Mineralogy and Geochemistry Characteristics of Tanjero Formation in Selected Locations, Northeast of Iraq

Abstract


Introduction
Tanjero Formation (Late Campanian-Maastrichtian) is predominantly made up of clastic sediments such as marl, siltstone, sandstone, shale, and conglomerate, according to Jassim and Goff (2006); Karim and Surdashy (2006) and Aqrawi et al. (2010), These clastic sediments formed as flysch deposits in a basin that was rapidly subsiding.The type section in Sirwan Valley, southeast of Sulaimaniyah, is divided into two sections: the upper section is made up of alternate bedding of silty marls, siltstone, conglomerates, and detrital limestone, with a thickness of up to 2010m; the lower section is made up of 484 m thick basinal marl, with some beds of limestone and siltstone (Sissakian et al., 2016).However, it becomes finer-grained and thinner-bedded as you move southwest.To the southwest, it becomes more finely grained and lightly bedded.The Balambo-Tanjero zone and a few locations in the low folded zone of the unstable shelf are the only places where the Tanjero Formation can be found.
The formation is exposed in certain regions and occasionally fills the troughs between the anticlines of the synclines (Sissakian et al., 2016).The lower part of the Tanjero Formation is conformable and gradational with the Shiranish Formation, whilst the higher boundary is unconformable with the Kolosh Formation.Many previous works deal with the petrographic characteristics of the Tanjero Formation to interpret the depositional environment.On the other hand, there is only one geochemical study on the formation in the study area by Al-Nakib and Dhannoun (2014), in which they pointed out the clear difference in the nature of the source rocks for the lower part of the formation compared to the upper part.The study showed that the lower part was deposited in deep marine basins, while the upper part was deposited in shallow basins.
The main objective of this study is to determine the mineralogical and geochemical characteristics, source rock, and correlation coefficient between geochemical elements of Tanjero Formation by conducting some geochemical and mineralogical analyses.

Materials and Methods
Twenty-four rock samples (12 from Dokan and 12 from Qamchuqa) were collected from two sections of the Tanjero Formation (Dokan and Qamchuqa) within latitudes (35°57'53.00,35°53'29.39")N and longitude (44°54'7.00,"45° 0'45.51"E) (Fig. 1).Geochemical analysis was conducted to determine the percentages of major Element ( SiO2, Al2O3, Fe2O3, CaO, MgO, Na2O, K2O,TiO2, LOI ) and trace element (Cd, Co, Cr, Cu, Mn, Ni, Pb, V, and Zn) using X-Ray Flourescence (XRF) techniques and the analysis was carried out at the Iraqi-Germany Lab (Department of Geology, College of Science, University of Baghdad).While eight samples were selected to be analyzed for mineralogical analysis using XRD techniques to determine the mineralogical constituents, and it was carried out at the labs of the Ministry of Sciences and Technology.

Geological setting
The study area lies in the unstable shelf-high folded zone.Deformation from the Cretaceous and Tertiary eras significantly impacts this region.The cores of the anticlines contain limestones from the Mesozoic era, while their flanks contain limestones and clastic from the Tertiary era.In northeast Iraq and in the north of Iraq, the anticlines of this zone tend to extend in a trend of NW-SE and EW, respectively, according to Jassim and Goff (2006).Due to the closing of the Neo-Tethys, there was a significant marine incursion during the Late Campanian-Maastrichtian. NW-SE extensional basins were created as a result of the ophiolite obduction and the closure of the Neo-Tethys.In a foredeep basin that was subsiding at the time, ophiolite sheets that had been lifted above sea level were eroded and left behind as flysh deposits, which are represented by Tanjero Formation.As a result, the Balambo-Tanjero, high folded, and some low folded zones are largely covered by the Tanjero Formation.Shiranish carbonate and basinal marl are deposited laterally into the Hadiena, Aqra, and Bekhma Formations, which were deposited to the southwest in shallow environments.

