Salt Basin Research Articles

Repeated evolution of blanched coloration in a lizard across independent white-sand habitats.

The White Sands lizards of New Mexico are a rare and classic example of convergent evolution where three species have evolved blanched coloration on the white gypsum dunes. Until now, no geological replicate of the pattern had been described. However, one of the White Sands species, the lesser earless lizard (Holbrookia maculata), has been discovered to also inhabit the Salt Basin Dunes of Texas, where it has also evolved a blanched morph. We here present a first phenotypic and genetic description of the Salt Basin Dunes population of H.maculata. Phylogenetic inference based on a housekeeping gene (ND4) and a classic candidate gene in the melanin-synthesis pathway (Melanocortin 1 Receptor; Mc1r) shows the newly discovered population as an independent lineage, with no evidence of genetic parallelism in the coding region of Mc1r. Initial morphological data suggest that while this population displays convergent evolution in blanched coloration, there are divergent patterns in limb length and habitat use behavior between the gypsum environments. Our findings present the White Sands/Salt Basin Dunes as an exceptionally promising comparative model for studies of adaptation and convergent evolution.

Coupling Crustal‐Scale Rift Architecture With Passive Margin Salt Tectonics: A Geodynamic Modeling Approach

AbstractContinental rifted margins are often associated with widespread, thick evaporite (i.e., salt) deposits and pronounced salt tectonics. The majority of salt basins formed during the latest stages of rifting, prior to continental breakup. We use 2D thermo‐mechanical finite element modeling of lithospheric extension to investigate the interplay between rifted margin architecture, late syn‐rift salt deposition, and post‐rift salt tectonics. We focus on four different types of continental margins: (a) narrow, (b) intermediate, (c) wide, and (d) ultra‐wide margins. We evaluate the: (a) interplay between laterally variable syn‐rift extension, salt deposition and salt tectonics, (b) influence of syn‐rift basin architecture on post‐rift salt flow, (c) spatial and temporal distribution of salt‐related structural domains, and (d) contrasting styles of salt tectonics for different margin types. Narrow and intermediate margins form partially isolated salt basins associated with prominent base‐salt relief, limited translation but significant diapirism, and minibasin development. Wide and ultra‐wide margins form wide salt basins with subtle base‐salt relief that results in significant seaward salt expulsion and overburden translation. These wide margins demonstrate significant updip extension with the development of post‐rift normal faults and rollovers, mid‐margin translation associated with complex diapirism and downdip diapir shortening. All margins contain a distal salt nappe that varies in width and complexity. We also test the effect of different salt viscosities, relative post‐salt progradation rates, and pre‐salt sediment thicknesses. The results are comparable to several examples of salt‐bearing rifted margins and improve our understanding of their dynamics and on the controls on their salt tectonics variability.

Basin-scale estimates of thermal stress and expelled petroleum from Mesozoic-Cenozoic potential source rocks, southern Gulf of Mexico

The Campeche and Yucatan salt basins remain two of the least explored areas of the Gulf of Mexico basin. This study uses a grid of 23,600 line-km pre-stack depth migrated (PSDM) 2D seismic reflection profiles, shipborne gravity data, and open-source geologic information to model the thermal stress of four potential source intervals (Oxfordian, Tithonian-centered, Cenomanian-Turonian, lower Miocene). We performed map-based, and 1D thermal modeling along two margin-perpendicular transects, each consisting of five pseudo-wells tied to the regional grid of seismic reflection data. Our modeling takes into account thermal stress variations related to the depth of base lithosphere, crustal type and thickness, paleo-water depth, Jurassic salt thickness, and the transient heat flow effects related to recent clastic sedimentation. We predict that deeply-buried, salt-related minibasins along the outer marginal trough are mature for petroleum expulsion with deeply-buried Mesozoic source rocks within the oil window from late Paleogene to early Neogene time. The ‘lag time’ required for vertical oil migration explains why oil maturation occurred during the late Paleogene to early Neogene but active oil seeps are observed today at the sea surface. We predict that oil is present in subsurface traps in the deepest part of the outer marginal trough and we calculate that the Oxfordian source interval has expelled a cumulative 20 million bbl of oil equivalent [BOE]/km2 and that the Tithonian-centered source interval has expelled 67 million bbl of oil equivalent [BOE]/km2.

