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Geochemical analyses of carbonate minerals yield multiple parameters which can be used to estimate the temperature and water composition at which they formed. Analysis of fluid trapped in minerals is a potentially powerful tool to reconstruct paleotemperatures as well as diagenetic and hydrothermal processes, as these could represent the parent fluid. Internal fluids play important roles during the alteration of carbonate fossils, lowering energetic barriers associated with resetting of clumped isotopes, as well as mediating the transport of elements during diagenesis. Here, we explore the behavior of the ∆47–∆48 “dual‐clumped” isotope thermometer during fluid‐carbonate interaction and demonstrate that it is highly sensitive to the water/carbonate ratio, behaving as a linear system in “rock buffered” alteration, and as a decoupled system in water‐dominated systems due to non‐linear mixing effects in ∆48. Dry heating experiments show that the extrapolated “heated” end‐member is indistinguishable from the predicted ∆47 and ∆48 value expected for the experimental temperature. Furthermore, we evaluate two common laboratory sampling methods for their ability to thermally alter samples. We find that the temperature of the commonly used crushing cells used to vapourize water for fluid inclusion δ18O analyses is insufficient to cause fluid‐carbonate oxygen isotope exchange, demonstrating its suitability for analyses of fluid inclusions in carbonates. We also find that belemnites sampled with a hand‐drill yield significantly warmer paleotemperatures than those sampled with mortar and pestle. We conclude that thermally‐driven internal fluid‐carbonate exchange occurs indistinguishably from isotopic equilibrium, limited by the extent to which internal water and carbonate can react., Plain Language Summary: Carbonate minerals contain multiple, independent, chemical and isotopic parameters which can be used to calculate the temperature at which the mineral formed. If these proxies agree with one another, it has been confidently assumed that the temperature is indeed genuine. Here, we investigate three such parameters and show how they record kinetic processes during mineral formation, as well as thermally‐driven processes which may alter a climate record. We find that this method could potentially be used to study the kinetic factors at play during biomineralization, even if the “true” temperature is unknown. We also find that some thermal processes result in all three parameters agreeing with one another. Because thermal alteration poses a potential dilemma for climate researchers, we investigate two common laboratory preparation techniques that involve heating a sample before analysis: drilling and heating sample for fluid inclusion analysis. We find that the heat of a drill is sufficient to facilitate these reactions, and potentially imparts a warm bias onto paleotemperatures, however the apparatus used for analyzing fluid inclusions does not appear to significantly alter the material. We conclude our approach using fluid inclusion analysis and dual‐clumped isotopes has the potential to resolve many ambiguities in interpreting climate records., Key Points: We explore the behavior of dual‐clumped and fluid‐inclusion isotope paleothermometers during thermal alteration. Different conditions during diagenesis may result in discrepant paleotemperature estimates, which may be used to identify altered records. Hand‐drilling belemnites produces sufficient heat to reset paleotemperatures, but the heat during analysis of fluid inclusions does not., DFG, https://doi.org/10.5281/zenodo.7565557

Increased use and improved methodology of carbonate clumped isotope thermometry has greatly enhanced our ability to interrogate a suite of Earth-system processes. However, interlaboratory discrepancies in quantifying carbonate clumped isotope (Δ47) measurements persist, and their specific sources remain unclear. To address interlaboratory differences, we first provide consensus values from the clumped isotope community for four carbonate standards relative to heated and equilibrated gases with 1,819 individual analyses from 10 laboratories. Then we analyzed the four carbonate standards along with three additional standards, spanning a broad range of δ47 and Δ47 values, for a total of 5,329 analyses on 25 individual mass spectrometers from 22 different laboratories. Treating three of the materials as known standards and the other four as unknowns, we find that the use of carbonate reference materials is a robust method for standardization that yields interlaboratory discrepancies entirely consistent with intralaboratory analytical uncertainties. Carbonate reference materials, along with measurement and data processing practices described herein, provide the carbonate clumped isotope community with a robust approach to achieve interlaboratory agreement as we continue to use and improve this powerful geochemical tool. We propose that carbonate clumped isotope data normalized to the carbonate reference materials described in this publication should be reported as Δ47 (I-CDES) values for Intercarb-Carbon Dioxide Equilibrium Scale.

