Diagenesis processes of the Gulneri Shale, Kometan, Mushorah formations within the upper Turonian - lower Campanian Supersequence from Bai Hassan area, North of Iraq

The upper Turonian - lower Campanian Supersequence is characterized with fine-grained, mixed siliciclastic-carbonate middle shelf to sub-basinal depositional system. The present study included the study of vertical and lateral changes of the diagenesis processes of the Gulneri shale, Kometan and Mushorah Formations within the sequences of the (upper Turonian-lower Campanian) cycle in two subsurface sections within the Dome of Daoud in the Bai Hassan field - northern Iraq. The first is represented by a section (BH-16) with a thickness of (213) m. In contrast, the second is represented by a section (BH-86) and a thickness of (233) m. The lithostratigraphy of the rock units of this study are consisting (206) slides were studied, (80) for well (BH-16) and (126) for well (BH-86).The study showed that the sequences of this cycle are unconformity with the lower Dokan Formation and upper contact with Hartha. The petrographic study showed that the rocks of the study were exposed to many diagenesis processes, like cementation, dolomitization, neomorphism, dissolution and compaction according to the degree of their prevalence with a large spread of locally authigenic minerals represented by the widespread pyrite mineral during the two sections of the study, in addition to a few presence of glauconite mineral. Depending on the petrographic description of the diagenesis processes, the vertical and lateral changes of the diagenesis processes were studied, and the diagenesis environments of the formations under study were deduced, where it was found that all the rocks of the two sections of the study were formed in the early stages of the diagenesis processes within the vadose environments as a result of exposure to tectonic processes that helped uplift their rocks to the surface and be affected by meteoric water.

studied the biostratigraphy of planktic foraminifera fossils of period the lower Turonian-lower Maastrichtian and determined the age of the Gulneri Shale Formation of lower Turonian-upper Turonian, and the Kometan Formation of lower Turonian-lower Campanian, and Mushorah Formation from the lower Santonian-lower Campanian, while [4] studied the biostratigraphy of the Gulneri Shale Formation and the lower part of the Kometan Formation in the Kosrat fold in northeastern Iraq, and showed that the Gulneri Shale Formation consists of the black shale and a thickness of about 1.5 m, which reflects the events of OAE _ 2, and that the lower and upper contact surfaces of the formation are unconformity with the Dokan Formation underline it and the Kometan Formation above it and determined its age with lower Turonian, [5] by studying the paleoenvironment of the Kometan Formation in the Dokan area, concluded that the formation was deposited in a deep marine environment depending on the masses of Ostracoda and some types of foramnifra., The study area included two subsurface sections within the Dome of Daoud in the Bai Hassan field in northern Iraq, consisting of two wells (BH-16 and BH-86) as shown in Table (1) [6] and located within the Low Folded Zone within the Western Zagros Fold -Thrust Belt according to the tectonic divisions of Iraq [7] Fig ( 1).
Figure 1.The tectonic divisions of Iraq show the wells in the study area modified by [7] 3rd Scientific Conference of Iraqi Desert Geology (

BH-86
The Bai Hassan field is located in the Governorate of Kirkuk in northern Iraq, approximately (30) km northwest of the city of Kirkuk, and represents a longitudinal convex fold consisting of two domes, the dome of Kithke and the Dome of Daoud, the axial length of which reaches more than 30 km in the north west direction -southeast parallel to the general direction of the Zagros mountain range in the region and neighbouring areas.It is a kind of fold formed on the advanced rifts, where the dome of Kithke is symmetrical and visible on the surface, which is larger and higher in composition than the northwestern dome called the Asymmetrical Dome of Daoud, where its southwestern wing is shorter and more inclined than its northern and northeastern wing, and the Dome of Daoud is affected by a large thrust fault with a maximum displacement of about 400 m, They are separated by a saddle called the Shahl saddle, in which the axis of the fold deviates slightly by (10° to 20°) west from the general direction of the axis of the fold [6], Fig (2).The thickness of the study section during a well (BH-16) is 213 m, while its thickness during a well (BH-86) is 233 m and consists of sequences of lamination grey and black calcareous shale, hard grey limestone, chalky limestone, dolomite limestone and marly limestone of medium hardness for the formations of Gulneri Shale, Kometan and Mushorah, as in Fig ( 3)(4).The current study aims to study the vertical and lateral changes in the diagenesis processes of the sequences (upper Turonianlower Campanian) and to indicate the amount of correlation between these different changes and their relationship to the change of their reservoir characteristics and their importance as oil storage rocks, as the reason for the change in reservoir properties and the amount of production of rocks produced within these sequences and their association with the change of diagenesis processes gave this justification for studying the vertical and lateral changes of the diagenesis processes.