Bioherms of the Bozhekhan uplift in the Cis-Baikal trough as a marginal barrier reef system of a Cambrian salt basin of the southern Siberian platform

Modern forecast, exploration and development of hydrocarbon deposits within natural carbonate reservoirs of buried bioherm (reef) structures in the north of the Irkutsk region and the Sakha Republic (Yakutia) areas within the NepaBotuoba Anticline apply the most advanced technologies of 3D seismic exploration and geoelectric prospecting supplemented with a set of new interpretation approaches and analysis attributes contrasted against wide range of well logging data. The recent discoveries of hydrocarbon deposits in the northern reefs shoved the bioherms of the Irkutsk amphitheater in the shadow. The purpose of this research is geological study of biohermal carbonate formations of the Lower Cambrian age in the outcrops of the Bozhekhansky megaswell in the Baikal region. The choice of this object of study is due to the fact that the first oil and gas inflows were obtained from the wells of the Atovskaya, Osinskaya, Birkinskaya, Khristoforovskaya, Balykhtinskaya and Tuturskaya areas. Field geological routes and office processing of data on cuts and polished thin sections of sample surfaces were carried out including microscopic studies in the thin sections of samples and archival collections of cores from deep oil and gas prospecting wells. In 2021–2022, while prospecting in the south of the Irkutsk amphitheater, the authors explored stratified, nodular and columnar stromatolites found within the compound Bozhekhan megaswell of Cambrian carbonate outcroppings. Carbonate intraformational sedimentary breccias identified in the area under investigation feature a great variety in their fragment sizes and inclusions. The stromatolites’ structural features were studied by the cuts and polished thin sections of sample surfaces. Microphytolites were found in the thin sections and described. The authors also took advantage of the opportunity to study an archive collection of the thin sections of VendCambrian and Lower Cambrian carbonate strata from the Akhinskaya area’s wells at the Bozhekhan megaswell and from the Upper-Lena uplift to the north-west. The conducted study implies that Cambrian bioherm outcroppings of the Bozhekhan megaswell-type uplift within the Cis-Baikal trough are, in a sense, model geologic objects. The study of biologic and genetic varieties of Lower Cambrian phytolites, diagnostic features of the organogenic structures, their inner structure and formation processes of the reef ecosystem may provide a region-level prognostic key to the research of Cambrian sediment system in the south of the Siberian platform.

Late‐Syn‐ to Post‐Rift Salt Tectonics on Wide Rifted Margins—Insights From Geodynamic Modeling

AbstractRifted 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.

Physical modelling of the interplay between salt‐detached gravity gliding and spreading across complex rift topography, Santos Basin, offshore Brazil

AbstractThe Santos Basin, offshore Brazil contains a complex set of salt‐tectonic structures, the origins of which are debated, that is, the Albian Gap and the São Paulo Plateau (SPP). The Albian Gap is a ca. 450 km long, 60 km wide feature characterized by a post‐Albian, counter‐regional rollover overlying depleted Aptian salt, and in which the Albian is largely absent. The SPP, located immediately downdip, is defined by a pre‐salt structural high overlain by ca. 2.5 km thick salt. Another prominent feature is the Merluza Graben, a rift‐related depocentre that underlies the southern portion of the Albian Gap and displays significant (3–4 km) base‐salt relief along its main faults. Two competing hypotheses have been proposed to explain the kinematics of these provinces. One invokes post‐Albian extension in the Albian Gap and kinematically‐linked contraction in the SPP. The other invokes post‐Albian salt expulsion in the Albian Gap and salt inflation in the SPP. Recent studies, however, suggest these processes likely alternate in time and space, contributing nearly equally to the evolution of these domains. We apply 3D physical modelling to (i) test this hypothesis; and (ii) to more generally understand how gravity gliding and spreading over three‐dimensionally variable base‐salt relief control regional salt tectonics. The results show a similar salt‐related evolution and structural styles to those proposed in the most recent studies. They also (i) explain the origin of the ca. 25 km wide diapir precursor of the Albian Gap by early salt inflation against base‐salt steps; (ii) show that normal faults with different polarities and rollover types form due to the interplay between gliding and spreading over different base‐salt domains and (iii) provide a mechanism for the origin of strata encased within salt structures. This improves our understanding of the distribution and origin of salt‐related structural styles in worldwide salt basins.

