First data on the geochemistry of fluvial deposits of Çaybağı and Palu formations (Eastern Elazığ, Turkey)

Öz In this study, the geochemistry (major, trace and rare earth elements) of fluvial deposits of the Çaybağı and Palu Formations, Eastern Elazığ, have been investigated. The basement of the studied basin is composed of the Guleman Group, Elazığ Magmatics, Hazar-Maden Group, and Kırkgeçit Formation which consist of volcanic materials derived from the Elazığ Magmatics. The Çaybağı Formation is composed of thick fluvio-lacustrine sedimentary sequence. Palu Formation consists of alluvial fan deposits and braided river, lacustrine sedimentary deposits. Samples were collected from braided river deposits of Çaybağı and Palu Formation along Hacısamdere–Çaybağı section (Ç-samples) and Hacısamdere-Palu section (PL samples). Significant positive correlation between Zr/Sc and Th/Sc ratios of two sample groups show that the siliciclastic sample groups do not represent considerable sediment recycling. Çaybağı and Palu samples have similar geochemical indices (Al2O3/TiO2, Ti/Zr, La/Th, La/Sc, Cr/Th, Co/Th, (La/Yb)N, (Gd/Yb)N, LREE/HREE ratios) and indicate derivation from intermediate-basic source rocks. In Si vs. Na/K diagram samples plot in arc field and La/Sc and Ti/Zr ratios show that samples were plotted in an oceanic island arc environment. Bu çalışmada Elazığ’ın doğusundaki Çaybağı ve Palu Formasyonu’na ait fluvial çökellerin jeokimyası (majör, iz ve nadir toprak elementler) incelenmiştir. İnceleme alanının temel kayaçlarını Guleman Grubu, Elazığ Magmatitleri, Hazar-Maden Grubu, Elazığ Magmatit’lerinden malzeme almış olan Kırkgeçit Formasyonu oluşturmaktadır. Çaybağı Formasyonu kalın fluvial-lakustrin sedimanter istiften, Palu Formasyonu alüvyon yelpazesi, örgülü nehir çökelleri, lakustrin sedimanlardan oluşmaktadır. Örnekler Hacısamdere-Çaybağı kesiti (Ç örnekleri) ve Hacısamdere-Palu kesiti (PL örnekleri) boyunca Çaybağı ve Palu Formasyonları’nın nehir çökellerinden alınmıştır. Zr/Sc ve Th/Sc oranı arasında önemli pozitif korelasyonun görülmesi örneklerin önemli bir sedimanter çevrime maruz kalmadığını göstermektedir. Çaybağı ve Palu örneklerinin benzer jeokimyasal indisleri (Al2O3/TiO2, Ti/Zr, La/Th, La/Sc, Cr/Th, Co/Th, (La/Yb)N, (Gd/Yb)N, LREE/HREE oranları), bunların nötr-bazik kaynak kayaçlarından türediğini göstermektedir., Si’a karşı Na/K diyagramında örnekler yay alanına düşmektedir. La/Sc, Ti/Zr oranları örneklerin okyanus adayayı ortamında depolanmış kayaçlardan türediğini göstermektedir.

During the Neogene to Quaternary various lacustrine and fluvial deposits (e.g. The Çaybağı and Palu Formations) were accumulated in Eastern Turkey (Figure 1a). These deposits consist of sandstone, siltstone, and carbonaceous claystones.
Perinçek and Özkaya, Özkul, Sungurlu et all., Çetindağ [22][23][24][25] studied the geological, hydrological, sedimentological characteristic of the study area. The depositional environment of the Çaybağı Formation is studied in detail by [26], [27] described five types of facies associations in the Çaybağı Formations; braided river, low-sinuosity river, lacustrine delta front, lacustrine shallow and open lacustrine environments. Mineralogical variations and authigenic mineral occurrences in the Çaybağı Formation were studied by Akkoca and Sağıroğlu [28]. Palu Formation was named and studied by [25], [29] investigated sedimentological characteristics of Palu Formation and they defined alluvial fan deposits and braided river deposits in the formation. Çolak et al. [30] mentioned lacustrine environment within the formation. In spite of these geological, sedimentological and mineralogical investigations, the geochemistry of these two formations has not been studied. Therefore the purpose of this paper is to evaluate the river deposits of Çaybağı and Palu Formations, in order to provide information on the provenance of detrital material, and to constrain tectonic setting of the sediments from these formations.

