Dissolution Of Evaporites Research Articles

Behaviour of Sr, Ca, and Mg isotopes under variable hydrological conditions in high-relief large river systems

To assess how chemical weathering processes in large high-relief river systems respond to climatic variability, we studied seasonal changes in radiogenic strontium (87Sr/86Sr) and stable calcium (δ44/40Ca) and magnesium (δ26Mg) isotopes in the Jinsha and Yalong rivers, which drain the southeastern Tibetan Plateau. During the low-runoff season, with discharge (Q) < 2000 m3/s, the river waters reflect the Sr, Ca, and Mg isotope signatures of recharge meltwaters, with additional isotope fractionation signals for Ca and Mg related to secondary mineral precipitation, which might imply that meltwater flushes soil solutions from the soil. During medium-runoff intervals (2000 m3/s < Q < 4000 m3/s), the Sr, Ca, and Mg isotope signatures in the Jinsha river waters are similar to those of the headwaters, which are influenced by evaporite dissolution, while the Yalong is affected by greater carbonate weathering relative to silicate weathering. In both rivers, bedrock dissolution governs the chemical composition of the river waters. During the high-runoff season (Q > 4000 m3/s), storms generate rapid overland flow, which transfers large volumes of soil into the rivers, such that soil weathering plays an important role in regulating riverine chemical compositions. At these times, the riverine Ca and Sr isotope evolution is influenced by secondary mineral dissolution and sediment–water cation exchange. Overall, this study highlights the potential of combining multiple isotope systems (Sr, Ca, Mg) to trace the dynamics of water–rock interaction under variable hydrological conditions.

Differentiating Nitrate Origins and Fate in a Semi-Arid Basin (Tunisia) via Geostatistical Analyses and Groundwater Modelling

Despite efforts to protect the hydrosystems from increasing pollution, nitrate (NO3−) remains a major groundwater pollutant worldwide, and determining its origin is still crucial and challenging. To disentangle the origins and fate of high NO3− (&gt;900 mg/L) in the Sidi Bouzid North basin (Tunisia), a numerical groundwater flow model (MODFLOW-2005) and an advective particle tracking (MODPATH) have been combined with geostatistical analyses on groundwater quality and hydrogeological characterization. Correlations between chemical elements and Principal Component Analysis (PCA) suggested that groundwater quality was primarily controlled by evaporite dissolution and subsequently driven by processes like dedolomitization and ion exchange. PCA indicated that NO3− origin is linked to anthropic (unconfined aquifer) and geogenic (semi-confined aquifer) sources. To suggest the geogenic origin of NO3− in the semi-confined aquifer, the multi-aquifer groundwater flow system and the forward and backward particle tracking was simulated. The observed and calculated hydraulic heads displayed a good correlation (R2 of 0.93). The residence time of groundwater with high NO3− concentrations was more significant than the timespan during which chemical fertilizers were used, and urban settlements expansion began. This confirmed the natural origin of NO3− associated with pre-Triassic embankment landscapes and located on domed geomorphic surfaces with a gypsum, phosphate, or clay cover.

Hydrogeochemical processes on inland aquifer systems: A combined multivariate statistical technique and isotopic approach

Groundwater is an important resource used for multiple purposes and should be protected, especially, in arid regions. The aim of this study is to assess the main processes on groundwater salinization from Menzel Habib shallow and deep aquifers, southeastern Tunisia, which could be applied to further groundwater quality assessment. Indeed, combined hydrogeochemical and isotopic fingerprints data approaches were used using multivariate statistical methods, highlighting, Hierarchical Clustering Analysis and Principal Component Analysis.A total of 36 groundwater samples were collected from the Menzel Habib aquifer system: 25 from shallow aquifer and 11 from deep aquifer. The obtained results from both stretches indicated three dominant hydrochemical facies: Chloride-sodic, Sulphated-sodic, and mixed water type. The determination of groundwater salinization origin, and the understanding of its hydrological and geochemical behaviors, were assessed by a combined statistical and hydrogeochemical approach. The study of correlations between major elements and Total Dissolved Solids is, thus, an important tool where dissolution of evaporites that can originate from the Triassic materials of Hadifa mountain, the precipitation and/or dissolution of carbonates, cationic exchange and inverse cationic exchange are the main processes associated to groundwater salinity increase.Moreover, the HCA has allowed to classify the groundwater samples into two clusters: the first one with low to moderate salinity and the second one with high salinity. In addition, the application of stable isotopes allowed a better understanding of the hydrodynamic functioning of this aquifer system. The isotopic data suggests a relatively high δ2H and δ18O values for groundwater samples located close to Global Meteoric Water Line that reflects recent recharge for the aquifer system by direct rainwater infiltration, respectively from bordered reliefs in the study area. It also showed a depletion in isotopic composition for almost groundwater samples that indicates the importance of evaporation on the hydrochemistry of the area.

