Evaporite Deposits Research Articles

Experimental Study of Ethylene Evaporites under Titan Conditions

Titan has an abundance of lakes and seas, as confirmed by Cassini. Major components of these liquid bodies include methane ($CH_4$) and ethane ($C_2H_6$); however, evidence indicates that minor components such as ethylene ($C_2H_4$) may also exist in the lakes. As the lake levels drop, 5 $\mu m$-bright deposits, resembling evaporite deposits on earth, are left behind. Here, we provide saturation values, evaporation rates, and constraints on ethylene evaporite formation by using a Titan simulation chamber capable of reproducing Titan surface conditions (89-94 K, 1.5 bar $N_2$). Experimental samples were analyzed using Fourier transform infrared spectroscopy, mass, and temperature readings. Ethylene evaporites form more quickly in a methane solvent than in an ethane solvent or in a mixture of methane/ethane. We measured an average evaporation rate of $(2.8 \pm 0.3) \times 10^{-4} kg \; m^{-2} \; s^{-1}$ for methane and an average upper limit evaporation rate of less than $5.5 \times 10^{-6} kg \; m^{-2} \; s^{-1}$ for ethane. Additionally, we observed red shifts in ethylene absorption bands at 1.630 and 2.121 $\mu m$ and the persistence of a methane band at 1.666 $\mu m$.

Seismic markers of the Messinian salinity crisis in the deep Ionian Basin

AbstractWe conduct the seismic signal analysis on vintage and recently collected multichannel seismic reflection profiles from the Ionian Basin to characterize the deep basin Messinian evaporites. These evaporites were deposited in deep and marginal Mediterranean sedimentary basins as a consequence of the “salinity crisis” between 5.97 and 5.33 Ma, a basin‐wide oceanographic and ecological crisis whose origin remains poorly understood. The seismic markers of the Messinian evaporites in the deep Mediterranean basins can be divided in two end‐members, one of which is the typical “trilogy” of gypsum and clastics (Lower Unit – LU), halite (Mobile Unit – MU) and upper anhydrite and marl layers (Upper Unit – UU) traced in the Western Mediterranean Basins. The other end‐member is a single MU unit subdivided in seven sub‐units by clastic interlayers located in the Levant Basin. The causes of these different seismic expressions of the Messinian salinity crisis (MSC) appear to be related to a morphological separation between the two basins by the structural regional sill of the Sicily Channel. With the aid of velocity analyses and seismic imaging via prestack migration in time and depth domains, we define for the first time the seismic signature of the Messinian evaporites in the deep Ionian Basin, which differs from the known end‐members. In addition, we identify different evaporitic depositional settings suggesting a laterally discontinuous deposition. With the information gathered we quantify the volume of evaporitic deposits in the deep Ionian Basin as 500,000 km3 ± 10%. This figure allows us to speculate that the total volume of salts in the Mediterranean basin is larger than commonly assumed. Different depositional units in the Ionian Basin suggest that during the MSC it was separated from the Western Mediterranean by physical thresholds, from the Po Plain/Northern Adriatic Basin, and the Levant Basin, likely reflecting different hydrological and climatic conditions. Finally, the evidence of erosional surfaces and V‐shaped valleys at the top of the MSC unit, together with sharp evaporites pinch out on evaporite‐free pre‐Messinian structural highs, suggest an extreme Messinian Stage 3 base level draw down in the Ionian Basin. Such evidence should be carefully evaluated in the light of Messinian and post‐Messinian vertical crustal movements in the area. The results of this study demonstrates the importance of extracting from seismic data the Messinian paleotopography, the paleomorphology and the detailed stratal architecture in the in order to advance in the understanding of the deep basins Messinian depositional environments.

