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Triassic evaporites represent the regional décollement of the Pyrenees and form two salt provinces north and south of the South Pyrenean Central Salient (SPCS). We present an updated Bouguer and residual Bouguer anomaly map built upon the homogenization of available gravity data of the SPCS together with four new and representative cross‐sections, constrained by geological data acquired in the field, seismic, well, and gravity data (gravity forward modeling). Gravity anomaly maps and cross‐sections are used to characterize the present‐day uneven distribution of Triassic evaporites. Outcropping Triassic evaporites is not necessarily associated with an underlying evaporite accumulation and the absence of it at surface does not involves its non‐existence at depth. Northwest of the salient, a major accumulation of Triassic evaporites floors a thick syn‐orogenic Upper Cretaceous basin. South of it, Triassic rocks core salt‐detached anticlines related to the Pyrenean orogeny. Along the southernmost (and youngest) thrust sheet of the salient, diapirs, and evaporite accumulations are associated with a salt‐inflated area. Plain Language Summary: Gravity depends on the density of the rocks under our feet. In the South Pyrenean Central Salient (SPCS), an accurate measurement of gravity allows us to recognize gravity anomalies related to low density rocks, such as the Middle‐Upper Triassic evaporites, and map their distribution. Among sedimentary rocks, evaporites have a particular behavior when deformed under geological forces: they flow. This characteristic determines a particular deformation style of the mountains. Characterize the present‐day distribution of Triassic evaporites helps to reconstruct the geological history of the SPCS. Despite the apparent asymmetry of the salient, Triassic evaporites are unevenly distributed and specially accumulated to the northwest and southwest conforming evaporite inflated areas. Key Points: Gravity anomalies help to assess the distribution of Triassic evaporites in the South Central Pyrenean SalientSeismically and gravity‐constrained sections permit a further interpretation of gravity anomaliesInflated salt occurs mainly to the northwest and southeast of the salient, along the northernmost and southernmost thrust sheets [ABSTRACT FROM AUTHOR]

The Ionian Zone (IZ) is one of the key elements of the fold and thrust belt (FTB) of the Albanian and Hellenides orogen and contains large outcrops of Triassic evaporites. The IZ consists of various thrust sheets with a general westward vergence, stacking over the Apulian and Pre‐Apulian zones, and repeating a thick carbonate sequence of Upper Triassic to Eocene age. Thrusting becomes younger toward the west with a piggyback sequence, starting during the latest Oligocene Epoch in the Internal Ionian and ending in the Pliocene in the External Ionian. We have studied the IZ in southern Albania and northwestern Greece using field observations and borehole data and by fully interpreting a recently acquired 2D seismic data set. Our objectives are to establish the geometry and nature of the contacts associated with the major Triassic outcrops, to unravel precursor salt diapirs, and to assess their role during the Alpine contraction. Salt structures include gentle salt pillows, isolated salt plugs and diapirs, thrust welds, and salt walls. Combining these observations with experimental modeling results, we show how these structures control the geometry and kinematics of the Alpine thrusts or the location and kinematics of recent strike‐slip faults. Salt minibasins have also been identified, demonstrating salt mobility conditioned Mesozoic sedimentation in the Ionian Basin. The use of salt‐tectonics principles to evaluate the structural style and evolution of the IZ FTB also opens new directions for interpreting the subsurface structure and evolution of the region. Key Points: The Ionian Zone in Greece and Albania is studied with surface geology, borehole data, and the interpretation of new seismic profilesTriassic salt pillows, isolated thick diapirs, and elongated salt walls condition the style of this Alpine fold and thrust beltThe role of pre‐existing diapirs is compared with experimental models [ABSTRACT FROM AUTHOR]

We present the first sequential structural restoration with flexural backstripping of the Gulf of Mexico US‐Mexico conjugate margin salt basin. We construct four large‐scale (100s of km) balanced, sequential structural restorations to investigate spatio‐temporal patterns of subsidence, geometry of the original salt basin, feedbacks between post‐salt structural and stratigraphic evolution, paleo‐bathymetry, and crustal configurations. The restorations are based on interpretations of 2D and 3D seismic data, and include sequential sedimentary decompaction, flexural isostatic backstripping, and thermal isostatic corrections. The spatially variable crustal thinning factor is directly measured from seismic data, and lithologic parameters are determined by well penetrations. We present a model for the original salt basin and discuss evidence for and implications of a deep water salt basin setting for the GoM. Our analysis suggests a salt basin that contained ∼1–2 km thick salt in a basin 175–390 km across with ∼1 km of bathymetry after salt deposition. The base of salt is mostly smooth with <1 km of local relief in the form of normal faults that disrupt a pre‐salt sedimentary section. We find that supra‐salt extension and shortening are not balanced, with measurable extension exceeding shortening by 18–30 km on each cross‐section. Our subsidence analysis reveals anomalous subsidence totaling 1–2 km during Late Jurassic and Early Cretaceous times that may reflect dynamic topography or depth‐dependent thinning. We offer an interpretation of crustal breakup invoking pre‐salt clastic sedimentation, salt deposition in a deep water syn‐thinning basin, and post‐salt lower‐crustal exhumation. Plain Language Summary: The Gulf of Mexico is a large basin that formed over 200 million years ago due to tectonically driven extension of a supercontinent. Early in its formation it accumulated thick salt deposits. Due to that salt and the later deposition of several kilometers of sedimentary rock that conceal the deep geology, it is difficult to know exactly how extension started and progressed. This study uses new 2D and 3D seismic data that images the deep geology corresponding to that early extension. We sequentially remove each rock layer to reconstruct what the margin looked like in the Mesozoic. By systematically moving back in time we are able to reconstruct the changing geometry, deformation, and bathymetry of the Gulf of Mexico. Our results reveal periods of time when the bathymetry was influenced by unknown factors, which we posit reflects mantle forces. Key Points: We present sequential structural restorations with flexural backstripping of the post‐rift eastern GoM conjugate US‐MX margin from Mesozoic to presentWe interpret the geometry and bathymetry of the restored Mesozoic salt basinOur analysis indicates significant and widespread Mesozoic anomalous subsidence [ABSTRACT FROM AUTHOR]