We use the chemical and isotopic composition of volcanic gases and steam condensate, in situ measurements of plume composition and remote measurements of SO2 flux to constrain volatile sources and characterize subvolcanic conditions at three persistently degassing and seismically active volcanoes within the Katmai Volcanic Cluster (KVC), Alaska: Mount Martin, Mount Mageik and Trident. In situ plume measurements of gas composition were collected at all three volcanoes using MultiGAS instruments to calculate gas ratios (e.g. CO2/H2S, SO2/H2S and H2O/H2S), and remote measurements of SO2 column density were collected from Mount Martin and Mount Mageik by ultraviolet spectrometer systems to calculate SO2 fluxes. Fumaroles were directly sampled for chemical and isotopic composition from Mount Mageik and Trident. Mid Ocean Ridge Basalt (MORB)-like 3He/4He ratios (~ 7.2–7.6 Rc/RA) within Mount Mageik and Trident's fumarole emissions and a moderate SO2 flux (~ 75 t/d) from Mount Martin, combined with gas compositions dominated by H2O, CO2 and H2S from all three volcanoes, indicate magma degassing and active hydrothermal systems in the subsurface of these volcanoes. Mount Martin's gas emissions have the lowest CO2/H2S ratio (~ 2–4) and highest SO2 flux compared to the other KVC volcanoes, indicative of shallow magma degassing. Geothermometry techniques applied to Mount Mageik and Trident's fumarolic gas compositions suggest that their hydrothermal reservoirs are located at depths of ~ 0.2 and 4 km below the surface, respectively. Observations of an unusually reducing gas composition at Trident and organic material in the near-surface soils suggest that thermal decomposition of sediments may be influencing gas composition. When the measured gas compositions from Mount Mageik and Trident are compared with previous samples collected in the late 1990's, relatively stable magmatic-hydrothermal conditions are inferred for Mount Mageik, while gradual degassing of residual magma and contamination by shallow crustal fluids is inferred for Trident. The isotopic composition of volcanic gases emitted from Mount Mageik and Trident reflect mixing of subducted slab, mantle and crustal volatile sources, with organic sediment and carbonate being the predominant sources. Considering the close proximity of the target volcanoes in comparison with the depth to the subducted slab we speculate that Aleutian Arc volatiles are fed by a relatively homogeneous subducted fluid and that much of the apparent variability in volatile provenance can be explained by shallow crustal volatile sources and/or processes.

The clumped isotopic composition of carbonate-derived CO (denoted Δ) is a function of carbonate formation temperature and in natural samples can act as a recorder of paleoclimate, burial, or diagenetic conditions. The absolute abundance of heavy isotopes in the universal standards VPDB and VSMOW (defined by four parameters: R , R , R , and λ) impact calculated Δ values. Here, we investigate whether use of updated and more accurate values for these parameters can remove observed interlaboratory differences in the measured T-Δ relationship. Using the updated parameters, we reprocess 14 published calibration data sets measured in 11 different laboratories, representing many mineralogies, bulk compositions, sample types, reaction temperatures, and sample preparation and analysis methods. Exploiting this large composite data set (n = 1,253 sample replicates), we investigate the possibility for a “universal” clumped isotope calibration. We find that applying updated parameters improves the T-Δ relationship (reduces residuals) within most labs and improves overall agreement but does not eliminate all interlaboratory differences. We reaffirm earlier findings that different mineralogies do not require different calibration equations and that cleaning procedures, method of pressure baseline correction, and mass spectrometer type do not affect interlaboratory agreement. We also present new estimates of the temperature dependence of the acid digestion fractionation for Δ (Δ*), based on combining reprocessed data from four studies, and new theoretical equilibrium values to be used in calculation of the empirical transfer function. Overall, we have ruled out a number of possible causes of interlaboratory disagreement in the T-Δ relationship, but many more remain to be investigated.

