Brine Body Research Articles

The two salinity peaks mode of marine salt supply to coastal underground brine during a single tidal cycle

Seawater salt is constantly supplied from the marine environment to coastal underground brine deposits, meaning that brine has the potential for continuous extraction. There is currently a lack of information about the processes that drive the fluxes of seawater salt to underground brine deposits in tidal-driven brine mining areas. We chose the Yangkou salt field on the southern coast of Laizhou Bay, a brine mining area, as our study site. We monitored the spatial and temporal distribution of the underground brine reserve and the changes in water level and salinity in the mining area and adjacent tidal flats using electrical resistivity tomography and hydrogeological measurements. We monitored cross-sections along two survey lines and observed that the underground brine reserve receives a stable supply of seawater salt, and calculated that the rate of influx into the brine body in the mining area near the boundary of the precipitation funnel was 0.226−0.232 t/h. We calculated that a total salt flux of approximately 5.50 t enters the underground brine body every day through a 150 m long shoreline and a 1322.3 m2 window, which is sufficient to sustain the daily extraction of one brine well. During tidal cycles, there are two peaks in the salinity of the water supplied to the underground brine reserve, which means that the brine supply is from at least two high-salinity salt sources in different tidal stages. The first salinity peak occurs during the initial stage of the rising tide after seawater inundates the tidal flat. At this time, seawater, which is a solution and carries a large amount of evaporated salt, is transported into the brine layer through highly permeable areas or biological channels and replenishes the brine in the mining area. The second salinity peak occurs during the early stage of the falling tide. Influenced by hysteresis-driven tidal pumping, high-salinity brine from the lower intertidal zone is rapidly transported into the mining area, thereby increasing the salinity of the underground brine.

Intergranular aragonite cement as evidence for widespread cryogenic brine formation during Quaternary glaciation in the McMurdo Sound region, Antarctica

Briny groundwater is present below the extremely cold and dry surface of the McMurdo Dry Valleys and below the seafloor of the adjacent McMurdo Sound in Antarctica. The lack of reliable groundwater samples in the region, however, has long limited understanding of its origin, nature, and spatial distribution. In this regard, intergranular carbonate cements, widespread in subsurface Cenozoic strata and recently recognized as brine precipitates, provide an indirect means of solving these issues. This study examines the petrography and isotope geochemistry of intergranular aragonite cement phases that occur in subsurface Pliocene-Quaternary sedimentary sections that formed in the lower Taylor Valley (cores DVDP-10, -11) and in offshore McMurdo Sound (core AND-1B). Aragonite cement in the coastal Taylor Valley sections is characterized by very low δ18O values (−26.9 to −19.4‰ VPDB) compared to values in the offshore section (−12.5 to −2.7‰ VPDB). These differences are interpreted to reflect two settings for cryogenic brine formation, which produced isotopically distinct brines during Quaternary glaciation. In the coastal region, seawater-meltwater mixtures were isolated and cryogenically concentrated in an ice-dammed lake setting that formed in response to the expansion of the East and West Antarctic Ice Sheets into the lower Taylor Valley. In McMurdo Sound, cryogenic concentration of seawater occurred in a semi-isolated flexural trough that was deepened by lithospheric depression of volcanic edifices and the expanded West Antarctic Ice Sheet. Aragonite cement phases serve as excellent proxies for tracing the extents of subsurface brine bodies along the continental margin of Antarctica. Given the propensity for cryogenic brine formation in glaciomarine settings, the likelihood of brine cements in rock records from other analogous high-latitude, cold settings must not be overlooked.

Combined electromagnetic geophysical mapping at Arctic perennial saline springs: Possible applications for the detection of water in the shallow subsurface of Mars

Perennial springs at the Gypsum Hill site on Axel Heiberg Island in the Canadian Arctic (79°24′N, 90°44′W) represent a high-fidelity analogue to hydrothermal systems that might exist on Mars. The springs were surveyed using an electromagnetic induction sounder (EMIS) and ground penetrating radar (GPR). Both instruments probed the subsurface to a depth of approximately 3m. Lateral EMIS soundings were performed every metre along a 400m long reconnaissance line roughly oriented SW-NE and extending through 23 active springs and 1 dry outlet to measure electrical conductivity. Two distinct zones were identified within the survey area on the basis of these data: in the southwest portion, sharp conductivity peaks correspond to isolated springs with well-defined outlets, flowing over dry rocky soil; in the northeast portion, the springs are fed by a pervasive network of saline fluids, resulting in high background readings and muddy surface conditions. These observations are consistent with vertical EMIS sounding data which showed that the brine body feeding the saline springs can be found closer to the ground surface towards the northeast portion of the survey site. In areas of high electrical conductivity, the GPR data exhibits strong scattering. The noisy areas are sharply defined and interpreted to correspond to narrow vertical conduits feeding individual spring outlets. The EMIS is a rugged instrument that could be included as payload in future rover-based Mars exploration missions aiming at probing the shallow subsurface for the presence of brine pockets.