Mineralogy
The results of XRD analysis showed that Dokan and Qamchuqa mudstones are composed of clay and non-clay minerals.Calcite was the most abundant mineral in the clay fraction of Tanjero Formation with an average of 45% (Table 1).It is identified in the range of 3.03 A° (Fig. 2), while the average of quartz is 41% (Table 1).It is identified in the range of d-spacing 4.25A° and3.33 A° (Fig. 2).Whereas Feldspar was identified at the peak of 3.19 °A in a small percentage in the study area (Table 1), compared with the calcite and quartz with an average of 3% (Fig. 2).The average of illite was 4% Table 1, and it can be identified by the basal reflection (001) d=10A°.The basic reflection of this mineral does not expand or collapse with respect to ethylene glycol when heated to 550°C (Faning et al., 1989) (Fig. 2).Weathering of silicates (mainly feldspar), metamorphism of other clay minerals, and degradation of muscovite give rise to the illite parentage, the predominant clay mineral in argillaceous rocks (Deer et al., 1975).
Illite minerals are alkali feldspar minerals, muscovite, and other alumino-silicates formed by direct weathering erosion or transformation, originating from acidic igneous and metamorphic rocks, and then migrated to sedimentary basins in the form of tiny clastic clays (Degnes, 1965 ;Grim, 1968 andMilott, 1970).This mineral is also formed by the weathering of ancient sedimentary rocks (Keller, 1962).Arid environments with low rainfall, high alkalinity (pH above 8.5), and rich potassium ions are ideal for Illite formation (Degnes, 1965).While the average of Chlorite was 45% Table 1 and can be observed in the basal reflections ( 001) and ( 003) at d=14-14.6 A° and d=4.7-4.9A°, respectively, (Fig. 2).Fechlorite and the higher-order peaks may weaken while the (001) chlorites peak may increase significantly at 550°C of heating (Moore and Reynolds, 1997).Chlorite minerals are frequently found in igneous rocks as hydrothermal alteration by-products of ferromagnesian minerals and low grade greenschist facies metamorphic rocks (Deer et al., 1992).Montmorillonite mineral was identified in all samples of Tanjero Formation except sample D15.It is recognized in the basal reflection (001) at the range of d=14.2 -15A° and the basal reflection 002 at 5.5 A° with an average of 4% (Table 1, Fig. 2).Montmorillonite is expanded when it is glycolated and the reflection present in d=17.18A°, and after heating to 550 C° the reflection is collapsed to 10 A°.This mineral is present in lower amounts compared to other clay minerals.Folk (1974) suggested that montmorillonite is usually developed in an Mg-rich environment and/or upon the weathering of Mg-rich ultrabasic rocks.It is most likely to form under conditions that are warm, dry, and poorly drained (Grim, 1968;Millot, 1970).

Geochemistry
Twenty-four samples were selected for analysis from two sections (Dokan and Qamchuqa) of Tanjero formation for the determination of the major oxides (SiO2, Al2O3, Fe2O3, CaO, MgO, Na2O, K2O,TiO2, LOI ) and trace element (Cd, Co, Cr, Cu, Mn, Ni, Pb, V, and Zn), The results and ranges of the chemical analyses for major and trace elements are listed in Tables (2 and 4).

