Search

Thick‐bedded halite sequences in the geological record are characterized by lateral variations, reflecting spatiotemporal variations in environmental forcing. Although temporal variations have been examined over seasonal scales or longer durations, there is a paucity of information regarding the dynamics of halite deposition at shorter durations of days and hours. Additionally, the influence of water discharges and surface salinity gradients remains poorly understood. Here, for the first time, in situ, hourly to weekly halite accumulation rates were measured on the Dead Sea floor (ca 20 m water depth), the only modern deep and hypersaline water body. Novel underwater photography methods were developed to directly observe halite precipitation at the lake floor, coeval with monitoring of the environmental drives, i.e. evaporation, meteorological and limnological conditions. Two fundamental environments were explored: a diluted plume environment arising from spring discharge; and a mixed hypersaline environment. The focus was on deposition during winter when the halite accumulation rate is highest, and the relationship between evaporation and halite accumulation is most straightforward since the water column is vertically uniform. Significant spatial variations in halite accumulation were found between the two environments, along with hourly variations in each environment. In the mixed hypersaline environment, over intra‐diurnal timescales, evaporation plays a more significant role in halite precipitation, whereas temperature has a greater impact on seasonal changes. In the diluted plume environment, the stability of the buoyant plume controls the rate of halite deposition; during windstorms, the plume is stirred, with higher surface water salinity and higher rate of halite accumulation. However, under calm winds, the plume is stable, with diluted surface water, and the rate of halite accumulation is a few times lower. Following these new findings, the implications for the interpretation of halite deposits are discussed. [ABSTRACT FROM AUTHOR]

Abstract\nKEY POINTSThe presence or absence of porphyritic textures in host rocks has no meaning for the genesis of ‘porphyry’ deposits. ‘Magmatic’ quartz, intergrown with K-feldspar and associated with some porphyry mineralisation, is unequivocally hydrothermal. Experiments show that magmas cannot carry concentrations of Cl required to yield fluids that can deposit the metals in porphyry Cu–Au deposits, and this is substantiated by the Cl concentrations in fluid inclusions in both mafic and silicic igneous rocks. Other experiments show that magmas generally have lower Cu concentrations than average crustal rocks. Igneous fractionation cannot produce melts with the required Cl or metal contents. Experiments also show that, if highly saline brines (or halite deposits) were to have been present during crustal melting, the magmas produced would have mineralogical and chemical characteristics most unlike the rocks that commonly host porphyry mineralisation. The metals in porphyry deposits must come from the medium- to far-field wall rocks and were most likely precipitated in veins when the host rocks underwent brittle fracture and fluid decompression. While still cooling, completely solid intrusive bodies can act as thermal eyes in a terrane, setting up hydrothermal circulations with flow toward the intrusions and upward toward shallower levels. The idea that precursor batholiths might be responsible for the supply and concentration of metals and Cl is untenable for numerous reasons. What applies to shallow igneous systems also applies to deeper ones. Thus, if magmas cannot carry the required concentrations of Cu and Cl, this applies to the seen as well as the unseen and potentially non-existent. Economic mineral deposits everywhere represent exceptional phenomena, so it seems likely that there is also something systematically exceptional about the sources of the necessary Cl in fluids that form porphyry deposits. At present, that source remains unidentified, but the possible role of evaporitic rocks needs to be explored.Porphyritic host intrusions are not the sources of the metals, and quartz–K-feldspar intergrowths that, in some cases, host the mineralisation are hydrothermal, not igneous.Magmas cannot readily produce the high-salinity fluids required to carry and deposit the metals in porphyry deposits.Igneous fractionation cannot enrich magmas significantly in the metals of porphyry deposits.The same principles apply to any igneous host rocks (‘porphyries’) and any postulated, deeper, precursor batholiths.There is something systematically exceptional about the source/s of the necessary Cl to form these deposits, and this ought to be the focus of future research. [ABSTRACT FROM AUTHOR]

The lake‐basin‐type model classified the stratigraphic record of ancient lake systems according to rates of potential accommodation relative to sediment + water supply. The model convolved all modes and paths of water supply (direct fall, surficial, subsurface) with amounts and types of sediment supply (clastic, biogenic, chemical) into a single basin‐filling volume term (sediment + water); its major strength was its widespread applicability. This was supported by subsequent investigations confirming the utility of this approach, but it also revealed some important limitations due to simplifications in the original model. The model has been expanded here to address all inland waters (lakes, ponds, wetlands, playas) as well as adding two major subdivisions of the sediment + water term: (1) water supply paths and (2) the volume of water supply relative to sediment supply. Water supply flow paths in the subsurface are subdivided into 'throughflow', 'recharge' and 'discharge'. Each of these groundwater hydrology states can be defined quite precisely by the ratio of net outflow to inflow, from persistently open to consistently closed. These paths can be deciphered using stable carbonate and oxygen isotope composition of primary lacustrine limestones, detailed sedimentology, stratigraphy, palaeontology and mineralogy. Distinguishing water supply paths provides additional insights into playa systems and the occurrence and character of evaporites and carbonates. The volume ratio of water to sediment supply most directly influences the water depths of lakes, ponds and wetlands, which affect water body hydrodynamics and ecosystem behaviour as well as the details of stratal stacking and depositional sequences. It helps fine‐tune estimates of the distribution of sediment texture, bedding, composition and organic matter content. The aim of this contribution is to address questions about the fundamental types of inland water bodies and to explain the new lake‐basin subtypes and provide examples that illustrate their potential to enable higher‐resolution, robust analysis of inland water systems and their stratigraphic records. [ABSTRACT FROM AUTHOR]

Large evaporite deposits, reaching several hundreds of metres of thickness, occur in many basins of our planet but remain poorly understood due to the absence of modern analogues. The origin of ancient evaporites and their highly variable sedimentation rates are often debated and ambiguous. The Danakil rift basin in northern Afar (Ethiopia) features several hundreds of metres of evaporites with deposition still continuing today and, as such, represents a unique modern analogue for older thick evaporite deposits. This study focuses on the multi‐proxy analysis of a 625 m long core from the central part of the basin. The core record, dominated by halite (ca 60%) with subordinate clastic sediments (ca 35%) and potash minerals (ca 5%) reveals, for the first time, the Late Pleistocene to Recent geological and environmental history of the basin. Sediments experienced restricted marine conditions after the last Late Pleistocene marine incursion in the basin, followed by a hypersaline stage leading to the near‐desiccation of the basin with the deposition of thick halite and potash deposits. Subsequent recycling of marginal halite deposits by meteoric waters in lacustrine and salt pan environments significantly increased the evaporite thickness in the subsiding central part of the basin. These findings have implications for the understanding of older thick evaporite deposits that formed in similar depositional settings. They show that several hundred of metres of evaporite can form in less than 128 kyr by evaporation of meteoric and seawater following a single marine flooding of the basin. [ABSTRACT FROM AUTHOR]

The Zagros Fold and Thrust Belt (ZFB) in southwestern Iran emerges as a geological marvel, defined by series of compact anticlines and synclines that the NW–SE trending structures of the Zagros belt. This unique configuration designates the ZFB as the dynamic boundary of the Arabian platform, shaped by the forces of nature. Over time, sedimentation in the expansive basin led to a gradual transformation, with folds originally oriented differently nowfolds axial line inclining southwestward, revealing a progressive shift in fold axial planes. This article presents a pioneering tectono-stratigraphic examination of Miocene Formations in the Fars and Bandar Abbas Hinterland, Southern Iran. The study meticulously explores five locations—Bastak, Taghdis-e Bahar, Dasht-e Arzhan, Saedi Mountain, and Yasuj—analyzing stratigraphic sections of the Miocene Formation. The Isopach map exposes variations in Miocene Formation thicknesses across these sites. In the Arjan plain, significant facies change unfolds, transitioning from Gachsaran Formation's evaporitic sedimentary rocks to Rzak Formation's marine sedimentary rocks and Asmari Formation's calcareous rocks along a northwest–southwest border. These facies change correlates intricately with subtle movements of fault zones—Kareh–Bas, Sabzpooshan, Sarvestan, and Kazerun. The tectono-stratigraphic journey unveils a profound connection between changes in sedimentary basin depth and nuanced alterations in sedimentary rocks' facies, orchestrated by the interplay of various basement faults, some following the Arabian trend, others aligning with the majestic Zagros trend—a symphony of geological forces shaping the Miocene narrative in the Fars and Bandar Abbas Hinterland. [ABSTRACT FROM AUTHOR]

