Salt Walls Research Articles

Transverse faulting in the Paradox Basin, Colorado Plateau, USA: Active, intermittent faulting over a 300 million year history of strain accommodation and fluid flow

The Paradox Basin (Colorado Plateau, USA) is dominated by major, first-order northwest-trending structures commonly 40 km or more in trace length, including (1) regional salt wall corridors related to passive diapirism during Pennsylvanian to Jurassic time, (2) gentle upright folds produced by Laramide shortening during the Late Cretaceous through early Cenozoic, (3) late Laramide normal faults, and (4) normal faults representing Neogene salt dissolution collapse. Less obvious at a regional scale are the fault zones aligned perpendicular (northeast-trending) to the dominant structural grain. There are 16 such faults zones, marked by short trace lengths (3−12 km), small offsets (10−100 m), and predominantly extensional kinematics. Based on published geological maps, field observations of fault zone properties (including fluid flow indicators), and kinematic analysis, we interpret these structures as transverse accommodation faults. Co-spatial structural associations reveal the transverse fault zones were active intermittently, likely as a means of minimizing along-strike strain incompatibility that accrued along the first-order structures as they evolved during late Paleozoic to Late Jurassic halokinesis, (mild) Late Cretaceous to Eocene folding, late Laramide normal faulting, and Neogene to recent collapse faulting. Locally, transverse faulting was influenced by reactivation of northeast-striking faults that offset sub-salt formations, including basement. Active, intermittent transverse faulting over the past ∼300 m.y. is consistent with the synthesis of published interpretations and age determinations focusing on the timing of diverse fluids that exploited the permeability of the transverse fault zones. The Paradox Basin, with its enormous subsurface salt volume and enduring fluid flow, has been an ideal dynamic environment for producing intermittently active transverse accommodation faulting.

A fresh look at the Gulf of St. Lawrence, Eastern Canada: Geophysical imaging of salt bodies and volcanic rocks in the upper Paleozoic Magdalen Basin

In the Gulf of St. Lawrence, the late Middle Devonian to early Permian Magdalen Basin hosts numerous salt bodies, but their number and geometry remained poorly constrained due to the poor quality of industry-seismic data. Salt originates from the Middle Mississippian (Visean) Windsor Group, which includes marine carbonates and evaporites. In this study, we use multibeam bathymetry as well as unpublished aerogravity and aeromagnetic data to better characterize the geometry of salt bodies. These datasets show a high degree of coherency and illustrate deformation on the seafloor, gravity lows and magnetic highs, all associated with salt bodies and overlying volcanic rocks. In map view, the geometry of individual salt bodies varies from nearly circular to ovoid and strongly elongated. Some salt bodies coalesce in complex-shaped salt walls elongated NNE, parallel to some of the faults that controlled the early stages of the Magdalen Basin development. Forward modeling indicates that low density salt bodies overlain by a 100–300 m thick volcanic pile may account for both gravity and magnetic signals. The ubiquity of mafic volcanic rocks indicates that the late Visean to Serpukhovian volcanic episode is more voluminous than previously thought. This episode is possibly associated with a series of dykes continuous for up to 225 km and with a period of underplating now recorded by a lower crustal layer with high seismic velocity.

Contourite-like deposits suggest stronger-than-present circulation in the Plio-Pleistocene Red Sea

