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This page highlights a selection of recently published, interesting scientific articles dealing with evaporite-related topics, along with a link that takes you to the article source.

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Linking mineral deposits to crustal necking: insights from the Western Alps

Although many studies link mineral deposit formation to rifting and hydrothermal processes, we present a study that focuses on the relationship between crustal necking and mineral deposit formation. Necking corresponds to the timing, location, and process of rift localization and abrupt crustal and lithospheric thinning. Although necking is well identified and described from present-day rifted margins and has been modeled numerically, little is known about the necking process and its possible link to ore deposit formation. We present observations from the Mont-Blanc fossil detachment system, one of the few exposed examples of a necking detachment fault. We show that fluids flowed along the fault zone and leached metals (mainly Pb and Zn). This process was associated with the hydrothermal breakdown of feldspar and biotite at temperatures of 200 °C and salinities ranging from 5 to 20 eq. wt% with a H2O-NaCl (-KCl) composition. The resulting metal-rich fluids reacted with mainly carbonate-rich units to form Pb-Zn ore deposits in basement and sedimentary cover rocks. A direct link can, therefore, be demonstrated between fluid and reaction-assisted breakdown of silicates, metal transfer and trapping along detachment faults, and the overlying sedimentary rocks during necking. Similar ore deposits can be found throughout the inner External Crystalline Massif of the Western Alps, interpreted as the former necking domain of the Alpine Tethys. This leads to the suggestion that necking and Pb-Zn deposit formation may be closely linked, a hypothesis, if correct, that has the potential to predict additional Pb-Zn-Ba-F resources in rifts, rifted margins, and reactivated fossil rifted margins forming collisional mountain belts.

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Figure 1. A) Fluid circulation and element transfer associated with crustal necking based on the example of the Mont-Blanc. At higher temperature, albitization occurs followed by sericitization and chloritization. Metal-rich brines move upward along the fault leading to the formation of ore deposits in the cover. The core zone (gouge) is acting as an impermeable barrier. B) Evolution of the hydrothermal system and fluid signature during rifting. 

The Geotectonic Peculiarities of the North Caspian Permian Salt-Bearing Basins (Kazakhstan)

The article examines the geotectonic and sedimentary features of the Upper Devonian–Carboniferous–Permian deposits of the North Caspian basin, represented by deposits of marine Paleozoic-isolated carbonate platforms formed during the subsidence of the basement on the passive continental margin. The top is covered by thick salt-bearing Kungurian deposits from the end of the Early Permian epoch. The formation of carbonate platforms is associated with a major tectonic restructuring of the basin at the turn of the Caledonian and Hercynian eras, when the Paleo-Tethys Ocean was formed and isolated carbonate islands began to grow in an open marine environment. The central part of the depression experienced a long and gradual subsidence that spanned the entire Paleozoic era and the beginning of the Mesozoic era. In the south and east, from the Devonian to the Permian periods, barriers were formed in the form of island carbonate massifs that separated the North Caspian basin from the Paleo-Tethys Ocean. During the formation of the salt-bearing basin, these barriers limited water exchange and ensured a one-way influx of sea water from the open ocean. As a result, at the end of the Permian period, thicker salts accumulated; however, during the collision of the continental massifs, an invasion of many kilometers of redbeds occurred. They initially stopped salt accumulation; however, gradually, in the north of the Caspian Sea during Roadian times, the salt accumulation continued. The post-Roadian time is associated with the influx of large quantities of redbed sediments, which caused gravitational instability in the underlying salt, and salt tectonics began with the formation of domal structures.

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Figure 1.  Distribution of salt domes in the North Caspian basin. Legend: 1- contours of salt domes identified from gravimetric and seismic data; 2- contours of salt domes, with identified oil and gas shows of overlying post-salt deposits; 3— inter-dome deposits of undivided post-salt Upper PermianTriassic beds; 4-boundaries of the North Caspian basin; 5-boundaries of the main structural elements: 6- definitions: C-D-Central Caspian trough; A-H-Astrakhan-Aktobe system of uplifts; T-S- Tugarakchan sag; E-E—eastern edge zone; N-E—northern edge zone; 7—zones characterizing different types of salt diapirs: (1)- eastern; (2)- south-eastern; (3)-Uyil-Emba; (4)-Azgir-Khobda; (5)- central; (6)-north-north-western; (7)-northern; 7-letter designations of allocated zones; 8- settlements; 9— rivers; 10-state border of the Republic of Kazakhstan.

Sulfuric acid caves of the world: A review

In soluble rocks such as limestone and dolostone there are two main types of cave genesis (speleogenesis); (i) epigenic speleogenesis, in which the aggressiveness that forms caves is derived from the surface, and (ii) hypogenic speleogenesis where upwelling gases and fluids acquire their aggressiveness at depth dissolving carbonate rocks to form caves. Whereas epigenic (surface) waters can be undersaturated respect to carbonates obtaining their aggressiveness mainly from soil CO2, hypogenic (deep rising) fluids can obtain their carbonate-dissolving capacity at depth from various processes and mechanisms. Hypogenic speleogenesis that involves dissolution of carbonate rocks by sulfuric acid, mainly derived by oxidation of upwelling hydrogen sulfide, is called sulfuric acid speleogenesis (SAS). Although this type of process has been described during the early 19th century, the first elaborated theories are rather recent, and a detailed model was proposed only in the mid-1970s. Only a few cave areas were known to host sulfuric acid caves, but studies were boosted with the discovery and understanding of the inactive Lechuguilla Cave in New Mexico (USA), and the still active Movile Cave in Romania, both discovered in 1986. Today 84 areas globally are known to contain sulfuric acid caves, offering a wide variety of environments. This review gives a historical overview of studies concerning these caves, explains the chemistry behind the formation of the dissolving fluids and their interaction with the carbonate host rock, and describes the chemical, mineralogical, geomorphological, and microbiological signatures typical of sulfuric acid dissolution. The significance of SAS caves in landscape evolution and their possible role in deep karstification, and thus hydrocarbon reservoirs and deep hydrogeology, is also briefly analyzed.

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Figure 1. Schematic representation of the various origins of sulfides involved in SAS, the migration paths of fluids and gases, and zones where oxidation and reduction take place. The orange arrow indicates slightly thermal fluids, the red one hot fluids. MVT stands for "Mississippi Valley Type" ore deposit.

Shallow brines: an enigmatic story

Shallow near-surface brines are a fundamental hydrochemical component of arid and semi-arid regions, providing commercially valuable elements and ecologically important environments, yet their chemical evolution is frequently misinterpreted. Some of this misinterpretation stems from the assumptions that evaporation has caused the observed concentration, that all “evaporate” minerals are formed by evaporation, or that there is a chemically closed system. These major processes, while obvious, are surprisingly nuanced and at times the wrong explanation.

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Figure 1.Salt mining in a sabkha on the Arabian coast, a few kilometers north of Dhahran, Saudi Arabia (photographer: Warren W. Wood)

Complex sulfur speciation in scapolite – Implications for the role of scapolite as a redox and fluid chemistry buffer in crustal fluids

Scapolite is a common S-, Cl-, and C-bearing mineral in metamorphic terranes, especially those that include meta-evaporites. Fluid interaction with scapolite-bearing rocks can result in albitisation of scapolite, and release of volatile components such as Cl−, CO32–, SO2 and/or SO42−. Hence, scapolite may play an important role in buffering the oxidation state, salinity and sulfur speciation of the rock and fluids in such terranes, and since Cl, S, and the redox state of S are vital for the transport and deposition of metals, scapolite may exert an important influence on hydrothermal mineralisation processes. We investigated the oxidation state of S and concentrations of S and Cl from 17 scapolite-bearing samples collected from various metamorphic and hydrothermal environments. The highest concentrations of S and Cl in the samples set are respectively 1.11 ± 0.04 wt% S (reported as SO3, n = 10 points measurements) and 3.84 ± 0.17 wt% (n = 11 points measurements). µ-XANES spectroscopy demonstrates that S chemistry in scapolite is complex, S being present in both oxidised (as sulfate and sulfite) and reduced forms (polysulfides and minor sulfide) in most scapolites. These results confirm that scapolite can buffer fluid oxidation state to sulfate/sulfide coexistence, at acidic to neutral pH. The proportion of reduced S in scapolite increases with increasing metamorphic grade from greenschist to amphibolite facies. Since scapolite contains highly reactive polysulfide and sulfite, its breakdown may promote alteration of sulfide minerals and release of hosted metals. Thus, the presence of scapolitic calc-silicate rocks can strongly influence regional syn-orogenic metallogeny and should allow the mobilisation of metals differently from other bulk compositions.

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Figure 1. Ternary diagram after Hoefs et al. (1982) showing volatiles composition (in wt% ratios) of scapolite from greenschist (GS), amphibolite (A), granulite (G) facies as well as kimberlite xenoliths (KX) from a compilation of Coolen (1980). Coloured dots are published data from Kwak (1977); Oliver et al. (1994); Porter and Austrheim (2016); Hammerli et al. (2014); Bernal et al. (2017) and Gajdosová et al. (2017). Our sample set plots into the GS and A domains. Carbonate (C) is calculated based on the formula (16 cations basis), assuming full occupancy of the volatile site in the scapolite structure (C + S + CI + F).

Gypsum-lined degassing holes in tumuli

Small, circular holes, lined with a thin gypsum veneer, and closely associated with gypsum tumuli (domes), occur at Salar de Pajonales, a salt flat in the northern Andes, Chile. We propose a model in which the formation of the gypsum-lined holes, and less commonly the formation of the tumuli itself, is controlled by the unique juxtaposition of physiographic, geologic and hydrologic conditions. On a regional scale, Salar de Pajonales is unusual compared to other salars, as it is located close to a large magmatic inflation centre (Lazufre), lies along strike of major regional structural trends, is a large ephemeral lake and contains high salt concentrations. On a basin scale, the lined holes are only present along strike of lineaments that are directly linked to the local stress regime. In turn, these lineaments control the location of degassing and subsequently the formation of the lined holes in the gypsum tumuli and, in part, the tumuli themselves.

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Figure 1. Tumuli (a) Plateau scale model for the source of uplift and gases. See text for explanation. (b-e) Possible tumuli-scale model stages for the formation of the lined holes in pre-existing tumuli (b,c) and on flat areas with tumuli nucleating from the holes (d,e). In the former, gases accumulate in sealed tumuli (b). When gas pressure in the tumuli chamber exceeds cap pressure, the tumuli breaches along weak zones (c). Atmospheric changes in the breached tumuli chamber result in evaporation and subsequently in the formation of gypsum lining at the vent. In flat-lying lined holes, the hole enables liquid and vapour water exchange between the subsurface cavity and the atmosphere (d). Textural and volumetric changes associated with expansion and contraction of Ca-sulphate phases during wetting and drying cycles result in upward warping around the hole (e)

Variations in extent, distribution and impact of dolomitization on reservoir quality of Upper Cretaceous foreland-basin carbonates, Abu Dhabi, United Arab Emirates

Petrography, petrophysics, and geochemistry of an Upper Cretaceous, foreland-basin carbonate reservoir, Abu Dhabi, United Arab Emirates, are used to constrain the spatio-temporal variations in the extent of dolomitization and its impact on reservoir quality. Dolomitization in highstand systems tracts (HST) is attributed to repeated tidal and evaporative pumping as well as seepage reflux of penesaline brines during restriction of the platform due to 4th and 5th order cycles of relative sea-level fall and particularly below parasequence boundaries. This interpretation is supported by the presence of rare poikilotopic gypsum cement and scattered laths and micro-nodules of calcitized gypsum in the dolomitized peritidal dolostones. Dolomitization along bioturbation sites, which is most common in the transgressive systems tracts (TST), is attributed to the development of suitable localized geochemical conditions (e.g., microbial sulfate reduction and related increase in carbonate alkalinity). Porosity and permeability of the dolostones are strongly controlled by depositional textures of precursor limestones and by subsequent diagenetic evolution. Dolomitization of mudstones, wackestones and matrix-rich packstones has resulted in the formation of micropore-dominated microcrystalline dolostones whereas dolomitization of the shoal grainstones resulted in the formation of coarse-crystalline dolostones with abundant well-connected intercrystalline and moldic macropores. Mesogenetic alterations of the dolostones, which are attributed to the flow of hot basinal brines along steep faults, include dolomite cementation and, subsequently, dissolution and calcitization of dolomite (dedolomitization) and calcite cementation. The lack of systematic differences in porosity and permeability of dolostones between the oil and water-saturated dolostones suggest that most diagenesis occurred prior to completion of oil emplacement and/or reflect the shallow maximum burial depths of the formation (around 1.3 km). This study demonstrates that variations in the distribution and extent of dolomitization within a sequence stratigraphic context across an oilfield should be considered as primary control on the spatio-temporal reservoir lithology and heterogeneity in carbonate successions.

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Figure 1. Conceptual model for the deposition of limestones and evaporative dolomitisation of the Upper Cretaceous carbonates across a ramp with lagoon isolated from the open sea by a barrier (A). Dolomitisation by seepage reflux occurred below parasequence boundaries, i.e. during 4th - 5th order relative sea-level fall and formation of penesaline brines (B, C and D). Conversely, major marine transgression events resulted in deposition of limestones.

