Salt Crust Research Articles

Seasonality Analysis of Sentinel-1 and ALOS-2/PALSAR-2 Backscattered Power over Salar de Aguas Calientes Sur, Chile

Seasonal changes control the development of salt crust over the Salar de Aguas Calientes Sur located in Andes Highlands, Chile. Precipitations throughout the Altiplanic winter (December to March) and austral winter (June to September) caused ponds to enlarge and surface salt crusts to dissolve driving roughness and dielectric features of the salar surface change over time. A four-year time series backscattering coefficient analysis, obtained by Sentinel 1 and ALOS-2/PALSAR-2 with 10 m of spatial resolution, demonstrated the capability of microwaves to discriminate seasonal patterns illustrated in this paper. Both sensors showed to be sensitive to changes in the surface crust due to weather conditions. Backscattered power gradually increased during the driest months as the rough salt crusts develop and decreased rapidly due to precipitations or flooding events, which lead to a smoothing appearance to radar. The high temporal frequency of acquisition in Sentinel 1 (5–13 scenes/month) allowed the discrimination among climate and annual seasonality and episodic events in the C-band backscatter coefficient. On the other hand, ALOS-2/PALSAR-2 showed subsurface changes at L-band since the salinity of the brine in the soil reduces the penetration depth of backscattered power for shorter wavelengths. Results might be useful to monitor salars with geographic and weather conditions similar to Salar de Aguas Calientes Sur.

Biosignature Analysis of Mars Soil Analogs from the Atacama Desert: Challenges and Implications for Future Missions to Mars.

The detection of biosignatures on Mars is of outstanding interest in the current field of astrobiology and drives various fields of research, ranging from new sample collection strategies to the development of more sensitive detection techniques. Detailed analysis of the organic content in Mars analog materials collected from extreme environments on Earth improves the current understanding of biosignature preservation and detection under conditions similar to those of Mars. In this article, we examined the biological fingerprint of several locations in the Atacama Desert (Chile), which include different wet and dry, and intermediate to high elevation salt flats (also named salars). Liquid chromatography and multidimensional gas chromatography mass spectrometry measurement techniques were used for the detection and analysis of amino acids extracted from the salt crusts and sediments by using sophisticated extraction procedures. Illumina 16S amplicon sequencing was used for the identification of microbial communities associated with the different sample locations. Although amino acid load and organic carbon and nitrogen quantities were generally low, it was found that most of the samples harbored complex and versatile microbial communities, which were dominated by (extremely) halophilic microorganisms (most notably by species of the Archaeal family Halobacteriaceae). The dominance of salts (i.e., halites and sulfates) in the investigated samples leaves its mark on the composition of the microbial communities but does not appear to hinder the potential of life to flourish since it can clearly adapt to the higher concentrations. Although the Atacama Desert is one of the driest and harshest environments on Earth, it is shown that there are still sub-locations where life is able to maintain a foothold, and, as such, salt flats could be considered as interesting targets for future life exploration missions on Mars.

Groundwater Evaporation for Salt-Affected Soil Under Plastic Film-Covered Cultivation Condition: a Review

Groundwater is a main type of natural resource, and groundwater evaporation is an important part of the cropland water cycle. Under recent years of poor land management, soil salinization is becoming a serious environmental issue, especially in the arid regions having strong evaporation and shallow groundwater table. Plastic mulching has therefore emerged gradually, becoming a globally applied agricultural practice for its benefits such as salt cumulation control, soil environment regulation, and crop yield improvement. However, knowledge of groundwater evaporation under plastic film-covered cultivation pattern remains vague in terms of action mechanism. This review critically discusses how plastic mulch, salt, and crop cultivation/plant by-products affect groundwater evaporation and further reveals their action mechanisms. For salt-affected cultivated soils, specifically, salt precipitation, crystallization, and capillary force are the non-negligible actions affecting water movement and evaporation. Besides, the physical and chemical effects of formed salt crust at plastic film holes cannot be ignored under plastic mulch underlying condition. Furthermore, the effect of changed canopy cover during growing period should be taken into consideration under crop cultivation underlying condition; meanwhile, the variation of water flow and evaporation induced by crop residues or direct straw return in farmland can be quantified through determining the amount of the hydrophilic oxygen-containing functional groups and the change of soil pore-size distribution. Based on the current research deficiency, future studies should focus on the groundwater contribution to crop, the diurnal variation of groundwater evaporation, the determination of suitable and ecological groundwater table, and the capillary rise models; and future interdisciplinary (e.g., physics and chemistry) research should be put into the interactive of salt and water in order to reveal the mechanisms of fresh and saliferous groundwater flow and evaporation; moreover, the issue on plastic pollution induced by plastic mulch should also be brought to the forefront. A clear understanding of groundwater evaporation under plastic film-covered cultivation on salt-affected soil benefits environmental protection in the saline regions.

