Basalt carbonation can permanently immobilize CO2, but the coupled controls of host-rock dissolution, carbonate growth, and secondary-product formation remain incompletely constrained. This study integrates petrography, powder X-ray diffraction, SEM-BSE-EDS, color cathodoluminescence, LA-ICP-MS, stable and clumped isotopes, and hydrothermal experiments to investigate banded carbonate cements in basalts from the Quaternary Sverrefjellet volcano, Svalbard. Two adjacent cement areas preserve the same outward sequence: irregular proto-dolomitic and dolomite-composition Ca-Mg carbonate, finely laminated and increasingly Mg-rich carbonate, radiaxial-fibrous Ca-bearing magnesite, and a fine-grained Fe-rich outer assemblage containing Ca-Mg-bearing siderite compositions. Si-rich reaction material occurs at the basalt-carbonate interface and along carbonate boundaries, indicating that carbonate precipitation was coupled to incongruent silicate alteration. LA-ICP-MS and principal component analysis distinguish substrate-influenced inner carbonate, trace-element-poor Mg-rich carbonate, and a chemically distinct Fe-Mn-Zn-Ni-rich outer assemblage. Bulk-carbonate δ13C values of -4.5 to -2.4‰ VPDB are compatible with a deep-seated carbon contribution, potentially of magmatic origin, within a mixed carbon system, whereas Δ47 thermometry yields apparent formation or re-equilibration temperatures of 113.3-206.2 °C. Hydrothermal carbonation of separately collected Sverrefjellet basalt-xenolith material at 100 °C for 45 days and 200 °C for 4 days produced magnesite-dominated assemblages with dolomite-composition Ca-Mg carbonate, localized Fe-rich carbonate, internal Ca-Mg zoning, and associated Si-rich reaction products. The experiments reproduce the principal mineralogical, compositional, and textural outcomes of the natural system, although not its complete spatial sequence. Together, the results are consistent with a reaction front in which possible external fluid renewal was superimposed on local reaction-driven evolution controlled by host-rock heterogeneity, changing cation availability, growth kinetics, redox-sensitive Fe behaviour, and reaction–transport feedbacks. Sverrefjellet therefore provides a process benchmark for phase-selection and reactive-transport models of engineered basalt CO2 mineralization.

Phreatic calcite that forms mammillaries has been found in the Petralona cave system in Mt. Kalavros, N. Greece. These speleothems are formed during the latest stages of hypogene speleogenesis, and their geochemistry can provide valuable insights into the formation water and the conditions of speleogenesis. Optical microscopy, chemical analyses of major and trace elements, gas composition in fluid inclusions, carbon and oxygen isotopes, clumped isotopes and U-Pb dating were conducted on representative phreatic samples of mammillary calcite from the mammillaries. The results suggest speleogenesis already active in the Late Miocene and Early Pliocene that was related to the local geothermal field, characterized by significant arsenic content and that the late stages of speleogenesis that formed the mammillaries took place at a relatively low temperature of about ~24–29 °C between 4 and 2 Ma. Cave-forming water in this field has a deep circulation, reaches the Monopigado Granodiorite before rapidly rising into the overlying limestone. Dissolution during speleogenesis was driven by carbon dioxide. In addition, gas hydrocarbons, traces of H₂S and SO₂ were found in the fluid inclusions, indicating a possible mixing of groundwater with a gaseous phase similar to the gas emissions at the broader area, in and around the Epanomi gas field. The uplifting of the Mt. Kalavros rocks, at a minimum average rate of 45 m Ma⁻¹ over the last ~4 Ma (oldest cave mammillary) and a maximum average rate of 71 m Ma⁻¹ of the last ~2 Ma, accompanied by denudation, brought the caves close to the surface.

Clumped isotope thermometry is a robust technique for reconstructing carbonate formation temperatures; however its analytical precision is highly dependent on instrumental stability. In this study, we address the challenge of achieving long-term 047 repeatability using a Thermo ScientificTM 253 Plus 10 kV isotope ratio mass spectrometer (IRMS) coupled to a Kiel IV automated carbonate preparation device. The IRMS is equipped with 1013 Omega resistors on high-gain Faraday cups. To minimize the impact of daily laboratory temperature fluctuations, we developed and implemented a prototype Peltier-based cooling system for the amplifier housing. The combined approach reduced long-term 047 standard deviation from 40 to 45 ppm (occasionally reaching up to 60 ppm under extreme conditions) to around 32 ppm. Validation was performed using international carbonate standards and natural travertine samples with known formation temperatures (10-95 degrees C), and results were bench-marked against previously published data. These improvements demonstrate a practical pathway towards achieving high-precision clumped isotope measurements under variable environmental conditions, and they provide a reproducible methodology for laboratories operating similar instrumentation in comparable settings.