Thermodynamic evidence of giant salt deposit formation by serpentinization: an alternative mechanism to solar evaporation

The evaporation of seawater in arid climates is currently the main accepted driving mechanism for the formation of ancient and recent salt deposits in shallow basins. However, the deposition of huge amounts of marine salts, including the formation of tens of metres of highly soluble types (tachyhydrite and bischofite) during the Aptian in the South Atlantic and during the Messinian Salinity Crisis, are inconsistent with the wet and warm palaeoclimate conditions reconstructed for these periods. Recently, a debate has been developed that opposes the classic model of evaporite deposition and argues for the generation of salt by serpentinization. The products of the latter process can be called “dehydratites”. The associated geochemical processes involve the consumption of massive amounts of pure water, leading to the production of concentrated brines. Here, we investigate thermodynamic calculations that account for high salinities and the production of soluble salts and MgCl2-rich brines through sub-seafloor serpentinization processes. Our results indicate that salt and brine formation occurs during serpentinization and that the brine composition and salt assemblages are dependent on the temperature and CO2 partial pressure. Our findings help explain the presence and sustainability of highly soluble salts that appear inconsistent with reconstructed climatic conditions and demonstrate that the presence of highly soluble salts probably has implications for global tectonics and palaeoclimate reconstructions.

An experimental study of gypsum dissolution coupled to CaCO3 precipitation and its application to carbon storage

Coupled gypsum dissolution-calcium carbonate precipitation experiments were performed in closed system reactors and in the presence of either aqueous 0.1 M Na2CO3, 0.1 M NaHCO3 or 0.1 M Na2CO3 + 0.2 M NaOH solutions. Gypsum dissolved immediately at the start of each experiment provoking the precipitation sequentially of vaterite, calcite and trace aragonite. Fine-grained amorphous carbon carbonate may also be present shortly after each experiment began. Each experiment approached equilibrium within 119 h leading to the maximum possible transformation of gypsum to calcite over this time frame. The rapid transformation of gypsum to calcite in these experiments suggests a similar rapid transformation of gypsum or anhydrite into calcite could occur during subsurface carbon storage efforts where evaporites are present. Evaporite deposits could thus potentially be used for carbonation if sufficient alkalinity is available to neutralize the acid liberated by the gypsum carbonation reaction. Due to a negative volume of the gypsum or anhydrite to calcite transformation, however, the carbonation of these minerals will potentially damage the integrity of evaporite caprocks.

Decoding sea surface and paleoclimate conditions in the eastern Mediterranean over the Tortonian-Messinian Transition

New sedimentological, micropaleontological and geochemical data from the Upper Miocene pre-evaporitic sedimentary sequence of the Faneromeni section (Crete Island, eastern Mediterranean) revealed a stepwise restriction of the Mediterranean Sea preceding the Messinian Salinity Crisis (MSC), which was modulated by a sedimentary cyclicity responding to orbital parameters. This cyclicity is manifested by lithological alternations from laminated to indurated homogeneous marls and clayey limestones, and covers the Tortonian-Messinian Transition (TMT; 7.6–6.7 Ma). This time window covers the successive closure of the marine Mediterranean-Atlantic gateways, which culminated in the onset of the MSC. In the present study, we present the first evidence for changes in the upper water column reflected by sea surface temperature (SST) and salinity (SSS) variations that correlate with pronounced paleoclimatic fluctuations. Planktonic foraminiferal isotopes, in combination with paired mixed layer Sr/Ca-derived SST data, reveal that the very warm late Tortonian interval has been followed by a strong long-term cooling (~10 °C) and desalination (~10‰) trend during the earliest Messinian, attributed to the paroxysmal phase of the so-called “siphon” event. In particular, the climate shift that occurred at the end of a global carbon isotope (δ13C) decrease suggests that changes in the carbon cycle were instrumental in driving late Miocene climate dynamics (cooling and aridity) in the progressively isolated eastern Mediterranean Sea. The observed salinity variability during this time interval also provides further insights about seasonal freshwater inputs and gives new support to the much-debated hydrologic regime (linear salinity increase vs step-function evolution with strong salinity fluctuations) preceding the deposition of evaporites. The novel methodology of foraminiferal Sr/Ca paleothermometry and results of this study could have numerous potential applications to other regions and relevant extreme geological events. Therefore, in the near future we expect this approach to add important new information to our understanding of Neogene climates.