Water Table Depth and Soil Salinization: From Pore‐Scale Processes to Field‐Scale Responses

AbstractThe accumulation of salts in soils adversely influences plant growth and biological activity resulting in loss of yields and soil ecosystem services. Water table depth plays an important role on solute distribution through the unsaturated zone. We focus on the relationship between saline water evaporation from soil surfaces and water table depths. When the water table was hydraulically connected to the surface, we found more evaporatively driven sodium chloride precipitation at the surface with deeper water tables relative to shallow ones. We attribute this result to lower surface water contents that reach solubility limit sooner and support an expanding salt crust. Thermal imaging confirmed that when surface is hydraulically connected to the water table, capillary flows through the porous precipitated salt maintain the evaporative flux. Macroscopic continuum‐scale numerical simulations demonstrate higher solute concentration closer to the surface in the case of deeper water tables supporting the microscopic picture attributed to fewer evaporation and solute deposition sites at the surface with deeper water tables. Insights from the laboratory‐scale experiments and numerical studies were used to describe soil salinity at much larger scales. We employed two global‐scale databases for topsoil salinity, soil texture, and water table depths to link our laboratory‐scale findings with long‐term and field‐scale observations. The results illustrate the importance of pore‐scale physics and processes on constraining the field‐scale responses.

Засолённые почвы Харамодонской низменности Баргузинской котловины

In “humid” latitudes within the lacustrine-alluvial part of the Barguzin depression, azonal saline soils are widespread. Genesis of these soils is affected by a combination of endogenous (current seismic activity and tectonic disturbance at the intersection of Nizhneargadinskiy and Khaskhal-Argadinskiy faults, discharges of low mineralized waters) and exogenous factors (aridity in the spring-early-summer period, permafrost, cryogenic metamorphism). The study was performed at the area of Kharamodon lowland near saline lakes. The conjugate series of soils located on the bottom of a dried-up lake and in the contact zone of the transition from the lake-alluvial plain to the terrace of the Upper Kuitun terrain were investigated. The soils developed in the zone of tectonic faults with deep waters wedging are characterized by extremely high dynamics of soil forming conditions such as the contrasting combination of physical and chemical properties of soil horizons, heterogeneous texture, soda and sulfate-soda type of salinity, and geochemical peculiarities of the element associations. The salt crusts, humus-underdeveloped or light-humus diagnostic horizons with signs of aeolian stratification and gleying are the features of the morphological structure of these soils. Within the saline soil profiles, dark, almost black layers and turbations are noted, which are typical for soils of active tectonic faults zones with thermal low mineralized waters unloading. The concentrations, salts distribution, degree and type of chemistry in the soils under the study are sharply changed over a short distance. In the soils of accumulative positions, solonchaks with very high soda salinity entire the profile are formed. There is no vegetation due to the strong salt toxicity. In the layered-aeolian humus saline permafrost soil located in the contact zone of the transition from the lake-alluvial plain to the terrace, surface salinity with less toxic sulfate anion prevails (salt crust). Downhill soda-sulfate and sulfate-soda types occurred, sodium predominates among the cations. Halophilic and halotolerant plant species form the low projective cover (30%). The maximum content of easily soluble and toxic salts is concentrated in the salt crusts of the quasi-clay cryoturbated solonchak and in the layered-aeolian soil. Light-humus saline aeolian-stratified permafrost soils developed at the highest hypsometric levels are of weak degree of mixed type salinity of the upper horizons that favors vegetation growth. The latent discharge of mineralized waters affects the saline soils composition. In comparison with the clark of the Earth's lithosphere, accumulation of Ba2,5, Sr2,3, Ca1,8, Mg1,7, P1,6 is occurred. In the saline soils of the Haramodon lowland, not typical for the parent rocks elements such as Mg3,2, S2,9, Li2,3, P2,0, Co2,0, Ca1,8, Mn1,7, V1,6, Cu1,6, Cr1,6, Ti1,5, Ni1,5, Fe1,4 are accumulated.