Quantitative reconstruction of temperature remains the major focus and challenge of paleoclimate research, especially in the terrestrial realm. This study is aimed at testing the usefulness of Δ47 of earthworm’s biospheroids (EBS) as a temperature proxy by comparing the EBS-derived T47 values to those obtained from previously studied land snails. For this purpose, the Dunaszekcső loess record in southern Hungary has been selected, which is an extensively studied section with a high resolution 14C chronology [1,2,3], revealing stadial-interstadial variations in sedimentation rates.Sixteen samples were collected in 10 cm resolution from the loess layers between 850-770 cm and 695-615 cm representing the GI-5.1 (30.6-30.8 ka) and GI-3.1 (27.5-27.8 ka) periods and surrounding stadials [4]. The associated temperature was calculated previously between 8-15 °C [4] based on the clumped isotope compositions of mollusc shells of these layers.The impact of sample preparation methods on Δ47 values of secondary carbonates is unknown and is a potential concern. To test this, two different sample preparation methods were applied on Trochulus hispidus shells recovered from the mentioned loess layers: 1) treatment in 1 m/m% HCl solution and 2) treatment with 3 m/m% H2O2 solution under vacuum and in ultrasonic bath in ultrapure water. The reconstructed temperatures based on the Δ47 values of the snail shells typically fell between 7-15 °C (HCl pretreatment) and 9-14 °C (H2O2 pretreatment), in very good agreement with previous published land snail T47 data [4]. The average temperatures obtained from biospheroids reveal the same stadial-interstadial temperature pattern previously reconstructed by molluscs. The mean T47 values of the two pretreatment methods are within the expected temperature range derived from the snail shells.Clumped isotope analysis was also performed on biospheroid samples from the same layers, and the calculated temperatures were compared with those obtained from snail shells by Újvári et al. [4]. To demonstrate that the biospheroid carbonates from the same layers are of the same age as the examined molluscs, we performed radiocarbon dating on the biospheroids. Our primary goal is to investigate whether the Δ47 compositions are affected by the so-called vital effect and to what extent the formation of biospheroid carbonates is influenced by these kinetic effects. To achieve this goal, a long-term experiment is going on. We perform climate chamber experiments [5,6,7] at temperatures of 8, 11 and 15 °C. Other variables, including relative humidity, CO2 concentrations and the stable isotope compositions of diet and spray liquid are also controlled. The first results will be presented. References:[1] Újvári, G. et al. 2014, Quaternary Science Review Vol. 106, 140-154[2] Újvári, G. et al. 2016, Quaternary Geochronology Vol. 35, 43-53[3] Újvári, G. et al. 2019, Palaeogeography, Palaeoclimatology, Palaeoecology Vol. 518, 72–81[4] Újvári, G. et al. 2021, AGU, Advancing Earth and Space Science, Paleoceanography and Paleoclimatology, Volume 36, Issue 8[5] Canti, M.G. 2009, Soil Biology & Biochemistry Vol. 41, 2588-2592[6] Lambkin, D.C. et al. 2011, Applied Geochemistry Vol. 26, S64-S66[7] Versteegh, E.A.A et al. 2014, Soil Biology and Biochemistry Vol. 70, 159-

The Eocene period experienced several hyperthermal events with the Paleocene-Eocene Thermal Maximum being the most significant. During this event, global mean surface temperatures were 5-6 degrees C higher and latitudinal temperature gradients were reduced compared to the late Paleocene. Unlike marine temperature records, terrestrial archives are limited, posing challenges for testing climate model competence in simulating the magnitude and spatial patterns of temperature change under a high carbon dioxide climate. Here we analysed mudstone paleosols from the Tremp Group in Spain to reconstruct soil temperatures using carbonate nodules. Clumped isotopes revealed median calcification temperatures of 33.9 and 39.2 degrees C for the Late Paleocene and Paleocene-Eocene Thermal Maximum, respectively. The findings suggest a similar to 5 degrees C summer soil temperature increase during the Paleocene-Eocene Thermal Maximum. Continental proxy and model data indicate reduced (0.7-0.4 degrees C/degree) meridional temperature gradients between 25 and 75 degrees N latitudes, indicating more uniform heat distribution across latitudes than at present.