Circular troughs in tessera terrain on Venus: Morphometry, structural analysis and possible formation model

Detailed observations on Venus tessera terrain reveal the presence of tectonic structures, characterized by a subcircular trough, limiting an internal area with the average elevation of the surrounding terrain. We named this new type of tectonic structures Circular Troughs. Here we show the results of a morphometric study and a structural analysis based on data from 609 structures obtained through a global survey on Venus. Circular Troughs have an average outer radius of 12 ± 4.4 km, an average inner radius of 9 ± 3.9 km and an average trough width of 3 ± 1.2 km. A comparison with other tectonovolcanic structures on Venus shows that they are smaller and their size-distribution is more bounded. Although Circular Troughs show morphological similarities with some corona types, their size distribution is significantly smaller than coronae indicating a shallower geodynamic formation process. A shape preferred orientation analysis shows that Circular Troughs in Western Ovda are elongated parallel to long-wavelength tessera folds indicating that they are at least partially deformed by them, thus Circular Trough formation predates or it is contemporary with folding. A detailed structural analysis suggests that they were generated by small scale diapirism exclusively developed in tessera terrain. Several hypotheses could explain this small scale diapirism inside tessera terrain including volcanically driven compositional diapirism, small scale thermal diapirism or compositional cold diapirism, considering that the probable dessication of an ancient ocean would have generated evaporitic deposits in the past later buried by younger geological units.

A lost Tethyan evaporitic basin: Evidence from a Cretaceous hemipelagic meta‐selenite – red chert association in the Eastern Mediterranean realm

AbstractAncient evaporite deposits are geological archives of depositional environments characterized by a long‐term negative precipitation balance and bear evidence for global ocean element mass balance calculations. Here, Cretaceous selenite pseudomorphs from western Anatolia (‘Rosetta Marble’) — characterized by their exceptional morphological preservation — and their ‘marine’ geochemical signatures are described and interpreted in a process‐oriented context. These rocks recorded Late Cretaceous high‐pressure/low‐temperature, subduction‐related metamorphism with peak conditions of 1·0 to 1·2 GPa and 300 to 400°C. Metre‐scale, rock‐forming radiating rods, now present as fibrous calcite marble, clearly point to selenitic gypsum as the precursor mineral. Stratigraphic successions are recorded along a reconstructed proximal to distal transect. The cyclical alternation of selenite beds and radiolarian ribbon‐bedded cherts in the distal portions are interpreted as a two type of seawater system. During arid intervals, shallow marine brines cascaded downward into basinal settings and induced precipitation. During more humid times, upwelling‐induced radiolarian blooms caused the deposition of radiolarite facies. Interestingly, there is no comparable depositional setting known from the Cenozoic world. Meta‐selenite geochemical data (δ13C, δ18O and 87Sr/86Sr) plot within the range of reconstructed middle Cretaceous seawater signatures. Possible sources for the 13C‐enriched (mean 2·2‰) values include methanogenesis, gas hydrates and cold seep fluid exhalation. Spatially resolved component‐specific analysis of a rock slab displays isotopic variances between meta‐selenite crystals (mean δ13C 2·2‰) and host matrix (mean δ13C 1·3‰). The Cretaceous evaporite‐pseudomorphs of Anatolia represent a basin wide event coeval with the Aptian evaporites of the Proto‐Atlantic and the pseudomorphs share many attributes, including lateral distribution of 600 km and stratigraphic thickness of 1·5 to 2·0 km, with the evaporites formed during the younger Messinian salinity crisis. The Rosetta Marble of Anatolia may represent the best‐preserved selenite pseudomorphs worldwide and have a clear potential to act as a template for the study of meta‐selenite in deep time.

Ultra-small microorganisms in the polyextreme conditions of the Dallol volcano, Northern Afar, Ethiopia

The Dallol geothermal area in the northern part of the Danakil Depression (up to 124–155 meter below sea level) is deemed one of the most extreme environments on Earth. The area is notable for being part of the Afar Depression, an incipient seafloor-spreading center located at the triple junction, between Nubian, Somali and Arabian plates, and for hosting environments at the very edge of natural physical-chemical extremities. The northern part of the Danakil Depression is dominated by the Assale salt plain (an accumulation of marine evaporite deposits) and hosts the Dallol volcano. Here, the interaction between the evaporitic deposit and the volcanisms have created the unique Dallol hot springs, which are highly acidic (pH ~ 0) and saline (saturation) with maximum temperatures ranging between 90 and 109 °C. Here we report for the first time evidence of life existing with these hot springs using a combination of morphological and molecular analyses. Ultra-small structures are shown to be entombed within mineral deposits, which are identified as members of the Order Nanohaloarchaea. The results from this study suggest the microorganisms can survive, and potential live, within this extreme environment, which has implications for understanding the limits of habitability on Earth and on (early) Mars.

