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Arabian Journal of Geosciences ISSN 1866-7511Volume 6Number 5 Arab J Geosci (2013) 6:1395-1406DOI 10.1007/s12517-011-0451-z

Geochemical and palynological analyses ofthe Serikagni Formation, Sinjar, Iraq

Moutaz A. Al-Dabbas & Rana A. Hassan

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ORIGINAL PAPER

Geochemical and palynological analyses of the SerikagniFormation, Sinjar, Iraq

Moutaz A. Al-Dabbas & Rana A. Hassan

Received: 6 May 2011 /Accepted: 19 October 2011 /Published online: 13 November 2011# Saudi Society for Geosciences 2011

Abstract Serikagni Formation (lower–middle Miocene) wasstudied at four outcrop sections within Sinjar Anticline, Para(the western plunge), Jaddala, Sinjar, (Southern limb), andNoaniaa (Northern limb) of Sinjar Mountain, which is part offoothill zone in northwest Iraq. This formation is composed ofGlobigerina limestone, marly limestone intercalated withmarl, deposited in quiet, deep marine environment. Palyno-logical analyses and the percentages of palynological matterwere determined. Palynofacies analysis was recorded forpaleoenvironmental interpretation. Mineralogical investiga-tions and petrographical analyses were done. Geochemicalanalyses for the determination of the major constituents (CaO,MgO, and I.R.),the secondary constituents (SiO2, Al2O3,Fe2O3, Na2O, K2O, and trace elements (Sr, Mn, Cu, Zn, Co,Cr, Pb) in the rock samples were accomplished. The calciteis the predominant mineral which is mostly of micrite typesas well as spary calcite. The insoluble residue (I.R.) hasnegative correlation with the carbonate percentages in therock formation as observed by the XRD analyses. Clayminerals show low occurrence represented by palygorskite,montmorillonite, and sepiolite. Geochemical differences canbe noticed between the limy and marly facies constituting thesame formation. Differences are also observed between thegeochemistry and mineralogy of the four studied localitiessuch as the relatively more pure limestone in Jaddala andPara sections than Sinjar and Noaniaa sections whichindicate the higher percentages of marly limestone. This isbelieved to be due to the geographic location of these

sections within the main depositional environment, as well asthe consequences of sea level fluctuation. Two palynofacies(PF-1) and (PF-2) were identified. Palynomorphs are morenumerous with high percentages (>80%) of amorphousorganic matter (AOM) is present in the PF-1. Thelithological association of this palynofacies is limestoneand marly limestone. This palynofacies 1, indicate thedeep marine depositional environment. The secondpalynofacies (PF-2) reflect low quantities (less than40%) of AOM, with increase of phytoclasts (translucent-type) to more than 30% and the miospores (small sporesand pollen grains) to more than 20%. The lithologicalassociation of this palynofacies is marl and marlylimestone. This palynofacies 2, indicate the nearshoreand shallow marine depositional environment.

Keywords Palynofacies . Mineralogy . Geochemistry .

Serikagni Formation . Sinjar . Iraq

Introduction

The organic and inorganic geochemistry of carbonatesthrough their elemental analyses is stressed, and manystudies are being carried on this subject. It has been shownby many workers that these elemental analyses can be auseful tool for the interpretation of the original depositionalenvironment, and for correlation purposes, (Al-Sayegh1972; Al-Kufaishi and Al-Aasm 1978).

The Serikagni Formation (lower–middle Miocene) whosetype locality is situated near the village of Para, at SinjarMountain, located at latitude (36°20′30″ N) and longitude(41°29′00″). Sinjar Mountain (east–west direction) is locatedwithin Nineveh governorate about 100 km west of Mosul city(Fig. 1). The Serikagni Formation rocks were composed

M. A. Al-Dabbas (*) :R. A. HassanCollege of Science, University of Baghdad,P. O. Box: 47138, Baghdad, Iraqe-mail: prof_aldabbas@yahoo.com