The central parts of Southeastern Europe, located along the northern boundary of the Mediterranean region, represent a transient zone affected by both Mediterranean and continental atmospheric influences. An impressive record of past climate variations in this region has been obtained mainly from lacustrine sediments in the southern parts and loess deposits in the northern parts. Although radiometrically dated speleothems provide higher resolution records with superior chronological constrains, not many published speleothem records are available from this region, with none covering Marine Isotope Stage (MIS) 7. We present here a record of MIS 8 – MIS 7 sub-orbital-scale climate variations obtained from a U-Th dated Macedonian subaqueous speleothem composed of mammillary calcite that deposited between 246.0±6.2 ka and 225.8±5.4 ka, covering Termination III (T-III), MIS 7e and MIS 7d. Proxy records were obtained from conventional and clumped isotopes, with an additional insight from uranium isotopes and petrography. The stable isotope data has relatively high resolution (60-310 yr) allowing identification of millennial-, and at sections centennial-scale climate variations. The speleothem record reflects an increased Mediterranean influence, as suggested also by other proxy records from the region, especially during MIS 7e. However, periodically increased continental influences are also identified, especially during T-III and MIS 7d. The calcite δ18O values seem to reflect mainly temperature-controlled precipitation δ18O, with changes between Mediterranean and Atlantic moisture source also noticeable. The δ13C values mainly reflect the alternating influence of continental and Mediterranean climates, expressed by summer moisture availability, partly overprinted by temperatures. Increased winter precipitation during MIS 7e is identified, corresponding to Sapropel 9. The abrupt climate change during T-III is represented in the stable isotope record with an event that corresponds to the S8.1 stadial event, as identified in a speleothem from Ejulve Cave (NW Spain), and the Younger Dryas-III weak monsoon interval, as identified by Chinese speleothem records, considered analogous to either Heinrich 1 or Younger Dryas in Termination I, respectively.

Knowledge of the formation temperatures of geological deposits is essential for investigating their genesis. Oxygen isotope thermometry (OIT), using the temperature dependence of oxygen isotope fractionation between host carbonate mineral and mineral-forming water trapped in fluid inclusions, and clumped isotope thermometry, based on the degree of 13C and 18O clumping, are receiving increasing interest. However, only a few studies have applied combinations of these methods, and their databases are limited. In this study, we compare OIT and clumped isotope temperatures obtained for 18 samples from Mesozoic to early Cenozoic calcite veins. Our analysis indicates that the formation temperatures were preserved in the clumped isotopic compositions (16–45 °C), whereas the OIT temperatures were shifted to lower temperatures (− 2 to 33 °C). An OIT temperature shift occurred, due to a retrograde oxygen isotope exchange between the fluid inclusion water and the host calcite. These results imply that the retrograde isotope exchange should be taken into consideration, even for low-temperature carbonate deposits, if a sufficiently long time is available.

Massive additions of 13C-depleted carbon to the atmosphere-ocean system at 55.9 Myr ago led to global warming of 5–8 °C, profound floral/faunal turnovers and alteration of the global hydrological cycle at the Paleocene-Eocene boundary. Climate and environmental changes over the late Paleocene and Paleocene-Eocene Thermal Maximum (PETM) are well-preserved in continental deposits, formed in the subtropical zone (paleolatitude ~35 °N), in the Tremp-Graus Basin, northern Spain. One of the key exposures is the Esplugafreda section, which is made up of ~250 m of red mudstones with abundant paleosols and contains numerous multi-episodic channel-like bodies of calcareous conglomerates and calcarenites. The paleosols contain abundant centimeter-sized soil nodules and gypsum indicating a semi-arid to arid paleoenvironment. The Paleocene-Eocene (P-E) boundary is located near the top of the continental section, based on a 6‰ negative carbon isotope excursion (CIE). The CIE spans more than 15–20 m of yellow cumulate paleosols formed during the Paleocene-Eocene Thermal Maximum (PETM). The post-PETM interval in the Esplugafreda section comprises 20 m of red paleosols rich in gypsum and characterized by normal soil nodule δ13C values.Here, we report the first carbonate clumped isotope thermometry data of selected soil carbonate bearing paleosol layers of the Esplugafreda sequence to quantify the magnitude of warming recorded in the sediments of this terrestrial subtropical site across the Paleocene-Eocene boundary. Soil nodules originated from red mudstone paleosols making up the upper part of the upper Paleocene Esplugafreda Formation and PETM yellow soils collected at two nearby sites. The nodules were sampled with a hand driller for Δ47 measurements, which were done using a Kiel IV carbonate device coupled to a Thermo Scientific 253 Plus IRMS at the Institute for Nuclear Research, Debrecen, Hungary. Stable carbon, oxygen isotope and clumped isotope compositions were calculated as the average of 8–16 replicate analyses of 100–150 μg of carbonate. The carbon and oxygen isotope ratios are reported in δ notation in per mil (‰) relative to the Vienna Pee Dee Belemnite (VPDB), while the temperature-dependent mass 47 anomaly on the I-CDES90°C scale. Temperatures were calculated using the Kele et al. (2015) calibration modified by Bernasconi et al. (2018) and the Anderson et al. (2021) calibrations.Soil carbonates of the Esplugafreda formation yield δ13Ccarb values between –8.55 and –5.85 ‰, while the PETM yellow soil carbonates are significantly more negative (–13.84 to –10.12 ‰), in good agreement with previous measurements. A much smaller, ~1.2 ‰ difference can be observed in the oxygen isotope compositions between these carbonates (δ18Ocarb: –5.46 to –4.13 versus –6.35 to –4.47 ‰). The Δ47-based paleotemperatures (T47carb) indicate mean soil carbonate formation of 33.8±9.5 °C during the late Paleocene, which are close to modern summer temperatures of subtropical regions. By contrast, a much higher mean temperature was recorded by soil carbonates of the PETM yellow soils (39±8.5 °C) with extreme (>40 °C) temperatures occurring 4 times more frequently than over the late Paleocene.This study was supported by the NKFIH through the OTKA K-137767 project.

