GEOCHEMISTRY OF BROWN DETRITAL LIMESTONE BEDS WITHIN SARMORD FORMATION, SULAIMANI, KURDISTAN REGION, IRAQ: IMPLICATION FOR DEPOSITIONAL ENVIRONMENT, PROVENANCE AND TECTONIC SETTING

Fifteen samples of brown detrital limestone beds within the Sarmord Formation from the Imbricated Zone (Qaiwan and Barzinjah sections) and High Folded Zone (Zewe section), Kurdistan region, NE-Iraq were analyzed. The analysis includes the major oxides, trace elements, and rare earth elements (REEs) to find out their provenance, tectonic setting, and depositional environment. These beds are mainly composed of detrital limestone in which calcite and traces of quartz are confirmed by XRD and the microscopic study. Al 2 O 3 /TiO 2 , La/Sc, La/Co, Th/Sc, Cr/Th and Th/Cr ratios and {(TiO 2 + V 2 O 3 ) - (MgO/ (MgO + Al 2 O 3 )}, (TiO 2 - Ni), (La/Th - Hf), (La/Sc - Co/Th) diagrams reveal sourcing from the mixed carbonate platform and felsic rocks. The ratios of major, trace, and REE with PAAS values fall within the range of felsic


INTRODUCTION
Geochemical study of major and trace elements can reveal information about the nature of the sediment, sedimentary rock origin, and depositional conditions (Nesbitt & Young, 1982;Taylor & McLennan, 1985).Sedimentary rock geochemical characteristics are directly tied to the tectonic setting of sedimentary basins (Bhatia & Crook, 1986).The distinction between individual units of clastic and carbonate layers was commonly done using the bulk chemical composition of sedimentary rocks (Bjørlykke, 1974).Soluble elements within carbonate, such as Vr, Mg, Cr, Ni, Cu, Na, Zn, P, Sr, U, and Mo can be used to represent the chemical composition of paleo seawaters (Tribovillard et al., 2006).
The Sarmord Formation (Valanginian-Aptian) was first defined by Bellen et al. (1959) in the Surdash anticline, Sulaimani government, Kurdistan region, Iraq.The formation's type section is 455 meters of uniform brown and blue marl with layers of argillaceous limestones (Bellen et al., 1959).The Sarmord Formation was fragmented by (Chatton & Hart, 1960) into three parts, lower, middle, and upper.Buday (1980) merged the lowest two sections to form the Lower Sarmord Formation, which is considered to be Berriasian-Aptian in age.
Previous works within the Sarmord Formation have mainly focused on stratigraphy, sedimentology, depositional environment, reservoir characteristics, and source rock potential (Fatah et al., 2023).According to Jassim & Goff (2006) from the outer shelf to the deep inner shelf environment is where the Sarmord Formation was formed.Al-Samarraie (2012) suggested that the Sarmord Formation might belong to the deep shelf margin of normal salinity while Ahmed et al. (2015) believed that the Sarmord Formation deposited in the outer shelf environment.
The current study examines the geochemistry of the brown detrital limestone beds of the Sarmord Formation in the Qaiwan, Barzinjah, and Zewe sections (Figures 1 and 2).The following paper aims to determine the tectonic setting, provenance, climate, salinity, and redox conditions for the brown detrital limestone beds of the Sarmord Formation.