Quantifying climate conditions for the formation of coals and evaporites

Coals and evaporites are commonly used as qualitative indicators of wet and dry environments in deep-time climate studies, respectively. Here, we combine geological records with climate simulations to establish quantitative relationships of coals and evaporites with temperature and precipitation over the Phanerozoic. We show that coal records were associated with a median temperature of 25°C and precipitation of 1300 mm yr−1 before 250 Ma. Afterwards, coal records appeared with temperatures between 0°C and 21°C and precipitation of 900 mm yr−1. Evaporite records were associated with a median temperature of 27°C and precipitation of 800 mm yr−1. The most remarkable result is that net precipitation associated with coal and evaporite records remained constant across time. The results here have important implications for quantifying climate conditions for other lithologic indicators of climate and for predicting exogenetic ore deposits.

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Figure 1. Distribution of coals and evaporites as a function of simulated Average Mean Temperature (AMT) during =the Phanerozoic, (a) Histogram of coals from 410 Ma-250 Ma (b) Coals from 410 Ma to present c) histogram of coals over 240 Ma-present, (d) Evaporites from 550 ma to present, (e) histogram of evaporites over 540 Ma-present. Colors indicate AMTs. The temperatures containing 25%, 50%, and 75% of the coal and evaporite records are marked by the vertical black bars in (a), (c) and (e).

Origin of lithium-rich salt lakes on the western Kunlun Mountains of the Tibetan Plateau: Evidence from hydrogeochemistry and lithium isotopes

Lithium-rich salt lakes have attracted much attention as important lithium resources. The source and enrichment mechanisms of lithium in salt lakes are fundamental to uncovering the genesis of brine-type lithium deposits. However, the origin of lithium in salt lakes has been controversial, especially for lithium-rich brines associated with hard rock lithium ore has not been concerned by scholars. In this study, for the first time, we investigated the lithium isotope and hydrochemical composition characteristics of a lithium-rich salt lake (Kushui Lake) and a series of surrounding water samples in the lithium pegmatites district of West Kunlun, Xinjiang, China. Hydrochemical composition shows that different samples in the basin are rich in Li, Na, and K and poor in Mg and Ca. The water chemistry of the Kushui River, the largest river within the catchment, changes from carbonate type to sulfate subtype through evaporation. The precipitate of sulfate and chloride minerals is also gradually increasing. In addition, Li, B, Sr, Rb, Cs, U, Ti, V, Mn, Cu, Zn, Cr, Co, Ni, and REE are abnormally enriched in the rivers and lakes of the basin, especially in the spring water, which is several times higher than in the rivers. Likewise, dissolved Li and δ7Li showed ranges of 0.01–287.86 mg/L and 3.28–16.44 ‰, respectively. These data were used to determine the origin of lithium and its enrichment process in salt lakes. The results show that the source of Li in Kushui Lake is closely related to the surrounding felsic volcanic rocks, pegmatite-type lithium ore and deep fluids, whereas the water–rock interaction in the deep crust and the chemical weathering in the supergene environment play an influential role during the formation of Li-rich fluids. In addition, the spring samples in the northwestern of Kushui Lake have inherited the lithium isotopic signature of lithium-bearing source rocks from the water–rock reaction process in the deep crust, allowing us further to isolate the source of Li in the target waters. With the movement of water, lithium exhibits a trend of continuous enrichment under the influence of evaporation and mixing. At different stages of evaporation, the Li/Na ratio in water in this catchment shows a trend of increasing, decreasing, and increasing due to the adsorption of 6Li by secondary minerals and the crystallization of Na. It suggests that strong evaporation under arid conditions is the main mechanism responsible for the rapid enrichment of Li in salt lakes. Moreover, the positive relationship between Li content and the δ7Li value of rivers along the discharge path indicated that the adsorption of 6Li by secondary minerals still existed even at a minor watershed scale, resulting in the fractionation of lithium isotopes in river waters. This study may contribute to a deeper understanding of lithium sources and their enrichment processes in Li-rich salt lakes. In addition, it is also beneficial to search for new lithium resources based on the source relationships among the various lithium reservoirs.

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Figure 1. Schematic conceptual model for mineralization of the lithium-rich salt lakes in the intermountain basin of West Kunlun Mountains.

Pleistocene aragonite crust diagenesis mimics microbialite fabrics (Danakil Depression, Ethiopia

Fibrous aragonite crusts occur in two consecutive Pleistocene successions in the Danakil Depression (Afar, Ethiopia). Lateral transitions between pristine and altered fibrous aragonite crusts document changes in texture associated with diagenesis. Crusts formed as essentially abiotic seafloor precipitates at the transition from marine to evaporitic conditions. Diagenesis started with the dissolution of aragonite fans at the interface between single fans in non-laminated crusts and along lamination planes in isopachous, irregular, or crudely laminated crusts. Incomplete dissolution resulted in the development of secondary porosity within a matrix of undissolved aragonite fibers. Subsequently, the porosity was filled with calcite that systematically encased remaining aragonite crystals. This was followed by the dissolution of remnant aragonite fibers, producing a network of elongated inter- and intracrystalline pores that were eventually filled with low-Mg calcite. The stepwise substitution of fibrous aragonite by low-Mg calcite resulted in sparry, sparry-cloudy, sparry-micritic (including clotted micrite), and peloidal textures, which obscure the fibrous nature of the original deposits. Stable C- and O-isotope compositions suggest that early diagenesis was driven by meteoric and evaporative fluids. These observations unequivocally demonstrate destructive diagenesis, resulting in secondary textures, which mimic micritic and grumous (peloidal and clotted) textures associated with sparry microfabrics. This suggests that these textures, classically interpreted as primary microbial precipitates and used as evidence of biogenicity in ancient microbialites, might be diagenetic products in some cases, even though at some stage, microbial processes and/or degradation of organic matter could have been involved in the diagenetic process.

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Figure 1. Crusts in the Danakhil sump A) Photomicrograph of a thin section showing an example of a pristine isopachous lamination inside an aragonite botryoid from a well-preserved crust. B) Thin section image showing isopachous laminated crust displaying initial dissolution along lamina (darker parts). C) SEM-SE image of a partially altered botryoid. Aragonite fibers are oriented from bottom to top. Note that fibers are sometimes interrupted by pores (black areas within the botryoid, and that these pores are dominantly arranged on planes perpendicular to the fibers (i.e. parallel to lamination Dianes. velow arrows. D) CI-image showing details of the three perpendicular planes of a reconstructed CT-scan of the partially altered crust. The lighter gray values of the scan correspond to aragonite or calcite and the darker correspond to pores. The homogenous upper part (white arrow) is made of primary aragonite. The more altered lower part shows a clear lamination made of darker and brighter laminae composed of alternating diagenetic calcite (bright) and fenestral porosity (dark bands highlighted with the yellow arrow). The basal plane shows that the crust is composed of discrete columns (purple arrow). Note that dissolution is strongest along lamination planes (dark bands) inside the columns. the sediment berween the columns is less The diameter of the columns is around I cm in the lower part.

The Role of Salt Tectonics in the Energy Transition: An Overview and Future Challenges

The fundamental properties of salt have long been exploited in the search for hydrocarbons, as they influence many of the hydrocarbon play elements. This industrial application has driven the pursuit of salt tectonic knowledge over the last century and led to major conceptual advances in the field. However, the current need, and social-political demand, to decarbonize suggests that the applicability of salt tectonic knowledge will expand to other aspects of the subsurface that are relevant to the energy transition. The pace of this change leaves the field of salt tectonics grappling with a fundamental question – what role does salt tectonics have as part of the energy transition? Here, we discuss the role salt tectonics can play in a number of key energy transition technologies, namely, energy storage as gas in salt caverns (e.g. hydrogen and compressed air), CO2 storage, and geothermal energy. For each of these technologies we explore: i) fundamental concepts and driving forces; ii) how and why the properties of salt are of importance; and iii) the key salt-related technical challenges, potential future research directions, and technical approaches needed for large-scale development. We highlight how salt basins offer vast potential for development throughout the energy transition including, but not limited to: i) the likely demand for thousands of new hydrogen storage caverns inside salt bodies by 2050; ii) a likely early focus for porous media CO2 storage sites in basins strongly influenced by salt tectonics; and iii) enhanced geothermal energy potential in and around salt bodies. Effective exploitation of these resources will require a deeper understanding of the internal composition, geometry, and evolution of salt structures and their surrounding sediments, and potentially the development of more predictive models of salt tectonic behaviour. Critically, we see the need to integrate learnings of salt tectonics gained in the academic, mining, solution mining, and oil and gas communities, and apply a fresh perspective to answer research questions of relevance to the energy transition. Developing this new understanding will help optimise design, reduce geotechnical risk, and improve efficiency for energy transition technologies, thus indicating a strong future demand for salt tectonic research.

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Figure 1. Conceptual model illustrating the role of salt tectonics on the effective deployment of a range of energy transition technologies (energy storage in salt caverns, CO2 storage, geothermal energy, oil and gas exploration). Note the influence of a wide range of salt diapir geometries and intra-salt heterogeneities. Diapir A is upward flaring and contains a boudinaged interval; Diapir B shows a salt sheet or wing developed and a complex configuration of'slippery' and soluble bittern salts; Diapir C is a wide and faulted diapir with contorted anhydrite; Diapir D shows a teardrop geometry and is composed of relatively homogeneous halite; and Diapir E is deep-seated. The geometries and statal relationships in sediments surrounding the diapirs also vary significantly due to salt tectonic processes. Ultimately, each salt basin and each salt diapir is unique and understanding of salt tectonic processes is required to successfully deploy energy transition technologies.

Plate tectonic control of strontium concentration in Phanerozoic and Neoproterozoic seawater: Evidence from fluid inclusions in marine halite

Chemical analyses of 1371 fluid inclusions in 131 halite samples with marine 87Sr/86Sr values were used to reconstruct the strontium concentrations [Sr]SW of Phanerozoic and Neoproterozoic seawater. [Sr]SW varied seven-fold and oscillated twice between high- and low-Sr concentrations over the past 550 million years (Myr), in rhythm with Ca-rich and SO4-poor paleoseawater intervals and calcite-aragonite seas. Variations in the [Sr]/[Ca]SW ratio from fluid inclusions were not significant over the past ∼270 Myr, and are within ±3 µmol/mmol of the modern [Sr]/[Ca]SW ratio of ∼8.5 µmol/mmol. These results agree with the [Sr]/[Ca]SW ratios obtained from fossil corals, benthic foraminifera, brachiopods, belemnites, and rudists. [Sr]/[Ca]SW in the early and middle Paleozoic was ≈ 2 times the modern [Sr]/[Ca]SW ratio. A major shift of the [Sr]/[Ca]SW ratio in the late Permian coincided with the initial rifting of the Pangean supercontinent. Seawater 87Sr/86Sr ratios plotted against 1/[Sr]SW show two distinct linear correlations: negative correlation from 515 to 252 Ma and positive correlation from 150 to 0 Ma, suggesting different controls on the global Sr cycle between these intervals. The negative correlation coincides with the long-term assembly of Pangea in the Paleozoic (∼500–250 Ma). The positive correlation from 150 to 0 Ma parallels the break-up of Pangea and the decrease of mid-ocean ridge (MOR) hydrothermal fluid flux and subduction zone length in the Mesozoic and Cenozoic

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Figure 1 Secular variation in Phanerozoic and Neoproterozoic seawater [Stlsw and [Srl/(Ca)sw ratios. Marine 87S/86Sr ratio (blue curve) are divided into three phases by McArthur (2010). [Sr]sw and [Sr|/|Ca|sw ratio (circles) were calculated from [Sr]*. [Ca]* published |Ca|sw (Weldeghebriel et al., 2022), and the partition coefficient (Kds) of gypsum (Kushnir, 1980). The indigo curves connect mean [Sr )sw and the [Sr|/| Ca lsw ratios calculated using mean Kdsr = 0.43. Gray bands around indigo curves show uncertainties in accuracy of calculated [Sr]sw and the [Sr]/|Ca]sw that is associated with Kdsr range between 0.2 and 0.8 and [Ca]sw range (Table 2) (Weldeghebriel et al., 2022). The red curve shows [Sr)sw calculated using the Doerner-Hoskins relation and ks of 0.7. [Sr]/| Ca]sw data from fossil brachiopods, belemnites, and rudists (crosses) (Steuber and Veizer, 2002), corals (triangles) (Gothmann et al., 2015), benthic foraminifera (diamonds) (Lear et al., 2003), mid-ocean ridge flank calcite veins (blue squares) (Coggon et al., 2010) and (cyan squares) (Rausch et al., 2013). [Sr]* and [Ca]* are [Sr]F and [CalF from fluid inclusions divided by degree of evaporation to correct tor their increase in concentration during evaporation. Dashed lines are best fitt curves to the ISrI* and |Cal* over the last 550 Ma. Uncertainties. shown by two SE bars (95% confidence interval), were calculated from the standard deviation of (n) fluid inclusion analyses in halite using STD/sqrt(n) (Table 2). Supercontinent cycle (dispersal, assembly) from Frizon De Lamotte et al. (2015) and Kroner et al. (2021). Blue and pink shading show SO4-rich and Ca-rich seawater, respectively (Weldeghebriel et al., 2022). Horizontal bars at the top and bottom of the figure are greenhouse-icehouse climates (McKenzie et al., 2016), MgSO4-KCI potash evaporites (Hardie, 1996), and aragonite calcite seas (Sandberg. 1983).