Carbonate clumped isotope analysis, a relatively new methodology, is still developing rapidly, that is well described by the frequency of changes in the applied methodological conventions. The extent of development is also characterized by the growing, sometimes special, nature of the application areas. Innovations, while promising, can present unforeseen challenges and sometimes brings unexpected difficulties, such as the integration of 1013 Ohm resistance in the amplification circuits of Thermo Scientific 253 Plus 10 kV Isotope Ratio Mass Spectrometer (IRMS).The goal of this improvement was that even very small ion beams can be analyzed with the factor of 3 better signal to noise ratio, which is an important aspect from the point of view of clumped isotope analysis. Unfortunately, 1013 Ohm resistance has a significant temperature dependency, which highly influences the magnitude of the detected intensities as well as on the overall long-term stability of the measurement. The daily temperature fluctuation in summer is very significant in Hungary. Under extreme conditions, when the lab's air conditioning could not maintain the desired temperature range, the long-term Δ47 reproducibility of the system achieved an SD = 60 ppm value.In order to reduce this effect a prototype Peltier cooling device has been installed on the surface of the detector house of our IRMS. To demonstrate the achieved accuracy, precision, and long-term stability (SD

Mineral crusts formed under glaciers and ice sheets record the basal hydrology in their isotopic and elemental composition as well as their petrology. However, many of these crusts have been reworked, and in Antarctica few locations preserve in-situ subglacial deposits in presently deglaciated areas and consist of calcite or aragonite. In the interior of Antarctica, subglacially-precipitated minerals have been encountered as clasts in moraines, implying transport from an unknown, but presumed basal ice sheet source. Clasts consisting of opal and calcite associations were retrieved from moraines in the Transantarctic Mountains region (TAM, Antarctica) of the East Antarctic Ice Sheet (EAIS), with previous research interpreting opal precipitates as a marker of almost complete freezing of reducing basal waters associated with Late Pleistocene (ca. 129,000-11,7000 years ago) cold oceanic and atmospheric conditions. In contrast, calcite was related to basal EAIS water flow and oxic conditions associated with warm mid to Late Pleistocene climate cycles. Here, novel high-resolution transmission electron microscopy (HRTEM) observations demonstrate that opal and calcite co-precipitated in the mid to Late Pleistocene subglacial environment. In addition, HRTEM observations revealed that calcite and opal coexist with allophane, which was not detected previously. The occurrence of nanotwins in the calcite crystals and absence of porosity at the boundary between calcite and amorphous silica strongly suggest that crystallization pathways in the subglacial environment included non-classical particle attachment. Geochemical simulations based on solubility data of silicates (Ca-plagioclase) present in the bedrock and kinetic rate laws are proposed to explain co-precipitation of opal-calcite-allophane. These indicate that differing degrees of regelation at basal ice/water interface would have increased both pH and supersaturation of the residual basal fluid, thereby enabling crystallization of (Al)-Si-OH phases or calcium carbonate at near-freezing temperatures in the same aqueous environment. Considering that nano-scale observations hint at non-classical crystallization pathways, it is proposed that low temperature and the presence of dissolved organic carbon may have significantly inhibited or delayed nucleation of calcite/allophane/opal, and, therefore, supersaturation thresholds for amorphous CaCO3 formation may have been reached. Co-precipitation of calcite and opal questions a previous basal hydrology reconstruction based on the hypothesis of their separate occurrence. Furthermore, opal and calcite may have incorporated chemical species inherited from precursors, whereby an interpretation of their chemistry in terms of past environmental variations may be inaccurate if not supported by a reconstruction of crystallization pathways.