Multispectral mapping of evaporite minerals using ASTER data: A methodological comparison from central Turkey

Evaporites are regarded as industrial raw materials with high economic value and are represented by chemical sedimentary rocks deposited in terrestrial and marine environments. Evaporite deposits rich in calcium sulphate, such as gypsum and anhydrite, are typically formed under arid climate conditions. These rocks are very important not only in paleo-environmental and paleo-climatic studies but also for oil and natural gas exploration as they may form trap where such hydrocarbons are accumulated. Some of the central Anatolian Tertiary basins such as Çankırı-Çorum, Sivas, Ulukışla, Tuz Gölü, Haymana and Beypazarı basins host outcrops of various terrestrial and marine evaporite deposits. In this study, gypsum minerals in the Aksaray and Niğde provinces (central Turkey), was mapped with ASTER imagery using band rationing, decorrelation stretching (DECOR), feature-oriented principal components (FOPCA) and sulphate index methods. Geochemical and spectroradiometer measurements were taken on samples collected during the field studies. Accuracy assessments using the maximum likelihood technique yielded highly accurate results (average 86%) and the best results were obtained from FOPCA and DECOR methods. Results were also checked with the field studies.

Bromine content and Br/Cl molar ratio of halite in a core from Laos: implications for origin and environmental changes

Bromine (Br) is one of the trace elements in halite. Br content and the Br/chlorine (Cl) molar ratio can be used to reveal dry climates, the degree of evaporation, and/or brine concentration. The Br content of basal halite is more useful than that the Br content of halite from later stages when being used to distinguishing marine from nonmarine origins. Evaporite deposits on the Khorat Plateau (KP) have been a primary source of evaporites in southeastern Asia. The origin (i.e., marine, nonmarine, or a combination of the two) of these deposits is still disputed. In this study, we used the Br concentration of basal halite and the Br/Cl molar ratio to explore the origin of these deposits and the environmental changes that took place in the Late Cretaceous. We analyzed a total of 330 halite samples from borehole ZK2893 for cations (K+, Ca2+, Na+, and Mg2+) and anions (Br−, Cl−, and SO42−). The Br content ranged from 24.04 to 277.87 ppm, and the Br/Cl molar ratio ranged from 0.02 to 0.27 ppm. The low Br content (24.04 ppm) and Br × 103/Cl molar ratio (0.02) of the basal halite suggested that no marine water was in the basin when the halite precipitation began. The temporal variations in the Br content and the Br × 103/Cl molar ratio of halite implied that: (1) the climate in this area during the Late Cretaceous was dry, with two dry stages occurring from 92 to 85 Ma and from 80 to 72 Ma; and (2) the drying trend increased from 92 to 85 Ma and from 80 to 72 Ma, with two extremely dry events occurring during the periods 89–85 Ma and 76–73 Ma.

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.

Using a coupled geochemical/physical mass balance model to gain insights into the deposition of subrecent evaporites: Searles Valley, California, USA

Modern and ancient saline lakes are important sites for the deposition of carbonates and evaporites. Here we describe a generalized computer model of chemical sediment production in a closed-basin lake subject to: (1) variable inflow sources through time; (2) variable volumes of these inflows; (3) variable temperature, and; (4) variable evaporation rates through time. We then apply our model to gain insights into some aspects of late Pleistocene evaporite deposits beneath Searles Lake, California, a well-described chemical sedimentary deposit. We tuned our model to match the masses and proportions of the major saline minerals trona and halite deposited in layers circa 32 ka to 24 ka. However, we could not reproduce the thicknesses of mixed siliciclastic, carbonate and organic layers sandwiched between the evaporites. The model is useful for interpreting and constraining the environmental conditions in and around any ancient saline lakes during evaporite deposition where the amounts, mineralogies, and vertical distribution of chemical sediments are known.