Sulfate–Borate Association (Glauberite–Probertite) In the Emet Basin: Implications For Evaporite Sedimentology (Middle Miocene, Turkey)

Abstract Probertite and glauberite are the main rock-forming minerals in the lacustrine Doganlar succession of the Emet basin. The present paper seeks to characterize and interpret the facies and depositional settings of this mineral association. Probertite is made up largely of microfibers arranged in microbundles, and displays a variety of lithofacies. Many lithofacies show deformation and flowage structures which can be assigned to multistage growth of probertite under synsedimentary conditions. Glauberite displays laminated lithofacies formed by fine-grained clear crystals, and thin- to thick-bedded lithofacies composed of coarser crystals and variable proportions of siliciclastic matrix. Depositional pairs of probertite and glauberite occur at millimeter (laminites), centimeter (alternations), and meter (cycles) scales. Probertite and glauberite are primary products grown subaqueously in a relatively shallow saline lake—either on the bottom (probertite and glauberite) or as cumulate crystals (glauberite)—and interstitially below and close to the bottom. The laminites are made up of microcycles composed of several types of laminae. The microcycles are interpreted as predominantly pluriannual precipitates. In the proposed lake model, the brine body is not deep, as indicated by frequent episodes of subaerial exposure recorded in the succession. This study provides new insight into the genesis of glauberite and probertite, the interpretation of nodular lithofacies, the type of “microfiber evaporites,” the evaporite units made up of sulfate–borate alternations, and the petrographic description of glauberite laminites and their paleoenvironmental interpretation.

Palaeogeographical zonation of gypsum facies: Middle Miocene Badenian of Central Paratethys (Carpathian Foredeep in Europe)

Studies on Middle Miocene Badenian gypsum in various parts of Central Paratethys, the oldest widespread primary marine gypsum, in western Ukraine, southern Poland and Moravia (Czech Republic) indicate that there are three principal gypsum facies: crystalline gypsum, stromatolitic gypsum and clastic gypsum. The latter typically occurs between crystalline and stromatolitic gypsum and between stromatolitic gypsum and the land. In addition, it is common in channels within gypsum microbialites, and is the main facies during the deposition of the upper part of Badenian gypsum when important bathymetric differences existed within the marginal part of the Carpathian Foredeep Basin, the largest foredeep basin in Europe. Within crystalline gypsum facies, it is observed the overall size of the crystals increases and that the layering declines towards the permanent, stabilized brine body, and thus the giant gypsum intergrowths–non-layered coarse-crystalline selenite – is the end-member of gypsum facies continuum. Typically it passes into layered selenites although owing to fluctuations of pycnocline level, some transitional gypsum subfacies may be missing both in the vertical section as well as in particular outcrops. The following important controls on the development of gypsum facies have been identified: pycnocline level fluctuations, brine level fluctuations including brine sheets and floods, rare marine transgressions, pedogenesis leading to “alabastrine” gypsum development, and rate of inflow of continental water.

Detection of Saline Groundwater Bodies between the Dead Sea and the Mediterranean Sea, Israel, Using the TDEM Method and Hydrochemical Parameters

A Time Domain ElectroMagnetic (TDEM) survey coupled with hydrogeological information was carried out along the Be’er Sheva valley between the Mediterranean Sea and the Dead Sea base levels, aiming to obtain the subsurface distribution of the different fresh and saline water bodies. Hydrochemical considerations and previous TDEM results hinted that the previously accepted model of an upper fresh water body underlain by solely Dead Sea (R-type) brines in the east and C-type brines in the west does not match the actual observations. Thus, the suggested working hypothesis of additional intruding seawater from the Mediterranean Sea to the Dead Sea base level was checked by the TDEM method. The results, indeed, exhibit an upper high resistivity fresh water body, an underlying low resistivity brine body and a moderate resistivity body in between. The origin of this body is not uniquely determined based on the geophysical measurements alone. Analysis of borehole data testifies that hydrochemical parameters of the body cannot be solely interpreted as a mixture of the above two end members, but rather calls for an additional contribution of intruding seawater. The suggested configuration consists of an upper fresh water body flowing to both base levels in the west and the east. Underneath there is a saline body resulting from seawater intrusion reaching from the Mediterranean to the Dead Sea base level. At the bottom there is a third body of the westward density driven Dead Sea brine. The entire configuration is supported by results of subsurface flow modeling.