Potential of Underground Hydrogen Storage in Oman

Hydrogen can provide a viable source of energy that can covers the world’s energy requirement in the next coming years. One of the major keys to wholly develop hydrogen energy is to provide a safe, cost efficient and compacted type of hydrogen storage. Geological reserves are considered a suitable space for hydrogen storage. In this research, we are trying to examine if there was any technical potential for hydrogen storage based on Oman’s geology by Identifying geological deposit in Oman that can be used for hydrogen storage and analyzing salt deposits for hydrogen storage suitability. By overviewing the possible underground hydrogen methods and based on Oman’s geology, deep aquifers were not suitable for hydrogen storage; due to the lack of large sedimentary basin, no experience for similar projects and the risks associated with surrounding environment. Depleted reservoir needs more study for deployment; there are no experiences of such projects for UHS. Salt basins are good candidate for underground storage; due to the large salt basin in Oman, salt caverns are known to successfully contain hydrogen and the guaranteed safety of the storage. Analysing the technical potential salt deposits was based on a good depth dome, salt thickness and salt dome size. The main findings illustrate that, two salt domes (Qarn Shamah and Qarn Alam) were offering a good potential of estimated working gas volume of hydrogen around 90 m3 hydrogen (0.2 TWh). Nevertheless, more future work is needed to confirm the geotechnical feasibility of salt domes in terms of internal complex structure, chemical composition and purity of salt.

Reconstructing 3D subsurface salt flow

Abstract. Archimedes' principle states that the upward buoyant force exerted on a solid immersed in a fluid is equal to the weight of the fluid that the solid displaces. In this 3D salt-reconstruction study we treat Zechstein evaporites in the Netherlands as a pseudo-fluid with a density of 2.2 g cm−3, overlain by a lighter and solid overburden. Three-dimensional sequential removal (backstripping) of a differential sediment load above the Zechstein evaporites is used to incrementally restore the top Zechstein surface. Assumption of a constant subsurface evaporite volume enables the stepwise reconstruction of base Zechstein and the approximation of 3D salt-thickness change and lateral salt redistribution over time. The salt restoration presented is sensitive to any overburden thickness change caused by tectonics, basin tilt, erosion or sedimentary process. Sequential analysis of lateral subsurface salt loss and gain through time based on Zechstein isopach difference maps provides new basin-scale insights into 3D subsurface salt flow and redistribution, supra-salt depocentre development, the rise and fall of salt structures, and external forces' impact on subsurface salt movement. The 3D reconstruction procedure is radically different from classic backstripping in limiting palinspastic restoration to the salt overburden, followed by volume-constant balancing of the salt substratum. The unloading approach can serve as a template for analysing other salt basins worldwide and provides a stepping stone to physically sound fluid-dynamic models of salt tectonic provinces.

Does the United Kingdom have sufficient geological storage capacity to support a hydrogen economy? Estimating the salt cavern storage potential of bedded halite formations

Hydrogen can be used to enable decarbonisation of challenging applications such as provision of heat, and as a fuel for heavy transport. The UK has set out a strategy for developing a new low carbon hydrogen sector by 2030. Underground storage will be a key component of any regional or national hydrogen network because of the variability of both supply and demand across different end-use applications. For storage of pure hydrogen, salt caverns currently remain the only commercially proven subsurface storage technology implemented at scale. A new network of hydrogen storage caverns will therefore be required to service a low carbon hydrogen network. To facilitate planning for such systems, this study presents a modelling approach used to evaluate the UK's theoretical hydrogen storage capacity in new salt caverns in bedded rock salt. The findings suggest an upper bound potential for hydrogen storage exceeding 64 million tonnes, providing 2150 TWh of storage capacity, distributed in three discrete salt basins in the UK. The modelled cavern capacity has been interrogated to identify the practical inter-seasonal storage capacity suitable for integration in a hydrogen transmission system. Depending on cavern spacing, a peak load deliverability of between 957 and 1876 GW is technically possible with over 70% of the potential found in the East Yorkshire and Humber region. The range of geologic uncertainty affecting the estimates is approximately ±36%. In principle, the peak domestic heating demand of approximately 170 GW across the UK can be met using the hydrogen withdrawn from caverns alone, albeit in practice the storage potential is unevenly distributed. The analysis indicates that the availability of salt cavern storage potential does not present a limiting constraint for the development of a low-carbon hydrogen network in the UK. The general framework presented in this paper can be applied to other regions to estimate region-specific hydrogen storage potential in salt caverns.