Hydrochemical characteristics and processes of groundwater in the Cenozoic pore aquifer under coal mining.

Mining activities considerably affect groundwater quality and resources. It is crucial to investigate water chemistry and hydrochemical processes under coal mining settings for water environment protection and sustainable utilization of groundwater resources. In this study, 36 groundwater samples from the Cenozoic pore aquifer in the Gubei coal mine in Huainan (Anhui Province, China) were analyzed using hydrochemical, multivariate statistical methods, and inverse geochemical modeling. Results revealed a hydrochemical boundary around 100m below the ground surface, forming two flow zones participating in different hydrological cycles. In the shallow (circulation) zone above the boundary, the main hydrochemical processes are silicate dissolution and cation exchange, followed by evaporite dissolution. In this zone, the Na+ + K+, Cl-, and SO42- concentrations are low and stable, forming low-salinity water (total dissolved solids [TDS] < 1g/L) dominated by Na*Ca*Mg-HCO3 and Na*Ca-HCO3 types. At greater burial depths, the pH, TDS, Na+ + K+, Cl-, and SO42- concentrations in the groundwater gradually increase, while the HCO3- concentration gradually decreases, which is mainly due to the enhanced evaporite dissolution and decarbonation in the deep (circulation) zone below the hydrochemical boundary. In this zone, the Na+ + K+, Cl-, and SO42- concentrations are high and variable, forming high-salinity water (TDS > 1g/L) dominated by Na-Cl and Na-Cl*SO4 types. A hydrochemical evolution model of the Cenozoic aquifer was finally established, which advances our understanding of the evolutionary processes of groundwater chemistry under mining drainage.

Broken Beds, but better science; using multiple hypotheses to interpret geological data

AbstractIn this study, we propose a multiple hypotheses approach to improve interpretations of limited remotely sensed datasets, such as sparsely exposed outcrops, subsurface datasets, or planetary objects using semi‐quantitative scoring and ranking of observable features. This method is demonstrated using an outcrop example from the Broken Beds of the Upper Jurassic–Lower Cretaceous Purbeck Limestone Group exposed along Britain's Jurassic Coast. Four published hypotheses regarding their origin are refined, represented in matrix form, scored and ranked based on carefully selected outcrop features. Semi‐quantitative scoring utilises knowledge of likely processes governing the occurrence of a range of features, some of which might be ignored or down‐played to favour a single hypothesis. Furthermore, by integrating expertise from different sub‐disciplines (e.g. basin analysis, sedimentology, diagenesis), we also consider the combined evidence of multiple features. This new method results in an interpretation that favours a multi‐process origin for the Broken Beds due to evaporite dissolution, overpressure release and tectonic folding, with identified uncertainty, all useful to guide further data collection.

Soil Column Experimental Study on the Effect of Soil Structure Disturbance on Water Chemistry.

The changes in soil/rock structure caused by engineering disturbance or earthquakes could affect water chemistry by increasing the reaction surface, enhancing the oxidation condition, or exposing soluble rocks. However, the details of the mechanisms of the disturbance of soil/rock are little known. Based on the soil column experiment, this study analyzed the concentrations of sulfate (SO4), sulfur, and oxygen isotopic composition of SO4 (δ34S-SO4 and δ18O-SO4) in effluent water. The water-rock interaction mechanisms in the disturbed soil and the contribution of this interaction to the SO4 in groundwater were studied. The results suggest that the concentration of SO4 in the first effluent water sample can reach up to 97 mg/L, much higher than that in natural groundwater (6.8 mg/L). The isotopic composition of SO4 further suggested that SO4 in the first effluent water sample was mainly derived from the dissolution of SO4-containing evaporites. The proportion was estimated to be 93%. SO4-containing evaporites accounted for 23% of the SO4 content in all effluent water samples during the experiment. The disturbance of soil structure led to the exposure and dissolution of SO4-containing evaporites, which were initially insoluble under natural conditions. This study is essential to the clarification of the water-rock interaction mechanisms following the changes in soil/rock structures.