Ca and SO4 in Phanerozoic and terminal Proterozoic seawater from fluid inclusions in halite: The significance of Ca-SO4 crossover points

Chemical analyses of 2,618 (1,640 new and 978 published) fluid inclusions in marine halite were used to define paleoseawater [Ca] and [SO4] over the past 550 million years (Myr). Three types of fluid inclusion brine chemistries were recognized based on measured [Ca] and [SO4]: (1) SO4-rich with [SO4] ≫ [Ca]; (2) Ca-rich with [Ca] ≫ [SO4]; and (3) Ca-SO4 crossover points with [Ca] ≈ [SO4]. The SO4-rich and Ca-rich fluid inclusion chemistries oscillated twice in the terminal Proterozoic and Phanerozoic. Transitions between SO4-rich and Ca-rich seas, here called “Ca−SO4 crossover points” occurred four times: terminal Proterozoic–Early Cambrian (544–515 Ma), Late Pennsylvanian (309–305 Ma), Triassic–Jurassic boundary (∼200 Ma), and Eocene–Oligocene (36–34 Ma). New fluid inclusion analyses using laser ablation-inductively coupled plasma-mass spectrometry better defined the [Ca] and [SO4] in seawater at the Late Pennsylvanian and Eocene–Oligocene crossover points and the timing of the Triassic–Jurassic crossover point. Crossover points coincide with shifts in seawater Mg/Ca ratios, the mineralogies of marine non-skeletal carbonates and shell building organisms (aragonite vs. calcite) and potash evaporites (MgSO4 vs. KCl types). Phanerozoic and terminal Proterozoic trends in seawater [Ca] and [SO4] also coincide with supercontinent breakup, dispersal, and assembly cycles, greenhouse–icehouse climates, and modeled atmospheric pCO2. Paleoseawater [Ca] and [SO4] were calculated from the fluid inclusion data using the assumption that the [Ca] × [SO4] ranged from 150 to 450 mmolal2, which is 0.5–1.5 times the [Ca] = 11 × [SO4] = 29 product in modern seawater (319 mmolal2). Two additional end-member scenarios, independent of the [Ca] × [SO4] = 150–450 mmolal2 assumption, were tested using constraints from fluid inclusion [Ca] and [SO4]: (1) constant [SO4] = 29 mmolal as in modern seawater, and variable [Ca], and (2) constant [Ca] = 11 mmolal as in modern seawater and variable [SO4]. Mg/Ca ratios calculated from the three scenarios were compared to independent data on the Mg/Ca ratios from skeletal carbonates (echinoderms and corals) and mid-ocean ridge flank calcite veins. Constant [Ca] of 11 mmolal is unlikely because this relatively low concentration generated unreasonably low seawater [SO4] during most of the past 550 Myr and high Mg/Ca ratios compared to independent data. Constant [SO4] of 29 mmolal produced unreasonably high seawater [Ca] and lower Mg/Ca ratios than those derived from fluid inclusions, echinoderms, corals, and calcite veins. Variable [Ca] and [SO4] showed the best agreement with the Mg/Ca ratios derived from fluid inclusions, echinoderms, corals, and calcite veins.

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Figure 1. Secular variation in Phanerozoic and terminal Proterozoic seawater [Ca and SO4], showing raw data (uncorrected for varying concentration factor) from 2618 brine inclusions in halite. Circles and diamonds are [SO4] and [Ca], respectively; white circles and orange diamonds are new data whereas blue circles and red diamonds are published SO4 and Ca, respectively; the indigo curve connects the median value of each dataset. The large range of SO4 and Ca from one particular age is due to halite precipitation at varying concentration factors-this is corrected. Orange curve is cumulative proportion of young zircon grains from globally distributed clastic sedimentary rocks used to track the spatiotemporal distribution of continental volcanic arcs. Blue curve is modeled Phanerozoic and Late Proterozoic atmospheric CO2 concentrations. Supercontinent cycle (dispersal, assembly) from Frizon de Lamotte et al. (2015) and Kroner et al. (2021). Blue and pink shading show SO4-rich and Ca-rich seawater, respectively. Horizontal bars at the top and bottom of the figure are greenhouse-icehouse climates, MgSO4-KCI potash evaporites , and aragonite-calcite seas. 

High-amplitude water-level fluctuations at the end of the Mediterranean Messinian Salinity Crisis: Implications for gypsum formation, connectivity and global climate

The formation and dissolution of salt giants impacts ocean chemistry on thousand-million year timescales. Gypsum precipitation and weathering changes the oceanic calcium concentration with implications for the carbon cycle and global temperatures. However, the connectivity of salt giants with the global ocean is necessarily restricted, making the timing of Ca2+ extraction and return more uncertain. Here we reconstruct the final phase of gypsum precipitation of the Late Miocene Mediterranean Salt Giant using micropaleontology, sedimentology and 87Sr/86Sr analyses on the most complete record preserved at Eraclea Minoa on Sicily and explore its implications for global climate. Precessional gypsum-marl couplets (Upper Gypsum) characterize the last 200 kyrs (Stage 3) of the Messinian Salinity Crisis (MSC; 5.97–5.332 Ma) in both intermediate (500–1000 m) and deep (>1000 m) Mediterranean basins. The interbedded selenitic gypsum layers contain well-preserved calcareous nannofossil assemblages dominated by Reticulofenestra minuta, a marine species which tolerates stressful conditions. Marine water is also required to explain the gypsum 87Sr/86Sr data, which describe a small range of ratios (0.708704–0.708813) lower than coeval ocean water. Mass-balance calculations indicate that during gypsum precipitation, the Atlantic made up ≤20% of a Mediterranean (“Lago-Mare”) water mass dominated by low salinity discharge from large river systems and Eastern Paratethys. This suggests episodic extraction of calcium and sulfate ions from the ocean throughout MSC Stage 3. The marls commonly contain shallow (30–100 m) brackish-water ostracods of Paratethyan (Black Sea) origin. Marls with Paratethyan ostracods are also found in both marginal (<500 m) and deep Mediterranean settings. This indicates that marl-deposition was not synchronous across the basin, but that it occurred in intermediate and deep basins during base-level lowstands at insolation minima and on the shallow Mediterranean margins during insolation maxima-driven highstands. These high-amplitude base-level fluctuations exposed the evaporites to weathering, but ponded the products in the Mediterranean basin until reconnection occurred at the beginning of the Pliocene.

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Figure 1. Lithofacies a of a complete UG cycle as a function of precession cycle and Mediterranean base-level according to Manzi et al. (2009) and this study. A comparison with the PLG interpretation is also shown (re-drawn after Roveri et al., 2008). The question marks in the figure to the left refer to the uncertainty over the paleodepth during deposition of sub-units A, B and C. Note that our new interpretation of the UG challenges the long-lasting idea that PLG and UG reflect similar depositional mechanisms and paleoenvironmental conditions (Manzi et al., 2009; Roveri et al., 2014a). This is consistent in a number of ways: (1) UG and PLG sequences comprise different facies (UG contains more abundant balatino gypsum and is missing the banded and branching selenite lithofacies of the PLG). (2) Euxinic shales interbedded with the PLG contain possibly in-situ marine fossils (e.g. Corbí and Soria, 2016), whereas the marls interbedded with the UG contain brackish and shallow water ostracods and brackish water foraminifera such as A. tepida (Grossi et al., 2015). This is likely to reflect greater proportion of marine water in the Mediterranean during Stage 1. (3) 87 Sr/86 Sr isotopes are consistent with the above interpretation, being, on average, close to, or within error of coeval ocean values on stage gypsums (average of 0.708941; Lugli et al., 2010; Reghizzi et al., 2018) and substantially higher than those measured 3 on Stage 3 gypsum samples (average of 0.708752). (4) The Stage 3 gypsum 87Sr/86Sr data are either constant within the layer or show a subtle decline from base to top. This is in a contrast with a larger base to top increase in 87Sr/86Sr ratio in Stage 1 gypsum layers from the Vena del Gesso Basin (Northern Apennines; Reghizzi et al., 2018). (5) The PLG is largely restricted to marginal basins (e.g. Lugli et al., 2010; García-Veigas et al., 2018), whereas the UG is only found in intermediate-deep basins. b: Summary outline of the main sedimentological (i), paleontological (ii) and geochemical (iii) data for each sub-units, their interpretation in terms of salinity (iv) and relationship with the base-level curve (V) and their paleoenvironmental and paleohydrological interpretation proposed in this work (vi).

Global metallogeny in relation to secular evolution of the Earth and supercontinent cycles

Mineral systems with their core of ore deposits require a rare conjunction of geodynamic settings, crustal or lithospheric fertility, crustal architecture and suitable host rocks, and preservation potential. They are thus an integral component of Earth’s thermal and tectonic evolution which also control the supercontinent cycles with progressive assembly and breakup of Ur, Kenorland, Columbia, Rodinia, Gondwana, and Pangea. Despite the ongoing debate, some form of plate tectonics has operated on Earth since the Eoarchean. However, the hotter Archean mantle generated a long-term double-layered convection system which was disrupted by episodic mantle overturns, with the largest in the early Neoarchean potentially enriching the mantle in metals that form the Earth’s core (Figure 1). Cratons with thick subcontinental mantle lithosphere (SCLM) or tectosphere keels commenced to form in the Mesoarchean as small continents amalgamated. The conjunction of pre-4.0 Ga crust, giant Ti, Cr, Fe, Ni and PGE-enriched layered mafic intrusions and major diamond fields provide strong evidence that the Kaapvaal and Zimbabwe Cratons and Wyoming Craton formed part of Ur with its early potentially core-metal-fertilized SCLM. Orogenic gold deposits and VMS Cu-Zn-Pb deposits with their high preservation potential were deposited in subduction-related convergent margins that activated the assembly of all supercontinents with giant provinces related to assembly of Kenorland, Columbia and Gondwana-Pangea. Erosion-susceptible porphyry Cu-Au and epithermal Au-Ag deposits were most abundant at the time of Gondwana and Pangea and in Cenozoic convergent margins and collisional orogens, although there are rare examples associated with assembly of all supercontinents. Magmatic intrusion-related Ni-Cu-PGE, and magmatic-hydrothermal IOCG Cu-Au and Kiruna-type Fe-P deposits formed near craton margins. However, although giant Ni-Cu-PGE deposits formed during the breakup of all supercontinents, giant IOCG deposits were largely restricted to extensional episodes related to Kenorland and Columbia and Kiruna-type deposits to those involved in Columbia. The evolution of the Earth’s atmosphere-hydrosphere-biosphere was an additional influence on that of the supercontinent cycle in terms of the evolution of metallogenic provinces (Figure 2). The Great Oxidation Event (GOE) at ca. 2.4–2.0 Ga witnessed the end of the great era of deposition of BIFs that became the hosts to high-grade Fe and Mn deposits which formed under more oxidizing conditions, with Oligocene sediment-hosted Mn deposits and late-Cenozoic Mn nodules becoming the dominant Mn resources and potential resource, respectively. The GOE was also responsible for the evolution of U deposits from the Mesoarchean paleoplacer uraninite deposits of the Witwatersrand, through Mesoproterozoic unconformity-related deposits to Phanerozoic sandstone roll deposits. The Cambrian ‘explosion of life’, following a second GOE event, magnified the importance of organisms, particularly those secreting Ca and Mg, carbonate in the formation or ore deposits in sedimentary basins. Late Paleoproterozoic-Mesoproterozoic shale-hosted SEDEX Zn-Pb-Cu deposits were progressively replaced by Phanerozoic carbonate-hosted MVT Pb-Zn deposits and Neoproterozoic-Cambrian Zambian-type Cu-Co deposits hosted in calcareous sedimentary sequences. Carlin-type Au-Ag deposits hosted by calcareous and carbonaceous sequences appeared in the Cretaceous to Paleogene epochs to rival the more ubiquitous orogenic gold deposits in terms of global importance. It is evident that the evolution of the great metallogenic belts of the Earth was intrinsically linked to the thermal and tectonic evolution of the Earth and particularly to plate tectonics and the supercontinent cycles. The nature of contained mineral deposits of elements with multiple valency states and those requiring particularly reactive host rocks was strongly influenced by the evolution of the atmosphere-hydrosphere-biosphere system.

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Figure 1. Evolution of plate motions and ore deposit drivers in time. (a) and (b) Schematic plate tectonic sketch showing Archean double-layered mantle convection and modern whole mantle convection. (c) Double-layered mantle convection in the Archean in between major overturn events.
Figure 2. Evolution of the atmosphere and hydrosphere. (a) Schematic compilation of the major phases during the secular evolution of Earth, environment, and life. (b) Major events in environmental and life evolution during Earth history. The age ranges of some of the supercontinents are also shown. GOE - Great Oxidation Event. NOE- Neoproterozoic Oxidation Event.