Alkaliphilic and alkalitolerant fungi in mud and salt crusts collected from Wadi El-Natrun lakes

A total number of alkaliphilic and alkalitolerant fungi (37 species related to 16 genera) were collected from mud and salt crusts of Wadi El- Natrun lakes on Czapek Dox agar adjusted at pH10 and pH13 during the seasons of study. The most dominant genera at both pH levels were Aspergillus (9 species) followed by Penicillium (9), Acremonium (3) and Fusarium (3), Of these genera, Aspergillus terreus and Pencillium chrysogenum were the most commonly encountered species.

Acidophilic and acidotolerant fungi in mud and salt crusts collected from Wadi El-Natrun lakes

Isolation some fungi from extreme source under extreme media and these were 42 species related to 14 genera of acidiphilic or/ aciditolerant fungi were collected from mud and salt crusts of Wadi El- Natrun lakes on Czapek Dox agar adjusted at pH 4 and pH 5 during the seasons of study. Aspergillus and Penicillium were the most common genera of the total propogules on the two pH levels.

Precipitation chemistry and atmospheric nitrogen deposition at a rural site in Beijing, China

Precipitation chemistry and atmospheric nitrogen (N) deposition are of great concern worldwide due to their close relationships with air quality and impacts on ecosystems. However, evaluation of the chemical composition of precipitation and N deposition flux in rural areas of Beijing has received little attention to date. This paper presents the chemical constituents, possible sources and wet deposition fluxes of water-soluble ions (NH4+, NO3−, SO42−, Cl−, Na+, K+, Ca2+, Mg2+) in precipitation samples collected during 2017–2018 at a rural site located at northwest of Beijing city; meanwhile, dry deposition of reactive N species (gaseous ammonia, nitrogen dioxide, nitric acid, and particulate (p) NH4+ and NO3−) were also quantified. During this 2-year period, the volume-weighted mean (VWM) pH of precipitation was 6.73, and all samples had pH values above 6.0. The VWM electric conductivity of precipitation and the mean sum of all measured ions was 43.8 μS cm−1 and 591.9 μeq L−1, respectively, indicating a significant impact of atmospheric pollution. Ca2+ and NH4+ were the dominant neutralizing species for precipitation acidity. Positive matrix factorization analysis further confirmed five sources for water-soluble ions, including sea salt aging, secondary formation, agriculture, crust, and biomass burning. The annual mean wet N deposition was 4.6, 3.4 and 8.0 kg N ha−1 yr−1 for NH4+, NO3− and total inorganic N, respectively. The total dry N deposition was dominated by gaseous ammonia (11.5 kg N ha−1 yr−1). The total N deposition (wet plus dry) was 27.7 kg N ha−1 yr−1, where dry deposition contributed to 75% and wet deposition 25% of the total. The simulations from the GEOS-Chem model indicate that agricultural (fertilizer use and livestock) and nonagricultural sources (industry, power plant, and transportation) are both important contributors to total N deposition. These results could be useful in evaluating/developing emission control policies to protect the eco-environment in Beijing.

Natural Formation of Chloro- and Bromoacetone in Salt Lakes of Western Australia

Western Australia is a semi-/arid region known for saline lakes with a wide range of geochemical parameters (pH 2.5–7.1, Cl− 10–200 g L−1). This study reports on the haloacetones chloro- and bromoacetone in air over 6 salt lake shorelines. Significant emissions of chloroacetone (up to 0.2 µmol m−2 h−1) and bromoacetone (up to 1. 5 µmol m−2 h−1) were detected, and a photochemical box model was employed to evaluate the contribution of their atmospheric formation from the olefinic hydrocarbons propene and methacrolein in the gas phase. The measured concentrations could not explain the photochemical halogenation reaction, indicating a strong hitherto unknown source of haloacetones. Aqueous-phase reactions of haloacetones, investigated in the laboratory using humic acid in concentrated salt solutions, were identified as alternative formation pathway by liquid-phase reactions, acid catalyzed enolization of ketones, and subsequent halogenation. In order to verify this mechanism, we made measurements of the Henry’s law constants, rate constants for hydrolysis and nucleophilic exchange with chloride, UV-spectra and quantum yields for the photolysis of bromoacetone and 1,1-dibromoacetone in the aqueous phase. We suggest that heterogeneous processes induced by humic substances in the quasi-liquid layer of the salt crust, particle surfaces and the lake water are the predominating pathways for the formation of the observed haloacetones.