Recognizing salt‐related structures and differentiating them from tectonic shortening‐related anticlines and synclines can be a very challenging task in salt‐bearing fold‐and‐thrust belts, especially in poor outcrop conditions. In this study, we explain several diagnostic structural and sedimentary features that may be used to distinguish pre‐orogenic halokinetic structures from shortening‐related structures on the example of the Silica Nappe (Inner Western Carpathians, Central Europe). Detailed structural mapping in this area resulted in the recognition of several pre‐orogenic salt‐related structures, including linear salt walls and minibasins. Initial evaporite movement started as early as the late Early Triassic, and widespread diapirism occurred during the Middle to Late Triassic, ultimately leading to facies differentiation, with carbonate platform growth in the subsiding minibasins and reduced basinal deposition on top of the diapirs. Later, the inherited salt structures localized the deformation during the Cretaceous Alpine orogeny, and exerted a strong control on the geometry and kinematics of the subsequent deformations. Our new interpretation explains previously unsolved structural problems in the Silica Nappe, like pre‐orogenic thickness variations during the post‐rift phase, frequent young‐on‐older type thrust contacts and multiple folding directions with variable vergencies. The results point out that the Silica Nappe is a fold‐and‐thrust belt, where pre‐orogenic salt tectonics and its effects on the fold‐and‐thrust belt evolution can be studied in detail. Key Points: Structural mapping resulted in the first recognition of pre‐orogenic salt structures in the Western CarpathiansTriassic syn‐sedimentary evaporite deformation led to minibasin formation, variations in formation thickness and facies differentiationThe results provide guidelines on how to distinguish inherited salt structures from shortening‐related structures in fold‐and‐thrust belts [ABSTRACT FROM AUTHOR]

Reinterpretation of the Organyà Basin, based on new detailed field observations and subsurface data, emphasizes the key contribution of Upper Triassic evaporites in the tectono‐sedimentary evolution of the South‐Central Pyrenees. Results are integrated in a 65‐km long restored cross‐section through the Serres Marginals, Montsec and eastern Organyà salt‐related depocenters. The reconstructed part of the Jurassic–Cretaceous northern Iberian salt‐rich rifted margin shows a template characterized by inherited Permo‐Triassic basement normal faults and an initial salt thickness of 0.7 km to the south and 1.5 km to the north. The Organyà Basin is part of the South Pyrenean Diapiric Province, a large system of salt related depocenters and minibasins, that is limited to the north by the more than 120‐km long Senterada salt wall complex separating the supra‐salt and sub‐salt domains in the Southern Pyrenees. Three main stages of diapiric activity are recognized along the northern Iberian margin from Asturias to the Eastern Pyrenees: a Jurassic early salt mobilization; a latest Jurassic–middle Albian main diapiric evolution associated with rifting; and a Campanian–Miocene diapiric reactivation during basin inversion that produced salt welds and thrust welds and translated the salt province some 60 km to the south. Key Points: Reinterpretation of the Organyà Basin indicates occurrence of a large and continuous salt tectonics province in the South‐Central PyreneesLate Jurassic early salt mobilization followed by Early Cretaceous passive diapirism and diapir reactivation from late CampanianThe restored 65 km wide salt‐bearing passive margin indicates asymmetrical Iberia‐Eurasia conjugate margins [ABSTRACT FROM AUTHOR]

Analog modeling is used to study the role played by the inherited salt‐sediment architecture of a salt‐bearing rifted margin, developed by minibasin downbuilding and margin‐scale gliding, and then incorporated into a fold‐and‐thrust belt system influenced by surface processes. Inherited salt bodies localize contractional deformation at different scales and the salt‐sediment architecture determines structural styles of fold‐and‐thrust belts. In our analog models, a large‐transport thrust detached along allochthonous model salt (silicone polymer) accumulated in a former distal raft system. And the squeezing of salt walls, together with the tilting of minibasins, accounted for most of the shortening in a salt wall‐minibasin province. Shortening and surface processes promote the extrusion and erosion of about 75% of the original model salt. The role played by salt tectonics during the contraction of salt‐bearing rifted margins could be underestimated because of the low salt‐sediment ratio found in fold‐and‐thrust belts. Our modeling results are compared with and assist in the interpretation of a section along the Northern Calcareous Alps. Key Points: Salt distribution determines the evolution and architecture of a salt‐bearing rifted margin incorporated into a fold‐and‐thrust belt systemSalt extrusion and erosion lead to an underestimation of the original amount of salt which may compromise structural restorationsAnalog modeling results support the salt‐influenced evolutionary model for the Northern Calcareous Alps [ABSTRACT FROM AUTHOR]

