Salt Sheets Research Articles

Impact of Salt Tectonics on Temperatures Distribution Revealed by RSCM Thermometry in the SW Alps (France)

Evaporites have a strong impact on the structural and sedimentary evolution of sedimentary basins and fold-and-thrust belts. They also have a thermal conductivity that can be more important than other sedimentary rocks and are thus able to modify the thermal history of these sedimentary basins and fold-and-thrust belts. Even though this property is known and has been of interest for the oil and gas industry, no field examples have been studied trying to decipher how salt rock impacts temperature distribution in fold-and-thrust belts. In this paper, we use the Raman Spectroscopy on Carbonaceous Material (RSCM) to track the record of the peak thermal event around three salt structures from the southern sub-Alpine fold-and-thrust belt in SE France. These three salt structures are (1) the Astoin allochthonous salt sheet and the associated overturned megaflap, (2) the Rocher de Hongrie and (3) the Daluis diapir. Our results show that the resulting record of peak temperatures around the structures is different depending on the type of salt structure and its kinematic. The Astoin structure shows that salt tectonics during the Jurassic-Cretaceous has impacted the temperature distribution around the allochthonous salt sheet while at Daluis and the Rocher de Hongrie, the temperatures have overprinted an already existing salt-related structure. The impact of the salt structure on temperature distribution is always local but the interpretation of the RSCM temperatures may systematically be difficult without considering early salt tectonics in the structural evolution of the area.

Salt sheet extrusion and emplacement within the South-Central Pyrenean fold-and-thrust belt: the Les Avellanes Diapir case-of-study

ABSTRACT A detailed geological map of the Les Avellanes salt Diapir (South-Central Pyrenees, Spain) that includes both the diapir body and adjacent areas is presented to understand the diapir evolution and geometry. Structural, stratigraphical, and sedimentary data north and south of the diapir is used to infer the timing of its emplacement. The northern diapir boundary is characterized by a set of extensional faults oblique to the main Pyrenean trend, while the southern boundary is an extrusive salt sheet that overlays the late Eocene-early Oligocene sequence in three adjacent sub-basins. Salt extrusion occurred due to synorogenic folding. The topography created as salt extruded trapped the arrival of external sediments from the north, blocking the transport pathways southward. Low sedimentation rates southwards allowed for the lateral salt extrusion, advancing southwards from the feeder. The salt sheet emplacement was postdated by Oligocene conglomerates, indicating that the salt extrusion was a relatively quick event.

The kinematics of a salt sheet recorded in an array of distorted intrasalt stringers (Les Avellanes Diapir – South-Central Pyrenees)

Stringers represent fragments of competent, brittle layers, formerly interstratified within a layered evaporite sequence (LES) that are entrained and deformed by viscous flow. To resolve the impact of the stringers on the deformation style of an extrusive salt sheet, an array of decameter-thick, carbonate stringers, preserved in the caprock matrix of the Les Avellanes Diapir (South-Central Pyrenees) was analysed. The diapir exposure was mapped in detail to produce a cross-section that shows the stringer assemblage. To understand the dynamic behaviour of stringers, this natural prototype has been reproduced using scaled analogue models. In the model, stringers were carried into the salt sheet, rotating and deforming while migrating toward the sheet front. The array of stringers can be divided into the following three structural domains: 1) a feeder domain mainly hosting vertical stringers parallel to the stem wall that rotate to a subhorizontal orientation as they approach the allochthonous sheet, 2) a sheet domain containing stack-like sets of subvertical and overturned, to subhorizontal stringers, as well as isoclinally and recumbently folded stringers, and 3) a sheet front domain characterised by stringers dipping toward the salt sheet front. Compartmentalization of the horizontal flow by the transported stringers controlled the deformation in the caprock matrix above. Finally, the similarity between the field observations and the model is evaluated and discussed to shed light on the Les Avellanes Diapir kinematic evolution.

Emplacement and associated sedimentary record of the Jurassic submarine salt allochthon of the Wurzeralm (Eastern Alps, Austria).

A fossil salt sheet emplaced in the Jurassic in submarine conditions is described in the Eastern Alps of Austria, providing unique insights into the emplacement of similar submarine structures and their potential control on depositional systems. The salt sheet is a plug-fed extrusion emplaced due to squeezing of a salt diapir under compression. The preserved mylonitic shear fabric in the evaporites indicates radial, south-directed emplacement of the salt sheet. Tectono-sedimentary relationships record the evolution of the salt structure, from initial diapiric growth, to salt sheet extrusion and posterior collapse. Syn-extrusion sediments record the variable bathymetry of the extruding salt sheet, with reefal carbonates building up on the crestal bulge while their deeper water equivalents accumulated on the extruding salt lobe. This is the first description of a salt allochthon still linked to its source diapir in the Eastern Alps.

