Evaporite Basin Research Articles

Natural and agricultural disturbances differentially impact seedling emergence from soil seed banks in hyperarid ecosystems

Saudi Arabia has implemented ambitious environmental protection programs by creating numerous nature reserves throughout the country. Establishment of the latter nature reserves has led to farm abandonment and the initiation of ecosystem recovery processes. Agricultural practices are known to impact the structure and physicochemical properties of soils while also often markedly affecting natural ecosystem restoration processes. Moreover, weed proliferation in crop fields may modify soil seed banks (SSB), thereby impacting subsequent vegetation recovery. Therefore, it is essential to assess SSB compositions in degraded sites, such as abandoned farms (AF), so as to identify weed species and design efficient restoration strategies in hyperarid ecosystems. In this study, SSB compositions in upper and deep soil layers, standing vegetation compositions, and soil chemical properties were analyzed and compared for two natural ecosystems (NE), two abandoned orchards (AO), two AF, and two natural evaporite basins (EB). NE, AO, AF, and EB all exhibited similar chemical properties, suggesting that former agricultural activities have been guided by a fine understanding of the local environments. Agriculture had impacted the species composition of the observed standing vegetation and germinable SSBs, which could be partly explained by soil property modifications. The findings highlighted that SSBs would warrant detailed study prior to designing ecological restoration strategies, and that the drivers of horizontal and vertical weed dissemination in hyperarid ecosystems should also be explored to gain further insight into weed proliferation patterns and to adapt restoration strategies accordingly.

Palaeogeographical and eodiagenetic settings of host‐replacing phreatic calcrete intervals developed in mud deposits of the Famennian Kinnesswood Formation in the Pennyseorach Subbasin of south‐west Scotland

ABSTRACTIn the Pennyseorach Subbasin of south‐west Scotland, the Famennian Kinnesswood Formation of the Inverclyde Group includes several, ca 1 to 3 m thick erosional remnants of host‐replacing phreatic calcrete hardpans developed in mud deposits. The latter are most unusual hosts for such calcretes due to their relative impermeability, which would normally prevent them from sufficiently accommodating the circulation of an aquifer. In previously documented phreatic calcretes, mud deposits clearly acted as aquicludes that sharply constrained calcrete development. In the Kinnesswood Formation at Pennyseorach, tall desiccation fissures allowed groundwater to circulate in thick, semi‐consolidated mud deposits. Because of the inferred development of an adjacent evaporitic basin, the mixing of fresh and evaporitic groundwaters raised the pH enough for the replacement of phyllosilicates by calcite to occur along the fissure walls, forming ‘fissure calcretes’. The latter gradually expanded and eventually coalesced into mature, ‘columnar host‐replacing phreatic calcrete hardpans’ in which 90 to 100% of the muddy host material was replaced by calcrete. At Pennyseorach, host‐replacing phreatic calcrete hardpan formation not only affected the transition zone between the Doughend Sandstone and Foul Port Members of the Kinnesswood Formation (the Dunagoil Calcrete interval), as in other localities of south‐west Scotland, but also affected the uppermost part of the formation, which is marked by several erosion surfaces downcutting into columnar host‐replacing phreatic calcrete hardpan intervals in association with the episodic rise and fall of base‐level. These newly recorded host‐replacing phreatic calcrete hardpan intervals from the upper part of the Kinnesswood Formation have a tightly constrained stable isotopic signature that is distinct from that of both the Dunagoil Calcrete and the successive host‐replacing phreatic calcrete hardpans of the Visean Clyde Sandstone Formation within the same group, underlining their potential as stratigraphic markers and palaeoenvironmental indicators.