GEOLOGICAL SETTING
The brown detrital limestones within the Sarmord Formation are studied throughout three sections: Qaiwan, Barzinjah, and Zewe.The first section is located 20 Km to the north of Sulaimani city, near the Little Qaiwan village at Latitude 35°42'32.53"Nand longitude 45°25'18.30"E.This section is located in a small fold, which is a part of the major Azmir-Goizha anticline.It is a part of the Imbricated Zone of the Zagros Collisional Belt in the Iraqi tectonic subdivision of Jassim & Goff (2006) (Figure 1).Most outcrops of this formation are clear inside the core.The second section, which is located in the Imbricated zone is 1 Km from the South of the Barzinjah district at Latitude 35°32'34.25"Nand longitude 45°41'44.62"E(Figure 1).The third section is located about 2 Km to the north of the Zewe district at Latitude 35°45'36.45"Nand longitude 45°14'36.09"E in the High Folded Zone (Figure 1).
The Formation consists entirely of an alternation of marl, marly limestone, and detrital limestone (Figure 3).The Sarmord Formation has conformable contact with the Chia Gara and Balambo formations at the bottom and top, respectively in the Qaiwan (Figure 3a) and Barzinjah sections (Figure 3b).It overlaps the Chia Gara Formation and underlies the Qamchuqa Formation in the Zewe section (Figure 3c).It is clear from the study that thin sections look like detrital limestone with some diagenesis (Figure 4).The lower contacts of the beds are sharp and erosional indicating sudden deposition and high energy condition.

METHODS AND MATERIALS
Fifteen samples were collected along these three sections from the exposed outcrops of the formation, seven samples from Qaiwan, six samples from Barzinjah, and two samples from the Zewe section.Thin sections were made for fifteen rock samples at the University of Sulaimani/ Department of Geology for microscopic studies for petrographic study.Two bulk carbonate samples were analyzed using the X-ray diffraction technique (PANanalytical, Goniometer PW3050/60) in Sulaimani University/ Department of Geology to determine the mineral content.
Fine crushing of 15 samples to 70% passing 2 mm, then pulverize samples up to 250 g to 85% passing 75 microns.Major oxides of these samples of Sarmord Formation with (LOI) and some trace elements (Mo, Cu, Ni, Co, Zn, and SC) after fused bead and acid digestion were analyzed by using the inductively coupled plasma atomic emission spectrometry (ICP-AES).Most of the trace elements (Ba, Cr, Zr, U, Nb, V, Rb, Sr, Th, Y, and Hf) and rare earth elements (REEs) were analyzed after four acid digestion by using inductively coupled plasma-mass spectrometry (ICP-MS) in Canada at the ALS international laboratory.Chemical analysis has precisions of up to (0.01 to 3) % for major elements and (0.01 to 10) ppm for trace and REEs.

RESULTS
The brown beds of the Sarmord Formation are characterized by thin-bedded streaks of limestone detrital, which is due to the high content of around 6 to 7% Fe2O3, fine crystalline calcareous ferruginous cemented.The iron comes from the source area, it is well known that source areas contain high iron content which has impacted on old sediments derived from them.It is fine crystalline, partly coarse to fine-grained, medium-hard, highly fractured in some places, and partly filled by calcite.Generally, these brown limestones in all sections are composed of detrital Limestone (Figure 4).Pellet and oolite are not present.All the beds have erosional sharp lower contact, which indicates possible calciturbidite.
From the XRD mineralogical point of view, these beds of limestones contain mainly calcite at 2 θ = 29.40°and traces of quartz at 2 θ = 26.6°(Figure 5).All samples were checked by calcimetry, XRD, and chemical analysis (ICP) showed that the beds are limestone, not dolomite.

Major oxides
The major components of 15 bulk samples were analyzed.Table 1 shows the brown beds are major oxide concentrations and loss on ignition (LOI) in (wt.%).Calcium oxide (CaO) % ranges between 33.8 to 39.9, which is the most abundant oxide in the examined rocks (average 36.41%)followed by little SiO2 (9.66 to 15.55) % (average 14%) and Fe2O3 (6.24 to 7.65) % (average 7.08%).

