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Cave-monitoring studies clarify the climatic, surface vegetation, and karst processes affecting the cave system and lay the foundation for interpreting geochemical stalagmite records. Here we report the monitoring of cave air, bedrock chemistry, and drip water [delta].sup.13 C.sub.DIC, [delta].sup.18 O, and [delta]D, as well as 16 trace elements, covering a full annual cycle spanning the 16 months between November 2019 and March 2021 in La Vallina cave in the northwestern Iberian Peninsula. While decreased rainfall and increased evapotranspiration in the summer months lead to a strong reduction in drip rates, there is little seasonal variation in [delta].sup.18 O and [delta]D in a given drip, likely reflecting the discrete moderately mixed to well-mixed karst water reservoirs. Small differences in [delta].sup.18 O and [delta]D between drip sites are attributed to variable evaporation intensity and/or transit times. The carbon isotope signature of the dissolved inorganic carbon of drip water ([delta].sup.13 C.sub.DIC) is likely driven by seasonal changes in the temperature controlling biological processes (vegetation and microbial soil activity), resulting in minimum [delta].sup.13 C.sub.DIC in summer and autumn months. Increased bedrock dissolution due to higher soil pCO.sub.2 in summer and autumn results in increased trace element concentrations of congruently dissolved elements. Cave air measurements (pCO.sub.2, [delta].sup.13 C.sub.air, and temperature) indicate the seasonal ventilation (winter) and stagnation (summer) of cave air. The opposite effects of reduced cave air pCO.sub.2, seasonally variable biological activity, and increased drip rate limit the extent of the seasonal variation in degassing and prior calcite precipitation (PCP) supported by trace elements (Sr/Ca index). Estimated stalagmite growth rates using monitoring data suggest biannual phases of potential calcite precipitation in summer and winter and growth cessation during spring and autumn, depending on cave and drip water conditions and the location within the cave, which has important implications for the proxy interpretation of stalagmite records.

Calcite veins are a common product of hydrothermal fluid circulation. Clumped-isotope palaeothermometry is a promising technique for fingerprinting the temperature of hydrothermal fluids, but clumped-isotope systematics can be reset at temperatures of > ca. 100 °C. To model whether the reconstructed temperatures represent calcite precipitation or closed-system resetting, the precipitation age must be known. LA-ICP-MS U–Pb dating of calcite is a recently developed approach to direct dating of calcite and can provide precipitation ages for modelling clumped-isotope systematics in calcite veins. In this study, clumped-isotope and LA-ICP-MS U–Pb calcite analyses were combined in basalt-hosted calcite veins from three settings in Scotland. Samples from all three localities yielded precipitation temperatures of ca. 75–115 °C from clumped-isotope analysis, but veins from only two of the sites were dateable, yielding precipitation ages of 224 ± 8 Ma and 291 ± 33 Ma (2σ). Modelling from the dated samples enabled confident interpretation that no closed-system resetting had occurred in these samples. However, the lack of a precipitation age from the third location meant that a range of possible thermal histories had to be modelled meaning that confidence that resetting had not occurred was lower. This highlights the importance of coupling clumped-isotope thermometry and LA-ICP-MS U–Pb calcite dating in determining the temperature of hydrothermal fluids recorded in calcite veins. This paired approach is shown to be robust in constraining the timing and precipitation temperature of calcite formation, and thus for tracking hydrothermal processes.

The development of alternatives to soil stabilization through mechanical and chemical stabilization has paved the way for the development of biostabilization methods. Since its development, researchers have used different bacteria species for soil treatment. Soil treatment through bioremediation techniques has been used to understand its effect on strength parameters and contaminant remediation. Using a living organism for binding the soil grains to make the soil mass dense and durable is the basic idea of soil biotreatment. Bacteria and enzymes are commonly utilized in biostabilization, which is a common method to encourage ureolysis, leading to calcite precipitation in the soil mass. Microbial-induced calcite precipitation (MICP) and enzyme-induced calcite precipitation (EICP) techniques are emerging trends in soil stabilization. Unlike conventional methods, these techniques are environmentally friendly and sustainable. This review determines the challenges, applicability, advantages, and disadvantages of MICP and EICP in soil treatment and their role in the improvement of the geotechnical and geoenvironmental properties of soil. It further elaborates on their probable mechanism in improving the soil properties in the natural and lab environments. Moreover, it looks into the effectiveness of biostabilization as a remediation of soil contamination. This review intends to present a hands-on adoptable treatment method for in situ implementation depending on specific site conditions.