Red Sea Deep Water is presently slow-moving, but was this true of the earlier Plio-Pleistocene (PP)? In seismic reflection records, the PP deposits are distorted by halokinetic deformation of their underlying Miocene evaporites. However, if reflections are flattened to a prominent reflector representing the top of the Miocene, they reveal mounded deposits within the earlier PP along both sides of the sea. Off Egypt, a plastered drift occurs along a salt wall. In the central Red Sea, they are mounded drifts. Seismic reflections from these deposits change shape gradually upwards to the modern seabed, which is commonly flatter, suggesting a gradual change in depositional conditions. To explain their origins, we appeal to other evidence. DSDP cores from the Late Pleistocene contain the rigid aragonite cements formed by restricted conditions, but not the lower and middle PP. Furthermore, mid-PP sedimentary δ18O values are similar to global ocean δ18O for that time, not enhanced as expected from excess evaporation. These data suggest that there was a greater exchange of Red Sea waters with the Indian Ocean during the mid-PP. That exchange may have allowed waters densified by evaporation in shallow regions of the northern Red Sea to flow south vigorously (the mounds would then be contourites). Alternatively, as the Pliocene seabed was shallower, wind-driven eddies may have affected more of the water column. Overall, the results indicate for the first time that deep circulation was stronger in the earlier PP compared with the present day. That circulation needs to be considered when evaluating organism dispersions across the Red Sea, regional climate, and influence of Red Sea Outflow Water on Indian Ocean Intermediate Water. Plain language summaryDuring the Pliocene (about 3–5 million years ago), temperatures on Earth's surface were similar to those predicted in some models of Earth's future climate. This has led to researchers becoming interested in studying geological evidence of conditions during the Pliocene as a clue to Earth's future. In detail, however, the comparison may not be exact. In our article, we describe mounds of sediment that were originally formed on the bed of the Red Sea in the Pliocene. They appear similar to snow drifts, and like snow drifts, may have formed under steady currents. Sea water becomes dense with evaporation (making it more saline). At the present day, dense water created in the Gulf of Suez cascades down into the deep Red Sea as a slow current. Perhaps such movements were more vigorous in the Pliocene, helped by the water escaping through a deeper barrier in the south into the Indian Ocean? Alternatively, these mounds were formed by giant eddies, such as those on the surface of the modern Red Sea, which are moved by strong winds. In either case, the deep waters of the Pliocene Pliocene Red Sea were more vigorously moving compared to the quiescent deep waters of the modern-day.

Stress Field Dynamics and Fault Slip Potential in the Paradox Basin

AbstractThe Paradox Basin, straddling Utah, Colorado, Arizona, and New Mexico is characterized by an intricate amalgamation of evaporites and clastic layers and is dominated by prominent salt walls and related subsurface structures. Our research offers a new examination of the stress distribution across the basin, deriving from continuous and discrete stress measurements conducted in boreholes in the region and focal mechanism analysis, emphasizing variations over salt structures. Integrating Coulomb failure criteria with probabilistic methods, we assess potential fault movements resulting from fluid pressure alterations. Our approach provides a comprehensive understanding of the Paradox Basin's state of stress, showing a continuous change of the maximum horizontal stress orientation from N‐S at the Wasatch Fault Zone to WNW‐ESE in the northern part of the Paradox Basin and to WSW‐ENE in the southern part of the basin. Further East, into the Colorado Plateau and the Uncompahgre Uplift, the SHmax orientation becomes E‐W. Decoding stress orientation dynamics has enabled critical insights into fault slip potential, especially in the basin's northern region. The salt wall faults are less likely to slip, and the Paradox Formation's evaporite and clastic rock sequence can serve as a potential low seismic risk target for carbon storage and hydrocarbon extraction.

3D variation of shortened salt walls from the Moroccan Atlas: Influence of salt inclusions and suprasalt sedimentary wedges

We present a field study of salt ridges and minibasins of the Moroccan High Atlas near Rich that shows the along- and across-strike variability of such structures. Salt walls evolved from halokinesis during Jurassic rifting, to shortening during Cenozoic orogeny. Salt wall segments exhibit variable degrees of welding due primarily to the local presence of intrasalt inclusions (basalt and gabbro) rather than orientation with respect to the shortening or position along the ridge. Flanking Jurassic minibasins may be upright and symmetric or tilted; tilting may have started during halokinesis but was largely acquired during shortening. Minibasins tilt away from welded diapiric segments towards inclusion-rich segments, indicating differential diapir rise. The structure of the central parts of the salt walls differs from the lateral terminations. While the central parts are relatively simple with aperture or welding governed by the inclusions, many salt walls end buried by suprasalt sedimentary wedges. These perched wedges were not arched upward during diapir squeezing but were unexpectedly folded into synclines. The folding was formed by the flanking minibasin tilting in one limb and by inhomogeneous diapir rise and lateral salt escape in the other, thus defining a new modality of roof and shoulder folding above salt diapirs.

Evolution of the Júcar-Cabriel fluvial system on the Mediterranean watershed of the Iberian Peninsula (Valencia, eastern Spain)