Cryptic sulfur cycling during the formation of giant gypsum deposits (Messinian Primary Lower Gypsum)

Salt giants are large-scale, basin-wide deposits formed sporadically in the geological past, from the early Paleozoic to the late Cenozoic. Their role as sinks for seawater dissolved ions is well known, however the biogeochemical conditions that accompany salt giant formation and their effects on carbon cycling remain poorly constrained. Here we show that massive gypsum deposits of the Mediterranean salt giant – the youngest salt giant on Earth – formed in a particularly dynamic biogeochemical environment controlled by orbitally-driven climate oscillations at the precessional scale. Using multiple sulfur isotopes combined with a steady-state sulfur cycle model, we show that, prior to gypsum precipitation, more than 80% of its constituting sulfate was first microbially reduced into sulfide, possibly stored as elemental sulfur, and then almost completely microbially reoxidized back to sulfate. This “cryptic” sulfur cycling contemporaneous to gypsum precipitation implies both negligible net sulfate consumption and sulfide production, despite a significant benthic flux of organic carbon remineralized through microbial sulfate reduction. This is the first known evidence of cryptic sulfur cycling in the geological past.

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Figure 1. Schematic representation of the biogeochemical conditions that accompanied The deposition of the Messinian Primary Lower Gypsum (PLG) deposition. (A) Deposition of organic rich marls during humid phases (precession minima). (B) Deposition of gypsum in the margins and marls in the depocenter during arid phases (precession maxima). The relative size of the arrows represents the approximate magnitude of fluxes. (C) Details of a gypsum twin.

Episodic venting of extreme subsalt overpressure through a thick evaporitic seal

Episodic venting from deep overpressured layers has rarely been documented in sedimentary basins, so the pressure evolution leading to these cyclical phenomena is poorly understood at present. Using three-dimensional (3D) seismic data from the West Nile Deep Sea Fan, the authors interpret >480 fluid escape pipes within a region of prolific leakage across a > 2 km thick sealing sequence of salt and claystones. Within this region, they map five linear trails of pipes with pockmarks or small mud volcanoes at their outlets and interpret them to have formed by episodic venting of overpressured fluids from beneath the salt, over a ∼2–3 Myr period, coeval with basinward displacement of the pipes by flow of the salt. Importantly, the pipe trails root to the crests of stratigraphic traps at the base of the salt seal. Direct measurements from nearby exploration wells are used to construct pressure-depth and pressure-time plots over the lifetime of the pipe trails and demonstrate that overpressure near to or in excess of the lithostatic pressure must be repeatedly achieved in the stratigraphic traps to breach the salt seal every 50–150 kyrs. This pressure evolution is best described by a sawtooth pattern with overpressure relieved by venting, followed by re-seal of the trap, and pressure recharge. The pressure recharge for this episodic venting can most easily be explained here by biogenic gas generation and aquifer pressure transfer in the traps, with some minor contribution from sustained disequilibrium compaction during the Pliocene to Recent. The conditions necessary for this type of episodic venting should occur more widely, particularly in basins with thick evaporite deposits. The recognition of episodic venting has important implications for prospect de-risking, drilling safety and CO2 and hydrogen storage.

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Figure 1. Seismic stratigraphy, base salt structure and mud volcanoes, pipes and pipe trails in the Western Nile region of the Mediterranean. A: A seismic cross-section through the 3D seismic of the studied area highlighting the key marker horizons and seismic stratigraphy. OM Oligo-Miocene, IOM Intra-Oligo-Miocene, LEU Lower Evaporitic Unit, UEU Upper Evaporitic Unit. B: IOM to Base Salt isopach map showing regional and anomalous thickness distribution of OM2 across the study area and erosional remnants (ER) and erosional depressions (ED). The location of all the mud volcanoes, pipes and 5 pipe trails (PT) are show. The erosional remnants correlate with increases in thickness of OM2. The erosional depressions and also circular to elliptical mud depletion zones that underly the mud volcanoes correlate with decreases in thickness of OM2.

Trace metals in saline waters and brines from China: Implications for tectonic and climatic controls on basin-related mineralization

Research into mineralization using a deposit-centric approach has identified three principal factors (evolution of the hydrosphere–atmosphere, secular decrease in global heat production, and long-term global tectonic trends) that have influenced the global pattern of metallogenesis. However, these factors do not explain the peak occurrences of basin-related mineralization during particular periods of Earth’s evolution. Here we shift the research perspective from an ore-deposit-centric approach to one focusing on the formation processes of ore-forming fluids by using mass spectrometry to analyze the concentrations of metallic elements (U, Cr, Fe, Mn, Co, Ni, Cu, Mo, Cd, Sn, Pb, Zn, and V) of naturally occurring saline water bodies (brines) in currently developing basins in China. Our aim is to determine the presence of metal-bearing fluids and establish the formation processes of ore-forming fluids that can subsequently generate mineral deposits. The concentrations of trace metals in evaporated seawater and surficial saline waters (brines) in continental basins can reach up to mg/L level, with the increase in salinity resulting from the significant evaporation that occurs in semi-arid to arid environments. The high salinities increase the density of metal-bearing brines, which in turn causes these brines to circulate and mix with groundwater, resulting in enriched metal element concentrations in the groundwater. Groundwater containing dissolved evaporites also shows relatively high concentrations of metal elements (up to mg/L level) that compare with fresh groundwater. These metal-bearing brines can be regarded as the initial ore-forming fluids of basin-related mineral deposits, such as unconformity-type U deposits, red-bed Cu deposits, and some stratiform Pb–Zn deposits. The metal-bearing brines are the result of substantial evaporation under arid to semi-arid climates. Therefore, we conclude that climate is an important control on the formation of basin-related mineralization and that the tectonoclimatic setting plays an essential role in the formation of metal-bearing brines in closed inland basins. The major climatic events, such as the snowball and greenhouse event can affect the basin-related mineralization globally. The super mantle plume event could affect the global basin-related mineralization by changing the global climate significantly.

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Figure 1. Formation processes of metal-bearing saline lakes in closed basins under the influence of semi-arid climatic conditions

Are fluid inclusions in gypsum reliable paleoenvironmental indicators? An assessment of the evidence from the Messinian evaporites

The paleosalinity of water from which the gypsum precipitated during the Messinian salinity crisis is a controversial issue. Recent microthermometry studies on primary fluid inclusions in gypsum provided very low salinity values not compatible with precipitation from seawater, and suggested strong mixing between seawater and nonmarine waters enriched in calcium sulfate. We applied a new microthermometric protocol on gypsum crystals from nine Mediterranean sections that were experimentally stretched to measure a larger population of fluid inclusions. The results show salinities ranging from 9 to 238 wt‰ NaCl equivalent, largely falling within the evaporation path of normal seawater. The data from previous studies were obtained mostly from those fluid inclusions capable of nucleating a stable bubble after a weak stretching, which probably correspond to those having a lower salinity acquired through post-depositional crack-and-seal processes. Our data suggest instead that the primary gypsum precipitated from a marine brine, later modified by post-trapping processes during tectonics and exhumation.

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Figure 1. (A) Growth mode of a swallowtail gypsum crystal. Yellow lines represent example isochrons within the growing crystal. (B) Crystal growth produces growth bands both in reentrant angle and in the clear portion at the side of the crystal, generating growth bands parallel to the twin plane 100. (C) Classical pyramidal-shaped fluid inclusion (FI) in reentrant angle (type A). (D) FIs showing very different salinities along same lateral growth band (type B); black arrows point to FIs falling within the expected field from seawater, whereas white arrows indicate Fls at lower salinities. Fls at 71%0, 65%0, 27%, and 86%0 show clear signs of leakage. (E) Perspective view of swallowtail gypsum crystal; larger Fls intercept more 010 cleavage planes. (F) Fl trains marking multiple lateral growth bands. (G) Examples of clearly modified Fls (leakage, necking-down, and presence of vapor bubble before any stress cycles).

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.

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Figure 1. Depositional model displaying spatial and lateral distribution of halite and carnallite-prone facies associations FA2 to FA8, with respect to each parent brine saturation stages and salinity increase.
Figure 2. Photographs of FA7 facies and micro-facies. A) Microcrystalline red carnallite cumulates and interbedded halite laminites (K1 well, 647.47 m, cycle IV). B) and C) Granoblastic equigranular fine-grained red carnallite texture, respectively under natural and polarized light (K55 well, 675.67 m, Top cycle IV). D) and E) Details of tinted fine-grained carnallite cumulates of B) (natural light). F) Example of white translucid to red medium-grained carnallite interlayered with red carnallitic laminites (natural light) (K55 well, 675.67 m, Top cycle IV). G) Detail of white to red medium-grained carnallite texture illustrated in F) (natural light).

Lacustrine carbonate towers of Lake Abhe, Djibouti: Interplay of hydrologic and microbial processes

Lake Abhe, located at the triple junction between the Red Sea, Gulf of Aden, and Main Ethiopian rift trends, is a hypersaline and alkaline closed lake that is known for its exposures of massive carbonate chimneys on the flat-lying sediments of the lake's eastern margin. This study describes the morphological, textural, and petrographic characteristics of these chimneys at the basin- to microscopic-scale in order to constrain the carbonate depositional system in the context of basin hydroclimate history. Chimneys occur in three main fields and are assessed according to 1) large-scale (>5 m) morphological variations, 2) meso-scale (cm to <5 m) textures, and 3) micro-scale (<1 cm) fabrics. The dominant chimney fabric is a porous crystalline framework of trigonal prismatic and dendritic calcite crystals that locally contain spherulites, sickle-cell calcite fabrics, and entombed microbial cocci. In addition to the crystalline chimneys, other carbonate sediments include stromatolitic crusts composed of microdigitate laminated columns dominated by crystalline fan microfabrics, as well as carbonate-rich mudstones and relatively rare, localized, carbonate-rich diatomites. Chimneys are interpreted to form primarily as products of mixing between hydrothermal sublacustrine springs and lake waters during lake highstand intervals, while stromatolitic crusts are interpreted to form during lowstand lake levels. Our interpretation of mixing processes is supported by the δ18O composition of chimney calcite, which is representative of lake water and area hot spring endmembers. The observation of stromatolitic crusts with more positive values of δ13C and δ18O than crystalline chimneys indicates that crusts formed during periods of high evaporation and low lake level. Crusts also contain Mg-silicate minerals, which are not present in crystalline chimneys, and further support the interpretation of lowstand depositional conditions. Although the age of chimney formation is not well constrained, evidence from seismic reflection data suggests a pattern of chimney formation during lake level rise and highstand times, followed by lake level fall, subaerial exposure and weathering that occurred at several times throughout the Late Pleistocene and Holocene.

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Figure 1. Large-scale chimney forms. A -Massive (base of exposure) and pinnacle (top of exposure) chimney shapes, illustrating how massive forms may arise from amalgamation c individual pinnacles. B -Isolated pinnacles next to a massive chimney; note that the massive form is relatively flat-topped in comparison to pinnacle forms. C -Bulbous chimney forms, characterized by rounded shapes. D -Barrel chimney form, characterized by more columnar shape. E -Frondose chimney forms, characterized by branching tubular structures forming tree-like structures.
Figure 2. Meso-scale chimney textures. A -Branching chimney texture defined by cm-scale dendritic branches; scale bar on the right (black box = 1 cm). B -Swallow's-nest texture defined by hollow, cup-like "nests". C -Honeycomb texture, characterized by hollow chambers separated by thin horizontal and/or vertical layers. Note that honeycomb textures are flatter and more box-like than swallow's-nest textures. D -Interchimney carbonate-rich mudstones, showing mm-to cm-scale horizontal bedding.

Geochemical proxies for water-soil interactions in the hyperarid Atacama Desert, Chile

The Atacama Desert is the oldest and driest non-polar desert on Earth. Millions of years of hyperaridity enabled salt accumulations through atmospheric deposition. These salts can serve as proxies to decipher the interaction between water and soil as well as to understand the habitability with changing environmental settings. Therefore, we investigated four soil profiles regarding their mineralogy, salt abundance, and sulfate stable isotopic composition. The profiles were located along an elevation transect in the hyperarid region southeast of Antofagasta, Chile. The two lower sites situated on the distal parts of inactive alluvial fan deposits were subject to occasional fog occurrences. The upper steeper-sloped sites experienced no fog but are subject to minimal erosion. In all soil profiles, sulfates are the dominant salts showing a downward transition from gypsum to anhydrite that is accompanied by an increase of highly soluble salts and a decrease of sulfate δ34S and δ18O values. These trends are consistent with downward directed water infiltration during rare rain events causing salt dissolution followed by precipitation within the deeper soil column. This conclusion is also supported by our Rayleigh fractionation model. We attribute the presence of anhydrite at > 40 cm depth to the cooccurrence of nitrate and chloride salts, which decreases water activity during sulfate precipitation and therefore drives anhydrite formation. Along the elevation transect, the total salt inventories of each profile show a trend for nitrates and chlorides concentration decreasing with elevation. This observation together with the sulfate stable isotopes indicates a fog-independent source and suggests remobilization of soluble salts through enhanced washout from hillslopes to alluvial fans. These findings are essential for assessing the long-term regional habitability of hyperarid environments and have also relevance for Mars.