Geochemistry of major oxides
The percentage of Silica in the Dokan section ranged from 21.23 to 41.65 , while it ranged from 18.26-45.11in the Qamchuqa section (Table 2).This low percentage may reflects the high content of carbonate rock fragments and ferromagnesian minerals and low content of quartz (Sarmad and Eman, 2018).Mud has more silica than other rocks, due to the presence of SiO2 within the structure of clay minerals.In addition, carbonate cement will reduce the SiO2 during replacement processes.Silica has strong positive relationships with Fe 2 O 3 and positive with Al 2 O 3 , Na 2 O, K 2 O, and MgO but an inverse relationship with CaO because the depositional conditions of the calcium oxides differ from those of silica (Table 3).The silica is unstable in basic conditions (pH more than 7) so the silica dissolved in the mud (and vice versa) (Sadiq, 1985(.While percentage of aluminum in the Dokan section ranged between 2.48 and 9.27, while it ranged between 3.74 and 9.63 in the Qamchuqa section, Table 2. Aluminum was a component of numerous minerals that arrived from rivers and wind sources.(Rubio et al., 2000) proposed aluminum as a resistant or stable element and one of the essential composites of clay minerals.The ratio of Iron oxide in the Dokan section ranged from 3.04 to 5.54 while its range in the Qamchuqa section was 3.03-6.72(Table 2).It is present in iron oxide-containing opaque minerals and makes up the majority of clay minerals including chlorite, montmorillonite, and kaolinite (Eslinger and Peaver, 1988;Sramek, 2000).It can exist as a matrix or as a coating around quartz crystals.It is transmitted as colloidal liquids and precipitated on the outer layers of clay minerals (Al-Samaani, 2011).Calcium is the most abundant oxide in the Tanjero Formation.Its range in Dokan was 24.1-54.5,While in the Qamchuqa section 17.79-54.3(Table 2).The relatively high percentage of calcium oxides is due to the high content of carbonate rock in the Tanjero Formation, which is mainly composed of calcite, and the high percentage of MgO due to the presence of dolomitic limestone.Another source of calcium oxide is most probably coming from the weathering of pyroxene and amphibole minerals in the other locations.CaO is deposited in shallow environments in excess of carbonate, which increases in the expense of silica concentration (Omar and Al-Shamary, 2018).The percentage of Magnesium oxide in the Dokan section ranged from 3.01-to 6.22 while it is range in the Qamchuqa section was 2.54 and 7.09 (Table 2).The high percentage of MgO in the Tanjero Formation refer to the dolomitic limestone of this succession.While the low percentage of MgO comes from the existence of these oxides in the clay minerals like palygoreskite, chlorite, and montmorillonite (Omar and Al-Shamary, 2018).Sodium oxide in the Dokan section ranged from 0.22 to 2.97 whereas its range in the Qamchuqa section 0.23-2.75(Table 2).
The alkali (Na2O and K2O) contents mainly reflect the presence of detrital feldspar but also occur in clays (sarmad and Eman, 2018) (Table 3).Due to its effect on denudation operations and its simple movement as a result of its considerable solubility due to its low ionic potential, as shown in Tables (3  and 2), sodium oxide lacks a significant correlation coefficient when compared to other oxides (Glodshmidt, 1970;Mason, 1966).Potassium oxide in the Dokan section ranged from 0.18-2.70 while its ranged in Qamchuqa 0.035-2.39(Table 2).The link between potassium and the other oxides is shown in (Table 4).There is a positive association between aluminum, silica, titanium, and iron oxides in the Dokan region, which suggests that it has entered the crystalline structure of the potassium feldspar, mica, and illite clay mineral (Tobia and Shangola, 2019;Avinash et al., 2016).K2O reveals a strong positive relationship with Al2O3 because both elements are included in the crystalline structure of illite clay minerals (Omar and Al-Shamary, 2018).The ratio of Titanium oxide in the Dokan section ranged from 0.023-0.55Dokan section whereas in Qamchuqa 0.032-1.32(Table 2).Al-Najjari (2019) reveals that Ilmenite (FeTiO₃), Rutile (TiO₂), and clay minerals chiefly montmorillonite contain significant amounts of Titanium oxide.Concentration antinomy in titanium oxide is due to its ability to replace instead iron and aluminum, and according to the cation exchange capacity, which increases with the increase of clay minerals and the volume of clay (Al-Jubouri, 2005).LOI values were from 10.6 to 20.1 and 9.78 to 17.73 in Dokan and Qamchuqa sections respectively (Table 2).The LOI ratio comes from the loss of water content in gypsum and clay minerals as well as the CO2 in carbonate minerals (limestone and dolomite) in the burning of samples (Omar and Al-Shamary, 2018).

