Hormuz Salt Research Articles

Structural evolution of the Handun salt diapir, Zagros fold and thrust belt, southern Iran

The Fars region, in the Zagros fold and thrust belt, hosts a wide range of diapirs piercing over 10 km of stratigraphic sequence. Comprising Precambrian to Early-Cambrian Hormuz Salt, these diapirs exhibit a prolonged history of evolution. Outcrop evidence for understanding the diapir deformation history is mostly limited to the Cenozoic contractive phase, and the seismic data lacks the necessary quality for an exhaustive understanding of the deepest structure's geometries. Through regional and field evidence we unravel the Handun salt structure evolution and propose a sequential restoration to describe the key deformational events. Our study presents a field-based novel regional balanced cross-section and a 3D-geological model, and addresses the role of structural inheritances and the position of the Handun diapir with respect to the decupled basement. The performed field studies describe folds and unconformities related to Cenozoic halokinetic sequences with exceptional clarity. It was possible to observe changes of the diapir activity along the structure and provide field evidence for the relative timing and kinematics of primary and secondary welding. Finally, our data suggest that the Handun diapir formed in the early Paleozoic above the shoulder of a basement extensional fault, and was partially translated above its southern hanging-wall during the shortening. In the Paleocene a sustained ratio of salt rise rate was enhanced by the Zagros/Oman contraction. In response to the Oligocene continental collision, the diapir was profusely supplied with salt, which flared upward to form overhangs. Since the middle Miocene the salt supply slowly depleted, with the diapiric walls remaining near the surface but tapering upward, probably due to primary welding or increased sedimentation. Secondary welding occurred post-Pliocene in the last stages of the diapir evolution with consequent development of a secondary minibasin.

Tectono-sedimentary evolution of prolific Permo-Triassic petroleum reservoirs offshore Iran: Insights from seismic stratigraphy

The foreland basin extending through the Persian Gulf is one of the world's most prolific petroleum resource-bearing regions. The structural evolution of parts of that basin has been strongly influenced by Late Proterozoic/Early Cambrian Hormuz Salt formation movements, which have also controlled the distribution of petroleum resource accumulations. Fields SP and BL are characterized to distinguish the tectono-sedimentary evolution of the central and eastern parts of the basin, respectively. Field-SP is located within the Qatar Arch in the central part of the basin, whereas Field-BL is situated in the southeastern part of the basin and is tectonically influenced by the Hormuz Salt movements. 3D seismic data and information from two exploration wells are assessed in detail to define and compare the deformation history of the Permo-Triassic succession in these two fields. The Dalan (Upper Permian) and Kangan (Lower Triassic) formations and their equivalent Khuff Formation to the west host more than thirty-three known gas and gas-condensate fields within the basin that have evolved structurally in this tectono-sedimentary setting. This study integrates 3D seismic, well log, core, and thin section analysis from two wellbores drilled in the two studied fields. It applies seismic stratigraphic methods and principles to distinguish the architecture of relevant depositional tracts and interfaces and determine how they have evolved through geologic time. The results reveal that the different thicknesses of the Hormuz Salt (Cambrian) underlying the two studied fields, and the salt tectonic activity it has driven, are ultimately responsible for the distinctive structural evolutions and Permo-Triassic reservoir qualities observed in those fields. The significance of this finding is that by applying the developed seismic stratigraphy techniques integrated with existing well data on a regional basis offers the opportunity to identify undrilled exploration targets with an improved chance of containing high-quality Dalan/Kangan reservoir sections.

The Palaeozoic of a future high potential hydrocarbon fold-thrust belt through the Zagros Basin, Iran

The Zagros Fold-and-Thrust Belt is one of the world's richest hydrocarbon regions, with Palaeozoic sediments being a key element in hydrocarbon plays. The main aim of this research is to provide a model for the formation and development of the sedimentary basin during the Palaeozoic Era in the Zagros and Persian Gulf regions. We utilize data from exploratory wells and surface outcrops of Palaeozoic sediments specifically in the northern parts of Iran's Zagros Mountains. The seismic profiles of the eastern region of the Persian Gulf provide more detailed information due to their distance from the Zagros hinterland. The investigation reveals that folds with wavelengths of several tens of km were formed on the Infra-Cambrian Hormuz Salt or its equivalent décollement.This study has identified halokinetic activities as the primary cause of Palaeozoic deformations in the Zagros region, with tectonic and orogenic factors playing a secondary role. The Palaeozoic sediments are divided into pre-kinematic, syn-kinematic and post-kinematic categories. Sedimentary sequences possibly including the Palaeozoic hydrocarbon source rock could be present throughout the study area.