Characterization of lithium cycling in the Salar De Olaroz, Central Andes, using a geochemical and isotopic approach

The Salar de Olaroz is one of the main Li operations in Argentina. In order to identify sources and to understand the dynamics of Li in this salt pan, chemical and isotopic analysis (δ7Li and 87Sr/86Sr) of brines, thermal and river waters, as well as ignimbrites and sediments that outcrop in the basin were performed. The Li concentrations in shallow brines (i.e., ∼0.6 m below surface) range from 260 to 890 mg L−1 (average = 841 mg L−1, n = 16), while in deep brines (i.e, 200–450 m b.s.) concentrations are higher (average = 993 mg L−1, n = 16) and range from 690 to 1490 approximately. δ7Li values range from +5.9 to +7.2 ‰ and from +8.1 to +10.2 ‰ in shallow and deep brines respectively, while δ7Li values of the regional rocks and sediments vary between -13.8 and +0.5‰. The 87Sr/86Sr values indicate that the chemical composition of brines in Olaroz is the result of mixing between solutes that are originated from bedrock weathering by shallow meteoric water and water that has a hydrothermal contribution. Due to evaporation, Li concentrations in shallow brines increase by two or three orders of magnitude when compared with the values determined in the main tributaries and in the discharge of thermal waters. This process does not produce measurable isotopic fractionation of Li, thus the isotopic signature of shallow brines and halite crystals in contact with these waters are similar. As brine density increases, water descends through layers of silt and as the brine ages at depth, the formation of secondary minerals enhance the preferential adsorption of 6Li onto clay minerals and Fe (hydr)oxides resulting in higher δ7Li values in deep brines. Nevertheless, Li concentrations remain nearly constant or slightly increase with depth, which suggests that the removal of this element from the water due to adsorption is offset by Li contributions derived from processes that do not produce any isotopic fractionation. Two processes may account for this in the study system: 1) the mixing with ancient Li-rich fluids trapped in the deeper evaporitic layers that preserved the isotopic signature of their contemporaneous brines; and 2) the release of loosely- bound Li from the exchangeable sites of smectites that compose the clastic fraction of the salt flat sediments as they acquire a more crystalline nature over time. Consequently, it is expected that sediments accumulated below the salt crust may provide an important additional reservoir of Li to the brine, but further experimental studies will be necessary to investigate the mechanisms that control the partition of Li between the aqueous and solid phases and its isotopic fractionation in extremely arid and saline environments.

Infrared Spectroscopic Detection of Biosignatures at Lake Tírez, Spain: Implications for Mars.

The detection of potential biosignatures with mineral matrices is part of a multifaceted approach in the search for life on other planetary bodies. The 2020 ExoMars Rosalind Franklin rover includes within its payload three IR spectrometers in the form of ISEM (Infrared Spectrometer for ExoMars), MicrOmega, and Ma-MISS (Mars Multispectral Imager for Subsurface Studies). The use of this technique in the detection and characterization of biosignatures is of great value. Organic materials are often co-deposited in terrestrial evaporites and as such have been proposed as relevant analogs in the search for life on Mars. This study focuses on Ca-sulfates collected from the hypersaline Tírez Lake in Spain. Mid infrared and visible near infrared analysis of soils, salt crusts, and crystals with green and red layering indicative of microbial colonization of the samples was acquired from across the lake and identified the main mineral to be gypsum with inputs of carbonate and silica. Organic functional groups that could be attributed to amides and carboxylic acids were identified as well as chlorophyll; however, due to the strong mineralogical absorptions observed, these were hard to unambiguously discern. Taxonomical assignment demonstrated that the archaeal community within the samples was dominated by the halophilic extremophile Halobacteriaceae while the bacterial community was dominated by the class Nocardiaceae. The results of this research highlight that sulfates on Mars are a mixed blessing, acting as an effective host for organic matter preservation but also a material that masks the presence of organic functional groups when analyzed with spectroscopic tools similar to those due to fly on the 2020 ExoMars rover. A suite of complementary analytical techniques therefore should be used to support the spectral identification of any candidate extraterrestrial biosignatures.

