Salt Tectonics Research Articles

Salt tectonics in the Eastern Mediterranean Sea: Where a giant delta meets a salt giant

AbstractThe circum-Nile deformation belt (CNDB) demonstrates the interaction between a giant delta and a giant salt body. The semi-radial shape of the CNDB is commonly interpreted as the product of salt squeezing out from under the Nile Delta. We demonstrate, however, that this is not the dominant process, because the delta and its deep-sea fan do not reach the deep-basin salt. The distal part of the deep-sea fan overlies the edge of the salt giant, but squeezing this edge (<150 m thickness) should have had only little effect on the regional salt tectonics. Only on the easternmost side of the deep-sea fan, toward the Levant Basin, does the squeeze-out model work. Here, the delta front reaches the thick salt layer and differential loading promotes basinward salt flow, even upslope. On the western side of the delta, downslope gliding of the sediment-salt sequence toward the Herodotus Basin is driven by the elevation gradient toward the deepest part of the basin. Our analysis shows that salt squeezing by differential loading was previously overestimated in the Eastern Mediterranean and raises the need to carefully map the boundary of salt basins prior to any interpretation. This conclusion is especially relevant in young basins where deltas and shelves have not propagated far enough into the basin.

Evaporite occurrence and salt tectonics in the Cretaceous Camamu-Almada Basin, northeastern Brazil

The Camamu-Almada basin is located at the South Atlantic Margin and, despite the availability of seismic data and the evidence of its hydrocarbon potential, is still considered a new exploratory frontier. In this study, the authors used fifty 2D seismic lines and twelve wells to: a) present a seismic stratigraphic interpretation of the transitional phase (i.e., the strata between the rift and the drift stages; b) investigate the distribution of evaporite deposits at the study area; b) verify the impacts of salt tectonics in the deep-water region, using basins situated in the same geotectonic context as reference. The development of the South Atlantic margin resulted in the formation of several rift basins - including the Camamu-Almada basin – and occurred through four tectonic phases: pre-rift, rift, transitional and drift. The regional deposition of evaporites marks the transitional phase, with occurrences both in Brazil and West Africa that increases in thickness and width southwardly. This work details that in the study area, the salt moved laterally and vertically, forming a highly deformed deposit that marks salt deflation and salt inflation zones, directly associated respectively with diapirs and mini-basins. Features related to salt tectonics that can be directly related to processes of migration and accumulation of hydrocarbons in the study area are also described.

Influence of Salt Tectonics On Fault Displacements and Submarine Slope Failures from Algeria To Sardinia

ABSTRACT We used previously obtained marine geophysical and geotechnical data for the proposed Galsi pipeline route from Algeria to Sardinia to analyze the buried salt distribution, rates of fault displacements, and frequency and lateral extent of submarine slope failures. Crossing the convergent African/Nubian–European plate boundary, the southern section of the pipeline route traverses continental shelves and slopes of Algeria and Sardinia as well as the Algerian abyssal plain of the western Mediterranean. Deeply buried Messinian-aged salt is present throughout this area. Being less dense and more buoyant than the overburden sediment, the salt tends to flow upward to form diapiric structures that, in turn, result in the formation of faults and landslides in the overlying sediment. Measured offsets from seismic profiles of different resolutions were compared with predicted sediment age at depth of each offset, yielding an average rate of fault displacement of 1.5 cm/kiloyear (ky). The highest rates of displacement are along the Cagliari slope near Sardinia (2.5-2.7 cm/ky) and near the convergent plate boundary (2.3 cm/ky). Utilizing the same geophysical data, the frequency and lateral extent of submarine slope failures in the study area can also be linked to the distribution of salt and the influence of salt tectonics. Turbidity currents and hyperpycnal flows are present within the Algerian basin, whereas local debris flows, landslide runouts, and channelized debris flows are present along the Sardinian slope. The low sedimentation rates, determined in this study, suggest that the most recent slope failures related to salt tectonics occurred more than 12,000 years ago.