Evaporite sequences as archives for Mg isotope compositions of seawater - Evidence from a Tethys marginal shelf basin in the Anisian

Evaporites have recently been suggested as a potential archive for recording the Mg isotope compositions (δ26Mg) of coeval seawater. However, episodic dolomitization during the deposition of massive evaporites could cause considerable Mg removal and isotopic fractionation. To constrain the hydrological changes and influence of dolomitization on ambient brine δ26Mg, we present petrographic and mineralogical features, as well as Mg-C-O-Sr isotope data extracted from carbonate phases of a middle Triassic (ca. 247 Myr) marine anhydrite-dolostone sequence from a drill core in eastern China. The drilled lithologies are characterized by massive dolostone layers in the lower part, followed by an upward decline in dolomite contents accompanied by a rise in anhydrite. Multiple lines of evidence consistently point to a syn-depositional origin for the dolostones in a marginal basin of the Tethys Ocean and a lack of diagenetic alteration since deposition. We reconstructed the dynamic changes of δ26Mg values of basin waters based on Mg isotope compositions in dolomite leachates. According to our findings, the δ26Mg values of the basin waters were remarkably high (about 0.38 ± 0.05‰) at the onset of evaporation, indicating a significant Mg sink of the massive dolomitization. The δ26Mg of brine in the basin then changed towards the value of coeval seawater (about −0.32 ± 0.05‰) starting with the deposition of evaporites. Concurrently, 87Sr/86Sr ratios of dolomites shift from radiogenic values towards contemporaneous seawater composition. Our results demonstrate that the evaporite basin was not strictly restricted, and water exchange with the open ocean never ceased. Modeling calculation reveals that, even when the seawater exchange rate is far below the average ocean circulation, δ26Mg of brine in the basin will reach the value of open ocean within 1 Myr, completely removing the influence of early dolomitization. We suggested that massive marine evaporite sequences have the potential to record the long-term evolution of seawater Mg isotopes.

Gypsum ridges as conduits for deep methane emission in an evaporite basin– Insights into the origin of atmospheric methane on Mars

The origin of atmospheric methane on Mars is attracting much attention because of its possible biological origin. We report the first detection of methane-dominated hydrocarbons trapped between the {010} cleavage planes of gypsum megacrysts from the evaporative Qaidam Basin, in the northern Tibetan Plateau. The gypsum makes ridges of kilometers long, tens of meters wide, and high that are deposited from deep circulated brine and later exhumed to the surface by wind erosion. The δ13C of methane (-33.3 ± 4.1 ‰), high CO2/CH4 ratio but low C1/(C2+C3) ratio indicate their thermogenic sources. These gypsum ridges are formed on intrabasin salt domes and form conduits for the volatile hydrocarbons to diffuse upward and escape into the atmosphere. We suggest the atmospheric methane on Mars is also derived from the deep basins and is emitted by the same pathway since the gypsum ridges/seams/veins in the Qaidam Basin show striking similarities to the irregular polygonal ridge networks and veins on Mars.

LITHOLOGICAL-STRATIGRAPHIC CRITERIA OF KARST ZONING OF THE MIOCENE SULFATE LAYER OF WESTERN UKRAINE

The proposed karst regionalization (zoning) is a novel approach to identifying the unique characteristics of karst processes in specific areas. The sulphate karst of western Ukraine, linked to the Miocene evaporite basin at the junction of the East European Platform and the Pre-Carpathian Foredeep, is a prime example. The previous karst zoning schemes of the East European Plain classified the entire area of sulphate rocks distribution in the west of Ukraine as the Podilsko-Bukovinsky karst Area, with the West Podilsky and Pokutsko-Bukovinsky karst Regions within it. However, with the emergence of numerous detailed stratigraphy works on the evaporite formation of this territory, a new approach to karst zoning in evaporites is necessary. This paper presents a systematic approach to upgrading the mentioned regions to the rank of sub-areas and distinguishing the regions within them based on lithologic-stratigraphic differences. The authors studied six localities as examples. In the first one, the gypsum layer is characterized by the stromatolite, grass-like and sabre-like facies. The last two contain thin carbonate-clay layers, leading to the collapse of large rock blocks inside the Kadubivska Cave. On the second site, the gypsum is composed of stromatolite, coarse-crystalline, and sabre-shaped facies. Only one small Tovtry Cave, which has a hypogene morphology, is known here. The third site has grass-like gypsum facies, and intensive modern karst occurs, with numerous sinkholes, underground rivers, and sinkholes. The influence of facies variability on the development of the mesomorphology of underground galleries is traced here in Pionerka Cave. The fourth area is built of nodular gypsum facies. There are no insoluble layers here, but the facies have many thin mineral films between the grains. Therefore, the entrance parts of the caves are unstable for physical weathering. The fifth section is highlighted as a section of the spread of metasomatic limestone, which replaces sulphate deposits here. They contain a significant cave labyrinth, but whether karstification occurred before or after metasomatization remains unclear. The sixth section is completely composed of stromatolite gypsum facies. It is characterized by stability to collapse due to the monolithic structure of gypsum, which is noticeable in the example of the Cave of Popeliushka (Zolushka) on the border of Ukraine and Moldova. The selected areas are proposed to be considered as examples of karst zoning based on lithologic and stratigraphic features. Key words: karst regionalization; gypsum, limestone; caves, breakdown; relief, landscape.

