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Modelling plumbing systems dynamics of active volcanoes through textural and chemical studies of mineral phases is crucial to unravel their eruptive behaviour, but it is rarely applied in ancient volcanic and volcano-plutonic systems. Here, we present an investigation of the architecture, magma dynamics and pre-eruptive timing of Middle Triassic plumbing systems in the Dolomites area (Southern Alps) through a detailed investigation of textures and compositional zoning of clinopyroxenes in lavas and dykes from Predazzo, Mt. Monzoni, Cima Pape and Sciliar volcano-plutonic complexes. The clinopyroxene composition varies between low-Mg# (67–78), low-Cr augite and high-Mg# (77–91), Cr-rich diopside. Diopside is less frequent and appears as variably thick single or multiple bands between augitic cores and rims or as resorbed homogeneous, or patchy-zoned and mottled cores. Rims are homogeneous or oscillatory zoned, with augitic composition. The mid- to low-crustal plumbing systems of all volcanic centres were characterised by the presence of a mildly evolved trachyandesitic magma (Mg# 45; T = 1044–1118 °C), where augitic clinopyroxene formed. Periodic mafic injections of more primitive and hotter trachybasaltic magma (Mg# 56; T = 1056–1170 °C) caused frequent crystallisation of diopsidic bands around augitic cores. The presence of resorbed or patchy-zoned mottled diopsidic cores in clinopyroxene phenocrysts, as well as of rare clinopyroxenitic xenoliths with analogous diopsidic composition, indicates the recycling and remobilisation of antecrysts from the deeper part of the plumbing system, which was probably located at a depth of 10–17 km. Diffusion chronometry models based on Fe–Mg interdiffusion in clinopyroxene revealed that the time elapsed from the mafic injection into the shallow portion of the plumbing systems to the eruption ranges from decades to < 1 year. Our findings enabled us to resolve the different plumbing system dynamics acting at the local scale beneath each volcanic centre. Our data indicate a striking similarity with magma dynamics and timing of pre-eruptive processes at active volcanoes: therefore, we posit that this work sets a starting point to deepen our knowledge of the volcano-plutonic links and, in turn improves our ability to interpret the main processes acting in active plumbing systems. [ABSTRACT FROM AUTHOR]

The forsterite zone of the Ubehebe Peak contact aureole, Death Valley, USA consists of an outer zone of tabular/jack-straw olivine and an inner zone of subequant polyhedral olivine. Subequant polyhedral forsterite crystals close to the intrusion are small and tabular forsterite crystals farther away are larger. To investigate the formation of the two morphologies, forsterite growth experiments were conducted in cold seal pressure vessels in the CaO-MgO-SiO2-CO2-H2O system. Forsterite precipitation follows a disequilibrium reaction pathway made of three reactions: [1] tabular forsterite growth from quartz and dolomite, [2] forsterite growth from tremolite dissolution, and [3] subequant polyhedral forsterite growth from tabular forsterite dissolution. Initially, quartz reacts with dolomite to simultaneously form twinned tabular forsterite and tremolite. As quartz reacts away, forsterite precipitation continues at a slower rate through tremolite dissolution. A second generation of forsterite then precipitates on top of some tabular forsterite but has different habit and tracht. Once all the tremolite reacts away, subequant polyhedral forsterite precipitation continues at an even slower rate through dissolution of tabular forsterite. The tabular morphology of jack-straw olivine is a consequence of twin-mediated unidirectional growth; the abundance of twins being due to rapid nucleation and growth at initially high reaction affinities. Twin junctions are preferential nucleation centers for steps, so faceted growth is enhanced on {100}. This phenomenon is the twin plane re-entrant effect. Subequant polyhedral forsterite in the Ubehebe Peak inner contact aureole recrystallized and ripened from tabular forsterite. In the outer contact aureole, conditions were not conducive to recrystallization and ripening so well-developed tabular forsterite persists. [ABSTRACT FROM AUTHOR]

Xianxian geothermal exploitation area is one of the areas with the best occurrence conditions of geothermal resource in North China, rich in medium and low temperature geothermal resource, and is a typical carbonate geothermal field. However, its hydrogeochemical evolution process is not clear, and no complete conceptual model of geothermal genesis has been established to guide the exploration, development and utilization of geothermal resource in the area. It restricts the sustainable development of regional geothermal resource and the realization of carbon emission reduction targets. In this study, geothermal fluids in the area were collected for testing and analysis in terms of hydrochemical characteristics and stable isotopes. Based on systematic geochemical research, the formation mechanism of geothermal fluids was analyzed, and a conceptual model of geothermal genetic in the study area was established. The main understanding is as follows: the hydrochemical type of geothermal water in the study area is Cl-Na type, and the water-rock interaction is not balanced. The formation of geothermal water in the area is affected by the infiltration of atmospheric precipitation, and it is terrestrial leached water. The flow path of geothermal water is long, the water circulation is slow, and the metamorphism is deep. Dolomite, calcite and gypsum dissolution are the main sources of Mg2+, Ca2+, , and in geothermal water, besides, other minerals containing calcium and magnesium are also part of their sources. The source of geothermal water recharge is atmospheric precipitation, and the recharge elevation of geothermal water is about 619–1069 m. The age of the geothermal water is between 16 000 and 18 000 years. The sulfur in geothermal water mainly comes from the leaching of sedimentary layer. [ABSTRACT FROM AUTHOR]

Flotation separation of magnesite and its calcium-containing carbonate minerals is a difficult problem. Recently, new regulators have been proposed for magnesite flotation decalcification, although traditional regulators such as tannin, water glass, sodium carbonate, and sodium hexametaphosphate are more widely used in industry. However, they are rarely used as the main regulators in research because they perform poorly in magnesite and dolomite single-mineral flotation tests. Inspired by the limonite presedimentation method and the addition of a regulator to magnesite slurry mixing, we used a tannin pretreatment method for separating magnesite and dolomite. Microflotation experiments confirmed that the tannin pretreatment method selectively and largely reduces the flotation recovery rate of dolomite without affecting the flotation recovery rate of magnesite. Moreover, the contact angles of the tannin-pretreated magnesite and dolomite increased and decreased, respectively, in the presence of NaOl. Zeta potential and Fourier transform infrared analyses showed that the tannin pretreatment method efficiently hinders NaOl adsorption on the dolomite surface but does not affect NaOl adsorption on the magnesite surface. X-ray photoelectron spectroscopy and density functional theory calculations confirmed that tannin interacts more strongly with dolomite than with magnesite. [ABSTRACT FROM AUTHOR]

