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Article

Role of Faulting in Salt Deformation and Hydrocarbon Trapping in the Missan Oilfields, Southeastern Iraq

by
Hayder Yousif
1,2,
Xuri Huang
1,* and
Guanyu Zhang
1
1
School of Geoscience and Technology, Southwest Petroleum University, Chengdu 610599, China
2
Geology and Reservoirs Department, Missan Oilfields Operating Authority, Missan Oil Company, Missan 62001, Iraq
*
Author to whom correspondence should be addressed.
Geosciences 2025, 15(11), 439; https://doi.org/10.3390/geosciences15110439
Submission received: 25 September 2025 / Revised: 8 November 2025 / Accepted: 12 November 2025 / Published: 18 November 2025
(This article belongs to the Section Structural Geology and Tectonics)
Browse Figures
Versions Notes

Abstract

In the Missan oilfields, the linkage among basement faults, halokinesis, and hydrocarbon accumulation, and their control on structural-trap geometry and seal effectiveness, remains insufficiently constrained, especially the timing/drivers of salt piercing and its coupling with regional folding. To address this, we integrate 3D seismic, well, and surface data to quantify these interactions across adjacent fields. Results show a clear correspondence between surface topographic highs and subsurface salt-related deformation. Buzurgan exhibits limited fault reactivation with persistent folding until the Late Miocene, whereas Fauqi and Abu Ghirab record Pliocene reactivation and intense salt deformation that generate disharmonic syncline-over-anticline geometries. The listric–conjugate faults are structurally linked to deep-seated basement faults and display clear spatial alignment with their orientations, enhancing halokinesis and accommodating differential shortening. At the same time, hydrocarbon charge pathways are primarily governed by the intensity of deep-seated faulting and the effectiveness of salt sealing. Critically, the study integrates disparate geological processes—fault reactivation, salt tectonics, and hydrocarbon migration—into a single coherent, field-validated model for the region and provides a practical method to anticipate subsurface complexity. The results show that variations in fault intensity across three adjacent fields (Buzurgan, Fauqi, Abu Ghirab) correspond to distinct reservoir outcomes: minimal faulting in Buzurgan confines charge to deeper Mishrif reservoirs; moderate faulting in Fauqi permits entrapment in Mishrif and Kirkuk; and intense faulting in Abu Ghirab facilitates vertical leakage to shallow Kirkuk. Collectively, the work moves beyond isolated case descriptions to provide a unified, exploitable framework for predicting how basement-involved faulting and salt mobility jointly control deformation style and hydrocarbon distribution in foreland basins.

1. Introduction

Faulting plays a critical role in tectonic and hydrocarbon systems, influencing salt deformation and reservoir dynamics [1,2,3,4,5,6]. In many compressional settings, particularly within foreland basins like the Zagros Fold–Thrust Belt (ZFTB), the interplay between deep-seated basement faults and overlying evaporite sequences governs both the geometry of structural traps and the effectiveness of sealing formations. Numerous studies in southwestern Iran have explored this dynamic, revealing how salt bodies behave under regional stress regimes and how their deformation relates to tectonic shortening and sedimentary loading [7,8,9,10,11,12,13,14,15,16,17]. These investigations address critical questions, such as when and why salt penetrates overlying layers, and whether a direct relationship exists between salt deformation and regional folding.
Salt-related studies remain ongoing, considering the necessity of penetrating salt-bearing layers to access oil reserves and the availability of extensive seismic and drilling data. Western Iran and southeastern Iraq represent a region where faulting and salt tectonics have significantly influenced the formation of hydrocarbon reservoirs. Despite several studies on hydrocarbon accumulation and petrophysical properties in southeastern Iraq [18,19,20,21,22], the role of faulting in facilitating or impeding hydrocarbon migration in the Missan oilfields remains insufficiently addressed.
Salt deformation is fundamental to the tectonic evolution of sedimentary basins and exerts a critical influence on hydrocarbon distribution [23]. In provinces with thick evaporite accumulations, such as the ZFTB, salt-related structures—including diapirs, pillows, and welds—respond not only to regional stresses but also actively influence the localization, geometry, and kinematics of fault systems. Conversely, basement-involved and strike-slip faulting can trigger salt mobilization and welding, producing rotated, segmented, and prematurely terminated faults—a reciprocal interaction documented across the ZFTB [9,24]. Understanding these bidirectional fault–salt interactions in the Missan oilfields is therefore essential for optimizing exploration and production strategies in salt-influenced foreland settings. To that end, this study builds a geomechanical model of fault–salt interaction by integrating 3D seismic, well logs from >300 wells, and seismic-attribute analysis, with objectives to: (1) classify fault types and quantify their spatial relationships to salt bodies; (2) evaluate how structural reactivation modulates deformation intensity across the Missan fields; and (3) interpret the implications for hydrocarbon migration and entrapment.

1.1. Regional Tectonic Evolution of the Arabian Plate

The Arabian Plate underwent rifting from the Late Permian to the Early Triassic, leading to the formation of the Neo-Tethys Ocean [25,26,27]. This rifting phase was followed by the development of a passive margin and post-rift thermal subsidence during the Jurassic to Late Cretaceous [25]. Nonetheless, multiple lines of evidence indicate renewed Cretaceous extension along segments of the future ZFTB, expressed by syn-depositional normal faulting, horst–graben architecture, and local back-arc opening on the northeastern Arabian margin [28,29]. This tectonic evolution is instrumental in forming some of the Middle East’s most significant oil-generating source rocks and hydrocarbon-bearing reservoirs [30]. In the Late Cretaceous, convergence between the Arabian Plate and the Neo-Tethyan oceanic lithosphere began, initiating obduction and inversion along the northeastern margin of the Arabian Plate [31]. The Neo-Tethys then closed diachronously, with final suturing from the Late Oligocene to early–middle Miocene, bringing the Arabian plate into direct contact with the Eurasian plate [31]. Collision drove crustal shortening, regional uplift, and foreland development; in the Mesopotamian foreland, thick Miocene clastic–evaporite successions (Fatha) accumulated in restricted-marine to lagoon–sabkha settings [32], and earlier salt layers were then buried to depths exceeding 2000 m in the study area, with local well data indicating burial to ~2800 m. Figure 1 illustrates the Middle Miocene depositional setting and the position of the study area in southeastern Iraq, where the Zagros Foredeep Fault (ZFF) intersects the region.
The Buzurgan, Fauqi, and Abu Ghirab oilfields, collectively referred to as the Missan oilfields, are situated in southeastern Iraq, with parts of Fauqi and Abu Ghirab extending across the border into Iran (Figure 2). These fields lie within the Dezful Embayment [16,34,35], specifically in the foothills subzone along the margin of the Mesopotamian Zone.
Structurally, the region is more complex than the adjacent Mesopotamian Zone, which lacks prominent surface folding [36]. It is characterized by narrow, asymmetrical anticlines often detached along Middle Miocene evaporite layers. These evaporites not only localize fault detachment surfaces but also influence the geometry of folds. In many cases, core zones of major anticlines expose younger clastic deposits due to erosion or late uplift [36].