A hydrochemical and multi-isotopic study of groundwater sulfate origin and contribution in the coal mining area

Coal mining cities are universally confronted with the degradation of groundwater quality, and the sulfate pollution of groundwater has become a widely studied environmental problem. In this study, we combined multi-isotope (δ34S, δ18O-SO42- and 87Sr/86Sr) approach with hydrochemical technique and a Bayesian mixed model to clarify sources and transformations and to quantitatively assess the contribution of sulfate from potential sources. The concentrations of SO42- in groundwater ranged from 7.7 mg/L to 172.9 mg/L, and the high-value areas were located in coal mining area and residential area. The total values of δ34S and δ18O-SO42- varied from 10.6‰ to 26.9‰ and 6.9‰ to 14.1‰, respectively, in the groundwater. Analyses of SO42- and Sr isotopes and water chemistry indicated that SO42- in groundwater originated from various sources, such as atmospheric precipitation, sulfide mineral oxidation, evaporite dissolution, sewage and mine drainage. The oxidation of pyrite and bacterial sulfate reduction (BSR) had no significant impact on the stable isotopes of groundwater. At the same time, the calculation results of the Bayesian mixed model showed that the sources of SO42- in groundwater mainly include evaporite dissolution in aquifer and mine drainage in the mixture of shallow and deep groundwater, with high contribution proportions of 39.8 ± 10.9% and 31.9 ± 5.7%, respectively, while the contributions of sewage (13.9 ± 8.5%), atmospheric precipitation (9.6 ± 8.6%) and the oxidation of sulfide (4.7 ± 3.3%) to SO42- were lower. The research results revealed the source of SO42- pollution in shallow groundwater in the coal mine area and provided an important scientific basis for the effective management and protection of groundwater resources.

Tracing Sulfate Source and Transformation in the Groundwater of the Linhuan Coal Mining Area, Huaibei Coalfield, China.

Mining activities cause surface sulfate enrichment, which has negative impacts on human health and ecosystems. These high concentrations of sulfate may enter groundwater through the unsaturated zone (UZ), threatening groundwater quality. Therefore, we combined hydrochemical and dual isotopic analyses of sulfate in surface water, soil water and groundwater with evaluations of the UZ to identify the groundwater sulfate source and transformation in the coal mining area. Soil profile samples were collected near gangue heaps (UZ-1, UZ-2) and the mean sulfate concentrations of the UZ-1 profile and UZ-2 profile were 35.4 mg/L and 69.63 mg/L, respectively. The shallow groundwater sulfate was mainly from dissolution of evaporite, sulfide oxidation and sewage. Different sulfate contaminated areas showed different characteristics of sulfate sources. The sulfate source to groundwater near the coal gangue heaps was sulfide oxidation. The groundwater sulfate near the gangue heaps and industrial park compound contamination area was mainly derived from industrial and domestic sewage and sulfide oxidation. In addition, the role of bacterial sulfate reduction (BSR) in the groundwater was not obvious. This research result is of great significance for promoting the safe mining of coal resources and sustainable utilization of groundwater in the Huaibei coal mining area and other coal mining areas in China.

