Variable behaviour of Abu Jir fault zone, western Iraq

This study sheds light on the dynamic nature of the Abu Jir fault zone, uncovering intriguing contrasts along its path. It was conducted to know the variation through the zone, western Iraq, that starts at Razzazah Lake’s west and continues to Anah city. It is divided into two parts, southern and northern, utilized seismic sections for the southern part whereas fieldwork for the northern part. Seismic sections indicate that the southern part of the fault zone is negative flower structure which develops depressions, while field studies reveal that the northern part is positive behaviour forms some structures such as ridges, relay ramps and controlled the distribution of valleys within its zone. The Abu Jir fault zone not continuous fault but consists of many segments that subject to differential forces of strike-slip movements during Early-middle Miocene. The variation of behaviours is attributed to the difference of the direction between the northern and southern parts of the fault with sense of movement.


Introduction
The Abu Jir Fault z0ne, spanning appr0ximately 600 km, creates a prominent linear feature across the Iraqi landscape, easily discernible in satellite imagery.Comprising numerous faults trending in the NW-SE direction, the zone extents from Anah Graben, travels through the valley of the Euphrates River t0 places like Heet, Awasil, Abu Jir, and Shithatha, and runs through Kerbala, Najaf, and Samawa on the Euphrates River's western bank before joining the Al-Batin lineament northwest of Kuwait and west of Basrah [1].The research area's coordinate is between latitude (32⸰ 46′ 17″ N, 34⸰ 11′ 43″ N) and longitude (43⸰ 22′ 59″ E, 42⸰ 23′ 09″ E) (Figure 1).Many Researchers utilized dividing stable and unstable shelves with the Abu Jir Fault Z0ne, but disagreed on whether the fault extends north beyond Heet city, following the Al-Thirthar valley to converge with the Hamrin -Makhul range, ultimately dissipating directly south of the Sinjar region [2][3] [4].or to meet Anah Graben to the west [1] [5].The Abu Jir fault z0ne exhibited characteristics of a right -lateral strike -slip fault.[6][7] [8].Importantly, The zones of the Anah and Abu Jir Faults were mobile, allowing Late Cretaceous extension through subsidence and Late Tertiary compression via lateral movement or structural inversion, this behavior stopped far-field stresses from propagating into the platform's stable area [1].Al0ng the Anah-Abu Jir Fault Z0ne, activity is visible.One instance of the zone's continued activity is the Abu Jir Fault Zone's Al Jabha Sag Pond's continuous subsidence.[1].This zone in western Iraq connects to the Anah Graben in the n0rth and marks the western edge of the Zagr0s f0reland basin.[9].The significance of this research lies in the absence of seismic sections within the Abu Jir fault zone's northern part, coupled with a lack of previous studies covering the entire region.Therefore, this study focuses on a detailed examination of the northern part, addressing this research gap.This study aims to explain why the behavior of the Abu Jir fault z0ne differently al0ng its c0urse.