Geology
The study area is located in the eastern part of Elazığ city (Figure 1a [27]).
Yazgan and Chessex [31] suggest that the ophiolites are formed around 85-76 Ma, based on K-Ar dating of biotite separates and whole-rocks [32]. Dönmez [33] studied the Upper Cretaceous Elazığ Magmatics around the Soğanlı and Uyandık Villages of the Kovancılar Country. They determined that magmatic succession includes basaltic pillow lavas, pyroxene-bearing andesitic lava flows, and pyroclastics volcanogenic sandstones. Geochemical data indicate that the Elazığ Magmatics consists of a calc-alkaline series and that they are the products of island-arc magmatism [31], [33]- [35]. These magmatic rocks are overlain by limestone, sandstone, and marls of the Kırkgeçit Formation, which was deposited in variable shallow to relatively deep-marine Middle Eocene-Lower Oligocene clastic sediments [36]. This formation is fed from Elazığ Magmatics and contains pebbles of magmatics exposing around the study area.
The Maden Group consists of limestones, red-green clayey limestones, sandstone and agglomerate, tuffs, reddish mudstone and basaltic-andesitic pillow lavas. There are several suggestions on the origin of Group. The Maden Group is a volcanosedimentary succession of Middle Eocene age representing a short-lived back-arc basin which reached the stage of an embryonic ocean [37]. The basaltic-andesitic rocks of Group would be possibly have formed by rifting of the forearc, probably related to oblique convergence in the Middle Eocene [38]. The Maden Group which conformably covers the Hazar Group was formed in an E-W trending extensional basin in the Middle Eocene. Hazar Group consists of conglomerates that are laterally and vertically in transition with limestone consisting of sandy limestone and grey-brown shales. Çelik [39] suggests that this formation was deposited in shallow parts of the Hazar-Maden Basin.
The Çaybağı Formation, which was named by Türkmen [41], was later studied in much detail by Koç Taşgın and Türkmen [42] for stratigraphical and sedimentological characteristics. The Çaybağı Formation unconformably overlies the Kırkgeçit Formation at north and east and Elazığ Magmatics at west (Türkmen 1991 According to Koç Taşgın and Türkmen [42], the Çaybağı Formation was deposited in a variety of environments which are from bottom to top, the Hacısamdere, the Yılankaya, the Ziyarettepe and the Arılar members. Koç Taşgın and Türkmen [42] states that Hacısamdere member, from which samples were collected, is fining-upward and was deposited by a fluvial system. Fluvial deposits of the formation consist of a matrixsupported conglomerate, tuff, sandstone, and red-grey clayey sandstone, limestone and claystone alternation (Figure 2a). Pebbles in the conglomerates are derived from the Elazığ Magmatics and Kırkgeçit Formation. The measured thickness of this member is about 350 m. Koç Taşgın and Türkmen [27] suggest that this sequence is composed of typical braided river deposits which directly fed lacustrine environment (Figure 2b). Based on fossil content the age of formation was suggested as Upper Miocene-Pliocene [42].
Palu Formation was first recognized and named by Çetindağ [25] in the Palu County. Formation is well-exposed along the northeastern margin of the Palu-Uluova basin, particularly in the west of Palu County. It consists mainly of braided river, fan delta, fluvial coarse clastics with fine-grained lacustrine sedimentary intercalations [30]. Alluvial fan deposits are formed by conglomerates and pebbly sandstones ( Figure  2(c)). Pebbles are partly well-to sub-rounded and partly angular clasts of mostly magmatic rocks such as andesite, basalt, sandstone and limestones and derived from the Elazığ Magmatics and Kırkgeçit Formation. Braided river deposits mainly composed of conglomerates, volcanogenic sandstone, and cross-bedded clayey sandstones (Figure 2(d)). Volcanogenic sandstone consists of unsorted, weakly lithified and matrix-supported pebbles and blocks (up to 1 m in diameter) of conglomerates and is partly well to sub-rounded and partly angular clasts of mostly magmatic rocks such as andesite, basalt, sandstone and limestones and derived from the Elazığ Magmatics. Kerey and Türkmen [29] suggest that transportation direction of alluvial fans is from north to south and that of braided rivers is from east to the west.