Rifted margins are often associated with widespread and thick evaporite (salt) deposits and pronounced salt tectonics. The largest salt basins formed during the latest stages of rifting, immediately prior to continental breakup. Salt tectonics along these rifted margins commonly exhibit structural domains characterized by gravity‐driven updip extension, translation, downdip shortening, and salt nappe advance. The precise spatial and temporal links between these structural processes, their relative contributions and dynamics are still a topic of debate on many margins. We use 2D thermo‐mechanically coupled finite‐element modeling of lithospheric extension to investigate the evolution of salt tectonics along wide rifted margins and the interplay between rifting and post‐rift deformation. The models integrate lithospheric extension with post‐rift salt tectonics using a geodynamically self‐consistent approach where the geometries of the lithosphere and salt basins are not prescribed. They confirm that wide salt‐bearing rifted margins are characterized by gravity‐driven updip extension and downdip shortening, but also that syn‐depositional salt flow and salt stretching occurs in their distal portions prior to and during continental breakup. This produces widening of the basin and emplacement of a salt nappe over newly formed oceanic crust. Post‐rift updip extension is mostly balanced by downdip diapir shortening, all related to Couette flow. The salt nappe initiated by late syn‐rift stretching advances further by post‐rift pressure‐driven Poiseuille salt flow so that its final width is a product of both processes. The results can be directly compared to examples from various salt‐bearing rifted margins and improve our understanding of their enigmatic genesis and evolution. Plain Language Summary: Rifting of the continental lithosphere may lead to continental breakup and formation of passive margins. These margins often exhibit thick rock‐salt deposits which are deposited in hypersaline basins, and which deform in a ductile, flow‐like manner, developing highly complex tectonic structures. Salt deformation in these settings is commonly characterized by linked domains of updip extension, translation, downdip shortening and distal salt advance. However, the precise spatial and temporal links between these processes and their contribution to the overall salt flow are still a topic of debate. In this paper, we use 2D thermo‐mechanical numerical models to explore how these salt basins develop and their interplay with continental rifting. The models show that typical, wide margin salt basins are characterized by broadly balanced post‐rift updip extension and downdip shortening, but that the salt starts to deform during its deposition due to ongoing continental rifting in the distal margin. This stretches the distal salt and emplaces an allochthonous salt sheet over newly‐formed oceanic crust, which is later amplified sediment‐load‐driven salt flow. These results can be directly compared to examples from various salt‐bearing margins and improve our understanding of their enigmatic genesis and evolution. Key Points: Geodynamic numerical models of lithosphere extension and post‐rift salt tectonics quantify different types of salt flow on rifted marginsThe models show that updip extension balances largely with downdip diapir shortening, but salt nappe advance is mostly unrelated to theseSalt nappes form by late syn‐rift salt stretching and post‐rift pressure‐driven salt flow and are largely disconnected from updip extension [ABSTRACT FROM AUTHOR]

The relative timing between crustal extension and salt deposition can vary spatially along passive margin salt basins as continents unzip, or as the locus of extension shifts toward the embryonic ocean spreading center. Determining the relative timing of salt deposition, rifting, and seafloor spreading is often problematic due to the diachronous nature of rifting, the ability of salt to fill pre‐existing topography, and the subsequent flow and deformation of that salt. We here use 2D PSDM seismic data and structural restorations to investigate the Merluza Graben, a large rift‐related depocentre located in the southern, most proximal part of the Santos Basin, Brazil, along‐strike of a failed spreading center, the Abimael Ridge. The graben is defined by up to 3.5 km of base‐salt relief along its basinward‐bounding fault and internal base‐salt horsts that are up to 1 km high. This compartmentalizes deformation, producing intra‐graben extensional and contraction salt structures, ramp‐syncline basins, and expulsion rollovers, resulting in a remarkably different salt‐tectonic structural style to that seen in the adjacent areas. We also conduct structural restorations to analyze the spatial and temporal evolution of salt‐tectonic structural styles and the relationship this has to potential prolonged crustal extension in the Merluza Graben. This approach further constrains local variations in the relative timing of rifting and salt deposition, and the impact this has on salt tectonics along the margin. The results of our study can be applied to better understand the tectono‐stratigraphic development of other salt‐bearing rifted margins. Key Points: The Merluza Graben is a large rift depocentre located in the proximal part of the Santos Basin, connected to a failed spreading centerThe graben compartmentalizes salt deformation producing extensional and contraction structures, ramp‐syncline basins and rolloversRestorations and discrepancies in salt area indicate that the Merluza Graben and related sub‐salt faults were active after salt deposition [ABSTRACT FROM AUTHOR]

Despite 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. Key Points: Ramp syncline basins offshore Lebanon are excellent records of translation on a salt‐influenced passive margin dominated by gravity‐glidingRates of basinward translation are approximately uniform at the km‐scale but show significant lateral variability at the margin‐scaleDifferential translation rates are predominantly controlled by "pulses" of salt flow, as well as the mechanics of the overburden [ABSTRACT FROM AUTHOR]