Methodology
The study was represented by reviewing the internal reports and the final reports of the study wells, where 206 slides available at the North Oil Company were studied, 80 slides for the BH-16 well and 126 slides for the BH-86 well and describing them petrographically under the polarized microscope (optika) to determine the reservoir properties and indicate the impact of the diagenesis processes and then derive diagenesis environments, Paint, Excel and Surfer programs were used to draw stratigraphic sections.

Diagensis processes
It includes all physical, chemical and bioprocesses that occur on sediments and lead to a change in their texture from the time of their deposition until they are rocked [8].Diagenesis processes are classified into several classifications, the most prominent of which is the classification [9], which classified the diagenesis processes into two categories: 3.1.Constructive Diagenesis

Isochemical Diagenesis
It is the process in which there is no change in the chemical and mineral composition of carbonate sediments represented by each of the processes of cementation resulting from the process of chemical deposition of solutions saturated with ions of various minerals filling pores and rock cracks partially or completely [10], and that the mineral composition of cement depends on the quality of solutions penetrating into the pores and the amount of saturation [11], and the process of cementation in the diagenesis environment is affected by several factors, including temperature, pressure, pH function and pressure.Partial CO 2 and chemical invasive solutions [12], Among the types diagnosed are granular cement, which is transparent limestone crystals of equal sizes that do not have a preferred direction of growth, and are usually incomplete to almost full-faceted, granular in shape and with overlapping or overlapping borders or edges [13], and refer to [14] that it is deposited within the phreatic and Vadose environments, and arises during the early stages of diagenesis processes [15], Fig ( 9/A), and druzy cement, which is pure transparent limestone crystals characterized by irregular and growing faces perpendicular to the inner walls of voids, where their sizes increase towards the center of the pores or space [13], and arises in the early and middle stages of diagenesis processes within the phreatic and vadose environments [16]; [ 11], Fig ( 9/B), blocky cement, which is a symmetrical calcareous crystals of relatively large size, semi-complete to full-faceted, with very clear crystalline boundaries, is found within the deep burial environment and the phreatic environment [13], Fig ( 9/C), and syntaxial cement is calcareous crystals that usually grow around the shells of Echinoderms, and is found in the deep burial environment and the phreatic environment and is also called edge cement [11], Fig ( 9/D), and cementation is considered the most influential diagenesis process during the two sections of the study, The process of neomorphism is the process of transformation of the metal from one state to another without a change in the mineral composition and is based on two processes, the process of recrystallization and the process of inversion [17], and explained [11] that the process of recrystallization includes a change in the size and shape of mineral crystals without changing in their chemical composition, and pointed out [18] that the most suitable environments for the process of neomorphism of carbonate rocks are subsurface and atmospheric diagenesis environments, Where the inversion process was not diagnosed in the present study, Fig ( 5)(6)(10/A).