The hydrogeochemistry of subsurface brines in and west of the Jordan–Dead Sea Transform fault

AbstractThis study is based on 113 analyses of brines with Cl > 0.57 mol l−1 (modern seawater), which were collected and analysed mostly during several decades of exploration for gas and oil in Israel. Based on critical evaluation of correlations of elements and ionic ratios and on spider patterns, six different brine events or source brines were identified in the Phanerozoic: the Triassic, Lower Cretaceous and the Mio/Pliocene brine families which were identified in boreholes Sdom‐1, Sdom Deep‐1 and Ha'on, and the Holocene Dead Sea brines. The Triassic brines are nowadays also encountered in under‐ and overlying rock units such as the Paleozoic Negev‐Yam Suf and the Jurassic Arad Groups, respectively. The southern Jordan–Dead Sea Transform (also known as the Rift) hosts the Mio‐Pliocene Sdom Deep and Sdom brine families. Brine bodies not sufficiently isolated by impervious sedimentary layers were flushed out during the Pliocene when the southern Valley drained north‐ and westwards through the Yizre'el Valley to the Mediterranean Sea. In the northern Rift Miocene to Pliocene seawater evaporated and infiltrated into the Rift sediments and into adjacent rocks. Further diluted by freshwater, it emerges as the Ha'on brine. Together with its derivatives, they form the Ha'on family. The derivatives of the Holocene Dead Sea brine family occur along the shoreline of the recent Dead Sea. Apart of all these evaporation brines, brines deriving from dissolution of evaporites locally occur in the area. The time‐bound chemical composition of paleoseawater is considered when discussing the ionic ratios of brines generated during different geological periods. Spider patterns of each brine family are compared and, where necessary, the relationship of brines to distinct families of brines is supported by inverse modelling.

New insights into the origin and evolution of Lake Vida, McMurdo Dry Valleys, Antarctica — A noble gas study in ice and brines

Unlike other lakes in the McMurdo Dry Valleys, Antarctica, Lake Vida has a thick (~ 19 m) ice cover sealing a liquid brine body of unusually high salinity (~ 245 g/L) from the atmosphere. To constrain the conditions under which the atypical Lake Vida ice cover formed and evolved, 19 ice samples were collected down to a depth of ~ 14 m, together with three brine samples trapped in the ice at ~ 16 m for analysis of helium, neon, argon, krypton, and xenon concentrations. The broad pattern of noble gas concentrations for Lake Vida samples is fundamentally different from that of air saturated water (ASW) at 0 °C and an elevation of 340 m for salinities of 0 (ice) and 245 g/L (brine). Overall, ice samples are enriched in He and depleted in Ne with saturation relative to ASW averages of 1.38 and 0.82, respectively, and strongly depleted in Ar, Kr, and Xe with relative saturations of 0.10, 0.06, and 0.05, respectively. By contrast, brine samples are generally depleted in He and Ne (relative saturation averages of 0.33 and 0.27, respectively) but enriched in Ar, Kr, and Xe, with relative saturation averages of 1.45, 3.15, and 8.86, respectively. A three-phase freezing partitioning model generating brine, ice and bubble concentrations for all stable noble gases was tested and compared with our data. Measured brine values are best reproduced for a salinity value of 175 g/L, a pressure of 1.1 atm, and a bubble volume of 20 cm 3 kg − 1. Sensitivity tests for ice + bubble samples show an ideal fit for bubble volumes of ~ 1–2 cm 3 kg − 1. Our results show that the conditions under which ice and brine formed and evolved at Lake Vida are significantly different from other ice-covered lakes in the area. Our brine data suggest that Lake Vida may be transitioning from a wet to a dry-based lake, while the ice + bubble data suggest at least partial re-equilibration of residual liquid with the atmosphere as ice forms at the top of Lake Vida ice cover.