Mud volcanoes guided by thrusting in compressional settings

Mud volcanoes are fed largely by fracture systems, but fracture systems are common in fold-and-thrust belts (FTBs), and not all of them extrude mud volcanoes. One popular hypothesis is that mud volcanoes extrude up normal faults and fractures in the crests of thrust-related anticlines. Using a high-resolution depth-migrated seismic cube in the northwestern Gulf of Mexico, we demonstrate the occurrence of buried mud volcanoes (shale sheets) that appear to have been fed by fluids moving up the thrust faults themselves. Mobile shales in this deepwater FTB detach a mostly welded allochthonous salt sheet. The main phase of shortening was during the Miocene, accompanying the sedimentation. Shortening generated multiple detachment levels, stacked duplexes, thrusts, and folds affecting the Oligocene mobile shales. Above these detachments, syn-sedimentary shortening initially generated detachment folds that progressively evolved into upward-propagating listric thrusts and fault-propagation anticlines. Shale sheets formed near the central thrust domains, associated with higher fault dips and larger fault displacements. We argue that their feeder systems were probably thrust-related shear zones that widened upward and comprised networks of anastomosing fractures. Finally, we propose that the position of mud volcanoes with respect to the underlying thrust systems depends on the path of least resistance to the surface. Although overpressured muds may vertically reach the surface via extensional fractures in the crests of thrust-related anticlines, we have shown to the contrary that when thrusts are emergent in a deepwater FTB, fluids continue up the inclined thrusts and adjacent fractures, forming mud volcanoes at the thrust tips.

Structural architecture and evolution of eastern Mississippi Canyon, northern gulf of Mexico

3-D, depth-migrated seismic data are used to evaluate the structural architecture and evolution of eastern Mississippi Canyon, northeastern Gulf of Mexico. The W-dipping base of the Louann salt is mostly unfaulted, such that basement faults did not influence Late Jurassic to Recent deformation. Instead, the suprasalt evolution was driven by a combination of lateral (gravity-driven) and vertical (differential loading) forces that varied in importance and direction over time. Salt movement was initiated in the Late Jurassic by SW-directed, convergent gravity gliding on an arcuate margin. This resulted in both contractional thrust faults and folds and dome-and-basin structures that set up the initial configuration of minibasins, salt plateaus, and early diapirs. The minibasins evolved as either turtle structures or expulsion-rollover structures, with the distribution of the two defining a convergent Mesozoic paleo-slope and age-equivalent basin floor. Gravity-driven deformation waned and differential loading gradually became more important during this time. The relative interplay between the two drivers reversed again during the Miocene due to a combination of progressive welding of the Louann salt and an eastward shift of Miocene deltaic shelf edges updip of the study area. The latter triggered SSE-directed gravity spreading, with most of the resultant extension and contraction located in more proximal and distal areas, respectively. The study area was mostly in the translational domain, which was bounded by a zone of sinistral strike-slip deformation downdip of the lateral edges of the deltaic depocenters. Miocene salt structures defined two provinces: a proximal domain characterized by counterregional feeders and basinward-flowing salt sheets; and a distal domain with vertical feeders and radially-spreading allochthonous salt. The boundary between the two marked the Miocene toe of slope. Lessons derived from the study area can be applied to help understand the more complex structures and evolution farther west in the northern Gulf of Mexico.

Salt geometry in the Central Basin of the Nova Scotia passive margin, offshore Canada based on new seismic data