Understanding the structural evolution of carbonate minerals with increasing pressure is essential to decoding the role of Earth's mantle in the global carbon cycle and long-term climate change. Here, we carried out synchrotron single-crystal X-ray diffraction measurements on a natural sample of manganese dolomite [kutnohorite, Ca1.11Mn0.89(CO3)2] in a diamond-anvil cell up to 51.2 GPa at room temperature with neon as the pressure-transmitting medium. The manganese dolomite sample remains stable in the rhombohedral structure from 1 bar to ~13.3 GPa. The equation of state of Ca1.11Mn0.89(CO3)2 was determined: V0 = 334.06 ± 0.29 Å3, K0 = 99.9 ± 4.7 GPa, and K 0 ′ = 4.3 ± 0.9 ; when K 0 ′ is fixed at 4.0, V0 = 334.04 ± 0.24 Å3, and K0 = 101.4 ± 1.5 GPa. Upon further compression at room temperature, the split and disappearance of diffraction spots were observed. That is, the rhombohedral structure of manganese dolomite becomes highly distorted to lose its long-range order at 13.3–51.2 GPa at room temperature. Moreover, our single-crystal X-ray difraction results reveal the mechanisms of the reported lattice and internal Raman mode splits of the same manganese dolomite sample approximately at 13 and 24 GPa, respectively. These results suggest manganese-bearing carbonates may play a distinct role in the deep carbon cycle. [ABSTRACT FROM AUTHOR]

Menilites, intriguing botryoidal rocks found in Galera, Granada, Spain, have been examined through a multidisciplinary approach integrating mineralogical analysis and advanced imaging techniques. Characterized as opal and dolomite-bearing rocks, their complex morphologies and diverse internal structures prompted an investigation into their origin. Employing microfocus X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectroscopy and X-ray computed tomography, we present a detailed study of the menilites, revealing opal-A, opal-CT, dolomite and quartz as primary constituents. Notably, the internal homogeneity contrasts with the diverse external shapes. The proposed hypothesis suggests a seismic influence in menilite formation. Seismic events in porous environments above the water table may induce fluidization, resulting in the distinctive menilite structures. Osmotic pressure differences between nodules and the surrounding rock, coupled with fluidization during seismic events, could explain the observed morphologies. Validation of the proposed hypothesis requires further fieldwork and analogue experimentation. This study contributes valuable insights into the mineralogical composition, internal structures and potential formation mechanisms of menilites, laying the groundwork for future research in the field of sedimentary geology and mineralogy. [ABSTRACT FROM AUTHOR]

The potential of the supercritical antisolvent micronization (SAS) technique was evaluated for the production of CaO-based particles with a size and a physical structure that could enable high performance for CO2 capture through the calcium looping process. Two sources of calcium derivative compounds were tested, waste marble powder (WMP) and dolomite. The SAS micronization of the derivate calcium acetate was carried out at 60 °C, 200 bar, a 0.5 mL min−1 flow rate of liquid solution, and 20 mg mL−1 concentration of solute, producing, with a yield of more than 70%, needle-like particles. Moreover, since dolomite presents with a mixture of calcium and magnesium carbonates, the influence of the magnesium fraction in the SAS micronization was also assessed. The micronized mixtures with lower magnesium content (higher calcium fraction) presented needle-like particles similar to WMP. On the other hand, for the higher magnesium fractions, the micronized material was similar to magnesium acetate micronization, presenting sphere-like particles. The use of the micronized material in the Ca-looping processes, considering 10 carbonation-calcination cycles under mild and realistic conditions, showed that under mild conditions, the micronized WMP improved CaO conversion. After 10 cycles the micronization, WMP presented a conversion 1.8 times greater than the unprocessed material. The micronized dolomite, under both mild and real conditions, maintained more stable conversion after 10 cycles. [ABSTRACT FROM AUTHOR]

The origin of the carbonatites that appear on Earth is one of the most controversial current topics in the petrogenesis of igneous rocks. Situated in the northern sector of the Basal Complex of Fuerteventura (Canary Islands), the Miocene Esquinzo ultra-alkaline plutonic rock complex is composed of pyroxenites, melteigites-ijolites-urtites, malignites-nepheline syenites, carbonatites, silicocarbonatites, nephelinites and nepheline phonolites. This work tries to establish the genesis of this massif of ultra-alkaline rocks with associated carbonatites from Fuerteventura (which are very rare in the oceans). The geochemical characteristics of these rocks and the minerals that are included in them have allowed us to establish their origin. This complex was generated by three successive magmatic events associated with differentiation of melanephelinite magmas emplaced in the oceanic crust. Silicocarbonatite and calciocarbonatite (sövites) dykes are related to the first magmatic event and were formed by fractional crystallization of H2O- and CO2-rich ijolite magmas. The melanephelinite magmas that formed these plutonic ultra-alkaline rocks were apparently generated as partial melts of asthenospheric mantle, which assimilated enriched lithospheric mantle material as they ascended. The upwelling of this large body of anomalous asthenospheric Miocene material exceeded the deformation associated with plate motions and led to an oceanic rifting event in Fuerteventura. [ABSTRACT FROM AUTHOR]

Featured Application: The findings of this study offer support for the design of laboratory experiments, monitoring indicators, and the selection of parameters for history matching, ultimately enhancing the accuracy of databases of mineral reactions induced by CO2 injection. Numerical simulation is a commonly employed technique for studying carbon dioxide (CO2) storage processes in porous media, particularly saline aquifers. It enables the representation of diverse trapping mechanisms and the assessment of CO2 retention capacity within the subsurface. The intricate physicochemical phenomena involved necessitate the incorporation of multiphase flow, accurate depiction of fluid and rock properties, and their interactions. Among these factors, geochemical reaction rates and mechanisms are pivotal for successful CO2 trapping in carbonate reactive rocks. However, research on kinetic parameters and the influence of lithology on CO2 storage remains limited. This limitation is partly due to the challenges faced in laboratory experiments, where the time scale of the reactions and the lack of in situ conditions hinder accurate measurement of mineral reaction rates. This study employs proxy models constructed using response surfaces calibrated with simulation results to address uncertainties associated with geochemical reactions. Monte Carlo simulation is utilized to explore a broader range of parameters and identify influential factors affecting CO2 mineralization. The findings indicate that an open database containing kinetic parameters can support uncertainty assessment. Additionally, the proxy models effectively represent objective functions related to CO2 injectivity and mineralization, with calcite dissolution playing a predominant role. pH, calcite concentration, and CO2 injection rate significantly impact dolomite precipitation, while quartz content remains unaffected. [ABSTRACT FROM AUTHOR]

Rockfalls can cause loss of life and material damage. In Northern Morocco, rockfalls and rock avalanche-deposits are frequent, especially in the Dorsale Calcaire morpho-structural unit, which is mostly formed by Jurassic limestone and dolostone formations. In this study, we focus exclusively on its northern segment, conventionally known as "the Haouz subunit". First, a rockfall inventory was conducted. Then, two datasets were prepared: one covering exclusively the source area and the other representing the entirety of the mass movements (source + propagation area). Two algorithms were then used to build rockfall susceptibility models (RSMs). The first one (Logistic Regression: LR) yielded the most unreliable results, where the RSM derived from the source area dataset significantly outperformed the one based on the entirety of the rockfall affected area, despite the lack of significant visual differences between both models. However, the RSMs produced using Artificial Neural Networks (ANNs) were more or less similar in terms of accuracy, despite the source area model being more conservative. This result is unexpected given the fact that previous studies proved the robustness of the LR algorithm and the sensitivity of ANN models. However, we believe that the non-linear correlation between the spatial distribution of the rockfall propagation area and that of the conditioning factors used to compute the models explains why modeling rockfalls in particular differs from other types of landslides. [ABSTRACT FROM AUTHOR]

