APPLICATION OF 18 O AND 13 C STABLE ISOTOPES COMPOSITION OF THE CARBONATE ROCKS OF THE JERIBE FORMATION EASTERN IRAQ; AN APPROACH TO DEFINE THE PALEO TEMPERATURE AND PALEO DEPTH

Stable isotopes 18 O/ 16 O and 13 C/ 12 C in the carbonate rocks of the Jeribe Formation are examined here to define the depositional characters in the basin includes paleo temperatures and paleo depth. The Jeribe Formation comprises a transgressive unit belongs to the Latest Eocene-Recent Megasequence (Ap11). Complete sections of the formation were studied in the core of Himreen structure in eastern part of Iraq. The Himreen structure lies in the outer platform margin of unstable shelf of the Arabian plate. The stable isotope ( 18 O/ 16 O and 13 C/ 12 C) of Jeribe Formation provides the first records of paleotemperature for the Neogene (middle Miocene Transgression) of the Southern Teythes, which indicate cooling during deposition. Microfacies study imply that the skeletal grains are composed of green and red algae, stromatolite and verities of benthic foraminifera. The non-skeletal grains are pellets and intraclasts. Analysis of microfacies suggests lagoon, reef, shoal and open marine environments. The depletion of both 18 O and 13 C indicated shallowing at the contact with overlying and underlying formations in the shoal and lagoonal facies respectively. While in the middle part in the coral reef facies reveals elevation of the sea surface temperature. These suggest that the enrichment of both 18 O and 13 C at the cool water temperature associated with upwelling and arise of sea level represented by reef and open marine facies .


INTRODUCTION
The Miocene Jeribe Formation is distributed from southeastern to northwestern Iraq.
It was deposited in two main basins; Mosul and Kirkuk -Dezfol basins.The formation composed basically of dolomite and dolomitic limestone rocks representing a transgressive unit belong to the Latest Eocene-Recent Megasequence (Ap11) in the stratigraphic column of Iraq (Jassim and Goff, 2006).The megasequence (AP11) is subdivided into three sequences of latest Eocene -Oligocene, Early -Middle Miocene and Late Miocene-Recent age.Furthermore, Early -Mid Miocene Sequence is subdivided into two second order sequences; Early Miocene and Mid Miocene sequences.The Jeribe Formation comprises Middle Miocene Subcycle representing a new transgressive stage in the foredeep shelf margin below the evaporate lagoon sediments of Fatha Formation (Jassim and Goff, 2006).
Isotopes geochemistry covered wide applications of the O and C stable isotopes in geology using to define the physical and chemical conditions of the sea waters in the sedimentary basin.C and O isotopes give characteristic geochemical signatures of the sediments as well as the dolomite origin.
This paper aims to estimate the paleo depth and paleo temperatures of the sea waters during the sedimentation of the Jeribe carbonate rocks in the basin.Moreover, constructing relationships between the O and C isotopes composition with the sedimentological properties such as microfacies types and associations.Finally, suggesting an environmental model based on the isotopic results of paleo depth and paleo temperatures relative to the environmental setting, microfacies types and associations.

GEOLOGICAL SETTING
The Jeribe Formation composed of thick massive and bedded dolomite and dolomitic limestones.The Jeribe Formation is exposed in the core of Himreen, Makhool and Sinjar structures in the east, middle and northwestern Iraq, respectively (Fig. 1).

Conformable contact was reported with underlying Dhiban Formation and overlying
Fatha'h Formation (Jassim and Goff, 2006).
Paleogeography of the shelf margins during the Early to Middle Miocene characterized by development of broad and relatively shallow basins.The axis of the basin is passing parallel to the main trend of the structures, the Jezira Subzone (submerged Khlesia High) and the Mesopotamian Zone.The successive deposits of the Jeribe Formation have coincided with continental collision between Arabian and Eurasian Plates extending from the Eocene up to the Recent time (Numan, 1997).This phase characterized by shallow epicontinental seas and lagoons.Tectonic classification of Fouad (2012) sited that the deposition of the Jeribe Formation is carried out in two main basins in unstable shelf.It is situated in the outer platform margin within Mesopotamia and western Zagros Fold -Thrust Belt in the Low Folded Zone.The study area is located within the Mesopotamian block (Jassim and Goff, 2006)