In salt‐detached fold‐and‐thrust belts, contractional modification of salt structures may include decapitation by thrusting, but examples are not well known in the subsurface and undocumented in outcrop. Here we present a surface exposure of an intrasalt, sub‐horizontal shear zone at the boundary between the Tarcău and Subcarpathian nappes in the Romanian Eastern Carpathians. The Mânzălești diapir forms the largest rock salt outcrop in Europe, with unique salt‐karst geomorphology. Numerous wells show that the outcrop is above deep‐seated salt of a precursor salt‐cored anticline or passive diapir whose base is at >3,500 m. Multiscale observations using UAV‐based digital outcrop models, fieldwork, and microstructure analysis show that the outcrop is characterized by sub‐horizontal foliation with isoclinal folds, unlike the subvertical fabric of most Romanian diapirs. The halite is rich in clastic inclusions, with a power‐law size distribution caused by tectonic reworking of originally impure salt. Microstructures show that the halite matrix is strongly deformed by dislocation creep, forming subgrains and dynamically recrystallized grains around large porphyroclasts with piezometry indicating relatively high differential stress of around 4 MPa, at pressures sufficient to suppress dilatancy. The observations are best explained by sub‐horizontal shear generated by an overriding nappe, overprinting an original coarse‐grained salt fabric during decapitation of the salt body. Plain Language Summary: In this study, we present the results of a new geological study of a massive salt body called "Mânzălești", located in the Romanian Carpathians mountain chain. The salt body is about 2.7 km by 1.3 km wide at the surface (with about 200 m of relief) and extends downward for about 3.5 km. It represents the largest rock salt exposure in Europe. It also hosts some of the longest salt cave systems in Europe and the world. At the surface, the salt presents internal sub‐horizontal folds and sub‐horizontal layering which seemed rather unusual, as other salt bodies in Romania have sub‐vertical folds or layers. Multiscale observations using drone‐based three‐dimensional digital outcrop models, fieldwork, and microscope analysis of salt samples have been used to decipher the nature of these structures. We conclude they formed due to decapitation of the deep‐seated salt structure (removal of its top part) due to shearing during the advance of the eastward propagating large sheetlike body of rock (called Tarcău nappe) during the mountain building process Key Points: The Mânzălești salt diapir is characterized by intensely folded, low‐dipping salt foliationsForeland‐directed movement of the nappe decapitated the salt body, shearing its upper portion at a shallow depth and fast strain ratesThis shear zone, exposed by uplift and erosion, forms the present‐day outcrop [ABSTRACT FROM AUTHOR]

We investigate the present‐day orogenic architecture of the Pyrenean‐Cantabrian junction corresponding to a boundary between inverted rift segments using seismic interpretation, field data, and borehole information. This junction was formerly attributed to a major NNE‐SSW striking Pamplona transfer fault segmenting the Basque‐Cantabrian and Mauléon basins during both rifting and convergence. Our study shows that the orogenic architecture results from a strong decoupling between the thick‐skinned (basement‐involved) and the thin‐skinned (detached in the Upper Triassic evaporites) modes of deformation. The evaporites decoupling horizon was responsible for the transport and allochthony of the former rift basins over large distances on top of the Basque massifs and the Ebro and Aquitaine foreland basins. A crustal‐scale cross‐section depicts the allochthony of the Basque massifs forming a crustal wedge over the crusts of Iberian, Ebro, and Eurasian affinity. Three‐dimensional analysis of the present‐day architecture suggests that two phases of rifting and related basins can be recognized: the Late Jurassic‐Barremian and the Aptian‐Cenomanian basins. Furthermore, we show that during the Aptian‐Cenomanian, the Mauléon and Basque‐Cantabrian rift segments spatially overlapped north and south of the Basque massifs and were controlled by WNW‐ESE striking extensional faults. These results discard the existence of a major Pamplona transfer fault and argue for NNE‐SSW direction of extension during the mid‐Cretaceous. This study emphasizes the role of inheritance during rifting and reactivation and provides a new syn‐rift template, which controlled the Alpine reactivation. Finally, these results have major implications for the Iberia‐Eurasia plate boundary and the kinematics of the North Pyrenean basins. Key Points: The orogenic architecture of the Pyrenean‐Cantabrian junction results from decoupled thin‐skinned and thick‐skinned modes of deformationThe Aptian‐Cenomanian rift segments spatially overlapped north and south of the Basque massifsThe Aptian‐Cenomanian rift architecture argues against a major Pamplona transfer fault [ABSTRACT FROM AUTHOR]

At present, salt tectonics in the Levant Basin comprises extension along the continental slope and folding and thrusting in the deep basin. However, here we show that the shape, the age, and the amplitude of deformation in the extensional and contractional domains do not fit the paradigm of "updip extension and downdip contraction." Deep basin shortening is not parallel to continental margin extension; it is younger and stronger. We propose that while extension of the Levant continental slope is an expression of basinward gliding, the deep basin shortening belongs to the circum‐Nile deformation belt (CNDB) propelled by out‐squeezing of salt from under the Nile delta. However, despite the independent driving forces, the two deformation systems seem to affect each other. In the southern part of the basin where the two systems meet, the NW gliding of the continental slope is restrained by the NE motion of the CNDB and vice versa. Interestingly, the beginning of folding along the CNDB (~2 Ma) coincides with the establishment of a continental shelf offshore Israel. We thus propose that these two apparently independent phenomena express maturity of the Nile delta that had reached a size and shape sufficient to trigger salt out‐squeezing and to form a continuous continental shelf from the Nile to Israel. This continuity allowed shelf alongshore sediment transport that further propagated the Israeli shelf northward and westward. Key Points: The salt tectonics paradigm of "updip extension and downdip contraction" doesn't fit the thin‐skinned deformation in the Levant BasinSlope extension is caused by basinward tilting, while deep basin shortening is caused by salt out‐squeezing from under the Nile deltaInitiation of a continental shelf offshore Israel coevally with deep basin folding suggests a common origin of Nile delta maturity [ABSTRACT FROM AUTHOR]

