Science Research and Application Center (YEBIM) in Ankara, Turkey.Details of the analysis techniques are given in Timothy and La (1989) and Johnson et al. (1999).

Results and Discussion
The results of the major and trace element values of the geochemical analysis of the BR samples are shown in Table 1.The statistical characteristics of the data (standard deviation, arithmetic mean, coefficient of variation, maximum, and minimum value) were calculated in order to observe general variability in the stream river sediment chemistry of the Balakian river (Table 1).The result displays that the major and trace element concentrations generally vary by (6.0 to 41.0 %) for Balakian river; with exception of Nickel, which is vary by (56.0%).Coefficient of variation (C.V.) is ≥ 20 % for major (Al2O3, Na2O and K2O), and trace (Cr and U) elements, and is within < 20% for other elements (Table 1).
The interrelationship between the major and trace components was determined using multiple regression analysis, and the results of Co-variation matrix for major and trace element values for the sediments of the BR are displayed in Table 2. Most of the major oxides show negative correlations with silica.Also, most of the trace elements have no significant correlation with SiO2.The negative linear relationships of SiO2 with Al2O3 indicate that quartz and feldspar have a diluting impact, whereas clay minerals act as main hosts for the majority of elements in the river sediments (Guanqiang et.al., 2008 ;Rahman et al., 2020).With exception of TiO2 showed a positive correlation with SiO2, this reveals that TiO2 has been combined with some fine particles of heavy minerals such as rutile and ilmenite in sedimentary rocks' sand fraction.Tobia and Kafy (2016) illustrated that the opaque minerals represented by spinel, magnetite, hematite, goethite, and ilmenite are the main heavy minerals in the sediments of the Balakian River.Heavy minerals were fıxed into the sediments due to their strong resistance to weathering coefficients, causing enrichment of weathering residual with TiO2 (Rankama and Sahama, 1950 andGoldschmidt, 1962).In addition, in the crystal lattice of clay minerals, the (Ti) percent is replaced by (Fe +3 ) and (Al +3 ) or forms small rutile particles (Hirst, 1962 ;Wright, 1974).As a result, a variety of clay phases and heavy minerals serve as the main carriers for these elements.The abovementioned results obtained for Balakian River sediments highlight the role of transport activities in regulating the constituent abundances of river sediments.Contributions from detrital carbonates may explain the positive correlation of MgO with Na2O, K2O, and CaO, as well as the significant positive correlation of LOI with CaO (Table 2) ( Al-Jaberi and Al-Humaidan, 2018;Al-Khalf and Al-Saad, 2019).
The Balakian River's drainage system originates from the south-east of Mergasur Town, flows southeastward to intersect the Sidekan River, about 23 km to the southeast of Mergasur, and continues southeastward until it intersects the Rawanduz River, about 10 kilometers southwest of Diyana Town, where it continues to flow until it meets the Greater Zab River.The assemblages of minerals represented by the high content of unstable and metastable minerals confirm that the Balakian river sediments generally are derived from the adjacent primary source rocks represented by the sedimentary rocks of the Shiranish and Tanjero formations, where the sedimentary rocks of the Shiranish and Tanjero formations are exposed along the Balakian River (Jassim, and Goff, 2006), in addition to the Ophiolite Complex, and igneous rock parts of the Walash Series in the northern part of the study area, north Iraq (Tobia and Kafy, 2016).Comparison of element abundances in the BR sediments with those in the Late Campanian-Late Maastrichtian Shiranish (marl, limestone, and marly limestone) (Kettaneh and Sadik, 1989;Ismail, 2016), and Tanjero (sandstone) formations (Ali and Mohmmad, 2018), Eocene-Oligocene Naopurdan Group (limestone), and Pliocene Red Bed Series (claystone) from northern Iraq (Mirza et.al., 2016), indicating that weathering has resulted in the loss of Ca, Mg, Na, and K from these rocks' outcrops.Thus, the chemical analysis of the sediment features of the Balakian stream river reflects the mineralogical and chemical composition of the rocks in the drainage basin.To determine the difference in mobile cation concentrations (CaO, Na2O, K2O) between originally fresh source rocks (Shiranis, Tanjero formations) and weathered recent sediments of BR, the index of mobility (Imob) was calculated and analyzed (Irfan, 1996).Mole-ratio (Imob) is represented as: The mobile index values (Imob) are 0.65, 0.58, and 0.50 for the Shiranish Formation (for marl, limestone, and marly limestone, respectively), with -0.130 for the Tanjero Formation (for sandstone), and 0.58 for Naopurdan limestone.Therefore, it refers to the change of chemical composition in rocks during weathering.The higher the mobile index, the greater the variation in the amount of mobile cation presence in the Balakian River sediments and the freshly weathered source rocks; thus, the weathering is more intense.