Dissolution-precipitation-driven upward migration of a salt crust.

Salt crusts forming at the surface of a porous medium can dynamically evolve with crust displacements leading to the formations of domes and blisters or simply to the upward migration of the crust. However, the mechanisms explaining the displacements are unclear. It has been conjectured that they could be related to dissolution-precipitation phenomena and/or to mechanical effects associated with the concept of crystallization pressure. We present a simple experiment where the crust upward migration is significant and can be entirely explained from the consideration of dissolution-precipitation phenomena. Equations governing the crust displacement are derived, leading to quite good agreement with the experimental results.

LITHIUM AND BORON OF SPRING WATER AND SALT CRUST FROM SALAR DE ASCOTÁN, SOUTHWESTERN ALTIPLANO

Lithium is an essential element for humans and animals, it is bio accumulated by plants and it is a relatively uncommon element in the Earth s crust, on the contrary boron is widely distributed and it is micronutrient for plants. Boron and lithium are incorporated in fertilizers for agriculture and they used in many industries. Economically lithium is considered a strategic element because it is important in energy markets. There are two main economically recoverable sources of lithium, those being mineral ores and the evaporate deposits (playa lakes, called “salars” in Spanish). Direct extraction of lithium from brines at the salars is a low cost method and generates byproducts such as boron. Salars with high concentrations of Li have been reported in the Andean region near the borders of Chile, Bolivia, and Argentina. In Chile, the brines at Salar de Atacama are considered an important commercial source of lithium. To the northeast of Salar de Atacama it is located Salar de Ascotan (21o27`01, 9``S; 68o15`8,5``W) where the commercial boron extraction has been done for many decades but lacks published information about lithium extraction. In this study concentrations and distribution of lithium and boron in the water, sediment and salt crust were analyzed in some of the east-side springs which have a high endemic biodiversity. The concentrations in the salt crust were higher than in water and sediment. Geographically, the concentration of lithium in salt crust increases from north to south, but the boron concentration was higher in the extreme north and south, in the southernmost spring, No11. The average concentration of B in the salt crust was 149 [mg/Kg] and for Li was 3000 [mg/Kg] at the east side of the salar, thus it is the area with the highest concentration of lithium and boron. The concentrations in the salt crust were high and geographically heterogeneous for using a non-invasive method, for environmental protection we propose an exploration superficial on the western side which lack spring water and present the higher concentration of lithium and boron of the salar.

Robust Archaeal and Bacterial Communities Inhabit Shallow Subsurface Sediments of the Bonneville Salt Flats.

We report the first census of natural microbial communities of the Bonneville Salt Flats (BSF), a perennial salt pan at the Utah-Nevada border. Environmental DNA sequencing of archaeal and bacterial 16S rRNA genes was conducted on samples from multiple evaporite sediment layers collected from the upper 30 cm of the surface salt crust. Our results show that at the time of sampling (September 2016), BSF hosted a robust microbial community dominated by diverse halobacteria and Salinibacter species. Sequences identical to Geitlerinema sp. strain PCC 9228, an anoxygenic cyanobacterium that uses sulfide as the electron donor for photosynthesis, are also abundant in many samples. We identified taxonomic groups enriched in each layer of the salt crust sediment and revealed that the upper gypsum sediment layer found immediately under the uppermost surface halite contains a robust microbial community. In these sediments, we found an increased presence of Thermoplasmatales, Hadesarchaeota, Nanoarchaeaeota, Acetothermia, Desulfovermiculus, Halanaerobiales, Bacteroidetes, and Rhodovibrio This study provides insight into the diversity, spatial heterogeneity, and geologic context of a surprisingly complex microbial ecosystem within this macroscopically sterile landscape.IMPORTANCE Pleistocene Lake Bonneville, which covered a third of Utah, desiccated approximately 13,000 years ago, leaving behind the Bonneville Salt Flats (BSF) in the Utah West Desert. The potash salts that saturate BSF basin are extracted and sold as an additive for agricultural fertilizers. The salt crust is a well-known recreational and economic commodity, but the biological interactions with the salt crust have not been studied. This study is the first geospatial analysis of microbially diverse populations at this site using cultivation-independent environmental DNA sequencing methods. Identification of the microbes present within this unique, dynamic, and valued sedimentary evaporite environment is an important step toward understanding the potential consequences of perturbations to the microbial ecology on the surrounding landscape and ecosystem.