Uncovering a Seismogenic Fault in Southern Iran through Co-Seismic Deformation of the Mw 6.1 Doublet Earthquake of 14 November 2021

On 14 November 2021, a doublet earthquake, each event of which had an Mw of 6.1, struck near Fin in the Simply Folded Belt (SFB) in southern Iran. The first quake occurred at 12:07:04 UTC, followed by a second one just a minute and a half later. The SFB is known for its blind thrust faults, typically not associated with surface ruptures. These earthquakes are usually linked to the middle and lower layers of the sedimentary cover. Identifying the faults that trigger earthquakes in the region remains a significant challenge and is subject to high uncertainty. This study aims to identify and determine the fault(s) that may have caused the doublet earthquake. To achieve this goal, we utilized the DInSAR method using Sentinel-1 to detect deformation, followed by finite-fault inversion and magnetic interpretation to determine the location, geometry, and slip distribution of the fault(s). Bayesian probabilistic joint inversion was used to model the earthquake sources and derive the geometric parameters of potential fault planes. The study presents two potential fault solutions—one dipping to the north and the other to the south. Both solutions showed no significant difference in strike and fault location, suggesting a single fault. Based on the results of the seismic inversion, it appears that a north-dipping fault with a strike, dip, and rake of 257°, 74°, and 77°, respectively, is more consistent with the geological setting of the area. The fault plane has a width of roughly 3.6 km, a length of 13.4 km, and a depth of 5.6 km. Our results revealed maximum displacements along the radar line of sight reaching values of up to −360 mm in the ascending orbit, indicating an unknown fault with horizontal displacements at the surface ranging from −144 to 170 mm and maximum vertical displacements between −204 and 415 mm. Aeromagnetic data for Iran were utilized with an average flight-line spacing of 7.5 km. The middle of the data observation period was considered to apply the RTP filter, and the DRTP method was used. We calculated the gradient of the residual anomaly in the N-S direction due to the direction of the existing faults and folds. The gradient map identified the fault and potential extension of the observed anomalies related to a fault with an ENE-WSW strike, which could extend to the ~ E-W. We suggest that earthquakes occur in the sedimentary cover of the SFB where subsurface faulting is involved, with Hormuz salt acting as an important barrier to rupture. The multidisciplinary approach used in this study, including InSAR and magnetic data, underscores the importance of accurate fault characterization. These findings provide valuable insights into the seismic hazard of the area.

Salt tectonics along the High Zagros Fault in Iran, faulting through welded salt walls

In salt-bearing foreland fold-thrust belts, precursor salt structures affect deformation and accommodate fault zones during orogenic shortening. The complex structure and the halokinetic history of these belts, including the spatiotemporal relationship between diapirism and thrust faulting, have yet to be fully understood. The well-exposed Ediacaran–Early Cambrian Hormuz salt diapirs and the Cambrian–Pliocene overburden stratigraphic sequences along the High Zagros Fault (HZF) in Iran are interesting examples in this regard. The detailed field investigation of the diapirs, the halokinetic deformations, and the thickness variations of the sedimentary units toward the flanks of eight salt structures along the fault show that the first movement of the Hormuz salt could be as old as the Middle Cambrian, occurring long before the initiation of regional folding in the early Miocene. This marks the first field-based and the oldest proposed time for the onset of Hormuz salt diapirism in the Zagros fold-thrust belt. Our field and remote-sensing mapping show the presence of precursor linear salt structures like salt walls. The Hormuz salt diapirs likely began to rise as elongated salt walls above extensional basement faults coeval with the Neo-Tethyan rifting in Early Mesozoic. The squeezing of the salt walls during Zagros shortening from Miocene resulted in the partial accommodation of the HZF as thrust welds. This spatiotemporal evolution, showing the interplay between salt diapirism and late thrusting, can be considered as an analog for other fold-and-thrust belts with pre-orogenic diapiric systems.