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Figure 1. Location of study area. a) overview map shows arid and hyperarid regions in South America (after Houston and Hartley 2003), black rectangle indicates study region; b) topographic map of the study region located southeast of Antofagasta, in the southern part of the hyperarid core of the Atacama Desert (topography based on ASTER DEM (USGS)), the black rectangle shows the study area; c) topographic map of the study site in the Yungay valley: three sites (HP, HM, HD) are located on the southern slopes of the mountain Cerro Herradura and one (TD) on the northern slopes of the mountain Cerro de las Tetas, eye symbol with indicated angle of view marks the position from which the photograph in d) was taken; d) panoramic photograph taken with ai unmanned aerial vehicle at ~ 1400 m a.s.l. showing the studied valley, covered by fog on 9 August 2019 8:22 AM, reaching the 1200 m a.s.l. threshold. All elevation values refer to sea level (a.s.l.).
Figure 2. Sketch of salt input and distribution within the Yungay valley. SO? and NO are brought into the system homogeneously by dry fall-out, eolian dust, or rain. Cl is more limited to lower elevations as the source is mainly the ocean, distributed by fog and eolian dust or saline groundwater, also redistributed by eolian dust. Once in the soil, salts can be redistributed again. Rare rain events lead to downward in-soil salt transport. However, there are indications on rare fluvial run-off and downslope transport, due to steeper hill slopes at HP and HM. All three transport mechanisms lead to incomplete leaching of the salts, causing a fractionation of salts by solubility, within the soil column as well as along the investigated transect.

Leaky salt: Pipe trails record the history of cross-evaporite fluid escape in the northern Levant Basin, Eastern Mediterranean

Despite salt being regarded as an extremely efficient, low-permeability hydraulic seal, an increasing number of cross-evaporite fluid escape features have been documented in salt-bearing sedimentary basins. Because of this, it is clear that our understanding of how thick salt deposits impact fluid flow in sedimentary basins is incomplete. The paper examines the causes and evolution of cross-evaporite fluid escape in the northern Levant Basin, Eastern Mediterranean. High-quality 3D seismic data offshore Lebanon image hundreds of supra-salt fluid escape pipes distributed widely along the margin. The pipes consistently originate at the crest of prominent sub-salt anticlines, where overlying salt is relatively thin. The fact the pipes crosscut the salt suggests that hydrofracturing occurred, permitting focused fluid flow. Sequential pipes from unique emission points are organized along trails that are several kilometres long, and which are progressively deformed due to basinward gravity gliding of salt and its overburden. Correlation of pipes in 12 trails suggests margin-wide fluid escape started in the Late Pliocene/Early Pleistocene, coincident with a major phase of uplift of the Levant margin. The consequent transfer of overpressure from the central basin area, in addition to gas exsolution from hydrocarbons already trapped in sub-salt anticlines, triggered seal failure and cross-evaporite fluid flow. Other causes of fluid escape in the Eastern Mediterranean, such as subsurface pressure changes driven by sea-level variations and salt deposition associated with the Messinian Salinity Crisis, played only a minor role in triggering cross-evaporite fluid flow in the northern Levant Basin. Further phases of fluid escape are unique to each anticline and cannot be easily correlated across the margin. Therefore, despite a common initial cause, long-term fluid escape proceeded according to structure-specific characteristics, such as local dynamics of fluid migration and anticline geometry. Hence, mechanisms triggering cross-evaporite fluid flow in salt basins vary in time and space.

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Figure 1. Seismic expression of different fluid escape pipe geometries. (a) Upward tapering conical pipe showing a clear pockmark terminus marked by an amplitude anomaly; (b) cylindrical pipe roughly maintaining the same diameter; (c) downward tapering conical pipes with large pockmark at the seafloor and in the shallow subsurface; (d) mud volcano feeder conduit showing lateral migration of fluid into the hosting sediments
Figure 2. Sketch of pipe trails evolution. An increased uplift of the Levant margin at ca. 1.8 Ma triggered enhanced fluid migration towards the sub-salt anticlines from the deeper areas of the basin (b). As a consequence, supra-lithostatic overpressure formed inside the anticlines leading to hydrofracture and the formation of the first pipes. During the subsequent period and until present, local processes govern overpressure build-up and the formation of cross-evaporite fluid escape.

The northern Gulf of Mexico offshore super basin: Reservoirs, source rocks, seals, traps, and successes

The northern Gulf of Mexico federal offshore area easily qualifies as a super basin based upon estimated petroleum endowment of more than 100 BOE and cumulative production of 60 BOE. Like other super basins, it has multiple petroleum systems and stacked reservoirs. Examination of four key elements of these petroleum systems (reservoirs, source rocks, seals, and traps) yields important insights to the geologic processes that result in such an exceptional habitat for conventional hydrocarbons.The bulk of hydrocarbon resources in federal offshore waters is in Cenozoic sandstone reservoirs such as the Paleogene Wilcox reservoir of deep-water subsalt areas. 

Overall, Cenozoic sandstone reservoirs in both suprasalt and subsalt fields yield the highest flow rates and cumulative production volumes. Notable is the recent addition of the deep-water Jurassic Norphlet sandstone play, the newest and second largest by ultimately technically recoverable resources. Overall, Gulf of Mexico reservoirs are diverse, formed in paleoenvironments ranging from aeolian to deep water.Powering this super basin are three primary marine source rocks centered in the Oxfordian, Tithonian, and Cenomanian–Turonian Stages. These source rock intervals commonly act as top seals, but other Neogene and Mesozoic shales and even carbonate mudstones are also important trap-sealing elements, as proven by analytical work and downhole pressure measurements. 

High rates of Cenozoic deposition on a mobile salt substrate also generated a myriad of salt tectonic structures, ranging from simple diapiric closures and extensional fault traps to complex subsalt configurations such as salt-cored compressional anticlines, salt-cutoff traps, and bucket weld traps. 

Geologically, salt is important because it can radically alter how petroleum basins evolve. Compared to other sedimentary rocks, it migrates easily through the Earth, creating space for oil and gas to collect. It helps moderate heat and keeps hydrocarbon sources viable longer and deeper. And it is a tightly packed mineral that seals oil and gas in large columns, setting up giant fields.

Exploration success in the past 20 yr is a direct result of improved seismic imaging around and below salt, as well as advances in drilling, completing, and producing wells and fields. 

A ccording to the paper, the bulk of the northern offshore basin's potential remains in giant, deepwater oil fields beneath the salt blanket. Although reaching them is expensive and enormously challenging, Snedden believes they represent the best future for fossil fuel energy. That's because the offshore -- where many of the giant fields are located -- offers industry a way of supplying the world's energy with fewer wells.

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Figure 1. Location map of the United States (northern) Gulf of Mexico Super Basin as defined here. The dashed line separates Mesozoic (MZ) fields and discoveries on the north from Cenozoic (CZ) fields and discoveries located basinward. PW = Paluxy-Washita supersequence; SH = Sligo-Hosston supersequence.
Figure 2. Regional map of the northern Gulf of Mexico shelf and continental slope showing the four major tectonically defined exploration provinces. From Weimer et al. (2016b) and reproduced with permission from the Gulf Coast Association of Geological Societies. Colors indicate age of stratigraphic fill in the Basins province: dark blue = Miocene; medium blue = Pliocene; light blue = Pleistocene. AC = Alaminos Canyon; AT = Atwater Valley; DC = Desoto Canyon; EB = East Breaks; EW = Ewing Bank; FP = Florida Plain; GB = Garden Banks; GC = Green Canyon; HE = Henderson; KC = Keathley Canyon; LL = Lloyd; LS = Lund South; LU = Lund; MC = Mississippi Canyon; SE AT = Sigsbee Escarpment Amery Terrace; WR = Walker Ridge.

Biomarker similarities between the saline lacustrine Eocene Green River and the Paleoproterozoic Barney Creek Formations

The Paleoproterozoic Barney Creek Formation, which is currently interpreted as a restricted, deep marine paleoenvironment, plays a disproportionate role in our understanding of Proterozoic ocean chemistry and the rise of complex life. The Barney Creek Formation hosts several unusual biomarker features, specifically its methylhopane and carotenoid signatures. Herein, we demonstrate that the saline lacustrine Eocene Green River Formation shares a similar distribution of methylhopanes and carotenoids, which is characteristic of saline lacustrine organic matter more generally. These distinct methylhopane and carotenoid patterns are not observed together in marine organic matter of any geologic age. These results imply a saline lacustrine depositional environment for the Barney Creek Formation, which agrees with earlier but now abandoned depositional models of this formation. As a result, models of Proterozoic ocean chemistry and emergence of complex life that rely on a marine Barney Creek Formation should be reexamined. Alternatively, if Paleoproterozoic marine biomarker signatures resemble those of younger saline lacustrine systems, then this must be recognized to accurately interpret geologic biomarker and paleoenvironmental records.

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Figure 1.  Saturated C40 carotanes. ß-carotane and y-carotane are labeled in the total ion chromatograms (TICs) of the saturated fractions of samples from different lake phases in the Uinta Basin PR-15-7c core (left). The ß-Car value is the percentage of the ß-carotane peak height relative to the average peak height in the TIC. The BCF saturated fraction TIC ) and a TIC for a saturated fraction from an interval of immature, marine Cretaceous lower Eagle Ford Group are shown for comparison at upper right and lower right, respectively.

Gypsum Deltas at the Holocene Dead Sea linked to Grand Solar Minima

Unique gypsum structures: large capes (termed ?gypsum deltas?) and small pitted gypsum mounds are exposed along the western shores of the currently retreating Dead Sea, the hypersaline terminal lake in the Dead Sea Basin. The gypsum deltas were formed during time-intervals of low lake stands (?420±10 m below mean sea level), when sulfate-rich Ca chloride brines discharged from the coastal aquifer via saline springs, mixed with the Dead Sea brine and precipitated the gypsum (outsalting process). The ages of formation of the gypsum structures coincide with times of North Atlantic cooling events and grand solar minima suggesting a direct impact of the latter on the Dead Sea hydrology and high sensitivity of the regional hydrology (controlling lake level) to global solar-related events. The temporal occurrence and numbers of the gypsum structures appear to follow the Hallstat Cycle that approaches minima at ?3000-2000 years before present. 

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The "gypsum delta" of Cape Qedem: (a) An oblique aerial photo of Cape Qedem depicting the sites of the three stratigraphic sections (the green lines) conducted on the cape, cutting through the gypsum delta. The location of Qedem drillhole is marked by the red dot. The photo was taken on January 2020, when lake level was at 434.4 m bmsl. (b) Schematic cross section along Gypsum-2 extending from the major fault line in the west to the Dead Sea in the east. The section depicts the: 1. Cretaceous marine carbonate rocks of the Judea Group, the lacustrine sediments of the last Glacial Lisan Fm.; 2. The unconformity between Lisan Fm. and the overlaying gypsum-rich layers of Cape Qedem; 3. Discordant gypsum mounds ; 4. The saline springs that discharge the Ein Qedem brine. The brine rises from a depth of ~1 km depth along the fault plain (thick solid purple line) filling the coastal aquifer (partly transparent purple area) and discharges at the shore; and 5. The interface between the Dead Sea-Ein Qedem brines. (c) Cross-section along the same line as in b depicting Cape Qedem during the time of the gypsum precipitation (e.g. ~3000-1000 y BP).

Ingredients for microbial life preserved in 3.5 billion-year-old fluid inclusions

It is widely hypothesised that primeval life utilised small organic molecules as sources of carbon and energy. However, the presence of such primordial ingredients in early Earth habitats has not yet been demonstrated. Here we report the existence of indigenous organic molecules and gases in primary fluid inclusions in c. 3.5-billion-year-old barites (Dresser Formation, Pilbara Craton, Western Australia). The compounds identified (e.g., H2S, COS, CS2, CH4, acetic acid, organic (poly-)sulfanes, thiols) may have formed important substrates for purported ancestral sulfur and methanogenic metabolisms. They also include stable building blocks of methyl thioacetate (methanethiol, acetic acid) – a putative key agent in primordial energy metabolism and thus the emergence of life. Delivered by hydrothermal fluids, some of these compounds may have fuelled microbial communities associated with the barite deposits. Our findings demonstrate that early Archaean hydrothermal fluids contained essential primordial ingredients that provided fertile substrates for earliest life on our planet.