In this study, we investigate the regional tectonic impact on salt movement at the northeastern margin of the intracontinental North German Basin. We discuss the evolution of salt pillows in the Bay of Mecklenburg in the light of thick‐ and thin‐skinned tectonics, including gravity gliding, and differential loading using seismic imaging. Stratigraphic and structural interpretation of a 170 km long, multichannel seismic line, extending from the Bay of Mecklenburg to northeast of Rügen Island, incorporates well information of nearby onshore wells. This new high‐resolution seismic line completely images the stratigraphic and tectonic pattern of the subsurface, from the base of the Zechstein to the seafloor. Our analysis reveals that subsidence during Late Triassic to Early Cretaceous at the northeastern basin margin was associated with transtensional dextral strike slip movement within the Trans‐European Suture Zone. We reinterpret the Werre and Prerow Fault Zones west of Rügen Island as an inverted, thin‐skinned normal fault system associated with the formation of the Western Pomeranian Fault System. Salt movement in the Bay of Mecklenburg was initiated in the Late Triassic and lasted until the Early Jurassic. A second phase of salt pillow growth occurred during the Coniacian until Cenozoic and correlates with compression‐related regional basin inversion due to the onset of the Africa‐Iberia‐Europe convergence. Thin‐skinned extensional initialization of salt pillow growth and compressional salt remobilization explains salt pillow evolution in the Bay of Mecklenburg. Additionally, we discuss an impact of gravity gliding on salt pillow evolution induced by basin margin tilt. Key Points: A regional high‐resolution seismic profile continuously images the SW Baltic Sea subsurface from the Zechstein salt base to the seafloorLate Triassic salt movement and Late Cretaceous‐Cenozoic remobilization correlate with regional tectonics at the North German Basin marginThe tectonic evolution of salt pillows is discussed in terms of thin‐skinned extensional/compressional deformation and gravity gliding [ABSTRACT FROM AUTHOR]

Surface, seismic, and borehole data characterize the Neogene‐Recent Tajik fold‐and‐thrust belt of the Tajik basin. The basin experienced little sub‐detachment basement deformation, acting as a rigid foreland plate during the Pamir orogeny. The Tajik fold‐and‐thrust belt contains variable thin‐skinned structural styles, changing along and across strike as a function of the thickness and facies of Upper Jurassic evaporites, which constitute the basal detachment, and the influence of the surrounding thick‐skinned belts. The southern Tajik fold‐and‐thrust belt shows regularly spaced, salt‐cored, thrusted detachment anticlines that transition northward into imbricated thrust sheets grouped in oppositely verging stacks facing each other across a common footwall syncline. The width of the fold‐and‐thrust belt decreases northeastward accommodated by the Ilyak fault, a lateral ramp developed over a seismically active dextral basement fault. The southeastern Tajik fold‐and‐thrust belt contains massive subaerial salt sheets, formed by squeezing of preexisting salt diapirs. The salt‐tectonic domain originates from a local depocenter within the Late Jurassic Amu Darya‐Tajik evaporitic basin. Serial cross sections, integrating the structural geometries, yielded minimum thin‐skinned shortening oriented at ~90° to the India‐Asia convergence direction, increasing from ~93 km in the south to ~148 km in the center, and dropping to ~22 km in the northeast; total shortening—including the foreland buttress—is ≥170 km. Most of the shortening in the central‐southern Tajik fold‐and‐thrust belt occurred by hinterland‐vergent, high‐displacement back thrusts. The Pamir played a dominant role in the transfer of shortening to the sedimentary infill of the Tajik basin with the Tian Shan acting as a semi‐passive buttress. Key Points: Surface, seismic, and borehole data show ≥150‐km, thin‐skinned Tajik‐basin shortening at ~90° to the India‐Asia convergence directionStructural geometries vary due to the buttressing by the surrounding thick‐skinned belts and variable Jurassic salt thickness and faciesStructures include flat‐ramp thrust sheets, piggy‐back and break‐back thrusts, faulted detachment folds, salt sheets, and squeezed diapirs [ABSTRACT FROM AUTHOR]

The 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. Key Points: The Nappe des Marbres Unit shows structures related to a preserved hyperextended basin, reactivated during later inversionTemperatures related to the HT‐LP Pyrenean metamorphism show some of the highest values of the entire belt, postdating early salt tectonicsThese results show that there is no large‐scale maximum temperature gradient along the Internal Metamorphic Zone (IMZ) across the Pyrenean belt contrasting with previous assumptions [ABSTRACT FROM AUTHOR]

Gravity‐driven salt tectonics along passive margins is commonly depicted as comprising domains of updip extension and downdip contraction linked by an intermediate, broadly undeformed zone of translation. This study expands on recently published physical models using discrete‐element modeling to demonstrate how salt‐related translation over pre‐salt rift structures produce complex deformation and distribution of structural styles in translational salt provinces. Rift geometries defined by horsts and tilted fault‐blocks generate base‐salt relief affecting salt flow, diapirism and overburden deformation. Models show how flow across pairs of tilted fault‐blocks and variably‐dipping base‐salt ramps associated with pre‐salt faults and footwalls produce abrupt flux variations that result in alternation of contractional and extensional domains. Translation over tilted fault‐blocks defined by basinward‐dipping normal faults results in wide, low amplitude inflation zones above footwalls and abrupt subsidence over steep fault‐scarps, with reactive diapirs that are squeezed and extrude salt as they move over the fault. Translation over tilted‐blocks defined by landward‐dipping faults produces narrow inflation zones over steep fault‐scarps and overall greater contraction and less diapirism. As salt and cover move downdip, structures translate over different structural domains, being inverted and/or growing asymmetrically. Our models allow, for the first time, a detailed evolution of these systems in cross‐section and demonstrate the effects of variable pre‐salt relief, salt sub‐basin connectivity, width and slope of base‐salt ramps. Results are applicable to syn‐ and post‐rift salt basins; ultimately improving understanding of the effects of base‐salt relief on salt tectonics and working as a guide for interpretation of complex salt deformation. Key Points: Pre‐salt rift structures (horst and tilted blocks) generate base‐salt relief acting as a major control on salt deformationVariable base‐salt slope, step height and connectivity between salt sub‐basins affect the kinematics of salt‐related deformationModels present cross‐sectional evolution related to complex structural distribution related to salt flux variations over base‐salt relief [ABSTRACT FROM AUTHOR]