High-Tech Material in a Salt Crust

High-Tech Material in a Salt Crust

Geomorphologic Characteristics of Polygonal Features on Chloride-Bearing Deposits on Mars: Implications for Martian Hydrology and Astrobiology

Over 600 chloride-bearing deposits (chlorides) have been identified on the southern highlands of Mars. These chlorides have critical implications for hydrology and astrobiology: they are indicators of an evaporating super saturated solution, and they could have provided habitat environments for halophilic microorganisms and preserved organic matter. One of the prominent geomorphology characteristics of these chloride-bearing regions is the polygonal features within them. The origin of these polygonal features is still in debate. In this study, we have surveyed 153 locations of chlorides using 441 high resolution imaging science experiment (HiRISE) images to characterize the geomorphology of polygonal features. We identified 3 types of polygonal features of distinct geomorphologic characteristics: fractures, raised ridges, and transitional polygons between fractures and raised ridges. We evaluate previously proposed hypotheses of the formation of the polygonal features, and suggest that the 3 types of polygonal features are indicators of different stages of salt crust formation. Salt crust is usually formed through multiple groundwater activities, and it often occurs in playa environment on Earth. The unique hydrological and astrobiological implications of the chlorides with polygonal features make these deposits of high priority for future landed on and/or sample return exploration missions of Mars.

The Effect of Flooding on Evaporation and the Groundwater Table for a Salt-Crusted Soil

Soil salt crusts have been shown to have a strong influence on evaporation and water movement in soils, and this has attracted considerable attention. However, there is little information available on these processes during flooding. The objective of this study was to investigate the evaporation rate, variation in the groundwater table, and soil water content of salt-crusted soil flooded by five floodwater depths: 2 mm (Treatment A), 6 mm (Treatment B), 10 mm (Treatment C) 14 mm (Treatment D), and 18 mm (Treatment E). The experiments were carried out using repacked homogeneous silt loam soil columns in the laboratory. The experimental results showed that salt crust formation led to a low evaporation rate. The salt crust tended to form a dome, and some breakage occurred when the salt crust was dry. The broken crust increased the evaporation rate, indicating that the evaporation occurred below the crust. The soil moisture did not significantly change in the soil profile from 20 to 70 cm during the experimental period, which indicated that the existence of the evaporation front located in a layer very close to the surface. The evaporation rate rapidly increased when floodwater was added to the soils and returned to its previous low value after the salt crust reformed. However, before the salt crust reformed, there was a total water loss of 2.1, 4.3, 6.6, 10.1, and 13.8 mm for treatments A, B, C, D, and E, respectively, indicating that only a portion of the floodwater evaporated; another portion of the floodwater was discharged into the groundwater, causing the groundwater table to rise, although only by a small amount (6 mm). Therefore, the groundwater recharge caused by flooding should be considered. Otherwise, groundwater consumption may be overestimated.

Evaporitic carbonates in the pre-salt of Santos Basin – Genesis and tectonic implications