DISCUSSION
The mineralogy and element composition of these samples will be used to interpret the results of this investigation.Our samples show traces of clay and quartz grain of less than 2% as detected from the thin sections.The average CaO concentration in the limestone of all sections is near to each other, and the fluctuations in CaO content in all samples are very low, implying that these sections are chemically homogenous limestones.Because CaO is mostly formed from carbonates, it exhibits a considerable positive correlation with LOI over all sections (Table 2).CaO shows a strong negative relation with Al2O3, TiO2, K2O, Fe2O3, Cr2O3, MgO, and MnO demonstrating that carbonate phases dominate CaO control and explains the detrital content in the studied limestones which contain a small amount of amorphous iron oxide which is not detected by XRD.The low content of MgO in all studied samples is due to the deficiency of dolomite and/or dolomitization with dominant microcrystalline calcite is the only major carbonate mineral.The major impurities observed by XRD and petrography are silicates.
Regarding the open ocean environment the place where limestone is deposited, major elements (Fe2O3 and MnO, except for CaO) of these studied limestone successions show a large positive correlation with Al2O3 (Zhang et al., 2017).On the spider diagram, major oxides have been shown normalized using PAAS values (Figure 6) (Taylor & McLennan, 1985).The figure shows that the samples with the greatest CaO concentrations are more stable and have fewer impurities.which are confirmed by XRD analysis and thin sections.(Figures 4 and 5).Generally, the brown detrital limestone samples of the Sarmord Formation are Compared to PAAS, the samples have a significant trace element depletion.except that of Sr which is geochemically associated with calcite (Brookins & Watson, 1969).Mo is near the PAAS value due to the detrital content in the studied limestones (Voegelin et al., 2010) 7).The PAAS plot REE normalized concentrations also show notable depletion due to the source area weathering and transportation through marine water (Figure 8).
Negative correlations between ΣREEs and CaO and strong positive correlations between ΣREEs and elements such as Co, Al, Ni, Rb, Si, Cu, Ti, Nb, and V imply that the small amount of detrital substances mostly regulated the observed changes in REE concentrations in the limestone.According to geochemical data, plagioclase and diagenetic processes may be responsible for the distinct positive Eu anomalies in the brown detrital limestone layers and may be considered as syn-hydrothermal fluids incorporated with sea water (Danielson et al., 1992) (Table 2).

Provenance
The use of the geochemical composition of sedimentary rocks has an important role in understanding the nature of source rocks (McLennan et al., 1993); (Roser & Korsch, 1988).When the source rocks weather, the majority of elements, particularly Na, Mg, K, and Ca, partly leak away.However, Ti, Zr, and Al can be regarded as basically immobile elements because the oxides and hydroxides of these elements have low solubility in low-temperature aqueous solutions (Morgan & Stumm, 1981); (Wesolowski, 1992).Sediments are derived from felsic rocks if the Al2O3/TiO2 ratio ranges from 21 to 80, sediments are derived from intermediate rocks if the ratio of Al2O3/TiO2 ranges from 8 to 21, and if the ratio of Al2O3/TiO2 ranges from 3 to 8, that means the sediments are derived from basic rocks (Hayashi et al., 1997).The Al2O3/TiO2 ratio of brown detrital limestone of Sarmord Formation samples in the Qaiwan, Barzinjah and Zewe sections (Table 3) varies from 19.03 to 21.68 (avg. 20.83), 19.66 to 21.75 (avg. 20.53) and 20.07 to 20.52 (avg. 20.29) respectively, which indicates the mixed source rocks and/or felsic as a whole.Grigsby (1992) suggested a discrimination diagram to identify the provenance source for sedimentary clastic facies as a provenance indicator (Figure 9a).On the plot of TiO2 + V2O3 vs MgO/ (MgO + Al2O3) the samples display felsic plutonic source rocks.(Gu et al., 2002).
Immobile trace elements such as TiO2, Ni, and Zr are geochemical proxies to discriminate the provenance of the sediments (Hayashi et al., 1997); (Floyd et al., 1989).In the provenance discrimination (TiO2 vs Ni) diagram of Hayashi et al. (1997), the samples of the Sarmord Formation from all sections plotted in the field of acidic(felsic) rocks (Figure 9b).A plot of La/Th versus Hf shows useful bulk rock discrimination between different sources and arc compositions (Floyd & Leveridge, 1987).On a Hf versus La/Th bivariate (Figure 9c) samples of Sarmord Formation are scattered between fields of felsic and andesitic suggesting the mixed felsic/ intermediate source rocks for the brown detrital limestone of Sarmord Formation.REE, Cr, Co, Th, and Sc are useful elements due to their brief residency in the water column and rapid incorporation into the record of sedimentary, monitoring the compositions of source areas Taylor & McLennan (1985).Co/Th and La/Sc ratios are reliable indications of the compositions of source rocks (Gu et al., 2002) because mafic rocks are depleted in Th and La and enriched in Co and Sc compared to felsic rocks (Cullers, 1994).On the plot of Co/Th versus La/Sc (Figure 9d) (Gu et al., 2002), the data reflect felsicintermediate source rocks.There are considerable differences between the ratios of La/Sc, La/Co, and Th./Sc, Cr/Th, and Th/Cr in felsic and mafic rocks, which might place limitations on the provenance composition (Cox et al., 1995).Comparing the ratios of the brown beds of Sarmord Formation in all sections with sediments sourced from felsic and mafic rocks of UCC and PAAS values of Taylor & McLennan (1985) as well as Cullers (1994).These ratios,