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mainly of Globigerina limestone, marly limestoneintercalated with marl, with 150 m thickness (Fig. 2;Bellen Van et al. 1959). All workers whom have studiedthe Serikagni Formation agree that it has been depositedunder marine environment according to the fossil contentand lithofacies characteristics. It is believed that the sourcearea from which the sediments of Serikagni Formationwere derived are the Pre- and Early Miocene, carbonate-rich rocks of the north and northeast of Iraq andsurrounding area. The presence of small grains of detritalquartz suggests that other rock units rich in suchconstituents have also contributed, in supplying sedimentsto the nearby sea where Serikagni Formation rocks weredeposited. Conditions in the source area in one hand, andat the site of deposition of Serikagni Formation, in theother hand, were also not homogeneous as indicated byfacies change from more calcareous rocks to more marlyonce, as well as the accompanied gradual modification onthe geochemistry and mineralogy of these rocks. Physio-graphically, it forms a distinct rock unit within SinjarMountain as a southern part of the foothill zone that ischaracterized by dense sedimentary basins, thick sedimentsequences, and with various sedimentary facies. Tectoni-cally, it is a part of unstable shelf in Iraq (Jassim et al.2006). Many researchers had been recommended or usedthe geochemical studies in solving geological problems,

especially those relating to the environments of deposition(Banat and Al-Dyni 1981; Kettaneh and Sadik 1989), butno attempt has been made previously to discuss thecomposition of the sedimentary organic matter in theSerikagni Formation (Hassan 2005). Therefore, it isbelieved that the use of chemical elements and thepalynofacies analysis are useful to interpret the deposi-tional environment of sedimentary rocks and their origin(Al-Kufaishi and Al-Aasm 1978, 2005). The formationhas been studied from paleontological, stratigraphic, andsedimentological point of view by many authors such asAl-Ameri et al. (2001) and Al-Ani (2005), but no one hasstudied this formation from the mineralogical, palynolog-ical, and geochemical point of view. Therefore, it is vitalto present palynological and geochemical observations onthe succession in the Serikagni Formation in Jabal Sinjarand to consider their implications with respect to environ-ments of deposition and the sea level flocculation duringthe regression and transgression (Batten 1996).

This research covers four sections, the first near thevillage of Jaddala, the second near the village of Sinjar atthe southern limb, the third near the village of Noaniaa atthe northern limb, and the fourth near the village of Para atthe western plunge of Sinjar Mountain, northwest Iraq(Fig. 1). The studied four sections were sampled, theJaddala section (95 m thickness), the Sinjar section (92 m

Fig. 1 Location and geological map of Sinjar mountain (after Maala 1977)

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thickness), where the formation has unconformable contactwith overlying Jeribe Formation. The third section is Noaniaasection (13 m thickness), and the fourth section, Para (19 mthickness) near the village of Para, where the SerikagniFormation has gradational contact with the overlying DhibanFormation. The Serikagni Formation (deep marine environ-ment) has unconformably underlying by Jaddala Formation,due to the Oligocene regression in all of these sections (BellenVan et al. 1959; Jassim et al. 2006).

The aim of this research is to determine the geochemical,mineralogical, and palynological characteristics of SerikagniFormation through four sections selected in the SinjarMountain, (Jaddala, Sinjar, Para, and Noaniaa), and toinvestigate whether these characteristics of Serikagni Forma-tion rocks can give better identification of the environmentalaspects of Serikagni Formation.

Materials and methods

Total of 105 samples were collected from the selected fourstratigraphic sections (Para 22 samples, Sinjar 35 samples,Jaddala 31 samples, and Noaniaa 17 samples). Thecollection of samples was made with reference to lithologic

and textural variations; also the color was considered animportant factor during collection of samples. The miner-alogical, geochemical, and palynological analyses weredescribed as follows:

1. Mineralogical investigation was done by using XRD;total of 16 samples (4 samples from each section) wereanalyzed to determine the mineralogy of the bulksamples and the insoluble residue (IR) (Hassan 2005).

2. The clay fractions were separated from the Serikagnirocks for eight samples (two samples from eachsection). Pipette analysis was used in the separation ofclays and oriented slides were prepared. Normal, heated(350°C and 550°C), and glycolated oriented slides ofthese separated clays were run by XRD for their fullidentification (Hassan 2005).

3. Petrographical analyses by using Polaroid microscopewere done (18 samples were chosen and thin sectionswere prepared).

4. Geochemical analyses including the partial digestion ofthe 19 samples by using diluted acetic acid for the purposeof analyzing the constituents of the trace elements (Sr,Mn, Cu, Zn, Co, Cr, Pb) were determined by AAS of theextract of the soluble residue.