This study describes the structural architecture of the central portion of the Scotian Basin and focusses on Mesozoic salt deposition and deformation linked to magma-rich rifting. BP acquired a high-quality 3D seismic survey called the Tangier survey and built a detailed velocity model with RFWI (Reflection Full Waveform Inversion) and tomography. This has allowed for high resolution seismic imaging of target sedimentary reservoirs but also for the first time, imaging of the complex crustal architecture along the central part of the Nova Scotia margin. We evaluated the regional basin architecture and salt tectonic evolution in context of Late Triassic and Early Jurassic rifting followed by passive margin gravity spreading. An exploration well (Aspy D-11) was drilled based on the 3D seismic interpretation and penetrated halite, carnallite and anhydrite salt in an allochthonous salt sheet. Basement is thought to have rifted during deposition of interlayered halite, shale, carnallite and anhydrite. Carnallite may have precipitated from enriched brines that formed at the more distal (southern) end of an elongated seaway of rifted basins which began opening first in the North in the Late Triassic and propagated southward towards Florida (e.g., Jansa, 1980; Jansa and Tucholke, 1986; Roberts and Bally, 2012). Water flowed southwards from Tethys along a chain of complexly interconnected areas of rifted basins. Flow of seawater along Nova Scotia is interpreted to have been southward along a widening and progressively subsiding region of rifts possibly as dynamic elevation associated with the CAMP (Central Atlantic Magmatic Province) dissipated southward much like what occurred in the Central South Atlantic and Gulf of Mexico (GoM) (e.g., Quirk et al., 2013; Morgan et al., 2020; Pindell et al., 2020; Pindell and Heyn, 2022). Brine was enriched along the seaway by evaporation, causing deposition of the most-soluble salt components furthest south along the sequence of basins. The presence of weathered basalt in salt and SDRs on the seismic supports magma-rich Mesozoic rifting and suggests that heating of brine pools may not have been exclusively caused by the sun, but that hydrothermal systems probably contributed to heating and the precipitation of Carnallite.

Contractional salt deformation in a recently inverted basin: Miocene to current salt deformation within the central Algerian basin

AbstractField analogues illustrating the early stage of deformation of shortening structures in salt‐bearing orogenic fold‐and‐thrust belts are not yet well illustrated in literature. The relatively young Messinian salt of the Algerian basin could represent a good case example of such systems. The Algerian Basin is a deep‐water Miocene back‐arc basin including a layer of mobile Messinian evaporites up to 2 km thick. The Messinian salt was deposited in an already inverted basin, after its extensive stage. Its inversion initiated in the Tortonian, with a N‐NW shortening induced by the north‐westward motion of the African plate. In this study, we use new 2D multichannel seismic data to identify, classify and map salt structures throughout the central Algerian Basin and re‐assess its structural style. We interpret contractional salt tectonic structures, such as buckle folds, squeezed diapirs and related salt sheets as evidence of regional thick‐skinned shortening episodes. We conclude that horizontal displacement loading has driven salt deformation within the basin since its deposition. We also show spatial variations in the structural style of the central Algerian Basin, both along‐ and down‐dip. We demonstrate that the initial shortening‐related salt deformation in the late Messinian was focussed along the Algerian margin and later shifted outward toward the Balearic margin in the Plio‐Quaternary. The shifting of the deformation front is interpreted to be a result of the thickening and strengthening of the overburden. The second peak of deformation may have reactivated faults along the Emile‐Baudot escarpment with thick‐skinned deformation. We also observe a variation in the intensity of the salt deformation along the margin from SW to NE, which may be due to variable tectonic loading applied along the Algerian margin or the pre‐shortening distribution of salt.

Innovative application of full-waveform inversion applied to extended wide-azimuth marine streamer seismic data in a complex salt environment

We demonstrate the application of full-waveform inversion (FWI) guided velocity model building to an extended wide-azimuth towed streamer (EWATS) seismic data set in the Gulf of Mexico. Field data are collected over a historically challenging imaging area, colloquially called the “grunge zone” due to the formation of a compressional allosuture emplaced between two colliding salt sheets. These data have a poor subsalt image below the suture with conventional narrow-azimuth data. Additional geologic complexities are observed including high-velocity carbonate carapace near the top of salt and multiple intrasalt sedimentary inclusions. As such, improved seismic imaging is required to plan and execute wells targeting subsalt strata. Significant improvements to the velocity model and subsalt image have been evident with wide-azimuth towed streamer and later EWATS data using conventional top-down velocity model building approaches. Subsequently, high-impact improvements have been made using EWATS data with an FWI velocity model building workflow; this study represents an early successful application of FWI used to update salt body geometries from streamer seismic data, wherein many prior applications were limited to improving sedimentary velocities. Later petrophysical data have verified the new FWI-derived model, which has significantly increased confidence in the structural and stratigraphic interpretation of subsalt reservoir systems below the grunge zone.