Limiting hydrochemical factors for sustainability of water resources: The Cisjordanian experience

In Cisjordan, surface- and groundwater flow are either towards the Jordan Valley–Dead Sea–Arava Valley (the Rift) or the Mediterranean Sea. Due to upstream exploitation by riparians to the Jordan River, the historical annual flow, which fluctuated between 250 and 1100 Mm 3, has declined to a mere 100–200 Mm 3. The remaining flow south of Lake Kinneret is highly polluted and heavily loaded with salts. Lake Kinneret (Sea of Galilee) is one of the major water resources in the area. Annually, between 200 and 700 Mm 3 reach the Lake as surface and groundwater flow. The relatively high salinity of the Lake is caused by thermomineral water discharging from springs and seepages located onshore and on the bottom of the Lake. The main factors causing deterioration of the groundwater quality in the Rift are of geogenic character. These are different types of brines, whose outflow and penetration into freshwater aquifers was triggered by overpumpage. Contemporary encroachment of seawater caused by intensive water exploitation in the Coastal Plain is manageable and reversible. However, due to lack of hydrogeological evidence, no such statement can be made about the circulation of seawater beneath the Coastal Plain and into the deep-seated Yarkon–Taninim aquifer or the upflow of brines in the Rift. The flow regimes of the different brine bodies could not be elucidated. Whether each such brine-body flows by its particular hydrological regime or whether the movement of the different bodies is intradependent or interdependent with the regional movement of fresh groundwater, remain open questions. Therefore, sustainable development of groundwater resources is clearly dependent on the elucidation of the relationship between changes in the pressure of the brine with depth and its relationship to the overlying freshwater. The average total annual recharge of all water sources in Cisjordan is 1820 Mm 3, which means that the total production of water must be managed within the limits of this annual volume. During drought years, total groundwater extraction exceeds the safe yield, causing drastic lowering of water levels and upflow of saline waters from greater depths. Because of the structural complexity of aquifers and hydrochemical variability of the numerous groundwater bodies, new hydrochemical methods have been developed for the identification of groundwater bodies and for the elucidation of their origins. These methods combine macrochemical, microchemical, and isotopic evidences. By combining distribution patterns of rare earths, yttrium and stable isotopes, a complete picture of catchment lithology and the altitude and latitude of precipitation could be obtained. The area west of the Jordan River is characterized by the occurrence of transboundary surface- and groundwater basins in which fresh and saline water and brines flow across political borders between Israel and the Palestinian Authority. It is very difficult to assess separately the annual safe yield of water resources for each of the two national entities. Neither country may dispose independently of its waters and is usually at the mercy of the other riparian. There is as yet no general multilateral international treaty in force allocating the water resources of international watercourses. At present there are two rules for the management of the waters of an international drainage basin—the rule of Equitable Distribution, and the obligation Not to Cause Significant Harm. The rules of equitable distribution have tended to focus on the issue of quantities of water rather than on quality of water, which is really relevant to the issue of equitable distribution. Future negotiations on the uses of the basin will need to deal with issues of characteristic salinities and geochemical features and on their impact on equitable sharing of water resources.

Hydrological and geochemical processes controlling variations in Na +–Mg 2+–Cl −–SO 42− groundwater brines, south-eastern Australia

Evaporative discharge of regional groundwater from more than 50 playa lakes at the 400 km 2 Raak Plain groundwater discharge complex forms a very large reservoir of hypersaline Na +–Mg 2+–Cl −–SO 4 2− type subsurface brine, but very little salt precipitates. The main processes controlling the formation and evolution of brine compositions are: (a) evapo-concentration of the regional groundwater, (b) mixing between the high – and low – TDS end-members and (c) subsurface gypsum precipitation. Uniformity in these processes across the entire groundwater discharge complex, coupled with the chemical similarity between the regional groundwater and local recharge sources, has led to remarkably similar brine chemistries and evaporite compositions across Raak Plain. The similarity between the source waters and the ultimate brine compositions indicates that solutes are generally conserved within the system. The greatest variation in groundwater chemistry at Raak Plain was found to occur within the playa lakes, particularly within the top 1–2 m of the subsurface brine body, rather than amongst the different lakes. This small-scale variability is a result of 1) advective and diffusive mixing between the hypersaline shallow (< 3 m below ground surface) brines and the less saline underlying groundwaters, 2) the transient precipitation and re-dissolution of surface salt efflorescences, and 3) differential diffusion rates of the various solutes over long time scales (> 20 kyr).

