New and interesting

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.

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.).
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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
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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.
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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
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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.
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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.
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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 https://minesonlinemaps.business.qld.gov.au/Html5Viewer/Tablet.html?viewer=momaps. KLB: Kalkadoon–Leichhardt Belt; MKFB: Mary Kathleen Fold Belt
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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.
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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).

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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
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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.
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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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