Abstract The lake‐basin‐type model classified the stratigraphic record of ancient lake systems according to rates of potential accommodation relative to sediment + water supply. The model convolved all modes and paths of water supply (direct fall, surficial, subsurface) with amounts and types of sediment supply (clastic, biogenic, chemical) into a single basin‐filling volume term (sediment + water); its major strength was its widespread applicability. This was supported by subsequent investigations confirming the utility of this approach, but it also revealed some important limitations due to simplifications in the original model. The model has been expanded here to address all inland waters (lakes, ponds, wetlands, playas) as well as adding two major subdivisions of the sediment + water term: (1) water supply paths and (2) the volume of water supply relative to sediment supply. Water supply flow paths in the subsurface are subdivided into ‘throughflow’, ‘recharge’ and ‘discharge’. Each of these groundwater hydrology states can be defined quite precisely by the ratio of net outflow to inflow, from persistently open to consistently closed. These paths can be deciphered using stable carbonate and oxygen isotope composition of primary lacustrine limestones, detailed sedimentology, stratigraphy, palaeontology and mineralogy. Distinguishing water supply paths provides additional insights into playa systems and the occurrence and character of evaporites and carbonates. The volume ratio of water to sediment supply most directly influences the water depths of lakes, ponds and wetlands, which affect water body hydrodynamics and ecosystem behaviour as well as the details of stratal stacking and depositional sequences. It helps fine‐tune estimates of the distribution of sediment texture, bedding, composition and organic matter content. The aim of this contribution is to address questions about the fundamental types of inland water bodies and to explain the new lake‐basin subtypes and provide examples that illustrate their potential to enable higher‐resolution, robust analysis of inland water systems and their stratigraphic records.

Focusing on the late Miocene succession stratigraphic successions including the evaporite deposits from the Messinian salinity crisis (MSC) of the Adriatic foreland basin, a revision of available boreholes and seismic data allowed us to recognize the presence of reservoirs and seals systems that can be considered of potential interest for the storage of natural and synthetic gas. Potentially good reservoir sites can be found where porous rocks referable to siliciclastic turbiditites (Marnoso‐arenacea and Laga Fms) or shallow‐water carbonates (Bolognano Fm) preferentially involved in anticlinal structures and covered by thick MSC evaporites, which may represent effective reservoir seals. The integrated reconstruction of porous rocks distribution and facies, thickness, and lateral continuity of the overlying evaporites, allows the identification and zonation of geological settings in the Adriatic foredeep, backbulge and foreland with peculiar stratigraphy and deformations, only partially considered before, that may deserve consideration in the research of potential gas storage sites. [ABSTRACT FROM AUTHOR]

The Qaidam Basin is the largest sedimentary basin within the Tibetan Plateau, with up to ∼15-km-thick deposits accumulated in the Cenozoic. Understanding how it deformed in response to the far-field effects of India-Eurasia collision is critical to improving our knowledge of the mechanism underlying northward plateau growth. Unlike typical compressional basins, where upper-crustal deformation concentrates at their margins, the Qaidam Basin features the development of many NW- to WNW-striking folds across the entire basin. Why crustal shortening occurred in the interior of Qaidam Basin, ∼100 km away from the margins, together with the underground geometries beneath these folds, remains unknown. Herein, based on newly acquired three- and two-dimensional (3-D and 2-D) seismic reflection data, borehole logging, and scaled physical analog modeling, we investigated the geometries, kinematics, and formation mechanisms of the folds within the interior of Qaidam Basin. For the first time, we reveal three local weak layers in the Lulehe, Upper Xiaganchaigou, and Shangyoushashan Formations, respectively. They consist mainly of mudstone intercalated with evaporites and limestones, and they have different spatial distributions that are likely confined by major faults and folds. These mechanically weak layers became locally thickened or thinned in response to tectonic loading and/ or facilitated detachment slip to form many décollement folds that were observed at the surface. The shallow deformation above the weak layers is largely decoupled from underlying basement-involved faulting and folding, which mostly terminate upward in these weak layers. Analog modeling results suggest that the lowermost and widely distributed décollement layer in the Lulehe Formation likely facilitated long-distance rapid propagation of deformation into the basin interior. In sum, our study highlights the significance of multiple weak layers during Cenozoic deformation in the Qaidam Basin interior. [ABSTRACT FROM AUTHOR]

The study presents a review of the Geology of the Senegalo-Mauritanian (S-M) sedimentary basin with a glance on stratigraphy, tectonic evolution, and integrated petroleum systems. The S-M basin is a typical Mesozoic-Cenozoic passive margin which opened westward from the Northwest African craton into the Atlantic Ocean. The basin overlies a Paleozoic sequence which represents part of the Taoudeni basin. Rifting and tectonic movements associated with the breakup of Gondwana and the formation of the Atlantic Ocean began in the Triassic and have led to a subdivision of the basin into three stages: pre-rift (Proterozoic-Paleozoic), syn-rift (Late Triassic-Middle Jurassic), and post-rift (Middle Jurassic-Present). Pre-rifting phase, made of sediments deposited between the Precambrian and Devonian, is mainly continental detrital rocks. The main deposits of the syn-rift stage are Triassic evaporites and Jurassic volcanic intrusion from the Central Atlantic Magmatic Province (CAMP). The post-rift segment consists of an Upper Jurassic-Lower Cretaceous carbonate platform overlain by a predominantly progradation and transgressive Cretaceous-Tertiary clastic sequence, up to 12,000 m thick in places. The S-M basin exhibits oil and gas potential. Indeed a total of three petroleum systems exist in the basin: the Lower Paleozoic Petroleum System (LPPS), the Subsalt Petroleum System (SSPS), and the Cretaceous-Tertiary Petroleum System (CTPS). Previous source rock analyses have shown a good quantity of total organic content (TOC) and type I kerogen; type I, II, and III for the LPPS and CTPS, respectively. The main reservoirs comprised fractured sandstone of Cambrian to Ordovician and Devonian, with good porosity up to 20%, karstified Oligocene limestone, and Maastrichtian and Miocene sandstones. The primary seals include the Upper Cretaceous and Tertiary marine mudstone and shale for these petroleum systems. Both stratigraphic and structural traps were derived from seismic profiles and included growth faults, slope truncation, turbidite-related traps, salt-related structures, carbonate bank deposits, and structures related to volcanism. Preserved extensional structures before the rifting and especially normal faults along the Paleozoic section have served as migration pathways for hydrocarbon in the Southern sub-basin. [ABSTRACT FROM AUTHOR]

The geochemical cycle of strontium is intimately linked to the long-term cycle of carbon, for instance, through their mutual involvement in continental weathering and marine carbonate sedimentation. Stable strontium isotopes (δ 88/86Sr) have recently emerged as a valuable tool, complementing radiogenic Sr isotope ratios (87Sr/86Sr), to further our understanding of the Sr cycle. Stable strontium isotopes are sensitive to both the sources of strontium (e.g., silicate versus carbonate weathering) and to earth surface processes (e.g., mineral precipitation from solution). Gypsum, a common evaporitic mineral, precipitates directly from seawater and holds the potential to serve as a marine archive for studying the elemental cycle of Sr. In addition, the impact of gypsum formation on the marine strontium isotope budget has been a matter of speculation due to the limited information on the isotope fractionation of Sr in gypsum. Here, we explore the behavior of strontium isotopes during gypsum precipitation and provide the first-order estimates of the associated isotope fractionation. Gypsum was produced through the evaporation of natural seawater in a series of experiments. Strikingly, in contrast to the fractionation of Ca isotopes into gypsum, as well as Sr isotopes into carbonate minerals, heavier isotopes of Sr are preferentially incorporated into gypsum with an estimated average isotope fractionation of ∼0.20‰ (range between 0.14–0.27‰). The variability in the observed experimental isotope fractionation is suggested to be the result of admixture of aragonite in the precipitate, surface-specific rate-controlled effects, and/or mineral occlusion (i.e., capturing of unfractionated Sr). Despite these complications, gypsum has the potential to effectively resolve significant variations in past seawater δ 88/86Sr following the suggested approach, which involves careful sample selection based on radiogenic Sr data, avoidance of aragonite admixtures, and ensuring a large dataset of coeval samples. Mass balance considerations indicate that the formation of giant evaporite deposits has the potential to induce only minimal, short-term, alterations in seawater δ 88/86Sr, largely not discernible due to the uncertainties in the existing Sr isotope records. Finally, we find that weathering of 88Sr-enriched marine gypsum exposed on the continents is likely a significant source of Sr to the ocean. This Sr source can explain at least 25% of the apparent mismatch between the observed global riverine δ 88/86Sr and that estimated from the weathering of carbonate and silicate lithologies only. [ABSTRACT FROM AUTHOR]