This study presents the characterization and chronology of the Quaternary terrace sequence developed in the confluence zone of the Júcar and Cabriel river valleys. The study area covers a radius of 10 km from the confluence of the two valleys near the locality of Cofrentes (Valencia). It is located in the northern zone of the Ayora-Cofrentes Graben in the northeastern sector of the External Prebetic Zone adjacent to southern Iberian Chain. This N-S graben is an inherited tectonic feature with an axial salt wall subject to different periods of fluvial dissection and refilling since at least the end of the Messinian Salinity Crisis (MSC). Regional isostatic uplift and local uplift and subsidence processes related to salt flow and dissolution during the Quaternary period, favored by fluvial entrenchment and terrace development. The terrace system and the previous pre-incision erosional and depositional surfaces are analyzed from a geomorphological point of view. The terrace system only develops within the soft Mio-Pliocene sedimentary fill of the graben, whilst upstream and downstream this zone the studied valleys develop important gorges (canyons) carved in the Cretaceous tablelands (Caroch Massif) and Mio-Pliocene deposits (Llanura Manchega). The geochronological control is established from 20 numerical ages obtained by different dating methods, such us Electron Spin Resonance (ESR), Optically Stimulated Luminescence (OSL) in detrital sequences and Th/U series in calcareous tufa deposits. Additionally, four K/Ar dates available for volcanic materials disrupting the upper and oldest terrace have been considered. A total of 14 terrace levels were identified between +130–135 m (T1) and +3–4 m (T14) of relative height above the river thalwegs. The T1 has an approximate age of c. 1.6–2.0 M.a. as indicate the age of the volcanic materials from the Agras Volcano intruded in the terrace, marking the onset of Quaternary fluvial dissection in the zone. The obtained geochronological data indicate that the Lower-Middle Pleistocene boundary is slightly above T6 (+60–65 m), which has an ESR age of 577 ± 43 ka. This terrace also documents the onset of the most important period of rise of the salt within the graben interfering drainage development. The geochronological data indicate the occurrence of a second eruptive event during the second half of the Middle Pleistocene related to the terraces T7 (+50 m) and T8 (+35–40 m), updating the volcanic activity in the zone. The beginning of the Upper Pleistocene is recorded by the top sequences of the T9 terrace (+25–30 m) where numerous OSL and Th/U data have been obtained with ages between ca. 105 and 81 ka (MIS 5). However, these young terraces (T8 to T13) are thickened (8–10 m) recording Middle Pleistocene sediments in their basal sequences with ages between ca. 193 and 137 ka (MIS 6). The study provides important data on valley evolution under the interference of volcanic activity, salt –related deformation (diapirism, solution subsidence) and fluvial incision fostered by the rise of the axial diapir (salt wall) protruding the graben since at least the Brunhes-Matuyama boundary. The analyzed fluvial evolution documents interesting cases of river capture, drainage antecedence and tectonic adaptation of the drainage throughout the Quaternary Period. The paper also poses interesting geochronological data on the long-term Quaternary evolution of Mediterranean valleys in the Iberian Peninsula, poorly explored to the date.

Stratigraphic evolution of a salt-walled basin: the influence of diapirism and compressional tectonics on the sedimentary record of the Estopanyà syncline (South-Central Pyrenees)

This contribution describes the influence of diapirism and compressional tectonics in the sedimentary record of the Estopanyà and Boix synclines (salt-walled basins) in the South-Central Pyrenees (NE Spain). Based on mapping and logging of five stratigraphic sections, two lithostratigraphic units (LU-1 and 2) along the eastern diapir margin of these synclines and five more (LU-3 to 7) in their inner parts are defined. LU-1 and 2 consist of monomictic breccias deposited probably during the Upper Triassic-Oligocene and the Upper Cretaceous, respectively. LU-3 to 7 constitute a marine to fluvial succession of the Tremp Group deposited during the Upper Cretaceous to Paleocene. The stratigraphic and sedimentological record indicates that the topography, position, and accommodation space of the Estopanyà and Boix synclines was actively controlled by the evolution of salt structures from the Late Cretaceous to the Oligocene in response to the advance of the Alpine compression in the South-Central Pyrenees. The growth of salt-inflated ridges with a near parallel orientation to the axis of the studied synclines since the Upper Cretaceous, progressively compartmentalized the Boix syncline until inhibiting sedimentation during the lower Paleocene. In the upper Paleocene, the Alpine compression approached the study area increasing salt evacuation and the subsidence of the Estopanyà and Boix synclines. During the early to middle Ypresian, onset of compression led to salt expulsion by piercing the sedimentary roof of the inherited salt-inflated ridges and forming two salt walls at the eastern margin of the Estopanyà and Boix synclines that were squeezed and welded (possibly through secondary welds) due to tectonic compression during the Oligocene. This contribution provides a new interpretation of the structural and stratigraphic evolution of the Estopanyà and Boix synclines, proposing an evolutionary model that includes the rejuvenation, growth, and extrusion of salt walls as deciphered from the stratigraphy, sedimentology, and petrology of the diapir margin breccias and the sedimentary succession of the adjoining salt-embedded basins. Hence, it provides a new analogue study for understanding the interplay between compressional tectonics, diapirism, and sedimentation to other inverted salt basins with precursor salt walls worldwide.