Feedback between synrift lithospheric extension, sedimentation and salt tectonics on wide, weak continental margins

Numerical modelling in 2D is used to explore interactions between synrift lithospheric extension, salt deposition and deformation, and pre- and post-salt sedimentation, for wide rifted margins with weak continental crust. Distributed aggrading synrift sedimentation enhances listric normal faulting of the sediments and crust in the mid and distal margin. In contrast, localized prograding sedimentation initiates a positive feedback between sedimentation, faulting and mid- to lower-crustal flow. This feedback causes localized crustal extension at the proximal margin, and leads to thick sediments in deep proximal basins. The feedback is more pronounced when more sediment is deposited, and does not develop in models with stronger, narrower rifted margins. Later initiation of the post-salt prograding sediments leads to a less pronounced feedback with lower-crustal flow and a more significant advancement of the prograding wedge over the salt body. We compare our model results with the rifted Nova Scotia Atlantic margin, contrasting margin evolution and salt tectonics between the northeastern region, which experienced significant post-salt synrift sedimentation, and the central region, where less post-salt sediment was deposited. We show that the northeastern margin may have experienced enhanced proximal graben development owing to prograding synrift sedimentation. Thematic collection: This article is part of the Mechanics of salt systems: state of the field in numerical methods collection available at: https://www.lyellcollection.org/cc/mechanics-of-salt-systems

Ultra-deepwater seismic plays offshore Brazil — Future drilling off Santos and Campos Basins

Contemporaneous seismic data acquisition in the Santos and Campos Basins offshore Brazil have focused on image characterization of deepwater and ultra-deepwater reservoirs and their relationship with hydrocarbons originating from synrift source rocks. Our interpretation has mapped the stratigraphy of postsalt turbidite reservoirs, and, on the presalt lithology, it has uncovered the underlying synrift sequences that embrace oil-bearing source rocks and the prolific, recently discovered, microbialite carbonate reservoirs. The new phase in geophysical data acquisition and offshore drilling that started in 1999 bolstered the Brazilian offshore petroleum production to record levels. The new, massive, nonexclusive, speculative 2D and 3D data acquisition surveys conducted offshore the Brazilian coast far exceed the amount of all existing cumulative vintage data. Deepwater drilling programs probed the interpreted new prospects. As whole, the modern geophysics data libraries offshore Brazil brought in the technology era to seismic interpretation, reservoir characterization, and geosteering operations in deepwater development drilling. Still, regional interpretation mapping of the outer shelf, slope, deepwater and ultra-deepwater provinces of the Santos and Campos Basins indicates plenty of prospective future drilling in the salt locked minibasins of the ultra-deepwater provinces. Salt tectonics shapes the architecture of these basins; hence, postsalt deepwater turbidite plays were readily interpreted from seismic amplitudes of the modern data that also allow for resolution images of the synrift source rocks, salt architecture, migration paths through faulting and salt windows, reservoir characterization, and regional seal mapping. The new techniques of prestack depth migration have enabled uncovering the imaging structure of the synrift that led to characterization of the presalt carbonate reservoirs and discovery of giant accumulations. Future offshore exploration will continue aiming at postsalt deepwater and ultra-deepwater minibasins plus presalt plays under the massive salt walls, still an underexplored frontier.

The Nappe des Marbres Unit of the Basque‐Cantabrian Basin: The Tectono‐thermal Evolution of a Fossil Hyperextended Rift Basin

AbstractThe architecture of the Pyrenean‐Cantabrian belt results from the inversion of a series of former Cretaceous rift basins. A HT‐LP metamorphic event dated at 105 to 85 Ma ago is commonly associated with an Albo‐Cenomanian episode of hyperextension of the continental crust. This metamorphism is well known in the eastern Basque‐Cantabrian Basin within the Nappe des Marbres Unit (NMU) that is preserved from intense compressional deformation during the Pyrenean orogeny. Based on a structural study at the scale of the eastern Basque‐Cantabrian Basin and on a dense sampling for TRSCM estimates with the Raman spectroscopy of carbonaceous material (RSCM) method (Raman Spectrometry on Carbonaceous Material), we show following results: (1) the NMU has recorded two major phases of deformation, related to a localized extensional ductile foliation (S1) during the Cretaceous rifting and later by the regional N‐S shortening, recorded by a regional cleavage (S2) observed only in shale sediments. (2) The NMU is affected by early salt tectonics related to several diapirs and salt walls fed by the Upper Triassic evaporitic layer. (3) The NMU recorded maximum temperatures exceeding 550°C, which represent some of the highest temperatures along the Pyrenees. These new data demonstrate that there is no E‐W lateral metamorphic gradient across the belt and that hyperextension rifting occurred consistently within a high‐thermal regime; (4) metamorphic isograds are oblique in respect of the main structures, suggesting that the metamorphic event postdates most of the early salt‐related deformations prior to or coeval with early stages of rifting. As it represents one of the best preserved example of preorogenic hyperextended basin, the eastern Basque‐Cantabrian Basin record may be used regionally to better understand the rift to orogen evolution of the Pyrenean Internal Metamorphic Zone but also more generally as an analog of salt‐bearing hyperextended rift record.