Dolomite as a heterogeneous catalyst can be used in biodiesel synthesis. Process material costs can be reduced by regenerating and reusing the catalyst. Two methods of regeneration of dolomite were studied: (1) washing for 30 min with methanol, filtration, and washing for 30 min with hexane and (2) calcination at high temperature. Catalytic efficiency and catalyst changes after 1–6 cycles were evaluated. X-ray, FTIR, and SEM studies were performed. Calcination has been found to be a more effective method of catalyst regeneration than washing with solvents. The catalytic effectiveness of dolomite only slightly decreased over six application cycles. The results of the instrumental analysis showed that the structure and composition of the dolomite do not change during calcination after three cycles, while obvious changes in the structure of dolomite during catalyst washing were observed. [ABSTRACT FROM AUTHOR]

The equilibrium oxygen isotope fractionation factor is widely used in geological thermometry. However, under most natural conditions, the oxygen isotope exchange is rare to reach equilibrium. Especially for the complex water–rock interaction process, the contribution of the H2CO3 solution, CO32− solution, Ca(HCO3)2 solution, and CaCO3 solution to the equilibrium oxygen isotope fractionation factor of this process is poorly understood. In view of this predicament, these key parameters are obtained by ab initio calculations. The results showed that the contributions of different carbonate minerals and different aqueous solutions to the equilibrium oxygen isotope fractionation factor were different. Among all nine carbonate minerals (dolomite, calcite, aragonite, magnesite, siderite, otavite, smithsonite, ankerite, and strontianite), the minerals with the highest and lowest reduced partition function ratios (RPFR) were siderite and strontianite, respectively. At the same time, the RPFR of nitratine, which has the same structure as carbonate, was studied. The RPFRs of the three most widely distributed carbonates in nature (dolomite, calcite, and aragonite) were dolomite > calcite > aragonite. Among the H2CO3 solution, CO32− solution, Ca(HCO3)2 solution, and CaCO3 solution, the H2CO3 solution had the strongest ability to enrich 18O. In addition, the equilibrium oxygen isotope fractionation factors between aqueous solutions and gas phase species (CO2(g), H2O(g), and O2(g), etc.) were calculated systematically. The results showed that the oxygen isotope fractionation factors between solutions and gas phases were often inconsistent with the temperature change direction and that the kinetic effects played a key role. These theoretical parameters obtained in this study will provide key equilibrium oxygen isotope constraints for water-rock interaction processes. [ABSTRACT FROM AUTHOR]

Cenozoic dolomitization of reefal carbonates has been widely found on many tropical islands worldwide. However, most ages and geochemical data obtained from bulk samples prevent a clear understanding of the previous complex diagenetic processes of these island dolostones due to a lack of in situ age and fluid composition. In this study, one deep borehole penetrated Cenozoic carbonates on Meiji Island in the southern South China Sea and massive dolostones with thicknesses over 400 m were uncovered. The in situ U–Pb geochronology and elemental analysis were conducted on the lower Nanwan Formation (upper Miocene) comprising undolomitized calcite (bioclast), replacive dolomite, and dolomite cement. Strontium isotope ages and U–Pb dates show that the penecontemporaneous replacive dolomitization occurred at 11.0–8.5 Ma, close to the deposition of precursor limestone. The dolomite cement precipitated at 8.5–6.0 Ma. In situ elemental analyses indicate that the formation of replacive dolomite and dolomite cement in the Nanwan Formation was probably controlled by seawater. The higher Mg/Ca ratio and lower Mn and Sr contents in dolomite cements show that their fluid underwent more evaporation. The dolomite content is positively related to the porosity of reefal limestones in the Nanwan Formation, suggesting that primary voids play an important role in fluid transportation during following dolomitization. Coralline algae and lime mud with algal fragments are beneficial for the rapid nucleation of dolomite. This study demonstrates that in situ elemental analysis using laser ablation has great potential for identifying the source of multistage dolomitizing fluids and can help refine the existing dolomitization model of isolated atolls. [ABSTRACT FROM AUTHOR]

In the paper, changes of pH value during 20 days of soil interaction with the solution have been traced. Differences in the reaction rate using ameliorants of different chemical nature for liming have been established. It was revealed that the ameliorative effect of using materials of silicate nature in the experiment was lower than that of carbonate nature. According to the effect all ameliorants used in the experiment can be arranged in the following descending order: dolomite flour (DF), crushed stone sieve (CSS) > conversion chalk (CC), dolomitized limestone flour (DLF) > blast furnace slag (BFS) > oil shale ash (OSA). For all lime fertilizers empirical models of pHKCL value change over the whole experimental interval were developed. Clustering of separate variants of the experiment, produced by different ameliorants on their influence on the index rNKCL on the whole interval of study was carried out.

For successful emulsified acid treatment, it is imperative to have emulsified acid that can maintain a water-in-oil emulsion state for 24 h at room temperature and 4 h at high temperatures. As a result, a hybrid emulsified acid was developed by combining cationic and nonionic emulsifiers, guaranteeing stability at both room and high temperatures. We assessed its viscosity and explored the interaction dynamics of the emulsified acid with carbonate rock samples using rotating disk apparatus experiments. Viscosity measurements revealed a non-Newtonian shear-thinning behavior modeled using a power-law approach. We examined limestone, dolomite, and chalk disks to evaluate weight loss tendencies, dissolution rates, and diffusion coefficients when exposed to the emulsified acid and hydrochloric acid (HCl). Both the weight loss and dissolution rate demonstrated that the reactivity of HCl surpasses that of the emulsified acid by up to 2.4 times at the same rotating speed. This indicates that the emulsified acid in our study can significantly slow the rapid reaction between acid and rock due to the diffusion barrier created by the oil phase. The diffusion coefficient for the limestone sample with emulsified acid was 1.46 times greater than that of dolomite (limestone: 1.64 E–7 c m 2 / s , dolomite: 1.12 E–8 c m 2 / s , and chalk: 1.47 E–8 c m 2 / s). Consequently, understanding the rock/mineral composition of the targeted reservoir is crucial when designing matrix acidizing with emulsified acid in carbonates. In summary, it is vital to account for the impact of emulsified acid on acid-rock reaction kinetics when establishing injection parameters for carbonate acidizing. [Display omitted] • This paper presents the reaction kinetics of an emulsified acid that secures fluid stability at room and high temperatures with various carbonate disks. • It was revealed that the dissolution rate and diffusion coefficient of the emulsified acid were lower than those of hydrochloric acid. • The emulsified acid used in this study can markedly retard the rapid reaction between acid and rock because of the diffusion barrier of oil phase. • The emulsified acid used in this study can effectively stimulate carbonate reservoirs as retarded systems. [ABSTRACT FROM AUTHOR]