Contrasting Styles of Salt‐Tectonic Processes in the Ionian Zone (Greece and Albania): Integrating Surface Geology, Subsurface Data, and Experimental Models

AbstractThe 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.

Late quaternary morpho-stratigraphic record of diapir rise in the Cardona salt extrusion, NE Spain. Halokinetic sequences, raised terraces and uplift rates

Active diapirism has received very limited attention from the geomorphological and Quaternary Science perspective, despite the role played by this ground deformation process in the development of landforms and sedimentary environments, and the important practical implications associated with mobile salt structures (e,g., mining, hydrocarbon production, geostorage). The Cardona salt extrusion (NE Spain) was initiated in late Quaternary times from the post-shortening unroofing of the crest of a salt anticline by the entrenchment of the transverse Cardener River. Detailed mapping, outcrop analysis, geophysical data and trenching indicate that the diapir-flanking deposits show halokinetic complexes comprising two types of morpho-stratigraphic units: (1) an older flap of coarse-grained drapefolded colluvial deposits; and (2) younger lacustrine and fluvial deposits in peripheral depressions confined between the upturned colluvial flaps and the country rock slope. These synkinematic units record an overall relief inversion and correspond to the so-called wedge and hook halokinetic sequences, recording ratios between diapir rise rate and sedimentation rate lower and greater than 1, respectively. The radiocarbon ages obtained from several raised late Holocene strath terraces carved in the salt indicate uplift rates within the range of 36.5–12.1 mm/yr, consistent with geodetic data. The spatial variability of the uplift rates can be related to increasing flow rates towards the axis of the salt wall and potential along-strike variations. The relatively high diapir rise rates observed at Cardona diapir, unaffected by contractional displacement loading (tectonic squeezing), is attributed to the youthful stage of the salt extrusion and the low dynamic viscosity of the Cardona Saline Formation, with a low proportion of impurities and a significant amount of potash salts.

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

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

Contrasting influence of salt structures and faults on the geothermal potential of regional structural highs: The Cleaver Bank High, Southern North Sea

High-quality 3D seismic reflection data, complemented by 448 bottom-hole temperatures (BHTs) from 48 boreholes, are used to investigate the influence of salt structures and faults on the geothermal potential of the Cleaver Bank High, Southern North Sea. Developed salt structures include multiple salt diapirs, salt pillows and a salt wall, with their presence influencing local geothermal potential. Strata deposited above the Zechstein Group record geothermal gradients that are enhanced proportionally to the thickness of this salt unit. Conversely, strata buried below the Zechstein Group reveal a moderate decreasing trend in geothermal gradients as salt thickens. Large supra-salt faults can act as fluid paths to deep and hot fluid into shallow strata, resulting in the presence of high geothermal gradients in shallow strata. Importantly, geothermal gradients on the footwall of these faults are much higher than that on the corresponding hanging-wall, decreasing as one moves away from them. For example, average geothermal gradients on the footwall of the largest supra-salt fault (Fault A) are, relative to its immediate hanging-wall, 105 % higher in the North Sea Group, 26 % higher in the Chalk Group, and 41 % higher in the Rijnland, Upper and Lower Germanic Trias Groups. Additionally, sub-salt faults influence the geothermal gradient of supra-salt strata in parts of the study area where there is very thin, or even absent, salt (<100 ms; or ∼230 m), forming distinct low-amplitude trails of fluid above these same faults. They also indirectly influence geothermal gradient by controlling the position, geometry and distribution pattern of salt structures. As a corollary, three potential geothermal exploration targets are suggested on the Cleaver Bank High, one located on the footwall of a large supra-salt fault, one above thick salt, and a third target above very thin Zechstein strata where low-amplitude fluid chimneys are found. The results in this work can be applied to similar salt-bearing structural highs in Northern Europe and worldwide.