International audience

International audience; The clumped isotopic composition of carbonate‐derived CO2 (denoted Δ47) is a function of carbonate formation temperature and in natural samples can act as a recorder of paleoclimate, burial, or diagenetic conditions. The absolute abundance of heavy isotopes in the universal standards VPDB and VSMOW (defined by four parameters: R13VPDB, R17VSMOW, R18VSMOW, and λ) impact calculated Δ47 values. Here, we investigate whether use of updated and more accurate values for these parameters can remove observed interlaboratory differences in the measured T‐Δ47 relationship. Using the updated parameters, we reprocess 14 published calibration data sets measured in 11 different laboratories, representing many mineralogies, bulk compositions, sample types, reaction temperatures, and sample preparation and analysis methods. Exploiting this large composite data set (n = 1,253 sample replicates), we investigate the possibility for a “universal” clumped isotope calibration. We find that applying updated parameters improves the T‐Δ47 relationship (reduces residuals) within most labs and improves overall agreement but does not eliminate all interlaboratory differences. We reaffirm earlier findings that different mineralogies do not require different calibration equations and that cleaning procedures, method of pressure baseline correction, and mass spectrometer type do not affect interlaboratory agreement. We also present new estimates of the temperature dependence of the acid digestion fractionation for Δ47 (Δ*25‐X), based on combining reprocessed data from four studies, and new theoretical equilibrium values to be used in calculation of the empirical transfer function. Overall, we have ruled out a number of possible causes of interlaboratory disagreement in the T‐Δ47 relationship, but many more remain to be investigated.

With the aim to understand prolonged and repeated marine anoxia after the Triassic-Jurassic massextinction event, a continuously cored, 338 metre thick succession of Rhaetian to Toarcian sediments was retrieved close to the village of Schandelah near Braunschweig (Lower Saxony, northern Germany). Here, preliminary biostratigraphical, lithological, sedimentological, geochemical, and geophysical borehole data are presented and discussed. Based on the presence of ammonites, ostracods, benthic foraminifers, calcareous nannofossils, and palynomorphs, all major Late Triassic and Early Jurassic stage boundaries and many of the standard Lower Jurassic ammonite zones could be defined. The deltaic Rhaetian sand- and siltstone succession (Exter Fm) contains evidence for seismic activity probably related to large-scale geodynamic processes. The Hettangian (Lias Alpha) is represented by a thick heterolithic succession composed of shallow marine sandy and silty beds with intercalated organic-rich shale, representing deposition on a shoreface with frequent storm activity. Progressive deepening during the Sinemurian to Toarcian resulted in repeated deposition of laminated organic-rich facies. Periods of relative sea-level fall likely occurred during the Late Hettangian, the Late Sinemurian, and Early Pliensbachian, where a series of hardgrounds occur indicating erosion on the sea floor followed by sea level rise leading to omission, and increased reworking. One of the most conspicuous features of the Lower Jurassic in the Schandelah-1 core is the presence of abundant authigenic carbonates (glendonites, concretions, beef-calcite) within the Upper Pliensbachian with partly very negative C-isotope values (down to -37%o V-PDB) suggesting the anaerobic oxidation of methane. A high-resolution organic carbon isotope record based on 485 analyses shows two major negative carbon isotope excursions (CIEs) within the lowermost Hettangian and Lower Toarcian, respectively. Both excursions coincide with the onset of black shale deposition and are well-known features of these time-intervals in other regions. Despite the fact that black shale deposition also characterizes parts of the Sinemurian and Pliensbachian in similar facies, no large negative CIEs are apparent. The Schandelah-1 core thus provides an unique archive of sedimentary, biotic and geochemical records of long-term Triassic-Jurassic palaeo-environmental change in the European Epicontinental Seaway.