Modeling the magnitude and timing of evaporative drawdown during the Messinian salinity crisis

The Mediterranean and Red Sea salt layers ofMessinian age reach up to 3 km in thickness in the subsurface of themodern abyssal plains and are rare to absent on the contemporary margin rims. Deposition of the full evaporite suite of carbonates, sulfates, halite, potash, dolomitic marl and debris from pervasive margin erosion took place during a regional Late Miocene salinity crisis once the restriction of two-way water flow through the portal from the Atlantic reached a threshold that triggered a rise in salinity everywhere sufficient for precipitation to commence on a regional scale. For the first 0.35my of the crisis the surface of the Mediterranean remained more or less at the level of the global ocean except possibly during brief episodes when brine reflux ceased as the consequence of sea-level fall in the exterior Atlantic. Evaporative drawdown on a large scale is an intra-salinity-crisis phenomenon and coincides with the precipitation of the bulk of the halite that makes up the giant flowing salt layer observed in reflection profiles. We present an integrated quantitative model that reproduces the closure of the Atlantic spillway, evaporative drawdown and eventual opening of the Gibraltar Strait for the Pliocene refilling. The model incorporates time-varying global eustacy, solar insolation, mixing of brine across sills between the Mediterranean and Red Sea depressions and water flow through subsurface aquifers. The model accounts for the precipitation of more than one million km3 of halite alone in just a few precession cycles. The closure results from the weight of the growing brine body and salt deposit that depresses the basin center and elevates its rims. Ground water leakage under high pressure from the Atlantic into the nearly empty Mediterranean corrodes and opens fissures in the Gibraltar barrier leading to eventual break through at this particular location followed by a run-away flood.

Plio-Pleistocene lacustrine evaporites of the Baza Basin (Betic Chain, SE Spain)

The Baza Basin (the eastern part of the Guadix–Baza Basin, in SE Spain) underwent a significant evaporitic sedimentation in non-marine settings during the Plio-Pleistocene. The largest of these settings developed in the central part of the basin as a shallow, saline lake system, where abundant gypsum deposits occur (Benamaurel and Galera Gypsum units). This paper studies these deposits from the cartographic, stratigraphic, sedimentologic, petrographic and isotopic points of view. All the gypsum has been preserved as primary enabling a good characterization of the environmental conditions of the original precipitates. Three interconnected subenvironments or zones –inner, intermediate and marginal– are differentiated in this saline lake system. In the inner zone (shallow to relatively deeper central lake), a regular alternation of gypsum and carbonate laminae accumulated suggesting a seasonal regime. Many of the gypsum laminae display size-gradation (both reverse and symmetrical) indicating free precipitation in a stable brine body. In the intermediate zone (mosaic of shallow lakes), carbonate (dolomitic) beds formed in association with dark lutite levels, gypsum beds, and gypsum nodules and micronodules. Moreover, anoxic conditions developed in this zone, which resulted in the formation of native sulphur occurrences of economic value. In the marginal zone, the evaporitic deposits are developed only locally (the Galera Gypsum unit, in particular). The various gypsum lithofacies in these marginal deposits suggest the presence of a number of shallow to exposed settings (saline mudflat, saline marsh and gypsiferous pond). The isotopic composition ( δ 34S, δ 18O) of the gypsum samples is consistent with a Triassic origin of the sulphate as a result of chemical recycling. These data also suggest that a similar recycling mechanism operated in the saline lake system, where the gypsum sediments from the margins were coevally recycled towards the inner part. Both the evaporitic mineralogy and the gypsum and carbonate lithofacies suggest that semiarid conditions prevailed in this basin during the accumulation of the evaporite units.

A direct tracking method for a grounded conductor inside a pipeline from capacitance measurements

We present a new non-iterative method for tracking conductive water in a pipeline using a single excitation pattern from an interleaved ECT system. The problem arises, for example, in the oil industry where brine is often mixed with oil in a pipeline. If the size of the body of brine is very large compared with the size of electrodes attached to the pipeline, the corresponding electric potential in the region of brine is close to zero. This model leads to the inverse problem of identifying the dynamic change of the cross section of a grounded conducting region in a pipeline. Unfortunately, standard iterative reconstruction algorithms in ECT associated with the sensitivity matrix do not work in this case. Furthermore, due to the unavailability of Neumann data at the drive electrodes, the previously published layer potential methods for capturing the inhomogeneity are not applicable to this system. In this work, we derive a formula providing a concrete relation between the capacitance change in each receive electrode and the dynamical change in a grounded conducting region inside the pipeline. The proposed method successfully reconstructs feature information such as location and rough shape of the cross section of the water region. We demonstrate the performance of our method in numerical simulations and actual experiments.