Reactive transport modeling (RTM) is an emerging method used to address geological issues in diagenesis research. However, the extrapolation of RTM results to practical reservoir prediction is not sufficiently understood. This paper presents a case study of the Eocene Qaidam Basin that combines RTM results with petrological and mineralogical evidence. The results show that the Eocene Xiaganchaigou Formation is characterized by mixed siliciclastic-carbonate-evaporite sedimentation in a semiclosed saline lacustrine environment. Periodic evaporation and salinization processes during the syngeneticpenecontemporaneous stage gave rise to the replacive genesis of dolomites and the cyclic enrichment of dolomite in the middle-upper parts of the meter-scale depositional sequences. The successive change in mineral paragenesis from terrigenous clastics to carbonates to evaporites was reconstructed using RTM simulations. Parametric uncertainty analyses further suggest that the evaporation intensity (brine salinity) and particle size of sediments (reactive surface area) were important rate-determining factors in the dolomitization, as shown by the relatively higher reaction rates under conditions of higher brine salinity and fine-grained sediments. Combining the simulation results with measured mineralogical and reservoir physical property data indicates that the preservation of original intergranular pores and the generation of porosity via replacive dolomitization were the major formation mechanisms of the distinctive lacustrine dolomite reservoirs (widespread submicron intercrystalline micropores) in the Eocene Qaidam Basin. The results confirm that RTM can be effectively used in geological studies, can provide a better general understanding of the dolomitizing fluid-rock interactions, and can shed light on the spatiotemporal evolution of mineralogy and porosity during dolomitization and the formation of lacustrine dolomite reservoirs. [ABSTRACT FROM AUTHOR]

The geological structure of the evaporite formation in the Amu Darya syneclise is a complex system that provides valuable insights into the region's geological history and economic potential. The study aims to analyse the main characteristics of the geological structure of the evaporite formation in the Amu Darya syneclise to expand knowledge of the geological and environmental history of the region and to identify the potential of these deposits for various applications. The methods used for this study included geological mapping, mineralogical analysis, stratigraphic analysis and geochemical research. The study identifies three distinct water-bearing horizons within the evaporite complex: Sharaplinsky, Yolotan, and Sakar. These horizons exhibit varying characteristics in terms of composition, water content, and distribution across the basin. Geomorphological manifestations, such as salt lakes and salt marshes, play a crucial role in understanding the ecological and geological history of the region. The evaporite formation holds substantial economic importance, hosting valuable resources including salts, oil, and gas. This geological structure supports regional industrial development, job creation, and overall economic growth. The study also highlights the need for further research into the geology and geomorphology of the Amu Darya syneclise to better understand the formation and dynamics of evaporite deposits and their role in the region's current environmental and economic sectors. The study emphasizes the need for efficient technologies and methods for resource extraction and management to ensure sustainable development and minimize environmental impact. The research provides crucial data for optimizing mineral extraction strategies and developing effective natural resource management approaches. It underscores the importance of understanding the geological structure for sustainable ecological and economic development in the region. The practical significance of this study is a basis for developing more effective natural resource management strategies based on an understanding of the geological processes of evaporite sedimentation in the Amu Darya syneclise, which is key to the sustainable development of the region's ecological and economic systems. [ABSTRACT FROM AUTHOR]

Under nonequilibrium conditions, inorganic systems can produce a wealth of life-like shapes and patterns which, compared to well-formed crystalline materials, remain widely unexplored. A seemingly simple example is the formation of salt deposits during the evaporation of sessile droplets. These evaporites show great variations in their specific patterns including single rings, creep, small crystals, fractals, and featureless disks. We have explored the patterns of 42 different salts at otherwise constant conditions. Based on 7,500 images, we show that distinct pattern families can be identified and that some salts (e.g., Na2SO4 and NH4NO3) are bifurcated creating two distinct motifs. Family affiliations cannot be predicted a priori from composition alone but rather emerge from the complex interplay of evaporation, crystallization, thermodynamics, capillarity, and fluid flow. Nonetheless, chemical composition can be predicted from the deposit pattern with surprisingly high accuracy even if the set of reference images is small. These findings suggest possible applications including smartphone-based analyses and lightweight tools for space missions. [ABSTRACT FROM AUTHOR]

During the Early Cretaceous, massive evaporite accumulations formed in the opening South Atlantic. However, the depositional model of these salts is still poorly constrained at the scale of the West African margin. The present study focuses along the proximal domain of the south Gabon‐Congo‐Cabinda margin and is based on (i) log interpretations of 246 wells crossing undeformed to weakly deformed evaporite intervals and (ii) a structural characterization of the basement. The evaporites show 11 regional evaporite depositional cycles (CI–CXI) bounded by meter‐thick shale beds. The cycles display alternating meter‐scale carnallite‐halite beds that can be correlated over several hundred kilometres, and CVI, CVII, CVIIIa and CX culminate in localized tachyhydrite accumulations. Cross section correlations and isopach maps help to understand the palaeogeographical evolution of each cycle and depositional environments that evolved from relatively deep at the base of cycles, to very shallow at their top. CI formed a mosaic of halite‐prone depocenters deposited in pre‐salt topographic relief. CII and CIII were deposited uniformly over a flattened basin in a highly extended brine pond. From CIV to CVIIIa, the stratigraphic architecture of the salts was shaped by freshwater inflow sourced from the north and possible basement movements. This setting, together with an increased confinement of the proximal domain from the distal one with basin drawdown, favoured the development of depocenters with perennial subaqueous conditions and extreme salinities, in which more than 70 m of tachyhydrite accumulation could locally be preserved. From CVIIIb to CXI, the basin returned to a flat depositional setting without well‐developed depocenters and with increasing subsidence westwards. Marine influx increased starting from CX, allowing the deposition of sulphate beds. The salt section is capped by anhydrite deposits interbedded with clastic and dolomite, before the final marine invasion of the basin. For the first time, this study provides a large‐scale depositional tectonostratigraphic setting of the Aptian salts in the proximal domain of the West African margin. The results are of interest for K‐Mg salts exploration resources in the Aptian and pave the way for further investigation of the salt depositional environment in the distal domain of the margin. [ABSTRACT FROM AUTHOR]

AbstractThe Paleoproterozoic Mârmorilik Formation in the Karrat basin of West Greenland hosts the Black Angel Zn–Pb deposit. Chlorine-rich scapolite, zones with vuggy porosity and quartz nodules in the ore-bearing marble are herein interpreted to represent metamorphosed, vanished, and replaced evaporites, respectively. Mineralization is closely associated with anhydrite with δ34S values (5.2–12.6‰) broadly comparable to published values for Paleoproterozoic seawater sulfate. Considering the fundamental attributes of the mineralization and host sequence, a Mississippi Valley-type (MVT) model is the most obvious explanation for mineralization. Overlying the ore-bearing sequence are organic-rich semipelites and massive calcitic marbles, which may have served as seals for hydrocarbon or reduced sulfur and acted as chemical traps for deposition of the sulfidic ore. The Mârmorilik Formation contained an interlayered sulfate-rich evaporite-carbonate sequence, a common setting for MVT deposits in the late Neoproterozoic and Phanerozoic, but unique among the few known MVT deposits in the Paleoproterozoic. This ca. 1915 Ma evaporite-carbonate platform is younger than sulfate evaporites deposited during and immediately after the ca. 2220–2060 Ma Lomagundi carbon isotope excursion and records a significant seawater sulfate level during a time interval when it was assumed that it had been too low to form extensive evaporite deposits. Therefore, MVT and clastic-dominated (CD) Zn–Pb deposits in the geological record might progressively fill the apparent gap in marine sulfate evaporites and provide unique insights into Proterozoic seawater sulfate level. Considering the sequence of tectonic events that affected the Karrat basin, the mineralization took place between Nagssugtoqidian collision (

Due to the pioneering work of Alexander Klimchouk (2007), hypogene karst is now recognized as being complex and extensive throughout Permian strata of the greater Delaware Basin in West Texas and southeastern New Mexico (USA). Klimchouk heavily influenced our current understanding of hypogene speleogenesis in the Permian Ochoan Castile Formation where we now recognize diverse hypogene manifestations that include verticallyextensive breccia pipes, laterally-extensive blanket breccias, morphologically-varied caves, diagenetically-altered sulfates, and unique venting structures. Underlying Bell Canyon strata provide the transmissive zone for delivery and removal of solutionally aggressive fluids to the conformably overlying Castile evaporites. Current speleogenetic models indicate that hypogene karstification in Castile evaporites began in the early Neogene in conjunction with regional uplift and tilting. Since that time, hypogene processes have shifted eastward across the Delaware Basin in conjunction with the eastward migration of the Pecos River. Surface denudation has exposed updip regions of the Castile Formation to the west creating the Gypsum Plain where hypogene karst is exposed to epigene processes and associated overprinting. Today, the Gypsum Plain continues to evolve with both hypogene and epigene processes still active within the Delaware Basin. [ABSTRACT FROM AUTHOR]