Progressive tilting of salt-bearing continental margins controls thin-skinned deformation

Abstract As a primary driving force, margin tilting is crucial for gravity-driven thin-skinned salt tectonics. We investigated how instant versus progressive margin tilting mechanisms influence salt tectonics using an analogue modeling setup where tilting rate could be controlled. Instant tilting resulted in initially high deformation rates, triggering widely distributed upslope extension and downslope contraction. Later, both the extensional and contractional domains migrated upslope as early extensional structures were successively deactivated, while deformation rates decreased exponentially. In contrast, progressive tilting led to downslope migration of the extensional domain by sequentially formed, long-lived normal faults. Contraction localized on a few, long-lived thrusts before migrating upslope. We attribute the distinct structural evolution of thin-skinned deformation, especially in the extensional domain, in the two tilting scenarios mainly to mechanical coupling between the brittle overburden and underlying viscous material. The coupling effect in turn is largely controlled by the deformation rate. By demonstrating the spatiotemporal variations of structural style and kinematic evolution associated with instant versus progressive tilting, we suggest that such variation is identifiable in nature and therefore can provide a new way to analyze margin tilting histories.

Characteristics and hydrocarbon seepage at the Challenger Knoll in the Sigsbee Basin, Gulf of Mexico

Active seafloor hydrocarbon seepage from three distinct, positive seafloor features, termed knolls, in the Sigsbee Knolls area, Gulf of Mexico (GOM), was investigated in March 2015. The study sites included the Challenger Knoll, which was drilled by the Deep Sea Drilling Program (DSDP) in 1969 and showed the influence of salt tectonics on its evolution and the presence of subsurface petroleum. This study used gas flare mapping in the water column, detailed seafloor bathymetry, backscatter mapping, sub-bottom profiling, and remote sensing of surface water to locate seafloor areas of hydrocarbon emissions. Flares of gas bubbles were detected in the water column above all three knolls, making them the deepest reported gas emission sites in the GOM. Although surface oil slicks above the Sigsbee Knolls have been detected by satellite imaging in the past; in this study, neither satellite imagery nor ship-based observations detected floating oil, this suggests that oil seepage in the region is intermittent. High-resolution video surveys of the seafloor at Challenger Knoll, using a camera system mounted on a lowered tow-vehicle, documented the presence of seep-related chemosynthetic fauna including clam fields and microbial mats at the western part of the knoll. These findings are consistent with previous investigations that link hydrocarbon seepage at Challenger Knoll to salt tectonics. During visual seafloor inspections, no asphalt deposits, such as those known from sites in the Campeche Knoll area in the southern GOM, were observed. These findings indicate that hydrocarbon seepage is less pronounced in the Sigsbee Knolls region, central GOM, than is the case in hydrocarbon systems in the northern or southern GOM.

Dome formation on Ceres by solid-state flow analogous to terrestrial salt tectonics

The dwarf planet Ceres’s outer crust is a complex, heterogeneous mixture of ice, clathrates, salts and silicates. Numerous large domes on Ceres’s surface indicate a degree of geological activity. These domes have been attributed to cryovolcanism, but that is difficult to reconcile with Ceres’s small size and lack of long-lived heat sources. Here we alternatively propose that Ceres’s domes form by solid-state flow within the compositionally heterogeneous crust, a mechanism directly analogous to salt tectonics on Earth. We use numerical simulations to illustrate that differential loading of a crust with compositional heterogeneity on a scale of tens of kilometres can produce dome-like features of scale similar to those observed. The mechanism requires the presence of low-viscosity and low-density, possibly ice-rich, material in the upper 1–10 km of the subsurface. Such substantial regional heterogeneity in Ceres’s crustal composition is consistent with observations from the National Aeronautics and Space Administration’s Dawn mission. We conclude that deformation analogous to that in terrestrial salt tectonics is a viable alternative explanation for the observed surface morphologies, and is consistent with Ceres being both cold and geologically active. Domes on the dwarf planet Ceres could form by solid-state flow of low-density, ice-rich parts of its crust—a process analogous to salt doming on Earth—according to numerical simulations.