1.2. Salt Tectonics in the Fatha Formation

The Fatha Formation (previously referred to as the Lower Fars Formation) primarily comprises evaporite rocks, such as anhydrite, marl, and locally halite, deposited in extensive lagoons and embayments during repeated marine incursions [37]. Salt deformation increases toward the Zagros Fold–Thrust Belt and decreases southwestward into the foreland basin, with minimal deformation in distant fields such as Amara and Halfaya (Figure 2). Salt deformation is primarily driven by variations in overburden load and compressional forces [38,39,40] associated with the Arabian–Eurasian plates collision, producing progressively weaker deformation southwestward from the ZFTB.

1.3. Stratigraphy and Regional Significance of the Fatha Formation

The formation is subdivided into distinct units across different regions. In Iran, it comprises seven formal units, while in northern Iraq, it is classified into three units [41]. Five informal subdivisions were identified by early oil exploration geologists in southeastern Iraq, from top to bottom, these are: MB5, consisting of alternating beds of anhydrite and shale; MB4, composed of interlayered anhydrite, shale, and salt; MB3, a thick anhydrite unit interbedded with salt, shale, and occasional limestone; MB2, characterized by massive salt deposits; and MB1, primarily composed of anhydrite with thin interbeds of shale and shaly dolomite (see Table 1).
The Fatha Formation, a key unit of the Middle Miocene, has been extensively debated regarding its age. Studies have proposed ages ranging from Lower to Middle Miocene, a strictly Middle Miocene age [41], a Lower Miocene age [42], and a diachronous age [37]. The formation was originally described in Iran by Busk and Mayo in 1918 [41]. In Iranian literature, it is now formally referred to as the Gachsaran Formation [43]. The Fatha Formation extends across Syria, Iraq, and Iran [9] which underscores its stratigraphic and tectonic significance across the region. It plays a crucial role as a cap rock for many oil reservoirs in eastern Iraq and western Iran due to its composition of low-permeability evaporites such as anhydrite and halite, along with shale, which effectively inhibits hydrocarbon migration [44,45].

2. Materials and Methods

We conducted a series of analyses to investigate salt deformation and fault interactions in the Missan oilfields.
A 3D post-stack time-migrated seismic dataset covering ~113 km2 across the Missan oilfields in southeastern Iraq was employed (Figure 2). The dataset, provided by the Iraqi Oil Exploration Company (OEC), has a 2 ms vertical sampling interval, 25 × 25 m bin size, and a dominant frequency of 28–30 Hz, yielding moderate vertical resolution suitable for horizon and fault delineation. Seismic interpretation was conducted in Schlumberger Petrel, and detailed mapping of structural and stratigraphic elements was achieved.
Two NE-SW-trending seismic lines were chosen to cross the Abu Ghirab, Fauqi, and Buzurgan anticlines, allowing for a structural analysis of fold geometries. Additionally, seven parallel seismic cross-sections were taken along the southeastern limb of the Fauqi Fold to examine the spatial distribution and geometry of salt-related deformation in relation to underlying deep-seated faults.
A comparative analysis was conducted between the present-day surface topography and subsurface deformation patterns associated with salt structures. This assessment, utilizing satellite imagery and elevation profiles derived from Google Earth, provided corroborative evidence linking surface morphological expressions to underlying salt-related deformation and associated deep-rooted faults.
More than 300 wells were analyzed using sonic and gamma-ray logs, complemented by density and velocity logs where available. From this extensive dataset, five representative wells located in the southern dome of the Buzurgan field, reaching depths of approximately 3700 m, were selected for detailed lithological assessment. These wells facilitated the characterization of lithofacies variations within the Fatha Formation, specifically targeting interbedded salt, shale, and anhydrite intervals of the Mobile Group. The salt-bearing intervals within this group occur predominantly at depths ranging from approximately 2350 to 2800 m. Additionally, synthetic seismograms were constructed to accurately tie seismic reflections to well-log data, thereby improving the precision of horizon correlations.
To establish the broader structural context, a regional tectonic framework was constructed using seismic inline 1748, integrated with structural trends and geological data from adjacent oilfields. This integration aimed to link present-day subsurface geometries with the region’s tectonic evolution and to constrain the timing and mechanisms of salt mobilization and fault reactivation.
To support the identification of deep-rooted compressional structures, regional fault data were incorporated from both published seismological sources and the tectonic map of Iraq. This national map, developed using 2D seismic interpretation, highlights the presence of reverse and thrust faults that traverse the study area. These features were used to guide and constrain the structural interpretation of the 3D seismic volume. To further enhance the visualization of fault geometries and stratigraphic discontinuities—particularly within the Jaddala Formation—a variance attribute was applied using a trace-to-trace similarity algorithm. The resulting attribute volume was compared with depth-structure maps to verify fault continuity and increase confidence in the interpreted structural framework.

3. Results

3.1. Thickness Variations of the Mobile Group in the Missan Oilfields

The sonic log measures the travel time (Δt) of acoustic waves as they propagate through geological formations in boreholes, providing essential insights into lithological characteristics [46]. Reliable lithological differentiation of evaporitic sequences—even those comprising thin interbeds—can be achieved using a combination of sonic and gamma-ray logs. Laboratory measurements and borehole data confirm that sonic values for pure halite typically range between 67 and 69 µs/ft. In contrast, anhydrite exhibits lower sonic values due to its higher density and rigidity, which allow faster acoustic wave transmission. Shale, despite its comparable density, exhibits higher sonic readings due to its greater porosity and produces elevated gamma-ray responses resulting from its enriched radioactive mineral content. Figure 3 displays sonic and gamma-ray logs from five representative wells in the southern Buzurgan oilfield, illustrating clear differences in MB2 thickness, an interval composed entirely of salt.
Across the broader Missan region, the Mobile Group (MB2) displays distinct spatial patterns in thickness. In the Halfaya and Amara fields, south and southwest of the study area (Figure 2), MB2 is relatively uniform at ~20 m. By contrast, substantial variability occurs in the Buzurgan, Fauqi, and Abu Ghirab fields, where thicknesses range from only 4 m in the well BU-S 89D to 96 m in the well AG-S 40. Figure 4 presents a time-thickness (isochron) map of the Mobile Group (MB4–MB2), illustrating pronounced lateral heterogeneity across the study area. These thickness variations provide the basis for interpreting the structural controls that influence salt deformation.