High-pressure phase transformations between the polymorphic forms I, II, III, and IIIb of CaCO 3 were investigated by analytical in situ high-pressure high-temperature experiments on oriented single-crystal samples. All experiments at non-ambient conditions were carried out by means of Raman scattering, X-ray, and synchrotron diffraction techniques using diamond-anvil cells in the pressure range up to 6.5 GPa. The composite-gasket resistive heating technique was applied for all high-pressure investigations at temperatures up to 550 K. High-pressure Raman spectra reveal distinguishable characteristic spectral differences located in the wave number range of external modes with the occurrence of band splitting and shoulders due to subtle symmetry changes. Constraints from in situ observations suggest a stability field of CaCO 3 -IIIb at relatively low temperatures adjacent to the calcite-II field. Isothermal compression of calcite provides the sequence from I to II, IIIb, and finally, III, with all transformations showing volume discontinuities. Re-transformation at decreasing pressure from III oversteps the stability field of IIIb and demonstrates the pathway of pressure changes to determine the transition sequence. Clausius–Clapeyron slopes of the phase boundary lines were determined as: Δ P /Δ T  = −2.79 ± 0.28 × 10 −3  GPa K −1 (I–II); +1.87 ± 0.31 × 10 −3  GPa K −1 (II/III); +4.01 ± 0.5 × 10 −3  GPa K −1 (II/IIIb); −33.9 ± 0.4 × 10 −3  GPa K −1 (IIIb/III). The triple point between phases II, IIIb, and III was determined by intersection and is located at 2.01(7) GPa/338(5) K. The pathway of transition from I over II to IIIb can be interpreted by displacement with small shear involved (by 2.9° on I/II and by 8.2° on II/IIIb). The former triad of calcite-I corresponds to the [20-1] direction in the P 2 1 / c unit cell of phase II and to [101] in the pseudomonoclinic C 1 ¯ setting of phase IIIb. Crystal structure investigations of triclinic CaCO 3 -III at non-ambient pressure–temperature conditions confirm the reported structure, and the small changes associated with the variation in P and T explain the broad stability of this structure with respect to variations in P and T . PVT equation of state parameters was determined from experimental data points in the range of 2.20–6.50 GPa at 298–405 K providing K T 0  = 87.5(5.1) GPa, ( δK T / δT) P  = −0.21(0.23) GPa K −1 , α 0  = 0.8(21.4) × 10 −5  K −1 , and α 1  = 1.0(3.7) × 10 −7  K −1 using a second-order Birch–Murnaghan equation of state formalism.

Die C/O-Isotopenzusammensetzung von Speläothemen der Makkaronihalle der Hüttenbläserschachthöhle in Iserlohn belegt eine klare Trennung zwischen kalt- und warmzeitlichen Calciten. Rhomboederkristalle und sphärolithische Speläopartikel weisen mit δ18O-Werten zwischen –8.9 und –17.9 ‰ (VPDB) sowie mit δ13C-Werten zwischen +0.7 und –6.1 ‰ eine von normalen Speläothemen (Stalagmiten, Excentriques, Mikrobecken - Kristalle, Sinterfahnen; δ18O: –4.0 bis –6.1 ‰; δ13C: –4.9 bis –10.9 ‰) deutlich abweichende C/O-Signatur auf. Die kaltzeitlichen Calcite zeigen in der C/O-Isotopenzusammensetzung einen Trend zu leichteren O- bei schwereren C-Werten. Dabei entsprechen die Partikel mit schwereren O- bei leichteren C-Werten einer kaltzeitlichen Genese in Wasserbecken auf Eis, während die Partikel mit leichteren O- bei schwereren C-Werten eine für Ausfrieren karbonathaltiger Wässer typische Zusammensetzung widerspiegeln. Mit 230Th/U-Datierungen werden mehrere Ausfrierzeiten von Eisseen zwischen 28.6 und 33.0 ka für die jüngere Weichselkaltzeit im nordwestdeutschen Raum belegt. Die Ausfrierzeiten in der Makkaronihalle belegen eine Mindestdicke von 34 m für den Permafrostboden dieser Zeiten im nördlichen Sauerland.