Characteristic and genesis of dolostone reservoirs around the Proterozoic/Cambrian boundary in the Upper Yangtze block for Mississippi valley-type Zn-Pb ores: A review

Reservoirs as the direct targets for hydrocarbon exploration represent the permeable and porous rocks. In this sense, reservoirs provide the crucial control for Mississippi Valley-type (MVT) Zn-Pb ore formation, but they have received less attentions in the research field of MVT deposits. Based on reprocessing published data and the field and petrographic observations, this study reviews the characteristics and genesis of the reservoirs for MVT ores in the Dengying Formation and the early Cambrian dolostone units around the Proterozoic/Cambrian boundary in the Upper Yangtze block. The reservoir horizons consist of breccias and coarse-grained carbonates at the top of a shallowing-upward sedimentary cycle mainly in the tidal flat facies and subordinately in the platform margin mound-shoal facies. Bird’s eye and zebra textures are common in the reservoir horizons and the pseudomorphs after evaporite minerals can be found in the breccias. Moreover, the breccia bodies have a large lateral extension up to kilometers level, sharp boundaries with the enclosing rocks, and are absent of carbonate dissolution-related internal sediments, where the clasts are angular and show a downward collapse from their primitive stratigraphic positions. These suggest that the reservoir dolostones deposited in a sabkha environment and the breccias mainly resulted from evaporite dissolution. Multistage dolomitization and silicification intensively superimposed on the reservoir horizons and might take advantage of pre-existing interclast, intergranular, and dissolution pores. The related intercrystalline pores provide the predominant spaces for the Zn and Pb sulfide precipitation. Pressure dissolution- and structural deformation-related factures provide minor reservoir spaces. Prospecting MVT Zn-Pb ores in the Proterozoic/Cambrian boundary dolostone units in the Upper Yangtze block should give priority to the sabkha environment of dolostone horizons with post-depositional brecciation and dolomitization/silicification at the top of a shallowing-upward sedimentary cycle in the tidal flat facies and in the platform margin mound-shoal facies.

Quantitative identification of nitrate and sulfate sources of a multiple land-use area impacted by mine drainage

The rapid increase in urbanization and intensive coal mining activities have accelerated the deterioration of surface water quality. Environmental problems caused by the accumulation of nitrate and sulfate from natural, urban, and agricultural sources have attracted extensive attention. Information on nitrate and sulfate sources and their transformations is crucial for understanding the nitrogen and sulfur cycles in surface water. In this study, we monitored nitrate and sulfate in three representative rivers in mining cities in northern China. The main pollution sources and biogeochemical processes were identified by using stable isotopes (δD, δ18OH2O, δ15N, δ18ONO3, δ34S and δ18OSO4) and hydrochemistry. The contribution of natural and anthropogenic sources was quantitatively estimated based on a Bayesian mixed model. The results indicated a large variation in sulfate and nitrate sources between the different rivers. Nitrate in the Tuohe River mainly derived from manure/sewage (57.9%) and soil N (26.9%), while sulfate mainly derived from manure/sewage (41.7%) and evaporite dissolution (26.8%). For the Suihe River, nitrate was primarily sourced from chemical fertilizer (37.9%) and soil nitrogen (34.8%), while sulfate was mainly sourced from manure/sewage (33.1%) and chemical fertilizer (21.4%). For the Huihe River, nitrate mainly derived from mine drainage (56.6%) and manure/sewage (30.6%), while sulfate predominantly originated from mine drainage (58.3%) and evaporite dissolution (12.9%). Microbial nitrification was the major pathway for the migration and transformation of nitrate in the surface water. However, denitrification and bacterial sulfate reduction (BSR) did not play a significant role as aerobic conditions prevailed. In this study, we elucidated the sources and transformation mechanisms of nitrate and sulfate. Additionally, we provided a reference for formulating a comprehensive strategy for effective management and remediation of surface water contaminated with nitrate and sulfate in mining cities.

Hydrochemical Characteristics and Genetic Mechanism of Geothermal Springs in the Aba Area, Western Sichuan Province, China