3.2. Stratigraphic and Tectonic Interpretation

The interpreted seismic section crossing the Buzurgan and Fauqi anticlines (Figure 5) shows a transition from continuous, parallel reflectors in deeper intervals to discontinuous and chaotic reflectors in shallower levels. In the deeper section, reflectors are continuous and parallel, representing mechanically competent carbonate strata that are predominantly composed of limestone. Upward, seismic reflectors become increasingly discontinuous and chaotic, especially near the core of the Fauqi anticline.
Five primary reflectors (R1–R5) are identified: R1 is a shallow near-surface reflector closely following surface topography; R2 marks the base of the growth strata, above which thickness variations indicate syn-depositional accumulation during folding; R3 defines the top of MB4, characterized by a pronounced salt-related structural uplift; R4 delineates the base of the Mobile Group, equivalent to the top of MB1 within the Fatha Formation, indicating the lower boundary of salt influence; and R5 corresponds to a deep reflector marking the top of a rift-influenced interval, likely of Triassic age.
Following [40], we adopt a simplified tripartite scheme tailored to the Missan sector: the Incompetent Group (Late Miocene–Quaternary clastics), the Mobile Group (Middle Miocene Fatha evaporites), and the Competent Group (pre-Miocene carbonates). In practice, the available seismic profiles image only these three divisions; O’Brien’s deeper units—the Basement and the Lower Mobile Group (Ediacaran–Cambrian Hormuz Salt)—lie below the imaged interval and are not observed in this dataset. The reflector–unit relationships are: R1–R2 within the Incompetent Group (with R2 marking the base of growth strata), R3–R4 bounding the Mobile Group (Fatha evaporites), and R5 lying within the Competent Group and marking the top of the rift-influenced interval.

3.3. Structural, Faults, and Salt Deformation Interpretation

The NE–SW seismic section along inline 1748 (Figure 5) images the subsurface beneath the Buzurgan and Fauqi structures and reveals two prominent anticlines. Within the inter-anticline syncline of the Mobile Group, a salt pillow (bulge) develops, where the salt thickens but does not breach the overburden. In contrast, a discrete salt diapir pierces the cover along the left limb of the Fauqi fold. Three fault families are distinguished in the Missan oilfields based on geometry, stratigraphic extent, and relationship to salt flow: (i) steep, basement-involved deep-seated faults; (ii) bedding-parallel detachment faults developed within the evaporitic units of the Fatha Formation (Mobile Group); and (iii) listric growth faults that sole into the detachment and propagate upward into the overlying strata. To better clarify the structural framework, these three fault families are grouped and described in terms of their kinematic characteristics and petroleum significance (Table 2).
  • Deep-seated faults are expressed as steep to near-vertical structures indicative of basement-involved deformation and reverse (thrust) kinematics. In the Dezful Embayment, where Hormuz salt is absent, the basal décollement is interpreted within Lower Paleozoic shales [8] consistent with a basement origin for these thrusts. Their upper tip lines are sharp and represent the steep, near-surface segments of thrusts captured by the seismic section; in compressional settings, such shallow segments commonly steepen due to folding and fault propagation, whereas at depth, the same faults are expected to flatten onto a low-angle décollement that lies below or outside the imaged window. Termination depths vary—some fault tips terminate at the base of the Fatha base (Figure 5; Fauqi fold), where salt accommodated shortening, whereas others root deeper, likely within Triassic units (Figure 5; Buzurgan fold). Diapiric salt flow absorbed a significant fraction of orogenic stress and focused thrust nucleation and growth, thereby exerting a first-order control on fault development [9].
Some deep faults were activated by the collision between the Arabian and Eurasian plates, which resulted in the formation of the ZFF fault. This fault delineates the boundary between the folded and the Mesopotamian zones [36]. The spatial configuration of these deep-seated faults, as interpreted from seismic data, corresponds closely to the regional structural framework. This relationship is illustrated in Figure 6, where (a) presents a regional tectonic map of Iraq showing the main tectonic zones and fault systems, with the study area in southeastern Iraq highlighted for reference (modified after [47]), and (b) displays the time-structure map of the Jaddala Formation within the Missan oilfields, highlighting the alignment of deep-seated faults with the fault traces mapped at the regional scale. Notably, in the Buzurgan area, such deep-seated faults are absent from the map in (b) because they terminate at considerable depth, below the imaged interval.
The variance attribute is applied to the seismic volume to enhance fault visibility and validate the structural interpretation (Figure 7). This analysis reveals distinct lateral amplitude variations along the Jaddala Formation surface, enabling the delineation of the horizontal extent and distribution of faulting and fracturing. In the Abu Ghirab area, prominent zones of intense faulting are identified, characterized by abrupt amplitude terminations and elevated variance values, indicative of significant structural disruption. By contrast, the Fauqi area exhibits moderate fault development. In contrast, the Buzurgan area shows continuous amplitude patterns and low variance values, suggesting limited fault activity and a more structurally uniform setting.
2.
Detachment faults formed within the evaporitic layers of the Fatha Formation, where salt served as a mechanical detachment zone in compressional regimes [48]. Numerous studies have identified these faults and regarded the Fatha as the upper main detachment surface [49,50,51,52,53]. Though not clearly visible in seismic sections due to their bedding-parallel nature, they were inferred from thickness variations within the Fatha, especially in salt-rich members MB4, MB3, and MB2 (Figure 3 and Figure 5).
3.
Listric faults and low-relief salt structures dominate thin-evaporite regions [48]. Conjugate listric thrust faults are documented in compressional fold-and-thrust settings [54,55,56] where horizontal shortening promotes the development of oppositely dipping, curved fault planes above a décollement. These faults are typical of folded belts under stable vergence conditions [57], commonly flatten at depth due to horizontal movement above the décollement surface [58].