The positive correlation between total organic carbon and specific surface area in sediments and mudstones implies the association between sedimentary organic matter (OM) and clay minerals. However, the traditional classification of OM, including insoluble kerogen and soluble OM (SOM), ignores the role of minerals, significantly limiting the understanding of the role of mineral-OM interactions in OM preservation and evolution. This paper reviews the mineral and OM characteristics and their relationship in argillaceous sediments and rocks and classifies sedimentary OM into three forms of occurrence, namely free SOM (FSOM), mineral-bound OM (MOM), and particulate OM (POM). FSOM, dominated by non-polar compounds, is physically adsorbed on the external surface of minerals or free in pores of different sizes, so it is susceptible to oxidation. MOM includes polar SOM and insoluble amorphous OM. The former is chemically adsorbed on the external surface, sheet edge and intercalated into interlayer space, and the latter is encapsulated in the clay microfabric. MOM is preserved by mineral adsorption, physical encapsulation, and degradation-recondensation, so it is very stable. POM is predominantly insoluble structured OM in the form of discrete particles and is preserved by selective preservation at the expense of chemical reactivity. The three forms of OM occurrence result from the synergistic operation of multiple preservation mechanisms, in which mineral-OM interactions dominate long-term OM preservation. Depending on environmental conditions, the change of mineral-OM interaction leads to the OM release or cracking, thereby promoting carbon cycling. Compared to traditional OM classifications, the new model of OM occurrence incorporates mineral protection mechanisms and provides a unifying principle linking inorganic and organic processes in OM preservation and evolution. OM preservation and evolution is essentially the process of mutual transformation of OM between different forms of occurrence, so this model is very useful for understanding carbon cycling and hydrocarbon generation and should be valued. • Sedimentary organic matter is divided into three forms of occurrence. • Mineral-organic matter interaction leads to the fractionation of organic matter. • The role of mineral-organic matter interactions in carbon cycling is discussed. [ABSTRACT FROM AUTHOR]

• Dolomite powder (DP) is used for replacing clay in clay masonry units. • The effects of DP on clay bricks properties depend on DP percentage. • Use of DP can improve the thermal conductivity of clay bricks. • The compressive strength of clay bricks decreases by increasing the DP percentage. • Possibility of replacing up to 30% of clay materials with DP. This paper evaluates the influence of dolomite industrial waste (dolomite powder (DP) on the properties, structure and durability of clay bricks. Four clay samples fired at 900 °C and 1000 °C containing 0 wt%, 10 wt%, 20 wt% and 30 wt% DP were prepared and investigated to measure their properties (shrinkage, bulk density, water absorption, thermal conductivity, apparent porosity, compressive strength), structure and durability (compressive strength after freeze thaw). The results showed a decrease in bulk density, compressive strength and an increase in apparent porosity and water absorption of the clay bricks produced by mixing 70–90 wt% clay and 10–30 wt% DP compared to the control bricks. Also, a significant improvement in the thermal conductivity of clay bricks produced by 70 wt% clay and 30 wt% DP (0.407–0.420 W/(m⋅K) compared to the control clay bricks (0.839–0.845 W/(m⋅K). As clay mixtures contain DP (chemical composition: CaO-49.68%, Loi-42.80%), CO 2 emissions during the firing process are increased (decarbonation reactions). However, the thermal conductivity of the fired clay bricks is significantly reduced (to 50%). These results showed the potential of DP for the manufacturing of clay masonry units. [ABSTRACT FROM AUTHOR]

Depressive model of the LGB for flotation separation of scheelite and dolomite. [Display omitted] • Selective depressant LGB used for scheelite flotation. • Selective flotation separation of scheelite from dolomite was achieved. • LGB is selectively adsorbed on the dolomite surface by chemisorption. • The selective adsorption lies in the more active Mg sites on the dolomite surface. Dolomite is a common vein mineral in scheelite, but how to selectively suppress dolomite in flotation of scheelite has not been addressedin the past research works. In this paper, the depressive behavior of locust bean gum (LBG) in separating scheelite from dolomite is investigated and a possible inhibition mechanism is proposed. The flotation results proved that LBG (18 mg/L) could effectively inhibit dolomite in scheelite flotation at pH = 9, and the obtained grade was 65.69 % of scheelite concentrate. Moreover, combined with the results of XPS, FTIR, Zeta potential, and contact angle experiments, it was inferred that LBG would selectively accumulate on the dolomite surface due to the presence of denser and more active action sites on the surface; and LBG could be stably adsorbed on the dolomite surface based on the stable complexation reaction between the carboxyl groups in LBG molecules and Mg2+ on the dolomite surface. Notably, the preferential adsorption of LBG not only brings a large number of hydrophilic groups to dolomite but also interference with the adsorption of sodium oleate, leading to a substantial decrease of the hydrophobicity of dolomite and finally realizing the selective inhibition of dolomite in scheelite flotation. [ABSTRACT FROM AUTHOR]

The composite concrete-encased steel (CCES) column member is made by the steel section embedded and covered in concrete from all sides. Due to the ability of the composite sections to bear heavy loads while using smaller sections, CCES columns have been widely used. Analytical studies on the CCES columns' behavior using crushed dolomite coarse aggregate (CDCA) with different shear connectors (SCs) types/shapes and sizes under axial loads are described here. This study also aims to evaluate the current design methods to determine the ultimate capacity of the CCES with CDCA concrete columns using nine available codes. The results show that the finite element (FE) analysis could accurately predict the ultimate capacity of the CCES columns; the column's capacity improved by about 41.75% as fcu increased by 60%. Increasing the IPE-shaped steel strength (fss) strategy is not very effective and gives brittle behavior even though enhancing the fss improves the capacity. The column's capacity increased as the tie stirrups and steel bars ratios increased. The column's capacity increased by about 17.63%, as steel bars ratios increased by 155.49%. The efficiency factors increased slightly as tie stirrups were raised but slightly decreased as steel bar ratios increased. Using the SCs system increases the columns' capacity by an average value of about 4.9% of the specimen without SCs. The computed capacities using the nine available codes are conservative and safe. The closest estimates made by the YB9082-06 code are 26% less on average than the test results; in contrast, the safest predictions made by the ECP-LRFD code are 68% less, on average, than test results. [ABSTRACT FROM AUTHOR]

The combination of Raman imaging and multivariate curve resolution (MCR) or classical least squares (CLS) has allowed us to explore the distribution and identification of components in a gigantic spherical dolomite concretion. It has been found by the MCR and CLS analyses of imaging data that the concretion contains dolomite, kerogen, anatase, quartz, plagioclase, and carbon materials with considerably large distribution of dolomite. The existence of these components has also been confirmed by the point-by-point analysis of imaging data. The distributions of these components were clearly observed by Raman images. Of note is that the amount of carbon materials is considerably large, and they are buried among the matrix sedimentary grains in the concretion, suggesting that there exist soft tissues with biological origin. Moreover, one of the loading spectra of CLS shows intense bands in the region of 3000–2800 cm−1, and bands at ca. 1658, ca. 1585, 1455, 1323, and 1261 cm−1. These bands indicate the existence of decomposed organic materials in the concretion. Raman imaging of concretions provides direct evidence that concretions are of biological organic origin. [ABSTRACT FROM AUTHOR]