Fig. 2 Lithological log atJaddala and Sinjar sections ofSerikagni Formation, SinjarMountain, (after Hassan 2005)

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5. Geochemical analyses (total of 44 samples, 11 fromeach section) included the total digestion of the samplesby using diluted HF acid for the purpose of analyzingthe major constituents CaO, MgO, and I.R., thesecondary constituents SiO2, Al2O3, Fe2O3, Na2O,K2O, as well as P2O5 and TiO2 and trace elementsSr, Mn, Cu, Zn, Co, Cr, Pb in the rock samples ofSerikagni Formation, Sinjar Mountain.

6. Standard palynological processing techniques wereused to extract the acid-resistant organic matter and todetermine the total organic carbon. All of the slides areprepared and stored in the palynological laboratory ofthe Department of Geology, University of Baghdad(Al-Ameri et al. (2001); Batten 1999) and by using(Pittet and Gorin 1997) classification to identify thepalynofacies.

Geochemical results and discussion

The geochemical and mineralogical analyses results of themajor constituents (CaO, MgO, and IR), the secondaryconstituents (SiO2, Al2O3, Fe2O3, Na2O, K2O), and traceelements (Sr, Mn, Cu, Zn, Co, Cr, Pb) in the SerikagniFormation rock samples are shown in Tables 1, 2, 3, and 4 .Representative vertical correlation of these constituents forSinjar section is shown in Fig. 3.

The results for the four sections show that the maincomponents are represented by CaO, MgO, and I.R. Theirconcentrations within the four sections were depending onthe diagenetic processes, such as dolomitization. The calciteis the predominant mineral which is mostly of micrite typesas well as spary calcite which was resulted from therecrystalization of fossil chambers. The calcite may reachmaximum of 97.1% in pure limestone rocks and reach60.4% as minimum amounts in the impure limestone rocks.The calcite followed by different proportions of dolomitereach maximum of 11% and 1.6% as minimum amountswithin the rock formation (Table 1). Dolomite as rhombscan be observed in subordinate amounts in some rockswhich were formed by the process of dolomitization ofmicrite and the existence of microcrystals of dolomitereflect the early dolomitization (Fig. 4).

The main components correlation coefficients variedwithin the four sections due to the variation in thediagenetic processes such as dolomitization and the minorchanges in the environment of deposition of the SerikagniFormation. The secondary components indicated by SiO2,Al2O3, Fe2O3, Na2O, and K2O varied in concentrationswithin the four sections. Silica is present as detrital grainsof quartz and chert fragments as well as very small roundedbodies with separated outlines which look very much likeradiolarian fossils. Clay minerals, pyrite, and glauconiteoccurred as insoluble residue (Table 2). Glauconite asrounded to oval-shaped grains, green-colored was observedespecially at the lower contact zone. Oval-shaped, lightbrown isotropic phosphate grains can be seen in fewsamples, the chemical analysis of P2O2 reflects that itrange from 0.02% to 0.3%.

The insoluble residue (I.R.) range from 1.0% to 31.0%with an average 15.4%, which has negative correlation withthe carbonate percentages in the rock formation as observedby the XRD analyses.

Clay minerals show low occurrence and as traces within theSerikagni Formation and the results had indicated that the clayminerals—palygorskite, montmorillonite, and sepiolite—arethe predominant minerals in Serikagni rocks, while mixedlayer of illite–montmorillonite is the subordinate clay in somerocks especially within the lower calcareous facies, kaoliniteappear in trace amount. Montmorillonite is the abundant claywithin the marly facies which lacks illite but contain traces ofkaolinite. Pyrite is existing as macroscopic concretionary formas tiny microscopic to submicroscopic grains.

Differences are also observed between the geochemistryand mineralogy of the four studied localities such as therelatively more pure limestone in Jaddala and Para sectionsthan Sinjar and Noaniaa sections which indicate the higherpercentages of marly limestone. Also, the relative increaseof silica concentrations at Sinjar and Noaniaa sectionscomparing with the lower concentration at Jaddala and Para

Table 1 The carbonate% range (indicated by calcite and dolomite%)with the range of quartz% of the studied four sections (Jaddala, Sinjar,Noaniaa, and Para) of Serikagni Formation

Carbonate minerals% Quartz% Section name

80% 1% Minimum Jaddala section88% 2% Maximum

Dolomite% Calcite%

1.6% 75.3% Minimum

5% 94.9% Maximum

78% 2% Minimum Sinjar section95% 5% Maximum

Dolomite% Calcite%

1.9% 70.7% Minimum

11.5% 87.1% Maximum

70% 1% Minimum Noaniaa section87% 3% Maximum

Dolomite% Calcite%

2.8% 60.4% Minimum

6.6% 91.8% Maximum

78% 1% Minimum Para section87% 2% Maximum

Dolomite% Calcite%

2.4% 65.3% Minimum

7.6% 92.2% Maximum

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sections, which is believed to be due to the geographiclocation of these sections within the main depositionalenvironment, as well as the consequences of sea trans-gressions that are recognized at the lower and upper part ofSerikagni Formation and the sea regression that is deter-mined during the middle part of the formation.