The thick late syn‐ to early post‐rift shallow water evaporites in the most distal part of wide rifted margins is paradoxical with the deep depression at crustal breakup time predicted by isostatically compensated lithospheric thinning. Elevation of the distal margin and water depth during deposition of the late syn‐rift evaporites in the central South Atlantic are not well constrained and remain to be quantified. We use forward 2‐D thermo‐mechanical modeling coupled with melt prediction and surface processes to assess the contribution of lithospheric and mantle processes on the distal margin topography and subsidence history during continental rifting. Models show that (a) counter‐flow of depleted lower lithospheric mantle during rifting explains the magma‐poor nature of these margins and (b) weak crust and syn‐rift sediment control the wide crustal necking and subsidence history of the distal margin. Integration of our modeling results with quantified geophysical and geological observations suggests that (a) base level was down to −600 m below present‐day global sea level (bsl) during distal margin formation in the Aptian before sag and evaporite deposition, (b) base level was about −300/−400 m bsl at the end of evaporite deposition, and (c) scenarios with a fixed shallow base level (−400 m bsl) or with an increasing base level from an initially deep position (−1,600 m bsl) during evaporite deposition can both fit the observed evaporite distribution. However, erosional features along the base of evaporites suggest a deep initial base level. Plain Language Summary: The opening of the Atlantic Ocean contributed to the fragmentation of the Pangaea supercontinent 100–200 millions years ago. Water depth in the basins formed during this process is not well constrained while it is fundamental to understand their environmental conditions. For instance, in the central South Atlantic that comprises the west African Gabon, Congo, and Angola margins and their conjugates along the Brazilian margin, a giant evaporite basin deposited during continental breakup in shallow water formed very far from the continent. In this study, we compiled data along these margins and used 2‐D numerical models to show that an initially deep basin isolated from global ocean can provide the conditions necessary for this giant evaporite basin to be deposited. Key Points: Weak lower crust and syn‐rift sedimentation rate are first‐order controls on the formation and geometry of wide distal rifted marginModeling suggests a base level ∼−600 m below present‐day global sea level (bsl) during the distal margin formation before evaporite depositionModeling suggests a base level of ∼−300/−400 m bsl at the end of evaporite deposition [ABSTRACT FROM AUTHOR]

The depositional history of the Bonneville Salt Flats, a perennial saline pan in Utah's Bonneville basin, has poor temporal constraints, and the climatic and geomorphic conditions that led to saline pan formation there are poorly understood. We explore the late Pleistocene to Holocene depositional record of Bonneville Salt Flats cores. Our data challenge the assumption that the saline pan formed from the desiccation of Lake Bonneville, the largest late Pleistocene lake in the Great Basin, which covered this area from 30 to 13 cal ka BP. We test two hypotheses: whether climatic transitions from (1) wet to arid or (2) arid to wet led to saline pan deposition. We describe the depositional record with radiocarbon dating, sedimentological structures, mineralogy, diatom, ostracode, and portable X-ray fluorescence spectrometer measurements. Gypsum and carbonate strontium isotope ratio measurements reflect changes in water sources. Three shallow saline lake to desiccation cycles occurred from >45 and >28 cal ka BP. Deflation removed Lake Bonneville sediments between 13 and 8.3 cal ka BP. Gypsum deposition spanned 8.3 to 5.4 cal ka BP, while the oldest halite interval formed from 5.4 to 3.5 cal ka BP during a wetter period. These findings offer valuable insights for sedimentologists, archaeologists, geomorphologists, and land managers. [ABSTRACT FROM AUTHOR]

Triassic evaporites represent the regional décollement of the Pyrenees and form two salt provinces north and south of the South Pyrenean Central Salient (SPCS). We present an updated Bouguer and residual Bouguer anomaly map built upon the homogenization of available gravity data of the SPCS together with four new and representative cross‐sections, constrained by geological data acquired in the field, seismic, well, and gravity data (gravity forward modeling). Gravity anomaly maps and cross‐sections are used to characterize the present‐day uneven distribution of Triassic evaporites. Outcropping Triassic evaporites is not necessarily associated with an underlying evaporite accumulation and the absence of it at surface does not involves its non‐existence at depth. Northwest of the salient, a major accumulation of Triassic evaporites floors a thick syn‐orogenic Upper Cretaceous basin. South of it, Triassic rocks core salt‐detached anticlines related to the Pyrenean orogeny. Along the southernmost (and youngest) thrust sheet of the salient, diapirs, and evaporite accumulations are associated with a salt‐inflated area. Plain Language Summary: Gravity depends on the density of the rocks under our feet. In the South Pyrenean Central Salient (SPCS), an accurate measurement of gravity allows us to recognize gravity anomalies related to low density rocks, such as the Middle‐Upper Triassic evaporites, and map their distribution. Among sedimentary rocks, evaporites have a particular behavior when deformed under geological forces: they flow. This characteristic determines a particular deformation style of the mountains. Characterize the present‐day distribution of Triassic evaporites helps to reconstruct the geological history of the SPCS. Despite the apparent asymmetry of the salient, Triassic evaporites are unevenly distributed and specially accumulated to the northwest and southwest conforming evaporite inflated areas. Key Points: Gravity anomalies help to assess the distribution of Triassic evaporites in the South Central Pyrenean SalientSeismically and gravity‐constrained sections permit a further interpretation of gravity anomaliesInflated salt occurs mainly to the northwest and southeast of the salient, along the northernmost and southernmost thrust sheets [ABSTRACT FROM AUTHOR]

We present a detailed description of the Middle Miocene (Chokrakian and Karaganian) depositional environments of the Eastern Paratethys Sea in the southern Caspian Basin. The Chokrakian comprises a 500-m-thick succession of marls and sandstones, termed herein Javarem Formation, which formed in coastal marine environments. The lower Javarem Fm. Developed in calm lagoonal settings, indicating frequent exposure under a predominantly dry climate and occasional formation of evaporites. The upper part of the Javarem Fm. Is characterized by mixed siliciclastic-carbonatic sediments with ooids of agitated, warm, hypersaline tidal shoals. Above follows the about 500-m-thick Vashi Formation, which is correlated with the Karaganian regional stage. The formation is characterized by an alternation of reddish marls with thick sandstones and gravel beds with terrestrial gastropods, ubiquitous pedogenetic features and occasional root horizons. The depositional environment is interpreted as a floodplain with gravelly channels of an arid to semiarid climate. The successions of the Javarem and Vashi formations capture the transition from the shallow marine Iranian shelf into the northern Iranian coastal plain around 13.8 Ma, following the onset of the Miocene Climate Transition and the coinciding global sea level drop around the Langhian/Serravallian boundary. [ABSTRACT FROM AUTHOR]

One of the most remarkable features of the central Northern Calcareous Alps (Eastern Alps, Austria) is the widespread presence of Upper Triassic deep-water carbonates (the Hallstatt facies) and Permo-Triassic evaporites resting on deep-water Middle Jurassic strata and their underlying Upper Triassic shallow-water carbonate platform successions. The Hallstatt facies and accompanying evaporites have been classically interpreted to originate either from a location south of the time-equivalent carbonate platforms, or to have been deposited in deeper water seaways within the broad platform domain. To date, this dispute has been addressed mostly through the analysis of Triassic and Jurassic facies distribution in map view, which, however, is subject to some degree of ambiguity and subjectivity. In this contribution we present, for the first time, sequentially restored regional cross-sections through the central Northern Calcareous Alps to understand the implications of the contrasting paleogeographic models. We present (a) an interpretation based on a highly allochthonous origin of the Triassic deep-water units and (b) an interpretation based on their relative autochthony in which we incorporate the potential influence of salt tectonics in the central NCA. The restored cross-sections provide a framework within which the alternative scenarios and their paleogeographic implications can be better understood. Through this analysis we propose that salt tectonics in the central NCA can provide a valid explanation for apparent inconsistencies in the relative autochthony scenario and thus constitutes a reasonable alternative to the currently accepted allochthony scenario. [ABSTRACT FROM AUTHOR]

The Angouran deposit (19.3 Mt at 23.4% Zn and 4% Pb) is the second-largest Zn-Pb deposit in Iran. The deposit is hosted in a Neoproterozoic-Cambrian marble-schist sequence within a breccia pipe in a domal structure, with sulfide mineralization under low-temperature hydrothermal conditions (<200 °C). The features of the ore-hosting breccias are similar to known halokinetic diapir breccias in the world but evaporite minerals are subtle. The common types of breccia clasts in the Angouran breccia pipe include a matrix-supported angular clast (float breccia) with highly variable sizes and orientations and exotic volcanic clasts. The volcanic clasts were derived from the underlying Miocene volcanic rocks, evidenced by the consistent petrography and zircon U-Pb ages dated at 20-19 Ma. Abundant smithsonite pseudomorphs after anhydrite and anhydrite inclusions within sphalerite and pre-ore marcasite in the breccia matrix indicate that the breccia pipe contains abundant anhydrite prior to the Zn-Pb mineralization. The enrichment of evaporite is also supported by the occurrence of considerable double-terminated quartz crystals that contain spherical and tabular carbonate inclusions and anomalously high Li, Na, and K concentrations, relatively high B concentration, and high d18O values (up to 28.3‰). These observations suggest the Angouran deposit formed in a former halokinetic diapir breccia pipe. The halokinetic diapirism was possibly triggered by thrust loading of the marble-schist sequence over the Miocene evaporite beds during the Arabia-Eurasia continental collision. Halokinetic structures elsewhere in the Angouran region warrant this consideration. Most of the evaporite minerals in the breccia pipe were dissolved and replaced before and/or during subsequent Zn-Pb sulfide and smithsonite mineralization events. This study provides a good example for the identification of vanished evaporites, halokinetic structure, and associated Mississippi Valley-type mineralization. [ABSTRACT FROM AUTHOR]