4. Discussion

4.1. Salt Distribution and Deformation in the Missan Oilfields

The occurrence of salt within structurally deformed zones exerts a pronounced influence on subsurface conditions by redistributing stress across mechanically weaker layers [59]. In the Missan region, the thick evaporitic successions of the Fatha Formation play a particularly critical role, as they govern both the style of deformation and the development of associated pressure anomalies. Consequently, salt not only represents a mechanically distinctive unit within the stratigraphic succession but also constitutes a key factor shaping the broader geomechanical framework of the study area.
Figure 3 and Figure 4 demonstrate that MB2 thickness varies significantly across the Missan oilfields. The greatest heterogeneity occurs in the Fauqi and Abu Ghirab fields, where proximity to deep faults enhanced salt deformation, whereas the Halfaya and Amara fields have relatively uniform thicknesses. The observed pinch-and-swell geometry reflects structural deformation driven by salt mobility. Consistently, the two-way travel time thickness of the MB4–MB2 interval ranges from ~200 to ~800 ms, with the highest values spatially coincident with mapped faults on the structural map (Figure 6), further supporting a fault-focused halokinetic control on thickness variations. This pronounced TWT contrast is diagnostic of diapir-related thickening near fault-proximal zones, indicating locally sufficient salt to initiate reactive diapirism.
Section 3.2 and Figure 5 show a transition from continuous, parallel reflectors in deeper carbonate strata to discontinuous and chaotic reflections near the anticline cores. This reflector geometry is consistent with the presence of evaporitic detachments that decoupled competent and incompetent units, generating disharmonic folding and localized thickening of growth strata during shortening.
In the Buzurgan field, salt deformation is limited because deep-seated faults were either not reactivated or experienced insufficient displacement to trigger salt swelling. The cover strata above the Mobile Group exhibit disharmonic folding, including local syncline-over-anticline geometries consistent with pinch-and-swell thickening of the underlying salt. Figure interpretations further show that shortening and folding are more pronounced in the upper two groups than in the deeper Competent Group, reflecting contrasts in compaction and lithological strength. The Competent Group, composed primarily of limestone, is more consolidated and mechanically robust than the overlying formations. Growth strata in Buzurgan are largely controlled by fold-related subsidence rather than direct faulting, with thicker packages along the eastern limb indicating asymmetric deformation during progressive shortening. By contrast, in the Fauqi and Abu Ghirab fields, listric faulting combined with salt swelling created additional accommodation space, directly controlling stratigraphic thickening and producing disharmonic geometries. The most diagnostic expression is the development of synclines overlying anticlines, which highlights the combined influence of listric faulting, halokinesis, and upper-stratigraphic deformation.
The variance attribute (Figure 7) highlights a strong spatial correspondence between high-variance anomalies and the fault traces interpreted from the time-structure map (Figure 6). This agreement supports the effectiveness of the variance attribute for fault detection and reinforces the reliability of the mapped fault geometries across the study area.
Study [60] summarized several studies of numerical models that demonstrated the relationship between faulting and salt deformation, showing how basement-rooted faults and salt structures interact. Additionally, Ref. [61] in the Kuqa fold-thrust belt and Ref. [62] in the Southern North Sea provided practical evidence from specific locations, highlighting the role of basement faulting in driving salt deformation. While these studies offer valuable insights from theoretical and real-world observations, our study confirms their findings, revealing how these structures interact in the Missan oilfields. This evidence underscores the importance of rifting and subsequent compression in driving salt deformation.
In the mechanically weak Mobile Group, listric faults developed under folding stresses associated with the Arabia–Eurasia collision. This deformation produced enhanced shortening along the basal décollement compared to the deeper Competent Group and was accompanied by uplift related to fault displacement and salt swelling. Conjugate listric faults formed during diapiric growth within the Fatha Formation and propagated upward into the Injana Formation and younger strata. Toward the northeast, faulting intensified and became more closely spaced, promoting greater deformation of the salt and leading to the formation of intersecting (conjugate) fault systems. This structural style aligns with analogue and numerical models [56], where horizontal shortening generates oppositely dipping fault pairs around vertical displacement zones such as rising diapirs. The distinctive curvature of these faults results from the interaction of two main forces: northeast-directed horizontal compression [63,64,65], accompanied by slight counterclockwise rotation, and vertical uplift from diapiric activity within the Fatha Formation. While they coincide spatially with deep-seated faults (Figure 5), their salt-controlled morphology warrants independent analysis. These faults do not appear at the surface, likely due to the presence of poorly consolidated clastic sediments and slow displacement rates along the fault planes. These conditions favored erosion and weathering, gradually obscuring and erasing surface fault expressions.

4.2. Salt Diapirism and Fault-Driven Deformation in the Buzurgan and Fauqi Fields

Salt diapirs are often positioned above inverted normal faults [66]. However, several studies conducted in Iran and Iraq [16,40,67] have not confirmed a direct correlation between salt deformation and deep-seated faults as the primary driving mechanism. These investigations, centered in areas closer to the collision zone, indicate that shortening and deformation are more pronounced in the upper stratigraphic layers than in the deeper ones, primarily due to contrasting rock competencies and the influence of salt movement. This dynamic has resulted in the displacement of salt diapirs or bulges away from the underlying deep faults. Consequently, some researchers have proposed that salt diapirism is largely governed by variations in overburden load or heterogeneities in overburden pressure, often originating from lateral variations in density or thickness [40,68]. Other suggested drivers include gravity-induced flow into structural lows [16], thermal gradients, buoyant forces, faulting [68], and tectonic pressurization of salt bodies [48]. Importantly, as emphasized by [69], salt deformation is not a one-mechanism phenomenon. Although salt is intrinsically buoyant and mobile, it can remain stable beneath thick overburden unless regional extension or shortening provides displacement loading. Such tectonic loading faults the overburden, generating zones of weakness that allow salt to mobilize. In this sense, faulting acts as a critical trigger, creating the structural conditions necessary for salt to respond to buoyant and gravitational forces.
The seismic data reveal the coexistence of salt pillows and salt diapirs, where pillows appear as low-relief uplifts adjacent to diapirs (Figure 5). Salt welds are also observed in places where migrating salt has evacuated, leaving direct contact between the overlying and underlying strata. These observed features indicate that pillows, diapirs, and welds represent different evolutionary stages of the same halokinetic system. Pillows likely formed under conditions of differential sedimentary loading or localized thinning of the overburden, and their spatial association with diapirs suggests that some later evolved into diapirs as regional compression and basement fault reactivation provided the additional displacement loading required for vertical piercing. Together, the occurrence of pillows, diapirs, and welds underscores the progressive nature of halokinesis in the Missan oilfields and its strong mechanical linkage with basement-involved faults.
Although some of the observed faults might superficially resemble outer-arc extension features, their geometry and position argue against this interpretation. Outer-arc extension faults typically develop along the crest of anticlines due to bending stresses; however, in the study area, these faults occur on the eastern limb of the Fauqi fold rather than its crest (Figure 5). Furthermore, the elevated surface topography above the faulted zone (Figure 8) indicates a strong association with salt swelling and mobilization, rather than flexural extension of folded strata. These observations suggest that the faults are more plausibly linked to salt-related uplift and localized reactivation than to outer-arc extension.
An integrated surface–subsurface profile (Figure 8) demonstrates a strong correspondence between surface morphology and subsurface deformation. Satellite imagery and the topographic profile [70] show localized highs that coincide with salt-related features in the seismic line, indicating structural control by salt mobility and basement-rooted faults rather than purely erosional or depositional effects. The seismic transect further reveals mechanical coupling between faults and salt, producing disharmonic folding in the overburden that is mirrored in surface relief. This independent surface–subsurface agreement supports the interpretation that salt–fault interactions exert first-order control on both subsurface architecture and surface geomorphology in the Missan oilfields. Practically, the correlation provides a cost-effective reconnaissance tool to anticipate salt-controlled structures, delineate migration pathways and traps, and improve pre-drilling risk assessment (e.g., abnormal pressures, salt-related hazards, and compartmentalization). Consequently, integrating topography with seismic data clarifies the structural framework and contributes to safer, more efficient exploration and field development in salt-influenced provinces.
The observed evolution of salt structures is consistent with the established stages of diapirism described by [60,69]. Initial broad pillows, observed in the study area as low-relief uplifts adjacent to diapirs (Figure 5), correspond to passive diapirism, driven by differential sedimentary loading. Subsequent intensification under regional compression reflects reactive diapirism, where regional shortening provided additional displacement loading. Finally, localized vertical piercing and strong upward propagation in stages (Figure 9(e–f)) are characteristic of the active phase, in which buoyancy and tectonic stresses jointly drove salt rise.
The timing of salt piercing through the overburden remains debated among researchers [40,71,72]. Diapirism in the present study area appears less intense than in the northeastern zones closer to the collisional margin. Therefore, the examined sections provide an optimal setting for investigating the onset of diapirism and offer valuable insight into the early stages of salt mobilization, particularly at the interface between the folded and Mesopotamian zones. Figure 9 presents a series of parallel inlines progressing southeastward, perpendicular to the fold axis on the western limb of the Fauqi anticline, illustrating the progressive development of diapirism and faulting through seven stages (a–g). The early stages show the initial piercement of the overburden by oblique listric faults formed under combined horizontal compression and vertical uplift from salt swelling. Faulting subsequently propagated upward, accompanied by conjugate fault patterns due to bidirectional salt movement. In later stages, deformation intensified within both the mobile and upper layers before gradually declining as deeper fault activity diminished. This evolutionary sequence—from passive pillows to active diapirism—defines a representative model for early halokinesis in transitional tectonic settings similar to the Missan oilfields.