METHODS AND MATERIALS
Two stratigraphic sections of Jeribe Formation are selected from Himreen structure east of Wasit and Dyiala Governorates in eastern part of Iraq.The first (Ja) is located in the SW core flank of Koolic1 anticline.The second (Jb) is located in core of Koolic (3) anticline in Showshareen valley (Fig. 1).The selected sections represent composite ideal column of Kirkuk-Dezfull basin.Forty-two (42) samples are collected represented the whole succession of the Jeribe Formation.Thin-section slides were prepared for petrographic study to identify mineralogical assemblages, textural components (skeletal and non-skeletal grains) followed the procedure listed in Tucker (1988).
XRF geochemical analysis of bulk carbonate samples is enhanced to determine the Ca, Sr and Mn concentrations in the XRF Laboratory, University of Baghdad.
Analysis of carbon and oxygen isotopic were carried out by Mass Spectrometry at Stable Isotopes Laboratories/ UK.Mass spectrometry is a method to obtain the relative numbers of each isotope of an atom in a 10 milligram powdered sample (Ebbing and Gammon 2009).The samples were weighed into clean Exetainer TM tubes and flushed with 99.995% helium.After flushing, phosphoric acid was added to the samples for 3 hours at 90 °C and leave overnight to allow complete conversion of carbonate to CO 2 .
Reference and control materials were prepared in the same way.The CO 2 gas liberated from samples was analyzed by Continuous Flow-Isotope Ratio Mass Spectrometry (CF-IRMS).Carbon dioxide was sampled from the Exetainer TM tubes into a continuously flowing He stream using a double holed needle.CO 2 gas was resolved on a packed column gas chromatograph and the resultant peak is carried forward into the ion source of a Europa Scientific 20 -20 IRMS where it is ionized and accelerated.Gas species of different mass are separated in a magnetic field and simultaneously measured using a Faraday cup collector array to measure the isotopomers of CO 2 at m/z 44, 45, and 46.Isotopic results are reported in per mil deviation from the V-PDB (Vienna Pee Dee Belemnite) using the standard delta notation.
-FA2; Inner shelf: FA2 composed of pelletal packstone abundant in foraminifera, mollusca and laminated algae, which are supported by micritic mud.While bioclasts grainstone microfacies contains red alga of Archaeolithothamnium sp., and predominance of milioliods idntified in the middle part of the formation.The major allochem are pellets and benthic foraminifera.The bioclastic dolomicrite grainstone is less common microfacies in the middle part.FA2 composed of very fine crystalline dolomite mixed with calcite cement (Fig. 4F).
-FA3; shallow, open-marine: FA3 is characterized by wackestone and packstone microfacies.These are composed of very fine crystalline dolomite with calcite cement mostly of secondary origin.This microfacies is dominated by benthonic foraminifera of soritidae, alveolinidae and miliolids species with red algal type.FA3 is characterized by bioclastic dolomicrite packstone, red algae packstone and peliodal packstone, which are repeated at various levels through the studied sections and in the upper contact with Fatha'h Formation, (Fig. 4B and H).
-FA4; Shallow/ reef-back reef: FA4 is characterized by framestone and boundstone microfacies recognized in the middle part of the formation.It is subdivided into coral framestone (the framework composed of red calcareous coralline algae), and coralline red algal boundstone (composed of coral, stromatolite and benthic foraminifera).The stromatolite framestone microfacies is characterized by laminated domal stromatolite and existed in upper part of Ja section.It is associated with coral and laminated algal mat in micritic matrix (Fig. 4D and G).

Oxygen and Carbon Isotopes Composition
The most abundant stable isotopes of oxygen are 18 O and 16 O and carbon is 13 C and 12 C.The concentration of 18 O and 13 C in a sample is conventionally estimated as per mil.δ 18 O and δ 13 C are reported between the isotope ratios in the sample and those in the international Pee Dee Belemnite (PDB) standard which, by definition has δ 18 O and δ 13 C values of 0‰ (Hudson, 1977).