Shallow marine carbonates of the Anisian H & aacute;mor Dolomite Formation in the B & uuml;kk Mountains, NE Hungary were studied to determine the mechanism and controlling factors of the dolomitization. Petrographic features, along with C and O stable isotope properties of the investigated rocks, indicate near-surface/shallow burial dolomitization of the shallow, subtidal-peritidal carbonate succession. This occurred via long-term circulation of relatively low-temperature fluid of sea-water origin. Geothermal convection may have been the driving force of this circulation. For application of this model, we need to assume that segmentation of a previously-established shallow ramp had already initiated in the Western Neotethys earlier in the middle Anisian. Unfortunately, we have only indirect evidence of this in the studied area. Still, the structural evolution and the related paleogeographic setting may have been the basic controlling factors of the pervasive early diagenetic near-surface/shallow burial dolomitization of the H & aacute;mor Formation. The coarse crystalline dolomite cement in the fractures and pores was precipitated from relatively high temperature (cc. 170 degrees C) water. Comparing the stable isotope values of the bulk rock and the fracture-occluding dolomite cement phase suggests a host-rock buffered fluid flow probably in the Late Cretaceous deformation phase.

Pleistocene loess records of the Khovaling Loess Plateau (KLP) in Tajikistan provide rich collections of lithic artifacts demonstrating past human presence in the region. To understand the timing of human activity and environmental conditions prevailing at that time U-Th dating and clumped/stable C/O isotope measurements have been applied to modern and Pleistocene soil carbonates (SCs) collected at several sites on the KLP and surroundings. U-Th ages were corrected by two methods: 1) assuming an initial [Th-230/Th-232] activity ratio of 0.85 +/- 0.25 based on gamma spectrometry of loess/paleosol samples, and 2) the isochron technique using leachates and fully dissolved subsamples. Diagenetic alteration and potential U/Th mobilization and related isotope fractionation due to alpha-recoil was also modelled and found to be minor in the studied soil carbonates. Compared to model ages as references, uncorrected 230 Th ages are only acceptable if measured [Th-230/Th-232] activity ratios of leachates are high (>30), while Th-230 ages derived using method 1 are mostly overcorrected. It appears that SCs can be reliably dated by the U-series disequilibrium method in this sedimentary setting, but isochron dating cannot be spared. Application of the isochron method is required to derive (230)Thmodel ages, which ensures that the non-zero initial (230) Th and possible U-Th gain/loss due to alpha-recoil can be simultaneously corrected and reliable U-Th ages obtained. U-Th ages of Pleistocene SCs clearly demonstrate postpedogenic ingrowth of multiple, non-contemporaneous populations of SCs within loess/paleosol units, and that SC formation happened in many cases under cold, presumably dry glacial climate conditions. Considering that U-Th ages of SCs provide minimum ages of the sediment in which they form, these ages can be useful in developing loess stratigraphic models and for correlation of paleosols with marine isotope stages. This implies that the age of a given paleosol and any lithic artifacts it may contain, indicating human activity, cannot be younger than the age of SCs formed in that paleosol. This is due to the nature of soil carbonates, which can be the product of both syn- and post-depositional processes. Clumped isotope thermometry of SCs collected from modern soils at three sites in Tajikistan provide evidence for SCs dominantly recording summer season soil temperatures, while the calculated soil water oxygen isotope signatures reflect annual signals and carbonate precipitation from source waters incorporating rainfall from prior to and during SC formation. In contrast, some Pleistocene SCs record soil temperatures and stable isotope compositions more appropriate to glacial conditions, confirming the findings of U-Th ages, and highlighting the primary role of aridity-driven soil moisture changes in SC precipitation in this setting. Considering the interpretative complexities of SC stable isotope compositions, involving issues such as SC formation depth within a soil/paleosol profile, seasonality of SC growth and violation of the law of superposition, SC stable isotope proxy records of past climates cannot be considered as a set of clearly sequential data through time. This implies that such SC-based stable isotope records must be accompanied by U-Th dating of carbonates to be meaningful.