High‐Resolution Local Earthquake Tomography Beneath the Zagros Simply Folded Belt (SFB): Implications for an Inhomogeneous Low‐Velocity Layer and Diapirism in the Upper Crust

AbstractHormuz salt formation is considered the origin of the evaporated salt deposits in the Zagros and its ductile behavior has been known as the reason for the inhomogeneous deformation in the Zagros. However, our knowledge about this formation has been limited to the salt domes on the surface. In our study, local earthquakes recorded by a temporary dense seismological network of 17 stations, deployed in the southern margin of the Zagros Simply Folded Belt (SFB) in southwestern Iran, have been used for seismic imaging. The high‐resolution earthquake local tomography revealed the first geophysical evidence about the Hormuz salt layer and its extension at depth. There is an uneven layer located at a depth of 8–12 km as the origin of extruded salt in this region through a shear fault zone and the production of the Dashti Salt Dome at the Kuh‐e‐Namak Mountain. Based on the obtained results, this layer is characterized by low seismic velocity volumes with significant Vp/Vs ratio variations. The seismic image is also consistent with a major NW‐trending NE‐dipping reverse fault, probably responsible for the 9 April 2013 Kaki earthquake. At depth of around 4 km, smaller scale high velocity anomalies, characterized by a high Vp/Vs ratio, may be related to the fluid saturated sediments in the uppermost sedimentary layer.

Tilt angle filter effect on noise cancelation and structural edges detection in hydrocarbon sources in a gravitational potential field

Noise cancelation is the process done to remove out-of-range anomalies and make better edge boundaries interpretation. One of the most challenging issues in describing gravitational maps is separating the anomalies related to shallow sources from the deep ones. Furthermore, Existing noise can make it arduous to separate shallow blurred boundaries. In this study in SE Iran, gravitational surveying was carried out in shallow areas from the west of Qeshm to the Hormuz islands in a regular network with a distance of one kilometer. The range of gravitational Bouguer was -297 to -330 mGal. Modeling and determining geometrical parameters revealed five negative anomalies from salt penetration. The residual gravity was computed by deducting gravitational effects related to deep sources from measured gravitational data. Correspondingly, estimating the boundary and edge of the subsurface masses will be better than local filters, and anomalies will be highlighted with more intensity. Furthermore, three major fault systems in the Zagros basin were determined as the primary origin of activity and expansion of Hormuz salt. Sensitivity analysis was employed utilizing analytical signals and maps of tilt angle filtering, which both revealed the same satisfying results of -297 to -330 mGal. In this article, the effect of the tilt angle local phase filter on a synthetic model was accomplished through numerical coding. As a result, Total Horizontal Derivative (THDR) provides location of salt intrusion in Qeshm area; whereas the best image of salt intrusion, in terms of feature edge illumination, presented by Analytical signal of residual gravity map.

Geology, geomorphology and geochronology of the coseismic? Emad Deh rock avalanche associated with a growing anticline and a rising salt diapir, Zagros Mountains, Iran

This work documents for the first time the prehistoric, but morphologically pristine, Emad Deh rock avalanche of the Zagros Mountains. The ca. 420 Mm3 rock avalanche was initiated as a rockslide on a dip slope affecting a weak unit of marls with interbedded limestones overlain by a thick and competent limestone formation. The slope is located on the northern limb of the growing Gavbast Anticline and at the edge of the inflating Gavbast Dome, related to a buried salt diapir of Hormuz salt. The unconfined rock avalanche deposits, covering 32 km2, were accumulated on coalescing alluvial fans and a floodplain environment. The depositional lobe shows sectors with distinctive morphological features attributable to the variable flow-depositional behavior of the debris stream, controlled by the nature of the substrate: (1) proximal continuous breccia flanked by levees; (2) intermediate depression; and (3) flat-topped polygonal hills and conical hills. A morphometric and spatial distribution analysis has been performed with the 550 conical hills (hummocks) mapped in the distal sector. The rock avalanche, with 914 m of maximal height drop (H) and 9280 m of runout (L), displays an extraordinarily high mobility (H/L index of 0.09), that can be attributed to the combined effect of dynamic rock fragmentation and basal lubrication by the soft substrate in the floodplain. Relief rejuvenation and slope over-steepening related to the growth of the anticline and the inflation of the Gavbast Dome are considered the main long-term preparatory factors that shifted the slope to a state of marginal stability. The slope failure was likely triggered by a large M ≥ 6.5–7 earthquake at ca. 5.4 ka, as indicated by OSL ages obtained from folded alluvium situated just beneath the rock avalanche deposit. The source of the earthquake was probably a blind reverse fault situated beneath the asymmetric Gavbast Anticline, as support the structural and geomorphic features of the fold. The identification and dating of large coseismic landslides in the Zagros Mountains, where large earthquakes are rarely accompanied by primary surface ruptures, could help to improve both landslide and seismic hazard assessments.

