Abstract Structural analysis of surface and subsurface data in the Dezful Embayment, the northern Fars, and the High Zagros provinces shows that the presence of the Eocambrian Hormuz and the Miocene Gasharan salt layers have a direct control on the structural style. Both are levels of major disharmony and decollement during the Neogene Zagros folding. There is some evidence that Hormuz salt doming started before the Neogene Zagros orogeny. Permo-Triassic Tethysian rifting along High Zagros northwest-southeast trends and Cretaceous-Paleogene obduction and compressive events associated with basement reactivation of north-south Arabian trends could have initiated some episodic salt diapir activity in the Central Zagros province. However, in the absence of high-quality, deep seismic imaging in most of the Zagros fold zone, early Paleozoic or Hercynian salt movements are not excluded. The Hormuz complex is known from emergent halite and anhydrite plugs in the Fars and High Zagros areas. The emergence of Hormuz evaporite plugs is closely associated with major thrusts parallel to the fold trend, such as the Dinar thrust. Plugs also occur along tear faults or where space is created by pull-apart along the north-south trending strike-slip faults. These faults and the associated salt plugs are clearly related to the Zagros folding event, even if they are sometimes located above reactivated paleo-structures. The analysis of the deformation of sandbox models using X-ray tomography suggests that the initiation of thrust and wrench faults is influenced by pre-existing salt domes (weak zones). The driving mechanism of Hormuz halo-kinesis and extrusion was the squeezing of pre-existing salt domes. Local pull-apart and wrench fault deflection probably also allowed for rapid rising of the evaporites. In the Fars and High Zagros areas, the Hormuz salt series played the role of a low friction, basal décollement level, and influenced fold style by free development of fore-thrusts and back-thrusts without any preferred vergence. The high competency contrasts within the sedimentary pile favored the development of “fish tail” structures and caused axial shifting of anticlinal crests from surface to depth. The Neogene sedimentary sequence begins with the deposition of the evaporitic Gachsaran Formation above the Asmari limestone reservoir. The lateral extent of this facies is restricted to the Dezful zone, marking the evolution of the area towards a fold belt and its associated flexural basin. Thickness variations and early diapirism show that this syntectonic deposit is contemporaneous with folding in this area. The Gasharan salt is a major level of décollement and disharmony in the north Dezful Embayment zone, south of the Mountain Front Fault. This interpretation implies that the surface expression of the structures does not reflect their geometry at depth. The Gachsaran evaporitic sequence also plays an important role in sealing Asmari reservoirs.

Abstract Qatar plays a key role in the understanding of the Phanerozoic petroleum geological history of the Arabian plate through the continuous influence of the Qatar High on the regional sedimentation patterns and deformation styles. This tectonic unit originated in the Late Pre-Cambrian, when it separated the Hormuz salt, as a high, into an eastern and western basin. Ever since it has functioned as a stable area in between two differently behaving halokinetic regimes and has provided a relative high at various times in the Mesozoic. Notably, in the Jurassic and Cretaceous, it formed a shallow water carbonate platform between intra-shelf basins, which later became the focus for oil and gas migration. Taking into account tectonic control, depositional systems, and climatic variations, the Phanerozoic history of Qatar can be subdivided into six tectono-sedimentary phases: 1) late Pre-Cambrian rifting with the development of the Qatar High surrounded by the Hormuz Salt Basin; 2) Paleozoic clastic-dominated, mostly shallow marine sedimentation, interrupted by a phase of erosion and non-deposition representing the local equivalent of the Hercynian orogeny–Ice age-influenced sedimentation occurred during the Silurian and early Permian; 3) Late Permian–Triassic regional carbonate-evaporite shelf deposition; 4) Jurassic to Middle Cretaceous carbonate platforms and intra-shelf basins, controlled by local subsidence patterns, eustatic sea level fluctuations, and local siliciclastic influx; 5) latest Cretaceous to Middle Miocene Foreland Basin creation and infill by siliciclastics and carbonates; and 6) Middle Miocene to recent mostly non-deposition due to both uplift caused by the Neo-Tethys closure with continued foreland basin development and glacio-eustatic sea level lows. Three known petroleum systems developed within this geological setting: the Paleozoic Khuff–Qusaibah system, the Mesozoic Arab-Hanifa, and the Middle Cretaceous–Hanifa systems. The crest of the Qatar High hosts both the Khuff gas reservoirs of North field, sourced by Silurian Qusaibah shales, and the stacked Middle Cretaceous oil reservoirs of the Al Shaheen field, sourced by the Jurassic Hanifa shales. The Jurassic oil reservoirs of the Dukhan field are located on the northern flank of the high, whereas smaller occurrences are present in Jurassic and Cretaceous strata of salt dome structures in the Rub Al Khali Basin in the east. Oil for these was sourced from the underlying Jurassic organic-rich intra-shelf basinal deposits of the Hanifa and Jubailah Formations, which matured in the oil kitchens adjacent to the Qatar High.

Abstract Four-dimensional analogue X-ray tomography imagery is used to investigate the role played by pre-existing salt structures during compressive deformation. Initially linear salt structures evolve towards more axisymmetric diapirs. Depending on the diapir geometry and on its thickness relative to the sedimentary column thickness, the diapirs are either (1) shortened and localize sharp overturned folds for vertical pipe-like diapirs or else (2) act as preferentially oriented ramps, the diapir being incorporated in the fold for pillow-like diapirs. The ridges have a strong effect on the lateral extent and orientation of folds: they disconnect the folds formed on either side of the salt wall. Compressional relays between ridges allow for a folded connection between both sides. The Zagros Mountains in southern Iran offer a large variety of comparable structures, associated with the Hormuz salt level which acts as the regional décollement. Most of the salt structures have been active from the Early Palaeozoic until the present day. The first-order critical taper is controlled by the distribution of Hormuz décollement level and by its thickness. At a smaller scale, the fold geometry and size are locally controlled by the pre-existing salt structures, which are the main source of heterogeneity in the deformation.

This paper briefly reviews the most important salt deposits of the Middle East. Their stratigraphic and geographic distribution is discussed in relationship to the general geologic history of the area. Recent field studies in Iran have presented new evidence for an Early Cambrian or Proterozoic age of the Hormuz salt. Stable platform conditions on the northeastern shelf of the Arabian Shield and in East Iran favored the development of semiclosed basins with evaporite deposits in Proterozoic (?) time and at repeated intervals in Paleozoic and Mesozoic time, culminating in the Late Jurassic. Their geographic outline is largely governed by old, Precambrian basement trends such as the Oman line and the Qatar line. These trends are essentially north-south and can partly be attributed to a late Precambrian, pre-Hormuz orogeny. The paleogeographic configuration was drastically changed by Alpine diastrophism which developed the Tertiary lagoon of the Persian Gulf and Mesopotamia and separated off the continental basin of Central Iran with its spectacular salt domes and modern Kawir salt wastes. Present salt deposition is displayed on a grand scale in the Great Kawir of Central Iran.