Chloride is the most important anion in ore-forming hydrothermal fluids, and chlorine isotopes are therefore potentially sensitive tracers of the origin and evolution of ore-forming fluids. However, they remain a relatively under-utilized tool in ore deposit geochemistry due to the lack of knowledge of chlorine isotope fractionation during ore-forming processes. Using first-principles density functional theory, this study estimates chlorine isotope fractionation factors for various ore-forming processes. All metal-Cl complexes in hydrothermal fluids are enriched in 37Cl compared to chloride ions, but the change in δ37Cl of the fluid trapped in ore minerals is small after the destabilization of metal-chloride complexes during ore mineral deposition. In the precipitation of evaporite minerals from brine, the sequence of enrichment of the heavy Cl isotope (37Cl) is halite > carnallite > aqueous chloride > kainite > sylvite > bischofite. The results of this study agree with the experimental observations that progressive precipitation of halite from brine lowers the δ37Cl value of the residual fluid until the formation of K-Mg chlorides. In low-temperature deposits, δ37Cl values for fluid inclusions and minerals reflect those of the hydrothermal fluid provenance and the mixing of this fluids with saltwater or basinal brines. In high-temperature magmatic-hydrothermal ore deposits that undergo liquid–vapour phase separation, chlorine isotopes fractionate among phases of silicate melt, vapour and chloride-rich liquid. The considerable range in δ37Cl in fluid inclusions may also reflect fluid mixing and hydrothermal alteration. At ambient temperature, the δ37Cl values may reflect evaporative processes and, in the case of chemical weathering of metallic mineral deposits, may record the supergene enrichment of the metals. This study highlights the use of chlorine isotopes as a new tool for interpreting ore-forming processes. [ABSTRACT FROM AUTHOR]

Laguna Verde's dome‐shaped structures are distinctive formations within the Central Andes, displaying unique geomicrobiological features. This study represents a pioneering investigation into these structures, assessing their formation, associated taxa, and ecological significance. Through a multifaceted approach that includes chemical analysis of the water body, multiscale characterization of the domes, and analysis of the associated microorganisms, we reveal the complex interplay between geology and biology in this extreme environment. The lake's alkaline waters that are rich in dissolved cations and anions such as chloride, sodium sulfate, and potassium, coupled with its location at the margin of the Antofalla salt flat, fed by alluvial fans and hydrothermal input, provide favorable conditions for mineral precipitation and support for the microorganism's activity. Laguna Verde's dome‐shaped structures are mainly composed of gypsum and halite, displaying an internal heterogeneous mesostructure consisting of three zones: microcrystalline, organic (orange and green layers), and crystalline. The green layer of the organic zone is predominantly composed of Proteobacteria, Bacteroidetes, and Cyanobacteria, while the orange layer is mostly inhabited by Cyanobacteria. The results of the study suggest that oxygenic photosynthesis performed by Cyanobacteria is the main carbon fixation pathway in the microbial community, supported by carbon isotopic ratios of specific biomarkers. This finding highlights the important role played by Cyanobacteria in this ecosystem. [ABSTRACT FROM AUTHOR]

In the Late Permian Zechstein Sea of Central Europe, up to 2000 m of evaporitic rocks were deposited in at least four consecutive cycles. The age of these evaporitic rocks could not yet be precisely determined, because they are virtually fossil-free and do not contain radiometrically datable volcanic layers. A chemostratigraphic age of the succession can be determined by comparing 87Sr/86Sr ratios of marine gypsum and anhydrite to the worldwide marine strontium evolution curve. Unfortunately, published 87Sr/86Sr data of the Zechstein succession are characterized by frequent outliers towards higher ratios, making an age assignment challenging. The scatter in 87Sr/86Sr ratios might be induced by different processes like the contribution of meteoric water to the brine, in-situ Rb decay, or post-depositional hydrothermal or diagenetic overprint. Here, we present a dataset of 26 new gypsum and anhydrite 87Sr/86Sr ratios from drill cores situated at "Alter Stolberg" in the northernmost Thuringian Basin. Evaporites of the Werra-, Staßfurt-, and Leine cycles were sampled. The close proximity of the drillings allows a very accurate assignment of the stratigraphic position of each sample, so that trends and outliers in 87Sr/86Sr ratios can easily be recognized. While the entire Werra Formation obviously revealed non-marine 87Sr/86Sr ratios, the lowermost 87Sr/86Sr ratios in the Staßfurt and Leine Formations can be assumed to represent marine ratios and allow estimating a chemostratigraphic age of 257‒254 Ma. The combination of the 87Sr/86Sr data with the mineral composition of the samples suggests a contribution of meteoric water, probably river water, to the Zechstein Sea as the main reason for the observed increase in 87Sr/86Sr ratios. Additional in-situ Rb decay, related to the riverine input of clay minerals, cannot be excluded. Modelling the amounts of sea water and meteoric water in the brine indicates that 83‒99% of meteoric water would be necessary to explain the highest 87Sr/86Sr ratios observed in the Werra Formation. [ABSTRACT FROM AUTHOR]

The Ediacaran-Ordovician strata within three major marine basins (Tarim, Sichuan, and Ordos) in China are analyzed. Based on previous studies focusing on the characteristics of the Neoproterozoic-Cambrian strata within the three major basins (East Siberian, Oman, and Officer in Australian) overseas, the carbonate-evaporite assemblages in the target interval are divided into three types: intercalated carbonate and gypsum salt, interbedded carbonate and gypsum salt, and coexisted carbonate, gypsum salt and clastic rock. Moreover, the concept and definition of the carbonate-evaporite assemblage are clarified. The results indicate that the oil and gas in the carbonate-evaporite assemblage are originated from two types of source rocks: shale and argillaceous carbonate, and confirmed the capability of gypsum salt in the saline environment to drive the source rock hydrocarbon generation. The dolomite reservoirs are classified in two types: gypsum-bearing dolomite flat, and grain shoal & microbial mound. This study clarifies that the penecontemporaneous or epigenic leaching of atmospheric fresh water mainly controlled the large-scale development of reservoirs. Afterwards, burial dissolution transformed and reworked the reservoirs. The hydrocarbon accumulation in carbonate-evaporite assemblage can be categorized into eight sub-models under three models (sub-evaporite hydrocarbon accumulation, supra-evaporite hydrocarbon accumulation, and inter-evaporite hydrocarbon accumulation). As a result, the Cambrian strata in the Tazhong Uplift North Slope, Maigaiti Slope and Mazatag Front Uplift Zone of the Tarim Basin, the Cambrian strata in the eastern-southern area of the Sichuan Basin, and the inter-evaporite Ma-4 Member of Ordovician in the Ordos Basin, China, are defined as favorable targets for future exploration. [ABSTRACT FROM AUTHOR]

Natural subsidence sinkholes (according to Gutiérrez et alii, 2008, 2014; Parise 2019, 2022), both in carbonates and evaporites, represent a severe threat to man-made structures. Especially when bedrock is mantled and in urban areas, the identification and characterization of these phenomena is always challenging. For this reason, multidisciplinary and multi-technique approaches are recommended and in detail, the integrated use of geophysical techniques (Electrical Resistivity Tomography, Reflection and Refraction Seismic, Electromagnetometers and 2D Ground Penetrating Radar - GPR) and most recently developed 3D GPR is strongly suggested. Thanks to the Agreements signed between the University of Trieste and the Geological survey of the Friuli Venezia Giulia Region (NE Italy), since 2007 the researchers approached these issues in specific test site areas. From the studies in urban mantled evaporitic bedrock areas, emerged the supremacy of the 3D GPR jointly with reflection seismic, being the former able to identify with high accuracy and detail shallow deformations, and the latter the best approach to identify the thickness of cover materials, the morphology of the bedrock and the sinkhole location. [ABSTRACT FROM AUTHOR]