Unisochemical Diagenesis
It is the process in which there is a change in the mineral and chemical composition of the sediments, including the process of dolomitization, which is the process of replacing the magnesium ion (Mg+ 2 ) with the calcium ion (Ca+ 2 ) in limestone rocks [19], and the limestone passes through several stages in order to turn into dolomite rocks, many limestone deposits contain dolomite mineral, but it is often secondary in origin and also exists as a cement material and is characterized by its rhombic crystals [20], and is considered one of the very important diagenesis processes because its rocks constitute more than 50% of the limestone rocks that store hydrocarbons in the world, and the increase in the intensity of the dolomitization leads to an increase in the percentage of porosity as the process of replacing the element magnesium with the element calcium leads to a decrease in the size of the crystals and thus increase porosity [21], Among the dolomite texture identified based on the classification [22] are both floating rhombic texture, which is characterized by its single rhombic crystals of large and small sizes scattered within the micrite or crystallized ground, and is characterized by incomplete to full-faceted crystals formed during the early stages of the dolomitization process [23], Fig ( 10/B), and contact rhombic texture, which is characterized by its adjacent crystals within the micrite or crystalline ground.Forms during the early and middle stages of the dolomitization process [24], Fig ( 10/C), While the authigenic minerals are minerals that are formed locally within the sedimentation basin as a chemical product, and the most important evidence of the locality of their origin is the limited appearance of these minerals to the gaps of structural and non-structural grains molded on the size and shape of the vacuum as well as the prevalence of these minerals and their spread in the form of colonies and clusters within the host facies negates the possibility of being transported [9], Among the most important authigenic minerals that have been diagnosed are pyrite (FeS 2 ), which is considered one of the important minerals in sedimentary rocks and the most common in the current study, and between [25] that most of the iron minerals associated with sedimentary rocks are formed by diagenesis processes and often early ones, and [26] pointed out that it is formed in reducing environmental conditions with high organic content, where anaerobic bacteria reduce dissolved sulfate ions, leading to the release of sulfur, which is in the form of (H 2 S) after its union with hydrogen Water and that (H 2 S) will combine with reduced iron compounds to form pyrite metal (FeS 2 ), Fig( 10/D), Glauconite, which is considered one of the clay minerals belonging to the mica group rich in silica, iron and aluminum, which is characterized by its bluish-green, yellowish-green or grayish-green colors and is easily identified in thin rock slides and in both ordinary and polarized lights [26], and its presence indicates unconformity surfaces and its chemical deposition in marine environments [27], Fig ( 5)(6) (11/A).

Destructive Diagenesis
They are the processes in which there is no change in the chemical and mineral composition of the sediments and include both the process of Compaction, which is the process that leads to the Compaction of the granules and thus a decrease in the primary porosity as well as the occurrence of fracture and deformation of the granules with the exposure of some of them to dissolution [28], refer to [29] that the process of Compaction and increased stresses on the sediment produces a set of structures and compressed tissues, some of which are visible in the field and others are not visible, Two types of compaction have been diagnosed, each mechanical Compaction, which is the process of Compaction, deformation, rearrangement and cracking of granules as a result of the weight of the sedimentary cover or as a result of tectonic movements, which reduces porosity by half of the total primary porosity present in newly deposited carbonate deposits that may reach approximately 80% [13]; [30], Fig ( 11/B), chemical compaction is one of the most important late diagensis processes in deep environments, which in turn leads to the formation of melting surfaces (Stylolite) [31], which is a common process in carbonate rocks due to its high solubility [32], Fig ( 11/C), The dissolution process represents the process of partial or total dissolution of some rock components, leaving voids that may be filled later with cement materials, and the reason for this is due to the exposure of unstable minerals to unsaturated solutions [33], while [34] referred to as the process of forming voids within carbonate rocks due to the exposure of their minerals to decomposition or dissolution.He explained [35] that it is one of the most important diagensis processes because of the formation of secondary porosity as a result of the dissolution and dissolution of part of the soluble rock components, and this type of porosity formed by dissolving the porosity of the solution, Examples include moldic porosity, which is formed as a result of complete selective dissolution of some structural and non-structural fossil shells [10], Fig ( 11/D) and Vuggy porosity which is formed as a result of the irregular distribution of nonselective dissolving processes during the early diagensis stages [10] Fig ( 12/A) and Caven porosity which is formed as a result of non-selective dissolution and is of large sizes and irregular shape [36] Fig ( 12/B), and the channels porosity of the where they are formed as a result of non-selective dissolution and are in the form of longitudinal gaps and sometimes branched [10], Fig ( 12/C) and Intercrystalline porosity, which is the porosity that resides within rocks exposed to recrystallization and dolomitization processes [37], Fig ( 5)(6)(12/D).