Geometry and kinematics of the Middle to Late Miocene salt tectonics, central Egyptian Red Sea margin

The Red Sea basin includes a thick Middle to Late Miocene evaporitic succession that underwent halokinesis and caused intensive reshaping of the seafloor and the development of salt-tectonic structures. However, the geometry and kinematics of these structures are still poorly understood. This study uses 2D and 3D seismic surveys and well data of the northern Egyptian Red Sea to systematically describe the distribution and morphology of salt structures, discuss their initiation, and construct a kinematic model for their origin. Our results indicate that the massive salt layer developed into five major NW-SE to NNE-SSW trending salt walls, characterized by relatively irregular crests and moderately dipping flanks. In addition, several symmetrical and asymmetrical folds and two categories of normal faults (subsalt and suprasalt) have been recognized. Based on our observations, salt mobilization in the study area started in the Late Miocene, during the precipitation of layered evaporites, and continued until the present day. In the northern Egyptian Red Sea, seismic interpretation indicates that halokinesis was triggered by a combination of thin- and thick-skinned systems, where the latter played a major role. The salt layer was welded during the Quaternary as several sags and grabens developed above the salt diapirs. Thick-skinned physical models are compatible with our observations, supporting the impact of basement faulting on Red Sea diapirism.

Salt Tectonics Versus Shortening: Recognizing Pre‐Orogenic Evaporite Deformation in Salt‐Bearing Fold‐And‐Thrust Belts on the Example of the Silica Nappe (Inner Western Carpathians)

AbstractRecognizing 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.

Late Paleozoic igneous rocks at Clarke Head, Nova Scotia: magmatism at an arc to back-arc transition

Abstract This study re-examines a reported mylonitic ‘metabasic granulite’ block in a megabreccia that is the most outboard igneous rock outcrop in the Avalon terrane, near the Meguma–Avalon terrane boundary in the northern Appalachians. The block of foliated gabbro is one of several igneous rock blocks in a largely dissolved salt wall and in style of deformation, mineralogy, lithogeochemistry and Sm/Nd isotopes resembles foliated and locally mylonitized late Devonian–early Carboniferous gabbro plutons along the Cobequid Shear Zone to the north. Garnet porphyroclasts in the foliated gabbro are exceptional, with a distinctive composition of Alm 55 Pyr 25 Grs 13 And 4 Sps 3 . Inclusions of pyroxene, andesine and ilmenite, lack of zoning and corroded rims suggest the garnets are antecrysts. Elsewhere in the world, garnets of similar composition in arc-related andesites are interpreted to be from disintegration of comagmatic cumulate material at 0.8–1.0 GPa under hydrous conditions. The Clarke Head foliated gabbro has two mafic components, one resembling arc-related hydrous magma and the other with tholeiitic back-arc character, similar to coeval rocks in the Cobequid Highlands. The gabbro is a product of complex mixing in crustal magma chambers and rapid rise of magma containing lower crustal antecrysts along strike-slip faults.

Inversion of accommodation zones in salt-bearing extensional systems: insights from analog modeling

Abstract. This work uses sandbox analog models to analyze the formation and subsequent inversion of a decoupled extensional system comprised of two segmented half-grabens separated by a diffuse accommodation zone with thick early syn-rift salt. The segmented half-grabens strike perpendicular to the direction of extension and subsequent shortening. Rifting first created a basement topography that was infilled by model salt, followed by a second phase of extension and sedimentation, followed afterwards by inversion. During the second phase of extension, syn-rift syncline minibasins developed above the basement extensional system and extended beyond the confines of the fault blocks. Sedimentary downbuilding and extension initiated the migration of model salt to the basement highs, forming salt anticlines, reactive diapirs, and salt walls perpendicular to the direction of extension, except for along the intervening accommodation zone where a slightly oblique salt anticline developed. Inversion resulted in decoupled cover and basement thrust systems. Thrusts in the cover system nucleated along squeezed salt structures and along primary welds. New primary welds developed where the cover sequence touched down on basement thrust tips due to uplift, salt extrusion, and syn-contractional downbuilding caused by the loading of syn-contractional sedimentation. Model geometries reveal the control imposed by the basement configuration and distribution of salt in the development of a thrust front from the inversion of a salt-bearing extensional system. In 3D, the interaction of salt migrating from adjacent syn-rift basins can modify the expected salt structure geometry, which may in turn influence the location and style of thrust in the cover sequence upon inversion. Results are compared to the Northern Lusitanian Basin, offshore Portugal, and the Isábena area of the South-Central Pyrenees, Spain.

Reconstructing the Iberian Salt‐Bearing Rifted Margin of the Southern Pyrenees: Insights From the Organyà Basin

AbstractReinterpretation 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.