Abstract: Eastern Iberia preserves a complex succession of Mesozoic rifts partly or completely inverted during the Late Cretaceous and Cenozoic in relation with Africa‐Eurasia convergence. Notably, the Valencia Trough, classically viewed as part of the Cenozoic West Mediterranean basins, preserves in its southwestern part a thick Mesozoic succession (locally ≈10 km thick) over a highly thinned continental basement (locally only ≈3.5 km thick). This subbasin, referred to as the Columbrets Basin, represents a Late Jurassic‐Early Cretaceous hyperextended rift basin weakly overprinted by subsequent events. Its initial configuration is well preserved allowing us to unravel its 3‐D architecture and tectonostratigraphic evolution in the frame of the Mesozoic evolution of eastern Iberia. The Columbrets Basin benefits from an extensive data set combining high‐resolution seismic reflection profiles, drill holes, seismic refraction data, and expanding spread profiles. The interactions between halokinesis, involving the Upper Triassic salt, and extensional deformation controlled the architecture of the Mesozoic basin. The thick uppermost Triassic to Cretaceous succession displays a large‐scale “syncline” shape, progressively stretched and dismembered toward the basin borders. We propose that the SE border of the basin is characterized by a large extensional detachment fault acting at crustal scale and interacting locally with the Upper Triassic décollement. This extensional structure accommodates the exhumation of the continental basement and part of the crustal thinning. Eventually, our results highlight the complex interaction between extreme crustal thinning and occurrence of a prerift salt level for the deformation style and tectonostratigraphic evolution of hyperextended rift basins. [ABSTRACT FROM AUTHOR]

The extensional period in the Bay of Biscay-Pyrenean domain during the Early Cretaceous influenced subsequent Upper Cretaceous contractional Alpine structures of the Pyrenean orogen. In the Pyrenees, the Lower Cretaceous rift system shows en echelon geometries for different basins, with the Organyà Basin being one of the most important. This basin is located in the southern central Pyrenees, and the inversion of its W-E southern margin has been related to the development of the Bóixols thrust sheet, the northernmost of the south Pyrenean thrust sheets. Detailed interpretation of outcrop and seismic reflection data has revealed the presence of a NNW-SSE trending relay area, which corresponds to the western boundary of the Organyà Basin. The postrift facies belts parallel this boundary. The geometry of the contractional structures shows related variations such as changes in the structural relief and the plunge and the wavelength across this relay area. The synorogenic sediments also show characteristic thickness variations and onlap geometries perpendicular to thrust-transport direction. These evidences highlight the presence of this extensional margin and corroborate its influence in the subsequent stages of the evolution of the area. Seismic, well, and field data have been incorporated into a 3-D structural model in order to better understand the 3-D geometry of the study area. [ABSTRACT FROM AUTHOR]

A methodology is presented to model coupled fluid flow and deformation in rifted continental margin composite salt and siliciclastic tectonic systems; and we investigate their compaction and overpressuring behavior associated with continental margin-scale gravitational spreading. Compaction-driven Darcy fluid flow in clastic sediments is coupled through the effective pressure to their frictional-plastic yielding and mechanical deformation. Viscous flow of underlying salt is independent of fluid pressure. Numerical models are adapted to the Oligo-Miocene phase of large-scale gravitational failure in the northwestern Gulf of Mexico, and represent the first study of this system that includes dynamically evolving fluid pressure. Here we present the methodology and prototype models with single uniform sediment lithologies and simple parameterizations of their properties. The models serve to illustrate the interactions among compaction, generation of fluid overpressure, and gravitational failure and spreading. Mechanical and viscous compaction behavior of sandstone-type and shale-type sediments are investigated. Results demonstrate that mechanical compaction can generate moderate overpressure in thick shale-type material, whereas high overpressure requires viscous compaction. In sandstone-type material, only viscous compaction can generate significant overpressure, though this requires tens of millions of years. Changes in the stress regime during gravitational-driven deformation enhance compaction and overpressure. Although illustrative of the methodology and basic processes, none of the prototype single-lithology models satisfactorily reproduces Oligo-Miocene fluid pressure and deformational regimes of the Gulf of Mexico. Numerical models of layered sediments together with an improved formulation of viscous compaction, presented in part 2 of this set of companion papers, are more successful. [ABSTRACT FROM AUTHOR]