A growing body of evidence suggests the interaction between arc magmas and crustal carbonates may play a large role in outgassed CO.sub.2 at arcs. We examine magma-carbonate interactions within the shallow ( 25% calcite assimilation, producing up to 11 wt% CO.sub.2, orders of magnitude higher than the CO.sub.2 solubility of the parent melt (0.11 wt% CO.sub.2). We interpret the orbicules as Ca-rich hybrid melts produced from limestone assimilation that did not homogenize with the host dike magma and underwent crystallization during rapid ascent, possibly propelled by the excess CO.sub.2. Our results inform on the amount and mechanism of CO.sub.2 transport at low crustal pressures ( 1.16 Tg CO.sub.2/year during its ~ 34 Myr lifespan.

The central part of the Bashkirian Meganticlinorium hosts abundant bodies of mafic intrusive rocks of the low-Ti (LTi) type (<1 wt % TiO.sub.2), which include picrites, picrodolerites, and metasomatic rocks (carbonate-talc and chlorite-quartz rocks with phlogopite, calcite, and dolomite) after picrites. Phlogopite was extracted from metasomatic rocks. According to the .sup.40Ar/.sup.39Ar studies, phlogopite shows a plateau with an age of 1356 ± 16 Ma. The picrites most likely underwent metasomatosis related to early magmatic processes almost synchronous with intrusion of picrites. Similar age values are known for a series of intrusive bodies in the north of the Bashkirian Meganticlinorium, which belong to the high-Ti (HTi) type. Our data indicate in favor of the possibility that the intrusions with LTi and HTi rocks formed synchronously, at least, at the late stage of the Mesoproterozoic magmatic activity.

The appearance of cracks is one of the reasons that affect the performance of asphalt pavement, and traditional repair methods have the potential problem of causing adverse effects on the environment. In this paper, an environmentally friendly method for asphalt concrete crack repair was investigated using microbially induced calcite precipitation (MICP) for asphalt concrete cracks of different widths (0.5 mm, 1.0 mm, 1.5 mm, and 3 mm), and the effectiveness of repair was evaluated using nondestructive and destructive experiments. A varied ultrasonic pulse velocity was used to evaluate the healing process, and it was found that the samples with an initial crack width of 0.5 mm showed the most significant increase in wave velocity of 18.06% after repair. The results also showed that the uniaxial compressive strength and indirect tensile strength of the MICP-repaired samples recovered up to 47.02% and 34.68%. Static creep test results showed that MICP-repaired samples with smaller width cracks had greater resistance to permanent deformation. The results of uniaxial compressive strength tests on larger width (3 mm) cracks repaired by MICP combined with fibers showed that the strength of the samples was significantly increased by the addition of fibers. In addition, the SEM/EDS results showed that the MICP products were spherical calcite particles with a particle size distribution from 0 to 10 μm. This study shows that MICP has some potential for repairing cracks in asphalt concrete of different widths within the range investigated.

Blue calcite mineral formations occurring within Paleozoic marbles of Central Anatolia have been investigated in terms of their mineralogical and geochemical characteristics, as well as their potential for use as ornamental stones or decorative objects. XRD analyses of samples with different color tones (white, grayish-blue, and blue) revealed that the white sample contains only calcite, the grayish-blue samples include calcite and dolomite, while the blue sample contains calcite and quartz. XRF and ICP-MS analyses indicate a marked enrichment of trace elements such as Fe, Cr, and Ni in the blue sample, and Mn and Fe in the grayish-blue samples, suggesting these elements may influence the observed color variations. The presence of dolomite in grayish-blue samples and quartz in the blue sample corresponds to elevated MgO and SiO2 contents, respectively. Based on their distinct colors, textures, transparency, and other aesthetic properties, the grayish-blue and blue marbles show significant potential for use as decorative stones or ornamental objects.