The major constituents CaO, MgO, and I.R

The results of the CaO show that it ranges from 45.2% to48.7% with average concentrations of 46.8%. The lowestconcentrations of CaO were determined in Noaniaa section.While the results of the MgO show that it ranges from 0.3%to 2.4% with average concentrations of 1.3%. The lowestconcentrations of MgO were determined in Jaddala section(Table 2).

Ca and Mg are controlled by carbonate and gypsumminerals precipitation, most sites Ca and Mg are well-correlated, probably due to co-precipitation of both elementsinto dolomite, or more likely, in a solid solution of Mg withcalcite or aragonite (Durfor and Becker 1972). Magnesium, asa major element, plays an important role in the chemistry ofthe analyzed sediments probably due to the large amount offine dolomitic detritus.

Also, the results of the analyzed rock samples at Sinjarand Noaniaa sections reflect a relative increase in silicaconcentrations compared to Jaddala and Para sections,which is believed to be due to the geographic location ofthese sections within the main depositional environment(Table 2).

Moreover, the results of the insoluble residues analysesreflect that their range in the pure limestone rocks is 1.5–3.6% and their range in the impure limestone rocks (marlylimestone and marl) is 5.5–31%.

The amounts of the insoluble residue may reflect thehumid climate occurred during the deposition of theformation. The analyzed samples at Jaddala section reflectthe lowest amount of the insoluble residue concentrationscomparing with the other studied sections.

Also, the results indicated that their variation within thestudied sections reflect the geographic location of each sectionwithin the depositional environment, such as the Jaddalasection (Jaddala wt.% of IR min=1.5%, max=20.5%; mean=11%) and the Para section (Para wt.% IR min=6.7%%, max=23.6%; mean=14.4%) had relative lower values of IR thatrepresent relatively basinal and deeper part of depositionalenvironment for Serikagni rock formation.While Sinjar section(Sinjar wt.% IR min=1.0%, max=31.0%; mean=16%) andNoaniaa section (Noaniaa wt.% IR min=10%, max=30.0%;mean=20%) represent the shallow nearshore depositionalenvironment and this may marked the distance of thesesections from the shoreline. Consequently, the SerikagniFormation rocks were classified according to Pettijohn(1975), as shown in Fig. 3. The Jaddala and Para sectionsreflect that they composed of relatively more pure limestonethan Sinjar and Noaniaa sections which indicate that theycomposed of higher percentages of marly limestone.

Table 2 The averages andranges of the CaO, MgO, and I.R.% of the studied four sections(Jaddala, Sinjar, Noaniaa, andPara)

Jaddala section Sinjar section Noaniaa section Para section

CaO% Range 42.7–54.3 39.7–55.1 34.0–51.0 33.0–49.0

Average 48.7 46.4 45.2 46.7

MgO% Range 0.35–1.1 0.42–2.4 0.3–1.5 0.3–1.2

Average 0.92 1.6 1.32 1.31

IR% Range 1.5–20.5 1.0–31.0 10–30.0 6.7–23.6

Average 11 16 20 14.4

Table 3 The averages of the SiO2, Al2O3, Fe2O3, Na2O, and K2O%of the studied four sections (Jaddala, Sinjar, Noaniaa, and Para)

Average%

Jaddalasection

Sinjarsection

Noaniaasection

Parasection

SiO2 7.4 11.3 12.4 10.5

Al2O3 1.7 2.3 2.6 2.2

Fe2O3 0.6 0.4 0.8 0.6

Na2O 0.24 0.22 0.45 0.3

K2O 0.5 0.3 0.5 0.41

Table 4 The averages of the Sr, Mn, Cu, Zn, Co, Cr, and Pb (in partsper million) of the studied four sections (Jaddala, Sinjar, Noaniaa, andPara)

Average inppm

Jaddalasection

Sinjarsection

Noaniaasection

Parasection

Sr 794 727 710 742

Mn 162 23 97 86

Cu 6.7 12.6 9.7 10

Zn 16.3 20 17.3 18

Co 40 39 37 38

Cr 14.2 30.6 31 26

Pb 32.5 30.6 35 32.3

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The secondary constituents

The secondary constituents representing SiO2, Al2O3,Fe2O3, Na2O, and K2O varied in concentrations within the

four sections (Table 3). SiO2% in Serikagni rocks rangefrom 7.4% to 12.4% in an average of 10.4%.