Origin and evolution of halite based on stable isotopes (δ37Cl, δ81Br, δ11B and δ7Li) and trace elements in Tuz Gölü Basin, Turkey

The Tuz Gölü basin located in Central Anatolia contains ancient (Miocene) and recent evaporite deposits. The aim of this study is to determine the origin and evolution of the ancient halite deposits in the basin, particularly whether there is a marine origin. For this purpose, the mineralogical, geochemical and isotopic properties of halite samples taken from three different drillings at the southern part of the Tuz Gölü basin were determined. Halite samples in the Tuz Gölü basin are characterized by Cl (60.20–61.00%), Na (39.00–39.40%) and Br (5-637 ppm) contents. The Cl−, Br−, Ca, Mg2+, SO42−, and K+ values and Cl/Br (948-86428) ratios indicated that during the formation of the ancient halites in the Tuz Gölü basin, the mixture of solutions had different compositions/origins and that the dissolution, recrystallization and dedolomitization mechanisms were effective.The δ81Br, δ37Cl, δ7Li, and δ11B isotopic compositions of the pure halites range from −0.06 to 0.82, −0.80 to 1.28, −0.70 to 30.60 and −14.70 to 11.60, respectively. The low δ37Cl (from −0.06 to 0.06‰), low δ81Br (from 0.03 to 0.95‰), high δ 11B (from −6.40–11.60‰) and high δ7Li (from 26.00 to 30.60‰) values clearly indicate that the brine involved in the formation of the halites of the Tuz Gölü basin was largely derived from seawater during the Mid-Miocene Climatic Optimum (MMCO) period. Additionally, the Cl−, Br−, Ca2+, Mg2+, and SO42− contents, as well as the intermediate δ81Br (0.34–0.95‰) values of the Tuz Gölü samples, indicated that the origin of the ancient halites in the basin is not only a marine composition but also a mixture of solutions having different compositions, ratios or origins (e.g., seawater or saline water and groundwater/fresh water).

Signature of ongoing brine reinjection on noble gas isotopes and fluid chemistry at Las Tres Vírgenes geothermal field, Mexico

A geochemical survey of the Las Tres Vírgenes geothermal field (LTVGF), Baja California Sur, Mexico, was carried out to determine the origin and evolution of its fluids, along with the influence of injection of local brines, and inhibitors intended to manage carbonate scaling issues. Major and minor cations, Cl, Br, Sr, O, H, and noble gas (He, Ne, Ar, Kr and Xe) isotopes were measured in fluids collected from four production wells, two injection wells, and one fumarole (El Azufre) in 2016 and 2018. Variations in the stable isotopes of water (δD and δ18O) and halogens (δ37Cl, δ81Br) over the years suggest that local brine reinjection might have started to modify the pristine chemistry of the fluids. However, relevant information on the original geothermal fluids has been preserved. The Na/Br and Cl/Br ratios suggest that LTVGF brines are seawater having leached evaporite deposits (halite). These deposits are absent in the area, but were likely present during the Miocene, prior to the breakup of the Gulf of California, suggesting that the saline fluid end-member at the LTVGF could be several million years old. Measured 3He/4He ratios (R) normalized to the atmospheric ratio Ra (= 1.384 × 10−6) plotted against the 4He/20Ne ratios suggest mixing between a mantle fluid with a R/Ra of 6.19, typical of the sub-continental lithospheric mantle and an atmospheric helium component. The R/Ra versus the 132Xe/36Ar ratio normalized to air suggests mixing between a mantle-rich pre-production fluid and air. The source of air appears to be linked to local gravity-controlled flow reinjection which causes the entrapment of air bubbles, leading to a fluid supersaturated in atmospheric noble gases. This pattern suggests that reinjection fluids are impacting the production area.