Geothermal resources have been a source of significant clean energy in the world. The Sichuan Province is famous for its abundant geothermal resources in China, especially in western Sichuan. The Aba area is a significant minority region in northwestern Sichuan with abundant geothermal resources. In this study, hydrochemical and D-O analyses were conducted on the eight collected geothermal springs to investigate the genetic mechanism of the geothermal resource in the Aba area. The exposed temperatures and pH values of the geothermal springs ranged from 23 °C to 48 °C and from 6.6 to 9.5, respectively. Based on the hydrochemical characteristics, the eight geothermal springs were classified into two types: class A and class B. The class A geothermal springs belonged to the hydrochemical type of Ca-Mg-HCO3-SO4 and Ca-Mg-HCO3 and were affected by the weathering and dissolution of carbonate and silicate. The class B hydrochemical type of geothermal spring was Na-HCO3, which was determined by the weathering and dissolution of evaporite and silicate. A Na-K-Mg triangle diagram revealed that the geothermal springs belonged to immature water. A chalcedony geothermometer indicated that the temperature of the class A shallow geothermal reservoir in the Aba area was 59.70–73.00 °C and 70.65–120.91 °C for class B. Silicon enthalpy approaches showed that the initial reservoir temperature for class A was 181.36–203.07 °C (mixed by 85.76–89.44% cold water) and 271.74–295.58 °C (mixed by 87.39–87.54% cold water) for class B. The recharge elevation of the geothermal spring was 3415–3495 m as calculated by the D-O isotopes. We have proposed these genetic models of the two typical geothermal springs. The achievements provide a vital reference for the further development of geothermal water and the sustainable utilization of geothermal resources in the Aba area.

Chemical weathering characteristics and controls in the Yarlung Tsangpo River Basin: Evidence from hydrochemical composition

The uplift of the Tibetan Plateau (TP) is thought to be closely related to the global climate. For the Yarlung Tsangpo River (YTR), the largest river on the TP, the hot spring input is an important source of solutes. Without considering hot spring input will lead to an overestimation of chemical weathering and CO2 consumption rate. Two sample series were collected in the basin before and after the monsoon season to evaluate the chemical weathering rates and controlling factors based on the hydrochemical composition. The results of improved forward model indicate that the highest contribution to the total cations comes from rock weathering (59%–99%, average value 93%), of which carbonate dissolution contributes the most (25%–79%, average value 61%), followed by evaporite dissolution (5%–42%, average value 19%) and silicate weathering (1%–29%, average value 13%). The hydrochemistry of tributaries in the middle reaches (Dogxung Tsangpo and Lhasa River) is affected by hot springs significantly, and the maximum contribution reaches 40%. The chemical weathering rates for the sub-basins show a sequence of Lhasa River > Dogxung Tsangpo > Nyang Qu, primarily controlled by lithology and runoff. For the mainstream above the YTR canyon and tributaries in the upper and middle reaches, chemical weathering is controlled by a transport limited regime, and the rest of the basin is governed by a kinetically limited regime. Overall, after deducting the hot spring input from the solutes, the silicate and carbonate weathering rates in the YTR Basin are 1.8 t/km2/yr and 6.3 t/km2/yr, respectively. The atmospheric CO2 consumption by silicate and carbonate weathering in the YTR Basin accounts for ∼0.17% and ∼0.28% of global, respectively, on ∼0.21% of the global land surface area. The carbon sink caused by chemical weathering and its effect on global carbon cycle in the YTR Basin are insignificant.

Tectonostratigraphic and paleoenvironmental settings of host-replacing phreatic calcrete hardpans developed at basin margins in the Upper Devonian Kinnesswood Formation of southwest Scotland

Abstract In the Firth of Clyde area of southwest Scotland, the Famennian Kinnesswood Formation includes an interval of massive, host-replacing phreatic calcrete hardpan (HRPCH), the likes of which have been documented only at few locations and few intervals in geological history. The HRPCH is found only at basin-margin shoulders, where the Kinnesswood Formation succession is thin and incomplete. The isles of Bute and Great Cumbrae provide well exposed sections in which adjacent shoulder and trough successions can be correlated and compared to clarify the tectonostratigraphic and paleoenvironmental settings of the HRPCHs. In the Cumbraes Trough, above a thin interval of peritidal limestone, the middle part of the Kinnesswood Formation (lower part of the Foul Port Member) is pervasively disturbed by large syndepositional dewatering structures interpreted to be products of the intermittent deposition and dissolution of evaporites. These structures occur at approximately the same stratigraphic interval as the HRPCHs on the isles of Bute and possibly Arran. The HRPCH in Bute is interpreted to have developed on a syndepositional shoulder adjacent to a growth fault (the Kerrycroy Fault) delimiting a trough that accommodated intermittent seawater incursions in a restricted, evaporitic setting. This is consistent with the current model for HRPCH formation, which involves the mixing of fresh groundwater issued from source areas with the high pH groundwater that surrounds evaporitic basins. A significant increase in silica solubility paired with a decrease in calcite solubility occurs in the mixing zone, thus promoting the thorough replacement of silicates with calcrete.