Hormuz salt distribution in the United Arab Emirates: Implications for the location of hydrocarbon fields

Hydrocarbon fields in the United Arab Emirates (UAE) are related with Neoproterozoic basement highs and/or Ediacaran–Early Cambrian Hormuz salt domes. However, neither the basement nor Hormuz salt are penetrated or imaged by available well and seismic data due to thick Phanerozoic sediments. In this study, we have used the residual gravity anomaly of the sedimentary layer throughout the UAE by subtracting the gravity response of the basement structure from the isostatic residual gravity anomaly. The structure and distribution of the low-density Hormuz salt were then delineated for the first time by applying a 3D constrained layer inversion method on the residual gravity anomaly of the sedimentary layer. Well data were used to constrain this inversion from which the density of the reference model and the isosurface of the Hormuz salt were defined, whilst seismic profiles were used to qualitatively check the location, shape and depth of the domal structures. The inversion model shows that the Hormuz salt is more widespread in offshore than in onshore UAE and generally occurs within NE-SW to N–S trending basins. The inverted Hormuz salt model has a thickness that ranges from 1000 to 4000 m, with an average thickness of 2100 m. Moreover, the model suggests that the Hormuz, Ara (central Oman) and East Rub’ Al Khali (Saudi Arabia) salt basins are most likely connected, except in regions of structural basement highs. In addition, the model reveals a low density (≤2290 kg/m3) shallow layer (0–6000 m below the sea level) in the foreland basin, which corresponds to the Aruma and Pabdeh sequences that infill the foreland basin. Many of the offshore hydrocarbon fields in the UAE such as Zakum, Umm Shaif and Sarb are associated with Hormuz salt domes. Also, several hydrocarbon fields adjoin basement highs, which are possibly related to the flexural bulge caused by the emplacement of the Semail ophiolite on the Arabian continental margin. The basement highs are probably bordered by faults, which could have initiated halokinesis of the Hormuz salt. Thus, the 3D inverted model provides a detailed distribution of Hormuz salt bodies, which allows an improved understanding of Palaeozoic hydrocarbon plays in the UAE.

Coevolution of diagenetic fronts and fluid-fracture pathways

Diagenetic boundaries are paleo-reaction fronts, which have the potential to archive the termination of metasomatic processes in sedimentary rocks. They have not been extensively studied, perhaps because they appear simple in outcrop. Recent work has demonstrated the significance of paleo-reaction fronts to decipher multiphase recrystallization processes and provide high porosity zones. This paper provides a detailed documentation of reaction front evolution in a tectonically active salt basin and reveals a high level of complexity, associated with multiple fluid flow and tectonic events. Here, consistent patterns of increasing dolomite stoichiometry and ordering, along with a change from seawater-derived, fabric-retentive dolomite to fracture-controlled, fabric-destructive hydrothermal dolomite are observed vertically across the stratabound dolomite bodies. These patterns, coupled with a decrease in porosity, increase in ∆47 temperature and δ18Owater values indicate multiphase recrystallization and stabilization by warm, Mg-rich fluids. The stratabound dolomite bodies apparently terminated at a fracture-bound contact, but the presence of dolomite fragments within the fracture corridor suggests that fracturing post-dated the first dolomitization event. The termination of dolomite formation is therefore interpreted to be associated with a decrease in the capacity of the magnesium-rich fluids to dolomitize the rock, as indicated by the presence of non-stoichiometric and poorly ordered dolomite at the reaction fronts. The fracture corridors are interpreted to exploit dolostone-limestone boundaries, forming prior to a later, higher temperature, hydrothermal dolomitization event, which coincided with the formation and growth of the anticline. Karstification subsequently exploited these fracture corridors, widening fractures and leading to localized collapse and brecciation. The results demonstrate that an apparently simple reaction front can have a complex history, governed by the inheritance of prior diagenetic events. These events modified rock properties in such a way that fluid flow was repeatedly focused along the original dolomite-limestone boundary, overprinting much of its original signature. These findings have implications to the prediction of structurally controlled diagenetic processes and the exploration of naturally fractured carbonate reservoirs for energy exploration globally.