Extreme aridity prior to lake expansion deciphered from facies evolution in the Miocene Ili Basin, south‐east Kazakhstan

AbstractCentral Asia witnessed progressive aridification during the Miocene, commonly related to mountain uplift, the Paratethys retreat and global climate cooling. However, the formation of Miocene lakes in Central Asia seems to oppose drier conditions, suggesting that the precise timing, extent and forcing of the aridification is still not well constrained. This study presents a facies model for the alluvial–lacustrine part of the Middle to Late Miocene of the Ili Basin, obtained from two successions. The model enables the semi‐quantitative assessment of regional water level and salinity, and characterizes the control of water level on evaporite formation and diagenesis. Both the proximal Kendyrlisai and the distal Aktau successions show an overall increase in water availability from dry mudflat deposits to lacustrine sedimentation with a transitional playa phase. Increasing evaporation rates outpaced the water supply and caused groundwater salinization. Subsequent lake expansion coincided with a basin‐wide desalinization and required a shift to a positive water budget. A climatic control of the hydrological evolution is inferred due to abrupt salinization and a minor tectonic influence. The long‐term water accumulation is probably related to the hydrological closure of the basin in the early Middle Miocene (15·3 Ma). Starting at 14·3 Ma, the step‐wise salinization occurred simultaneously with the global cooling of the Miocene Climate Transition. The Miocene Climate Transition led to extreme aridity in the Ili Basin, highlighted by the early diagenetic formation of displacive anhydrite in the basin centre. The expansion of the freshwater lake (12·7 to 11·5 Ma) was possibly promoted by lower evaporation rates due to decreasing air temperatures in the Ili Basin after the Miocene Climate Transition. The extreme aridity in the Ili Basin is interpreted as a continental counterpart to the Badenian Salinity Crisis in the Central Paratethys. This emphasizes the role of atmospheric forcing on evaporite sedimentation across Eurasia during the Middle Miocene.

Evaporite deposition in the mid-Neoproterozoic as a driver for changes in seawater chemistry and the biogeochemical cycle of sulfur

Evaporite deposition in the mid-Neoproterozoic as a driver for changes in seawater chemistry and the biogeochemical cycle of sulfur

Identification of gypsum karstification using an electrical resistivity tomography technique: The case-study of the Sivas gypsum karst area (Turkey)

The Sivas district is the most important gypsum karstified area in Turkey. The oldest evaporites in the region were formed during the sedimentation process of the Oligocene period. Generally, these units extend along the southern part of the Sivas basin. After the Early Miocene Sea drained from this region, extensive evaporite deposition developed. An electrical resistivity tomography (ERT) study was carried out between the Hafik and İmranlı districts of the Sivas gypsum karstified area. In this research, the prior aim was to determine the general characterization, geometry, sedimentary cover and resistivity properties of gypsums. In addition, the study includes the synthetic modelling of different gypsum karstification types. The evaluation and interpretation were based on ERT data that was collected from the Hafik-İmranlı region. First, the different karstifications were identified, together with the characteristic features of gypsum in the area. The ERT studies showed that there are large and old karst structures between the Hafik and Zara district. However, the karst structures that are located between the Zara and İmranlı regions were interpreted as smaller and younger. The characteristics of both of the regions are different in terms of the morphometric properties. It is certain that the Kızılırmak River has an important impact on the formation of these structures. ERT studies have shown that the cover- and bedrock-type collapse sinkholes are very spread out across the area, and their geometries are different. Throughout time, the suffosion type of cavities formed inside the cover-type sinkholes as a consequence of geological and geomorphological events. The ERT sections showed that certain parts of these structures collapsed, and then alluvial materials filled in. The shallow groundwater level in the drilling results and the conductive zone in the ERT results are compatible with each other. ERT studies clearly determined the various karstification typologies of gypsums in the region, which also contributed to the creation of a detailed conceptual geological model.

Origin of fluids in Las Tres Vírgenes Geothermal Field

A geochemical survey of fluids in the Las Tres Vírgenes geothermal field (LTVGF) in Baja California Sur, Mexico, was carried out to describe their origins and evolution within the reservoir. Major and minor elements and noble gas isotopes (He, Ne, Ar, Kr, and Xe) were measured in fluids from three production wells, one injection well, and one fumarole (El Azufre). Stable isotopes of water (δD and δ18O) show mixing between Quaternary recharge, lighter than present-day rainfall, and a deep fluid of andesitic origin. The Na/Br and Cl/Br ratios indicate that deep brines from the LTVGF are seawater having leached evaporite deposits (i.e., halite). These deposits are presently absent in the area, but likely occurred during the Miocene, prior to the breakup of the Gulf of California, suggesting that the saline fluid end-member of the LTVGF is several million year old. Measured 3He/4He ratios of greater than 6.5 Ra (where Ra is the atmospheric ratio of 1.384 x10-6) show that LTVGF fluids are a mixture of meteoric waters and deep magmatic fluids, with the hotter and more pristine mantle fluids found in the southern part of the exploitation zone.