Authigenic quartz reveals the triple oxygen isotope composition and diagenetic temperature of saline brines

Triple oxygen isotope compositions of authigenic minerals are an emerging tool for the reconstruction of fluid temperatures and the fluid isotopic composition. In this study, we analyzed euhedral authigenic quartz crystals from a halite deposit of the Upper Permian Zechstein evaporitic basin for their triple oxygen isotope composition using laser fluorination isotope ratio mass spectrometry. In the triple oxygen isotope space, additional information, such as the triple oxygen isotope composition of the ambient water, provides insights into equilibrium conditions during quartz formation that cannot be identified from δ18O alone. The triple oxygen isotope composition of authigenic quartz shows, that single oxygen isotope (δ18O) thermometry is not applicable for samples from evaporitic environments, where the fluids' δ18O deviates from dynamic oxygen isotope equilibrium. By combining the Craig and Gordon evaporation model with H2O – SiO2 triple oxygen isotope equilibrium fractionation, we reconstruct the formation temperature of authigenic quartz and the triple oxygen isotope composition of the marine-derived saline brine pore fluid in equilibrium with the quartz. We obtain temperatures of 90 to 130 °C that is interpreted as crystallization temperatures of microcrystalline quartz in pore fluid of halite during burial diagenesis. The triple oxygen isotope composition of authigenic quartz from evaporitic environments is suited as a geochemical tracer for fluid oxygen isotope compositions and ancient fluid or diagenetic temperatures.

Hydrochemical and isotopic characteristics of water sources for biological activity across a massive evaporite basin on the Tibetan Plateau: Implications for aquatic environments on early Mars

Covered by vast eolian landforms, gravel deposits, and playas, the worldwide typical evaporite deposit land, Qaidam Basin, in northwestern China is analogous to early Mars when the aridification process had lasted for millions of years since the end of a wetter climate. This study aims to investigate the chemical and isotopic characteristics of waters in an evaporite-rich environment, as well as the habitable conditions therein, that have undergone a transformation similar to early Mars. In May 2023, a total of 26 water samples were collected across the representative central axis of a longitudinal aridity gradient in the Qaidam Basin, including categories of meteoric water, freshwater, standing water accumulated after precipitation, salty lacustrine water, and hypersaline brines to inspect compounds made up of carbon, nitrogen, phosphorus, sulfur, halogen, and metallic elements. As evaporation intensified, the salt types transformed from HCO3-Ca·Na to Cl·SO4-Na or ClMg. The dominance of carbonate will gradually be replaced by sulfate and chloride, leaving much more dilute and less detectable contents. The presence of trace ClO4−, ClO3−, ClO2−, and BrO3− was confirmed in a few of the sampled Qaidam waters, indicating the preservation of oxyhalides in waters within an arid region and possibly the presence of relevant microbial enzymes. The isotopes of water, carbonaceous, and nitrogenous compounds provide valuable references for either abiogenic or biogenic signatures. With undetectable amount, phosphorus was found to be the limiting nutrient in evaporative aquatic environments but not necessarily antibiosignatures. Overall, these results suggest that the paleo-lacustrine environments on Mars are more likely to preserve biosignatures if they feature the dominance of carbonate minerals, bioavailable nitrate, phosphorus, and organic carbon, the presence of thermodynamically unstable oxyhalides, and isotope ratios that point to the involvement of biological activity.