The study of acid fracture conductivity stands as a pivotal aspect of petroleum engineering, offering a well-established technique to amplify production rates in carbonate reservoirs. This research delves into the intricate dynamics influencing the conductivity of acid fractures, particularly under varying closure stresses and in diverse rock formations. The conductivity of acid fractures is intricately interconnected with the dissolution of rock, etching patterns on fracture surfaces, rock strength, and closure stress. To accurately predict fracture conductivity under different closure stresses, a robust model is necessary. This model involves assessing both the baseline fracture conductivity under zero closure stress and the rate of conductivity variation as closure stress fluctuates. Key among the influential factors affecting fracture conductivity is the type of rock within the reservoir. Understanding and predicting the behavior of different formations under disparate closure stresses poses a significant challenge, as does deciphering the diverse effects of treatment parameters such as acid injection rate and strength on fracture conductivity. In this study, the predictive power of XGBoost, a machine learning algorithm, was explored in assessing acid fracture conductivity in dolomite and limestone formations. The findings revealed XGBoost's ability to outperform previous studies in predicting fracture conductivity in both types of formations. Notably, it exhibited superior accuracy in forecasting fracture conductivity under varying treatment conditions, underscoring its robustness and versatility. The research underscores the pivotal role of closure stress, dissolution rate of rock (DREC), and rock strength in influencing fracture conductivity. By integrating these parameters into the design of acid fracturing operations, accurate predictions can be achieved, allowing for the optimization of treatment designs. This study illuminates the potential of XGBoost in optimizing acid fracturing treatments, ultimately bolstering well productivity in carbonate reservoirs. Furthermore, it advocates for the essential nature of separate modeling and analysis based on rock types to comprehend and optimize fracturing processes. The comparison between dolomite and limestone formations unveiled distinct conductivity behaviors, underlining the significance of tailored analyses based on rock type for precise operational optimization. [ABSTRACT FROM AUTHOR]

Metallogenic studies carried out in the Holy Cross Mountains indicate a relationship between mineralization and fault tectonics in Devonian formations. The impact of fault formation on the geochemistry of host rocks has not yet been studied. Mineralogical and geochemical studies of fault core gouges and damage zones in the fault walls of Devonian dolomites in the Budy and Jurkowice quarries were carried out. In the clay-carbonate filling of the fault fissure, the presence of two generations of Fe sulfides, the increased content of Zr, Nb, U and Th in relation to the surrounding rocks was noted. In the fault walls of the dolomites, iron sulfide and hematite mineralization were found. Research on the REE content indicates that it is lower in the fault walls than in those located far from it, while it is clearly higher in the fault gouge, especially in terms of the content of "heavy" elements (HREE). This indicates both the supply of some components to the fault zone from external sources and their displacement from the surrounding rocks. It was also found that the fault was renewed before and after the Neogene at least twice (Badenian). [ABSTRACT FROM AUTHOR]

To improve the magnesite flotation system with sodium oleate (NaOL), dodecyl dimethyl betaine (BS-12), an environmental-friendly surfactant, was first used in the flotation of magnesite and dolomite with NaOL. Micro-flotation tests, surface tension measurements, and contact angle experiments were carried out to evaluate the effects of BS-12 on the flotation of magnesite and dolomite with NaOL. The results demonstrated that BS-12 had little collection effect on both magnesite and dolomite, but the mixture of BS-12 and NaOL had better low-temperature resistance than NaOL, meanwhile, the mixture collector could effectively promote the flotation of magnesite to improve the separation of magnesite and dolomite, when their ratio was 3:2. The addition of BS-12 in NaOL flotation system could also enhance the surface activity and hydrophobicity of magnesite and dolomite. The effect mechanism of BS-12 on the flotation of magnesite and dolomite with NaOL was studied through zeta potential measurements, Fourier-transform infrared spectroscopy (FTIR), and molecular dynamics simulations. The results demonstrated that NaOL and the mixed collector could adsorb on the surfaces of the minerals by chemical interaction. The addition of BS-12 could weaken the electrostatic repulsion between NaOL ions and generate hydrophobic association with NaOL, which improves the adsorption of NaOL on surfaces of the minerals and enhances the flotation separation of magnesite and dolomite. [ABSTRACT FROM AUTHOR]

Dolomite reservoirs flourished during arid climatic periods in the Middle East, primarily in the Permo-Triassic, Upper Jurassic, and Oligo-Miocene formations. These dolomitized reservoirs are frequently linked to evaporites, exhibit isotopically enriched signatures, and tend to occur predominantly in the more restricted regions of carbonate platforms. These observations strongly support their origin through sabkha and evaporative reflux processes. Consequently, dolomite formation and distribution are primarily influenced by early diagenetic processes and climatic conditions during arid periods. Dolomitization has exerted a significant influence on reservoir properties within the studied carbonate platforms. Porosity distribution and variation are jointly controlled by several factors, including dolomite content, texture, crystal size, anhydrite abundance, dolomite cementation, and the extent of burial compaction. While dolomite textures can vary from fabric-preserving to fabric-destroying, the overall reservoir properties exhibit an ascending pattern from intertidal to shoal facies. This trend is primarily determined by the proximity to the source of dolomitizing brines. The downward percolation of brines, coupled with decreasing dolomitizing potential, leads to an increase in dolomite crystal size within depositional cycles as one moves further away from the anhydrite facies. Proximal areas, characterized by fine-grained intertidal and lagoonal facies, are more susceptible to anhydrite cementation and overdolomitization, resulting in significant porosity reduction. Conversely, in more distal regions, reservoir quality substantially improves, particularly in areas dominated by sucrosic dolomite or grain-rich facies. While this trend may be altered by compaction during burial, it underscores the crucial role of dolomitization in preserving porosity, especially in deeply buried carbonate reservoirs. [ABSTRACT FROM AUTHOR]

The Astaneh Fault is one of the active and seismic faults in the Shahroud sinistral fault system. Fault gouges can be seen in a completely pristine and unchanged form in the portions of this fault that have affected the carbonate rocks. Fault gouges are the direct product of lithology and are formed as a result of the fault slip from the host rocks. Studying these rocks for type, composition, mineralogical phases and structure can provide results on how the fault slip and gouge process occurs. The result of a seismic slip in faults, and especially in gouges, are different types of deformations, such as mineralogical and compositional deformations, depending on the conditions of their formation. From this deformation model, we can mention the thermal decomposition of calcite and dolomite, as well as the presence of siderite in gouges. In this article, by studying the combined [aggregated] microstructures in the Astaneh fault gouge, their relationship with seismic slip has been investigated. According to previous research, the Astaneh Fault is certainly a seismic fault. The presence of the resulting thermal decomposition of calcite and dolomite (calcium and magnesium oxide or periclase) and the welding of particles due to heat may be the key to seismic slip in this fault. [ABSTRACT FROM AUTHOR]

