Sedimentology Study Of Exposed Formations In Al-Assad Valley, Al-Baghdadi Area, Western Iraq

The presence of the Sheikh Alas Formation, the Shurau Formation, and the Euphrates Formation in the area of the current study. The inference of the Sheikh Alas Formation was from Nummlite fossils and planktonic Foraminifera fossils. The Euphrates Formation was deposited in a shallow marine environment, the Sheikh Alas Formation was deposited in an environment in for reef, and the Shurau Formation was deposited in an environment Back reef. The environment of the Euphrates Formation is a shallow lagoon environment for the presence of milliolied fossils, which represent the Miocene age as evidenced by the presence of the Borlis melo melo fossil. As for the environment of the Sheikh Alas Formation, it was deposited in a marine environment in for reef due to the presence of Planktonic foraminifera fossils and the Nummlite fossil, which represents the Oligocene age, and the environment of the Shurau Formation In a shallow, lagoon marine environment Back reef, there are abundant milliolid fossils. The boundary between the Miocene formations and the Oligocene formations is characterized by an unconformable boundary composed of a layer of basal conglomerate with a thickness of 6.5 m, which is affiliated with the Euphrates Formation in terms of age.


Introduction
The study area is located in Anbar Governorate -western Iraq, near Ain Al-Asad Air Base and about 6 kilometers from the city of Al-Baghdadi.The study included the petrographic aspects, microfacies and stratigraphy of (25) rock samples from the outcrop (Euphrates Formation, Sheikh Alas Formation, and Shurau Formation) in Al-Assad Valley, which has a thickness of (18.5 m).Samples for the current study were collected from the al-Assad Valley outcrop, which consists of the Euphrates Formation, which is Miocene age, the Sheikh Alas Formation, and the Shurau Formation, which is Oligocene age, which is located between two latitudes and longitudes (33° 51' 18"N and 42° 53' 17" E) and Figure (1) Represents the location of the study area.The presence of Nummlite in the basal laboratory layer indicates the presence of the formation of Sheikh Allas below the formation of the Euphrates in the Al-Baghdadi area [6].The Sheikh Alas Formation was inferred from Nummlite fossils, and the total thickness of the formation in the Suhailia area was not determined.The Anah Formation appears directly under the basal conglomerate in Al-Assad Valley, with a thickness of (7 m), and the Sheikh Alas Formation does not appear [8].The Sheikh Alas Formation appears below the Euphrates Formation in Hajar Valley in Haditha area, and its microfacies has not been determined [7].The Sheikh Alas Formation below the Euphrates Formation is shown in a subsurface section in well (AKK.1) in the Akaz field [2].The Sheikh Alas Formation and the Shurau Formation appear in the al-Assad Valley outcrop under the basal conglomerate layer of the Euphrates Formation [9].The presence of the Sheikh Allas Formation below the Euphrates Formation is inferred from the appearance of fossilized Nummlite in the basal conglomerate layer [4], The Euphrates formation appears in the city of Al-Baghdadi and its thickness is 16 meters, but its lower limit is not visible [10].

Tectonic Setting
The study area Al-Assad Valley is located in the northeastern part of the Arabian plate, and is located within the main tectonic division within the stable shelf in western Iraq [20].The study area is bordered to the north by the Al-Jazeera Zone, to the east it is bordered by the Al-Salman Zone, and to the west it is bordered by Syria and Jordan, Figure (2).The outcrop is also bounded by two types of transverse fault zones, it's the Sirwan Fault Zone to the south and the Diza Castel Zone to the north, inside the Iraqi block.The study area is bordered by the Abu Al-Jir Fault along the Euphrates River, and the Abu Al-Jir Fault also represents the boundary between the stable shelf and the unstable shelf in the Arabian Plate [5]. 3