Vertical and horizontal variations in the diagenesis processes
We note through the study of the rock slides of the two sections of the study that the rocks of the Gulneri Shale Formation within the two sections are slightly affected by the diagenesis processes and are formed during two stages, the intermediate stage in terms of druzy cement and tangential Compaction that is formed within the phreatic environments and the late stage in terms of granular cement inside the skeletal grains, whose formation indicates the late stages of the diagenesis processes within the deep burial environments as a result of dissolution the granules in the early and middle stages and filling them in the late stages, As for the lateral changes of the rocks of the two sections, we notice that they are affected by the same proportions of the diagenesis processes, Fig ( 5)(6)(7) (8).
As for the rocks of the Kometan Formation within the lower part of the lower Kometan unit of the section (BH-16), we notice their formed during two stages, the intermediate stage in terms of druzy cement and tangential Compaction that is formed within the phreatic environments and the late stage in terms of granular cement within the skeletal grains, whose formed indicates the late stages of diagensis processes within deep burial environments, While rocks of the same part are formed within the section (BH-86) during two stages, the early stage in terms of caven and vuggy porosity that form within the vadose environments and the late stage in terms of granular cement within the skeletal grains and chemical compaction represented by the dissolution surfaces (stylolite) that are formed within deep burial environments, that accompany the signs of the early and late stages together within the same depths we conclude from it that the rocks of this part have been subjected to tectonic IOP Publishing doi:10.1088/1755-1315/1300/1/01203610 processes that helped to uplift their rocks to the surface and affected by meteoric water, Fig ( 5)(6) (7) (8).
The rocks of the Kometan Formation within the upper part of the lower Kometan unit of the section (BH-16) formed during two stages: the early stage in terms of vuggy porosity and point compaction that are formed within the vadose environments and the late stage in terms of granular cement within the skeletal grains, whose formed indicates the late stages of the diagenesis processes within the deep burial environments, while the rocks of the same part are formed within the section (BH-86) during three stages, early stage in terms of caven and vuggy porosity and floating dolomite rhombic that are formed within vadose diagensis environments, intermediate stage in terms of moldic porosity, blocky cement and tangential compaction that forms within phreatic diagensis environments, and late stage in terms of granular cement within skeletal grains and chemical compaction represented by dissolution surfaces (stylolite) that are formed within deep burial environments, The evidence of the early stage with the middle and late stage are accompanied together within the same depths, we conclude from it that the rocks of this part have also been subjected to tectonic processes that helped to uplift their rocks to the surface and be affected by meteoric water, while we note the lateral changes of the rocks of the two sections within the same unit to increase the process of dolomitization and dissolution and formed of caven and vuggy secondary porosity towards the section (BH-86) and this indicates their exposure and exposure to surface conditions more in addition to the increase in the transfer of solutions as a result of being affected by the activities Subsurface tectonics as well as increased slope, Fig ( 5)(6) (7) (8).
While the rocks of the Kometan Formation within the middle unit of the two sections of the study, we observe their formed during two stages, the early stage in terms of caven, channel and vuggy secondary porosity, as well as floating dolomite rhombic and point Compaction that are formed within the vadose diagenesis environments and the late stage in terms of granular cement within the skeletal grains, whose formed indicates the late stages of the diagenesis processes within the deep burial environments.Signs of both early and late stages within the same rock unit indicate that its rocks were subjected to tectonic processes that helped to uplift their rocks to the surface and were affected by meteoric water, while no obvious lateral changes were observed between the two sections, Fig ( 5)(6) (7) (8).
As for the rocks of the Kometan Formation within the lower part of the upper unit of the section (BH-16), we observe their formed during three stages, the early stage in terms of channel and vuggy secondary porosity, floating dolomite rhombic that are formed within the vadose diagensis environments, the intermediate stage in terms of moldic secondary porosity, druzy and blocky cement and dolomite contact rhombic, tangential compaction that forms within the phreatic diagensis environments and the late stage in terms of chemical Compaction and the formed of dissolution surfaces (stylolite) and granular cement within the skeletal grains, whose formed indicates the late stages of diagensis processes within deep burial environments, Also rock of the formation are formed within the same part of the section (BH-86) during three stages, the early stage in terms of channel secondary porosity, floating dolomite rhombic that are formed within the vadose diagensis environments, the intermediate stage in terms of moldic secondary porosity, blocky cement that forms within the vadose diagensis environments, the late stage in terms of chemical Compaction, the formed