Base‐salt relief controls salt‐related deformation in the Outer Kwanza Basin, offshore Angola

AbstractSalt‐influenced passive margins are widespread and commonly hydrocarbon‐rich. However, they can be structurally complex, with their kinematic development being poorly understood. Classic models of salt tectonics divide such margins into updip extensional, mid‐slope translational and downdip contractional kinematic domains. Furthermore the faults, folds, and salt walls associated with each kinematic domain are typically assumed to form perpendicular to the maximum principal stress, which in gravitationally driven systems means broadly perpendicular to base‐salt dip. We use high‐resolution 3D seismic reflection data from the Outer Kwanza Basin, offshore Angola to show that these models cannot explain the diversity of salt structures developing on passive margins, especially those defined by considerable relief on the base‐of‐salt surface. Overburden seismic‐stratigraphic patterns record the basinward translation and rotation, allowing us to reconstruct the origin and evolution of the salt structures. We show structures in the transitional domain of the Outer Kwanza Basin display three dominant trends, each characterised by different structural styles: (a) salt walls perpendicular to the overall base‐salt dip, (b) salt walls parallel to the base‐salt dip and (c) salt walls oblique to the base‐salt dip. We show that each set of walls has a unique history, with synchronous phases of extension and compression occurring in adjacent structures despite their close spatial relationship. Our analysis suggests that, in the Outer Kwanza Basin, the structural evolution of the salt and overburden is predominantly controlled by translation over relief on the base‐salt surface formed above fault scarps associated with a preceding phase of rifting. Changes in the downdip volumetric flux and velocity of the salt over topographic features can cause local extension or contraction of the salt and its overburden, associated with local acceleration or deceleration of the salt, respectively. This interaction with base‐salt relief creates locally variable stress fields that deform the salt and its overburden, overprinting the broader, margin‐scale salt tectonics typically associated with gravity gliding and spreading.

On the Significance of Salt Modelling—Example from Modelling of Salt Tectonics, Temperature and Maturity Around Salt Structures in Southern North Sea

Salt structures are attractive targets for hydrocarbon exploration. Salt can flow as a viscous fluid, act as hydrocarbon seal, and salt-related deformation may create reservoir traps. The high conductivity of salt can be crucial for hydrocarbon maturation in a basin. Here, we present results from the study of salt structures on the Eastern flank of Central Graben, on the Norwegian sector of the North Sea. By using our in-house basin modeling software (BMTTM), we modelled the salt structure evolution and the effects of salt on temperature and maturation. Our results show up to 85 °C cooling due to the salt heat pipe effect. An integrated impact of cooling is the depression of vitrinite Ro by up to 1.0% at the base of a large salt balloon. Our work shows that it is of critical importance to correctly identify salt volumes and to have a good geological model, and to understand the timing and geometrical evolution of salt structures. This study is, to our knowledge, the most specific analysis of the impact of salt on basin temperature and maturation published so far, and is an example of how basin modeling in the future should be an integrated part of exploration.

Numerical modelling of Cretaceous Pyrenean Rifting: The interaction between mantle exhumation and syn‐rift salt tectonics

AbstractThe preshortening Cretaceous Pyrenean Rift is an outstanding geological laboratory to investigate the effects of a pre‐rift salt layer at the sedimentary base on lithospheric rifting. The occurrence of a pre‐rift km‐scale layer of evaporites and shales promoted the activation of syn‐rift salt tectonics from the onset of rifting. The pre‐ and syn‐rift sediments are locally affected by high‐temperature metamorphism related to mantle ascent up to shallow depths during rifting. The thermo‐mechanical interaction between décollement along the pre‐existing salt layer and mantle ascent makes the Cretaceous Pyrenean Rifting drastically different from the type of rifting that shaped most Atlantic‐type passive margins where salt deposition is syn‐rift and gravity‐driven salt tectonics has been postrift. To unravel the dynamic evolution of the Cretaceous Pyrenean Rift, we carried out a set of numerical models of lithosphere‐scale extension, calibrated using the available geological constraints. Models are used to investigate the effects of a km‐scale pre‐rift salt layer, located at the sedimentary cover base, on the dynamics of rifting. Our results highlight the key role of the décollement layer at cover base that can alone explain both salt tectonics deformation style and high‐temperature metamorphism of the pre‐rift and syn‐rift sedimentary cover. On the other hand, in the absence of décollement, our model predicts symmetric necking of the lithosphere devoid of any structure and related thermal regime geologically relevant to the Pyrenean case.