Factors controlling lithium accumulation in brines from Upper Cretaceous to Lower Eocene aquifers of a continental evaporite basin

The origin of deep-seated Li-rich brines in a continental evaporite basin remains poorly understood. To clarify hydrogeochemical processes governing the Li enrichment, this study investigated chemical compositions and multi-isotopic (H–O–Li–Sr) features of a set of water samples from Upper Cretaceous to Lower Eocene sedimentary brines, saline groundwaters and oilfield brines, thermal waters and surficial river waters in the Jiangling Basin, central China. Waters from deep reservoirs evolve through multiple hydrogeochemical processes including evaporation, dilution, water-rock reactions and evaporite dissolution. These processes cause a range of Li and Sr contents (5.43–100 mg/L and 32.8–1307 mg/L) and isotope compositions (+8.6 to +19.3‰ and 0.706926–0.712480), indicating contributions from reservoir rock dissolution to δ7Li values and 87Sr/86Sr ratios. Chemical geothermometers applied to brines, saline waters and thermal waters give reservoir temperature values ranging between 70 and 200 °C. Temperature has a distinct effect on advancing host rock-water interactions, while high-temperature waters enhance leaching of Li in rocks compared to the low- and medium-temperature waters. The variable δ7Li values lower than river waters and high Cl/Br ratios in the Upper Cretaceous to Lower Eocene aquifers suggest a result of evaporite dissolution to different degrees, whilst waters in the Upper Cretaceous aquifers have the lowest δ7Li values similar to the thermal waters and the highest Cl/Br ratios suggest a stronger salt dissolution effect. Multi-isotope tracing highlights the role of temperature, reservoir rock types and different hydrogeochemical processes in defining the geochemical and isotopic water composition. Combination of these factors, together with high heat gradients associated with intense volcanic activity eventually results in Li accumulation in deep-seated brines from the Jiangling evaporite basin. Our results contribute to a further comprehensive understanding of hydrogeochemical processes that dominate deep brine formation and Li enrichment in an ancient continental evaporite basin.

The Potash Identification (PID) Plot: A Rapid Screening Crossplot for Discrimination of Commercial Potash

Potash minerals are the primary source of potassium (K), which is used for the manufacture of gunpowder, fertilizer, and as a sodium-seasoning substitute. Commercial potash minerals are all evaporites. Because potassium-40 (40K) is radioactive (decaying to argon-40 (40Ar) and releasing a gamma ray (GR) in the process), commercial potash mineralization is often discovered when GR (γ ray) logs in petroleum wells drilled through evaporite sequences “go off scale.” However, not all potash minerals may be commercial sources of potassium via underground mining techniques, and potassium is not the only radioactive element. For example, the mineralogy of the McNutt “potash” Member of the Salado Formation in southeast (SE) New Mexico is extremely complex, consisting of multiple thin (i.e., less than 10 ft thick) beds of six low-grade (radioactive) potash minerals, only two of which are commercial for underground mining. There are also four nonradioactive evaporite minerals, one of which may interfere with potash milling chemistry and numerous claystones and marker beds (shales and/or volcanics), with GR count rates comparable to the low-grade potash mineralization in this sequence. Because of this complexity, traditional borehole wireline (WL) and logging-while-drilling (LWD) potash assay techniques, such as GR log-to-core assay transforms, may not be sufficient to identify potentially commercial potash mineralization for underground mining (Teufel, 2008) in SE New Mexico. Crain and Anderson (1966) and Hill (2019) developed linear programming and multimineral analyses, respectively, to estimate potash mineralogy and grades from multiple borehole geophysical measurements. However, both of these approaches require large sets of multiple log measurements. In SE New Mexico, petroleum wells are drilled through the Salado Formation evaporite (including the McNutt “potash” Member) with air, then cased and cemented in place without running WL measurements. Then, the wells are drilled out to total depth (TD) in the underlying sediments with water-based mud. Complete log suites are run from TD to the casing shoe, with only the GR and neutron logs recorded through the cased evaporite sequence for stratigraphic and structural correlation. As a result, essentially all recent oil and gas wells in SE New Mexico have casedhole gamma ray and neutron logs through the Salado evaporite. Hill and Crain (2020) developed a simple crossplot involving only GR and neutron log data, which could discriminate between anhydrous and hydrated potassium evaporite minerals. Logs from these wells could provide a rapid potash screening database if used properly. This technique can be used with both openhole and casedhole petroleum well logs, as well as corehole WL logs, and provides discrimination of commercial potash mineralization from noncommercial (potash and non-potash) radioactive mineralization. Case histories of the use of PID crossplots in evaporite basins of Michigan, Nova Scotia, Saskatchewan, and SE New Mexico are described. This technique may also be useful in screening potential potash deposits elsewhere in the world.