CHEVRON-TYPE HALITE AND NODULAR ANHYDRITE IN THE TRIASSIC SUBSURFACE EVAPORITES OF THE IONIAN ZONE (WESTERN GREECE)

Samples of the Ionian zone (western Greece) subsurface evaporites, obtained from well cores in salt bodies and in depths ranging from 1000 to 3500m, are texturally studied. Layered halite rocks consisting of chevron-type halite crystals represent most of the specimens. Between the chevron -type halite crystals, which are fluid inclusions-rich, clear halite without inclusions has been diagenetically formed by dissolution and precipitation processes. Anhydrite always accompanies the halite rocks as crystals or nodules. No-occurrence of gypsum has been detected. Along halite grain boundaries dolomite crystals occur. Dolomite grew on halite crystal surfaces as an early diagenetic mineral. Some dolomite crystals are clearly derived by replacement of anhydrite crystals. Halite layers are rich in clay and carbonaceous material favoring reducing environment (presence of pyrite crystals). Chevron-type halite supports accumulation beneath a body of brine, possibly recording annual precipitation cycles. However, its close association with nodular anhydrite cannot exclude the possibility of halite development, in a shallow-water or emergent environment by displacement from capillary brines. Since the studied halite crystals show evidence of mineral replacements and displacement, we suggest an analogous mechanism including accumulation from a standing body of brine and subsequent textural modification in the groundwater zone. Although, Ionian subsurface evaporites have undergone the above-mentioned diagenetical processes, they still reU in their primary textural characteristics. Real brecciation has not been detected in subsurface, except of an in-situ pseudo-brecciation. This observation clearly shows that the outcropping evaporite solution-collapse breccias were formed in the realm of meteoric zone, after the Ionian zone orogenesis.

Neogene evaporites in desert volcanic environments: Atacama Desert, northern Chile

The Upper Miocene and Pliocene evaporite deposits of the Atacama Desert of northern Chile (Hilaricos and Soledad Formations) are among the few non‐marine evaporites in which aridity not only formed the deposits, but has also preserved them almost unaltered under near‐surface conditions. These deposits are largely composed of displacive Ca sulphate and halite together with minor amounts of glauberite, thenardite and polyhalite. However, at the base and top of these deposits, there are also beds of gypsum crystal pseudomorphs that originally formed as free‐growth forms within shallow brine bodies, rather than as displacive sediments. The halite is present as interstitial cement, displacive cubes and shallow‐water, bottom‐growth chevron crusts. Most of the calcium sulphate is presently anhydrite, pseudomorphous after gypsum, that was the primary depositional sulphate mineral. The secondary anhydrite formed under early diagenetic conditions after slight burial (some metres) resulting from the effect of strongly evolved pore brines. The anhydrite has been preserved without rehydration during late diagenetic and exhumation stages on account of the arid environment of the Atacama Desert. Both the Hilaricos and the Soledad Formations contain geochemical markers indicating that these Neogene evaporites had a largely non‐marine origin. Bromine content in the halite is very low (few p.p.m.), indicating neither a sedimentological relation with sea water nor the likelihood of direct recycling of prior marine halites. Moreover, the δ34S of sulphates (+4·5‰ to +9‰) also reflects a non‐marine origin, with a strong volcanic influence, although some recycling of Mesozoic marine sulphates cannot be ruled out. δ34S of dissolved sulphate from hot springs and streams in the area commonly displays positive values (+2‰ to +10‰). Leaching of oxidized sulphur and chlorine compounds from volcanoes and epithermal ore bodies, very common in the associated drainage areas, have been the main contribution to the accumulation of evaporites. The sedimentary and diagenetic evolution of the Hilaricos and Soledad evaporites (based on lithofacies analysis) provides information about the palaeohydrological conditions in the Central Depression of northern Chile during the Neogene. In addition, the diagenesis and exhumation history of these evaporites confirms the persistence of strongly arid conditions from Late Miocene until the present. A final phase of tectonism took place permitting the internal drainage to change and open to the sea, resulting in dissolution and removal of a significant portion of these deposits. Despite the extensive dissolution, the remaining evaporites have undergone little late exhumational hydration.