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Black baryte associated with originally sulfidic stromatolites in the 3.45 Ga  Dresser Fm. near Marble Bar, West Australia
Inserts a, b represent enlargements of respective areas in the chromatogram marked by dashed lines. Triangles denote oxygen-bearing compounds, circles denote aromatic hydrocarbons and stars denote sulfur-bearing compounds. n-Hexane (Hex) was used as a retention time standard (RT std.). COS carbonyl sulfide, Ea ethanal, MT methanethiol, Bu but-1-ene, Pa prop-2-enal, Pa’ propanal, ET ethanethiol, MSM (methylsulfanyl)methane, Po propan-2-one, Ba but-2-enal, Ox oxolane, TP thiophene, B benzene, Ac acetic acid, TL thiolane. Note the presence of methanethiol and acetic acid, the stable building blocks of activated acetic acid

Dams and reservoirs in karst? Keep away or accept the challenges

The distribution and flow of groundwater in karstified rocks can be extremely complex and not readily predictable, a far from friendly environment for constructing dams and reservoirs. There have been many expensive failures such as unacceptable leakage rates at and around dams, and/or reservoirs that could not be filled to the design levels. This is never the fault of site geology but always of human mistakes due to inadequate investigation programmes and/or erroneous interpretation of the karst processes at work. Remedial works are expensive, time-consuming and frequently do not justify the money invested. As a result, those undertaking engineering works in karst terrains may approach with two fears—of the exceptional risk and/or of a failure. The key question, so often, is whether to build the dam in karstified rocks or keep away from such a risky environment. However, construction of water storage reservoirs is essential in many karst regions for socio-economic development. The challenge must be accepted. Based on much field experience, the best practices for selection of adequate dam and reservoir sites are defined and illustrated with specific examples from many different climatic, topographic, lithologic and hydrogeologic settings in Europe and Asia. This work emphasises that the amount of certainty or uncertainty in the crucial parameters—geological structure, groundwater regime, intensity and depth of karstification—should be recognized.

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Flow chart of the engineering karstology approach In dam and reservoir construction

Towards a low-carbon society: A review of lithium resource availability, challenges and innovations in mining, extraction and recycling, and future perspectives

The demand for lithium has skyrocketed in recent years primarily due to three international treaties—Kyoto Protocol, Paris Agreement and UN Sustainable Development Goals—all of which are pushing for the integration of more renewable energy and clean storage technologies in the transportation and electric power sectors to curb CO2 emissions and limit the adverse effects of CO2-promoted climate change. Over 60% of lithium produced in 2019 were utilised for the manufacture of lithium-ion batteries (LIBs), the compact and high-density energy storage devices crucial for low-carbon emission electric-based vehicles (EVs) and secondary storage media for renewable energy sources like solar and wind. In 2019, the global market value of lithium reached around US$213 B and is forecasted to grow by around 20–25% until 2025. In this review, the current state of global lithium resources, global lithium material flow, and forecasts of future lithium supply–demand dynamics are discussed. Persistent challenges in mining, processing and industrial-scale recycling operations are also examined and recent innovations to address these issues are introduced. Finally, unconventional lithium sources like submarine/deep-sea ferromanganese (Fe-Mn) nodules and crusts, industrial wastes (e.g., desalination brines, geothermal brines and coal fly ashes), mining wastes and effluents, and extra-terrestrial materials are explored.

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(a) Global lithium consumption from 2010 to 2019; (b) Global production (supply) and consumption (demand) from 2010 to 2019 (excluding US production), their growth forecasts until 2025 pre-COVID-19 and updated 2020 supply-demand estimates factoring in the effects of COVID-19; and (c) Global Li demand of the three main Li consumers battery, ceramics & glass, and grease-and projections of their growth until 2025.
Global lithium resources, resource type and production in 2019 (excluding US production)

Rift and salt-related multi-phase dolomitization: example from the northwestern Pyrenees

The Meillon (Callovo-Oxfordian) and Mano (Tithonian) Formations are dolomitized carbonate reservoirs that actively produce oil and gas (Aquitaine Basin, France). In this study, the dolomitization conditions of their counterparts exhumed in the northwestern Pyrenees are detailed using a combination of field observations, petrography, fluid inclusion microthermometry, elemental and isotopic geochemistry, and carbonate U–Pb geochronology. Dolomitization occurred in several stages spanning from the Neocomian (pre-rift) to the Albian (syn-rift, associated with mantle exhumation and active salt tectonics). Both formations were first massively dolomitized in near-surface to shallow burial conditions during the Berriasian-Valanginian, likely triggered by the influx of marine-derived waters. Between the Barremian and the Albian, the Early Cretaceous rifting caused the upward influx of hot fluids associated with the partial to complete recrystallization of the initial dolomites. During the Albian, subsequent dolomites precipitated in both formations as high-temperature (T > 160 °C) vein- and pore-filling cement. Distinct fluid inclusion chlorinities and rare earth element patterns between the Meillon and Mano Formations point to fluid compartmentalization during this stage. Whereas dolomite cements indicate the involvement of evaporite-derived brines in the Meillon Formation, precipitation was likely related to clay-derived water in the Mano Formation. Lastly, a final episode of dolomite cementation occurred only in the vicinity of faults and volcanic intrusions during the Albian when the highest temperatures were recorded in both formations (T > 250 °C). These saddle dolomites precipitated from hydrothermal water with a mixture of mantle-, crustal-, and evaporite-derived waters channeled by faults and active diapirs. Subsequent quartz and calcite cement precipitation reveals a temperature decrease in a post-rift to inversion setting (post-Cenomanian) and indicates fluid compartmentalization between both formations. This study highlights the major control exerted by rifting, combined with the presence of diapiric salt, on dolomitization, making carbonate platforms of modern salt-rich passive margins potential targets for exploration.

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General model of the evolution of fluid chemistry, fluid circulation, and diagenesis phases set in the schematic reconstruction of the Mail Arrouy chaînon and its structural and geochemical evolution. The rightmost sketches detail the inferred fluid circulations in the near-sampled area.

Coupling of paleo-environment and biogeochemistry of deep-time alkaline lakes: A lipid biomarker perspective

Studies of alkaline lakes have critical biological–environmental–economic properties, but deep-time alkaline lakes are challenging to investigate. Lipid biomarkers can provide valuable insights into such lakes and their biogeochemical significance. The paper reviews and compares typical examples of ancient alkaline lakes across the world. Lipid biomarker evidence, including C30-steranes, Pr/Ph, Pr/n-C17-Ph/n-C18, (β − +γ-carotane)/n-Cmax, and gammacerane/C30αβH values, suggests these alkaline lakes were reducing, hypersaline, and stratified. The n-alkanes, steranes/hopanes, C28-St/C27–29-St%, and C28/C29-St values indicate that the preserved biomass of the alkaline lakes were dominated by algae and bacteria, with less input from higher plants. The algae were mainly halotolerant green algae, rather than cyanobacteria. The different alkaline lakes have some subtle differences in their sedimentary environments. The paleoenvironmental setting and biomass of the alkaline lakes co-vary systematically. The ratio of algae/bacteria is positively correlated with increasingly reducing and saline conditions, because the increase in salinity improves the competitiveness of halotolerant green algae. The changes in these extreme alkaline environments are too small to cause obvious variations in the proportion of green algae/total algae, and the abundance of cyanobacteria, photoautotrophs, and/or type I methanotrophic proteobacteria. Lipid biomarker data show that the primary controlling factor on the biomass of saline and alkaline lakes is their geologic age and, to a lesser extent, their salinity. The abundance of organic matter in these sediments varies greatly, and the types of organic matter are generally good for hydrocarbon generation. The formation of oil and gas is controlled by factors such as abundance of organic matter, thermal maturity, size of lake basin, and thickness of the organic-rich sediments.

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Alkaline saline lake across time and their stratified palaeohydrologies, as indicated by their preserved lipid biomarkers

The genesis of a giant mud canopy by catastrophic failure of a thick evaporite sealing layer

Three-dimensional seismic imaging and well calibration reveal a large allochthonous mud edifice that is composed of several mud extrusions and covers an area >740 km2 on the outer shelf slope of the Nile Delta. The allochthonous material was sourced from beneath the ∼1-km-thick Messinian evaporites in the Eastern Mediterranean and extruded synchronously as eight large mud volcanoes directly on top of the Messinian evaporites in a catastrophic remobilization event at the end of the Messinian salinity crisis. These large extrusive flows coalesced to form a single edifice with an exceptional volume of ∼292 km3 that is connected to eight widely spaced conduits. We argue that this large mud body represents a new morphological type and scale of mud extrusion. We propose that mud extrusions that coalesce on a surface forming a multi-conduit-fed edifice be referred to as mud canopies, by analogy with salt canopies, with implications for basin reconstruction, paleo–overpressure release events, and fluid migration.

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A) Location of seismic area and exploration wells (Kg45, La52) used for calibration. Highlighted are margins of salt (light blue line) and three-dimensional (3-D) seismic survey area (green outline). B) Schematic cross-section Nile Delta and seismic study area, in which Messinian evaporites are overlain by allochthonous Tortonian shale. Sf—seafloor; ABT—allochthonous body top; TS—top salt; BS—base salt. C) Seismic profile through Kg45 well. The TD (total depth) of the well is within the allochthonous body (AB), which directly overlies Messinian evaporites (Mess. evap.). Sf—seafloor; ABT—allochthonous body top; Tort.—Tortonian; Amp.—amplitude. D) Isopach map of AB (see Fig. 1A for location), with location of Kg45 well, margin of seismic survey (green outline), and welds between the AB and pre-salt units.
Figure 2. Seismic character of allochthonous body (AB) (see Fig. 1A for seismic profile and time-slice locations). A) Seismic profile through AB, which directly overlies top salt (TS) of Messinian evaporites (ME). Base of AB and base salt (BS) connect locally, forming a weld. Sf—seafloor; P-R—Pliocene–recent; ABT—AB top surface; PS—pre-salt; PO—pinch-out; IL—interdigitating lenses. TWT—two-way traveltime; Amp.—amplitude; V.E.—vertical exaggeration. B) Seismic profile of lateral margin of AB showing pinch out (PO) of ABT with its basal surface at TS and onlap onto ABT. C) Seismic profile highlighting an oblique reflection (OR; red dotted line) that extends from TS to ABT. IG—irregular geometry. D) Time slice through AB and OR, showing curvilinear geometry to OR.

Salt anomalies in potash beds of the Esterhazy Member, Devonian Prairie Evaporite Formation, Saskatchewan, Canada

The Esterhazy Member of the western Canada Prairie Evaporite has been mined underground for sylvite (KCl) since the early 1960s. Although the geology of the Esterhazy Member ore body is largely considered a regional flat lying continuous series of thin potash hosting beds, there are numerous occurrences where the ore has been either replaced or removed leaving behind uneconomical halite-rich sections. An explanation of the underlying controls on the formation of these salt anomalies has been somewhat elusive although the overwhelming assumption remains that these features developed in lows on a salina. This paper proposes that salt anomalies formed because of two processes, early compaction of carbonate shoals of the Winnipegosis Formation and tectonics that resulted in multiple stages of block movement during the deposition of the upper Prairie Evaporite. Since these two processes can result in a significantly different size to a salt anomaly, encountering one or the other type can have a significant effect on the economics of the ore body. This paper looks at some of the geological methods that might provide geologists with means to predicting salt anomalies.

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A production room was cut over this Winnipegosis shoal after a 3D seismic survey was shot. The room is approximately 20ms above the shoal top. Elevation changes in the room mimic the “W” shape of the Shell Lake Member (blue line) over the shoal, characteristic of the subsidence found over isolated shoals in the area. The profile was hung from the underlying Ashern Formation. TWTT = two way travel time content.

Volcanic and Saline Lithium Inputs to the Salar de Atacama

The Li-rich brine contained within the halite body of the Salar de Atacama is uncommon for two reasons: First, it has an exceptionally high Li concentration, even compared to other closed basins in the Li triangle of South America; and second, it is widespread within the halite nucleus and not restricted to a localized area. This study focusses on the southern half of the salar where Li production occurs and draws comparisons with its northern neighboring basin through which the Loa river flows. Concentration and isotope data for water inflowing to this part of the salar were obtained from surface inflow as well as wells located within the alluvial fans on its eastern margin. Lithium varies between 0.2 and 20 mg/L before reaching the salar where small amounts of the brine and or salts that precipitated from it can increase its concentration up to 400 mg/L or higher. The δ7Li of the inflow water varies between +4.9‰ and +11.2‰ and increases to +12.6‰ within the salar margin, consistent with salar brine based on reported measurements. Boron isotopes indicate that it is unlikely that solutes are derived from sedimentary evaporites or mineral cements, unlike the situation in the adjacent Loa basin. Water that flows through an aquifer laterally confined by a basement block and a line of volcanoes has a notably higher δ7Li than other inflow water, around +9‰, and increasing to +10.5‰. δ7Li values are overall higher than were measured in the adjacent Loa basin, indicating that here the water–rock reactions for Li are more evolved due to longer residence times. Lithium concentrations increased with sodium and chloride, but sedimentary evaporites are shown to be unimportant from δ11B. This is accounted for two ways: evaporated saline inflow leaks from higher elevation basins and inflows are partly derived from or modified by active volcanic systems. Active and dormant volcanoes plus the massive Altiplano–Puna magmatic body are important as heat sources, which enhance water–rock reactions. The large topographic difference between the mean elevation of Altiplano on which these volcanoes sit and the salar surface allows hydrothermal fluids, which would otherwise stay deep below the surface under the modern arc, to uplift at the salar.