Petrophysical characterizations and shale distribution analysis of Kissenda reservoir sands, Gabon

A gas field in western Gabon is penetrated by an exploration site N field with a major fault dividing the well locations. The upthrown block and the downthrown block have different characterization based on the history of Gabon Basin located in Equatorial West Africa, as part of the salt basin complex. In addition to major fault separating the blocks, four wells are selected in this study to identify each block. Petrophysical properties was undertaken by using wireline logs to generate each well composite. These properties include shale volume, total porosities, water saturation and permeability. The presence of shale in sandstone reservoir can affect the producibility rate of the reservoir. Shale volume and density porosity are cross-plotted using the Thomas-Stieber method to determine the shale distribution of both blocks, including the distribution types of laminar shale, dispersed shale and structural shale. Based on this method, the upthrown block has relatively small grain diameters with mostly laminar-dispersed shale distributions, while in downthrown block the grain diameters are four times larger with more dynamic shale distributions.

Genetic Model of Mud-Clast Conglomerates in Salt Rocks and Their Significance for Salt Mineralization in Mohei Area, Simao Basin, China: A Case Study of Well L-2.

The Simao Basin is one of the most important Mesozoic salt basins in China, and the salt rocks generally contain mud-clast conglomerates. The characteristics of mud-clast conglomerates can provide effective information indicating the evolution process of the salt deposits. A combined analysis of trace elements and clay minerals was performed to characterize the genetic model of mud-clast conglomerates in the salt rocks. The results show that the sedimentary materials are felsic rocks from the Upper Crust. Ternary plot diagrams show that the tectonic settings are between the continental margin and the continental island arc. The clay minerals in the samples mainly contain illite and illite–smectite mixed layers. A dry and hot climate prevailed during the deposition of the Mengyejing Formation, and the warm-humid climate that also occurred is interspersed in some periods. Evaporation makes the water bodies shallower, and the concentrated brine starts to precipitate salt under the arid and hot climate conditions. Redox proxies indicate that most of the samples were deposited in relatively oxic conditions. The Sr/Ba ratios (average of 0.5) and paleosalinity (average of ∼35‰) during the depositional period indicate an increase in terrigenous freshwater input and carry of clasts into the evaporation basin. Furthermore, the freshwater supply enhances the hydrodynamics; as a result, the detritus that deposited in the early stage is broken into mud-clast conglomerates and co-deposited with the salt rocks. The results provide a geochemical basis for further study of mud-clast conglomerates in the Simao Basin and supply recommendations for the origin of salt deposits in similar basins around the world.

Species Composition and Diversity Dynamics of Actinomycetes in Arid and Semi-arid Salt Basins of Rajasthan.

Species composition and diversity dynamics of the actinomycetes was studied in five salt basins of arid and semi-arid areas of Rajasthan, India. A novel approach integrating molecular (16S rRNA gene) and diversity indices was applied to reveal species composition and diversity dynamics. Fifty-three actinomycetes isolates were isolated from five arid and semi-arid salt basins. Molecular characterization resulted in the identification of actinomycetes species belonging to three genera namely, Streptomyces, Nocardiopsis, and Actinoalloteichus. The diversity study among actinomycetes species validates their universal occurrence in arid and semi-arid regions of Rajasthan. The species N. dassonvillei subsp. albirubida was omnipresent in all the five salt basins but its relative manifestation was not static across habitats. The study revealed that three species N. chromatogenes, S. durbertensis, and S. mangrovicola are being reported for the first time from India. The maximum species of actinomycetes were recorded from Pachpadra (14) and the minimum from Didwana area (6). This study not only documents the hitherto wealth of actinomycetes species in arid and semi-arid salt basins of Rajasthan but also reveals the composition and diversity dynamics of actinomycetes.

Geological risk characterization of traps and migration pathways for gas in an inverted salt basin

Inversion of the Lower Saxony Basin produced large-scale broad antiforms, hosting Germany's largest gas accumulations in stacked Permian and Triassic reservoir systems. Locally, however, several exploration and production wells failed in the upper Permian Zechstein-2-Carbonte (Ca2) due to missing reservoir (hiatus) or formation-water wet conditions despite of drilling the topmost position of the trap structure. Seismic interpretation indicates lateral shear of the structural topmost Ca2 reservoir by oblique inversion-related collision with the overlying rigid sandstone unit of the Triassic Bunter Formation (Fm.), triggering a halokinetic redistribution of Permian Zechstein (Z2-Z4) salt in between. Lateral shear was enabled along a thin Zechstein (Z1) salt decollement, underlying the Ca2 reservoir. This ultimately led to a full detachment of large intra-salt Ca2 allochthonous gas reservoirs (‘stringers’), leaving behind areas of Ca2 autochthonous absence (‘bald highs’). These kinematics triggered hydraulic connection and gas leakage from both, the ‘bald high’ margins of the autochthonous Ca2 and the Ca2 ‘stringers’ into the sandstone reservoir of the Bunter Fm. Methane-rich fluid inclusions in sub-horizontal tectonic veins and from within vertical stylolites sampled from cores of wells, which tested the Ca2 reservoir to be formation water-wet, proof gas leakage as a result of inversion. Identification criteria for gas leakage and reservoir presence have been established from this study to frame geological subsurface scenarios for pre-drill risk assessments of inverted settings. The generalized conclusion from this study is that the topmost position of structural highs in inverted salt basins may be actually exposed to the highest geological risk.