Salt tectonics of the offshore Tarfaya Basin, Moroccan Atlantic margin

Salt tectonics play a critical role on passive margins evolution controlling aspects like structural style, subsidence patterns and thermal history, amongst others. The salt-bearing Atlantic passive margin of Morocco hosts one of the oldest stratigraphic records documenting the opening history of the Central Atlantic. However, the available seismic data is scarce and some offshore basins are still poorly studied, particularly in southern Morocco. Through the interpretation of an unpublished 2D/3D seismic dataset from the offshore Tarfaya Basin (SW Morocco), this study aims to highlight the key events that conditioned the evolution of this salt-bearing basin. From proximal to distal regions, the structural style of the basin is characterized by expulsion rollovers and salt-cored anticlines delimited by primary welded surfaces, evolving to buried salt sheets surrounded by thick minibasins and finally, diapirs actively deforming the modern seabed. From Late Triassic to Early Jurassic times, salt was deposited with a basinward thickening wedge-shaped geometry on a narrow trough developed over thinned continental crust. During the Jurassic, sedimentation and associated salt withdrawal triggered early salt deformation. Gravity gliding is a common process in salt-bearing passive margins that requires an originally continuous autochthonous salt layer with a minimum slope angle and longitude to thickness ratio of the overburden. However, in the Tarfaya Basin, the narrow geometry of the salt-bearing depocenter hampered this process. Early salt tectonics was probably triggered by slope progradation during the Early Jurassic. During the Early Cretaceous, the progradation of the Tan-Tan Delta promoted a continued basinward expulsion of salt, the development of a local salt-detached gravitational system and the proximal extrusion of salt sheets. Finally, from Late Cretaceous to the Present-day, shortening related to the convergence between Africa and Eurasia resulted in thick-skin inversion and the rejuvenation of precursor salt structures.

Mechanical relationship between strike-slip faulting and salt tectonics in the Northern Tunisian Atlas: The Bir-El-Afou salt structure

Wide variety of salt structures –from typical diapirs to large allochthonous salt sheets– are recognized in the Northern Tunisian Atlas. In this study, we present for the first time the presence of a diapiric structure, Bir-El-Afou Salt Structure (BEASS), which has formed in response to strike-slip tectonics. Structural mapping, mesoscale field observations, fault kinematic analysis, and interpretation of gravity data are used to interpret BEASS, which is currently associated with a restraining bend. The present-day NNE– trending restraining stepover is formed as a result of E-W dextral fault system. We assume that the restraining stepover is a product of the inversion of a pre-existing pull-apart basin that formed during the Cretaceous South Tethyan extension. Tectono-sedimentary relationship is used to argue for an early Cretaceous NW-SE regional extension and local transtension. During the opening of the pull-apart basin, salt movement took place in the southwestern corner of the basin which must have thinned due to its extension facilitating diapiric emplacement. Diapir growth during Aptian was followed by brief salt flow from the diapir crest towards the basin forming a salt sheet. A period of Tertiary contraction resulted in the inversion of the pull-apart basin and consequently, squeezing of BEASS.

Composition and deformation patterns of the caprock on salt extrusions in southern Iran – Field study on the Karmostaj and Siah Taq diapirs

Two iconic salt diapirs in the Zagros Mountains in Iran – Karmostaj (Gach) and Siah Taq – are regarded as world-class examples of salt extrusions and are frequently called "salt glaciers". However, our field survey revealed that their glacier-like parts are formed by thick, variegated and deformed caprock, only locally mixed with salt. Caprock is a layer of insoluble residuum that consists primarily of dissolution breccia and gypsum surrounding blocks of non-halite lithologies of the original evaporite sequence. Deformation within the caprock was accommodated primarily by shearing along gypsum-rich zones (gypsum mylonites) that surround subdomains of dissolution breccia and folded and fragmented blocks of carbonates and siliciclastics. Ductile flow in these mylonite shear zones was accommodated by pressure solution-precipitation creep of the lath-shaped gypsum grains. The ductile shearing of gypsum was locally accompanied by increased fluid-pore pressure driven fracturing of the surrounding lithologies. Since the subsurface shape of the salt diapirs is unknown, we present three hypothetical scenarios trying to explain the extrusion process of the studied diapirs and the associated deformation history of their caprocks. The diapiric structures represent either, 1) the remnants of degraded paleoglaciers, 2) advancing salt extrusions, or 3) only slightly reactivated, wide diapirs. To test these hypothetical scenarios, a geophysical survey is required to gain insights into the subsurface structures of the exposed diapirs and salt sheets.