Sustained wet-dry cycling on early Mars.

The presence of perennially wet surface environments on early Mars is well documented1,2, but little is known about short-term episodicity in the early hydroclimate3. Post-depositional processes driven by such short-term fluctuations may produce distinct structures, yet theseare rarely preserved in the sedimentary record4. Incomplete geological constraints have led global models of the early Mars water cycle and climate to produce diverging results5,6. Here we report observations by the Curiosity rover at Gale Crater indicating that high-frequency wet-dry cycling occurred in early Martian surface environments. We observe exhumed centimetric polygonal ridges with sulfate enrichments, joined at Y-junctions, that record cracks formed in fresh mud owing to repeated wet-dry cycles of regular intensity. Instead of sporadic hydrological activity induced by impacts or volcanoes5, our findings point to a sustained, cyclic, possibly seasonal, climate on early Mars. Furthermore, as wet-dry cycling can promote prebiotic polymerization7,8, the Gale evaporitic basin may have been particularly conducive to these processes. The observed polygonal patterns are physically and temporally associated with the transition from smectite clays to sulfate-bearing strata, a globally distributed mineral transition1. This indicates that the Noachian-Hesperian transition (3.8-3.6 billion years ago) may have sustained an Earth-like climate regime and surface environments favourable to prebiotic evolution.

Recharge processes limit the resource elements of Qarhan Salt Lake in western China and analogues in the evaporite basins

Recharge processes limit the resource elements of Qarhan Salt Lake in western China and analogues in the evaporite basins

Triassic-Early Jurassic evaporites of the Saharan Platform, Algeria: Astronomical and geodynamic constraints on stratigraphy and sedimentation

The sequence stratigraphy of the Late Triassic - Early Jurassic evaporites of the Berkine Basin is described. Disconformities occur between all the major evaporitic units but lack of biostratigraphy (or other) chronostratigraphic control precludes their precise dating. The S4 and S3 Halites are predominantly non-marine halites deposited in low-lying salinas with a barrier to the north. The top of the S4 depositional sequence is marked by the D2, usually regarded as the Tr-J boundary in the Berkine Basin. Both the S3 and S4 salt deposits thin rapidly to the south-east and are thicker in the basin centre coincident with a subcrop of Carnian? aged volcanics. A combination of thermal cooling, rifting and reactivation of N–S lineaments parallel to the Hassi Messaoud-El Biod Arch controlled the (∼1500 m thick) depocenter.Time series analysis shows that astronomical forcing played a key role in the deposition of the S3 and S4 bedded halites. The prevailing climate was monsoonal with major replenishment of the basin indicated by long eccentricity cycles (405 kyr). Sedimentation rates were estimated using eCOCO analysis with average rates of 15 cm/kyr. Well to well comparisons shows that in marginal areas thinner sedimentary sequences relate to slower accumulation rates and periods of non-deposition or deflation. The pattern is similar in the S4 and S3 halite, but the reduced mud content and amalgamation of halite beds suggests a more arid climate in S3 times.The S1+S2 unit marks the first widespread deposition of sulphate in the basin. The lowermost anhydrite beds of the S1 + S2 rest unconformably on the underlying S3 and overstep the basin margins in the south-east; the sequence is capped by the B Horizon a basin-wide carbonate shelf deposit about 25 m thick indicating increased marine influence. Above there is a rapid return to thinly bedded mudstone-halite dominated sedimentation (Lias Salifère) which is overlain by the Lias Anhydritique an alternating sequence of halite and anhydrite deposits. Astronomical parameters of the whole sequence indicate an average sedimentation rate of ∼10 cm/kyr in this marine-influenced section, slower than the halite units. Although the time series analysis cannot provide precision dating of the evaporitic sequences the results indicate that there are important breaks in the depositional record. The combined S4 and S3 halites account for 4.75 Ma and the rest of the Liassic 9.4 Ma. It seems clear that much of the depositional record is missing.These Saharan Platform basins bear much in common with other western Mediterranean evaporite basins. Many show the same overall pattern of sedimentation with increased sulphate deposition above the Tr-J boundary. In late Triassic time they formed a contiguous low-lying zone flanked by cratonic highlands. This zone spanned the Gondwana-Laurussia boundary immediately prior to its break-up and Greater Adria formed a barrier between these basins and the developing Neotethys to the east. The major changes seen in the Saharan Platform are mirrored by the break-up of Adria and the separation of Gondwana and Laurasia and the ultimate connection of the western Mediterranean and the central Atlantic.Although the cyclostratigraphy can tell us much about the absolute duration of sedimentation, the lack of significant anchor points forbids the construction of a detailed chronostratigraphic framework. In particular, the precise location of the Tr-J boundary remains unclear. Although it is usually placed at the base of the D2 Horizon, biostratigraphical evidence from Southern Tunisia places the S3 in the Norian. The sharp contrast between the S4 and S3 halites with the later evaporite sequence suggests that positioning the boundary between the S3 halite and the S1 + S2 unconformity should be given consideration.