Hybrid distributed energy sources providing climate security to the agriculture environment and enhancing the yield

Connected field of Mahanadi Basin, India, have been investigated with the adaptation of climate change techniques. The focus on improving food security and preserving environmental quality was followed by an integral approach. The Hadley Climate Center combined earth's weather models has derived global warming forecasts. Evaluation of effect and adaption methods using the plant model level and the freshwater and salt basin (WSBM) modeling level watershed was carried out. Three eras are evaluated in which the timeframe 1961–1990 is being used to adapt the forecasts for rising temperatures to particular conditions and also to reflect the given rise to a new in the short term (2010–2039) and the near future (2070–2099). As a consequence of the increased cultivar development owing to greater CO2 and a modest rise in precipitous rates, the overall effect of environmental Change on food safety and environmental integrity seems favorable. Nevertheless, throughout the future, extremities would be deeper and adaptive techniques would be needed. The outcomes of the modeling technique were provided as a way of making good judgments on needed adaptation measures, in a form that is open to water management managers and planners.

Burial wedges—Evidence for prolonged progressive burial of the Paradox Basin salt walls—With a detailed example from Gypsum Valley, Colorado

AbstractMany Paradox Basin passive salt diapirs underwent a prolonged history (>65 my) of progressive burial during the Early Triassic to Jurassic. Burial is recorded by a series of geographically limited wedge‐shaped stratal panels of diapiric roof, termed ‘burial wedges’, which partly covered the diapirs, thereby gradually narrowing them. Tectonostratigraphic analysis of the Triassic Chinle Fm. burial wedge developed on the Gypsum Valley diapir illustrates the typical features and processes associated with burial wedges. Burial wedges represent the first description of the geometry and deposition of strata deposited on a partially buried diapir. Recognition of burial wedges allows reinterpretation of Paradox Basin diapirs where large areas of the roof strata were syndepositionally folded rather than deformed in the Neogene. The observations and concepts can also be applied to the terminal histories of passive salt diapirs in other salt basins. Preserved burial wedges cover 97 km2, or 64% of the original Gypsum Valley diapir and overlie regional unconformities. Onlapping strata stack into wedge halokinetic sequences (HS). Caprock‐clast conglomerates indicate deposition on exposed diapirs. Syndepositional deformation of burial wedge strata formed small synclinal ‘microbasins’ and contractional chevron folds trending subparallel to the diapir margin. A four‐stage burial wedge model includes the following: (1) erosion of the diapir roof during formation of regional unconformities; (2) onlap and partial burial of the diapir; (3) local dissolution and possible concomitant gravity‐driven folding and (4) ongoing rotation during deposition, forming wedge HS signifying continued inflation of the top of the diapir. Post formation, the burial wedges were deformed in ways that obscure their original geometry. The most common deformation is downwarping of the burial wedge into the diapir due to dissolution or lateral movement of salt, creating an anticlinal fold that overlies the underlying diapir margin. These anticlines may be offset on small normal faults subparallel to the diapir margin. Burial wedges were faulted during later diapir breaching and solution collapse.

Linked detachment folds, thrust faults, and salt diapirs: Observations and analog models

Contractional deformation in salt-bearing rifted- and convergent-margin settings often involves diapirism. Diapirs may predate the onset of shortening, such that they exert a pronounced influence on how contractional strain is accommodated, or they may be triggered by the shortening. Analog models have been used to help understand the interaction and evolution of detachment folds, thrust faults, and diapirs, but few surface or subsurface datasets provide adequate three-dimensional images to test and refine the experimental results. Here we use 3D depth-migrated seismic data from the Sureste Basin, offshore SE Mexico, to map two structures, one dominated by salt-cored anticlines and one characterized by thrust faults. Associated diapirs include both pre- and syncontractional stocks and walls. We show that although analog models in the literature nicely reproduce some of the seismic geometries, there are also apparent mismatches. Whereas models often generate decapitated diapirs and thrust-fault salients centered on the diapirs, such features are absent in the study area. Moreover, in contrast to model thrust faults that dip 20-45°, faults in the study area are steeper, ranging from 50 to 75°. We bring in observations from other salt basins to discuss these discrepancies, possible explanations, and suggestions for improving the applicability of models to nature.