Microfacies studies were carried out on the Middle Miocene Marmarica Formation exposed at the Gabal Western Bahi El-Din and Gabal El-Najdeen, the Siwa Oasis, northwestern Desert (Egypt). It was distinguished into the lower, middle, and upper members. Eleven microfacies types were recognized, which include skeletal lime-mudstone, dolomitic lime-mudstone, intraclastic wackestone, bryozoan wackestone, foraminiferal wackestone, foraminiferal bryozoan packstone, glauconitic molluscan packstone, molluscan intraclastic packstone, pelletal peloidal skeletal packstone, dolostones, and claystone microfacies. This formation includes several types of emergence- meter-scale cycles (shallowing-upward). Field observations and petrographic analyses revealed that these cycles consist of pure carbonates and mixed siliciclastic carbonates. These cycles consist of four types of gradual cycles and six types of non-gradual cycles. The gradual emergence cycles indicate a balance between the rate of subsidence, sea level oscillations, and sedimentation rate. The non-gradual cycles indicate an irregular balance between sedimentation rate and subsidence rate. The non-gradual cycles denote high-frequency sea level variation and/or short-term sea level oscillations, which are associated with high carbonate formation. The depositional environments of the Marmarica Formation are restricted to lagoonal at the base, followed upward to open marine conditions. Both environments most probably characterize the platform setting. [ABSTRACT FROM AUTHOR]

Recently, a series of prolific fracture-vug reservoirs have been discovered in the lower Ordovician dolostone successions of the northern Tarim Basin. However, the genesis of these reservoirs remains unclear. In this study, observations on drilling cores and thin sections identify the pore space characterized by dissolved fractures, fissures, and vugs. Petrology, cathodoluminescence, and homogenization temperatures of fluid inclusions aid in establishing the diagenetic paragenetic sequence. Dissolving enlargement occurred after chemical compaction of overlying limestone and before the Permian volcanic activity. Breccia pores containing unique fillings of terrestrial materials (quartz sand and allogenic kaolinite) and calcite cements with negative δ18OPDB values (−18.4‰) along with 87Sr/86Sr ratios (up to 0.71026) indicate that the dissolving fluid originated from meteoric freshwater at the surface. The δ18OSMOW values of the calcite precipitating fluid (−2.1‰ to −8.7‰) further suggest freshwater as the source of the dissolving fluid, buffered by the Ordovician wall rocks or formation water. As the distance from the unconformity surface increases, both the homogenization temperature and δ18OPDB values of the breccia pore-filling calcite in the southern study area gradually elevate and deplete, respectively, indicating a rise in temperature during the infiltration of meteoric freshwater with increasing subsurface temperatures. The abnormal reflection bodies identified as reservoirs in seismic profiles along deep-seated strike-slip faults delineate these faults as the channel for the infiltration of meteoric freshwater. The penetrating strata of these faults and the high 87Sr/86Sr values of breccia pore-filling calcite suggest that karstification occurred during the Devonian period. Accordingly, we establish a deep karst model in which the Devonian meteoric freshwater penetrated along the strike-slip faults and dissolved the Ordovician dolostones, resulting in the development of deep buried karstic fault reservoirs in the southern region of the northern Tarim Basin. [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]

The issue of oversimplified Norian conodont taxonomy has set back the development of Norian conodont biostratigraphy of the western Tethys Realm for decades. The majority of stratigraphic studies used the name Epigondolella multidentata , a North American endemic, to gather specimens indicative of strata from the lower part of the middle Norian substage. Detailed conodont biostratigraphic investigations were carried out on the Norian hemipelagic cherty dolostones of the Mátyás Hill section in the Buda Hills (Hungary) in order to resolve the ' multidentata problem'. The age of the section ranges from the upper part of the lower Norian substage (Lacian-3) to the lower part of the middle Norian substage (Alaunian-1). The new species Ancyrogondolella manueli n. sp. is introduced, and A. transformis is documented for the first time in the Tethys. The studied conodont fauna significantly improves the correlation potential between the western Tethys and the eastern Pacific. [ABSTRACT FROM AUTHOR]

Seismic ruptures often propagate along fault zones cutting km‐thick sequences of carbonates (e.g., Wenchuan Mw 7.8, 2008, China; L'Aquila Mw 6.1, 2009, Italy). As a consequence, fault rock assemblages may record the seismic cycle under a wide range of loading conditions, temperatures (>1,000°C during co‐seismic slip), and fluid‐rock interactions. The Monte Camicia Thrust Zone in the Italian Central Apennines is exhumed from ∼3 km depth. We studied the seismic cycle recorded by a network of faults cutting bituminous dolostones in the footwall of the Monte Camicia Thrust. These faults accommodate up to several meters of displacement. Slip zones are mm‐ to cm‐thick and bounded by ultra‐polished ("mirror‐like") surfaces independently of their displacement. At the microscale, deformation is accommodated by cataclasis and pressure‐solution in carbonates, and viscous flow in the foliated bitumen. Some of the faults with displacements >0.10 m have multiple slip zones, separated by "mirror‐like" surfaces, and include clasts of foliated bitumen and fragments of older slip zones sealed by calcite precipitation. We conclude that (a) slip zones record post‐ to inter‐seismic (foliated bitumen) and co‐seismic (fragments of bitumen) deformation in a fluid‐rich environment (calcite precipitation) and (b) mirror‐like surfaces formed during all phases of the seismic cycle. Plain Language Summary: Earthquakes originate and propagate along faults and release elastic strain energy stored in their wall rocks for centuries to millennia in a matter of seconds. Consequently, earthquakes represent the paroxysmal phase of the seismic cycle, which includes pre‐, co‐, post‐, and inter‐seismic phases. Most deformation mechanisms occurring in fault zones during the seismic cycle are transparent to seismological and other geophysical investigations. Instead, ancient fault zones exposed at the Earth's surface allow us to investigate the deformation mechanisms activated during the seismic cycle. These mechanisms operate under varying conditions of temperature, stress, fluid‐rock interaction and slip rate (relative motion of the fault wall rocks >10−4 m/s during co‐seismic slip and from 0 to ≈10−7 m/s in the other phases). We studied a network of faults that cut through bituminous dolostones in the Italian Central Apennines. These faults are characterized by the presence of light‐reflecting (mirror‐like) surfaces. We found that the slip zones beneath the mirror‐like surfaces (MSs) recorded deformation mechanisms associated with the four phases of the seismic cycle. Furthermore, MSs, whose mechanism of formation is debated in the literature, may form during all phases of the seismic cycle. Key Points: Bituminous dolostones are cut by a dense network of fractures and faults that record the main phases of the seismic cycleAseismic slip occurs via cataclasis, pressure‐solution, and viscous flow in bitumen while larger faults record multiple seismic rupturesMirror‐like surfaces are found in all faults, regardless of their displacement, and are formed during all phases of the seismic cycle [ABSTRACT FROM AUTHOR]

In the Bakony Region, in the mines of dolomite (dolostone) surfaces between the settlements of Márkó and Pétfürdő (Várpalota), in rubble beds exposed by them and with the consideration of these, the process of rubble formation is studied here in order to interpret the characteristics of rubble beds (different thicknesses and vertical changes in grain size) in the studied area. The mines in the area (differentiated between old-school/traditional mining or mechanical mining) were classified with the consideration of mining methods. Rubble varieties were differentiated, the bedding of rubble beds was studied along profiles, and the elevation difference between mines of mechanical mining and Stream Séd was determined. The calcareous content and structure compactness of 124 samples originating from dolomite, rubble, and non-rubble in the Bakony Region were compared. The data prove that the rubble developed by dissolution. Dissolution might have been caused by both meteoric water and karstwater. The rubble of mines excavated by traditional mining mainly developed to the effect of the dissolution effect of meteoric water (the rubble beds are of coarser and coarser grain size downwards), while the mines excavated by mechanical mining were formed to the dissolution effect of karstwater (the rubble beds are coarser and coarser upwards). The formation of rubble by karstwater origin has not been mentioned in the literature yet. However, dissolution of meteoric water origin may also take place in the case of the latter, and dissolution of karstwater origin also plays a role in the development of mines excavated by traditional mining. [ABSTRACT FROM AUTHOR]