The Tyuya-Muyun massif in SW Kyrgyzstan hosts a number of caves some of which contain Ra- and U-bearing minerals that were extensively mined in the early 20th century. Previous studies have suggested that the caves of the Tyuya-Muyun have experienced a complex speleogenetic history, including epigene and hypogene processes. Here, we reconstruct the late stages of hypogene processes by studying subaqueous (calcite and barite spars, cave clouds), near-water table (rafts, folia) and vadose (flowstone) mineral deposits in Great Barite and Surprise caves. We determined the chronology (Th-230 dating), stable isotope composition (delta O-18, delta C-13 and Delta(47)), and formation temperature (fluid inclusion microthermometry and Delta(47)) of these minerals and reconstructed the oxygen isotopic composition of the paleo-water (delta O-18(w)). In contrast to previous hypotheses about cave evolution, we found no evidence of an initial epigenic karst phase. The earliest mineral deposits suggest already hydrothermal conditions, with calcite and barite forming at similar to 40-50 degrees C prior to 600 ka. Cave clouds in Great Barite Cave mark the beginning of the lowering of the groundwater table and also record a decrease in water temperature from 29.7 +/- 8.3 degrees C to 12.7 +/- 5.6 degrees C, as shown by Delta(47) thermometry. The latter temperature remained stable, within analytical uncertainties, during the past 600 ka, as indicated by Delta(47) results of near-water table and vadose speleothems in Surprise Cave. At the same time, the decrease in delta O-18(w) suggests a reduced contribution of thermal water and an increased input of colder meteoric water. By around 540-450 ka Surprise Cave emerged from the phreatic zone, as indicated by Th-230 ages of the highest folia and flowstone. This lowering of the water table continued until 84 ka and may have been related to the final uplift phase of the Tyuya-Muyun massif and the concomitant incision of the Aravan River forming the Dangi Gorge.

A combination of morphological observations, geochemical data from calcite minerals and geochronology by burial age dating and U-series is used to constrain the geological and geomorphological setting and the evolutionary stages of a hypogene karst system. This methodological suit is applied to Melni & ccaron;ka Pe & scaron;tera, a horizontal cave developed in carbonate breccia overlying dolomite marble in Melnica locality (N. Macedonia), where hydrothermal karst development occurred in both dolomite and calcite marble. The passage morphology of the cave, having a reverse triangle, Laugh & ouml;hle cross-sections, suggests development near the water table by slowly moving waters. Calcite crusts are found throughout the cave, and based on their relationship to passage morphology, appear to pre-date main horizontal passage formation. Their carbonate stable and clumped isotope and fluid inclusion noble gas compositions indicate cooling of the hydrothermal system with an increased contribution of shallower groundwater. U-series data suggests Early Pleistocene deposition of the calcite crusts. Water table notches and convectional features carved into breccia bedrock and calcite crusts point to subsequent development at and above the water table by condensation corrosion. The solutional aggressiveness near the water table was likely related to CO2, 2 , that previously degassed from the deeper parts of the system where calcite was depositing, and redissolved in the cooler, shallower waters. Due to poor connection with the surface, the cave air above the water table likely had high pCO2, 2 , that further helped to maintain aggressiveness of the groundwater at the water-air contact, and boosted condensation corrosion above it, preventing deposition of related secondary calcite minerals. The cave-hosting carbonate breccia deposited as an alluvial fan filling up a paleovalley cut into Upper Miocene sediments. Cosmogenic nuclide burial age dating of quartz fragments confirms Early Pliocene age for the breccia, and constrains the paleovalley incision to Late Miocene, likely related to base level lowering caused by the Messinian Salinity Crisis.

Dawsonite (NaAlCO3(OH)2) is widely known as a CO2 trapping mineral during the geological storage of CO2 (Carbon Capture and Storage). Dawsonite can occur naturally in various geological environments, however only few surface occurrences are known. The Covasna area (Eastern Carpathians) gives an excellent opportunity to study dawsonite in surface outcrop in the Hank ' o Valley and extend our knowledge about the possible precipitation environments of dawsonite. Based on the detailed petrographic and geochemical investigations of the rock and water samples from this area, formation environment of dawsonite and the concomitant mineral assemblage (e.g. alumohydrocalcite) were constrained. Based on our results, dawsonite and alumohydrocalcite formed at low temperature (7.6-20 degrees C). Utilizing the stable carbon, oxygen and hydrogen isotope composition of dawsonite separates (delta 13CDaw: +8.0 -+10.1 %o, delta 18ODaw: +40.7 -+46.7 %o, delta 2HDaw:-55 --42%o), the isotopic composition of the parental fluid was determined. Our results indicate that the dawsonite formed from a CO2 source, which has mantle origin. In addition, H2O which was present during the formation of dawsonite, had similar hydrogen isotope composition to recent spring waters, whereas the oxygen isotope composition is characterized by more positive values. This oxygen shifts relative to Global Meteoric Waterline might be related to water-rock interaction or contribution of metamorphic/magmatic water and oxygen isotope exchange between H2O and CO2.