Origin and Evolution of Saline Spring Water in North and Central Laos Based on Hydrochemistry and Stable Isotopes (δD, δ18O, δ11B, and δ37Cl)

This paper discusses the origin and evolution of saline springs in north and central Laos, based on chemical and stable isotopes (δD, δ18O, δ11B, and δ37Cl). All the saline springs in this study are of the Na–Cl geochemical type. The geochemical and water isotope values suggest that the saline springs in this study are mainly derived from meteoric water and/or ice and snow melt from the surrounding mountains and that they also experienced strong evaporation and intense rock–water interactions. The ionic ratios, characteristic coefficients, ternary Ca–SO4–HCO3 phase diagrams, and saturation indices of minerals show that the dissolution of halite, sulfate, and carbonate rocks may be the solute sources for saline springs in this study, whereas the underground brines in the Thakhek potash mining area are geochemically influenced by the dissolution of carnallite and sylvite. The global geothermal δ11B–Cl/B relationship and δ11B values (5.50 to 36.01‰) of saline springs suggest a continental origin of B. This B is most likely derived from marine carbonate rocks and marine evaporates (gypsum and halite) of the late Cretaceous, which is similar to the saline springs of the Nangqen–Qamdo–Simao Salt Basin. The δ37Cl value (−0.12 to +0.79) and the Cl/Br ratio (4076 to 9853) show that dissolution of late cretaceous marine halite layers, atmospheric precipitation, and water–rock interactions between volcanic rocks, mudstones, and sandstone can restrict the δ37Cl values in saline springs. Results from silica geothermometry and multi–mineral equilibrium diagrams indicate that the reservoir temperatures for the saline springs range from 87–137 °C and experience deep circulation. Hydrochemical characteristic coefficients suggest that saline springs in the Muang Say basin may have leached sylvinite and carnallite and that the potash exploration prospect in this area is relatively good.

Depositional and diagenetic model of the Aptian potash-bearing Loémé evaporites in onshore Congo

The evaporites of the Aptian Loémé Formation occur along the stable structural domain of onshore Congo as horizontally well-stratified depositional halite interbedded with Mg-poor potash minerals including carnallite, bischofite, tachyhydrite and sylvite. Eleven correlative depositional recharge-to-evaporation cycles are composed of suites of organic-prone shale followed by primary halite and carnallite beds, sometimes punctuated by a bischofite-tachyhydrite end-member.A sedimentological and petrographical analysis performed on cores and thin sections allowed an interpretation of nine facies associations, named as FA1 to FA9, relying upon the occurrence of bands of fluid inclusions, grain-size, dissolution features, detrital sediments, minute inclusions and sedimentary structures. A depositional model reconciles the spatial distribution of primary textures, hydrology, brine saturation and palaeo-depth during a standard regressive evaporation cycle. Shallow burial eo-diagenesis led to compaction-driven dissolution and recrystallization into fine-grained halite and carnallite laminites but poorly affected the overall preservation of primary deposits.Measurements and profile analysis of bromine trace element concentrations reveal a palaeo-salinity increase of the parent brine for cycle II to base IX caused by a relative brine level fall and a gradual confinement of the salt basin, likely associated with an excess of saline elements inflow from hydrothermal vents. Similar depositional textures and bromine concentration variations are observed in the lower cycles of the Aptian evaporites from the counter-part Sergipe Basin in the northern part of the Brazilian margin, testifying of a progressive brine salinity rise due to a palaeogeographic confinement along the northern segment of the South Atlantic Ocean.In Congo, the sylvite displays horizontal “pseudo-stratifications” that unconformably overlay the crests of anticlines and propagate along flanks as a sharp-based caprock. The flushing and transformation of depositional carnallite – halite into secondary sylvite – halite is interpreted as having been caused by down-stepping incremental dissolutions sourced by younger pervasive connate to phreatic waters. In Sergipe, the sylvite is interpreted as secondary but further results from syndepositional dissolution of carnallite and tachyhydrite due to a regional North Atlantic Ocean ingression.