of dissolution surfaces (stylolite) and granular cement within the skeletal grains, whose formed indicates the late stages of diagensis processes within the deep burial environments, and we did not notice clear side changes between the two sections only an increase in the dolomitization process and the formed of contact rhombic within the section (BH-86) and this is on the impact of the section by faults and increased transport of solutions loaded with magnesium, While the rocks of the Kometan Formation within the upper part of the upper unit (Upper Kometan) of the section (BH-16) we observe their formed during three stages, the early stage in terms of caven and vuggy secondary porosity, floating dolomite rhombic that formed within the vadose diagensis environments, the intermediate stage in terms of moldic secondary porosity, druzy and blocky cement that are formed within the phreatic diagensis environments, the late stage in terms of chemical Compaction and the formed of dissolution surfaces (stylolite) and granular cement within the skeletal grains, which indicates formed IOP Publishing doi:10.1088/1755-1315/1300/1/01203611 to the late stages of diagensis processes within deep burial environments, While rocks of the same part of the section (BH-86) we observe their formed during two stages, the early stage in terms of caven, channel, vuggy, dolomite floating rhombic and point compaction that form within the vadose diagensis environments and the late stage in terms of granular and druzy cement inside the skeletal grains, whose formed within the granules indicates the late stages of the diagensis processes within the deep burial environments, we observe through the lateral changes of the two sections an increase in dissolution and dolomitization towards the section (BH-86) through evidence caven, channel, vuggy secondary porosity and floating dolomite rhombic, and this indicates, as we have indicated, subsurface tectonic activities, increasing slope and increasing the transfer of solutions towards the section, Fig ( 5)(6) (7) (8).
As for the rocks of Mushorah Formation in the section (BH-16) and the lower part of the formation in the section (BH-86), we observe their formed during two stages, the early stage in terms of caven and vuggy secondary porosity and floating dolomite rhombic that form within the vadose diagensis environments, and the late stage in terms of granular cement within the skeletal grains, whose formed within the granules indicates the late stages of diagensis processes within deep burial environments, While rocks the formation in the upper part of the section (BH-86) we observe their formed during three stages, the early stage in terms of caven and channel secondary porosity that is formed within the vadose diagensis environments, the intermediate stage in terms of moldic secondary porosity and syntaxial, druzy and blocky cement that are formed within the phreatic diagensis environments, and the late stage in terms of convexconcave and chemical Compaction and formed of dissolution surfaces (stylolite) and granular cement within the skeletal grains, whose formed indicates the late stages of diagensis processes within the deep burial environments, and the association of the signs of the three stages within the same rock unit indicates that its rocks have been subjected to tectonic processes that helped to uplift them to the surface and be affected by meteoric water, We did not observe significant lateral changes between the two sections only a few increase in the dolomitization represented by some dolomite rhombic as well as a few increase in dissolution represented by the moldic porosity during the section (BH-16) as a result of the effect of the faults in the field and uplift their rocks up and increasing the transfer of solutions through them, Fig ( 5)(6)(7) (8).While the vertical changes of the diagensis processes during the rocks of the two sections, we note the spread of both the process of cementation and authigenic minerals represented by pyrite, neomorphism and dissolution according to the degree of prevalence along the two sections with a few presence of the compaction and dolomitization processes and their presence was limited to different depths of the Kometan and Mushorah formation, Fig ( 5)(6)(7)(8).

Conclusions
The rocks of the Gulneri Formation in the two sections consist of a black laminated calcareous shale, while the Kometan Formation of two sections is divided into three units.The middle unit in the two sections consists of a brown laminated calcareous shale, while the lower and upper units, as well as the formation of a consultation, mostly consist of sequences of limestone and marly limestone in both sections.sequences of this cycle are unconformity with the Dokan Formation that underlies it and the Hartha Formation of that above it.The rocks of the formations are affected differently by the diagenesis processes, and the most influential was the process of cementation and authigenic minerals represented by pyrite, then the neomorphism and dissolution and Compaction and finally the process of dolomitization.We see the spread of pyrite and cementation along the two sections, while the rest of the diagenesis processes appear and disappear along the two sections and in very few proportions.We observe evidence of the early stages of the diagnosis processes formed within the vadose environments in most of the rocks of the two sections of the study as a result of their exposure to tectonic processes that helped to uplift their rocks to the surface and affected by meteoric water.

Table 1 .
Show the coordinates of the study wells with the contact, the thickness of the formations and the number of slides[6] 3