Alternative materials need to be mapped, characterized, and valued in order to reduce clay usage. A study was conducted on the utilization of waste dolomite material from a mirror manufacturing factory in the production of bricks where the factory disposes 2500 tons of dolomite waste annually. Dolomite residue was mixed with clay raw material in various mass ratios of 90/10, 87.5/12.5, 85/15, and 82.5/17.5 wt%, extruded with proper moisture content, dried at 110 °C, and fired at 1000 °C and 1100 °C. The addition of dolomite resulted in an efflorescence on the surface of the bricks while also providing thermal insulation advantages and higher fire resistance. The addition of dolomite allowed for an increase in firing temperature to 1100 °C, which was initially not possible due to the melting characteristics of the clay. Dolomite also decreased the density of the bricks, which is crucial in order to decrease the dead load in structures. The produced bricks are intended for internal wall applications because of the efflorescence on the surface of the bricks. Overall, the addition of dolomite improved thermal conductivity and density, and other characteristics also showed suitable results. [ABSTRACT FROM AUTHOR]

Estimating the performance of acid fracture in naturally fractured formation is a complex and computationally expensive process. Therefore, machine learning was utilized in this research to simplify a complex physics-based acid fracture model in naturally fractured dolomite formations. The physics-based model integrates fracture propagation, reactive transport, heat transfer, and reservoir productivity model. The performance of acid fracture depends strongly on acid design parameters (i.e., injection rate, acid concentration, etc.) and reservoir/natural fractures properties (i.e., reservoir permeability, natural fractures spacing, etc.). A parametric study was conducted, and based on a statistical analysis of 4900 simulation scenarios, we found that the acid volume, reservoir permeability, and natural fracture spacing are the most significant parameters. Also, the injection rate and fluid rheology are of paramount importance. A model based on machine learning tools such as support vector machine, fuzzy logic system, and Artificial neural network (ANN) was developed. The artificial neural network model outperforms the other two tools and has a prediction error of 3.3%. Finally, an empirical equation has been obtained from the ANN model. [ABSTRACT FROM AUTHOR]

The sanding process caused by karstification in dolomite creates a special sandy dolomite stratum, where the frequent catastrophic instability of the surrounding rock occurred during tunnel construction. In this study, the micro-origin and macro-performance of the sandy dolomite stratum are first discussed. Then, a numerical model based on the coupling method between the discontinuous deformation analysis and smoothed particle hydrodynamics is proposed to depict the heterogeneous dolomite formation with different sanding degrees. Following, the mechanical behaviors of the heterogeneous dolomite samples under uniaxial compression are studied after calibrating the numerical parameters with the two single materials sampled from the tunnel site respectively. Further, the instability disasters of the dolomite surrounding rock with different sanding degrees are reproduced, and the failure behaviors of tunnels are explained with respect to the stress distribution and plastic zone. The obtained results show that the rotation and dislocation of the remained dolomite block contribute to the unsmooth stress-strain curve and deterioration in uniaxial compressive strength. However, the block serves as the skeleton in the transmission of field stress in underground space, which improves the stability of the formation. [ABSTRACT FROM AUTHOR]

The natural wettability of apatite and dolomite and the effect of sulfuric acid (H2SO4) and sodium oleate (NaOl) on the floatability and wettability of both minerals were studied using single-mineral flotation and contact angle measurement. The flotation experiments demonstrated that adding NaOl, apatite, and dolomite had good floatability. After adding H2SO4, the floatability of apatite decreased significantly. H2SO4 effectively inhibits apatite flotation. Contact angle measurements show that the use of H2SO4 induces a significant difference in surface wettability between apatite and dolomite. The moderate addition of H2SO4 can increase the contact angle of dolomite. In order to study the selective inhibition mechanism of H2SO4 in phosphorite flotation, molecular dynamics simulations (MDSs) were conducted to investigate the interaction between H2SO4 and fluorapatite and dolomite at the atomic–molecular level. The results of MDSs reveal that H2SO4 interacts with Ca sites on both fluorapatite and defective dolomite surfaces, hindering the interaction of NaOl with Ca sites on both mineral surfaces. SO42− ions cannot prevent the interaction of oleate ions with Mg sites on dolomite surface. It is worth mentioning that SO42− ions occupy the defective vacancies formed due to the dissolution of CO32− on the surface of dolomite and interact with Ca sites. The remaining H2SO4 is subsequently adsorbed onto the surface of dolomite. Experimental and simulation results show that, due to the interaction of H2SO4 and NaOl, the surface of apatite can still undergo hydration forming a water molecule layer and maintaining a macroscopic hydrophilic property. In contrast, the oleate ions form an adsorption layer on dolomite transitioning it from a hydrophilic to a hydrophobic state. During the phosphate flotation process, the addition of an appropriate amount of sulfuric acid can further diminish the hydration of the dolomite surface, so that the surface of dolomite is more hydrophobic. [ABSTRACT FROM AUTHOR]

The "dolomite problem", which has confused scientists for nearly two centuries, is an important fundamental geological problem. The mineralogical characteristics of carbonate minerals show that the dolomite structure consists of an ordered arrangement of alternating layers of Ca2+ and Mg2+ cations interspersed with C O 3 2 − anion layers normal to the c-axis. The dolomite structure violates the c glide plane in the calcite structure, which means that dolomite has R 3 ¯ space group symmetry. The ordered dolomite has superlattice XRD reflections [e.g., (101), (015) and (021)], which distinguish it from calcite and high-Mg calcite. The calculation of thermodynamic parameters shows that modern seawater has a thermodynamic tendency of dolomite precipitation and the dolomitization reaction can be carried out in standard state. However, the latest thermodynamic study shows that modern seawater is not conducive to dolomitization, and that seawater is favorable for dolomitization in only a few regions, such as Abu Dhabi, the Mediterranean and the hypersaline lagoons in Brazil. The kinetic factors of dolomite formation mainly consist of the hydration of Mg2+, the presence of sulfate and the activity of carbonate. Current studies have shown that the presence of microorganisms, exopolymeric substances (EPS), organic molecules, carboxyl and hydroxyl functional groups associated with microorganisms and organic molecules, clay minerals with negative charges and dissolved silica facilitate magnesium ions to overcome hydration and thus promote Mg2+ incorporation into growing Ca-Mg carbonates. Similarly, the metabolic activity of microorganisms is conducive to the increase in alkalinity. However, the inhibitory effect of sulfate on dolomite formation seems to be overestimated, and sulfate may even be a catalyst for dolomite formation. Combining the carbonate crystallization mechanism with thermodynamic and kinetic factors suggests that the early stage of dolomite precipitation or the dolomitization reaction may be controlled by kinetics and dominated by unstable intermediate phases, while metastable intermediate phases later transform to ordered dolomite via an Ostwald's step rule. [ABSTRACT FROM AUTHOR]