Engineering applications pose major challenge in designing structures that are safe, durable, and sustainable in various environmental situations. The slake durability index (SDI) test is commonly used to evaluate weak rock disintegration, such as evaporates, which are widely found in the Abu Dhabi area near the foundation levels, encountering construction challenges due to their disintegration. This study intends to provide insight into the disintegration characteristics of evaporitic rocks in the Abu Dhabi region under acidic and alkaline environmental conditions. Distilled water and groundwater which was collected from the study area is used as slaking fluids. As a result, rock blocks from the Abu Dhabi region, which is divided into four zones, were collected, and six sets of representative SDI test samples for each zone were prepared and tested using slaking fluids of pH values 2, 4, 6, 8, 10, and 12, as well as distilled water and groundwater. In addition, the macroscopic and microscopic (thin section, X-ray diffraction, X-ray fluorescence, and scanning electron microscopy) descriptions of representative samples from each zone were carried out. According to the findings, the overall average slakes durability weight loss of evaporates lies in the range of 60–72 wt% and could be classified as medium durably for Zones 1 and 4 under the basic environment, and for Zones 2 and 3 under the acidic environment. Thus, this study delivers the detailed explanation about the slaking characteristics of evaporitic rocks under various pH level conditions for engineers and decision makers to overcome degradability problems. [ABSTRACT FROM AUTHOR]

The durability and degradability of evaporitic rocks are always a critical concern in geological, civil, and geotechnical engineering applications, necessitating careful consideration for reliable, secure, and sustainable construction. This dataset is based on a comprehensive collection of geotechnical data involving both mechanical and physical properties as well as geochemical analyses for the evaporitic rocks in Abu Dhabi and its vicinity. The purpose of this dataset is to be an important source for construction professionals, engineers, and decision-makers in the region by providing basic insights into the challenges associated with building projects on and in evaporitic rocks. This data is obtained from extensive field investigations and laboratory analyses and will help to ensure that construction activities are carried out safely and efficiently when dealing with evaporitic rock formations. The prevalence of evaporitic rocks in Abu Dhabi highlights the importance of this geotechnical data compilation in facilitating informed decision-making and supporting safe construction.

Abstract In northern Switzerland, Middle Muschelkalk evaporites (Zeglingen Formation) were deposited under arid conditions in the southernmost part of the epicontinental Central European Basin during times of reduced inflow of sea water from the Tethyan realm. Because of their marginal position in the basin, direct and detailed correlation of Muschelkalk sediments of northern Switzerland with equivalent strata in interior parts of the basin is not straightforward. Based on detailed sedimentological logging of 640 m of drill cores from ten wells in northern Switzerland, 22 lithofacies and 10 lithofacies associations were distinguished for the Middle Muschelkalk evaporites. High-resolution regional correlations of gamma-ray logs record substantial thickness variation of the evaporites. Locally, dissolution was recognized by visual core examination that could be dated to Middle Triassic times and that was likely related to subsurface fluid flow along deeper seated faults. In combination with the regional thickness variation, the dissolution phenomena suggest a tectonically active depositional setting in the Middle Triassic. Middle Muschelkalk evaporites consist of nine types of mainly auto-cyclic shallowing- or brining-upward mini-cycles which form a correlatable succession of five distinct 4th order cycle-sets. Despite the tectonically active depositional environment, most lithofacies encountered appear to have nearly flat bounding surfaces. Thus, marine transgressions flooded wide areas nearly simultaneously. The corresponding deposits serve as reference levels to tie the peripheral facies of northern Switzerland into the supra-regional context.

Abstract Laguna Verde's dome‐shaped structures are distinctive formations within the Central Andes, displaying unique geomicrobiological features. This study represents a pioneering investigation into these structures, assessing their formation, associated taxa, and ecological significance. Through a multifaceted approach that includes chemical analysis of the water body, multiscale characterization of the domes, and analysis of the associated microorganisms, we reveal the complex interplay between geology and biology in this extreme environment. The lake's alkaline waters that are rich in dissolved cations and anions such as chloride, sodium sulfate, and potassium, coupled with its location at the margin of the Antofalla salt flat, fed by alluvial fans and hydrothermal input, provide favorable conditions for mineral precipitation and support for the microorganism's activity. Laguna Verde's dome‐shaped structures are mainly composed of gypsum and halite, displaying an internal heterogeneous mesostructure consisting of three zones: microcrystalline, organic (orange and green layers), and crystalline. The green layer of the organic zone is predominantly composed of Proteobacteria, Bacteroidetes, and Cyanobacteria, while the orange layer is mostly inhabited by Cyanobacteria. The results of the study suggest that oxygenic photosynthesis performed by Cyanobacteria is the main carbon fixation pathway in the microbial community, supported by carbon isotopic ratios of specific biomarkers. This finding highlights the important role played by Cyanobacteria in this ecosystem.

A comparative study of the mineral-species distribution by various systems in evaporites from the Inder deposit (Kazakhstan) and in marbles of the Luc Yen deposit in North Vietnam, as well as a comparison of these locations in the distribution of species-defining elements, has been conducted. The obtained data show that both locations are almost identical in the set of species-defining elements (O, H, Si, Ca, S, Al, Na, Mg, K, C, F, Cl, and B), but slightly differ only in the Luc Yen marble enrichment in Al, Si, C, and F. The differences in the mineral abundance between evaporites and metamorphic rocks are due to landscape environments and physicochemical conditions of their formation. A comprehensive analysis of the evaporite and marble mineralogy with the identification of species-defining elements (mineral systems) may provide an objective basis for the assumption that evaporites with minor terrigenous material rocks were involved into the formation of ruby and gem spinel deposits. [ABSTRACT FROM AUTHOR]

The Fengcheng Formation in the Mahu sag of the Junggar Basin was primarily composed of detritus, pyroclastic material, carbonates, and evaporites. In order to establish the diagenesis pathways of the Fengcheng Formation, some methods of polarized light microscope, SEM, CL, EPMA, LR, and fluid inclusion analysis were applied to discuss the diagenesis process. The results showed the following: (a) The formation of an alkaline lake was the result of the influence of a high concentration of sodium-rich sources, and it led to the preservation of alkaline minerals in the stratum. (b) After the sediments were buried, three mineral assemblages were formed in the Fengcheng Formation, which are carbonate mineral assemblages (i.e., calcite + ferreous dolomite), reedmergnerite and carbonate mineral assemblages (i.e., reedmergnerite + calcite + ferreous dolomite), and reedmergnerite and alkaline mineral assemblages (i.e., reedmergnerite + shortite + trona), respectively. (c) According to the homogenization temperature of reedmergnerite primary fluid inclusions, the alkaline diagenesis of Fengcheng Formation was divided into an early stage (≤100 °C) and a middle stage (>100 °C), respectively. The earlier stage is marked by the formation of ferrous saddle dolomite, quartz dissolution, and the agglutination of laumontite. These processes occurred under normal burial conditions. The latter is marked by the reedmergnerite's appearance, which is correlated with the deep hydrothermal activity controlled by faults. (d) Based on sedimentary and diagenetic factors, including climate, provenance, diagenetic surroundings, and the action of subsurface fluid, the alkaline deposition-diagenesis model for shale series in four stages of the Fengcheng Formation was established. [ABSTRACT FROM AUTHOR]

Alkaline lakes (pH > 9) are among the few modern sedimentary environments that are hydrochemically favourable for low‐temperature dolomite formation. While Mg‐clays and Mg‐evaporites also form more easily in alkaline environments, few studies have focused on how the kinetically inhibited dolomite wins the competition for Mg2+. Here, a basin‐wide survey of the distribution, paragenesis and stable C, O and Mg isotopes of main Mg‐rich minerals in the Late Palaeozoic saline alkaline lake deposit of the north‐west Junggar Basin, north‐west China, is conducted to study the influence of the formation and diagenesis of eitelite, northupite and Mg‐clays on dolomite formation. Large, isolated dolomite crystals (20 to 70 μm in diameter), show positive δ13C values (ranging from +1 to +7‰) and a restricted distribution in the mudstones of the lake‐transitional zone. These crystals have been interpreted as organogenic dolomite driven by methanogenesis via fermentation of organic substrates. The δ18O values of dolomitic mudstones (from −7.4 to +3.4‰), calcitic mudstones (from −15.1 to −3.3‰) and bedded Na‐carbonate evaporites (from +0.08 to +3.7‰), together with their Mg isotopic compositions, suggest that dolomite was not enriched in the most concentrated environments or during stages with most Mg sources, but in the organic‐rich deposits containing few other authigenic Mg‐rich minerals. Dolomite is at a competitive disadvantage for Mg2+ ions compared to Mg‐evaporite and Mg‐clay minerals due to its slow crystallization rates and the deficiency of micritic calcium carbonate precursors. However, it can nucleate and progressively grow into large crystals (>20 μm) if bacterial methanogenesis could effectively lower porewater pH (<8.5) and induce the dissolution of generated eitelite, northupite or Mg‐clays. These findings suggest that high salinity and/or high alkalinity are not always favourable conditions for dolomite formation and highlight the active role of pH fluctuations in inducing low‐temperature dolomite formation. [ABSTRACT FROM AUTHOR]