Sampling & Methodology
The current study is based on 25 samples, including (7) samples from the Euphrates Formation, (9) samples from the Sheikh Alas Formation, and (9) samples from the Shurau Formation, The samples of the Shurau and Sheikh Alas formations were horizontal samples, with one sample for every 10 cm, And two samples for each Formation in a side way to be sufficient evidence and identify the two Formations by studying the microfossils components.The total thickness of the outcrop is (18.5 metres), whereas the thickness of the Euphrates Formation was (17 metres), the thickness of the Sheikh Alas Formation was (0.5 metres), and the thickness of the Shurau Formation (0.5 metres) were samples from the al-Assad valley outcrop Figure (3).
The aim of this study is to shed more light on the facies, diagenetic changes, and depositional environment of each formation and to identify the formations present in the outcrop of this study.It is worth noting that we returned to the field two additional times due to insufficient evidence to determine the Sheikh Alas Formation and the Shurau Formation, The main reason that prompted us to return twice to the field and adequate samples is the reason for the disagreement and conflicting opinions about determining the Formation.Specifically in this outcrop, (6 samples) were taken the first time, and (8 samples) the second time, and I chose the largest thickness in which the two formations appear in the study area, where I found the largest thickness in which the two formations appear is (0.5 m) for each formation.
Petrographic study includes microscopic examination of all samples under the polarized microscope to give us a clear idea of the main ingredients and rock fabric, All thin section made in this work were stained with alizarin red according to Friedman's staining procedures in order to distinguish IOP Publishing doi:10.1088/1755-1315/1300/1/0120384 between calcite and dolomite and estimate their proportions in the thin section.The carbonate rocks of the formations were classified according to Dunham's classification with modification by Embry and Clovan [13] depending on the depositional fabric of the rocks.Types of granules such as lithomicrit, peloids, and ooids.The identified microfacies were compared with Wilson's standard microfacies types (SMF) and facies zones (FZ).Their depositional environments are interpreted as classified by Flugel.

A. Stratigraphy 1-Euphrates Formation
The lower part of it is a thick layer of basal conglomerate, 6 m thick, consisting of limestone rocks varying in size, some of which are more than half a meter in diameter, It is the result of a process of weathering of ancient rocks, leaving them in their original places, and gradually graduates upward into smaller, more rounded rock masses.[7] considered that the basal conglomerate layer belongs to the Euphrates Formation, as evidenced by the presence of a fossil (Borelis melo melo).The layer of conglomerate is above the Euphrates Formation, which consists of well-stratified limestone rocks that transform into solid dolomite rocks, followed by a layer of chalky limestone rocks with a little shale in the upper part.The upper part of the rocks of the Euphrates Formation consists of crystalline, hard, shattered rocks affected by weathering processes, with a thickness of half a meter.

2-Shurau Formation
It was described by Beilin in 1956, in the Kirkuk well No. 109, which is about 18 meters thick, and consists of about 5.5 meters of thick gray limestone and 13 meters of porous rocks.In the Kirkuk field, the Shurau Formation lies below the Sheikh Alas Formation and is conformable, and unconformable, with the Baba Formation above it.Part of its facies is behind the reef with the Sheikh Alas and Blani formations in the lower Oligocene age [29].According to [22] in the Kirkuk area, the bottom of the Formation was deposited in coral reefs, and the upper part in a tidal environment.The Shurau Formation is only exposed in the Al-Assad valley outcrop, and it is one of the oldest formations in the current study, as it matches in terms of age with the Sheikh Alas Formation, which is at the base of the outcrop in Al-Assad valley.It is (0.5 m) thick and consists of recrystallized limestone rocks with a gray to light gray color.The Shurau Formation forms the base on which the Sheikh Alas Formation sits.

3-Sheikh Alas Formation
The type locality of this formation, which is approximately (732 m) from the village of Sheikh Alas on the northern summit of the village of Qara Juqa-Dagh in northern Iraq, was first described by Bellen (1956) [29].Its thickness is about (26 m), composed of dolomitic and crystalline porous limestone, which is generally porous and sometimes limestone.The lower limit is unconformable with the shallow Eocene limestone while the upper limit is conformable with the Shurau Formation.According to [22], the lower part of this formation was deposited in a slope-front environment, while the upper part represents a lagoon environment, without any explanation while these two different facies appear next to each other.The formation has been identified only by rare, poorly preserved fossils of foraminifera such as Nummulites intermedius-fichteli, d'Archiac and Haimeand, and is considered to be of lower Oligocene age [29].This formation was identified for the first time in the Ousbi section by [17], Lawa, and [17].The rocks of the Sheikh Alas Formation were described in the lower part of this outcrop.The Sheikh Alas Formation consists of hard, recrystallized limestone rocks with a white color that tends slightly to a gray color.It is a thin layer with a thickness of about 0.5 metres, followed by the Shurau Formation, also about 0.5 metres.