In paper 1 we described a methodology to model coupled fluid flow and deformation in composite salt and siliciclastic tectonic systems and investigated their compaction and overpressuring behavior prior to and during continental margin-scale gravitational spreading. Compaction-driven Darcy fluid flow in clastic sediments is coupled through the effective pressure to their frictional-plastic yield and mechanical deformation. Viscous flow of the underlying salt is independent of fluid pressure. Paper 1 presented prototype models that are limited to single uniform sediment lithologies, either sandstone-type or shale-type, that undergo mechanical and volumetric viscous compaction. In this paper we present models with layered sandstone-type and shale-type lithologies designed to better approximate the more complex stratigraphy of the Gulf of Mexico, our natural example. A first set of models demonstrates that layered lithologies can produce fluid pressure regimes similar to those observed in sedimentary basins. We then introduce an improved formulation of viscous compaction that includes a stronger dependence on porosity and depth (used as proxy for temperature), thereby more effectively self-limiting viscous compaction. A second set of models with the improved viscous compaction formulation demonstrates that the onset of gravity spreading is mainly controlled by overpressuring in the landward end of the salt basin and that resulting shortening in the distal part is partly accommodated by horizontal compaction. Models with moderately high fluid pressure best reproduce conditions considered to have been necessary for large-scale gravitational spreading in the northwestern Gulf of Mexico, which led to the formation of the Perdido Fold Belt. [ABSTRACT FROM AUTHOR]

Having established the first-order controls of the three primary salt tectonic structural styles of the Scotian Basin in paper 1, in this paper (paper 2) we investigate and show that many unexplained structures can be attributed to more complex initial geometries of the autochthonous salt basins than the simple rectangular shapes used in paper 1. Basement highs modify and reduce the efficiency of salt evacuation during sediment aggradation followed by progradation. Low-angle taper (∼3°) of the basin edge slows Poiseuille flow and allows for trapping of salt beneath distal salt sheets. Seaward basement step ups do not necessarily hinder salt flow, and basement step downs can localize diapirs. Midbasin salt sheets can emerge when basement blocks as high as the salt is thick divide a basin into two subbasins. Deep salt basins that form above basement lows are efficiently evacuated. Weak overburden sediments augment the formation of salt sheets. [ABSTRACT FROM AUTHOR]

Three primary salt tectonic structural styles of the Scotian Basin are compared with plane strain finite element models in order to investigate their origin. Here, we focus on simplified model salt basins with initial rectangular cross-sectional geometries and follow their evolution in the context of tectonic and parametric thermal subsidence and under various sedimentation regimes. Structural style A, an open-ended roho system with a synkinematic wedge, is reproduced by models including deltaic progradation and seaward spreading/gliding of sediments above a salt detachment. Structural style B, a linked salt tectonic system with landward regional normal faults and allochthonous salt sheets climbing seaward over Late Cretaceous and Paleogene strata, is shown to be a consequence of early aggradation followed by progradation. Structural style C is characterized by salt diapirs and intervening minibasins and is reproduced by models with Rayleigh-Taylor instabilities requiring compaction driven density inversions, weak sediments, and initial perturbations of the overburden-salt interface. [ABSTRACT FROM AUTHOR]

The Zagros Mountains result from the ongoing collision between the Arabian and central Iran plates. The main features of the eastern Zagros are (1) numerous emerged or buried salt diapirs, made up of Late Precambrian Hormuz salt and (2) the irregular along-strike shape of the collision-related detachment folds with frequent bending. To understand this layout, four geological cross sections have been constructed from the Persian Gulf foreland basin to the inner part of the Zagros Fold-and-Thrust Belt. Shortening in the deformed parts of the sections is less than 10% and is mainly accommodated by detachment folding. We show that late Cenozoic folding occurred in a region that was already punctuated by salt domes and diapirs. In fact, almost continuous halokinesis developed since the earlier Paleozoic, i.e., just short time after the deposition of the Hormuz salt, and continued up to the Present. These preexisting salt structures and their relevant local thickening strongly influenced both the localization and the direction of folds. [ABSTRACT FROM AUTHOR]

The Perdido Fold Belt (PFB) is a prominent salt-cored deep water structure in the northwestern Gulf of Mexico. It is characterized by symmetric, kink-banded folds of a ∼4.5 km thick prekinematic layer and its vicinity to the extensive Sigsbee Salt Canopy. We use 2-D finite element numerical models to study the evolution of the PFB as a gravity-driven fold belt both in a local context and in the context of the larger-scale passive margin, influenced by adjacent allochthonous salt structures. We show that parameters such as overburden strength, salt geometry, or salt viscosity determine timing, extent, and location of the modeled fold belt. Simplified models of the Gulf of Mexico show that toe-of-slope folding is a viable mechanism to develop diapirs in the deep salt basin and to delay folding of the distal overburden. In this scenario, the PFB likely represents the terminal folding of a much larger, diachronously formed fold belt system. [ABSTRACT FROM AUTHOR]

We explore exhumation in the coastal Kwanza Basin by combining analyses of Tertiary hiatuses and apatite fission tracks. Planktonic biozones show five major hiatuses in the Oligo-Miocene and Plio-Pleistocene. Between gaps, Oligo-Miocene strata accumulated under marine conditions. A marine setting refutes the idea of a massively raised coastal plateau in the mid-Tertiary. Marine conditions continued until ∼5 Ma. Fission track data suggest three thermal events: ∼150 Ma, during rifting and volcanism; ∼100-70 Ma, during shortening and volcanism; and ∼20-10 Ma, during exhumation. Tertiary uplift was spatially highly variable. For the Kwanza Basin, we infer that Tertiary uplift on the West African margin is indeed a fact but that estimates of uplift timing and size are unreliable when extrapolated to adjoining areas. Massive uplift (2000-4000 m) of the Precambrian craton had little structural effect in the outer basin. Instead, minor uplifts on the shelf drove late Tertiary deformation on the slope. [ABSTRACT FROM AUTHOR]