Statistical analyses of hydrochemistry in multi-aquifers of the Pansan coalmine, Huainan coalfield, China: implications for water-rock interaction and hydraulic connection

Understanding the groundwater hydrogeochemical processes and aquifer hydraulic connections are essential for effective prevention of water inrush in concealed coal mines. In this study, 40 groundwater samples were collected from the loose layer aquifer (LA), coal measure aquifer (CA), and limestone aquifer (LA) in the Pansan coal mine, Huanan coalfield, China, and the major ion concentrations were analyzed by bivariate diagrams (Na+ + K+ - Cl− versus Ca2+ + Mg2+ - SO42− - HCO3− and CAI-I versus CAI-II), multivariate statistical methods, and receptor model in order to identify the water-rock interactions and aquifer hydraulic connections. Piper diagram showed that groundwater in LA and TA was dominated by the Na–Cl type, while groundwater in CA was mainly of the Na–HCO3 type. Based on the results of bivariate diagrams and PCA/FA, weathering of silicate minerals and cation exchange (source 1), sulfate dissolution (source 2) and chloride dissolution (source 3) were the main processes controlling the groundwater chemistry. Unmix model revealed that the mean contribution of source 1 to CA samples was 74%, while LA and TA samples have higher contributions from evaporite dissolution (source 2 and source 3) relative to CA samples. Moreover, both clustering analysis methods (Q-type hierarchical and K-means cluster) confirmed the existence of a hydraulic connection between LA and TA in the northeastern part of the study area. It is concluded that the application of multivariate statistical analysis to interpret groundwater chemistry can provide useful guidance to prevent water inrush in coal mines.

Hydro-chemical assessment of fluoride and nitrate in groundwater from east and west coasts of Bangladesh and India

Groundwater from the coastal alluvial plain is the primary water source in coastal areas. Its contaminants, such as nitrate and fluoride, are significant concerns for freshwater supply and human health issues. Although spatiotemporal variability of nitrate and fluoride levels has been analyzed individually in the Indo-Bangladesh coastal region, their drivers and hydro-chemical analysis have scarcely been studied. Thus, to assess the groundwater quality, hydro-chemistry, and drivers in coastal alluvial aquifers, 123 groundwater samples were collected from the east (Bangladesh) and west coasts (India) for assessment of nitrate and fluoride levels and major physiochemical parameters. Multivariate statistical and hydro-chemical analysis and public health risk appraisal were carried out for this purpose. The results showed that 25% (East coast) and 22.39% (West coast) of groundwater samples surpassed the allowable limit of fluoride with a maximum concentration of up to 16.11 mg/L and the tolerable nitrate limit slightly exceeded 10 mg/L. Furthermore, we note that industrial waste, synthetic pesticides, and agricultural fertilizer triggered the leaching of nitrate into groundwater, while the release of fluoride into groundwater was possibly due to evaporite dissolution, carbonate mineral weathering, and ion exchange processes on both coasts. About 28.36% (26.79%) of groundwater samples possessed poor quality on the east (west) coasts. Considering the uncertainties of the variables, the mean hazard quotient ingestion values of fluoride faced by children (adults) were 10.5 (1.39) and 5.56 (6.9 × 10−1), respectively, on the east (west) coasts, demonstrating a high non-carcinogenic risk to people, particularly, children, who cannot be neglected. Children had two times higher health risks than the adult inhabitants in both regions studied. Probabilistic models can reveal health risks more extensively than deterministic models. This study came up with strategies for improving sustainable groundwater quality and managing health risks in coastal regions.