B. Petrography
By examining thin section with a polarizing microscope, the main components of the rocks of the Oligocene -early Miocene formations were identified for the current study.In general, limestone rocks consist of Skeletal and non-Skeletal components [28].The petrographic study includes the study of these components as well as the diagenetic processes, as the change in the texture of limestone rocks reflects the differences that occurred in the conditions of their depositional environments [24].

1-Skeletal grains
The skeletal grains that have been identified in the rocks of the Oligocene-Early Miocene formations include a group of fossils.Fossils are the main proportion of limestone rocks and are one of their components, especially in marine environments.It was noted in the samples of the current study that the fossils are characterized by their diversity and good preservation, and the most important types of fossils identified in the rock samples are Benthonic foraminifera fossils, planktonic foraminifera fossils, gastropods, echinodermata, and algae.The following is a description of the skeletal grains: a) Foraminifera One of the most important types of foraminifera that has been distinguished is the Milolid, which belongs to the benthic foraminifera.Milliolid genera appear in complete form or in the form of moldic filled with lime cement or in the form of complete fossils.They are spread in the rocks of the upper part of the Euphrates Formation and are also identified in the rocks of the Shurau Formation, Also, one of the most important types of foraminifera that has been distinguished is Borelis melo melo, which belongs to the benthic foraminifera and appears in the rocks of the upper part of the Euphrates Formation.This fossil is a biological indicator of the age of the (Early Miocene) [1].These fossils are an important factor in precise facies analysis, as well as determining the shallow marine environment IOP Publishing doi:10.1088/1755-1315/1300/1/0120386 [15].Then another type of foraminifera Rotalia vianotti was identified in the Euphrates Formation in its lower part, and a fossil Dendriting rangi was also found in the Euphrates Formation and also It was identified in the rocks of the Shurau Formation, as well as a fossil Austrotrilina Sp. in the lower part of the Euphrates Formation and also identified in the rocks of the Shurau Formation.Fossils Peneroplis Sp., Quinqueloculina and Lenticulina are found in the rocks of the Shurau Formation, and fossils Nummulite fichteli and Ammonia beccarii are found in the Euphrates Formation in the lower part.[19] [21] stated that the common presence of the species Ammonia beccarii with Miliolids is evidence of an environment with mixed salt water and open bays with a depth ranging between 10-20 metres.Among the most important types of foraminifera that have been distinguished in the Sheikh Allas Formation are the planktonic foramanafera, through which it has been shown that the environment of the Sheikh Allas Formation is in Fore-reef, and Nummulite, which belongs to the benthic foramanafera and which appears in the rocks of Sheikh Alas formation, which is considered the fossil indicating the formation of Sheikh Alas, as mentioned by [6].

b) Mollusca
These fossils belong to the phylum of gastropods, which includes gastropod fossils that were found in the rocks of the Euphrates Formation in its central part, and the presence of Gastropod indicates that the depositional environment was relatively close to the shore line [1].

c) Algae
Algae are the main contributor to the production of limestone rocks and are divided into several types, including green, red, blue, and yellow algae [27].Algae were observed in the rocks of the Euphrates Formation, especially in its lower part.It was also found in the rocks of the Shurau Formation.

d) Echinodermata
Echinoderms are marine invertebrates with a hard skeleton and made up of calcareous plates.They are spread in marine environments with moderate salinity near the shore line all the way to deep environments [26].In the Euphrates Formation in its lower part, [14] indicated that it lives in the open marine environment.

2-Non Skeletal grains a) Pellets
They are structureless, shapeless, amorphous clay-limestone nodules [23].They have irregular shapes and are rich in organic materials, which are found in shallow marine sediments [28].[12] indicated that Pellets spreads in areas with low energy, and because of its soft nature, it destroys areas with high energy.Pellets were distinguished in different sizes and oval shapes, devoid of internal structures, and they spread in large quantities in the Euphrates Formation in its lower part, and were also found in the rocks of the Shurau Formation.

b) Ooids
It is one of the non -Skeletal components of carbonate rocks.The Ooids are formed in warm water environments at a depth of less than (2 m) and are located within the high -energy continental sidewalks [24].[14] indicated that the Ooids indicate the high energy of the sedimentation environment, and in the sedimentary environment in which the energy is high, especially shore line environments, and since the movement of waves in the water moves back and forth, and this water is often saturated with calcium carbonate, so the sedimentation of calcium carbonate occurs around the nucleus In the form of covers [15].The Ooids were distinguished at the bottom of the Euphrates formation rocks and their percentage is few c) Matrix They are soft materials composed mostly of micrite, the size of which does not exceed 4 microns [14].Limestone clay is characterized in the rocks of the Euphrates Formation with fine sizes not exceeding 4 microns and subjected to the process of recrystallization to form microspar.It is also found in the rocks of the Shurau Formation.