The silica amount is considered small in comparisonwith their values in carbonate rock (Table 5). However, and

Fig. 3 Vertical correlation of the major constituents CaO, MgO, and I.R., the secondary constituents, and the trace elements at Sinjar section, ofSerikagni Formation, Sinjar Mountain, vertical scale 1 cm=4 m (after Hassan 2005)

Fig. 4 The Serikagni Forma-tion rock classificationaccording to their insolubleresidue% within the fourstudied sections (Pettijohn1975 and Al-Ani 2005)

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as mentioned before, the silica and clay minerals representthe insoluble residues which are of importance in reflectingthe shoreline with their higher values and the deep marinedepositional environment with their lower values (Kettanehand Sadik 1989).

Al2O3% in Serikagni Formation rocks is ranging from1.7% to 2.6% in an average of 2.2%. These amounts areconsidered small in comparison with their values incarbonate rocks (Table 5). Moreover, aluminum content ismainly controlled by the clay content. The lowest alumi-num contents are found in Jaddala section that containhigher carbonate contents such as dolomites and limestone(Windom et al. 1989).

Fe2O3% is ranging in Serikagni rocks from 0.4% to 0.8%in an average of 0.6%. These amounts are considered small incomparison with their values in carbonate rocks (Table 5).Iron cycling is biogeochemically driven by abiotic and bioticreactions. Although the oxidation rate of iron is instantaneous(Stumm and Lee 1961), most aquatic sediments are anoxicdue to bacterial degradation of organic matter. Therefore, Fe2+

is produced in situ and is often associated with sulfideprecipitating as pyrite (Todorova et al. 2005). Total ironconcentration is a critical biogeochemical property of thesediments. Because of the large adsorption capacities of iron,its accumulation in sediment impacts (1) concentrations ofother ions, (2) sorption of trace elements such as Cd and As(Carroll et al. 1998), (3) decomposition of organic matter(Tessier et al. 1996), and (4) ecosystem nutrient cycling(Burdige 1993; Olivie-Lauquet et al. 2001). Migration of Fe2+

from anoxic conditions to oxic/anoxic boundaries as a resultof re-suspension of bottom sediments produces Fe-hydrousoxides, which incorporate organic matter and inorganic oxideparticles that scavenge both heavy metals and organics(Taillefert et al. 2000). The value of Fe2O3 in Noaniaa sectionis higher than in the other studied sections.

Na2O is ranging in Serikagni Formation rocks from0.22% to 0.45% in an average of 0.3%. These amounts areconsidered small in comparison with their values incarbonate rocks (Table 5).

Sodium is the most abundant of the alkali elements andconstitutes 2.6% of the Earth’s crust. Compounds of

sodium are widely distributed in nature (Weast 1973).Weathering of salt deposits and contact of water withigneous rock provide natural sources of sodium (OntarioMinistry of the Environment 1981). Most sediment containssodium in the range of 0.1–1%, mainly as silicate mineralssuch as amphiboles and feldspars. The concentration of thesodium is observed in Serikagni Formation rocks to behigher in Noaniaa section.

K2O is ranging in Serikagni Formation rocks from 0.3%to 0.5% in an average of 0.43%. These amounts areconsidered small in comparison with their values incarbonate rocks (Table 5). K+ is commonly found insedimentary rocks and released slowly upon dissolution ofrocks (potassium feldspars and mica minerals). K+ isstrongly held by clay particles in the sediment.

In addition, TiO2 and P2O5 were analyzed in this study.The results indicated that TiO2% in Jaddala, Sinjar, Parasections are ranging from less than 0.006–0.012%, while inNoaniaa section ranging from 0.006% to 0.037%. In fact,there is a positive relation between TiO2% and I.R.% wherethe TiO2 is determined by very fine grains transported withfragments of rutile or illeminite and the clay and silt sizeproduct of weathering. The amount of TiO2 depends on theintensity of weathering processes (Al-Ani 2005). Accord-ingly, it is believed that Noaniaa section rocks weredeposited in relatively shallower deposition environmentthat is affected with severe weathering processes. While theresults indicated that P2O5% in Jaddala, ranging from0.03% to 0.39%; Sinjar, ranging from 0.03% to 0.19%;Para, ranging from 0.02% to 0.15%; while in Noaniaasection it ranges from 0.07% to 0.2%.