Taking the Pulse of Salt‐Detached Gravity Gliding in the Eastern Mediterranean

AbstractDespite having a profound impact on the structural evolution of salt‐influenced basins, spatial and temporal variations in rates of salt flow, and their key controls, remain largely unconstrained. We investigate early stage salt‐detached gliding using a 3D seismic data set from the Levant Margin in the Eastern Mediterranean, where gravitational instability due to margin uplift has caused north‐westward translation of the Messinian salt sheet and its overburden. Large base‐salt anticlines mean that basinward translation is recorded by the development of supra‐salt ramp syncline basins (RSBs) and fluid escape pipes, the latter forming due to the leakage of fluid from the anticline crests. The trails of pipes provide kinematic vectors of transport direction, while the stratigraphic record of the RSBs not only constrains the relative ages of the pipes, but allows us to quantify the magnitude and approximate rate of translation. We correlate intra‐RSB horizons across the margin to analyze lateral variations in translation rate, and how these vary through time. We show that translation rates are broadly uniform on the length‐scale of individual anticlines (c. 10 km), but that there is significant margin‐scale (c. 100 km) lateral variability in both the direction and magnitude of translation. We attribute temporal variations in local rates of translation to cyclical “pulses” of salt flow due to volumetric flux imbalances across the anticlines, while the distribution of elastic strain in the overburden modulates the overall basin‐scale trend. These results demonstrate the importance of local stresses in controlling the local direction and rate of salt flow, and further our understanding of salt and overburden rheology.

Intra-salt structure and strain partitioning in layered evaporites: implications for drilling through Messinian salt in the eastern Mediterranean

We use 3D seismic reflection data from the Levant margin, offshore Lebanon to investigate the structural evolution of the Messinian evaporite sequence, and how intra-salt structure and strain varies within a thick salt sheet during early-stage salt tectonics. Intra-Messinian reflectivity reveals lithological heterogeneity within the otherwise halite-dominated sequence. This leads to rheological heterogeneity, with the different mechanical properties of the various units controlling strain accommodation within the deforming salt sheet. We assess the distribution and orientation of structures, and show how intra-salt strain varies both laterally and vertically along the margin. We argue that units appearing weakly strained in seismic data may in fact accommodate considerable subseismic or cryptic strain. We also discuss how the intra-salt stress state varies through time and space in response to the gravitational forces driving deformation. We conclude that efficient drilling through thick, heterogeneous salt requires a holistic understanding of the mechanical and kinematic development of the salt and its overburden. This will also enable us to build better velocity models that account for intra-salt lithological and structural complexity in order to accurately image sub-salt geological structures.

Restoration of multiphase salt tectonic deformation using passive strain markers

AbstractSeveral salt basins globally have been subject to multiphase deformation. The geometry of structures formed within a salt sheet during an early phase of deformation can be concealed by overprinting during later deformation phases, impeding an informed investigation into the early drivers for salt flow. The layered Messinian Evaporites in the deep basins of the Eastern Mediterranean have undergone a Late Messinian phase of deformation, punctuated by truncation of the top of the deformation structures, followed by a Late Pliocene‐Recent phase of deformation. Seismic reflection data show that the Messinian Evaporites are internally dominated by contraction structures that verge basinward in the Late Pliocene‐Recent flow direction, with several apparent detachments. Planform linear trails of fluid escape pipes, documented in the North Levant Basin, that cross‐cut the Messinian Evaporites present natural passive markers for the internal flow kinematics of the salt sheet throughout the Late Pliocene‐Recent phase of deformation. Using the Couette (simple shear) strain profile implied by the fluid escape pipes, we remove the effects of the Late Pliocene‐Recent deformation through cross section and map restorations. The subsequent geometries are far simpler, with upright folds that are now vertically aligned. Once apparently detached structures are demonstrably connected through the Messinian Evaporites. The vergence of the present day intrasalt folds can be taken as an indicator for the Late Pliocene‐Recent flow direction and distinct deformation geometries that connect at various levels through the salt sequence once retro‐deformed can assist when interpreting the salt flow profile. The retro‐deformation is essential for how intra‐Messinian deformation and its drivers are interpreted going forward. Furthermore, simple shear deformation results in erroneous apparent percentage shortening calculations as line length is not conserved, obscuring the strain from the pre‐Pliocene deformational phase. The methodology employed here has important implications for all salt basins that have undergone multiphase deformation.

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.