Iraqi Bulletin of Geology and Mining
Vol.20, No.1, 2024 p 103 126 119 according to the comparison, fall into the range of felsic rocks (Table 4).These felsic rocks are possibly the main outcrops of an area during the Early Cretaceous that coincides with the present Western Desert, in this connection many carbonate formations are mentioned by Bellen et al. (1959) and Sissakian & Mohammed (2007) during Jurassic and Early Cretaceous.These brown beds are possibly affected too by remote volcanic arcs that were surrounding Neotethys during the Early Cretaceous from which some REE and trace elements are transported from volcanic arcs shown in Figure ( 10).This effect is reflected by the anomalous location in the diagram of Hf -La/TH (Figure 9c).Th/Cr 0.13 -2.70 0.018 -0.046 0.13 0.13 0.10 0.13 0.12 1) (Cullers, 1994); 2) (Taylor & McLennan, 1985); 3) This study.

Tectonic setting and depositional model
Limestone forms in a variety of tectonic settings, including continental margin, oceanic margin, oceanic floor, and inland (Wilson, 1975).Primarily, during these varieties of depositional environments trace elements and REE are introduced which are mainly influenced by the basin plate tectonic environment (Murray et al., 1991).(Zhang et al., 2017).Older marine carbonates and weathering of volcanic ash layers are two plausible origins of the increased Sr in the shale (Cochran et al., 2010).This is evident by drawing a tectonic model based on the previous model constructed by Mirza et al. (2021), which explained and showed that the SSZ of the southern part of Neo-Tethys was a deep basin during the Early Cretaceous, so these detrital limestones are transported from the erosion of the platform into deep marine and interbedded with the green marl and weakly supplied by some elements from the arc components (Figure 10).They are well-sorted lithoclast due to transportation for very long distances by turbidity current.

Paleoredox
Tyson & Pearson (1991) used the words oxic, dysoxic, suboxic, and anoxic to describe the oxygenation of bottom water (Table 5).When hydrogen sulfide is present in the water column, anoxic conditions are also known as euxinic circumstances (Tribovillard et al., 2006).Euxinic environments are those in which the water column contains free H2S Trace element ratios are useful for assessing sedimentary bottom water conditions because the behavior of specific elements associated with organic and/or terrigenous components is influenced by redox conditions (Hallberg, 1976) The following ratios U/Th, V/Cr, and Ni/Co are employed in this study to identify the paleoredox state since (Jones & Manning, 1994) considered them to be the most accurate indicators.
A redox indicator may be made from the ratio of uranium to thorium (Adams & Weaver, 1958).According to Jones & Manning (1994) U/Th below 0.75 indicates oxic circumstances, whereas those between 0.75 and 1.25 indicate dysoxic conditions, and those beyond 1.25 indicate suboxic and anoxic conditions.. In the present study, the U/Th value is less than 0.75 in all sections (Figure 12 and Table 3) which indicates oxic conditions.
Numerous research has proposed and used the ratio V/Cr as an indicator of paleoredox (e.g., Ernst, 1970).Values of V/Cr ratios less than 2 indicate oxic circumstances, between 2 to 4.25 imply dysoxic situations, and it indicates suboxic and anoxic conditions when it is more than 4.25 (Jones & Manning, 1994).The V/Cr value is less than 2 in all sections except one