The geologic emissions of greenhouse gases (CO2 and CH4) give an important natural contribution to the global carbon budget. However, the contribution of these emissions to the global carbon cycle and their possible role on the climate change remain still poorly quantified (Guliyev and Feizullayev, 1997; Milkov, 2000; Etiope et al., 2015 and references therein). Methane, the most abundant organic compound in Earth's atmosphere, may be created either from existing organic matter or synthesized from inorganic molecules. Accordingly, it can be differentiated in two main classes: a) biotic (either microbial or thermogenic) and b) abiotic. For this study, 115 gas samples of fumarolic, thermal and cold discharges from all over the Hellenic territory were collected and both chemical (CO2, H2S, CH4, N2, O2, Ar, H2 and light hydrocarbons) and isotopic (13C-CO2, 13C-CH4, D-CH4) analyses were performed, in order to investigate the genetic processes that produced CH4 in fluids related with the complex geodynamic setting of Greece. On the basis of the spatial distribution of the gas discharges and their type of emission, the whole dataset was subdivided into 3 main “domains”, as follows: 1) Volcanic Arc (VA) - 34 samples; 2) External Hellenides (EH) - 23 samples of cold emissions and of hyperalkaline aqueous solutions; 3) Internal Hellenides (IH) - 62 samples of cold and geothermal emissions. Almost each group is characterized, as long as subdivided in 3 groups based on the type of emission (on-land free or dissolved gases and subaqueous gases) and a 4th group includes literature data.

The Greek territory belongs to the geodynamically active Alpine-Himalayan orogenic belt. As such, it shows intense seismic activity, active volcanic systems and areas of enhanced geothermal fluxes. One of these areas is the Sperchios basin and the northern part of Evia island in central Greece, which present widespread thermal manifestations (D’Alessandro et al., 2014). Five of them with temperatures from 33 to 80°C present bubbling gases whose dominating species are either CO2 or N2. All gases contain from 27 to 4000 ppm of CH4. The isotopic composition of CH4 in these gases covers a wide range with δ13C values ranging from -21.7 to +16.9 ‰ and δ2H values ranging from -124 to +301 ‰. The hottest manifestation displays the lowest isotopic values within the typical range of volcanic and geothermal systems. All the remaining samples fit a methane oxidation trend reaching very positive values. If we consider the lowest values as the deep hydrothermal marker the obtained ΔH/ΔC values range between 5 and 13 which are close to those typical of microbially driven oxidation (Kinnaman et al., 2007). Although the outlet temperature of the hottest manifestations is at the upper limit for methanotrophic microrganisms (Sharp et al., 2014), we can hypothesize that environmental conditions are not favorable for their survival at this site while they can thrive in the other, strongly consuming methane and producing very positive isotopic values. D’Alessandro, W., Brusca, L., Kyriakopoulos, K., Bellomo, S., Calabrese S. (2014): A geochemical traverse along the "Sperchios Basin-Evoikos Gulf" Graben (Central Greece): origin and evolution of the emitted fluids. Mar. Petrol. Geol., 55, 295-308. Kinnaman, F.S., Valentine, D.L., Tyler, P.A. (2007): Carbon and hydrogen isotope fractionation associated with the aerobic microbial oxidation of methane, ethane, propane and butane. Geochim. Cosmochim. Acta, 71, 271-283. Sharp, C.E., Smirnova, A.V., Graham, J.M., Stott, M.B., Khadka, R., Moore, T.R., Grasby, S.E., Strack, M., Dunfield, P.F. (2014): Distribution and diversity of Verrucomicrobia methanotrophs in geothermal and acidic environments. Environ. Microbiol., 16, 1867-1878.