Structural Geology Study of Tuba Oilfield, Southern Iraq

Tuba oilfield is one of the Iraqi oilfields located in southern Iraq within the Mesopotamian Plain. The main purpose of this study is to carry out a structural geology analysis of the Tuba oilfield. The structural analysis included geometric and genetic analyses of the study area. According to geometric and genetic analysis results, some formations folds are classified as Thickened folds and others as Supratenuous folds. Two folding mechanisms (bending and buckle) are characterized as responsible for folding the Tuba structure. The bending mechanism forms a Supratenuous fold, perhaps due to the vertical force of salt structure and/or basement faults, while the buckle produces Thickened fold because of the horizontal force of the collision between the Arabian Plate and Eurasian Plate. The correlation sections and contour maps show that the structural development of the Tuba oilfield may be less than adjacent oilfields (Zubair and Rumaila oilfields). The fold axis of the Tuba oilfield is NW-SE, and this is perhaps attributed to the anticlockwise motion of the Arabian Plate. The results of geometric and genetic analyses may be revealed that the Tuba oilfield was formed by tectonic activities (Hormuz salt, basement faults, and collision between Arabian and Eurasian Plates) with intensity less than surrounding oilfields.

Characterization of Structural Geology of Faihaa Oilfield, Southern Iraq

Faihaa Oilfield is a new exploration Iraqi Oilfield located in southern Iraq and within Mesopotamian Plain, including the Block 9 exploration area, along the Iraqi-Iranian border. The study area included Faihaa Oilfield (in Iraq) and Yadavaran Oilfield (in Iran). They belong to one anticline (Dome) structure separated by the Iraqi-Iranian border, without a geological boundary between the fields. The current study aims to achieve structural geology analysis to the study area (Faihaa/Yadavaran structure). The structural analysis included geometric and genetic analyses of the study area. According to geometric and genetic analyses results, the Faihaa/Yadavaran structure is classified as an anticline, gentle, upright, non-plunge, and asymmetrical. According to thickness variation, there are two types of formations’ folds are recognized, Thickened and Supratenuous fold generated by two folding mechanisms bending and buckle mechanisms. Bending form Supratenuous fold, perhaps due to the vertical uplift of salt structure and/or basement faults, while buckle produces Thickened fold because of the parallel tectonic movement causes collision between Arabian Plate and Eurasian Plate. Consequently, a special strain pattern was formed and the reservoir quality in the crest of Mishrif and Yamama Formations was the best. The fold axis of the Faihaa/Yadavaran structure has a Boomerang shape, whereas it is almost straight from south to the center of the structure, then tends to the NW with different deviations over the study area formations. This direction may be due to the anticlockwise rotation of the Arabian Plate motion. The results of geometric and genetic analyses revealed that may be Faihaa/Yadavaran structure is one structural trap formed by tectonic activities; Hormuz salt structures, reactivated Basement faults, and Collision between Arabian and Eurasian Plates. The intensity of the tectonic activities of the study area maybe be less than surrounding Oilfields, therefore, the Faihaa Oilfield formation's depth was deeper than adjacent Oilfields.