The model of the oil and gas system of the Devonian sedimentary complex of the Biloliskyy block of the Dobrudja foredeep

The purpose of the article is to find out the main principal features of the ontogenesis of the oil and gas system of the Devonian deposits of the Dobrudja Foredeep. Methods and methodology - generalization of data on the lithology of Devonian deposits, analysis of materials on the development of paragenic facies associations in evaporite basins, construction of a principled model of the hydrodynamics of the Dobrudja basin on this basis and predicting the distribution of various lithogenetic types in the Devonian period. Historical-catagenetic reconstructions were carried out on the basis of the provisions of the fluid-dynamic concept of catagenesis. Results. On the basis of the reconstruction of the dynamics of the sea basin and the nature of the lithofacies zonation, the conditions of Middle-Late Devonian sedimentation were modeled. A wider development of sediments enriched in organic matter, both in the section and laterally, is argued. First of all, this applies to the Middle Devonian deposits, which, together with the Lower Devonian black shale formations, formed the body of oil and gas formation centers, that were localized in the depocenters of the Tuzliv and Alibey depressions. The Devonian sediments were affected by two major cycles of catagenesis, with active substages (so-called critical moments) associated with large-scale fluid migration. The time of manifestation of the active substage of the first cycle (Middle-Late Carboniferous) was the main one in the migration of hydrocarbons, which is associated with a sufficiently high degree of post-diagenesis of the generating strata: gradation of catagenesis MK5 (Lower Devonian), MK3 - MK4 (Eifelian). Hydrocarbons moved through the zones of regional decompaction, which were developed at three hypsometric levels. In this case, flows of hydrocarbons of different phase composition were formed. The source of the gas was the Lower Devonian deposits, and the main volume of oil was generated in the Eifelian layers. During the second cycle of catagenesis, due to a decrease in reservoir temperatures and a significant depletion of the potential of organic matter, only processes of reformation of previously formed hydrocarbon deposits are predicted. Due to the fact that the generation centers were confined to deposits of different ages, differed in temperature regime, ways of fluid migration, and were separated from each other, there are reasons to assume the existence of three oil and gas systems. Scientific novelty and practical significance. For the first time, a wider spatial and age range of development of oil and gas source strata, localized centers of generation, discrete paths and time of large-scale migration of hydrocarbons have been scientifically substantiated. The studies carried out provide good grounds for predicting the possibility of the formation of large volumes of hydrocarbons that could be accumulated in the Devonian deposits of the Dobrudja Foredeep.