3-Digenetic Processes
These are the chemical, physical and biological changes that affect carbonate rocks after sedimentation and before the Digenetic process and lead to a change in their original texture and chemical and crystalline composition [27] [28].

a) Dissolution: Dissolution processes appeared in the form of gaps or voids in the Euphrates
Formation, and dissolution also appeared in the rocks of the Shurau Formation, resulting from the solutions that work to dissolve the limestone rocks, which led to the formation of gaps and voids in them, and these pores were generated as a result of the dissolution process with the solutions, Acidic water penetrates carbonate rocks and dissolves them within vadose zones, or when there is a decline in sea level or when the rate of sedimentation increases and the surface of sediments rises, this leads to the dissolution of these rocks and the formation of gaps and pores [30].b) Dolomitization: It is a change in size or shape, or both, or a change in the orientation of the crystal with a very small change in mineralogy [15].The dolomitization process is one of the most important diagenetic processes affecting carbonate rocks.One of the most important factors that facilitate the dolomization process in limestone rocks is the source of the magnesium ion  +2 and the mechanical processes that cause the pushing and movement of solutions within the carbonate deposits with the physical conditions of pressure and temperature [28], appeared in the upper part.From the Euphrates formation.c) Recrystallization: It is the change in the size or shape of crystals as a result of thermal instability, which leads to larger grain sizes [18].The recrystallization process is very clear in the rocks of the Euphrates Formation, and the recrystallization process results in an increase and growth in the size of the crystals.The micrite recrystallized and its size increased to micro spar with the grain size (4-10) microns, and it also appeared in the rocks of the Shurau Formation.d) Cementation: Cementation is defined as the diagenetic process of filling a cavity or open space through chemical deposition of materials from the surface [14].In the cementation process, the conditions affecting cement deposition depend on the minerality of the rock and the chemical composition of the precipitated solution [12].Among the most important types of cement identified with this Formations are: I. Syntaxialrim cement: Defined as the continuous visual growth of calcite cement crystals on echinoderm fragments, this cementation is relatively indicative of a freshwater (phreatic) environment [27].

II.
Drusy mosaic cement: It is a cement with fine crystals perpendicular to the walls of the granule [11].It is also common and is represented by crystals increasing in size towards the center of the void.This cement indicates a diagenetic environment type of the Metoric [16].

III.
Micritic Envelope cement: It is the cement that is like Cryptocrystaline cement, which covers granules, especially the fossils [11].IV.
calcite cement: One of the characteristics of this cement is to fill the voids between granules and spaces inside the granules [3].

V.
Meniscus cement: It is cement contact between grains.Druzy cement and Micritic Envelope cement in early diagenetic processes indicate a shallow marine environment [12].Euphrates Formation and at a thickness of (9 m).The proportion of its components ranges from (40-60%), represented a little of Forominifera and pellets affected by the process of cementation and dissolution.This facies matches the standard facies (SMF, 18) deposit Within the facies zone (FZ, 8) which is formed within Restricted.d) Lime Grainstone Microfacies: This facies was identified in the Euphrates Formation, in which the percentage of grains is more than 90%, and most of the grains are pellets and a few ooid affected by the dissolution process, as their presence is limited to the lower part of the Euphrates Formation at a thickness of 10 m.This facies matches the standard facies (SMF-16) within the facies zone (FZ,8) deposited in a restricted sea environment.
e) Lime Crystalline Microfacies: This facies was identified in the Euphrates Formation, and this facies contains a high percentage of secondary dolomite formed after sedimentation processes.This facies was strongly affected by diagenetic processes, which led to its strong cohesion.It was also affected by the process of dolomitization, dissolution, and recrystallization, which formed dolomite within this facies.As this facies was determined by [25] that it matches the standard facies (SMF, 21) deposited within the facies zone (FZ, 8) in the restricted sea environment within (Platform interior).