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Vol.20, No.1, 2024 p 103 126 121 sample in the Barzinjah section is 2.2 (Figure 12 and Table 3), this indicates oxic conditions in both Qaiwan and Zewe sections while oxic to dysoxic in the Barzinjah section.
Table 5: Terminology for the description of bottom water oxygenation (Tyson & Pearson, 1991).Ni/Co has also been utilized as a redox index (e.g., Dypvik, 1984).Ni/Co ratios of less than five imply an oxic environment, those of five to seven dysoxic, and those of seven or more suboxic and anoxic (Jones & Manning, 1994).Ni/Co ratio in Qaiwan section range from 3.37 to 5.33 (avg.4.37), in Barzinjah section range from 3 to 7 (avg.5.38) and in Zewe section range from 3.6 to 3.8 (avg.3.7), which indicates oxic to dysoxic conditions in Qaiwan and Barzinjah sections while oxic conditions in Zewe section (Figure 12 and Table 3).The samples from the Qaiwan Barzinjah and Zewe sections have very low average Sr/Ca ratios (0.0014, 0.0017, and 0.0013, respectively) compared to the deep-sea carbonate samples (0.00525) reported by Turekian (1964) indicating a shallow marine environment for the Sarmord Formation.
Deep marine shale is distinguished from shallow marine and freshwater shale in (Figure 13), which displays V against Al2O3 (after Mortazavi et al., 2014).Consistently, the examined samples were found in a shallow sea environment.This paleoenvironmental interpretation is correlated with the above paleo-redox conditions (oxic to dysoxic conditions).So the origin of

Geochemistry of brown detrital limestone beds within Sarmord Formation, Sulaimani, Kurdistan Region, Iraq
Sardar M. Ridha and Sehad A. Eminki 122 the detrital brown beds was continental or shallow marine but deposited in deep marine and associated (during deposition) with ammonite and nano fossil.

Paleoclimate
The geochemistry and mineralogy of sediments are significantly impacted by climate (Yan et al., 2010).The best chemical maturity trend as a function of climate can be shown in the SiO2 versus total (Al2O3 + K2O + Na2O) diagram (Suttner & Dutta, 1986).Based on the binary diagram of SiO2 versus (Al2O3 + K2O + Na2O), the samples of the Sarmord Formation indicated deposition in an arid climatic condition in all studied sections (Figure 14a).
To determine the paleoenvironmental conditions of fine-grained siliciclastic rocks, the concentrations of some major oxides and trace elements were used (Roy & Roser, 2013).Rogers & Adams (1969) proposed the ratio of Σ (Fe + Mn + Cr + Ni + V + Co)/ Σ (Ca + Mg + Sr + Ba + K + Na) (termed as C-value) as a climate proxy.In the present study, the Cvalues of the Sarmord Formation samples range from 0.15 to 0.19% (avg. of 0.18% in the Qaiwan section, 0.05 to 0.15% (avg. of 0.11% in the Barzinjah section and 0.14 to 0.15% (avg. of 0.15% in the Zewe section (Table 3), reflecting a generally arid climatic condition for the source area (present western desert) (Figure 14b).
Additionally, the Sr/Cu ratio has been used for palaeoclimatic investigations (e.g., Meng et al., 2012).Sr in the sediment being produced leaches away, and the Sr/Cu ratio in the deposited sediment is decreased when the environment is more humid and warmer to encourage greater weathering (Deng & Qian, 1993).According to Lerman (1978), Sr/Cu ratios between 1.3 to 5.0 indicate a warm humid climate, whereas ratios over 5.0 indicate a hot, arid climate.The samples from the s hot arid conditions.Rb/K and Sr/Ba ratios suggest brackish water conditions for the brown detrital limestone beds of the Sarmord Formation.