SaltSeg: Automatic 3D salt segmentation using a deep convolutional neural network

Salt boundary interpretation is important for the understanding of salt tectonics and velocity model building for seismic migration. Conventional methods consist of computing salt attributes and extracting salt boundaries. We have formulated the problem as 3D image segmentation and evaluated an efficient approach based on deep convolutional neural networks (CNNs) with an encoder-decoder architecture. To train the model, we design a data generator that extracts randomly positioned subvolumes from large-scale 3D training data set followed by data augmentation, then feed a large number of subvolumes into the network while using salt/nonsalt binary labels generated by thresholding the velocity model as ground truth labels. We test the model on validation data sets and compare the blind test predictions with the ground truth. Our results indicate that our method is capable of automatically capturing subtle salt features from the 3D seismic image with less or no need for manual input. We further test the model on a field example to indicate the generalization of this deep CNN method across different data sets.

Between plate and salt tectonics—New stratigraphic constraints on the architecture and timing of the Dead Sea basin during the Late Quaternary

AbstractThe Dead Sea is an extensional basin developing along a transform fault plate boundary. It is also a terminal salt basin. Without knowledge of precise stratigraphy, it is difficult to differentiate between the role of plate and salt tectonics on sedimentary accumulation and deformation patterns. While the environmental conditions responsible for sediment supply are reasonably constrained by previous studies on the lake margins, the current study focuses on deciphering the detailed stratigraphy across the entire northern Dead Sea basin as well as syn and post‐depositional processes. The sedimentary architecture of the late Quaternary lacustrine succession was examined by integrating 851 km of seismic reflection data from three surveys with gamma ray and velocity logs and the stratigraphic division from an ICDP borehole cored in 2010. This allowed seismic interpretation to be anchored in time across the entire basin. Key surfaces were mapped based on borehole lithology and a newly constructed synthetic seismogram. Average interval velocities were used to calculate isopach maps and spatial and temporal sedimentation rates. Results show that the Amora Formation was deposited in a pre‐existing graben bounded by two N‐S trending longitudinal faults. Both faults remained active during deposition of the late Pleistocene Samra and Lisan Formations—the eastern fault continued to bound the basin while the western fault remained blind. On‐going plate motion introduced a third longitudinal fault, increasing accommodation space westwards from the onset of deposition of the Samra Formation. During accumulation of these two formations, sedimentation rates were uniform over the lake and similar. High lake levels caused an increase in hydrostatic pressure. This led to salt withdrawal, which flowed to the south and southwest causing increased uplift of the Lisan and En Gedi diapirs and the formation of localized salt rim synclines. This induced local seismicity and slumping, resulting in an increased thickness of the Lisan succession within the lake relative to its margins. Sedimentation rates of the Holocene Ze'elim Fm were 4–5 times higher than before. The analysis presented here resolves central questions of spatial extent and timing of lithology, deposition rates and their variability across the basin, timing of faulting at and below the lake floor, and timing and extent of salt and plate tectonic phases and their effect on syn and post‐depositional processes. Plate tectonics dictated the structure of the basin, while salt tectonics and sediment accumulation were primarily responsible for its fill architecture during the timeframe examined here.

Internal deformation and uplift-rate of salt walls detected by a displaced dissolution surface, Dead Sea basin

Despite numerous studies examining salt tectonics, relatively little is known regarding the internal movements of salt units that build diapirs such as the Mount Sedom salt wall. In this study we focus on the recent deformation processes of southern Mount Sedom. We choose a fossilized dissolution surface known as the “salt mirror” of Mount Sedom as a structural datum, in order to understand and resolve the deformation processes during the last 14 ka. Surveying the salt mirror surface from outcrops and natural dissolution “chimney” caves, sets constraints for the structural map. Our results indicate that the salt wall rises as a telescopic antenna, with the internal salt units sliding across each other along bedding-plane slip faults, influenced by the subsiding Dead Sea basin. The flow of the rising salt forms an elongated ridge, distinctly asymmetric across its short dimension. The uplift rate of the Southern part of Mount Sedom throughout the last 14 ka is at least 11 mm/yr. This result is somewhat higher but in a fair agreement with the results of previous studies that assessed the rates in a variety of methods. The telescopic behavior of the salt wall represents a mode of internal deformation that might be applicable to other salt diapirs worldwide.