Conclusion:
The environment of the Euphrates Formation is a shallow laconic environment for the presence of milliolied fossils, which represent the Miocene age as evidenced by the presence of the Borlis melo melo fossil.As for the environment of the Sheikh Alas Formation, it was deposited in a marine environment in for reef due to the presence of Planktonic foraminifera fossils and the Nummlite fossil, which represents the Oligocene age, and the environment of the Shurau Formation In a shallow, lagoon marine environment Back reef, there are abundant milliolid fossils.
The Euphrates Formation consists of five microfacies, and when its facies were measured by standard facies, the sedimentary environment of the Euphrates Formation was within platform interior, and the Shurau Formation consisted of two microfacies, and when measured by microfacies, it fell within open marine and restricted.The Sheikh Alas Formation consisted of two microfacies, and when measured

Figure ( 2 )
Figure (2) Tectonic divisions of Iraq(Jassim and Goff, 2006) : A-Drusy mosaic cement.B-Meniscus cement and pellets.C-Borlis melo melo and calcite cement.D-Milioled and pellets.E-Nummulite.F-Planktonic Foraminifera G-Syntaxialrim cement.H-Dissolution and Dolomite.C. Microfacies 1. Microfacies of Sheikh Allas formation a) Nummulite Lime Mudstone Microfacies: This facies is characterized by the fact that it is mainly composed of micrate matrix, and the percentage of grains in it does not exceed (10%).This facies was identified in the Sheikh Alas Formation, in which the predominant percentage is limestone clay, and it contains a fossilized nummulite grain affected by the dissolution process, with a thickness of ( 0.75) meters, The numulite-bearing muddy limestone facies is more widespread in open environments within the shallow slope up to the deepest point of the photogenic potential (Holzmann) .This facies matches the standard facies (SMF-3) within the facies range (FZ,3) deposited in the open sea (Toe-of-slope) environment.b) Planktonic Foraminiferal Lime wackstone Microfacies: The percentage of grains is (10-40%) and is affected by the dissolution process.This facies was .1088/1755-1315/1300/1/012038 9 identified in the Sheikh Allas Formation at a thickness of (0.75) metres.Most of the grains in it are Planktonic foraminifera fossils Globigerina, as their presence is limited to the Sheikh Allas Formation.This facies matches the standard facies (SMF-8) within the facies zone (FZ,2) deposited in the deep sea environment (Deep Shelf) as determined by [2]. 2. Microfacies of Shurau formation a) Lime Packstone Microfacies: This facies was identified in the Shurau Formation at a thickness of (0.5 metres).Its composition ranges from (40-60%), represented by benthic Foraminifera fossils such as Miliolid, Austrotrillina, Quinqueloculina affected by the process of dissolution and dolomitization.This facies matches the standard facies (SMF-18) within the facies range (FZ,8) deposited in a restricted sea environment.b) Miliolids Lime Grianstone Microfacies: This facies was identified in the Shurau Formation, in which the percentage of grains is more than 90%, and most of the grains are milliolides affected by the process of recrystallization, dissolution, and cementation.This facies matches the standard facies (SMF-18) within the deposited facies range (FZ, 7).In an open sea environment.3. Microfacies of Euphrates Formation a) Lime Mudstone Microfacies: This facies was found in the Euphrates Formation at a thickness of 6 m.It is also called limestone mud or terrestrial sediment if its components contain less than 10% of skeletal grains .The current clayey limestone facies is comparable to the standard microfacies (SMF, 23).Deposited within the facies zone (FZ, 8), and formed within the restricted zone.b) Lime Wackestone Microfacies: The percentage of grains is (10-40%) from Miliolid, Austrotrillina and Algae and is affected by the cementation process.This facies appeared in the Euphrates Formation and has a thickness of approximately 14 m.The amount of calcareous clay is controlled by several factors from within the depositional basin, the most prominent of which is The effectiveness of water and waves within the depositional environment, and the different types of fossils and the nature of their presence within these facies may determine the appropriate depositional location.The current Wacky limestone facies can be measured by the standard fine facies (SMF, 10).Deposited within the facies zone (FZ, 7) and formed within open marine.c) Lime Packstone Microfacies: This facies was identified in the facies in the