Paleosalanity
The paleosalinity of brown detrital limestone of the Sarmord Formation was measured by using the Rb/K ratio and Sr/Ba ratio (Table 3).Degens et al. (1957) proposed Rb as a possible indicator of paleoenvironment stating that Rb is concentrated in marine shales.(Campbell & Williams, 1965) suggested that the elemental ratio of Rb/K less than 0.004 suggests freshwater conditions, 0.004 to 0.006 suggests a brackish water condition, and more than 0.006 designates a fully marine water environment.The Rb/K ratio of brown detrital limestone in the Sarmord Formation ranges from 0.0045 to 0.0049% (avg.0.0047%) in the vs V for the brown Qaiwan section, 0.0027 to 0.0055% (avg.0.0047%) in Barzinjah section, and 0.0051 to 0.0052% (avg.0.0052) in Zewe section, indicating a brackish water sedimentary environment in all sections (Table 3).
The geochemical behavior of strontium (Sr) and barium (Ba) in various sedimentary environments is different (Liu et al., 1984; The elemental ratio of Sr/Ba is often accepted as an empirical indicator of paleosalinity (B.J. Liu, 1980).A Sr/Ba ratio of 0.2 distinguishes between fresh water and brackish sediments, whereas a ratio of 0.5 distinguishes between brackish and marine sediments (Wei Algeo, 2020).The Sr/Ba ratio ranges from 4.21 to 13.26 (avg.8.48), 2.12 to 23.4 (10.23), and 4.50 to 6.62 (5.56) in the Qaiwan, Barzinjah, and Zewe sections respectively, which indicate marine water condition in all studied sections (Table 3).
Figure 1: a) Tectonic subdivision of the Unstable Shelf of Iraq shown on the location map of Iraq (modified from Buday, T., and Jassim (1984); b) geological map of the study area (after Karim et al., 2021).

Figure 2 :
Figure 2: Field photos of a) Qaiwan section (intercalation of 7 brown beds of limestone with grey marl and marly limestone; b) Zewe section (only two thin beds of brown limestone); and c) Barzinjah section (intercalation 6 thin beds of brown limestone with grey marl and marly limestone).

Figure 10 :
Figure 10: Location of Sarmord Formation on the Arabian platform which is geochemically affected weakly by island arc, deep marine water in addition to the geochemistry of its original location of the platform (modified from Mirza et al., 2021).
Zhang et al. (2017) plot a triangular diagram for the Sr -Rb -Ba andMirza et al. (2021) plot a diagram for the Sr/Ba versus Sr/Rb, the studied samples of brown detrital limestone reveal that these samples are distributed between the continental margin and inland field (Figure11a and b).This is dueGeochemistry of brown detrital limestone beds withinSarmord Formation, Sulaimani, Kurdistan Region, Iraq Sardar M. Ridha and Sehad A. Eminki 120 to the low Ba and Sr concentration in differentiation with open ocean limestones

Figure 12 :
Figure 12: The distribution of U/Th, V/Cr, and Ni/Co ratios in the study area (fields after Jones & Manning, 1994).

Table 2 :
Correlation coefficient of major and trace elements for brown detrital limestone of the Sarmord Formation.

Sarmord Formation, Sulaimani, Kurdistan Region, Iraq Sardar M. Ridha and Sehad A. Eminki 116
Figure 8: Post Archean Australian Shale (PAAS) normalized REEs patterns for the brown detrital limestone samples of the Sarmord Formation.PAAS values were taken from

Table 3 .
Paleoredox parameters, paleoclimate parameters, and paleosalinity parameters for studied samples of Sarmord Formation.

Table 4 :
Ratios of elements for the brown detrital limestone of Sarmord Formation in comparison with fine fractions source rocks derived from felsic and mafic.