In fact, there is a positive relation between P2O5% and I.R.% where the P2O5 determined by very fine grainstransported with the clay particles as product of weathering.

The trace elements

The results of the trace elements concentration are shown inTable 4 and discussed below.

Mn in Serikagni rocks is ranging from 23.0 to 162 ppmin an average of 91.8 ppm. These amounts are considered

Table 5 Comparison of the averages of the SiO2, Al2O3, Fe2O3, Na2O, and K2O% and Sr, Mn, Cu, Zn, Co, Cr, and Pb (in parts per million) ofthis study with other authors results

Element\research Al2O3% Fe2O3% Na2O% K2O% SiO2% Sr inppm

Mn inppm

Cu inppm

Zn inppm

Co inppm

Cr inppm

Pb inppm

Rankama and Sahama 1950 0.43 0.45 0.037 0.27 425–765 385 20.2 50? <0.3 2 5–10

Turekian and Wedepohl 1961 0.79 0.54 0.054 0.324 722 1,420 4 20 20 11 9

Hawekes and Webb 1962 – 1.3 – – – 1,300 5–20 4–20 0.2–2 5 5–10

Horn and Adams 1966 1.66 1.17 0.053 0.287 730 1,086 5 16 13 7 17

Kettaneh and Sadik 1989 1.04–1.9 0.63–0.85 0.08–0.12 0.6–1.24 5.7–11.4 403–538 – 11–22 16–21 – – 4–32

This study 2.2 0.6 0.3 0.43 10.4 743 91.8 9.8 17.9 38.5 19.3 32.5

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small in comparison with their values in carbonate rocks(Table 5). Mn is one of the important elements in the studyof carbonate rocks due to its relation with the environmentof deposition which comes from the ability of Mn toreplace Ca in the space lattice. Accordingly, the study ofMn may concern the indication of the physicochemicalconditions of seawater during deposition. The reductionenvironment which took place directly after depositioncreate suitable conditions that have high amount of Mncould replace Ca in the space lattice of calcite, and theseconditions are available in deep sea environment. Accord-ingly, the little amount of Mn in the Serikagni rocksindicates absence of such conditions, suggesting generalshallow depositional environment.

Mn is one of the most abundant trace elements in thelithosphere, and its common range in rocks from 350 to2,000 ppm. Its highest concentrations are usuallyassociated with mafic rocks. Mn forms a number ofminerals in which it commonly occurs as the ions Mn2+,Mn3+, or Mn4+,but its oxidation state +2 is most frequentin the rock-forming silicate minerals (Kabata-Pendias andPendias 2001).Under oxic conditions, Mn forms oxides,which can be important reservoirs for trace metals,especially Co, Zn, and Cr, (Tonkin et al. 2004). Sr isranging in Serikagni rocks from 710 to 794 ppm in anaverage of 743 ppm.

The amount of Sr is considered to be within therange in comparison with its average in carbonate rocks(Table 5); however, this amount is acceptable because therocks of Serikagni formation were deposited in relativelyshallow environment (Veizer and Demovic 1974). More-over, the amount of Sr concentration could be due todiagenetic aragonite–calcite transformation process whichacted intensively in Serikagni Formation where the X-raydiffraction diagrams showed absence of aragonite. Thechemical similarity of strontium to calcium, having similarionic radius and the same valence, means that strontiumtends to behave similarly to calcium in most systems(Simon 2003).

According to Veizer and Demovic (1974) and Simon(2003), there are many factors that control the Sr content incarbonate rocks such as age, salinity, clay mineral content,and depositional environment in addition to the kind ofdiagenetic process, mechanism of aragonite–calcite trans-formation. The depositional environment also played itsrole in modifying the amount of Sr. Its role comes throughtheir effects on the amount of insoluble residues, where thisamount reflects the nature of the basin and water agitationand source rocks (Hassan 2005).

Cu is ranging in Serikagni rocks from 6.9 to 12.64 ppmin an average of 9.8 ppm. These amounts are considered tobe within the range in comparison with their values incarbonate rocks (Table 5).

Copper, like lead, is a chalcophile that forms discretesulfide minerals (Achterberg et al. 1997) or may associatewith pyrite (Huerta-Diaz et al. 1993; Schoonen 2004a, b).