Material and methods
Eighteen sandstone samples were collected from braided river deposits of Çaybağı and Palu Formation along Hacısamdere-Çaybağı section (Ç samples, river facies from Hacısamdere member) and Hacısamdere-Palu section (PL samples, braided river facies) (Figs. 1 and 3).
Chemical analyses of representative samples were conducted at Acme Analytical Laboratories Ltd. (Canada). Trace element and major oxide compositions of samples were determined byICP-AES and REEs were analyzed by ICP-MS. Major, trace and rare earth elements were measured ICP-ES and ICP-MS techniques on glass pellets which were produced in platinumgold crucible adding 1/5 ratio of sample and lithium tetraborate (Li2B4O7) at 1150 ºC. Correlation coefficients were calculated from the data set for geochemical analyses. Accordingly, the significance level is α = 0.05.

Major and trace element geochemistry
Major and trace element concentrations, average (ẋ), standard deviations (St.D.) of the analyzed samples are given in Table 1 (Figure 4(a)). In the [43] diagram, samples of two groups are defined as "Fe-sand" (Figure 4(b)).      The trace element contents of two sample groups were compared to Post Archean Australian Shale (PAAS; [44]). Th, Zr, and U are initially partitioned to melts through crystallization and for this reason, these elements are enriched in felsic rather than mafic rocks [45]. Sc content is higher at the arc-related mafic rocks [46]. Th, Cs, Zr, Ba, Rb, Hf, Nb, U are lower and Sc, Ni, V and Co concentrations are higher relative to PAAS showing that our samples are do not have an acidic character (Figure4(c)). Lower Cs, Ba, and Rb contents may reflect also weak weathering and recycling conditions [47].
Correlation analysis can reveal the element associations [48]. Some correlation graphics for major and trace elements are shown in Figure 5. Fe, Na, Ti, and P show positive correlation with Al2O3, indicating that these elements are mainly dependent on feldspar and clay minerals ( Figure 5(a),(b),(c). The Zr/Sc ratio is an indicator of heavy mineral concentration [44].
In first-cycle sediments, Th/Sc ratios show a positive correlation with Zr/Sc, on the other hand Zr/Sc ratios in recycled sediments yield variation with slight change accompanying the Th/Sc ratio [49]. There is a significant positive correlation between these ratios in two sample groups, showing that the siliciclastic sample groups are not exposed a considerable amount of sediment recycling ( Figure  6).

REE geochemistry
Concentrations of rare earth elements (REE) are listed in  (Figure 7a-b). The sorption of REEs by clay minerals was reported by [50], [51]. The negative correlations between total REEs, CaO and MgO are consistent with the decrease in REE concentrations with increasing carbonate content (Figure 7a).