Red calcite veins are found in Mesozoic limestones at several locations within the Transdanubian Range, western Hungary. Opinions on the origin and the formation conditions of the red calcites vary widely, with concepts ranging from high-temperature hydrothermal processes to speleothemic formation. The present study aims to constrain the formation temperatures and determine the fluid origins of the red calcites. Samples were taken from three locations previously investigated in earlier studies: the Sint & eacute;rlap quarry at S & uuml;meg, the Kesel & odblac; Hill quarry at Tatab & aacute;nya, and the Piliscsaba-J & aacute;szfalu quarry at Piliscsaba. Formation temperatures for the dark red calcites, presumably the earliest, ranged between 30 and 37 degrees C, as determined by the clumped isotopes method. The oxygen isotope compositions (518O) of the calcite-forming water were calculated using clumped isotope temperatures and the 518O values of calcite. These calculations revealed a fluid that had either undergone high-temperature water-rock interaction or contained an 18O-enriched component and the temperatures are much lower than thought previously, but higher than those of speleothems. The hydrogen isotope compositions of inclusion-hosted waters, along with the carbon and oxygen isotope values of red calcites, suggest that the three red calcite occurrences were caused by distinct fluid movements, likely at different times. This indicates that a single red calcite formation event can be ruled out.

Carbonate clumped isotope analysis, a relatively new methodology, is still developing rapidly, that is well described by the frequency of changes in the applied methodological conventions. The extent of development is also characterized by the growing, sometimes special, nature of the application areas. Innovations, while promising, can present unforeseen challenges and sometimes brings unexpected difficulties, such as the integration of 1013 Ohm resistance in the amplification circuits of Thermo Scientific 253 Plus 10 kV Isotope Ratio Mass Spectrometer (IRMS). The goal of this improvement was that even very small ion beams can be analyzed with the factor of 3 better signal to noise ratio, which is an important aspect from the point of view of clumped isotope analysis. Unfortunately, 1013 Ohm resistance has a significant temperature dependency, which highly influences the magnitude of the detected intensities as well as on the overall long-term stability of the measurement. The daily temperature fluctuation in summer is very significant in Hungary. Under extreme conditions, when the lab's air conditioning could not maintain the desired temperature range, the long-term Δ47 reproducibility of the system achieved an SD = 60 ppm value. In order to reduce this effect a prototype Peltier cooling device has been installed on the surface of the detector house of our IRMS. To demonstrate the achieved accuracy, precision, and long-term stability (SD <= 30 ppm) of the modified measurement system, we present results of clumped isotope analyses of international carbonate standard samples and naturally formed travertine samples (known formation temperatures are in the range of 5-95°C) and compare them with formerly published data of two reputable laboratories from the clumped community, which use different measurement equipment: ETHZ: Thermo Scientific MAT253 IRMS and Kiel IV automatic carbonate device [1] MIT: Nu Perspective IRMS and NuCarb automated sample preparation unit [2] Additionally, we offer insight into the infrastructure and analytical methodology of the clumped isotope laboratory established at ICER (ATOMKI, Debrecen, Hungary). The modification implemented and the attained long-term stability may serve as a valuable reference for other laboratories encountering similar challenges. Keywords: carbonate clumped isotope, Peltier cooling, long-term reproducibility References [1] Bernasconi, S. M., I. A. Müller, K. D. Bergmann, et al. (2018) Reducing uncertainties in carbonate clumped isotope analysis through consistent carbonate-based standardization. Geochemistry, Geophysics, Geosystems, v. 19, 2895-2914. [2] Anderson, N. T., J. R. Kelson, S. Kele et al. (2021) A Unified Clumped Isotope Thermometer Calibration (0.5–1,100°C) Using Carbonate-Based Standardization. Geophysical Research Letters, v. 48, e2020GL092069.