Since 90 Ma, the nonmarine Salar de Atacama Basin has been the largest, deepest, and most persistent sedimentary basin of northern Chile. Integration of 200 km of two-dimensional seismic reflection data with surface geological data clarifies Oligocene and Neogene evolution of the northern part of the basin. A normal fault with 6 ± 1 km of vertical separation controlled the western boundary of the basin during the accumulation of the Oligocene-lower Miocene Paciencia Group. The combination of this structure, a similar one in the Calama Basin, and regional structural data suggests that localized extension played an important role within a tectonic environment dominated by margin-perpendicular compression and margin-parallel strike-slip deformation. Seismic data substantiate the surface interpretation that much of the Cordillera de la Sal ridge resulted from diapiric flow of the Paciencia Group. Diapiric flow initiated during the late early Miocene or middle Miocene, associated with a deep reverse fault. [ABSTRACT FROM AUTHOR]

Diapirism in the La Popa basin NE Mexico was triggered and sustained by compressional décollement tectonics. Coeval development of contractional structures and diapirs was recorded by growth strata of Late Cretaceous-Tertiary age. A palinspastic reconstruction of a regional cross section, based on the restoration of growth strata related to both diapirs and detachment folds, was carried out. On the basis of this reconstruction and field data, a three-dimensional geometrical study was done to quantify the movement of evaporites within the detachment horizon and two diapirs. The latter allowed determining the tectonodiapiric potential of a structure or set of structures (i.e., the amount of ductile rocks forced to flow in association with the growth of a tectonic structure, which is not accommodated by thickening of the ductile horizon nor by the tectonic structure itself, and is capable of producing diapiric phenomena). This study demonstrates that there is a direct coupling between tectonodiapiric potential and diapiric activity. Geometrical results show that the main factors that controlled the amount of ductile material moved as a consequence of compressional tectonics were shortening, the depth to detachment, the folding style, and the style of deformation process (i.e., pure shear/simple shear). In response to folding, the overburden experienced a downward movement that was the major cause of diapiric phenomena. In addition to field and geometrical data, mechanical data indicate that forceful intrusion was the prevailing emplacement mechanism. Temperatures (>150°-197°C) and strain rates (in the order of 10−16-10−17 s−1) calculated for top of the evaporite layer were adequate for the flow of these rocks from the initiation of compression onward. However, an inferred overpressure in the ductile layer should be considered the key factor for the emplacement mechanism. [ABSTRACT FROM AUTHOR]

The relations between detachment folding, fold amplification, and salt diapirism in contractional settings have been investigated by means of scaled analogue models. The viscosity of the silicone layer simulating salt in nature and the shortening rates were combined in order to reproduce weak (type 1 models) and strong (type 2 models) décollements. Deformation patterns in the roof sequence exhibited two contrasting styles, (1) outward propagation of detachment folding along the décollement (OFP mode) and (2) passive roof duplex (PRD mode). In type 2 models, detachment folding propagated away from the most external thrust in the floor sequence, while in type 1 models, long-lived detachment folds almost invariably localized amplified above a floor thrust tip as a result of strain localization. A silicone wall intruded occasionally into the crestal graben of detachment folds in type 1 and OFP models. Best fitting of transition models data points indicates nonlinear relations with regression curves close to the equilateral hyperbola equation for both OFP-PRD and amplified detachment folds-box folds transitions. A quantitative comparison of model results with nature has been attempted by plotting salt-based fold-and-thrust belts data points on the scaled transition curves obtained from the modeling. Such a comparison relates shear stress products and ratios to the conditions favoring the amplification of detachment folds and the potential emplacement of ductile diapirs in their core. By reducing the roof sequence strength, pore fluid pressure λb is inferred to shift the equilibrium of fold-and-thrust belts toward the field of OFP and diapirism. [ABSTRACT FROM AUTHOR]

The role of the heterogeneous rheological architecture of rifted margins in the building of mountain belts has challenged our view of how a collisional orogen formed. We show, using two‐dimensional numerical experiments of collision built by the inversion of rifted margins, that a weak pre‐extensional evaporitic layer delays the growth of topography and the onset of syn‐orogenic sedimentary record in foreland basins. In tectonic models lacking a weak décollement layer, the orogen grows by progressive accretion of basement thrusts. With a 2‐km‐thick salt layer, the orogen develops an antiformal stack in the deep crust that is kinematically connected to a shallow thin‐skin thrust belt in the foreland as observed in many orogens. A 5‐km‐thick weak layer leads to the quasi‐absence of topography and widespread salt tectonics and obliterates thrusts propagation while promoting crust and mantle underthrusting. During convergence, the preservation of a marine seaway emphasizes that collision may involve a significant period of submarine continental accretion, which duration is controlled by the thickness of the weak décollement layer. From these experiments we infer that the thicker the salt layer, the longer the delay between the onset of far‐field shortening and the formation of the orogen. Our study explains first‐order features recognized in many orogens controlled by variable salt thickness and extension. Key Points: The presence of a weak pre‐extensional evaporitic layer delays the growth of orogenic wedgeIn presence of an intermediate thick salt layer the orogen develops an antiformal stack in the deep crustImportant amount of salt leads to the quasi‐absence of topography and widespread salt tectonics obliterating thrusts propagation [ABSTRACT FROM AUTHOR]