Anatomy and evolution of the Astoin diapiric complex, sub-Alpine fold-and-thrust belt (France)

The structure of the southwestern branch of the Alpine orogen is affected by the extensive Late Triassic evaporites. These evaporites have been involved in polyphased salt tectonics since the early Liassic, coeval with the Tethyan rifting, and are the décollement level for thrusts in the external parts during Alpine orogeny. The role of salt tectonics in this branch of the Alpine arc is re-evaluated in order to determine the relative importance of early deformation related to salt motion with respect to deformation related to main Alpine compressional events. This paper focuses on one structure identified as diapiric since the 1930’s: the Astoin diapir (Goguel, 1939). Analysis of geological maps together with new field work have allowed to better define diapirism in the Upper Triassic evaporites outcrops around Astoin. Study of the diapir and the surrounding depocenters reveals a major involvement of salt in the structuration of the area, since the Liassic. Several salt ridges are linked to a main diapiric structure, explaining why we call it the “diapiric complex” of Astoin. Salt tectonics was initiated during the Liassic rifting, and a few locations show evidence of reactive diapirism whereas in others evidence of passive diapirism as early as the Liassic is seen. Passive diapirism continued during the post-rift stage of Alpine margin history in the Late Jurassic and Cretaceous when an allochthonous salt sheet was emplaced. Diapirism also occurred during the Oligocene while the Alpine foreland basin was developing in this part of the European margin of the Alps. Serial interpretative cross-sections have been drawn in order to illustrate the lateral variations of diapirism and structural style. Sequential evolutions for each cross-section are proposed to reconstruct the diapiric complex evolution through time. The Astoin diapir shows a complex structural framework with an important along-strike variation of diapiric activity. Most of the geometries are inherited from salt tectonics that occurred during extension, and in some places these early structures are overprinted by Alpine compressional structures.

Salt tectonics in the Sureste Basin, SE Mexico: some implications for hydrocarbon exploration

Abstract The Sureste Basin salt became diapiric soon after deposition in the Bajocian (169 Ma). Salt ridges and diapirs grew throughout the Jurassic–Cretaceous. The Mexican Fold and Thrust Belt propagated into the Sureste Basin at 70–60 Ma, causing squeezing/extrusion of allochthonous salt sheets. The more intense Mid-Miocene ( c. 13–11 Ma) compression (‘Chiapaneco Event’) produced folding and thrusting over a north–south distance of 600 km. The Mid-Miocene–Recent bulk horizontal flow is indicated by anticline and thrust traces mapped from seismic data and bathymetry. In the SE sector of the salt basin, flow is towards N60°E, where thrusting is intense and the salt is thin. The flow swings to a northerly direction in the basin centre, where folding is important. A parabolic fold arc was produced due to drag on the edges of the salt basin. This indicates that both salt and overburden behaved in a ductile manner at a large scale. Mesozoic carbonate slabs were overthrusted up to 20 km during the Mid-Miocene. Intense fracturing and karstification produced potential reservoir rocks with many untested structures that are leaking hydrocarbons. Pre-Mid-Miocene clastic reservoirs may be trapped in folds below the allochthonous salt, which also have not been drilled.

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.

Interconnection salt diapir–allochthonous salt sheet in northern Tunisia: The Lansarine–Baoula case study

Surface and subsurface data are used to illustrate the halokinetic style, structural evolution and kinematics of the Lansarine–Baouala salt structure in the Alpine domain of Tunisia. It corresponds to a salt structure showing a large salt canopy overhanging buried diapir. The salt structure is located along the main fault systems, inherited from the southern Tethyan passive margin periods. The Northern domain of Tunisia is undergoing diapirism, which has been recognized as active during the Upper Aptian and Lower Albian periods. Above the diapir apex, salt flows outward and spreads by gravity downslope. A minibasin has formed during this period of salt outward evacuation. The minibasin has a thickness practically correlated to the budget of salt evacuation toward the diapiric structure. During Cenozoic times, compressional deformation stages do not reflect active diapirism. The Lansarine–Baouala salt structure, consisting of connected salt sheets, was passively transported on the Southeast-verging major thrusts that are deeply rooted in the salt beneath the Mateur basin. The Northern Atlas of Tunisia reveals, as many others salt provinces, an interconnection of salt diapirs and significant laterally spreading allochthonous salt sheets (canopies?). In this domain, the inherited allochthonous Triassic salt sheets interlayered within recent series and connected to buried diapir have a significant role in the shallow structural complexity observed in the sedimentary cover during the subsequent contractional events.