Uncertainties of balanced sections and the role of basement in the southern Fars area, Iran

The frontal Zagros fold belt in the Fars area of Iran is generally considered to be detached on the Hormuz salt. Shortening rates and the proportion of thick-skinned deformation are debated and published balanced sections show large differences in style and amount of deformation. We believe that the main uncertainties are related to stratigraphic thickness variations, the degree of thick-skinned deformation and/or the flexural response of the crust. We analysed the stratigraphic thickness ranges interpreted from seismic data and conclude that the interpretational uncertainties, combined with the uncalibrated interval velocities of the largely undrilled Paleozoic strata, yield a wide range of outcomes for the total Phanerozoic thickness (9.5–16.5 km). With an area balancing approach, we show that geological surface cross sections could be matched by various structural subsurface scenarios, including pure thin-skinned deformation with flexure and/or thick-skinned deformation. Given the input uncertainties, we discuss the merits and shortcomings of our balanced sections and propose a geological model including a subtle control on the deformation style by the inherited pre-salt basin morphology. Given the uncertainties, we conclude that the contribution of thick-skinned deformation to the structural evolution remains indefinite and published shortening values may be much more unconstrained than typically specified.

Hormuz salt distribution in the United Arab Emirates: Implications for the location of hydrocarbon fields

Hydrocarbon fields in the United Arab Emirates (UAE) are related with Neoproterozoic basement highs and/or Ediacaran–Early Cambrian Hormuz salt domes. However, neither the basement nor Hormuz salt are penetrated or imaged by available well and seismic data due to thick Phanerozoic sediments. In this study, we have used the residual gravity anomaly of the sedimentary layer throughout the UAE by subtracting the gravity response of the basement structure from the isostatic residual gravity anomaly. The structure and distribution of the low-density Hormuz salt were then delineated for the first time by applying a 3D constrained layer inversion method on the residual gravity anomaly of the sedimentary layer. Well data were used to constrain this inversion from which the density of the reference model and the isosurface of the Hormuz salt were defined, whilst seismic profiles were used to qualitatively check the location, shape and depth of the domal structures. The inversion model shows that the Hormuz salt is more widespread in offshore than in onshore UAE and generally occurs within NE-SW to N–S trending basins. The inverted Hormuz salt model has a thickness that ranges from 1000 to 4000 m, with an average thickness of 2100 m. Moreover, the model suggests that the Hormuz, Ara (central Oman) and East Rub’ Al Khali (Saudi Arabia) salt basins are most likely connected, except in regions of structural basement highs. In addition, the model reveals a low density (≤2290 kg/m3) shallow layer (0–6000 m below the sea level) in the foreland basin, which corresponds to the Aruma and Pabdeh sequences that infill the foreland basin. Many of the offshore hydrocarbon fields in the UAE such as Zakum, Umm Shaif and Sarb are associated with Hormuz salt domes. Also, several hydrocarbon fields adjoin basement highs, which are possibly related to the flexural bulge caused by the emplacement of the Semail ophiolite on the Arabian continental margin. The basement highs are probably bordered by faults, which could have initiated halokinesis of the Hormuz salt. Thus, the 3D inverted model provides a detailed distribution of Hormuz salt bodies, which allows an improved understanding of Palaeozoic hydrocarbon plays in the UAE.

Impact of salt layers interaction on the salt flow kinematics and diapirism in the Eastern Persian Gulf, Iran: Constraints from seismic interpretation, sequential restoration, and physical modelling

Interpretation of reflection seismic profiles, sequential restoration, and physical modelling are presented to understand the kinematics of salt flow and diapirism in the Eastern Persian Gulf, offshore Southern Iran. Salt tectonics in this area result from the overlapping Ediacaran–Early Cambrian Hormuz Salt, which is regionally present, and Oligocene–Early Miocene Fars Salt, which is locally developed. The Hormuz and Fars salts began flowing at Cambrian(?) and Early Miocene times, respectively. Diapirs fed by the Hormuz Salt rose passively during Palaeozoic and Mesozoic times and were rejuvenated by contractional deformation events in the Cenozoic. Fars-Salt structures exist either as salt walls and anticlines around those diapirs of Hormuz Salt that developed allochthonous salt bodies during a Palaeocene–Eocene contractional squeezing before deposition of the Fars Salt, or as gentle shallow salt pillows above deep pillows of Hormuz Salt, suggesting a kinematic linkage. Flow of Fars Salt was mainly triggered by differential sedimentary loading. It seems that its lateral flow kinematics was controlled by the behaviour of the underlying Hormuz-Salt sheets. More than ~10-km-long salt sheets were efficiently evacuated back towards the Hormuz-Salt diapir, and consequently, maintained the Fars-Salt evacuation and flow to the same direction, accompanied by welding of both salt layers. Conversely, smaller, less than ~3-km-long salt sheets allowed limited salt evacuation or rearrangement that was probably still sufficient to trigger Fars-Salt flow near the central (Hormuz-Salt) diapir. Fars-Salt evacuation was enhanced by differential sedimentary loading, resulting in incipient primary welds. Subsequently, the depocentres migrated towards the areas of available Fars Salt away from the central diapir. In both cases, layer-parallel shortening related to regional contraction probably played also a role in triggering the Fars-Salt flow at Early Miocene, but was more influential at later stages by squeezing the salt structures (Hormuz and Fars) since about Late Miocene onwards.