Abstract Since the first discoveries of oil accumulations in the carbonate reservoirs of the Lower Cretaceous Barra Velha Formation of the Santos Basin, their genesis has been the subject of intense discussion. Different depositional models have been proposed, with some authors advocating a microbial origin, while others an abiotic origin as travertines or travertine-like rocks. This search for a modern carbonate analogue for these unusual rocks may have disregarded an intriguing alternative: an evaporative model supported by our petrographical and geochemical data. Evaporitic sediment patterns in endorheic basins, in a depositional framework of brine drawdown, are dominated by ephemeral salt pan hydrology. Bedded salt crusts form a stack of subaqueous aligned crystal beds at the sediment-water interface; salt grows diagenetically within saline and mud layers beneath the dry pan surface; finally laminated sediments are deposited. We observe a similar cyclic pattern in the pre-salt core we described: beds of shrub-like crystals and diagenetic spherulites growing in magnesium clay matrix are followed by laminites. The model we propose attempts to contribute solving the puzzle of Pre-Salt carbonate deposition by integrating sedimentology and geochemistry with basin tectonics. Our observations and basin tectonics point to the exciting possibility that the sag phase carbonates of the Santos-Campos basin were deposited as the initial/transitional stage of a closed sub-sea-level evaporite basin whose rising salinities culminated in the deposition of halite and bittern salts (carnallite, sylvite, tachyhydrite). Basinwide evaporites are singular events in the geological record. They form when a giant sub-sea-level basin becomes a sump of continental, marine and hydrothermal fluids, producing unexpected brine compositions in unusual depositional settings present in ancient evaporitic basins but absent from most modern ones. The novelty in this paper is that we apply to pre-salt carbonate deposition the sedimentology, hydrology and geochemistry of ancient evaporitic basins. With this concept in mind, we propose a geochemical model for the unusual pre-salt carbonate precipitation of the Santos Basin. Regarding the Walvis-Rio Grande volcanic high as a topographic barrier during the Aptian, we suggest that the main sources of calcium to the Barra Velha paleolake were hydrothermal brines, mostly from infiltrating seawater that reacted at depth with the basalts of the volcanic barrier. Hyperextension of the lithosphere, with a shallow Moho, increased geothermal gradients to levels favorable for the generation of hydrothermal CaCl2 brines, a process facilitated by the already elevated Ca++ ion and low sulfate concentration of the Cretaceous ocean. These CaCl2-rich fluids would pass through the volcanic barrier into a sub-sea-level paleolake in the rift basin. The high salinity paleolake would become saturated in calcium bicarbonate/carbonate as internally drained NaHCO3-bearing alkaline waters, formed by physical/chemical weathering of penecontemporaneous basaltic rocks, mix with the CaCl2-bearing hot brines percolating through the barrier, producing a hybrid brine (2NaHCO3 + CaCl2 = Ca(HCO3)2 + 2NaCl). Such a depositional system, integrating the geochemical-depositional controls of sag phase carbonates with those of the South Atlantic evaporites, has important implications for unravelling the genesis of these exotic deposits.

Geoheritage Resource of Small Mud Lakes in the Semi-Arid Environments of the Russian South

Lakes constitute a significant freshwater resource and are often regarded as being an important part of a country’s natural heritage. However, their geological heritage (geoheritage) value remains significantly understudied. Three small lakes, namely the Salt Lake, the Gruzskoe Lake and the Big Yashalta Lake, located in the central part of the Russian South were studied in this paper. The main focus of this research was to search for relevant unique geological features. This paper established that these lakes are distinguishable from other lakes by the presence of dark-colored mud that is rich in sulfides and methane. As a result of excessive summer evaporation, the lakes desiccate (partly or even fully) and this results in exposure of the mud as well as the formation of salt crystals and crusts. This bottom mud (peloid, therapeutic mud) forms as a result of highly-complex biogeochemical processes in semi-arid environments. This mud is interpreted as being part of the lake’s geoheritage as it belongs to sedimentary, geochemical and other types. Moreover, this geoheritage has a high ranking nationally. The most representative example can be found at the Big Yashalta Lake and for that reason, this lake is proposed as a geosite. Established sites of geoheritage importance are vital to geoscience research and geotourism activities and thus, these sites are considered to be a resource. Together with the development of local ecotourism and the use of peloids for the health industry purposes, the exploitation of this geoheritage resource would contribute to the sustainable development of the local area.

Marine Coastline Polygonal Ridges and Surface Roughness Development on a Salt-Crusted Playa: Recognition by Structure-from-Motion Photogrammetry

Salt crust is a normal landform in drying-out salt lake basins or marine regression coastlines, but the surface evolution processes over a decadal or even centenary period are not well understood due to poor data records. Microrelief characteristics control erodibility and erosivity, which will significantly influence wind erosion and dust emission. It is essential to classify the microrelief pattern of salt crust for mapping its spatial distribution and evaluating the environmental process. A desiccated inland tail-end lake would be an example of the coastline surface evolution after regression and represent a good case study of salt crust because of the fewer exogenic process interruptions. For this paper, field work was performed in the Lop Nur playa in China, about 90° E, 40° N, which used to be a salt lake half a century ago. Ground-based photos of the salt crust were acquired and imported into structure-from-motion (SfM) software to produce a fine centimeter-scale digital elevation model (DEM). Two indexes were introduced and extracted from the digital elevation model to classify various types of salt crust: roughness was calculated to evaluate the magnitude and the gray-level co-occurrence matrix (GLCM) score was derived to describe the structure pattern of the salt crust. Moreover, in this paper, sedimentary features during different parts of a playa evaporation cycle are reviewed and peculiar kinds of salt crust found on Lop Nur are further discussed.