Composition of oxygen isotope values in the carbonate rocks of the Jeribe
Formation show significant variation ranging from (-1.15 -2.86) ‰.The majority of samples are enriched by 18 O, which are approximately the same values recorded by Veizer and Hoefs (1976) for the Tertiary period.While carbon isotope composition shows significant variation ranging from -1.14-2.42‰,which are approximately the same values recoded by Veizer and Hoefs (1976), for Tertiary period.These are compared with compiled data in an attempt to verify to previously reported measurements of pre-Quaternary rocks.He was measured both O and C isotopes in both limestone and dolomite rocks (Fig. 5) and (Table 2).(Nelson and Smith, 1996).δ 18 O and δ 13 C cross-plot was prepared by Hudson (1977), who distinguished a number of characteristic isotope fields for carbonate having different origins.Many workers have been followed, adapted and extended such as δ 18 O -δ 13 C plots (Bathurst, 1980;Choquette and James, 1987;Moor, 1989;and Morse and Makenzie, 1990).A modified version of Hudson's plots reproduced by Nelson and Smith (1996).
The plot data of δ 18 O and δ 13 C from the Jeribe Formation display unaltered samples and have primary signature of isotopes (Fig. 6).Mn/Sr ratios are estimated in the same samples as the stable isotope measurements.Kaufman and Knoll (1995) observed that both limestones and dolostones with Mn/Sr <l0 commonly retain near-primary δ 13 C, while in the Jeribe Formation Mn/Sr range from 0.19 to 0.64 with average 0.3 (Table 3).Ratio and plotted δ 18 O and δ 13 C infer primary proxy for the isotope composition.The 18 O/ 16 O ratio is measured as δ 18 O in the waters, which is mostly controlled by temperature, where salinity can have an impact as well (Wanamaker et al., 2007).A relationship was established between water temperature and the 18 O/ 16 O ratio, which can be used to reconstruct the sea-surface temperatures and seasonal variability (Yan et al., 2013).Emiliani and Epstein (1953) were firstly developed equation for calcite paleo temperature that used to calculate the "isotope temperature" of calcite formation by providing δ 18 O value of the water from which the calcite precipitated.The equation is: where T is the temperature in °C (based on a least-squares fit for a range of temperature values between 9 °C and 29 °C, with a standard deviation of ± 0.6 °C, and δ is δ 18 O for a calcium carbonate sample.This equation has since undergone many revisions by Rye and Sommer (1980).The results of the studies by Epstein et al. (1951) and Emiliani and Epstein (1953) have implications that are still relevant today in archaeology.
The estimated paleo temperature of the carbonate rocks of the Jeribe Formation are ranged from (5.3 -15.9) and few samples show high temperature (Table 3).(Shackleton, 1967), and by the changes in temperaturedependent isotopic exchange with the oceanic crust (Gregory and Taylor, 1981;Muehlenbachs and Clayton, 1976).

Paleo
The dominant factor influenced the δ 18 O of the global ocean is related to paleo climatic changes.The enrichment of 18 O in sea water suggest glacial period at the middle Miocene.
During glacial periods, low δ 18 O in waters is stored in the ice sheets, and the mean δ 18 O value of the world oceans is relatively high (Zachos et al., 2011), which mean enrichment of 18 O in the sea water during glacial period.Ando et al. (2010) used ∆δ 18 O for determination the paleo depth of water by the equation: The estimated paleo-depth of the sediments in the Jeribe Formation suggests thermocline and shallowing upwards represented by mixed layer within water column except sample Jb 11, which shows depletion in 13 C suggest deeper depth.While Jb 27 shows enrichment in 13 C reflect minimal deeper (Fig. 7 and Table 3).

DISSUASION AND INTERPRETATION
The C and O isotopic (δ 13 C and δ 18 O) compositions used as main geochemical tools to reconstruct the paleoecology of carbonate minerals, water depth and presence/ absence of algal photo symbionts compositions (Edgar et al., 2015).Hoefs (2015) pointed that well preserved textures and trace element contents have recorded the primary oxygen isotope composition and can be used to deduce the past ocean composition.The Mn/Sr ratio of less than (2) indicates no significant influence of diagenetic process (Jacobsen and Kaufman, 1999;Marquillas et al., 2007;Nagarajan et al,. 2008;and Kano et al., 2007).The estimated low Mn/Sr ratios (0.09 -0.64) (  , 1992).The δ 18 O isotope is increasing with depth according to decreases in temperature, in which oxygen isotope fractionation between ambient seawater and foraminiferal calcite during calcification is strongly depends on temperature (Bemis and Howard, 1998;Emiliani and Epstein (1953);and Pearson, 2012).The C and O isotopic variations are demonstrating facies controlled (Veizer and Hoefs, 1976).Three samples show variation in δ 18 O and δ 13 C composition because non-equilibrium precipitation owing to very shallow water, where the environment influences by freshwater runoff, warm temperatures and algal activity.exchange.This suggests mixed layers as a paleo-depth in water column (Figs. 8 and 9).