The Greek territory belongs to the geodynamically active Alpine-Himalayan orogenic belt. As such, it shows intense seismic activity, active volcanic systems and areas of enhanced geothermal fluxes. One of these areas is the Sperchios basin and the northern part of Evia island in central Greece, which present widespread thermal manifestations [1]. Five of them with temperatures from 33 to 80°C present bubbling gases whose dominating species are either CO2 or N2. All gases contain from 27 to 4000 ppm of CH4. The isotopic composition of CH4 in these gases covers a wide range with δ13C values ranging from -21.7 to +16.9‰ and δ2H values ranging from -124 to +301‰. The hottest manifestation displays the lowest isotopic values within the typical range of volcanic and geothermal systems. All the remaining samples fit a methane oxidation trend reaching very positive values. If we consider the lowest values as the deep hydrothermal marker the obtained ΔH/ΔC values range between 5 and 13 which are close to those typical of microbially driven oxidation [2]. Although the outlet temperature of the hottest manifestations is at the upper limit for methanotrophic microrganisms [3], we can hypothesize that environmental conditions are not favorable for their survival at this site while they can thrive in the other strongly consuming methane and producing very positive isotopic values. [1] D’Alessandro et al. (2014), Mar. Petrol. Geol. 55, 295-308; [2] Kinnaman et al. (2007), Geochim. Cosmochim. Acta 71, 271-283; [3] Sharp et al. (2014), Environ. Microbiol. 16, 1867-1878

The geologic emissions of greenhouse gases (CO2 and CH4) have an important natural contribution in the global carbon budget. Tectonics, through faults in geothermal and oil producing areas, play a significant role in the release of C-gases in many non-volcanic regions of the Earth. Methane, the most abundant organic compound in Earth’s atmosphere, has a potential global warming that is 28 times higher than that of CO2 on a 100-year time horizon. In this study, δ13C-CH4, δ2H-CH4 and light hydrocarbon (alkane: CH4, C2H6, C3H8, C3H6, i-C4H10, n-C4H10; alkene C3H6, iC4H8; and aromatic C6H6) gas concentration data of 119 gas samples (103 unpublished data and 16 literature data) from volcanic-hydrothermal, geothermal and cold discharges are used to shed light on the genetic processes that have formed CH4 in the complex geodynamic setting of Greece. On the basis of the spatial distribution of the gas discharges and their type of emission, the whole dataset was subdivided into 4 main “domains”, as follows: 1) Volcanic Arc (VA); 2) External Hellenides (EH); 3) Internal Hellenides (IH); 4) Hellenic Hinterland (HH). Almost each group is characterized, as long as subdivided, in 3 groups based on the type of emission (on-land free or dissolved gases and submarine gases) and a 4th group includes literature data. Concentrations of CH4 range from < 2 to 925,200 µmol/mol and its isotopic ratios cover a wide range (δ13C from -79.8 ‰ to +45 ‰; δ2H from -311 ‰ to +301 ‰) indicating the different primary sources and the secondary post-genetic processes (oxidation) that can significantly affect the origin of this gas compound. Hydrocarbons in the CH4-dominated gases discharged from the EH are showing a clear biotic origin. In particular, those collected in the Gavrovo-Tripolis zone are showing a dominating biotic origin, whereas it is also noticeable that some gas samples of the Ionian zone are produced by both microbial activity and thermal maturation of sedimentary organic matter. The CO2-dominated gas discharges from the main geothermal systems of the IH and from the VA most likely predominantly contain abiogenic CH4 deriving from CO2 reduction. However, some of the gas discharges of the geothermal and volcanic-hydrothermal systems located in the neritic sedimentary Pelagonian, Gavrovo-Tripolis and Attico-cycladic zones (IH) and in Rhodope massif (HH), seem to exhibit significant contributions from thermogenic sources. The presence of abiotic methane was also recognized in the hyperalkaline aqueous solutions that are issuing from the ophiolites of Othrys and Argolida (Pindos zone (EH)). Most of the geothermal gases of Subpelagonian and Vardar/Axios zones (IH), the cold manifestations of the Rhodope massif (HH) and some of the volcanic-hydrothermal ones of the Attico-cycladic zone (VA) are presenting a microbial oxidation of CH4.