The clumped isotope paleo-thermometer has become a valuable proxy for the burial history reconstruction of carbonate formations. To maximise the accuracy of these reconstructions, post-depositional alterations, such as recrystallisation and Δ47 isotope exchange reactions, must be understood. In this study, we examine the isotopic behaviour of calcites and early dolomite samples from the same stratigraphic intervals, and thus with similar burial history. This approach provides additional constraints on the kinetics of Δ47 reordering in dolomite during exhumation. Clumped isotope measurements were performed on 19 calcites and 15 early dolomites from the Permian, Jurassic, and Cretaceous periods from four locations in Oman spanning different burial regimes. The calcite and dolomite samples were collected from the rock matrix, based on the assumption that fine material was more susceptible to recrystallisation. Our results show that calcites and dolomites record different Δ47 values despite being subjected to the same thermal history. The maximum Δ47 temperature recorded in dolomites (181 ± 13 °C) corresponds to the oldest and most deeply buried Permian rock. This value is approximately 35 °C higher than those measured in the co-located and coeval calcite matrix (145 ± 14 °C). This discrepancy suggests that calcite and dolomite have different kinetic parameters. Our data confirm (1) that dolomite Δ47 values are more resistant to alteration during burial and exhumation than Δ47 calcite values, and (2) that dolomite has a higher Δ47 closing temperature than calcite during cooling. The presence of two mineral phases with distinct kinetic parameters in the same stratigraphic unit provides additional constraints on models of burial and uplift. In addition, mineralogical data coupled with Δ47 and burial depths suggest that the progressive development of dolomite cation ordering is driven by temperature elevation, as previously suggested. [ABSTRACT FROM AUTHOR]

To investigate the mechanical properties of fractured dolomite, this study analyzed the fracture characteristics (dip angle, length, position, quantity) using the Pearson coefficient and MIC coefficient. Subsequently, the data pertaining to fracture characteristics is preprocessed using a third-degree polynomial, and a three-classification strategy is implemented to improve the logistic regression algorithm to establish the strength prediction model of fractured dolomite. Furthermore, the significance order of the impact of fracture characteristics on rock strength was determined using the numerical simulation software PFC3D, and the dip angle effect was explained from the perspective of internal fracture propagation within the rock. The results show that: (1) When the regularization coefficient λ = 10,000, the algorithm has the highest prediction accuracy and the strongest model generalization ability. (2) The numerical simulation analysis software PFC3D can accurately invert rock failure process and characteristics, and the order of influence of fracture characteristics on rock strength is dip angle > length > position. [ABSTRACT FROM AUTHOR]

Microbially induced carbonate precipitation (MICP) is a new foundation treatment technology, which can improve the mechanical properties of soil. In this study, sand specimens containing different magnesium/calcium ion concentration ratios (Mg2+/Ca2+=0/0.5 , 0.1/0.4 , 0.2/0.3 , 0.25/0.25 , 0.4/0.1 , and 0.5/0) were selected. Moreover, the effects of magnesium ions on the mechanical properties and mechanism of the biocemented sand were explored by oedometer tests, unconfined compressive strength tests, cyclic triaxial tests, scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results showed that when the Mg2+ concentration is low, with increasing Mg2+/Ca2+ , the compressibility of the biocemented sand decreases, the unconfined compressive strength increases, and the antiliquefaction performance improves. When Mg2+/Ca2+=0.2/0.3 , the sand specimen showed the worst compressibility and the best unconfined compressive strength and antiliquefaction performance. When the Mg2+ concentration was high, all the mechanical properties of the specimen were weakened. Low Mg2+ concentrations promote the formation of aragonite, whereas high Mg2+ concentrations promote the formation of dolomite. In addition, the SEM and XRD results verified the effect of Mg2+ on the crystal morphology and composition. This study showed that low Mg2+ concentrations can be added to improve the mechanical properties of the sand specimen and achieve a better reinforcement effect when using MICP to consolidate the soil. [ABSTRACT FROM AUTHOR]

Methane‐derived authigenic seep carbonates occur globally along continental margins. These carbonates are important archives to identify seep dynamics, the source of the ascending methane‐enriched fluids together with their timing, and are an important carbon sequestration mechanism. Recently, seep carbonates were discovered in the Levant Basin in the south‐eastern Mediterranean Sea. To elucidate past seepage activity and dynamics across the basin, different seep carbonate morphologies (chimneys, crusts and pavements) retrieved from the Levant Basin were mapped based on remotely operating vehicle data and analysed using standard sediment petrographic techniques, X‐ray diffraction and stable carbon and oxygen isotope analyses. Carbonate chimneys consist of micrite (δ13CVPDB of −10‰ to +5‰) with dispersed baryte and dolomite crystals, fan‐shaped aragonite (δ13CVPDB of −52‰ to −30‰) and high‐magnesium calcite cements, with the latter often growing from low‐magnesium calcite spherules. Botryoidal low‐magnesium calcite cements are forming in small cavities. Carbonate crusts consist of micrite with low‐magnesium calcite breccias, high‐magnesium calcite nodules (δ13CVPDB of −35‰ to −20‰) and cements, and partially replaced fan‐shaped aragonite cements. Carbonate pavements consist of low‐magnesium calcite microsparite, micritic dolomite and high‐magnesium calcite. Fan‐shaped aragonite is locally present as pore‐lining cement. Iron oxides are often seen coating the low‐magnesium calcite, high‐magnesium calcite and dolomite cements. Chimneys and crusts, characterised by high amounts of high‐magnesium calcite and aragonite, are interpreted to have formed through advective methane fluxes. Pavements, with high quantities of dolomite, are explained as the product of diffusive methane flux. Sediment petrographic and geochemical analysis of the different carbonate morphologies and cement phases therein witness distinct modes of ascending fluid fluxes and their mixing with marine pore water and/or sea water during precipitation of the individual phases. [ABSTRACT FROM AUTHOR]

The low-temperature formation of dolomite (CaMg(CO3)2) is undoubtedly a long and interesting geological problem, which has troubled many researchers for centuries to explore the formation of dolomite. Recently, efforts have been made by synthesizing dolomite analogues such as norsethite (BaMg(CO3)2), PbMg(CO3)2, with Ba and Pb to replace Ca and investigating their reaction pathways. In this study, we reported our efforts to synthesize dolomite-related complex carbonates by using the mechanical ball milling method as a new approach to control the solid–water ratio compared to the commonly used solution method. Two analogues of norsethite and PbMg(CO3)2 have been simply obtained even at stoichiometric molar ratio of Ba/Mg = 1:1 and Pb/Mg = 1:1 with various parameters examined; and product properties including morphology and phase compositions were investigated by a range of techniques, including XRD, SEM-EDS, and FTIR. Finally, we attempted to synthesize dolomite and compared the differences from the synthesis of analogues. In conclusion, we have synthesized norsethite and PbMg(CO3)2 in one step by the ball milling method, which greatly reduces the reaction time compared with the conventional solution method and may provide other choices for the formation of dolomite. [ABSTRACT FROM AUTHOR]