Controls on evaporite facies distribution during the early phases of the Zechstein Basin development (Zechstein 1, Upper Permian): Implications from the marginal part of the basin in SW Poland

Amongst the least understood issues in the giant evaporite basin evolution is their early development. Here, we use a unique set of archival data from the Fore-Sudetic Homocline in SW Poland to investigate the controls on evaporite facies distribution in the marginal part of the Zechstein Basin after the Zechstein Sea transgression (Upper Permian, Z1 cycle). Based on integrated data from boreholes, subsurface mining survey and seismic profiling we constructed a 3D structural model, which showed that the carbonate, sulphate and chloride facies boundaries originally extended W–E, irrespective of the fault patterns in the basement. The thickness distribution for the Zechstein Limestone (Ca1), Lower Anhydrite (A1d) and Upper Anhydrite (A1g) evidences carbonate and sulphate platform development in respective evaporitic phases. Although the sea bathymetry and progressive seawater evaporation were the main factors responsible for the northward progradation of the evaporite facies, the relief over the sulphate platforms implies a significant influence of sea currents on the sulphate deposition. The channelised circulation of variably saturated seawater decreased the overall accumulation rate in the channels and promoted the high-and-trough topography development over the platforms. The Upper Anhydrite (A1d) top relief was evened by the Oldest Halite (Na1) rocksalt deposition. Prior to the Zechstein Limestone (Ca1) deposition, the distribution of clastic facies was mostly restrained by the dune relief inherited after the aeolian sedimentation in the Rotliegend. This old relief partly influenced also the Zechstein Limestone (Ca1) carbonate thickness and subfacies distribution and was eventually buried by the Lower Anhydrite (A1d) sulphates. There is no evidence on tectonic controls on evaporite depositional patterns throughout the Z1 cycle in the studied area.

Seasonal dynamics of evaporite mineral precipitation, dissolution, and back-reactions in shallow and deep hypersaline lakes

Seasonal water temperature variations exhibit a first-order control on the mineralogy, texture, and timing of formation of modern, temperate zone lacustrine evaporites. However, seasonality is generally absent from the thermochemical models used to interpret ancient nonmarine evaporites. Here, a seasonal model is presented which correctly reproduced the complex history of evaporite precipitation, dissolution, and back-reactions observed during the drying up of the shallow (2.4 m) Owens Lake, California (ca. 1969). Additional parameters were then added to simulate a deep (>10 m), perennial lake with the same chemical composition (e.g., ancient Searles Lake). Variations in temperature drive saline mineral precipitation and syndepositional alteration in both models, but in different ways. In shallow, well-mixed temperate lakes, minerals crystallize and transform in rhythm with seasonal temperature fluctuations. In deeper stratified lakes, alteration occurs when salts settle from surface waters (variable seasonal temperatures) to the bottom waters (constant temperatures). The deep lake model shows that more than half of the salts that precipitate at low temperatures later dissolve or back-react in warmer bottom waters. Closed basin evaporite deposits formed in temperate lakes thus preferentially preserve high temperature salts. This means that midlatitude lacustrine evaporites contain more climatic and limnological information than previously recognized, and can be interpreted in terms of seasonal temperatures, mean annual temperatures, and lake depths.

The Paleogene continental basins from SE France: New geographic and climatic insights from an integrated approach

New insights into the geodynamic evolution, the paleogeographic framework and the paleoclimatic setting of the Upper Eocene-Oligocene lacustrine basins from South-East France have been provided by an integrative approach combining geochronology, micropaleontology and stable isotope analyses. UPb dating on calcite, pollen-based climatostratigraphy and strontium and sulfur isotope signatures of sulfates provided a robust chronostratigraphic framework for the Upper Eocene and Oligocene succession from the Vistrenque, Alès and Roussillon basins. The thick Priabonian- lower Rupelian lacustrine succession from the Vistrenque Basin is interpreted to be deposited in a strike-slip basin associated with the latest stages of pyrenean shortening. Floral assemblages are used to reconstruct the vegetation cover in the lacustrine systems and their neighbouring lowlands and highlands. Composition of saltwater inferred from strontium and sulfur isotope signatures of sulfates, the occurrence of calcareous nannofossils, dinoflagellate cysts and pollen grains of mangrove-related plants provided strong evidence for marine intrusions into the Alès Basin during the Priabonian and the Vistrenque Basin during the Rupelian and Chattian. Paleogeographic reconstructions of Southeast France during the Priabonian and late Rupelian strongly suggest marine incursions from the Alpine Sea via two potential pathways: upper Rhône Valley via the Crest Sill and lower Rhône Valley via the Haut-Var Pyrenean synclines. On the other hand, Upper Oligocene evaporite basins in the Camargue area have been subjected to marine intrusions from the Western Mediterranean Sea following the collapse of the eastern pyrenean relief during the Liguro-Provençal rifting stage. Finally, pollen analysis and Climate Amplitude Method revealed a brief but significant stage of cooling and aridification at the very base of the Rupelian which could represent the regional and terrestrial expression of the global climate cooling following the Eocene-Oligocene Transition.