CONCLUSIONS
The variable composition of δ 13 C and δ 18 O of the Jeribe carbonate rocks is controlled by sea level oscillation and facies types.Depletion of both δ 13 C and δ 18 O isotopes are associated with drop of sea level and restricted to shallow facies.While enrichment of both δ 13 C and δ 18 O isotopes is associated with sea level rise.The Middle Miocene is a relatively steady period of cool water, which is indicated by enrichment of stable isotopes.Furthermore, implies that transgression and deepening of water depth was took place at amidst of mixed layer and thermocline zone.
, confining between two transverse fault zone.Sirwan and Takhadide strike slip faults passing under the Kut -Dezfull strike slip Fault in the depocenter of Kirkuk -Dezful basin.The study area is effected by Makhul -Hemrin Fault.

Fig. 1 :
Fig. 1: Geological and location maps of the studied areas show the selected stratigraphic sections (red lines) (A) Ja, and (B) Jb

Fig. 6 :
Fig. 6: Shows δ 18 O and δ 13 C plot(Nelson and Smith, 1996) Depth and Pale Climate δ 18 O composition of Miocene seawater given as calculated δ 18 O sw values by the following equation: δ 18 Ovsmow = 1.03092 δ 18 Ovpdb + 30.92Where δ 18 Ovsmow is Vienna Standard Mean Ocean Water, δ 18 Ovpdb is Vienna Pee Dee Belemnite (VPDB), 1.03092 and 30.92 are constant.The δ 18 O of seawater can vary with time due to several processes, which influence the δ 18 O of the global ocean, and the local dδ 18 O of seawater.The δ 18 O of the global ocean is primarily influenced by the changes in amount of stored water as ice on land, which influences the δ 18 O of the global ocean on the timescale

Fig. 7 :
Fig. 7: Shows ∆δ 18 O of determine paleo depth in the water column, (after Ando et al., 2010) The curve of C and O isotopes shows three negative excursions in the lower part of lagoon environment at the contact with underlying Dihban Formation.The lower part is characterized by abundant calcareous foraminifers, mollusca and calcareous algae.The other two samples of the middle part show negative value of both 18 O and δ 13 C which are associated with coral reef environment, which is virtually originally calcitic.The samples of the upper part of the formation represent shoal environment, which is characterized by calcareous peloids suggest short term shallowing event in Middle Miocene basin.The most negative values of oxygen isotope are observed in the lower and upper parts of the formation, suggest non-steady state in sedimentary basin, most probably due to tectonic effect (Fig.9).The interpretation of paleo-depth of the Jeribe isotopic is based on uses of ∆δ 18 O fractionation plots afterAndo et al. (2010), which is inaccurate due to rejection of δ 13 C results.Edgar et al. (2015) was mentioned to use δ 13 C aid to determine comparatively paleo depth.Their utility arises because 12 C is preferentially utilized by photo symbionts and phytoplankton, leaving the foraminiferal microenvironment and ambient seawater enriched in 13 C. Below the photic zone, the 12 C of the water column increases relative to surface waters as a function of reduce photosynthetic activity and remineralization of 12 C enriched-organic matter.This is leading to decrease δ 13 C values in the test of microfossils (many foraminifera are lacking photo symbionts) (Figure10).

Fig. 8 :
Fig. 8: Shows distribution of δ 13 C and δ 18 O through the stratigraphic log of the studied sections of the Jeribe Formation and their temperature

, δ 13 C and Mn/Sr Ratio Bivariate
plots involving δ 18 O and δ 13 C are common and convenient way of distinguishing the depositional and/ or diagenetic (paleo) environments responsible for carbonate formation

Table 3
(Jones et al., 2012)ocks indicate less effects during diagenesis and have primary isotope signature.Ratios and plotted δ 18 O and δ 13 C together with well-preserved texture infer primary proxy for the isotope composition.The δ 18 O values of carbonate rocks primarily depends on the δ 18 O of the seawater (δ 18 O sw) and the temperature of the depositional environment.While carbon isotope data linked to marine bicarbonate and biological kinetic isotope fractionation, which is not sensitive to temperature changes as in δ 18 O.It indicates the magnitude and the time of upwelling events(Jones et al., 2012).The δ 18 O of seawater can be vary with time due to several processes, which influence the δ 18 O of the global ocean related to paleo climate.Since the fractionation is based on temperature by evaporation of lighter 16 O to cause enrichment of 18 O in times of cold sea water.Isotopic results of the Jeribe Formation show that the seawater is relatively enriched in 18 O, which is most probably marked cold climate e.g.glcial period event.(Fig.8).Most of δ 18 O and δ 13 C of the Jeribe samples are clustered at small positive values with extension of small negative values for both δ 18 O and δ 13 C.The group of samples of small positive δ 18 O and δ 13 C, suggest mainly precipitated of carbonate close to isotopic equilibrium with ambient shelf water (Roa and Nelson