Chlorine and bromine isotope evolution within a fully developed Upper Permian natural salt sequence

The behaviour of chlorine and bromine isotopes in evaporite deposits differs significantly. We studied the isotope variations of both elements in a fully developed natural salt sequence from Zechstein evaporite deposits (Wuchiapingian, Upper Permian) in the Northern Netherlands. We observed that the Cl isotope variations follow previously predicted characteristics, showing slightly positive δ37Cl (relative to seawater) in halite (NaCl) dominated layers (up to +0.05‰), decreasing to moderately negative values in carnallite (KMgCl3·6H2O) and bischofite (MgCl2·6H2O) dominated layers (down to −0.55‰). Bromine isotope variations, the first ever measured in marine evaporite samples, show a different characteristic. δ81Br values decrease quickly in layers dominated by halite (from +0.2 to −0.5‰) and increase again in layers dominated by carnallite and bischofite (up to −0.1 ± 0.2‰). These observations suggest that the Br isotope fractionation (103lnα) during precipitation of halite can be as high as +1.3, 3.8 times as large as Cl isotope fractionation. The increasing δ81Br values during precipitation of magnesium salts may suggest a negative fractionation (103lnα) of −0.9, meaning that the Br isotope ratio in the precipitated salt is lower than in the brine. We suggest that the difference in behaviour between Cl and Br can be explained by the fact that Br, as a minor component in the brine, has to compete with Cl to fit into the crystal lattice of Cl salts, where it does not fit perfectly due to its slightly larger ionic radius than Cl, resulting in relatively large isotope fractionation. Further research is however needed to confirm or reject this suggestion.

Integrated bio-magnetostratigraphy of the Badenian reference section Ugljevik in southern Pannonian Basin - implications for the Paratethys history (middle Miocene, Central Europe)

The Central Paratethys was a large-scale Oligo-Miocene epicontinental sea located in Central and Eastern Europe. It was separated from the Mediterranean by the Alpine orogenic belt. The Paratethys progressively flooded the Pannonian back-arc basin that formed during the early to middle Miocene. Along the southern margin of the basin, the maximum extension of the Paratethys onto the flanks of the Dinarides Mountains occurred during the middle Miocene (Badenian). We have studied the most complete middle Miocene (Badenian-Sarmatian) Paratethys section located at this southern margin. It comprises a >1.5 Myr long, continuous marine depositional sequence, which is highly relevant for our understanding of the interplay between global climatic and regional geodynamic perturbations in this semi-isolated epicontinental basin. The investigated record is particularly important to assess the impact of the Middle Miocene Climate Transition, the Langhian-Serravallian glacial Mi-3b event, the syn-rift climax of the Pannonian Basin and the Badenian Salinity Crisis. Moreover, we present the first high resolution age model for the regional Badenian stage based on integrated biomagnetostratigraphy. According to our age model, the marine flooding reached the area at ~14.15 Ma, during the regional Badenian stage. Open marine conditions persisted until ~12.6 Ma when the extinction of the fully marine fauna marks the beginning of the regional Sarmatian stage. Sea-level fluctuations are reflected in the section by four transgressive regressive cycles coinciding roughly with 400-kyr-eccentricity periods. The largest sea-level fall occurred after the first cycle and corresponds to the end of the Middle Miocene Climate Transition marked by glacial event Mi-3b. Elsewhere in the Pannonian Basin, this marked drop in base-level triggered deposition of evaporites during the Badenian Salinity Crisis. At Ugljevik however, there are no evaporites and the short-term Mi-3b regression was followed by a transgression and re-establishment of deeper marine conditions at 13.76 Ma, i.e. during the earliest Serravallian. Diversified planktonic and benthic assemblages suggest fully marine conditions with a persistent connection to the Mediterranean at this time. Such conditions prevailed until the mid Serravallian (latest Badenian) when sediment input increased and coastal environments prograded seawards. The Badenian/Sarmatian boundary roughly coincided with a 400-kyr-eccentricity as well as with a 1.2-Myr obliquity minimum.