A fossil salt sheet emplaced in the Jurassic in submarine conditions is described in the Eastern Alps of Austria, providing unique insights into the emplacement of similar submarine structures and their potential control on depositional systems. The salt sheet is a plug‐fed extrusion emplaced due to squeezing of a salt diapir under compression. The preserved mylonitic shear fabric in the evaporites indicates radial, south‐directed emplacement of the salt sheet. Tectono‐sedimentary relationships record the evolution of the salt structure, from initial diapiric growth, to salt sheet extrusion and posterior collapse. Syn‐extrusion sediments record the variable bathymetry of the extruding salt sheet, with reefal carbonates building up on the crestal bulge while their deeper water equivalents accumulated on the extruding salt lobe. This is the first description of a salt allochthon still linked to its source diapir in the Eastern Alps. [ABSTRACT FROM AUTHOR]

Tropical coastal karst areas represent dynamic, fragile, and biodiverse environments. Central America's karst regions have been scarcely studied, with most of the research focused on the northern part of the region and on several larger cave systems. The coastal carbonate zones of the Central American region represent a unique karstic landscape, which, so far, has been insufficiently studied. Therefore, in this paper, we aim to describe the (i) landscape geomorphology and (ii) chemical conditions that define Ciénega de El Mangle in Panama as a distinctive karstic site. Carried geomorphological mapping and the characterization of karstic features have resulted in the identification of the different karstic forms and processes that are present within this unique karstic area. Considering that the chosen karstic study area is located in a marine–coastal fringe on the periphery of a lagoon, it is affected by a combination of several factors and processes, including seawater intrusion (through sinkholes), the formation of conchiferous limestone (CaCO3), and NaCl precipitation related to efflorescence. Due to the seasonally humid tropical climate, the chemical weathering processes are intense, thus forming alkaline soils that are hindering the development of mangrove vegetation. The geomorphology of the area results from intense evaporation combined with an influx of brackish groundwater, due to which a landscape has evolved in the marine–coastal strips, of seasonal tropical climates, that exhibit saline beaches, known as a littoral shott. In total, 24 karstic microdolines have evolved within the shott, of which six represent domical geoforms formed by gradual evaporitic precipitation, while seven other geoforms represent active karstic sinkholes filled with brackish water. These results are key for understanding the past and present climate interactions and conditions that have led to the formation of tropical karst environments. [ABSTRACT FROM AUTHOR]

In this study, the boron isotopic composition of Paleoproterozoic seawater is reconstructed using δ11B of tourmaline from the Paleoproterozoic Pb-Zn deposits of Rajpura-Dariba, Zawarmala, and Rampura-Agucha in the Aravalli-Delhi Fold Belt (ADFB) as well as non-mineralized tourmaline bearing metapelites from the Mangalwar Complex (MC) and Gangpur Schist Belt (GSB). This is then used to constrain the source of the mineralizing fluids in Sedimentary Exhalative (SEDEX)- and Mississippi Valley Type (MVT)-deposits. Based on textural relations and chemical variations, tourmaline in the Rajpura-Dariba and Zawarmala deposits can be grouped into two generations: syn -mineralization Tur-I and metamorphic Tur-II. In contrast, a single generation of metamorphic tourmaline is identified in the Rampura-Agucha deposit and in the MC. Tur-I from Rajpura-Dariba has X Mg of 0.14–0.56, while Tur-II is more magnesian (X Mg = 0.58–0.77). Similarly, Tur-I from Zawarmala has a wide compositional range (X Mg = 0.22–0.67), whereas Tur-II is Mg-rich (X Mg = 0.39–0.67). Tourmalines from Rampura-Agucha and MC are also magnesian (X Mg = 0.66–0.70 and 0.59–0.69, respectively). The δ11B values of syn -ore tourmaline from Rajpura-Dariba and Zawarmala vary between −18.8‰ and −16.1‰, and between −6.6‰ and −4.0‰, respectively. Metamorphic tourmalines from Rajpura-Dariba, Zawarmala, Rampura-Agucha and MC have δ11B values between −19.1‰ and −7.7‰. The δ11B of the pelitic sediments in Rajpura-Dariba, Rampura-Agucha, the MC and the GSB were estimated from the δ11B of metamorphic tourmaline hosted in them using mass balance constraints and P-T pseudosection modelling. Applying the B-isotope fractionation factor between Miocene shale and modern clay (Δ11B miocene shale − modern clay = −3.8‰ to −2.2‰) to the modelled δ11B of post-diagenetic protoliths of the metapelites, the δ11B of marine sediments for these basins were constrained between −15.1‰ and −10.2‰. Subsequently, using the B-isotope fractionation factor between modern clay and seawater (Δ11B modern clay − modern seawater = −45.2‰ to −40.8‰), the δ11B of Paleoproterozoic seawater is estimated to have been between +27.3‰ and +33.4‰. The isotopically light δ11B of syn -mineralization tourmaline from Rajpura-Dariba and Zawarmala (−18.8‰ to −16.1‰ and −6.6‰ to −4.0‰, respectively), and worldwide SEDEX/MVT-type deposits in general (a median value of −9.6‰; compilation of Trumbull et al., 2020), implies that the B was most likely sourced from continental evaporites and not evaporated seawater and/or connate brine. Dissolution of early rift-related continental evaporites most likely act as a major source of basinal brines for the formation of SEDEX/MVT deposits during the sag-phase of basin development. [ABSTRACT FROM AUTHOR]

Hydrothermal Iron-oxide-Cu-Au (IOCG) deposits are important exploration targets for a number of metals of economic importance. Voluminous sodium metasomatism is ubiquitous in most IOCG provinces. The origin of the metasomatic fluid responsible for the formation of albite-rich rocks in such terranes is contentious; both evaporite-derived fluid and magmatic fluid have been advocated. The Singhbhum IOCG province in India is known for hosting several polymetallic deposits from which U, Cu, and apatite-magnetite are mined as principal commodities together with Ni, Au, Ag, Se, Te, Mo, and low-Ti magnetite as by-products. Voluminous albite-rich rocks occur at several sites along the mineralized belt. Metasomatic albite schist comprising predominantly albite and quartz at Pathargora contains tourmaline intricately associated with albite. Based on textures and mineralogical associations, tourmaline is classified as: tur 1 : coarse nodular tourmaline ± albite ± magnetite aggregate; tur 2 : disseminated fine-grained tourmaline in a schistose matrix; and tur 3 : tourmaline + biotite + magnetite + apatite clots. All tourmaline belongs to the alkali group and most to the dravite sub-group. Very low concentrations of Li (avg 3.8 ppm), Zn (avg 6 ppm) and Mn (avg 21 ppm) but high V (avg 2130 ppm) and Ni (avg 306.5 ppm) in tur 1 core (tur 1c) co-genetic with albite contrast with what is reported in magmatic/magmatic-hydrothermal tourmaline of granitic affinity. The δ11B values of tourmaline are mostly positive, ranging between –4.0 and 9.2 ‰ (avg 4.0 ± 3.0; n = 79); values of tur 1 cores are 4.9–9.2 ‰. Previous fluid inclusion studies described the presence of halite and barite daughter crystals in primary fluid inclusions and demonstrated the involvement of a high-temperature (≥450 °C) and high-salinity (≥50 wt% NaCl equivalent) brine in the formation of cores of tur 1. Calculated δ11B values of the hydrothermal fluid in equilibrium with tur 1c range from 7.3 to 11.5 ‰ (for a crystallization temperature of 450 °C). Based on the textural setting of the tur 1c -albite assemblage, geochemical and boron isotope composition of tur 1c , and evidence of a high saline brine, we propose that the albite schist is the product of Na-metasomatism by brines that derived major constituents from the dissolution of marine evaporite. The inferred paleo-latitude and geological environment of sedimentation related to the host lithologies are consistent with the evaporitic model. We further suggest that a similar mechanism might have played an important role in the formation of albite-rich rocks in other IOCG provinces where the involvement of evaporite-derived fluids in mineralization/alteration have been demonstrated. Similar major element, trace element and positive boron isotope (1.5–6.3 ‰) composition of tur 3 suggest similar source of fluid as that of tur 1c , and tur 3 formed either during the same alteration event or during a separate fluid pulse. On the other hand, the mode of occurrence, very low trace element concentration and weakly negative to positive δ11B (−4 to 2.3 ‰) value of tur 2 suggest their metamorphic origin. [ABSTRACT FROM AUTHOR]