Dynamics of the carbon dioxide system in the Dead Sea

–Because the Dead Sea is a Ca-chloride hypersaline lake and is virtually lifeless, it is an excellent system to investigate the physical and chemical paths of the carbon cycle in terrestrial aquatic environments that are generally overwhelmed by biologic carbon fluxes. The Dead Sea is known to form massive aragonite deposits in the form of varves at present and during the Lisan period (late Pleistocene). The commonly accepted season for the main aragonite precipitation was summer, and the trigger for precipitation was attributed to evaporation and the warming of surface water (“whitening” events). To determine the main carbon fluxes in the Dead Sea, we followed changes in the carbonate system of the mixed layer, from February 1993 to December 1994, after stratification formed due to heavy flooding during the winter of 1992. The stratification isolated the mixed layer, a relatively small reservoir from the main brine body, causing an amplification of the chemical signals. The data show that partial pressure of CO 2 in the lake was very high (≈2000 μatm). Total alkalinity and total carbon of the mixed layer decreased with time, whereas δ 13C increased. The high P CO 2 originates from precipitation of aragonite and implies that in many aquatic systems it may originate from an inorganic process and not only from degradation of organic matter. Thermodynamic calculation estimated the degree of aragonite saturation to be ≈15 when 10% of Dead Sea brine with a high Ca content mixed with 90% runoff freshwater with high-bicarbonate content. Therefore, mixing during winter flooding triggers massive aragonite deposition in the Dead Sea. The general conclusion is that inorganic carbonate precipitation by mixing of two solutions, one supplying Ca 2+ and the other HCO 3 − should be considered in the evaluation of the carbonate system in a wide range of aquatic environments. A mass-balance model for total alkalinity, total carbon, and carbon isotopes reveals two main carbon sinks and one carbon source. The sinks are a chemical deposition of aragonite (1.4 mol · m −2 · y −1), and CO 2 escape to the atmosphere (4 mol · m −2 · y −1), and the source is bicarbonate input by floods (2.1 mol · m −2 · y −1). The precipitation rate of the present Dead Sea is approximately sixfold lower than the average precipitation rate during the Lisan period, implying a wetter climate during that period. The present CO 2 escape rate from the mixed layer is twice the bicarbonate input and threefold the aragonite precipitation rate, indicating a net CO 2 loss. We suggest that such a scenario is possible if the Dead Sea was meromictic (stratified) for a very long period of time.

Factors controlling the configuration of the fresh-saline water interface in the Dead Sea coastal aquifers: synthesis of TDEM surveys and numerical groundwater modeling

TDEM (time domain electromagnetic) traverses in the Dead Sea (DS) coastal aquifer help to delineate the configuration of the interrelated fresh-water and brine bodies and the interface in between. A good linear correlation exists between the logarithm of TDEM resistivity and the chloride concentration of groundwater, mostly in the higher salinity range, close to that of the DS brine. In this range, salinity is the most important factor controlling resistivity. The configuration of the fresh–saline water interface is dictated by the hydraulic gradient, which is controlled by a number of hydrological factors.

Parent Brine of the Castile Evaporites (Upper Permian), Texas and New Mexico

ABSTRACT The Upper Permian (lower Ochoan) Castile Formation is a major evaporite sequence (10,000 km3) of calcite, anhydrite, and halite in west Texas and southeastern New Mexico. Traditionally the Castile brine has been considered to have been derived from seawater. This tradition has recently been challenged by two versions of the closed-basin drawdown model. They call for deposition from a mixed brine, in part marine and in large part nonmarine. They propose drawdown of as much as 500 m to form a major sink for ground water issuing from the surrounding Capitan reef complex. A large fraction of the solute in the brine body is inferred to have been recycled from older Permian evaporites on the surrounding shelf. Strontium-isotope analyses show no evidence that meteoric ground water was contributed to the Castile brine. From a stratigraphic, geographic, and lithologic array of 65 samples of anhydrite, gypsum, and calcite, 59 have an 87Sr/86Sr ratio of 0.706923 (sw of -225.0), a ratio that is the same as that of strontium in early Ochoan ocean water. If considerable (>15%) influx of meteoric water had occurred, enough continental strontium would have been introduced to have resulted in higher ratios. Low bromide values (20-40 ppm) in Castile halite, which have been used to argue for meteoric influx and for recycled salt, probably resulted from diagenesis. During shallow burial by halite, centimeter-size, bottom-grown crystals of gypsum were altered to nodular anhydrite. The rising water of dehydration caused the halite to recrystallize. During the recrystallization, some bromide was expelled. Despite the large volume of water that evaporated annually from its surface (52 km3/yr, assuming an evaporation rate of 2 m/yr), the Castile brine body never completely desiccated. The surrounding shelf was flat, hot, and generally dry. It probably could not have supplied a significant volume of meteoric spring water to the basin over tens of thousands of years. More likely, during the entire history of the evaporite sequence, influx was dominantly marine. Marine ground water flowed through the Capitan Formation into the evaporite basin along its southern and possibly western margin probably with a rate of flow that was usually fast enough to prevent major drawdown of the brine surface.