4.3. Tectonic Evolution and Structural Development of the Buzurgan and Fauqi Anticlines

Building on [50]—who showed that pre-existing normal faults in rifted basins are commonly inverted to thrusts during fold-and-thrust belt development and that salt/shale horizons act as effective décollements decoupling structural levels—a kinematic model is proposed for the Buzurgan and Fauqi anticlines. The model, constrained by regional tectonic history and seismic evidence along inline 1748, synthesizes key observations (Figure 5 and Figure 9) within the established geodynamic framework. Figure 10 presents this conceptual kinematic evolution and the successive stages inferred from the data.
(a)
Rifting Phase: During the Triassic, regional extension associated with the opening of the Neo-Tethys Ocean initiated rifting, forming normal faults within the basement and overlying strata.
(b)
Post-Rift Passive Margin: Following rifting, horizontal strata accumulated in a passive margin setting from the Late Triassic through much of the Cenozoic, during which the Neo-Tethys Ocean remained open in the area, forming a prolonged passive margin.
(c)
Onset of shortening (Late Miocene): Convergence across the Arabia–Eurasia margin initiated folding and reverse reactivation of older normal faults; syn-kinematic growth strata developed adjacent to active structures.
(d)
Progressive folding and faulting (Pliocene–Quaternary): Shortening intensified; reverse faults propagated upward, piercing the Mobile Group (salt-bearing Fatha units), with continued syn-kinematic deposition.
(e)
Decoupling and structural disharmony: A primary, low-angle décollement formed within the Mobile Group, promoting mechanical decoupling between incompetent and competent packages and fostering the development of listric and conjugate fault systems.
(f)
Present-day 3D architecture: Significant shortening is concentrated within the Mobile and Incompetent Groups; a major detachment occurs along R4 with localized detachment along R2, explaining observed disharmonic folding and local syncline-over-anticline geometries.
Growth strata above R2 (Figure 5 and Figure 10f) display more pronounced folding and shortening than those below, reflecting their younger age, lower compaction, and greater susceptibility to deformation. In contrast, strata below R2 have been deformed over a longer timespan but are more lithified, showing reduced folding. Similarly, layers above R4 exhibit greater folding than those below, with R4 representing the principal décollement surface where total shortening reached approximately 3.5 km [73] and R2 acting as a secondary, localized décollement.
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Figure 10. Integrated seismic–tectonic kinematic model of the Buzurgan and Fauqi anticlines, derived from seismic interpretation (inline 1748) and the regional tectonic history from previous studies. The stages (a–f) illustrate the structural evolution from Triassic rifting to the present-day configuration, emphasizing fault reactivation, salt-related décollement, and progressive folding. The stages are as follows: (a) Rifting phase, (b) Post-rift passive margin, (c) Onset of shortening (Late Miocene), (d) Progressive folding and faulting (Pliocene-Quaternary), (e) Decoupling and structural disharmony, and (f) Present-day 3D architecture.
Figure 10. Integrated seismic–tectonic kinematic model of the Buzurgan and Fauqi anticlines, derived from seismic interpretation (inline 1748) and the regional tectonic history from previous studies. The stages (a–f) illustrate the structural evolution from Triassic rifting to the present-day configuration, emphasizing fault reactivation, salt-related décollement, and progressive folding. The stages are as follows: (a) Rifting phase, (b) Post-rift passive margin, (c) Onset of shortening (Late Miocene), (d) Progressive folding and faulting (Pliocene-Quaternary), (e) Decoupling and structural disharmony, and (f) Present-day 3D architecture.
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4.4. Structural Evolution of the Dezful Embayment

The Dezful Embayment contains numerous north–south and northeast–southwest trending structures, widely interpreted as expressions of reactivated deep-seated basement faults [8,74,75]. Within the study area, the northwest–southeast trending structures are interpreted to be more strongly controlled by basement architecture and the rheological layering of the cover than by Alpine compression alone [76]. Alpine deformation, acting on this inherited fabric, played a key role in localizing anticlines [36]. Seismic sections (Figure 5 and Figure 11) reveal a spatial coincidence between deep-seated faults and anticlinal culminations, growth strata above R2, and mechanical decoupling across the Fatha evaporites, collectively indicating basement fault reactivation, block uplift, and fault-related folding in the study area.

4.5. Deep-Seated Fault Dynamics

The ZFF delineates the frontal boundary of the ZFTB, separating it from the Mesopotamian Foredeep and Persian Gulf [33,77]. Seismic activity in the ZFTB is mainly concentrated along major arcuate basement faults termed “master blind thrusts,” of which the ZFF is considered one [78,79].
Many studies interpret the ZFF as a reverse (thrust) fault formed during the Arabian–Eurasian collision [80,81,82]. However, others argue—based on seismic evidence—that it originated as a normal fault during the Late Triassic opening of the Neo-Tethys Ocean, later reactivated in reverse during the Pliocene to the present [33,36,77,83,84]. Ref. [36] further suggested that Late Cretaceous extensional events influenced parts of the fault zone. This view is consistent with observations from the Buzurgan field, where Cretaceous formations (e.g., Mishrif Formation) are not affected by faulting. In contrast, in the Fauqi and Abu Ghirab fields, the ZFF clearly offsets Cretaceous units (Figure 5 and Figure 11). This contrast indicates either localized Cretaceous extension or spatial variability in fault reactivation. Seismic data indicate two distinct fault behaviors. Some faults terminate in deeper stratigraphic levels and appear inactive. In contrast, other faults extend upward into younger strata and are associated with reactivation, particularly within the Mobile Group.
Ref. [40] proposed that the ZFF in Iran, along with the Badra-Amarah Fault, Makhul Fault, Sinjar Fault (Iraq), and Abdul-Aziz Fault (Syria), constitutes a segmented fault system divided by transverse faults. These segments are collectively referred to as the ZFF, a naming convention adopted here, as the fault in this region is part of the Badra-Amarah system. However, the exact trace and lateral extent of the ZFF remain uncertain in several areas.
Folding geometry and growth-strata relationships provide further temporal constraints. In the Buzurgan field (Figure 5), deformation styles remained relatively consistent until the Late Miocene, when variations in growth-strata thickness began to appear. In contrast, the Fauqi and Abu Ghirab fields exhibit significant deformation in the overlying layers, attributable to fault reactivation coupled with salt mobilization. Collectively, these observations suggest that folding and reverse reactivation along the ZFF were most pronounced during the Pliocene, following the deposition of the Injana Formation in the Late Miocene.