Determining Infracambrian Hormuz Salt and Basement Structures Offshore Abu Dhabi by Joint Analysis of Gravity and Magnetic Anomalies

SummaryHydrocarbon fields that are located offshore Abu Dhabi, United Arab Emirates (UAE), are known to be associated with undulating thick sedimentary sequences. These undulations are mostly influenced by variations in the depth of Infracambrian Hormuz salts that generate negative gravity anomalies. Nonetheless, a few known oil fields are uncorrelated with the airborne gravity observations. This is attributed to the interference from large positive gravity anomalies from basement highs. To filter out the effect of basement, we calculate the pseudogravity effect of the airborne magnetic anomalies and subtract it from the gravity anomalies. The resultant gravity anomalies mainly represent the effect of the salt domes. The results uncover deep salt structures and introduce potential traps for hydrocarbons that have proved difficult to map accurately with current seismic techniques. A nonlinear 3D inversion modeling of corrected magnetic and decreased gravity data is also used to determine the depth to basement and the Infracambrian Hormuz salts over two regions. Our findings demonstrate that the depth to basement in these regions changes from 7100 to 9700 m, and the depth to Infracambrian Hormuz salt changes from 5800 to 9400 m, with a variable thickness with a maximum of 2700 m.

High resolution upper crustal velocity structure beneath Qeshm Island (SE Zagros) from surface wave, first arrival, and interevent interferometry tomography methods

The Qeshm earthquake with magnitude Mw 6.0 occurred on November 27, 2005, on a southern island in Iran and was followed by many aftershocks. We analyzed the aftershock waveforms and the first arrival traveltimes to calculate the 3D velocity model. The tomographic procedure was conducted in three different depth ranges from the subsurface to a depth of 17 km beneath Qeshm Island. The subsurface was probed by the Rayleigh wave tomographic method. The waveforms were filtered in the period range of 0.6 to 6 s, the dispersion curves were calculated for the selected signals, and a 2D tomography procedure was then performed. The resulting group dispersion measurement maps were inverted to obtain the shear wave velocity model to a depth of 5 km. However, the first arrival traveltimes were applied to obtain the VP and VP/VS models using the SIMULPS program in the depth range of 5 to 14 km, while depths ranging from 14 to 17 km were considered by the event interferometric approach. All appropriate interevent empirical Green's functions (EGFs) were extracted in the 4 different slices/depths, and the Rayleigh wave tomography processing was then repeated for these layers at the period of 1.2 s. Our results demonstrate that analysis of the interevent EGFs can yield useful information from depths for which a velocity model cannot be obtained via classic techniques. In addition to the Qeshm Fault, which appears as a stretched low-velocity anomaly, the Hormuz salt and evaporites may be other sources with low velocity. Although finding a direct relation between faulting and folding and/or any other mechanism of folding is difficult on Qeshm Island, the role of the Hormuz salt in generating them is undeniable. The rise of the Hormuz salt and evaporites, which appear as a low-velocity (weak) zone, can directly affect crustal layering (lower sedimentary cover and basement), fault dip and anticline formation and deformation at depths to 14 km. According to the effect of these tectonic features, folding and secondary faults, the soft sedimentary thickness varies between 2 and 3 km.