Three wetland‐shallow lakes were studied with the aim of analysing the processes and factors that control hydrochemistry and evaporite deposits in them in basins of the Pampean Plain, Argentina. In this sense, water balances and analysis of the water content of the lakes with normalized water difference index were made, and geologic‐geomorphological characteristics and groundwater flows were defined. Groundwater, surface water and evaporite samples were taken, along with sediment samples from wetland‐shallow lakes and surroundings. In situ pH, electrical conductivity and temperature, and laboratory chemical determinations of major ions of the water were measured. x‐ray diffraction (XRD) and scanning electron microscope (SEM)‐energy dispersive spectroscopy (EDS) analyses of evaporite and sediment samples were carried out. The results obtained allow the identification of two different systems. One of them is represented by Leubucó wetland‐lake basin, which is topographically higher and smaller than the other system, with Na‐HCO3 and Na‐Cl/SO4 groundwater inflows, with high concentrations of Ca2+ and Mg2+. In periods of high evaporation, the regional water table drops, and due to its topographic position, the lake dries. These determine the formation of thick layers of halite associated with magnesium salts on surface, and gypsum layers interbedded with clastic sediments. The other system involves de la Sal and Chasilauquen wetland‐lake basins, which have larger extensions. They receive Na‐HCO3 and Na‐Cl/SO4 groundwater inflow, but with low Mg2+ and Ca2+. Their lower topographic position determines that even during deficit periods, the water table intercepts the lakes surface and therefore, lakes have a shallow surface water level almost all the year, which is hypersaline, Na‐Cl type. These systems only have thin evaporite crusts, composed of halite and thenardite at the edges of the lakes, and the formation of Ca‐Mg sulfates is not observed. It is concluded that topographic position, basins size, geology, groundwater inflow and evaporation are the main processes and factors controlling hydrochemistry and evaporitic deposits. [ABSTRACT FROM AUTHOR]

In northern Switzerland, Middle Muschelkalk evaporites (Zeglingen Formation) were deposited under arid conditions in the southernmost part of the epicontinental Central European Basin during times of reduced inflow of sea water from the Tethyan realm. Because of their marginal position in the basin, direct and detailed correlation of Muschelkalk sediments of northern Switzerland with equivalent strata in interior parts of the basin is not straightforward. Based on detailed sedimentological logging of 640 m of drill cores from ten wells in northern Switzerland, 22 lithofacies and 10 lithofacies associations were distinguished for the Middle Muschelkalk evaporites. High-resolution regional correlations of gamma-ray logs record substantial thickness variation of the evaporites. Locally, dissolution was recognized by visual core examination that could be dated to Middle Triassic times and that was likely related to subsurface fluid flow along deeper seated faults. In combination with the regional thickness variation, the dissolution phenomena suggest a tectonically active depositional setting in the Middle Triassic. Middle Muschelkalk evaporites consist of nine types of mainly auto-cyclic shallowing- or brining-upward mini-cycles which form a correlatable succession of five distinct 4th order cycle-sets. Despite the tectonically active depositional environment, most lithofacies encountered appear to have nearly flat bounding surfaces. Thus, marine transgressions flooded wide areas nearly simultaneously. The corresponding deposits serve as reference levels to tie the peripheral facies of northern Switzerland into the supra-regional context. [ABSTRACT FROM AUTHOR]

The internal structure and architecture of evaporite sequences is often overlooked, with attention frequently concentrating on the external geometries that salt bodies form. The availability of extensive 3D seismic data affords the opportunity to interpret the internal structures within these evaporite sequences and comprehensively characterise the different structural facies over large areas. This paper concentrates on the Zechstein Supergroup evaporite deposits within the Southern North Sea of the United Kingdom's Continental Shelf. This analysis of the internal structural complexity and stratigraphic heterogeneity utilises 26,000 km2 of 3D seismic data together with over 96 wells from the Southern North Sea. Characterisation of the different structural facies present was undertaken alongside mapping their spatial distribution to understand the relationship they have with one another and the structural evolution that may have been taken. This work has (1) characterised and mapped six different internal structural facies present within the Zechstein with increasing levels of deformation; (2) shown the internal lithological heterogeneity is indicative of variations in the vertical strength profile of layered evaporite sequences; (3) discontinuous high‐amplitude reflections within the Zechstein are as a result of the geometries being too steeply dipping for the seismic data to image; and (4) the ability to possibly predict the internal heterogeneity of areas of poorly imaged salt, such as within large diapiric salt structures, from surrounding structural facies. These findings suggest that there is significant internal complexity even within areas of the basin with minor mobilisation to the external salt geometry. [ABSTRACT FROM AUTHOR]

Abstract The Qaidam basin in W China is an immense hyperarid intramontane basin with flat vast playas and salt lakes on the Qinghai-Tibet Plateau. The central basin is about 2800–2900 m a.s.l. elevation and enclosed by mountain ranges reaching > 5800 m in the Qilian Mountains and > 6200 m in the eastern Kunlun Mountains. The extensive playas of the basin are covered by gypsum or halite with very subordinate additional solids. In this contribution we report on the chemical composition of salt lakes and inflows to the Qaidam basin (analysis of 30 water samples collected in the summer of 2008 and 2009) together with the composition of 22 salt samples. Salt lakes and small salt ponds formed at topographic depressions. Some of the lakes cover > 300 km2 surface but are very shallow (1–2 m deep). Most salt lakes and salt ponds are NaCl dominated and contain typically 250–300 g kg−1 total dissolved solids (TDS). Some lakes are industrially used and produce KCl fertilizer, LiCl, and boron or are strongly modified by deep water produced in oil fields. Lakes along the borders to the high mountains are typically not fully saturated with halite. However, also these lakes lost most Ca and are drastically enriched in Mg and some lakes also in B and Li. The chemical development of the most natural salt lakes follows a path producing Ca-deficient water that ultimately precipitate Mg-bearing carbonates and chlorites in addition to halite upon evaporation. The salt lakes form by continuous and drastic evaporation of the waters supplied by the inflows to the lakes in the basin. All inflows carry considerable amounts of Cl and are characterized by very high Cl/Br ratios. These chemical characteristics suggest that the salt load of the inflows originates mostly from re-dissolved windblown halite deposited together with sand up to high altitudes in the bordering mountain ranges. Also, thermal waters ascending along deep faults along the Qilian Mountains carry considerable amounts of chloride. Their low Cl/Br ratio however suggests that most of the dissolved Na is derived from minerals of the basement rocks by fluid-rock interaction at T > 130 °C. The thermal fluids also carry considerable amounts of boron, indicating that co-precipitated borax in the salt lakes ultimately also derives from minerals in the basement rocks (tourmaline). Consequently, the presented data improve the understanding how the brines and salt lake waters develop from a wide range of chemically distinct low-TDS inflows and how the sequences of minerals precipitated upon evaporation in the Qaidam basin formed.

The Danakil depression in Ethiopia, at the southern end of the Red Sea, has been the place of volcanic crises in 2004–10, with emplacement of at least 15 dykes. One of them, non-emergent, occurred in dry lake Asale next to Black Mountain and south of Mount Dallol during fall 2004. We report on the opening of a 4.5 km-long fissure in the ground at the same time the Black Mountain dyke was intruding the crust 2 km westward and parallel to it. The fissure, located north and south of Yellow Lake (Gaet’ale) and trending NNW-SSE, is still hydrothermally active. First, we describe the remarkable diversity of morphologic expressions of the fissure, made possible by development in an evaporite sequence. Satellite image monitoring reveals that its formation is coeval with the latest intrusion stage of the Black Mountain dyke. Hydrothermal activity in the fissure area is, however older than ∼60 years. It is suggested that hydrothermal activity is primarily a side effect of the igneous processes, probably sill intrusion, that resulted in the uplift of Mount Dallol area, in a ∼400 m thick, fluid-saturated evaporite pile. We suggest that, in 2004, emplacement of the Black Mountain dyke caused dilation within the evaporite pile overlying it, where extension was also facilitated by pressured pore fluids. This study documents the delicate intermingling of magmatic, tectonic, hydrothermal, and geomorphologic processes in evaporitic environments at the transition between continental rifting and oceanic spreading.

The Piedmont basin (NW Italy) records a Messinian Salinity Crisis (MSC) succession including a selenite gypsum deposit assigned to the Primary Lower Gypsum (PLG, MSC stage 1). Strontium isotope ratios are in the range of the PLG deposits of the Mediterranean area. Sulfate isotope compositions of vertically oriented selenite gypsum beds, in the lower part of the succession, are similar to those reported in other PLG deposits. However, flattened branching selenite cones in the upper part show higher isotope compositions, mainly in δ34S values, suggesting intense BSR conditions, stronger than reported in other PLG deposits. We interpret this chemical shift during deposition of the upper part of the PLG as the result of increased marine restriction assisted by the marginal position of this basin in the Adriatic Gulf during the Apennine and Alpine uplifts.