Zn is ranging in Serikagni rocks from 16.25 to 20.0 ppmin an average of 17.9 ppm. These amounts are consideredto be within the range in comparison with their values incarbonate rocks (Table 5).

Zinc is a chalcophile element that forms distinct sulfidephases under anoxic conditions (Bostick et al. 2001). Therelatively highest concentration value is determined in theSinjar section.

Co is ranging in Serikagni rocks from 37.0 to 40.0 ppmin an average of 38.5 ppm. These amounts are consideredhigher in comparison with their values in carbonate rocks(Table 5).

Cobalt is a siderophile, frequently found in associationwith Fe. In anoxic sediments, Co can form a discrete phase(CoS) or may be associated with disulphides includingpyrite and marcasite (Schoonen 2004a, b). In oxic orsuboxic sediments, Co typically associates with oxides,including both Fe and Mn oxides (Davison 1993).

Cr is range in Serikagni rocks from 14.2 to 31.0 ppm inan average of 19.3 ppm. These amounts are consideredhigher in comparison with their values in carbonate rocks(Table 5).

Chromium, like Mn, is a lithophile element and isgenerally not associated with sulfides (Huerta-Diaz et al.1993; Morse and Luther 1999). The Co and Cr or the acid

Fig. 5 Organic matter of the Serikagni Formation plotted on theternary kerogen plot of Tyson (1993)

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soluble can be used as energy index indicators. They existin or on clay minerals and organic matter which aregenerally more abundant in the quieter, lower energymarine environment. This assumption applies well on thesituation concerning the depositional environment and thefacies variation of Serikagni Formation. The geochemistryof Serikagni rocks showed increase of Ca, I.R., and Srtowards the more limy facies, while the most otherelements, i.e., MgO, SiO2, Al2O3, Fe2O3, Na2O, K2O,

Mn, Zn, Co, Cr, Pb, and Cu varies between the limy and themarly facies.

Pb is ranging in Serikagni rocks from 30.6 to34.6 ppm in an average of 32.5 ppm. These amountsare considered higher in comparison with their values incarbonate rocks (Table 5). Under anoxic conditions, Pb,which is a chalcophile element, forms distinct sulfidephases (Morse and Luther 1999). Pb may be present as adiscrete phase (i.e., Cerrusite, PbCO3), or more likely,

Fig. 6 Sedimentary organic matter isolates from Serikagni Formation

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exists in solid solution with or sorbed to aragonite oranother carbonate phase (Kersten and Forstner 1986).

In addition, comparing the results with that of Rankamaand Sahama (1950), Turekian and Wedepohl (1961),Hawekes and Webb (1962), Horn and Adams (1966), andKettaneh and Sadik (1989), the Co, Cr, and Pb constituentsrepresent higher concentrations in Serikagni Formationwhich could be due to the occurrence of clay mineralswithin the Serikagni Formation. Also, the results indicatethat Sr, Cu, and Zn concentrations are within the range ofother known carbonate rocks, while the Mn concentration islower than that of known carbonate rocks. However, such aresult is believed to be due to the minor changes in thedeposition environment and the nature of the dolomitizationsolutions (Tables 1, 2, 3, 4, and 5).

Palynofacies analysis

In this study, many sedimentary organic matter wererecognized, such as the palynomorphs that are composedof fossils with organic wall that resist the acid dissolutionwhich consist of dinoflagellate cysts, the miospores (smallspores and pollen grains), algae, acritarch, fungal remains,spores and foraminifera’s test linings, phytoclasts (opaqueto semi-opaque (as charcoal) and translucent), structuredorganic matter and unstructured organic matter such asamorphous organic matter (Batten 1999; Al-Ameri et al.1999; Al-Ameri et al. 1999; Al-Ameri et al. 2009).Theabundance of marine palynomorphs might indicate thepresence of upwelling currents and high organic productiv-ity at the time of deposition, while rapid sedimentationquickly buried the organic matter, preventing oxidation, andreducing the rate of microbial alteration. The percentages

data reflect environmental controls on each palynofacies.The abundance of spores and (to a lesser extent) pollengrains, coupled with impoverished assemblages of dinofla-gellate cysts, imply swamp, marsh, and fluvial-dominatedenvironments of deposition. The nearshore depositionreflect lack of wood-dominated palynofacies or containvery few palynomorphs and other types of organic matter.The low numbers of small spores and pollen grains, muchgreater percentages of dinoflagellate cysts, and lithologicalconnections with limestone and associated marine deposits,reflect more offshore environments (Pittet and Gorin 1997).The results of palynological matter recorded from thestudied cross-sections discussed according to the ternarydiagram (APP) taken from Tyson (1993, 1995) forsedimentary organic matter. Moreover, the results werecompared with Pittet and Gorin (1997) classification anddiscussed with Buday (1980) and Al-Taee (2003) conclu-sions of the depositional environment of Serikagni Forma-tion. The results reflect that the Serikagni Formation rocksconsist of the two following palynofacies (Figs. 5 and 6):