4.6. Impact of Deep-Seated Faults on Hydrocarbon Migration and Reservoir Development

Faults played a crucial role in the migration and accumulation of hydrocarbons, particularly in regions with significant stratigraphic separation between source rocks and reservoir units. The effectiveness of fault-assisted migration depended on the magnitude of displacement activity, rate, and timing relative to hydrocarbon generation and expulsion [85,86]. In faulted basins, faults often serve as primary conduits for vertical migration. Their efficiency was influenced by activity intensity, fault geometry, and the formation of secondary structures such as fractures, which could enhance or impede fluid movement [87,88].
The Abu Ghirab, Fauqi, and Buzurgan oilfields in southeastern Iraq are adjacent fields, yet they exhibit distinct hydrocarbon distribution patterns due to variations in fault dynamics and sealing formations.
  • Abu Ghirab Oilfield
Hydrocarbon production was primarily sourced from the Kirkuk (Asmari) Formation, which was heavily influenced by active faulting. Significant structural deformation occurred, including the development of numerous secondary faults and fractures (Figure 11), establishing effective vertical migration pathways from deeper units into the Kirkuk reservoir. Therefore, the Mishrif Formation demonstrated limited productive capacity. The Fatha Formation served as a robust regional seal, preventing further vertical migration of hydrocarbons.
2.
Fauqi Oilfield
Hydrocarbons were extracted from both the Kirkuk and Mishrif Formations. Although fault activity was less intense than in Abu Ghirab, it remained sufficient to facilitate migration into both reservoirs. The observed hydrocarbon distribution reflected a balance between moderate fault activity and the sealing integrity of surrounding strata.
3.
Buzurgan Oilfield
Hydrocarbon production was concentrated in the Mishrif Formation, with limited vertical migration to the Kirkuk Formation. Faults in the Buzurgan field appeared less prominent. They were characterized by subdued expression in seismic profiles (Figure 5), with minimal vertical displacement and limited lateral continuity, thereby reducing their effectiveness as migration pathways. As a result, hydrocarbons remained confined to the deeper Mishrif reservoir.
In summary, variations in fault activity and associated deformation exerted a primary control on hydrocarbon migration across the three fields. In Abu Ghirab, intense faulting and pervasive fracturing created efficient vertical pathways, allowing hydrocarbons to bypass deeper reservoirs and accumulate in the Kirkuk Formation. Meanwhile, the Fatha Formation—comprising largely evaporites, including thick layers of salt—served as a robust regional seal. Although its salt-rich intervals were involved in deformation and interacted with faults, their inherently ductile and sealing nature prevented hydrocarbons from migrating into shallower stratigraphic levels. In Fauqi, moderate fault activity supported migration into both the Mishrif and Kirkuk reservoirs, reflecting a balance between fault-assisted connectivity and sealing capacity. In contrast, Faults in the Buzurgan field are subdued in seismic expression and largely inactive, which reduces their effectiveness as migration pathways and confines hydrocarbons largely to the Mishrif reservoir. Collectively, these differences highlight how fault dynamics, deformation timing, and the sealing capacity of the Fatha Formation jointly governed the spatial distribution of hydrocarbons in the study area.

4.7. Operational and Drilling Implications of Salt Deformation

The structural impact of salt has direct implications for drilling operations in the Missan area. Thick, deformed evaporitic intervals within the Fatha Formation redistribute stress within mechanically weaker layers—particularly shale—thereby elevating formation pressures. As shown in Table 1, the onset of salt in unit MB4 coincides with a sharp increase in the pressure coefficient—from approximately 1.04 in the overlying interval to ~2.2—which persists through MB2 owing to the continuity of salt layers. By contrast, MB1, where salt is absent, shows a rapid return to near-normal pressure conditions. These anomalies highlight the structural complexity induced by salt deformation and directly contribute to operational challenges, such as mud loss, stuck pipe, and cementing difficulties, particularly across intervals with abrupt pressure transitions.
From an operational standpoint, recognizing these structural controls is crucial for accurate pre-drilling hazard prediction and effective well design. In structurally complex zones, such as Abu Ghirab and Fauqi, where salt deformation is most pronounced, proactive design strategies and continuous pressure monitoring are essential. By contrast, the Buzurgan field generally exhibits lower-intensity salt deformation and a correspondingly lower pressure risk, although localized complications may still arise. Integrating the structural model into drilling engineering helps reduce errors in casing-setting depth selection, lowers the risk of shoe instability and unexpected kicks, and ultimately enhances both safety and efficiency.

5. Conclusions

The deep-seated faults in the Missan region record a complex history of early extensional and later compressional reactivation. Some faults terminate within Triassic–Jurassic strata, while others, belonging to the Badra–Amarah branch of the Zagros Foredeep Fault (ZFF), extend upward into the Mobile Group, indicating Pliocene reverse reactivation following Late Miocene deposition.
The structural evolution varies spatially among the Missan fields. In Buzurgan, limited fault reactivation produced relatively uniform folding, whereas in Fauqi and Abu Ghirab, listric faulting combined with salt swelling generated structural disharmony and syncline-over-anticline geometries. These variations reflect the degree of fault activity and salt mobility across the area.
Clusters of closely spaced faults promoted intense halokinesis, forming conjugate listric systems mechanically linked to basement faults. Regionally, this deformation corresponds to Alpine compressional stresses from the Arabia–Eurasia collision, which drove basement uplift and fault-related folding.
Fault activity exerted a first-order control on hydrocarbon migration and trapping. High fault connectivity in Abu Ghirab facilitated vertical leakage to shallow reservoirs, moderate activity in Fauqi allowed dual reservoir charging, and limited faulting in Buzurgan confined hydrocarbons to deeper layers. These relationships highlight fault reactivation and seal integrity as key controls on hydrocarbon distribution in the Missan oilfields.
Finally, the strong correspondence between surface morphology and subsurface structure confirms the mechanical coupling between salt mobility and faulting. This relationship reaffirms previous findings and provides a practical framework for predicting subsurface complexity and optimizing exploration strategies in salt-influenced foreland settings.

Author Contributions

Conceptualization, H.Y. and X.H.; methodology, H.Y.; software, H.Y.; validation, X.H. and G.Z.; formal analysis, H.Y.; investigation, H.Y.; resources, X.H.; data curation, H.Y.; writing—original draft preparation, H.Y.; writing—review and editing, X.H. and G.Z.; visualization, H.Y. and G.Z.; supervision, X.H.; project administration, X.H.; funding acquisition, X.H. All authors have read and agreed to the published version of the manuscript.