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Geology and sampled wells in the Salar de Atacama basin

Evaporite-bearing orogenic belts produce ligand-rich and diverse metamorphic fluids

Detailed petrologic and chemical investigation of mid-amphibolite facies calcareous, scapolite-rich metasedimentary rocks from the Mount Isa region in northern Australia is used to explore changing fluid chemistry with prograde metamorphism. The presence of widespread scapolite with Cl- and variably SO4-rich compositions in upper amphibolite facies rocks makes it unavoidable that the regional metamorphic fluids were locally highly saline and oxidised, and that high salinities persisted throughout metamorphism. Electron microprobe analyses and chemical maps of individual scapolite grains show zoning in Cl and S, likely to reflect buffering of the metamorphic fluid by scapolite during progressive metamorphism. The zoning in Cl and S demonstrates that scapolite has the potential to record changes in fluid chemistry during metamorphism. The variation in scapolite composition between samples, in combination with whole rock geochemistry, shows that different layers within this heterogenous rock package generated fluids of different chemistries. Interaction between scapolite-bearing rocks and externally-derived magmatic or metamorphic fluids that are out of equilibrium drives scapolite breakdown, releasing Cl to the fluid. In the Mount Isa region, metamorphic fluid production was enhanced by periods of magmatism, which promoted development of a regionally extensive and unusually saline fluid system that was active at multiple stages over a 250 million-year period. The highly saline and oxidised fluids formed through interaction with scapolite are well suited to transporting a broad range of metals, and may explain the diverse range of syn-orogenic mineral deposits in the Mount Isa Inlier. Metamorphic belts with large volumes of evaporitic material are ideal for generating a broad spectrum of syn-orogenic hydrothermal ore deposit types - including Fe oxide Cu-Au, Fe sulphide Cu-Au, Mo-Re and U-REE, but lacking the Au-only deposits found in typical orogenic belts. Unlike regions hosting traditional orogenic gold deposits, belts containing evaporitic sequences can preserve Cl-rich minerals such as scapolite in the metamorphosed source region, allowing them to remain active as ore forming systems through relatively high-grade metamorphism and multiple stages of tectonism. Periods of supercontinent breakup, such as the Mesoproterozoic, may have resulted in the formation of large, intracontinental basins well suited to the development of widespread evaporitic sequences. This, in combination with overprinting orogenesis and high temperature magmatism, may have provided the ingredients for widespread ore deposit formation at a global scale.

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Map of the Eastern Fold Belt, after Oliver et al. (2004). Sedimentary rocks are depicted in grey, with the Corella Formation and equivalents depicted as the darkest grey. Sedimentary rocks equivalent to the Corella Formation are widespread in the Eastern Fold Belt. Historical Cu and Au workings, major deposits and currently operating mines (Cu, Au and Zn) are also plotted. Data from KLB: Kalkadoon–Leichhardt Belt; MKFB: Mary Kathleen Fold Belt
Schematic model for the generation of saline fluids in a purely metamorphic system, interlayered metasedimentary rocks containing variable proportions of mudstone, carbonate and evaporite will generate fluids of different chemistries. Calcareous and halite-bearing layers will contain Cl-rich scapolite. Fluids escape along layers or small shear zones, preserving internally buffered metamorphic assemblages. Mixing between different metamorphic fluids may result in small-scale albitisation. In a mixed magmatic-metamorphic system, crystallising magmas are a source of heat to drive metamorphic fluid production and will also introduce fluids of different chemistries. These fluids may result in scapolite breakdown, releasing Cl and increasing fluid salinity where migration of saline, oxidised fluids through the crust may result in phase separation.

An epeiric glass ramp: Permian low-latitude neritic siliceous sponge colonization and its novel preservation (Phosphoria Rock Complex)

Glass ramps are shallow-marine depositional settings in which siliceous sponge meadows dominate coastal environments. They are increasingly recognized throughout the Phanerozoic and represent a biosiliceous counterpart to neritic carbonate factories. Detailed reexamination of the Permian Tosi Chert in the Bighorn Basin indicates that it records a glass ramp that extended over at least 75,000 km2. Outcrops, cores, and wireline logs are used to discriminate previously unidentified shallow subtidal to peritidal facies in its landward extent. These facies indicate that sponge meadows ranged from variably oxygenated offshore settings through low-energy, well-oxygenated, and saline shallow subtidal settings, with spicules transported into supratidal environments affected by enterolithic evaporite growth. This range of subenvironments is largely unique among glass ramps. This is the result of the Tosi's accumulation in an epicontinental sea where waves impinged offshore but frictional attenuation caused low-energy nearshore environments. As a result, the Tosi shares similarity with epeiric sea carbonate deposition and is referred to herein as an epeiric glass ramp. The low palaeolatitude of the Tosi and hot and arid desert it bordered also contributed to its uniqueness as shallow waters were warmer and more saline than higher-latitude counterparts. As a result, a minor sea-level fall at the termination of biosiliceous deposition was associated with increased lagoonal circulation and refluxing brines that caused evaporite and dolomite precipitation within the upper Tosi. Preservational attributes of the Tosi also add to the range of unique traits that can be used to reconstruct neritic biosiliceous environments. These include three disparate colours of chert (black, grey, and purple) related to the host strata and diagenetic redox conditions, early chertification that preserved sedimentary structures within nodules, and nodule shape related to bioturbation intensity. The Tosi glass ramp thus expands the known extent and context of Permian glass-ramp deposition along the western Laurentian margin and illustrates key properties that will aid future glass ramp identification.

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Depositional model of the Tosi epeiric glass ramp (Time 1) and the end-Tosi minor sea-level fall (Time 2) that led to seepage reflux of hypersaline brine into the Tosi in the shallow subsurface. All models are vertically exaggerated. SB, sequence boundary; TST, transgressive systems tract.
Tosi chert: A) A simplified representation of the formation of chert nodules from silica remobilized from sponge spicules and subsequent replacive silicification of host rock. B) Summary figure showing the range of replacive chert nodule shapes and colours as they relate to interpreted depositional setting along the glass ramp.

Mass-transport complexes (MTCs) document subsidence patterns in a northern Gulf of Mexico salt minibasin

Mass-transport complexes (MTCs) dominate the stratigraphic record of many salt-influenced sedimentary basins. Commonly in such settings, halokinesis is invoked as a primary trigger for MTC emplacement, although the link between specific phases of salt movement, and related minibasin dynamics, remains unclear. IN this papare the authors use high-quality 3D seismic reflection and well data to constrain the composition, geometry and distribution (in time and space) of six MTCs preserved in a salt-confined, supra-canopy minibasin in the northern Gulf of Mexico, and to assess how their emplacement relate to regional and local controls.

They define three main tectono-sedimentary phases in the development of the minibasin: (a) initial minibasin subsidence and passive diapirism, during which time deposition was dominated by relatively large-volume MTCs (c. 25 km3) derived from the shelf-edge or upper slope; (b) minibasin margin uplift and steepening, during which time small-volume MTCs (c. 20 km3) derived from the shelf-edge or upper slope were emplaced; and (c) active diapirism, during which time very small volume MTCs (c. 1 km3) were emplaced, locally derived from the diapir flanks or roofs. They present a generic model that emphasizes the dynamic nature of minibasin evolution, and how MTC emplacement relates to halokinetic sequence development. Although based on a single data-rich case study, the model may be applicable to other MTC-rich, salt-influenced sedimentary basins.

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(a) W-trending un-interpreted seismic section. (b) Interpreted W-trending seismic section showing the overall salt-tectonic structure of the study area, and the nine key seismic horizons (H0 to seabed) and main MTC-bearing intervals (MTC 1 to MTC 5).


Conceptual model for extrabasinal MTCs, intrabasinal MTCs, slope channels and background slope sediments.

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Stock market response to potash mine disasters

The authors show that news about a mining accident affects the stock of the competitors of the affected company as well the greenfield potash firms. Moreover, the impact of the accident on the stock of the competitors and greenfield firms strongly depends on the type of mining disaster.

The stock of the affected companies responds the most to information on brine inflow in potash mines. Inflows of water into a potash mine can result in its closure, which can lead to significant losses at the company, as this type of accident is often uninsured. In contrast, man-made accidents result in only a small reaction of the stock of the affected companies. In most cases, such accidents do not have a negative impact on potash production and potential losses related to the event are insured. The stock of competing companies and greenfield firms reacts, however, negatively to information on work accidents in the affected companies.

They also find that the stock of competing companies is not affected by natural disasters and attribute a lack of reponse to the oligopolistic structure of the market controlled by cartels, which have a surplus of capacity. 

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Closed depressions in Kotido crater, Arabia Terra, Mars. Possible evidence of evaporite dissolution-induced subsidence

The identification of karst sinkholes in Mars may provide evidence of dissolution processes caused by liquid water and information on paleoclimatic and paleohydrological conditions. This work presents a comprehensive cartographic inventory of 513 closed depressions developed on evaporite-bearing Equatorial Layered Deposits (ELDs) within Kotido crater, Arabia Terra. Detailed mapping, morphometric analyses and spatial distribution relationships reveal a number of features supporting that the depressions correspond to collapse sinkholes related to evaporite dissolution: (1) suitable topographic and litho-structural conditions for the development of a fracture-controlled epigene evaporite karst; (2) presence of open fissures at the foot of the scarped margins; (3) dimensions and frequency-size distributions comparable with those reported on Earth; (4) spatial association with high-permeability zones (i.e., fractures).

Some characteristics of the depressions indicate that they have been re-shaped and enlarged by wind erosion: (1) dominant orientation consistent with the prevalent one-directional winds; (2) differing morphological characteristics on the downwind- and upwind-sides; and (3) nested depressions associated with the upwind sector. The relatively fresh appearance of the depressions and the lack of impact craters suggest a poorly constrained Amazonian karstification phase in the region.

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HiRISE images (ESP_016776_1810 and ESP_016921_1810) illustrating some of the main features in the study area and the mapped closed depressions. A: Elongated depressions with a broader and steeper SW side and a pointed and a gentler NE edge (star). Sharp-crested NE-oriented ridge attributable to a yardang (arrow). B: Aligned and partially coalesced elongated depressions associated with fractures with a prevalent NNE trend. Note the difference between the gentler NE and steeper SW sides of the depressions and the prominent ridge-like morphology of some edges. C: Composite depressions with scarped edges developed on fractured light-toned resistant layers. The floor of the depressions is largely mantled by aeolian deposits a scattered fallen blocks. D: Elongated scarp-edged depressions some of them with stepped floors and nested basins associated with the SW sector. E and F: Depressions with fissures at the foot of the marginal scarps indicative of ground deformation. Butte capped by a resistant layer in the NE corner of the image. Inset images show enlarged fissures. Inset in Fig. F corresponds to a RGB image.

Ichnofossils, Cracks or Crystals? A Test for Biogenicity of Stick-Like Structures from Vera Rubin Ridge, Mars

New images from Mars rover Curiosity display millimetric, elongate stick- like structures in the fluvio-lacustrine deposits of Vera Rubin Ridge, the depositional environment of which has been previously acknowledged as habitable. Morphology, size and topology of the structures are yet incompletely known and their biogenicity remains untested. Here we provide the first quantitative description of the Vera Rubin Ridge structures, showing that ichnofossils, i.e., the product of life-substrate interactions, are among their closest morphological analogues. Crystal growth and sedimentary cracking are plausible non-biological genetic processes for the structures, although crystals, desiccation and syneresis cracks do not typically present all the morphological and topological features of the Vera Rubin Ridge structures. Morphological analogy does not necessarily imply biogenicity but, given that none of the available observations falsifies the ichnofossil hypothesis, Vera Rubin Ridge and its sedimentary features are now recognized as a privileged target for astrobiological research.

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Stick-like structures imaged on the surface of Mars. Are they mud cracks, preserved crystal efflorescences, water escape features, or biogenic?

Origin and Evolution of the Halo-Volcanic Complex of Dallol: Proto-Volcanism in Northern Afar Rift (Ethiopia)

Contextual early observations on volcano genesis are valuable but scarce. Resembling a shield volcano, the Dallol dome is a complex 40 m-high geological structure on the Danakil depression, a North-South-elongated salt plain lying 120 m below sea level in the North Afar (Ethiopia). Dallol has become a tourist destination famous for its colorful hydrothermal features and raised scientific interest due to its life-challenging polyextreme conditions. Although some general models for its genesis exist, little is known about the origin and temporal evolution of both, the dome and its geothermal activity resulting in hyperacidic and halite-oversaturated brines. In this study, data obtained from three multidisciplinary field campaigns (January 2016, 2017, and 2019) are combined to refine the geological mapping of the North Danakil and the Dallol dome. The analysis of stratigraphic, geomorphological, geochemical, and hydrogeochemical data as well as satellite, drone and infrared aerial images shed light in its complex temporal evolution. Results suggest that the recorded history of the dome began when at least one deep magmatic basalt intrusion occurred later than 6000 years ago, forcing the uplifting of the lacustrine deposits of that age covering the west side of the dome. The interaction of the magma with the buried salt deposit resulted in a halo-volcanic activity with, likely, several melted-salt effusion events. Substrate accommodation after effusion led to the current collapsing crater on the dome top and the geothermal still-ongoing degassing. An important hydrothermal reactivation took place after a dyke intrusion event in October–November 2004. It triggered the appearance of new fractures on the dome top and the northward migration of the hydrothermal activity, as inferred from the analysis of historical aerial images combined with high-definition visible and infrared images taken from a drone during our field campaigns. Based on theseobservations, an updated hydrogeothermal conceptual model linking deep magmatic activity with halokinetic processes and geothermal fluids is used to explain the origin and evolution of the Dallol halo-volcanic complex. These geothermal manifestations may potentially inform about rarely documented premises of a volcano’s birth.