The concentrations of the major elements in the studied sediments were normalized with those of theUCC (Mclennan, 1995;Rudnick and Gao, 2003), and PAAS (Taylor and McLennan, 1985;Pourmand et.al., 2012), since river sediments are composites of weathering products of all the lithologies (spatially carbonate rocks and sandstone) in the catchments area ( Fig. 2).To evaluate the elemental mobility during weathering and transportation, it is common practice to normalize the elemental concentration of river sediments with those of the UCC (Fig. 3) (Taylor and McLennan, 1985).The UCC and PAAS normalized ratios for the major (SiO2, Al2O3, Na2O, K2O, and TiO2) elements in the Balakian river sediments are less than 1 (Fig. 3), which would indicate that these elements were lost from nearby source rocks during weathering, alteration, and transport.The loss of feldspars through chemical weathering at the source rocks is suggested by the depletion of main feldspar chemical constituents such as Na2O, K2O, and Al2O3 relative to the UCC..This was also demonstrated by the average of SiO2/Al2O3 ratio (8.96), which was higher than the Upper continental Crust (UCC = 4.34) and Post-Archean Australian Shale (PAAS = 3.30).With the exception of TiO2, which has a UCC normalized ratio of greater than 1.This suggests that the residual elements like TiO2 are probably associated with phyllosilicates clay and heavy minerals (Edema et al., 2016;Awadh and Al-Ankaz, 2016), and concentrated in the source area as a result of chemical weathering (Dokuzi and Tanyolu, 2006).However, the normalized UCC and PAAS ratios for Fe2O3, CaO, and MgO are more than 1(Fig.3).This observation would seem to confirm the idea that MgO and CaO are derived from the nearest supplied outcrops of source rocks represented by late Campanian carbonate rocks (Tanjero and Shiranish) formations and Pliocene (Red Bed Series) in the catchment areas (Tobia and Kafy, 2016).The relatively high increase in Fe2O3 may be related to the presence of heavy minerals, organic matter, and iron oxide as colloidal sediments.
The average content of Al2O3 (5.77%) in the Balakian river sediments is significantly lower than the universal average (average sediment = 13.39%)(Mason, 1966).The lower mean value of Al2O3 in the sediment of a river points out a low abundance of the shale or/and clay components (Table 1, Fig. 2  and 3).Where the high clay content and aluminum concentration in the river particulates and sediments are produced by the effect of weathering in river basins.To evaluate the weathering intensities in the river catchments, the Chemical Index of Alteration (CIA) and Chemical Index of Weathering in molar percentage of the chemical oxide components of Balakian river sediments were determined according to Nesbitt and Young (1984) and are calculated by: Iraqi Geological Journal Ali and Ali 2023, 56 (1C), 1-12 The BR sediments' CIA and CIW values ranged from 47.51 to 71.12% and 50.48 to 74.15%, with an average of 57.77% and 60.70%, respectively.According to these values, the source rocks in the basin are experiencing a moderate intensity of chemical weathering (Fig. 4).For the first cycle of sediments obtained from weathered igneous rocks, the value of the chemical index of alteration of the sediments is typically 50%.The typical tends to rise as chemical weathering intensifies and the percentage of remaining clay minerals, such as kaolinite, chlorite, illite, and gibbsite, rises.High clay abundances and thus high content of aluminum in sediments are the products of high-intensity weathering (Nesbitt and Young, 1982).More soluble cations, such as Ca and Na, are released into the solution during the chemical weathering of silicates, leaving Al in the residue products like clay.In contrast to stable residue elements like Al and Ti, the loss of labile cations like Na, K, and Ca suggests extensive weathering or recycling under humid and warm paleoclimatic conditions, on other hand, minimal CIA readings suggest minimally or almost no chemical alterations, which often denotes cool and/or arid climatic conditions (Rahman et al., 2020).The chemistry of the major element content of sediments of the BR is depicted in Fig. 4 in the Al2O3-(CaO + Na2O)-K2O ternary diagram, which shows that most of the studied sediments lie above the K-feldspar-plagioclase line, along the clay mineral line, where the alteration phases as a result of weathering are biotite, illite, kaolinite, and chlorite.This indicates that clay minerals, rather than non-clay silicate phases, control the composition of major elements in the analyzed river sediment samples (Moosavirad et al., 2010).It also means that the nature of river sediments is felsic in provenance.The concentration of trace elements in the BR sediments is presented in Table 1.The behavior and distribution of trace elements within the constituents of the river sediments were identified using the statistical Co-variation correlation analysis and are shown in Table 2. Chromium (Cr) and copper (Cu) have the highest average concentrations of trace