Characterization of groundwater in the arid Zenaga plain: Hydrochemical and environmental isotopes approaches

The Zenaga inlier, located in an arid area in southeastern Morocco, is mostly characterized by igneous and metamorphic fractured rocks. The surface water is quasi-absent and local populations (95% rural) are entirely dependent on groundwater resources for drinking and irrigation purposes. To evaluate the main factors controlling the origin and salinization of groundwater resources, we have investigated the chemical and stable isotope compositions of 23 groundwater samples. In addition, water quality assessment parameters including sodium absorption ratio (SAR) and water quality index (WQI) were also calculated. The results show that the majority of wells and boreholes are characterized calcium bicarbonate water type (78% of samples), with the following ionic sequence Ca2+>Na+ >Mg2+ >K+, and HCO3−> Cl−>SO42−>NO3− for cations and anions, respectively. A significant enrichment on major ions is steadily rising with depth as the water type changes toward calcium chloride. The interpretation of hydrochemical data suggests that the silicate weathering, cation exchange and evaporites dissolution are responsible for the groundwater chemistry. The majority of water samples are good to permissible for irrigation and poor to good for drinking purposes. The mineral salts found at greater depths degrade groundwater quality. In some areas, nitrate contents imply anthropogenic contamination derived especially from traditional septic tanks. Stable isotopes δ18O and δ2H reveal a distinction between the shallow aquifer and deep circulations. The uncommon depleted isotope signature found in deep circulations was associated with cold altitudes recharge, whereas the heaviest groundwater observed in shallow aquifer was interpreted as the contribution of surface water from Taghdout Dam. The Anti-Atlas Mountains and Siroua Massif's high altitude served as a source of recharge. The mixing at considerable depths and along the groundwater path appears to decrease the isotopic variability in the shallow and deep groundwater.

Chemical and isotopic evidences on evaporite dissolution as the origin of high sulfate water in a karst geothermal reservoir

Using multiple isotopes including 87Sr/86Sr in water, δ34SSO4, δ18OSO4, δ18OH2O and δ2HH2O, δ13CDIC and 14CDIC in water, we have investigated the origin and evolution of sulfate concentration (1472 mg/L) in the Tangquan Karst geothermal system in Nanjing, China. The sulfate has been found to be mainly derived from dissolution of gypsum and other evaporite minerals occurring in the carbonate reservoir. The dissolution of evaporite minerals is relatively easier than carbonate at elevated temperatures. We confirmed this differentiated dissolution process by reverse hydrogeochemical simulation using the PHREEQC code. The origin of sulfate is supported by 87Sr/86Sr isotope ratio (0.7088–0.709) with a typical marine signature. We further constrained the origin of sulfate with δ34S in aqueous SO4 (27.6‰–34.2‰) and δ18O in aqueous SO4 (14.3‰–18.4‰). Such sulfate-rich geothermal water usually occurs in open karst geothermal systems, favorable for Spa therapy in many places of the world.

Seismic characterization and depositional significance of the Nahr Menashe deposits: Implications for the terminal phases of the Messinian salinity crisis in the north‐east Levant Basin, offshore Lebanon

AbstractOver the last decade, there has been a resurgence of interest in the climatic and tectonic mechanisms that drove the Messinian salinity crisis (MSC) and the associated deposition of thick evaporites. The MSC represents an unprecedented palaeoceanographic change that led to a very short (ca. 640 kyr) ecological and environmental crisis. However, across the Levantine offshore basin, the sedimentological nature of the top evaporitic units and the mechanisms that controlled the transition from a hypersaline evaporitic unit to brackish deposits (final MSC stage 3) are still disputed. Here, we re‐evaluate the deposits associated with the terminal phase of the MSC, named in offshore Lebanon as the Nahr Menashe Unit (NMU). We describe the NMU seismic facies, characterize and map its internal seismic stratigraphy and provide a new interpretation of its depositional environment, which persisted during the late Messinian and then evolved through a regional reflooding event. The base of the NMU overlies semicircular depressions, randomly distributed linear marks and surface collapse features, which are indicative of a period of intense evaporite dissolution. The NMU seismic facies observed from the slope to the deep part of the basin support the interpretation of a layered salt‐evaporite‐sand depositional system subject to complex reworking, dissolution, deposition and final erosion. A drainage network of valleys and complex tributary channels incising into the top NMU shows marked erosional characteristics, which indicate a dominant southwards sediment transfer following deposition of the NMU. The drainage network was subsequently infilled by layered sediments interpreted here to represent the post‐MSC marine sediments. Our analysis adds important details regarding previous interpretations of the NMU as fluvial in origin. Specifically, the presence of subcircular, linear dissolution features coupled with mound‐like features indicates that the NMU is composed dominantly of evaporites that were subject to dissolution prior to erosion associated with the drainage network. The NMU is interpreted to represent the deposition/redeposition of a mixed evaporite‐siliciclastic succession in a shallow marine or lacustrine environment during the tilting of the offshore Lebanese basin.