Provenance and tectonic setting
The geochemical compositions of terrigenous sediments are frequently used by many researchers to infer the provenance, because they tend to reflect source rock composition. Provenance studies are common for sedimentary rocks [7], [8], [53]- [55]. In order to characterize the provenance of shales, it is necessary to rely on elements that are the least mobile during weathering, transport, diagenesis and metamorphism [56].
In geochemical studies, Al/Ti ratios of most clastic sediments display the average composition of the source area [57]. In most igneous rocks, Ti resides in mafic minerals (e.g., pyroxene, hornblende, chlorite, biotite, ilmenite) and Al in feldspars. Al/Ti ratios generally increase with increasing SiO2 content. Al2O3/TiO2 ratios range from 3 to 11 for mafic rocks, 11-21 for intermediate rocks and 21-70 for felsic rocks [57]. The average Al2O3/TiO2 ratios are 15.33 for Çaybağı and 13.42 for Palu samples showing an intermediate source rock for these samples (Table 1).
In the provenance discrimination diagram of Roser and Korsch [10], the discriminant functions are based on concentrations of immobile and mobile major elements. In this diagram, 4 samples from the Çaybağı Formation plot in sedimentary detrital field and must be taken material from Kırkgeçit Formation (Figure 8)  The rare earth elements (REEs) and Ti, Nb, Zr, Y, Sc, Th, and Co are the most suitable for provenance determination of the clastic sedimentary rocks [21], [58], [59]. Geochemical investigations have shown that during the sediment transport and deposition, these immobile elements concentrate in the suspended load of the river, and therefore they are useful for provenance characterization [59], [60]. These elements are transported in terrigenous components of the sediment and they reflect the chemistry of their source rocks [61]. Figure  9(a) compares the TiO2 vs. Zr of the studied samples, and in the diagram, two groups of samples characterize the intermediate rocks.
La/Sc, Sc/Th, Cr/Th, and Co/Th ratios of immobile elements are also used to determine sediment provenance [44]. La/Sc and Th/Co ratios (Figure 9b) show that two sample groups have similar character (intermediate in composition) lying between acidic and basic rock types. Likewise Sc/Th ratio is also between felsic and basic compositions. Cr/Th and Co/Th are higher than those of basic rocks which can be explained by the enrichment of basic materials during sedimentary processes (Table 3). and Palu samples (after [57]). (b); La/Sc versus Th/Co plot displaying source rock composition for two sample groups (fields after [65]).
Enrichment or depletion of LREEs and HREEs was quantified by the ratio of (La/Yb)N (N: chondrite normalized; [62]). The average of this ratio is similar for two sample groups, displaying geochemical similarities of Çaybağı and Palu samples (Table 2). Additionally, the REE patterns are also used to estimate the provenance. Basic rocks contain low LREE/HREE ratios and no Eu anomalies, whereas more silicic rocks usually comprise higher LREE/HREE ratios and negative Eu anomalies [63]. Chondrite normalized patterns of sample groups show that REE patterns have low LREE/HREE ratios and little or no Eu anomalies ( Figure 10).  (Table 2).
These findings also show that the source of two samples groups is intermediate-basic in character. [33] studied the Elazığ Magmatics around study area, and they suggested that those magmatics are derived from tholeiitic type magmatic rocks which contain basaltic pillow lavas, pyroxene-bearing andesitic lava flows. Sedimentary rocks from different tectonic settings have varying geochemical characteristics [10]. Trace elements and their various bivariate and multivariate plots are mostly suitable for tectonic diagrams of paleotectonic settings [9]. Tectonic environment interpretations for samples based on major element chemistry can be performed using a SiO2 versus K2O/Na2O diagram [10] (Figure 11a). Samples plot in the fields are grouped as arc related. In the plot of La/Sc vs. Ti/Zr, samples fall in the oceanic island arc field ( Figure 11b). As previously stated, Elazığ Magmatics consisting of arc type rocks are the source rock of both groups. Likewise Dönmez [67] suggested that these magmatics were formed in the Late Cretaceous island-arc which is related to the supra-subduction zone of the southern branch of Neotethys.

Conclusions
Integrated geochemical analyses of samples from the Çaybağı and Palu Formations ensure understanding for the determination of the source rock composition and tectonic setting. In Si vs. Na/K diagram, samples fall in the arc field. In La/Sc vs. Ti/Zr graphic samples fall in the oceanic island arc field. These findings are in consistent with results of previous investigations on Elazığ Magmatic rocks.
The concentrations of major, trace and rare earth elements (REE) considered are mainly related to the source rock composition and are in accord with provenance rocks of the studied two river systems. Sedimentological investigations suggest that basic-type rocks occur within the drainage basin (e.g. Elazığ Magmatics and Kırkgeçit Formation). consistent with recent interpretation of regional geologic history. The source rocks could be accepted as Kırkgeçit Formation and Çaybağı Formation at the east of Hacısamdere section of Çaybağı Formation, and Elazığ Magmatics at the east of the Palu section. This study presents the initial findings based on a limited number of samples from river deposits from Çaybağı and Palu Formations. Provenance reconstruction could be made by detailed geochemical analyses coupled with mineralogic-petrographic descriptions on vast number of samples collected from different parts of alluvium fan and lacustrine deposits in these basins.

Acknowledgement
The financial support of the Fırat University (Turkey) Scientific Research Projects Unit under FUBAP MF.16.13 project number is gratefully acknowledged. We are grateful to the editor and anonymous reviewers whose helpful reviews have greatly improved the manuscript.