Geological setting
Stratigraphically, The studied area is exposed to numerous formations, The Anah Formation is revealed intermittently, characterized by massive, brecciated, grey, c0ralline limest0ne and recrystallized detrital [10].The Euphrates Formation is revealed al0ng the Euphrates River's path, extending fr0m the cities 0f Heet t0 AlQaim.It is comprised of a lower unit characterized by basal conglomerate succeeded by f0ssilifer0us limest0ne.The upper part of this f0rmati0n exhibits a sequence marked by the alternation of robust limest0ne and pseud0plastic limest0ne.[11].The Fatha F0rmati0n is characterized by recurring cycles encompassing bedded limest0ne, green marl, and gypsum.While the first cycle is evident in the Dulab region, the Heet area reveals the exposure of three cycles.In the southern and eastern extents of the research field, the Nfayil Formation is apparent, comprising green marl and fossiliferous grey limestone [12] (Figure 2).Tectonic and Structurally, the geological evolution of the region was characterized by extension of Late Cretaceous.The presence of various structural elements points to a period of extension, notably highlighted by a documented listric normal fault.The reactive during Early-middle Mi0cene.This fault traverses the entire Euphrates F0rmati0n that extends d0wnward into the Sihailiya outcrop, a phase of transpressional def0rmation occurred al0ng the Abu Jir fault z0ne, resulting from strike-slip m0vement [9].The Abu Jir Fault Z0ne divides the inner and outer platf0rms 0f Iraqi territ0ry and is S1:Awasil Sag ponds S2: Al-Jabha sag ponds S4 :Abu Jir sag ponds S3: Al-Mudowar sag ponds rec0gnized as the eastern b0rder 0f the Western Desert, ultimately defining stable part 0f the platf0rm [1] [5].There are two separate sections n0rthern and s0uthern parts.S0uthern part which extends fr0m the Razzazah Lake's west t0 Heet City.This regi0n is characterized by a negative fl0wer structure, intricately linked with the presence of f0ur sag ponds.[1][6][13] [14].N0rthern part is between cities of Heet and Anah is characterized by ridge.To the n0rth, the Abu Jir fault intersects with the Anah Graben, creating a division int0 two segments, namely the eastern and western sections.[9].The fault zone and the western section of the Anah Graben are characterized as inverted structures..The Abu-Jir Fault Zone doesn't extend continuously northward; Rather, it intersects with Anah Graben , bending t0 the west to create the Anah-Abu Jir Fault System [1].The Abu Jir Fault Z0ne, which produces a variety of ge0m0rph0l0gical features, is the m0st notable subsurface structure, including the Abu Jir Sag P0nds, Awasil, Al-Jabha, and Al-Mud0war.[14].
Figure 2. A ge0l0gical map that shows the stratigraphic units that are exp0sed in the research area.

Methodology
Two basic methodologies were used in the research.Firstly, analysed the behaviour of the Abu Jir Fault z0ne in the s0uthern part, relying on seismic sections in areas south of the Heet city.Secondly, due to the unavailability of seismic sections in the northern part which extends from Heet northwestwards to Haditha, relied on fieldwork to research northern part of the fault zone.In order to identify the faults and subsurface structures, the seismic sections were interpreted, and the horizons were detected using synthetic seismograms and using the paint program to plot them.ArcGIS software v. 10.8 is used to create location and geological maps.. utilized in addition to image processing software.During multiple field trips, structures resulting from the Abu Jir Fault z0ne activity in Earlymiddle Mi0cene were examined.

The Southern part of Abu Jir fault zone
Seismic secti0ns were utilized in this region due to their availability in addition to providing precise information about subsurface structures.In this part of the area of research, behavior of the Abu Jir Fault Z0ne was examined using three seismic reflection sections.Reflection seismic section AR-50 located in south of Heet region was used.The reflection seismic section AR-38 across northwest of Razzazah and southwest Habbaniya Lakes used to investigate behaviour of the Fault Zone across west of Razzazah and Habbaniya Lakes, the third section is AR-18 southwest Razzazah Lake.

Seismic reflection section AR-50
The Abu Jir survey is the name of this seismic line (south of Heet region).The position of this seismic section is situated n0rth AR-38 but in the same region.The length of this seismic section line is approximately 42.3 km, traversing the study area perpendicular to the Abu Jir fault, situated in the s0uthern part 0f the Heet regi0n.Employing synthetic seism0grams fr0m the cl0sest 0il well, three reflect0rs are selected.The reflectors dipping slightly northeastern and are parallel to sub parallel with one another.They are tops in the following formations (Figure 3).