Morphology of the basement and Hormuz salt distribution in offshore Abu Dhabi from constrained 3-D inversion of gravity and magnetic data

Many seismic surveys and exploration wells have been conducted in offshore Abu Dhabi, United Arab Emirates. However, the Neoproterozoic basement and the Infracambrian Hormuz salts were not imaged or penetrated by seismic and well data. To delineate the morphology of the basement and distribution of salt bodies, we applied a 3-D constrained inversion method to aerogravity and aeromagnetic data covering offshore Abu Dhabi. Well and seismic data were used to constrain and validate the inversion results. The magnetic inversion model resulted in a robust basement model that varies in depth from 8 to 10 km with two highs at 8 and 8.5 km highlighting possibly magmatic bodies. In contrast, the gravity inversion model does not delineate very well the basement morphology, possibly due to the lower density salt bodies masking the gravity response of the higher density basement. By calculating and removing the gravity response of the magnetic basement model from the observed gravity data, we recovered the residual gravity response of the Hormuz salts. The 3-D gravity inversion of the residual shows that the Hormuz salts are more wide-spread and thicker than previously thought with a depth to top of salt varying from 5.5 to 8.5 km. This salt model suggests that the giant oilfields in offshore Abu Dhabi, such as Umm Shaif, Nasr, Abu Al-Bukhoosh, Zakum, Sarb and Hail, occur exactly above crests of salt pillows. In addition, a series of smaller oilfields are found located at the margin of the northern basement high, and three structural lineament trends (NE-SW, NW-SE, and N-S) were identified from the inverted basement and salt models. Reactivation of these fault trends and associated diapiric salt uplifts, as observed in the seismic sections and curvature map, played a major role in shaping the basement morphology and mobilization of the Hormuz salts.

Investigating Role of the Hormuz Salt Bodies in Initiation and Evolution of the Strike Slip Faults in the Fars Zone of the Zagros Fold and Thrust Belt: Insights from Seismic Data and Sandbox Modeling

The Zagros Belt has examples of strike-slip faults affected by precursor Hormuz Salt bodies. We attempted to examine the role of salt walls in localizing the strike-slip faults using field observations, seismic profiles and understandings from the sandbox modeling. Setting and performance of the pre-Hormuz features in connection to the salt tectonics are major questions. The inherited topography below the salt is an important parameter which controlled the structuration of the basin. The antecedent troughs provided accommodation for the thick Hormuz Salt. Differential loading above the salt helped generation of salt-related structures. The salt-walls caused formation of elongated highs. These highs were re-shaped in form of strike-slip faults during the Zagros Orogeny. The intersection of the salt walls and the Zagros-induced deformation fronts are location of potential diapirs needless of bending points along the tear faults. In contrast, the underlying deep-seated basement faults are hardly believed to be strike-slip.

Salt tectonics in a double salt‐source layer setting (Eastern Persian Gulf, Iran): Insights from interpretation of seismic profiles and sequential cross‐section restoration

AbstractSalt tectonics in the Eastern Persian Gulf (Iran) is linked to a unique salt‐bearing system involving two overlapping ‘autochthonous’ mobile source layers, the Ediacaran–Early Cambrian Hormuz Salt and the Late Oligocene–Early Miocene Fars Salt. Interpretations of reflection seismic profiles and sequential cross‐section restorations are presented to decipher the evolution of salt structures from the two source layers and their kinematic interaction on the style of salt flow. Seismic interpretations illustrate that the Hormuz and Fars salts started flowing in the Early Palaeozoic (likely Cambrian) and Early Miocene, respectively, shortly after their deposition. Differential sedimentary loading (downbuilding) and subsalt basement faults initiated and localized the flow of the Hormuz Salt and the related salt structures. The resultant diapirs grew by passive diapirism until Late Cretaceous, whereas the pillows became inactive during the Mesozoic after a progressive decline of growth in the Late Palaeozoic. The diapirs and pillows were then subjected to a Palaeocene–Eocene contractional deformation event, which squeezed the diapirs. The consequence was significant salt extrusion, leading to the development of allochthonous salt sheets and wings. Subsequent rise of the Hormuz Salt occurred in wider salt stocks and secondary salt walls by coeval passive diapirism and tectonic shortening since Late Oligocene. Evacuation and diapirism of the Fars Salt was driven mainly by differential sedimentary loading in annular and elongate minibasins overlying the salt and locally by downslope gliding around pre‐existing stocks of the Hormuz Salt. At earlier stages, the Fars Salt flowed not only towards the pre‐existing Hormuz stocks but also away from them to initiate ring‐like salt walls and anticlines around some of the stocks. Subsequently, once primary welds developed around these stocks, the Fars Salt flowed outwards to source the peripheral salt walls. Our results reveal that evolving pre‐existing salt structures from an older source layer have triggered the flow of a younger salt layer and controlled the resulting salt structures. This interaction complicates the flow direction of the younger salt layer, the geometry and spatial distribution of its structures, as well as minibasin depocentre migration through time. Even though dealing with a unique case of two ‘autochthonous’ mobile salt layers, this work may also provide constraints on our understanding of the kinematics of salt flow and diapirism in other salt basins having significant ‘allochthonous’ salt that is coevally affected by deformation of the deeper autochthonous salt layer and related structures.