Funding

This work was partially supported by the National Natural Science Foundation of China (42241206, U24B2022).

Data Availability Statement

Restrictions apply to the availability of the seismic and well data used in this study. These data are owned by the Missan Oil Company and are available only upon official request and subject to company and government approval. As a result, the data cannot be made publicly accessible.

Acknowledgments

The authors would like to express their sincere gratitude to the Iraqi Ministry of Oil and Missan Oil Company for providing access to seismic and well-log data, which made this research possible. We also extend our appreciation to Southwest Petroleum University and Zhenhua Oil for their continuous support.

Conflicts of Interest

Author Hayder Yousif was employed by the Missan Oil Company. All other authors declare that they have no commercial or financial relationships that could be interpreted as a potential conflict of interest.

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Figure 1. Regional paleogeographic map illustrating the depositional setting of the Middle Miocene Fatha Formation across the Mesopotamian Basin. The pink-shaded area indicates lagoonal evaporitic deposition. Key structural features, including the Zagros Mountains and major depositional environments, are illustrated. The study area is marked with a blue box in southeastern Iraq, where the ZFF also passes through. The base map was modified from [32], with the location of the ZFF added in accordance with [33].
Figure 1. Regional paleogeographic map illustrating the depositional setting of the Middle Miocene Fatha Formation across the Mesopotamian Basin. The pink-shaded area indicates lagoonal evaporitic deposition. Key structural features, including the Zagros Mountains and major depositional environments, are illustrated. The study area is marked with a blue box in southeastern Iraq, where the ZFF also passes through. The base map was modified from [32], with the location of the ZFF added in accordance with [33].
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Figure 2. Time-structural map of the top MB1 horizon within the Fatha Formation, representing the base of the Mobile Group. The map illustrates the structural configuration and spatial distribution of the Missan oilfields, specifically Abu Ghirab, Buzurgan, and Fauqi, within the boundary of the interpreted 3D seismic survey. Color contours indicate structural depth in milliseconds (two-way travel time), with warmer colors corresponding to shallower intervals. Profiles A–A′ and B–B′, together with the labeled lines a–g, mark the locations of the seismic inline sections that are analyzed in later figures. The inset map shows the locations of the Missan oilfields in southern Iraq.
Figure 2. Time-structural map of the top MB1 horizon within the Fatha Formation, representing the base of the Mobile Group. The map illustrates the structural configuration and spatial distribution of the Missan oilfields, specifically Abu Ghirab, Buzurgan, and Fauqi, within the boundary of the interpreted 3D seismic survey. Color contours indicate structural depth in milliseconds (two-way travel time), with warmer colors corresponding to shallower intervals. Profiles A–A′ and B–B′, together with the labeled lines a–g, mark the locations of the seismic inline sections that are analyzed in later figures. The inset map shows the locations of the Missan oilfields in southern Iraq.
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Figure 3. Cross-section showing sonic and gamma-ray logs from five wells in the Buzurgan oilfield, illustrating significant variations in salt bed thickness, particularly in the MB2 unit.
Figure 3. Cross-section showing sonic and gamma-ray logs from five wells in the Buzurgan oilfield, illustrating significant variations in salt bed thickness, particularly in the MB2 unit.
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Figure 4. Isochron (time-thickness) map of the Mobile Group (MB4–MB2) across the Missan oilfields, illustrating spatial variations in interval thickness. Fault locations are shown for reference in Figure 6.
Figure 4. Isochron (time-thickness) map of the Mobile Group (MB4–MB2) across the Missan oilfields, illustrating spatial variations in interval thickness. Fault locations are shown for reference in Figure 6.
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Figure 5. Seismic section A-A′ across the South Buzurgan and Fauqi structures. The upper panel shows the uninterpreted post-stack time-migrated section (inline 1748), while the lower panel presents the interpreted version. Key structural features include deep-seated reverse faults, a salt bulge, a salt diapir, and listric faulting above the Mobile Group. Stratigraphic horizons and mechanical stratigraphy (Competent, Mobile, and Incompetent Groups) are also highlighted. The reflectors R1 to R5 represent key seismic horizons used for interpretation and analysis. The location of this seismic section is shown in Figure 2.
Figure 5. Seismic section A-A′ across the South Buzurgan and Fauqi structures. The upper panel shows the uninterpreted post-stack time-migrated section (inline 1748), while the lower panel presents the interpreted version. Key structural features include deep-seated reverse faults, a salt bulge, a salt diapir, and listric faulting above the Mobile Group. Stratigraphic horizons and mechanical stratigraphy (Competent, Mobile, and Incompetent Groups) are also highlighted. The reflectors R1 to R5 represent key seismic horizons used for interpretation and analysis. The location of this seismic section is shown in Figure 2.
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Figure 6. (a) Regional tectonic map of Iraq depicting the major tectonic zones and fault systems, with the study area in southeastern Iraq delineated for reference (modified after [47]) (b) Time-structure map of the Jaddala Formation within the Missan oilfields, highlighting the configuration of deep-seated faults that spatially correspond to the fault traces observed in the regional framework shown in (a).
Figure 6. (a) Regional tectonic map of Iraq depicting the major tectonic zones and fault systems, with the study area in southeastern Iraq delineated for reference (modified after [47]) (b) Time-structure map of the Jaddala Formation within the Missan oilfields, highlighting the configuration of deep-seated faults that spatially correspond to the fault traces observed in the regional framework shown in (a).
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Figure 7. Variance horizon slice of the Jaddala Formation illustrating (a) amplitude variability and (b) interpreted fault patterns (red lines) from seismic data, revealing a strong spatial correlation between variance anomalies and fault structures.
Figure 7. Variance horizon slice of the Jaddala Formation illustrating (a) amplitude variability and (b) interpreted fault patterns (red lines) from seismic data, revealing a strong spatial correlation between variance anomalies and fault structures.
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Figure 8. Integrated surface–subsurface profile along section A–A′ from west of the Buzurgan oilfield to the Fauqi oilfield. (a) Satellite imagery from Google Earth Pro (modified) showing the trace of the profile (red line) across the study area. (b) Topographic profile derived from Google Earth elevation data along the same trace, illustrating elevation changes with minimum, average, and maximum values indicated. (c) Corresponding seismic section oriented SW–NE, revealing subsurface structural configuration. The surface topography clearly corresponds with salt-related deformation, which is spatially linked to deep-seated fault systems.