Mud volcanism by repeated roof collapse: 3D architecture and evolution of a mud volcano cluster offshore Nigeria

Abstract Using 3D seismic data, we document the subsurface architecture of a cluster of 3 mud volcanoes located on the upper continental slope offshore Nigeria. In a background of gently dipping stratified sediments, the subsurface of the cluster contains 8 seismic sequences made of one subcircular syncline, 1–3 km in diameter, and adjoining unstratified units. Synclines flatten out upward through intercalation of unstratified concave-up lenses between stratified units and are eventually filled by a convex-up unstratified lens onlapped by background sediments. The lower boundary of each sequence is a 0.5–1.5 km-deep bowl-shaped unconformity across which high-dip strata rest above truncated low-dip series. We interpret each seismic sequence as a mud volcano system (MVS) sourced from a connected region and evolving through episodes of roof collapse. Three are associated with the surface mud volcanoes and another 4 to fossil ones. Mud volcano systems are dynamic features that record the evolution of: 1) the material extruded from one single connected source region (depletion zone) as it grows downwards and stepwise becomes depleted; 2) the basal unconformity, which joins strata originally separated by material evacuated in the remobilization process; by analogy with salt tectonics, we propose to call it a “mud weld”; 3) the conduits; and 4) the successive collapsed roofs of the depletion zone. The evolution of each mud volcano system in this interpretation records progressive growth of the depletion zone by downbuilding, punctuated by episodes of roof collapse and extrusion. The geometry and evolution of this type of MVS can be interpreted in the light of analogue models of magmatic caldera development: in early stages, the thin roof experiences downsagging while remobilized material is extruded through an axial pipe-like conduit; in later stages the thickened roof undergoes piston-like subsidence, and mud extrusion occurs along the peripheral fault.

The Impact of Salt Tectonics on the Thermal Evolution and the Petroleum System of Confined Rift Basins: Insights from Basin Modeling of the Nordkapp Basin, Norwegian Barents Sea

Although the thermal effect of large salt tongues and allochthonous salt sheets in passive margins is described in the literature, little is known about the thermal effect of salt structures in confined rift basins where sub-vertical, closely spaced salt diapirs may affect the thermal evolution and petroleum system of the basin. In this study, we combine 2D structural restorations with thermal modeling to investigate the dynamic history of salt movement and its thermal effect in the Nordkapp Basin, a confined salt-bearing basin in the Norwegian Barents Sea. Two sections, one across the central sub-basin and another across the eastern sub-basin, are modeled. The central sub-basin shows deeply rooted, narrow and closely spaced diapirs, while the eastern sub-basin contains a shallower rooted, wide, isolated diapir. Variations through time in stratigraphy (source rocks), structures (salt diapirs and minibasins), and thermal boundary conditions (basal heat flow and sediment-water interface temperatures) are considered in the model. Present-day bottom hole temperatures and vitrinite data provide validation of the model. The modeling results in the eastern sub-basin show a strong but laterally limited thermal anomaly associated with the massive diapir, where temperatures in the diapir are 70 °C cooler than in the adjacent minibasins. In the central sub-basin, the thermal anomalies of closely-spaced diapirs mutually interfere and induce a combined anomaly that reduces the temperature in the minibasins by up to 50 °C with respect to the platform areas. Consequently, source rock maturation in the areas thermally affected by the diapirs is retarded, and the hydrocarbon generation window is expanded. Although subject to uncertainties in the model input parameters, these results demonstrate new exploration concepts (e.g., deep hydrocarbon kitchens) that are important for evaluating the prospectivity of the Nordkapp Basin and similar basins around the world.