Carbonate geothermometry is a fundamental tool for quantitative assessment of the geothermal and geochemical evolution of diagenetic and hydrothermal systems, but it remains difficult to obtain accurate and precise formation temperatures of low-temperature calcite samples (below ~ 40 to 60 °C). Here, we apply three geothermometry methods (∆47-thermometry, nucleation-assisted fluid inclusion microthermometry—hereafter NA-FIM—and oxygen isotope thermometry) to slow-growing subaqueous calcite spar samples to cross-validate these methods down to 10 °C. Temperatures derived by NA-FIM and Δ47-thermometry agree within the 95% confidence interval, except for one sample. Regression analyses suggest that the real uncertainty of ∆47-thermometry exceeds the 1 SE analytical uncertainty and is around ± 6.6 °C for calcite spar that formed at 10–50 °C. The application of δ18O thermometry was limited to a few samples that contained sufficient primary fluid inclusions. It yielded broadly consistent results for two samples with two other geothermometers, and showed higher temperature for the third spar. We also found that calcite with steep rhombohedral morphologies is characteristic of low temperatures (11–13 °C), whereas blunt rhombohedra prevail in the 10–29 °C domain, and the scalenohedral habit dominates > 30 °C. This suggests that the calcite crystal morphology can be used to qualitatively distinguish between low- and higher-temperature calcite.

Massive additions of 13C-depleted carbon to the atmosphere-ocean system at 55.9 Myr ago led to global warming of 5–8 °C, profound floral/faunal turnovers and alteration of the global hydrological cycle at the Paleocene-Eocene boundary. Climate and environmental changes over the late Paleocene and Paleocene-Eocene Thermal Maximum (PETM) are well-preserved in continental deposits, formed in the subtropical zone (paleolatitude ~35 °N), in the Tremp-Graus Basin, northern Spain. One of the key exposures is the Esplugafreda section, which is made up of ~250 m of red mudstones with abundant paleosols and contains numerous multi-episodic channel-like bodies of calcareous conglomerates and calcarenites. The paleosols contain abundant centimeter-sized soil nodules and gypsum indicating a semi-arid to arid paleoenvironment. The Paleocene-Eocene (P-E) boundary is located near the top of the continental section, based on a 6‰ negative carbon isotope excursion (CIE). The CIE spans more than 15–20 m of yellow cumulate paleosols formed during the Paleocene-Eocene Thermal Maximum (PETM). The post-PETM interval in the Esplugafreda section comprises 20 m of red paleosols rich in gypsum and characterized by normal soil nodule δ13C values. Here, we report the first carbonate clumped isotope thermometry data of selected soil carbonate bearing paleosol layers of the Esplugafreda sequence to quantify the magnitude of warming recorded in the sediments of this terrestrial subtropical site across the Paleocene-Eocene boundary. Soil nodules originated from red mudstone paleosols making up the upper part of the upper Paleocene Esplugafreda Formation and PETM yellow soils collected at two nearby sites. The nodules were sampled with a hand driller for Δ47 measurements, which were done using a Kiel IV carbonate device coupled to a Thermo Scientific 253 Plus IRMS at the Institute for Nuclear Research, Debrecen, Hungary. Stable carbon, oxygen isotope and clumped isotope compositions were calculated as the average of 8–16 replicate analyses of 100–150 μg of carbonate. The carbon and oxygen isotope ratios are reported in δ notation in per mil (‰) relative to the Vienna Pee Dee Belemnite (VPDB), while the temperature-dependent mass 47 anomaly on the I-CDES90°C scale. Temperatures were calculated using the Kele et al. (2015) calibration modified by Bernasconi et al. (2018) and the Anderson et al. (2021) calibrations. Soil carbonates of the Esplugafreda formation yield δ13Ccarb values between –8.55 and –5.85 ‰, while the PETM yellow soil carbonates are significantly more negative (–13.84 to –10.12 ‰), in good agreement with previous measurements. A much smaller, ~1.2 ‰ difference can be observed in the oxygen isotope compositions between these carbonates (δ18Ocarb: –5.46 to –4.13 versus –6.35 to –4.47 ‰). The Δ47-based paleotemperatures (T47carb) indicate mean soil carbonate formation of 33.8±9.5 °C during the late Paleocene, which are close to modern summer temperatures of subtropical regions. By contrast, a much higher mean temperature was recorded by soil carbonates of the PETM yellow soils (39±8.5 °C) with extreme (>40 °C) temperatures occurring 4 times more frequently than over the late Paleocene. This study was supported by the NKFIH through the OTKA K-137767 project.