Seismic reflection section AR-38
This seismic secti0n line lies across northwest of Razzazah and southwest Habbaniya Lakes.The position of this seismic secti0n is situated t0 the n0rth of (AR-18) and s0uth of (AR-50) but in the same area.The length of this line is approximately 42.3 km, extending through the study area and positioned perpendicular to the Abu Jir fault z0ne.This seismic secti0n, five reflect0rs are ch0sen, and the f0rmati0n dates of these reflect0rs are ascertained using log characteristics from various oil wells distributed across the region and synthetic seismograms.The reflectors exhibit a parallel to subparallel orientation with each other, featuring a slight dip towards the northeast.Tops of the following formations are represented by them [14].(Figure 4).I.
Alan Fm (late Liassic).Stratigraphically, the sequences appear as a thin section in the west part while it became thicker towards the eastern parts, Mesopotamian basin.All sequences are parallel or sub-parallel dipping and deeper towards Mesopotamian basin.Structurally, this seismic secti0n intersects the Abu Jir Fault z0ne.There are five faults maj0r high angle apparent dip faults, these faults cross all the sequence.The main fault F1 has high angle apparent dips t0ward n0rtheast.The two groups of min0r faults that dipping t0ward each other form the fault flower.The minor synthetic faults dip parallel t0 the main fault, while the min0r antithetic faults dip 0pp0site to the main fault made up negative fl0wer structure.Faults F2 and F3 in seismic secti0n appeared steeply dipping normal faults cutting across all formations in the seismic section without reaching the basement.One of these fault dips towards the other at the bottom, diverging upward, forming depressional zones between them Graben structures.F4 and F5 in the seismic section are also more intense and impactful normal faults compared to F2 and F3.This characteristic allows them to reach down to the basement.These faults are steeply, one of them dipping towards the other at the bottom and diverging upward made up Graben.

Seismic reflection section AR-18
Abu Jir survey is the name of this seismic secti0n line (west Razzazah Lake).The position of this seismic secti0n is situated s0uth of the (AR-38) in the same area.The orientation of this line extends from the northeast to the southwest, lying between shot points )1014.5-1437.5.(The length of the line spans approximately 42.3 kilometers, traversing the width of the research area and aligning perpendicularly to the Abu Jir faults zone.The seismic section consists of three sequences.This reflector's quality changes depending on the differences of bed's lithology.The reflectors exhibit a parallel to sub-parallel orientation with each other, featuring a slight dip towards the northeast.We noted that the stratigraphic reflectors or Formation thicknesses increase towards the northeast toward Mesopotamian basin.They are tops in the f0ll0wing f0rmati0ns (Figure 5).
Structurally, five major planar faults comprise the Abu Jir Fault Z0ne, which is crossed by the seismic section (F1, F2, F3, F4 and F5).F1 and F2 extends across the whole Paleogene and Mesozoic eras and might even reach the basement.The main fault F1 is apparent high angle dip t0ward the n0rtheast.It high angle fault fl0wer is included.Several normal faults that high angle and diverge upward are present.The negative fl0wer structure of the fault flower is made up of two sets of small faults that dip toward one another.F2 appears to dip at a high angle southwestward, additionally, the negative fl0wer structure of this fault fl0wer is made up of two sets of min0r faults that dip t0ward 0ne an0ther.. F3 and F4 They represent normal faults with a steep dipping that diverge upward making up Graben.F5 structure bounded by a fault along one side of its boundaries made up half Graben toward eastern ward.The reflectors have got the same dip which are dipping and became deeper towards the northeast (sediments basin).Through seismic sections we noted that the stratigraphic reflectors H3.
There was a uplift while the reflector H1 and H2 were depression that indicates the presence of strikeslip m0vement al0ng the fault z0ne.Due to the absence 0f seismic secti0ns f0r this part 0f the Abu Jir Fault z0ne, we relied on fieldwork within this area.Exposed rocks in this area varies from the Oligocene to the Middle Miocene.The Sheikh Alas F0rmati0n, which includes the earliest rocks from the early Olig0cene, appears in the Ain Al-Asad valley and lies in an unconformable with the Euphrates Formation.The study's main f0cus was 0n the Fatha and Euphrates f0rmati0ns, they, in turn, relate lower -middle Mi0cene.The study area encompassed three main 0utcrops: Heet, Sahliyah, and Dulab 0utcrops.

Heet outcrop
Exact measurements of the Heet outcrop were taken at (N 33°.37'04.5",E 42°50' 45.7").The topmost layer is made up of thin layers of secondary gypsum interspersed with marly limestone strata.This layer is followed by the third stratum, which is formed of greenish to yellowish marl with occasional anhydrite interspersion and shows evidence of weathering in some places.At the sequence's conclusion lies the fourth layer, distinguished by hard, white gypsum rocks, Reverse and normal faults good indicator of strike-slip m0vement within Abu Jir fault z0ne, with hydrocarbon seepage in high fractures gypsum (Plate 1).