Base‐salt relief controls salt‐tectonic structural style, São Paulo Plateau, Santos Basin, Brazil

AbstractBase‐salt relief influences salt flow, producing three‐dimensionally complex strains and multiphase deformation within the salt and its overburden. Understanding how base‐salt relief influences salt‐related deformation is important to correctly interpret salt basin kinematics and distribution of structural domains, which have important implications to understand the development of key petroleum system elements. The São Paulo Plateau, Santos Basin, Brazil is characterized by a >2 km thick, mechanically layered Aptian salt layer deposited above prominent base‐salt relief. We use 3D seismic reflection data, and physical and conceptual kinematic models to investigate how gravity‐driven translation above thick salt, underlain by complex base‐salt relief, generated a complex framework of salt structures and minibasins. We show that ramp‐syncline basins developed above and downdip of the main pre‐salt highs record c. 30 km of Late Cretaceous‐Paleocene basinward translation. As salt and overburden translated downdip, salt flux variations caused by the base‐salt relief resulted in non‐uniform motion of the cover, and the simultaneous development of extensional and contractional structures. Contraction preferentially occurred where salt flow locally decelerated, above landward‐dipping base‐salt and downdip of basinward‐dipping ramps. Extension occurred at the top of basinward‐dipping ramps and base‐salt plateaus, where salt flow locally accelerated. Where the base of the salt layer was broadly flat, structures evolved primarily by load‐driven passive diapirism. At the edge of or around smaller base‐salt highs, salt structures were affected by plan‐view rotation, shearing and divergent flow. The magnitude of translation (c. 30 km) and the style of salt‐related deformation observed on the São Paulo Plateau afford an improved kinematic model for the enigmatic Albian Gap, suggesting this structure formed by a combination of basinward salt expulsion and regional extension. These observations contribute to the long‐lived debate regarding the mechanisms of salt tectonics on the São Paulo Plateau, ultimately improving our general understanding of the effects of base‐salt relief on salt tectonics in other basins.

Salt tectonics in the Maknassy-Mezzouna region of Tunisia: Example of intrusive and extrusive Triassic evaporites in the central and Southern Atlas

In the North African Atlas, Triassic sedimentary rocks exhibit a variety of deformation styles that are caused by the interaction between halokinesis, tectonics and sedimentation. This paper aims to present an integrated study documenting the occurrence of salt-tectonic processes in the Maknassy-Mezzouna orogenic system. The interpretation of both, field mapping and seismic data suggests the existence of a complex tectonic evolution of these Triassic evaporites, with the occurrence of Mesozoic extensional/transtensional and Tertiary compressional/transpressional tectonic regime accompanied by sedimentary loading. This evolution took place along three major events of either lateral or vertical migration of Triassic evaporites. The first one is tectonic-driven and is related to the extensional/transtensional tectonic regime, which occurred during the break-up of Pangea and rifting of Neotethyan Ocean in the Early Jurassic. The second remobilization of salt Triassic rock developed during the Cretaceous. The initial mobilization of the Triassic salt was probably induced by sedimentary loading with a limited contribution of tectonic forces. During its third stage of evolution, salt Triassic rocks evolve into salt sheets due to the shortening deformation occurred during Tertiary and Quaternary in relationship with the closure of the Neotethyan realm. Salt migration controls subsidence, generates depocenter shifts and causes thickness variation of the entire post-Triassic sedimentary sequence. The signature of salt Triassic syn-sedimentary control is confirmed by thickness reduction and abrupt variation of structural dip that affects all the sedimentary pile in the flanks of salt sheets. In seismic sections the syn-sedimentary salt tectonic control is observed by geometries like pinching out, thickness reduction, onlap termination geometry as well as unconformities identified along the flanks of the salt sheets.

Structural Evolution and Halokinesis of Khaje Salt Diapir, North‒West of Iran

The northeastern part of the Tabriz, Khaje area has been studied to determine the relationship between the orientation of local structures and regional tectonics, and the influence of both on salt deformation. All the pre-Pliocene sedimentary rocks in the area belong to the Miocene Upper Red Formation. Sandstones form most of the outcrops because the other main components of the formation, marl and gypsum, are easily eroded and therefore recessive. The small thickness of sedimentary rock overlying the salt layer indicates that buoyancy of the salt was not the main factor causing diapirism. Folds related to the main faults of the region have been formed as result of the compressive tectonic forces. Two compressive stress systems have operated in the study area. In the first one, the direction of principal stress was NE‒SW and the resulting geological structures have an approximate E‒W trend. This stress system also controlled the salt tectonics in the region. The principal stress in the second system was oriented NW‒SE and is responsible for the most recent structures. The stress systems also caused rapid salt movement. The Khaje diapir is characterized by a series of salt walls trending NW‒SE that has been caused by the first stress system. This diapirism was principally the result of compressive tectonic stresses and faulting, particularly related to the North Tabriz Fault.