Tectonostratigraphic evolution of the Helleh Paleo-high (NW Persian Gulf): Insights from 2D and 3D restoration methods

Seismic and well data, restored cross sections and surfaces, as well as non-seismic data were utilized to reconstruct the tectonostratigraphic evolution of the Helleh Paleo-high, a gentle, elongated, N-NE trending structure in the Iranian sector of NW Persian Gulf. Based on Bouguer gravity anomaly and basement depth maps, the southeastern margin of the Helleh Paleo-high is defined by the Bushehr Fault, a NE-SW trending deep-seated fault which contributed to the deposition of thicker late Precambrian-early Cambrian Hormuz Salt to the SE. There is also a significant increase in thickness of the Late Devonian to latest Triassic succession in the southeastern block of this fault, a feature which is interpreted as evidence for syn-depositional fault activity.After a period of relative tectonic quiescence during the Jurassic and Early Cretaceous, the Helleh Paleo-high became emerged and eroded from the Cenomanian to Maastrichtian-early Paleocene. Uplift and erosion continued until the early Miocene, but at lower rates compared to the Late Cretaceous. The repeated reactivations of the Bushehr Fault together with the remobilization of the Hormuz Salt in the core area of the Helleh Paleo-high could have contributed to these phases of amplified erosion.In the early Miocene, the peripheral loading related to the southward advance of the Zagros Fold and Thrust Belt resulted in the establishment of the Zagros foredeep basin. This event exerted a NE downward tilting on the Helleh Paleo-high. The progressive tilting continued during the middle Miocene when the structure attained its maximum extent as a 4-way closure. The latest Miocene- Pleistocene was a critical period in the structural history of the Helleh Paleo-high when the final stage of Zagros foredeep basin evolution tilted the structure to such a degree that all pre-existing structural reliefs in the post- Upper Triassic reservoir units were completely destroyed. In fact, the Helleh Paleo-high is an example of a damaged hydrocarbon trap due to recent tectonic tilting.

Diapir kinematics in a multi-layer salt system from the eastern Persian Gulf

The eastern Persian Gulf hosts several salt structures sourced from two different evaporite layers, the Neoproterozoic-Cambrian Hormuz Salt and the Oligocene-Miocene Fars Salt. Based on seismic interpretation, we discuss the kinematics and dynamics of this autochthonous multi-layer salt system for three case studies: the Tunb and Hengam diapirs, and the Taftan salt anticline. Halokinetic sequences related to Hormuz salt evacuation suggest three main stages of evolution: i) onset of Hormuz Salt diapirism (Paleozoic), ii) diapir squeezing, and emplacement of allochthonous Hormuz Salt (Late Cretaceous to Oligocene-Miocene), and iii) development of secondary and tertiary salt welds (Upper Miocene). Since Fars Salt structures are absent in areas devoid of allochthonous Hormuz Salt, our structural model interprets that the driving mechanism for Fars Salt diapirism is directly related to the emplacement of allochthonous Hormuz Salt during the Zagros-Oman contractional event. The related halokinetic sequences suggest that the Fars Salt diapir kinematic style depends on to the timing of Hormuz Salt extrusion with regards to Fars Salt deposition. Our results provide new insight into the interaction between salt structures sourced from two distinct autochthonous salt layers.