Results and discussions
Considering the availability 0f seismic secti0ns in the s0uthern part of the Abu Jir fault z0ne, good reflectors have been selected in the seismic sections.The appearance of reflector interruptions reveals a clear image of the Abu Jir fault z0ne.Through the seismic secti0ns, we observe the evolution of the fault z0ne in the s0uthern part extending west 0f Razzazah lake t0 the s0uth of the Heet city.Because of the exposure to strike-slip m0vement that took place during the early-middle Mi0cene, this part displays a negative inversion, the fault zone experienced reactivation due to forces coming from the south towards the north originating from Afar mantle plum [9].During the Mi0cene epoch, these forces reached the Abu Jir fault z0ne, which in turn caused the Red Sea to open.This reactivation resulted in seismic activity along the fault zone causing both positive and negative inversions along this fault zone.These structures serve as evidence of the strike-slip m0vement.These structures typically manifest as depressions which were clearly discernible in aerial imagery and seismic secti0ns in the s0uthern part 0f the Abu Jir fault z0ne.By interpreting the seismic secti0ns in the s0uthern part 0f the fault z0ne, we observe the development of strike -slip m0vement al0ng this fault.Upon comparing seismic sections (AR-50, AR-38, and AR-18), it becomes apparent that the influence 0f the Abu Jir fault z0ne exhibited slight variability.As we move s0uthward, the number of faults increases, indicating that the extent and the fault z0ne's width are greater in the s0uth than in the n0rth.Upon comparing sections AR-18 and AR-38, it is evident that the region was initially subjected to normal faults.The flower structures, especially noticeable F1 and F2 in seismic section AR-18 (Figure 5), originated as normal faults forming grabens and then evolved into negative flower structures.Depressions form by various mechanisms These are negative flower structure, relay-ramp basin and releasing bend on strike-slip faults (Figure 6).Through seismic sections, we can infer the mechanics that led to the development of the depressions.The relay-ramp basin theory can be ruled out since the study area appears to consist of a single block, evidenced by the similarity in structures and the number of faults, indicating the geometry and kinematic similarity.Additionally, the releasing bend on strike-slip faults theory is also excluded because the area is composed of several faults not a single fault.Therefore, the researchers conclude that the most plausible explanation for the formation of these depressions is the presence of negative flower structures.The exposed rock formations in the area extending from Heet City to Haditha city range from the Olig0cene to the Middle Mi0cene [15].It is evident that this region has been influenced by strike-slip m0vement occurring on the Abu Jir fault z0ne.However, the behaviour of this n0rthern part differs from the southern part where the effects of the strike-slip movement led to a positive inversion characterized by positive flower structures that manifest on the surface in the form of ridge.The impact 0f the Abu Jir fault z0ne was clearly evident in the Heet outcrop.Several normal faults were identified with reverse structures, and the presence of layers exposed to uplift.All of these observations can be considered evidence of the region being subjected to strike-slip movement.Additionally, the hydrocarbon seepage was observed through the gypsum layers through the first cycle 0f the Fatha F0rmati0n.The influence of the Abu Jir fault caused the gypsum layers to fracture, rendering them highly permeable and forming channels for seepages.Measuring the direction of the IOP Publishing doi:10.1088/1755-1315/1300/1/01204310 maximum stress axis (σ1) that led to the inversion, it was determined to be at 168 degrees.This indicates that the stress responsible for this activity al0ng the Abu Jir fault z0ne originated fr0m the south to the northward direction.
To the northwest of the city of Heet, specifically in the Sahiliyah area (Plate 2). the upper part of the Euphrates F0rmati0n (Early Mi0cene) is exp0sed.Due to tectonic activity resulting from the Abu Jir fault z0ne's reactivation, a large ridge is visible in this area.The presence of collapses which typically form during extensional phases in addition reverse faults in the same location serves as evidence of the exposure of this area to strike-slip movement that occurred along this fault zone.
To the northwest of the Al-Sahiliyah area specifically in the Dulab area (Plate 3).The Euphrates Formation (Early Miocene).The presence of positive flower structures was clearly observed on the surface, confirming the region's exposure to strike-slip movement.Additionally, the presence of Graben, the undulation of layers, and collapses are all evidence of the area being influenced by the activity 0f the Abu Jir fault.
The drainage pattern as an indicator through which can potentially determine the direction 0f the Abu Jir fault.Due t0 the elevation caused by the Abu Jir fault activity, the valleys in the region were unable to flow in multiple directions, leading them to converge into a main valley where begins the ridge of the fault zone, that ultimately drains into the Euphrates River (Figure 7).This pattern extends from Al-Mahmudiya valley south of Heet city to Hjallan Valley south of a Haditha city.A decrease in the influence of the fault was observed towards the northwest.Finally, Abu Jir fault zone consists of some segments in the north part, the two important segments are Sahiliyah and Dulab, that limit typical relay ramp between them.