Understanding deformation band formation across a range of length scales in the Paradox Basin, Utah

In evaporite basins, salt flow can drive complex deformation of high porosity sedimentary units adjacent to salt and this has been demonstrated by recent numerical modeling studies, however field evidence of this deformation has remained elusive. Detailed analysis of high-porosity wall and cover rocks adjacent to a large salt-cored anticline in Salt Valley, UT yields three observable deformation band gradients. A long-wavelength gradient of steeply dipping normal/shear bands is recognized along structural transects up to 5 km away from the Salt Valley anticline axis. A shorter-wavelength (5–60 m) deformation band gradient shows band density increasing toward similarly-oriented brittle normal faults. A third gradient of intense compactional deformation banding is recognized adjacent to the salt diapir. Importantly, cement phases are undamaged in these bands, indicating that they likely experienced plastic critical-state deformation prior to cementation. The steeply-dipping deformation bands and normal faults are interpreted to be broadly contemporaneous and result from outer arc extension of the Salt Valley anticline; the dense compactional band network adjacent to salt likely accommodated compression during diapiric rise contemporaneous with folding. This integration of field and petrologic studies with forward modeling makes a critical step toward developing predictive models for deformation band formation in hydrocarbon systems.

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.

Stable Isotopes and Halogen Geochemistry of the Huayuan Carbonate‐hosted Pb‐Zn Ore District, South China: Implications for the Salt Source of Ore‐forming Fluids

AbstractThe Huayuan Pb‐Zn ore district in China, located in western Hunan Province, is a giant carbonate‐hosted Pb‐Zn ore district. The source of ore‐forming brines in this ore district remains poorly constrained. Whether the highly saline brines are derived from evaporated seawater or dissolved evaporates continues to be intensely debated. Carbonate minerals associated with Pb‐Zn mineralization have δ13CV‐PDB and δ18OV‐SMOW values ranging from −5.55‰ to +1.35‰ (mean value of −0.69‰; n = 14) and +16.28‰ to +25.05‰ (mean value of +20.22‰; n = 14), respectively. This indicates that carbonate minerals are dominantly formed from dissolved ore‐hosted carbonate rocks. The δ34S values of sulfides range from +20.2‰ to +36.8‰, with an average value of +30.0‰ (n = 27). These results suggest that sulfur is predominantly derived from the thermochemical sulfate reduction of marine sulfate. The crush‐leach analyzed solute data of fluid inclusions in sphalerite show the ore‐forming fluids have Cl/Br molar ratios range from 118 to 384, and Na/Br molar ratios from 39 to 160 (n = 8). These Cl/Br ratios of hydrothermal fluid are much lower than those of seawater (657 to 564), but are consistent with bittern brines through early halite precipitation. We propose that ore‐forming fluids are mainly derived from evaporitic basin brines, which leached base metals from the basement and/or country rocks. The brine then migrated to the basin margins through clastic rocks of basement and then precipitated sulfides by thermochemical sulfate reduction.

Conditions for the formation sellaite in saline deposits

The conditions for precipitation of magnesium fluoride (sellaite) from seawater with salinity of 35–105‰ were experimentally determined. It was established that precipitation of MgF2 at salinity of 35, 70, and 105‰ occurs at the concentration of dissolved fluorine above 37, 46, and 51 mg/l, respectively. In isolated evaporitic basins, the fluorine concentration required for the formation of sellaite is not achieved at all stages of the evaporation of seawater. It is assumed that high concentration of fluorine sufficient for the precipitation of sellaite arise as a result of the combined effect of evaporation and additional inflow of this element into evaporitic basins with river runoff or/and the release of coprecipitated and adsorbed fluorine during of postsedimentary recrystallization of salt minerals.