Delineation of highland saline groundwater sources in Ba'kelalan region of NE Borneo to improve the salt-making production using geochemical and geophysical approaches

The extraction of mountain salt from the saline waters is the basic livelihood of the Ba'kelalan communities of Sarawak. The current integrated approach is the first attempt to study the sources and geochemical processes of the saline groundwaters in this mountain region. Hence, in this study, saline groundwater samples from five existing wells in different seasons were analysed for hydrochemical parameters and multi-isotope composition (δ18O, δD, δ34S, δ11B and δ37Cl). The significant increase in TDS, EC and salinity was due to seasonal variation and fluctuation in water level based on hourly, daily and monthly observations. The geochemical ratios and the statistical techniques revealed that the salinity was due to the dissolution of marine evaporites as a dominant process, coupled with other factors such as water-rock interaction, ion exchange and sulphate reduction. From the isotopic signatures, it was inferred that the origin of saline groundwater was from the intense dissolution of marine evaporites such as halite dissolution and oxidation of -sulphide (pyrite). 2D electrical resistivity and seismic refraction methods were used to identify the lithological variations, depth of potential sources of saline groundwater, and the subsurface structures. It was inferred the probability of a conductive zone at a depth of 1–14 m, from which the saline groundwater plume migrates towards the perched aquifer. The presence of subsurface faults facilitated the movement of hypersaline groundwater from the saturated zone to the surface. The outcome of the study will support the dependent community to enhance their commercial salt production.

Early diagenetic calcite replacement of evaporites in playa lakes of the Quiricó Formation (Lower Cretaceous, SE Brazil)

Evaporites are abundant in modern playa lakes, where efflorescence, inorganic and/or bioinduced precipitation coexist with siliciclastic deposition. Overall, the sensibility of salts to slight physicochemical changes results in partial to complete dissolution of evaporites in surface and shallow subsurface. However, in some cases, salt minerals are pseudomorphically replaced, providing a snapshot to depositional settings and diagenetic processes of evaporite-bearing successions. This is recorded in the Quiricó Formation (Lower Cretaceous), Sanfranciscana Basin, southeastern Brazil. This studied succession portrays a playa lake system subdivided in saline flat and saline lake deposits, whose diagenesis was marked by ubiquitous cementation and replacement reactions. Petrographic and geochemical techniques were undertaken to characterise primary and secondary textures, mineralogy and distribution of mudstone- and sandstone-hosted pseudomorphs. The pseudomorphs frequently underlie the stratigraphic contact of playa lake-aeolian beds. Pseudomorphs occur as coalescent nodules and as chaotically-distributed chevron crystals, composed of inequicrystalline calcite mosaics. Nodular pseudomorphs have cubic/sub-cubic “ghost” inclusions and displacive contacts with the matrix, whereas the contacts of chevron pseudomorphs and the matrix are undisturbed. Both types exhibit morphological replication of precursor minerals and non-luminescent euhedral relicts. Stable isotopic signatures are covariant and range between −1.6–0.6 ‰ δ13C and 1.4–2.5 ‰ δ18O for nodular pseudomorphs, and −2.2 to −1.5 ‰ δ13C and 0.3–1.3 ‰ δ18O for chevron pseudomorphs. Nodular crystals reflect subaerial and intrasedimentary crystallisation of Ca-sulphates in saline flats, whereas chevron-shaped pseudomorphs indicate bottom-growth halite in shallow lakes. Textural evidences from pseudomorphs and host lithologies constrain the diagenetic overprint to surface and shallow burial settings (syndepositional/eodiagenetic stages). Despite multiple generations of calcite, the constant isotopic signatures of pseudomorphs reflect water chemistry fractionation in a closed-lake basin. Widespread calcitisation of playa lake sediments was caused by calcium-rich groundwaters, influenced by limestones from the Precambrian basement. The playa lake deposits record the onset of aridification processes that culminated in the Thermal Cretaceous Maximum.