Figure 8. Integrated surface–subsurface profile along section A–A′ from west of the Buzurgan oilfield to the Fauqi oilfield. (a) Satellite imagery from Google Earth Pro (modified) showing the trace of the profile (red line) across the study area. (b) Topographic profile derived from Google Earth elevation data along the same trace, illustrating elevation changes with minimum, average, and maximum values indicated. (c) Corresponding seismic section oriented SW–NE, revealing subsurface structural configuration. The surface topography clearly corresponds with salt-related deformation, which is spatially linked to deep-seated fault systems.
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Figure 9. (a) Non-interpreted and (b) interpreted parallel inline seismic sections trending southeast, perpendicular to the fold axis on the western limb of the Fauqi fold. The sequence from (a) to (g) illustrates the progressive deformation and diapir development of the Mobile Group, coinciding with the weakening of the overburden by deep-seated faults and driven by deep fault zone activity (location shown in Figure 2).
Figure 9. (a) Non-interpreted and (b) interpreted parallel inline seismic sections trending southeast, perpendicular to the fold axis on the western limb of the Fauqi fold. The sequence from (a) to (g) illustrates the progressive deformation and diapir development of the Mobile Group, coinciding with the weakening of the overburden by deep-seated faults and driven by deep fault zone activity (location shown in Figure 2).
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Figure 11. Inline seismic section B–B′ across the Abu Ghirab anticline (location in Figure 2), illustrating intense faulting and fracturing associated with salt deformation within the Mobile Group. The section displays features such as a salt diapir, salt weld, and salt pillow, along with deep-seated basement faults that significantly influenced the structural evolution and hydrocarbon migration in the field.
Figure 11. Inline seismic section B–B′ across the Abu Ghirab anticline (location in Figure 2), illustrating intense faulting and fracturing associated with salt deformation within the Mobile Group. The section displays features such as a salt diapir, salt weld, and salt pillow, along with deep-seated basement faults that significantly influenced the structural evolution and hydrocarbon migration in the field.
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Table 1. Stratigraphic column of the Buzurgan oilfield, including geologic age, formation tops, pressure coefficients, drilling risks, lithological descriptions, tectonic mega-sequences [25], and mechanical competency classification [40]. Pressure and lithological data are based on well data from the study area.
Table 1. Stratigraphic column of the Buzurgan oilfield, including geologic age, formation tops, pressure coefficients, drilling risks, lithological descriptions, tectonic mega-sequences [25], and mechanical competency classification [40]. Pressure and lithological data are based on well data from the study area.
AgeStrataTop Depth (TVDss) Pressure CoefficientDrilling RisksLithology DescriptionCompetencyTectonic
Mega Sequence (TMS)
QuaternaryBai Hassan-
Mukdadiya		--Bit ballingClay, Gravel, and SandIncompetent GroupZagros Orogeny (AP11)
TertiaryUpper Injana (Upper Fars)≈−600about 1.04Caving & bit ballingMainly Clay (upper), Mainly Shale interbedded with Sand (lower)
Middle MioceneFatha
(Lower Fars)		(Mb5)−2074.5Transition
zone		Natural flowAlternation of anhydrite, Shale
(Mb4)−2379.52.20~2.22Super pressure and gas cutAlternation of anhydrite, Shale, and SaltMobile Group
(Mb3)−2648.52.20~2.22Super pressure and gas cut Thick beds of anhydrite interbedded with salt and shale, with rare limestone
(Mb2)−2789.52.20~2.22Super pressure and gas cutMassive salt
(Mb1)−2793.5Transition
zone		LossAnhydrite with thin inercalation of shale and shaly dolomiteCompetent Group
Lower MioceneJeribe−Euphrate−2821.51.1LossMassive dolomite, locally limestone, and anhydritic interbedded with reddish brown shale
Upper Kirkuk−2876.51.1LossMainly dolomite interbedded with sandstone, limestone, and mudstoneClosure of
Neo-Tethys
(AP10)
Oligo- ceneMiddle−Lower Kirkuk−2990.51.1LossSandstone and shale
Paleocene- EoceneJaddala−3205.871.1LossArgillaceous Limestone, Marl, Shale, and Chert
Aaliji−3336.691.1Gas cut Limestone Active northeastmargine (Ophiolite obduction)
(Ap9)
CretaceousUpper CretaceousShiranish−3380.361.1Hole shrinkageArgillaceous Limestone
Hartha−3401.531.1Loss & Sloughing shale & gas cutChalky and argillaceous Limestone
Sadi−3471.811.1Gas cut & Sloughing shaleArgillaceous limestone and marl with thin shale
Tanuma−3609.71.1Sloughing shaleShale, limestone with marl
Khasib−3627.681.1Sloughing shale& Loss & Gas cutCompact limestone Post rift passive margine of the Neo-Tethys ocean opening
(AP8)
MishrifMA−3692.461.1LossCompact limestone
MB11−3793.41.1LossCompact limestone interbedded with thin packstone
Mb12−3802.81.1LossCompact limestone interbedded with thin packstone
MB21−3834.810.91LossMainly grainstone
MB22−3890.551.12 Limestone
MC11−3958.191.12 Limestone
MC12−3990.981.12 Limestone
MC2−4026.941.12 Limestone
TD−4117.8
Table 2. Classification of fault types in the Missan oilfields.
Table 2. Classification of fault types in the Missan oilfields.
Fault GroupCharacteristicsStratigraphic LevelKinematics/GeometryObserved Role
Deep-Seated Basement FaultsHigh-angle faults rooted in the basement; some extend upward into the mobile group, others terminate in Triassic–Jurassic strata.Basement to Triassic–Jurassic to Fatha Formation.Reactivated from normal to reverse during Pliocene compression.Controlled regional folding and provided vertical migration pathways.
Detachment (Décollement) FaultsLow-angle, regionally extensive detachments within the Mobile Group (salt/shale/anhydrite).Primarily along R4 (major) and locally along R2 (minor).Acted as mechanical decoupling surfaces, accommodating significant shortening; facilitated disharmonic folding above salt.Produced syncline-over-anticline geometries and localized listric/conjugate fault systems.
Listric FaultsInclined, curved geometries; often conjugate sets; flatten into décollement at depth.Propagate through the Mobile Group into overlying formations (Fatha–Injana).Developed under the combined influence of horizontal compression and salt uplift.Enhanced salt mobilization
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Yousif, H.; Huang, X.; Zhang, G. Role of Faulting in Salt Deformation and Hydrocarbon Trapping in the Missan Oilfields, Southeastern Iraq. Geosciences 2025, 15, 439. https://doi.org/10.3390/geosciences15110439

AMA Style

Yousif H, Huang X, Zhang G. Role of Faulting in Salt Deformation and Hydrocarbon Trapping in the Missan Oilfields, Southeastern Iraq. Geosciences. 2025; 15(11):439. https://doi.org/10.3390/geosciences15110439

Chicago/Turabian Style

Yousif, Hayder, Xuri Huang, and Guanyu Zhang. 2025. "Role of Faulting in Salt Deformation and Hydrocarbon Trapping in the Missan Oilfields, Southeastern Iraq" Geosciences 15, no. 11: 439. https://doi.org/10.3390/geosciences15110439

APA Style

Yousif, H., Huang, X., & Zhang, G. (2025). Role of Faulting in Salt Deformation and Hydrocarbon Trapping in the Missan Oilfields, Southeastern Iraq. Geosciences, 15(11), 439. https://doi.org/10.3390/geosciences15110439

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