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Main steps in the evolution of the halo-volcanic Dallol complex.(A) Salt lake precipitates on the west side over an incipient dome in the east side of Dallol. (B) Magmatic intrusion and updoming. (C) Salt flowing and collapsing. (D) Dyking, faulting and recent geothermal activity. Note a lack of at-surface volcanic material.

Chronology with a pinch of salt: Integrated stratigraphy of Messinian evaporites in the deep Eastern Mediterranean reveals long-lasting halite deposition during Atlantic connectivity

The Messinian Salinity Crisis (MSC; 5.97–5.33 Ma) is considered an extreme environmental event driven by changes in climate and tectonics, which affected global ocean salinity and shaped the biogeochemical composition of the Mediterranean Sea. Yet, after more than 50 years of research, MSC stratigraphy remains controversial. Recent studies agree that the transition from the underlying pre-evaporite sediments to thick halite deposits is conformal in the deep Eastern Mediterranean Basin. However, the age of the base and the duration of halite deposition are still unclear. Also disputed is the nature of the intermediate and upper MSC units, which are characterized as periods of increased clastic deposition into the Eastern Mediterranean based on marginal outcrops and seismic data. We provide a multidisciplinary study of sedimentary, geochemical, and geophysical data from industrial offshore wells in the Levant Basin, which recovered a sedimentary record of deep-basin Mediterranean evaporites deposited during the MSC. In combination with previous observations of the MSC throughout the Mediterranean Basin, our results promote the need for a new chronological model. Remarkably, the one-kilometer-thick lower part of the evaporitic unit is composed of essentially pure halite, except for a thin transitional anhydrite layer at its base. The halite is undisturbed and homogeneous, lacking diverse features apparent in more proximal sections, indicating a deep-sea depositional environment. We find that distinct, meters-thick non-evaporitic intervals interbedded with the halite, previously thought to be clastic layers, are diatomites. While XRD analysis confirms an increase in clastic components in these sediments, they are composed primarily of well-preserved marine and freshwater planktonic diatoms. The occurrence of marine planktonic diatoms in these intervals indicates the input of Atlantic waters into the Mediterranean Basin during the deposition of the massive halite unit. Seismic stratigraphy and well-log cyclostratigraphy further support deep basin halite deposition, which started about 300 kyr earlier than widely assumed (~5.97 Ma). We propose that halite deposition in the deep Mediterranean took place during stage 1 of the MSC, rather than being limited to the short 50 kyr MSC acme when sea level was presumably at its lowest. Thus, brine formation, salt precipitation, and faunal extinction occurred at least in part in a deep, non-desiccated basin, with a restricted yet open Mediterranean-Atlantic connection that allowed inflow of oceanic water. We observe an increase in heavy minerals and reworked fauna within the clastic-evaporitic, Interbedded Evaporites of the basinal MSC section, and argue that these settings correspond in the deep basins with a significant sea-level drawdown during stage 2 of the MSC, as observed in the marginal sections. This correlation is corroborated by astrochronology and chemostratigraphic markers, such as the distribution of n-alkanes and biomarker-based thermal maturity indices.

The Levant deposits indicate that high sea level and partial connectivity with global oceans promoted the deposition of deep-basin deep-water halite, while sea-level drawdown promoted deposition of reworked and transported material from the margins into deep Mediterranean basins. This study modifies the current understanding of the mechanisms governing salt deposition throughout the MSC with implications for other evaporitic events in the geologic record.

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Geophysical data and seismic stratigraphy of the Dolphin and Leviathan-1 wells
Astronomical age model and regional correlation of the Levant MSC

Origin and recharge model of the Late Cretaceous evaporites in the Khorat Plateau, SE Asia

Evaporites commonly occur in the Mesozoic-Cenozoic Tethyan domain, which characterized by extensive Late Cretaceous potash deposits in the Lanping-Simao Basin (LSB) in southwestern China and in the Khorat Plateau (KP) in Thailand and Laos. The LSB and the KP are located in the eastern Tethyan tectonic belt. The origin of the Late Cretaceous evaporites in these basins is controversial; possibilities include marine, continental, or hydrothermal origins. In addition, the recharge model for the major solutes into these evaporitic basins is inadequate, whether it is from the KP to the LSB or from the Qiangtang to the LSB to the KP. In this study, 34 gypsum, anhydrite, and halite samples from two sediment cores collected from the KP were analyzed to determine their stable B-Sr-S isotopic compositions. This is the first time that δ11B values have been reported for the anhydrite in the study area. The origin and evolutionary relationships of these evaporitic basins were investigated based on the geochemical data, sedimentary features, mineral sequences, and stratigraphic ages of the evaporites in the LSB and KP. The tectonic evolution and stratigraphic comparisons during the Triassic-Cretaceous in the eastern Tethyan domain were systematically reviewed and summarized in order to determine a preferred recharge model for the evaporites in the KP. The following conclusions were reached. (1) The reconstructed δ11B values (+38.20‰ to + 51.23‰) of the parent solution, which were based on those of the anhydrite (+8.20‰ to + 21.23‰), and the isotopic fractionation levels (30.2‰ to 32.7‰), 87Sr/86Sr ratios (0.70743–0.70846), and δ34S values (+14.39‰ to +15.94‰) of the anhydrite and halite in the KP overlap with those of Late Cretaceous seawater, suggesting a marine origin. (2) The similar mineral sequences and B-Sr-S isotopic signatures, and the comparable sedimentary features and inherited ore-forming ages indicate that evaporites in the LSB and KP have similar solute sources and evolutionary relationships. (3) The tectonic evolution and stratigraphy demonstrate that during the Late Cretaceous, paleoseawater from the Shan Boundary Ocean (the eastern segment of the Meso-Tethys Ocean) most likely passed through the southwestern part (Tengchong-Baoshan block) of Sibumasu and preferably recharged marine solutes into the LSB and KP.

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The recharge model for paleoseawater (Shan Boundary Ocean) in the Lanping-Simao Basin and the Khorat Plateau.
Stratigraphy of the Sibumasu Terrane (sections 1–3), the Indochina Block (sections 6–10), the Sukhothai Arc Terranes (sections 4 and 5), the Lanping-Simao Basin (sections 11 and 12), the Qamdo Basin in the Qiangtang Block (section 15), Biru and Chayu in Lhasa (sections 14 and 16)), and Myitkyina (section 13) in West Burma). The red shaded area is the Mesozoic continental red bed outcrops.

Characterization of Oligo-Miocene evaporite-rich minibasins in the Sivas Basin, Turkey

The Sivas Basin in Turkey displays in its central part an Oligo-Miocene halokinetic province which acts as a major outcrop analogue to study salt-sediment interactions. Based on field geology observations, the present paper focuses on the geometry and sedimentology of several minibasins having the particularity of being mainly filled by gypsiferous deposits. Such type of evaporite-rich minibasins remain difficult to identify and are poorly studied in other halokinetic provinces. In the Sivas Basin, the evaporites were recycled from diapiric salts and precipitated in saline ponds emplaced above deflating diapiric stems. Diapir deflation resulted either from local transtensive strain, cessation of diapir feeding and/or subsurface dissolution of the diapiric salt. Minibasin subsidence was likely enhanced by the fast emplacement rate of the capping evaporites, together with the high density of the depositional sulfates compared to the diapiric halite. The evaporite-rich minibasins stand out from their surrounding siliciclastic counter-parts by their small dimension (lower than 1 km-wide), their encased teardrop shape, and their high internal deformations. The later include well-developed halokinetic sedimentary wedges, aerial mega-slumps or inverted flaps. Such structural features probably resulted from the ductile rheology of the evaporite infill and the complex pattern of downbuilding. Although secondary evaporitic minibasins have never been identified in other ancient halokinetic settings, our study highlights that they could developed in any evaporitic environments, coastal or continental, such as in the Precaspian Basin. The secondary minibasins described here can also act as field analogues of other primary evaporite-rich minibasins already suspected in salt giant basins (e.g. in the Santos Basin, Brazil).

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Synthesis of the depositional evaporites in an evaporite-rich minibasin of the Sivas Basin.

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

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

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(A) Chronostratigraphic chart of the Almada Sub-basin. (B) Representative section of a well illustrating the transitional section in the study area; (C) Interpreted seismic section situated in the proximal areal illustrating the main unconformities; (D) Interpreted seismic section situated in the distal areal illustrating the main unconformities and main evaporite deposits.

Constraints on Meso- to Neoproterozoic seawater from ancient evaporite deposits

Marine sulfate is intimately connected to the global carbon and oxygen cycles through its important role as an electron acceptor for the microbial respiration of organic carbon. The biogeochemical feedbacks within the sulfur, carbon, and oxygen cycles may have changed through time, reflecting changes in the concentration of sulfate in the oceans. Unfortunately, there is much uncertainty about the size of the marine sulfate reservoir throughout Earth history. In particular, conflicting estimates for marine sulfate exist during the latest Neoproterozoic, an interval of time associated with striking changes in Earth system evolution and oxidation: published interpretations of fluid inclusion chemistry place sulfate greater than 16 mmol/kg, whereas other interpretations of carbonate-associated sulfate data suggest concentrations less than 2 mmol/kg. Calcium isotope ratios in evaporite successions provide an independent method for deriving semi-quantitative constraints on sulfate concentrations, as well as other properties of seawater chemistry. Here, the calcium isotope behavior of bedded sulfate evaporites from ∼1050 Ma (Baffin and Bylot Islands, Nunavut, Canada), ∼830 Ma (Officer Basin, Western Australia), and ∼545 Ma (South Oman Salt Basin, Sultanate of Oman) are examined. In combination with other geological observations, the results suggest relatively low, millimolal-level sulfate in the latest Mesoproterozoic and a more specific range of 6–10 mmol/kg sulfate during the latest Neoproterozoic. These new constraints suggest that previous interpretations of sulfate concentrations and seawater chemistry need to be revised, opening up new possible solution spaces for the major ion composition of seawater.

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Constraints on seawater chemistry during deposition of the Iqqittuq Formation, Browne Formation, and Ara Group, based on evaporite modeling results. Each simulation is represented by a circle, with the color scale showing the degree of calcium isotope distillation for relevant simulations. A: constraint that gypsum saturates before halite with progressive evaporation. B: constraint for sulfate-rich fluid inclusions and magnesium sulfate salts (versus calcium-rich fluid inclusions and potassium chloride salts). C: constraint for a limited range of δ44Ca/40Ca values . D: constraint from fluid inclusion K/SO4 ratios in the Ara Group. Markers T, M, K, P, and S indicate estimated seawater composition of today, Messinian, Cretaceous, Permian, and Silurian time, respectively, which capture the classical “aragonite sea” and “calcite sea” compositions. The pink shaded region is consistent with late Mesoproterozoic and Tonian seawater. The blue shaded region is consistent with latest Ediacaran seawater. 

Hydrodynamics of salt flat basins: The Salar de Atacama example

The Salar de Atacama is one of the most well-known saline endorheic basins in the world. It accumulates the world main lithium reserves and contains very sensitive ecosystems. This paper characterize the hydrodynamics of the Salar de Atacama, and quantifies its complex water balance prior to the intense brine extraction. The methodology and results can be extrapolated to the groundwater flow and recharge of other salt flats. A three-dimensional groundwater flow model using low computational effort was calibrated against hundreds of hydraulic head measurements.

The water infiltrated from the mountains ascends as a vertical flux through the saline interface (mixing zone) produced by the density contrast between the recharged freshwater and the evaporated brine of the salt flat nucleus. This water discharges and is largely evaporated from lakes or directly from the shallow water table. On the other hand, the very low hydraulic gradients, coupled with the presence of the mixing zone that operates as barrier, leads the salt flat nucleus to act as a hydrodynamically quasi-isolated area. The computed water table shows the lowest hydraulic head in the salt flat nucleus near the discharge at the mixing zone. The groundwater balance of the Salar de Atacama in its natural regime was quantified resulting in an inflow/outflow of 14.9 m3·s−1. This balance considers the basin as an endorheic system. The very low infiltration values that are generally assumed for hyperarid basins are not consistent with the hydrogeology of the Salar de Atacama. Indeed, very high infiltration rates (up to 85% of rainfall) occur because of the high degree of fracturing of rocks and the scarce vegetation. This high infiltration is consistent with the light isotopic composition of the water from the recharge area (Altiplano). Therefore, the existence of additional inflows outside the basin is unlikely.

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Atacama hydrology
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