1. Palynofacies 1 (PF-1)Palynomorphs are more numerous in this palynofa-

cies than in the palynofacies 2 (PF-2). The assemblageof dinoflagellate cysts (Fig. 6c, e, k) is more diversethan that of the miospores (small spores and pollengrains; Fig. 6d, f, g, i, j), although along with fungalremains and foraminiferal linings, spores are common.Amorphous organic matter (AOM) is present inquantities more than 80% of the total organic compo-nent (Fig. 6l), whereas phytoclasts comprise less than5–15% (Fig. 6a, b, h), while the miospores (smallspores and pollen grains) comprise less than 10%. The

Fig. 7 Environmental model forSerikagni Formation deposits atstudy area

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lithological association of this palynofacies is marl andmarly limestone; it is observed in Jaddala and Sinjarcross-sections at about 0–38 and 61–92 m.

2. Palynofacies 2 (PF-2)By comparison with the general aspect of PF-1, the

palynomorphs component of PF-2 AOM is present inlow quantities (less than 40%) with increase phytoclasts(translucent-type) to more than 30%, while the mio-spores (small spores and pollen grains) comprise morethan 20%. The lithological association of this palynof-acies is marly limestone; it is observed in Jaddala andSinjar cross-sections at about 37–61 m.

Conclusion

Geochemical differences can be noticed between the limyand marly facies constituting the same formation. Themarly facies is richer in all major elements except Ca, K,and I.R. and in all analyzed trace elements.

The percentages of TiO2% and P2O5% indicated apositive relation with I.R.%. Accordingly, it is believedthat Noaniaa section rocks and, to less extent, Sinjar sectionrocks were deposited in relatively shallower depositionenvironment that is affected with severe weatheringprocesses. Actually, these conditions are similar in generalto the effect of the deposition during the regression of thesea throughout the middle part of the Serikagni Formationdepositional environment (Al-Ani 2005; Hassan 2005).

The existence of sulfides (pyrite) and glauconite atrelatively high concentration in the lower and upper parts ofthe formation indicate prevalence of reducing conditionsduring the deposition of Serikagni Formation under quietmarine environment, while the iron at relatively highconcentration in the middle part of the formation indicatesprevalence of oxidizing conditions. It is believed that ironwas brought to the basin of deposition of SerikagniFormation from nearby continental mass to the northeastas detrital grains and iron-rich minerals.

The results of palynological matter from the studiedcross-sections show that the depositional environment ofSerikagni Formation is as follow:

(a) The result of the palynofacies-1 of the studied cross-sections in their upper and lower parts coincides withthe VIII and IX (Tyson 1993; Fig. 5). Palynofacies thatreflect the distal suboxic–anoxic basin are character-ized by the relatively high percentages of AOM thatrepresent the deep marine facies. Moreover, theexistence of the pyrite and glauconite within the upperand lower parts of the Serikagni Formation are inconcordance with this conclusion that indicates thedeep marine reduction environment (Al-Taee 2003).

(b) The result of the palynofacies-2 of the studied cross-sections in their middle parts coincides with the IV(Tyson 1993). Palynofacies that reflect the transitionfrom the basinal environment to shelf environment,which are characterized by high percentages of phyto-clasts in general and their differences, reflect theirdistance from the source of the sedimentary organicmatter. Moreover, this finding is representing regressionconditions that coincide with the palynofacies-2 of themiddle part of the Serikagni Formation.

In conclusion, it is believed from the results of this study,that the geochemical and palynological analyses areessential in reflecting the minor changes of the environmentof deposition of the Serikagni Formation. The resultsmarked the events in the depositional environment ofSerikagni Formation, such as the transgression periods thatmay represent at the early and late deposition stages of theformation and the regression period that may indicatewithin the middle depositional stage of the formation(Fig. 7).

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