The anomalous magmatism in the southern part of the Santos basin, and the non-continuous salt layer over Abimael Ridge

The magmatism in the Santos Basin is related to the following main events: (1) the pre-rift volcanic episode; (2) the syn-rift to late syn-rift episode; (3) the late Cretaceous episode; and (4) the Paleogene episode. This works focuses on the characterization of these events using seismic data and borehole interpretation in the southern part of the basin. The late Cretaceous magmatic episode is recorded in the shelf break region by 3D seismic data. A mini-basin with possible turbidite reservoirs was tested by an exploratory borehole that revealed several igneous features, including volcaniclastic sequences, sills, and volcanic plugs. Basinward, the evaporite layers are thicker and form salt walls above a detachment at the base of the salt reflector, which climbs up oceanward. The analysis of strong reflectors within the distal salt wall suggested three alternative interpretations, including igneous sills within the salt mass, anhydrite lenses, carbonate rafts, carbonate stringers, pre-salt microbialite buildups, and pre-salt volcanic rocks. The interpretation of the seismic and potential field data, constrained by the borehole results, indicates that the strong reflector corresponds to the top of the volcanic layers below the pre-salt microbialites.The anomalous magmatism and salt tectonics styles in the southern part of the Santos Basin are related to a swath of embryonic oceanic crust that was emplaced during the late Aptian to early Albian. The interpretation of a regional profile extending from the continental shelf to the oceanic crust provides evidence for the separation of the salt masses by a failed oceanic spreading center, which is corroborated by the gravity and magnetic models.

The nature of fracturing in the Mozyr salt uplift (Gomel region of Belarus)

The regularities of the internal structure of salt uplifts have not been studied enough at present. Analysis of the shape of the cavities obtained by sonar in the cavities blurred in the Mozyr dome in Belarus shows that their walls in some cases have a rectilinear shape, and the shape of the cavity in horizontal sections looks like a polygon. The experience of previous studies suggests that the appearance of rectilinear walls is associated not only with the presence of insoluble interlayers, but also with the preparation of crack systems. The relative location of fractures and cavities suggests the stress field that created them. The conducted experiments on the dissolution of salt dams confirm the great role of fractures in the formation of the relief of salt walls.

Integrating petrophysical, geological and geomechanical modelling to assess stress states, overpressure development and compartmentalisation adjacent to a salt wall, gulf of Mexico

Multi-well pressure data from the Magnolia Field, located on a flank of the salt-bounded Titan passive mini-basin in the Garden Banks area of the continental slope of the Gulf of Mexico, indicate remarkably high overpressures that vary, at similar depths, by up to 10 MPa between sand bodies 1 km apart. In the present paper, we integrate geological and geophysical analysis with 2D forward hydro-mechanical evolutionary modelling to assess the contribution of both disequilibrium compaction and diapir-related tectonic loading to the observed overpressure and to understand controls on pressure compartmentalisation. The 2D finite element evolutionary model captured the sedimentation of isolated sand channels bounded by mud-dominated sediments close to a rising salt wall which led to tectonic loading on sediments. Comparison of results from the 2D and 1D models shows that disequilibrium compaction can explain most of the overpressure as a result of very rapid deposition of mainly mud-rich, low permeability sediments; tectonic loading contributes around 7% of the observed overpressure. The models also show that linked to the high sedimentation rates, small variations in the permeability and connectivity of the mud-rich sections that bound the channel sands result in highly compartmentalised pressure distributions in adjacent sand bodies.

A new look at old debates about the Corbières (NE-Pyrenees) geology: salt tectonics and gravity gliding

In the Corbières area, a large-scale nappe has been identified at the beginning of the 20th century: the “Nappe des Corbières Orientales” (NCO) resting over a thick Triassic sole. This geological object is located at the NE of the Pyrenees, close to the Gulf of Lions. At this place, the chain changes in orientation from E-W to NE-SW and presents in detail, a great complexity. The existence of the nappe itself has never been contested. However, due to its overall complexity, several controversies exist regarding the style and chronology of deformation of its substratum in the so-called the “Pinède de Durban” in particular. We show that the new concepts of salt tectonics can clarify these old debates. Indeed, the rise of the Triassic salt during Mesozoic rifting episodes results in the development of characteristic sedimentary sequences (halokinetic sequences) on top of salt walls. It is along one of these, coinciding with the prolongation of the Cévenole Fault System, that the NCO has been individualized. During its Cenozoic emplacement, a gravity-gliding component, explaining the importance of the observed translation, could result from an uplift preceding the rifting at the origin of the Gulf of Lions.