Geochemistry of Trace Element
Vanadium (V) ranged from 24 to 531 ppm in Dokan whereas in the Qamchuqa 28 to 531 ppm (Table 4).V is adsorbed on clay minerals surface within the mineral structure or combined with iron oxides (Landergren, 1978).V found in ferromagnesium such as pyroxene and amphibole were altered to clay minerals ) Omar, 2005).V shows a positive correlation with Zn, Cu, and Mn while it shows a negative to strong negative with Co, Ni, and Cr (Table 5).The range of chromium (Cr) was 40-2346 and 15-2779 ppm in Dokan and Qamchuqa sections respectively (Table 4).Lithogenic Cr is inactive and harmless and is frequently exists in endured source materials like chromite and clay minerals as a replacement for octahedrally coordinated aluminum.Cr is a toxic element that occurs naturally and anthropogenically in soil (Becquer et al., 2003;Oze et al., 2004).Concern exists over Cr that is anthropogenically derived, particularly when it is detected in the hexavalent form.According to Gattullo et al. (2020), the metal differentiation between hexavalent and trivalent forms affects the soil toxicity of Cr.The increase of Cr because it is one of the remaining non-transitional elements during the weathering and transformation processes (Rose et al., 1979).
Manganese (Mn) ranges from 478.2 to 7481 ppm in Dokan and 196.4 to 2233 ppm in the Qamchuqa section (Table 4).Mn content in sedimentary rocks depends on the source rocks' geochemistry and the redox potential in the sedimentary environment (Goldberg and Humayun, 2016).Iron is usually associated with Mn due to similar geochemical behavior (Hylander et al., 2000) The abundance and distribution of Mn in carbonate sediments are considered a significant indicator utilized to recognize deep marine sediment from shallow, where Mn content is higher in the lithofacies of the deep marine environment than the facies of shallow environment ) Shanmugen and Bendict, 1983).Mn shows a strong positive correlation with lead positive with zinc, cadmium, and copper, and negative with other elements (Table 5).Cobalt (Co) ranged from 3.9 to 206 and 3.9 to 202 ppm in Dokan and Qamchuqa respectively (Table 4).Pourret and Faucon (2018) revealed that Co is one of the components of numerous minerals like cobaltite, skutterudite, erythrite, spherocobaltite, and heterogeneity and it is common in igneous and sedimentary rocks.Co occurs naturally and resembles both iron and nickel in several ways.single stable isotope of cobalt exists in nature, where it coexists with other elements like oxygen, sulfur, and arsenic (Al-Saady, 2008).Strongly positive correlation with nickel and only a weak negative with zinc and lead (Table 4).
Nickel (Ni) was ranged between 18.1 and 2667 ppm in Dokan while 0.6 and 3132 ppm in Qamchuqa (Table 4).Ni is present with clay minerals and iron oxides in the sedimentary rocks due to the substitution and adsorption of magnesium and ferrous iron, or both (Bide et al., 2008).Ni shows a negative correlation with V and Mn and showed strong positive with Cr and Co (Table 4).A transition metal that is not present in great concentration in the crust of the earth.The most prevalent forms of it, oxides, were found in soil that contained serpentine.Copper exists in sediments as a replacement, adsorption on secondary iron and manganese oxides, clay minerals, or both, according to (Van Everbroeck et al., 2020).It ranges from 11 to 132.5 ppm in Dokan and (3.8-134.5)ppm in Qamchuqa (Table 4).Due to its high transferability, Cu is easily lost from clay during chemical weathering (Wedepohl, 1978).Zinc can also be found in sedimentary rocks as iron oxide and clay minerals (Berger et al., 2017).It is ranged between 41.3 and 154.7 and 26.4 and 145.2 ppm in Dokan and Qamchuqa sections respectively (Table 4).Zinc shows a positive correlation with V, Mn, and Cu which indicates that these elements may come from the same sources, Table 4. Cadmium (Cd) ranged between 0 and 2 ppm in the Dokan section while it was 2 ppm in all samples of the Qamchuqa section (Table 4).(Callender, 2003;O'Connor et al., 2018).It is ranged from 0.5 to 28.5 ppm in Dokan and 0.4 to 14.7 ppm in Qamchuqa (Table 4).Pb showed a positive link with silica, iron, and aluminum oxides (Table 5), indicating that Pb is absorbed onto the clay particles' surface.The increase in Pb reflects the reducing conditions during the sedimentation period if they are suitable conditions for sedimentation.It shows a strong positive with Mn and a positive with zn and cd indicating that these elements may come from the same source, reflecting the high levels of trace elements (Ni, and Cr) the origin of the prepared source rocks rich in these elements.These are the basal igneous rocks that contributed to the preparation of the clastics of the Tanjero Formation, as reflected in the rise of the ratios of these elements to the reducing conditions during the deposition period (Table 5).

Conclusions
The mineralogical study showed that calcite is considered the most common in the Tanjero Formation, followed by quartz.The percentages of clay minerals such as illite, chlorite, and montmorillonite were very low.
Silica and calcium, aluminum, magnesium, and iron oxides are considered basic components while alkali oxides (potassium and sodium) and titanium oxide are secondary components.Most major oxides of the Tanjero Formation showed diverse relationships that reflect various constituents and their sedimentary conditions and origins.
High values of some trace elements (Cr, and V) reflect their origin from the source rocks which are basic and ultrabasic igneous rocks.The high content of Mn in the carbonate rocks of the formation reflects the depositional environment which is a deep marine environment.Most trace elements in the present study have positive correlations with SiO2, Al2O3, and K2O suggesting their association with clay minerals.

Table 1 .
Clay and non-clay minerals and their percentage (%) in Dokan and Qamchuqa sections in the Tanjero Formation.

Table 2 .
Results of major oxides% of the studied succession.

Table 4 .
The concentrations of trace elements (ppm) in Tanjero Formation (Dokan and Qamchuqa) sections.Pb) is due to weathering, erosion, and deposition of crustal material, as well as Pb deposits released into the atmosphere of the Earth by eruptions, Pb is a naturally occurring element in the Earth's crust and can appear heterogeneously in soils