Geoquímica de las lagunas saladas de los Monegros (Zaragoza). l. determinación experimental de los efectos del reequilibrio mirabilita-solucion con la temperatura en un sistema natural

Geochemical evolution of Los Monegros playa-lakes is affected by temperature fluctuations in the brine body at different time scales. Temperature shifts promote seasonally, daily and even during minor cycles mineralogical and compositional changes. Seasonal impacts of temperature change the brine composition and the crystallized mineral sequences (Pueyo, 1978-79). So, during summer cycle minerals crystallize according to the sequence: carbonates-gypsum-halite; and during winter the sequence of precipitation changes to carbonates-gypsum-mirabilite. Daily cycles also exist during winter brine evolution: mirabilite crystallization occurs during spring nights by lowering temperature, whereas diurnal temperatures promote its dissolution. And when high saturation levels are reached by evaporative concentration and the amount of precipitated mirabilite is important in the system (mirabilite stage, at spring), diurnal temperature fluctuations induce quick mirabilite-solution reequilibrium processes. Sampling of brines during this stage and thermodynamic calculations through the extended HMW model (Harvie, Moller and Weare, 1984) enclosed in the PHRQPITZ code (Plummer et al., 1988) indicate that mirabilite equilibrium holds in spite of variations in the concentration degree and temperature of samples. Field observations confirm that the reequilibrium process is efective in a few minutes when temperature varies only sorne degrees. Experimental determination of mirabilite solubility between Oand 30oC, using a natural brine sampled in advanced concentration stage, allows to isolate temperature effects on solution composition from those of evaporative concentration. Results indicate that modifications of mirabilite solubility produce their maximum effects between 20-30oC, fluctuation common in the natural system during spring: several hundreds of grams/kg water of mirabilite are mobilized, brine ionic strength changes from 4 to 8 molal and water activity varies from 0.943 to 0.896. Thenardite, bloedite and glauberite saturation states are affected by that reequilibrium process but those of gypsum and halite are almost insensitive to it. Predicted brine evolution by means of classical chemical divide or generalized residual alkalinity rules fails because of the special characters of these systems (high concentration solutions and evolution paths under variable temperature conditions). This non-isothermal evolution must be taken into account in more elaborated physicochemical approaches to brine evolution: the normal simplification using isothermal conditions (25oC) in thermodynamic calculations leads to important discrepancies in the predicted timing of mirabilite precipitation refered to field observations. Partial validation of the extended HMW model by comparison of laboratory and field solubility data appear to be confirmed.

The fate and accumulation of bromide during playa salt deposition: An example from Lake Frome, South Australia

An advectivn/diffusion model describing the distribution of Br− in porewaters underlying an accumulating deposit of halite on a playa lake can be used to predict the evolving composition of the accumulating salt growing as a result of evaporation. The Br/Cl ratio of the accumulating halite is proportional to the concentration or Br− at the surface of the brine body from which it is growing. The evolution of interstitial Br− and therefore the composition of the accumulating salt is a function of (1) the diffusion coefficient of Br− in the brine-saturated sediment, (2) the advective velocity of the interstitial water, (3) the initial concentration of Br− and Cl− at the onset of evaporation, and (4) the distribution coefficient of Br into the accumulating salt, all of which can be estimated for the sediments and brines of Lake Frome, South Australia. At Lake Frome, the model is used to estimate mean evaporation rates for the salt-covered surfaces which are found to be between 0.5 and 3.0 cm/y. These rates are lower than the rates estimated for the salt free surfaces of the lake by Allison and Barnes (1985) but are consistent with the expectation that groundwater input and therefore evaporation rates will be focused at the salt-free lake margins rather than at the salt-covered central regions of the playa and that the surface albedo of the salt-covered zones will reduce energy penetration to the sediment and thus evaporation.