elements in The BR sediment, with values of 631.19 and 427.88 ppm, respectively.These two elements are followed by strontium (Sr), zinc (Zn), nickel (Ni), cobalt (Co), vanadium (V), and uranium (U), which have average values of 319.35, 319.19, 383.50, 276.63, 274.94 respectively (Table 1).Most of these elements (Co, Ni, Cr, Cu, and Zn) in the BR sediments have positive correlation coefficients among themselves, indicating that a common mechanism controls their abundance.Additionally, it has been noted that these components exhibit covariations with Al2O3 (Table 2), which leads to the deduce that the presence of Al rich phases, like clay minerals, significantly influence the abundance of these elements.This, together with the finding that these trace elements also exhibit positive correlations with CaO, K2O, and Na2O, indicates that it is associated mainly with carbonate minerals and feldspar.In oxic and aqueous environmental conditions, alkaline earth elements like Sr are known to be relatively mobile (Gaillardet et al., 1999).Sr exhibits a strong positive association with both LOI and CaO.This demonstrates that in addition to being mainly associated with carbonate minerals, it is also correlated with clay minerals since it is transported into the depositional basin mostly structurally combined in the clay mineral lattices.Strontium (Sr) is substituted into clay minerals via base ionic exchange (Goldschmidt, 1962).In calcium-bearing minerals like calcite and gypsum, Ca and Mg are often substituted by Sr (Ali et al., 2021).
The values of trace elements in the studied sediment samples were likewise compared with the mean values of trace element concentrations in the UCC and PAAS (Fig. 5).The UCC and PAAS normalized trace element diagram (Fig. 5) showed high enrichment values of most trace elements (Co, Ni, Cu, Cr, Zn, V, U) and slightly enriched values of Sr.This demonstrates how different rock sources from various geological formations contributed to an enrichment in the concentration of these elements in the sediments of the Balakian River.In addition to the Late Campanian carbonate rocks (limestone, marl and marly limestone) of the Shiranish formation and carbonate rich sandstone of the Tanjero Formation, these sediments are derived from the nearest supplied crops out of source rocks represented by Pliocene age Red Bed Series rocks in the catchment areas (Tobia and Kafy 2016).

Conclusions
The major and trace elements in the BR sediments, northern Iraq were subjected to geochemical studies to determine their provenance and weathering of the source area.The majority of these elements have negative and insignificant associations with SiO2.The negative linear relationships of SiO2 with Al2O3 suggest that quartz and feldspar have a diluting effect while clay minerals serve as the main hosts for the majority of the elements in the river sediments.With the exception of TiO2, which showed a positive correlation with SiO2, this indicates that TiO2 has been associated with some fine particles of heavy minerals such as rutile and ilmenite in sedimentary rocks' sand fraction.On the other hand, the positive correlation of CaO, MgO, K2O, and Na2O with most of the trace elements indicating that the abundance of carbonate and clay minerals significantly influenced the concentrations of these elements during the weathering and transport of BR sediments.
According to the Chemical Index of Weathering (CIW) and Chemical Index of Alteration (CIA) values of the sediments from the Balakian River, the source rocks in the basin are experiencing a moderate intensity of chemical weathering.Among the major elements, UCC and PAAS normalized ratios for SiO2, Al2O3, Na2O, K2O, and TiO2 are less than 1, which suggests that these elements were lost during weathering, alteration, and transport from adjacent source rocks.While the normalized UCC and PAAS ratios for Fe2O3, CaO, and MgO are more than 1, which suggests that MgO and CaO are derived from the supplied outcrops of source rocks represented by the Late Campanian carbonate rocks (Tanjero and Shiranish) formations and the Pliocene (Red Bed Series) in the catchment areas.The comparatively high value of Fe2O3 in river sediments may be associated with the presence of heavy minerals, organic matter, and iron oxide as colloidal sediments.In Balakian River sediments, lower values of normalized ratios (UCC and PAAS normalized 1) for alkaline trace elements such as Sr indicate that Sr is effectively more solubilized and more mobile than other metals.This illustrates how various rock sources from various geological formations contributed to an enrichment in the concentration of some elements in the river sediments.

Fig. 1 .
Fig.1.Geological map of part of northern Iraq and location of the Balakian Stream river sediment samples, modified from(Stevanovic and Markovic, 2001 in Tobia andKafy 2016)

Table 1 .
The concentrations, ranges, and rates of major and trace element in BR sediments Table2.The Correlation Coefficient matrix for major and trace element concentration of Balakia sediments