Conclusions
The Mesopotamian Graben, Oblique fault, flower structures (depression and ridge) and extensional faults Present confirms strike-slip movement.The distortion and deformation observed in the western part of the fault compared to the eastern part, see seismic sections, are indicative of a right-lateral strike-slip movement.The presence of collapses, sediment dike and undulation as evidence that the activity of the fault and inversion occurred shortly after the upper part 0f the Euphrates F0rmati0n was dep0sition, before the rocks reached the solidification stage.It was otherwise, fractures without collapses would be expected.The inversion resulted from stresses originating from the south due to the activity of the Afar mantle plume.The water drainage pattern in the western region controlled by the ridges of the fault.The fault zone consists of some segments in the north part, the two important segments are Sahiliyah and Dulab, that limit typical relay ramp between them.The segments subject to variable stresses.The variable behaviour 0f Abu Jir fault z0ne due to the relation between direction 0f the stresses with the two main parts of the fault zone, orientation the southern part tends to be S -N, while the northern part, the faults direction NW -SE.

2 Figure 1 .
Figure 1.Map of the study area showing the location and structural features.S1. awasil sag p0nd.S2.Al-Jabha sag p0nd.S3.Al-Mud0ar sag p0nd.S4.Abu Jir sag p0nd Structurally, The seismic section displays a typical form of strike-slip m0vement where it intersects the Abu Jir Fault z0ne.Measured the Abu Jir Fault z0ne's width based on the Dammam reflect0r, is 8 km.There are four faults.There are three main apparent dip faults with high angles, F1, F2 and F3.The three faults cross all the sequence, Cainozoic and Mesozoic.F4 is Listric normal fault crosses Mesozoic sequence.F1, F2 and F3 are n0rtheastern straight fault dips, inv0lving high angle fault fl0wer.It has tw0 n0rmal faults that high angle and diverge upward.F1 fl0wer c0mp0ses of tw0 sets of min0r faults, synthetic and antithetic, dipping toward each 0ther made up Negative fl0wer structure.F2 is straight fault steeply dipping which inv0lves high angle fault fl0wer.F2 The fl0wer is comprised of tw0 sets 0f min0r faults namely antithetic and synthetic, inclining t0wards one another made up negative fl0wer structure.F3 the fault fl0wer comprises a antithetic min0r faults dipping in the 0pp0site directi0n of the maj0r fault.The seismic secti0n reveals that strike-slip faults exhibit a spectrum of characteristics fl0wer structure.F4 a curving, concave-up fault plane which dip decreases with depth.Presence of these structures (F1, F2, F3 and F4) gives convincing proof that strike -slip m0vement has transpired al0ng the fault z0ne that was superimposed on the earlier normal fault.

Figure 5 . 5 .
Figure 5. Seismic section AR-18 F0rmati0n; A. reverse fault.B. normal fault.C. normal fault and uplift.D. hydrocarbon seepage in high fractures gypsum.5.2 Sahliyah outcropExact measurements of the Sahliyah outcrop were taken at (N 33° 43'23.2",E 042°42' 66.7").It is situated in the north-western part of the Heet outcrop.This outcrop is representing only the upper part 0f the Euphrates F0rmati0n.Within this area big ridge is evident stemming from tectonic processes (Plate 2).

Figure 6 .
Figure 6.Depressions form by various mechanisms; A. Negative flower structure, B. Relay-ramp basin, C. Releasing bend on strike-slip faults.

Figure 7 .
Figure 7.The drainage pattern within the study area and relationship to the Abu Jir fault zone.