Sections of Michigan Basin sediments were exposed to hydrothermal fluids during the Ordovician. Secondary calcite and dolomite occur as fracture-filling veins/vugs and replacement minerals in host Ordovician limestones-which occur at depth beneath the Bruce Nuclear site (near Tiverton) in southwestern Ontario. To provide insights on the evolution of diagenetic fluids responsible for secondary mineral growth and the effects of temperature-dependent alteration in the basin, clumped isotope geothermometry was applied to these carbonates. Ordovician calcite in veins/vugs have delta 18OC values of +20.0 to +23.4 %o (VSMOW) and are estimated to have formed at 65-83 degrees C from various waters (delta 18Ow = +0.1 to +4.4 %o) including Ordovician to modified (an evolved 18O-enriched) seawater, and mixed seawater and basinal brines at depth. Calcite veins/vugs in the lower Cambrian units formed at 74-91 degrees C, have lower delta 18OC values (+14.9 to +17.0 %o) and precipitated from 18O-depleted hydrothermal brines (delta 18Ow =-4.6 to-3.1 %o). Calcite in the matrix of host limestones yielded higher apparent temperatures (T(Delta 47) = 49-82 degrees C)) that are inconsistent with precipitation from Ordovician seawater and burial diagenesis of the sediments but instead, reflect a solid-state isotope reordering due to a Late Devonian-Mississippian rift-related basinal heating. Diagenetic dolomitization in the basin occurred during shallow to intermediate burial, where dolomite primarily replaces calcite in the limestone matrix or occur as secondary infill in fractures and vugs. The clumped isotopic signature in dolomite is more resistant to low-temperature heating than calcite, whose Delta 47 composition reflects a 367-322 Ma regional heating event at 125-150 degrees C during burial, in agreement with, but more precise than previous estimates based on fluid inclusion micro-thermometry in secondary quartz and saddle dolomite.

The use of clumped isotopes (Delta(47)) as a geothermometer in carbonates has become widespread in geosciences because carbonates are ubiquitous in the environment and this technique also constrains the precipitating fluid delta O-18 composition. However, in some contexts, Delta(47) values cannot be used as a geothermometer. Instead, they provide insights into processes affecting the isotopic composition of CO2 and dissolved inorganic carbon (DIC) prior to and during precipitation, as observed in speleothems, corals, and cold seep-associated authigenic carbonates. Among all these precipitates, authigenic carbonates associated with cold seeps stand out, as the measurement of their clumped isotopic abundances has revealed an unprecedented range of isotopic ordering, and several explanations were put forward to explain the various signals observed. To get a firmer understanding of the cause of natural variability in modern cold seeps, here we report delta C-13, delta O-18 and Delta(47) results performed on carbonates from two deep-sea cold seeps offshore Nova Scotia, Canada, i.e., >2300 m water depth and within the gas hydrate stability zone. We report a broad Delta(47) range (i.e., 0.502-0.663 parts per thousand I-CDES) that differs from values expected at isotopic equilibrium at seafloor temperatures (i.e., 0.671-0.672 parts per thousand I-CDES). Using micro computed X-ray tomography, micro-X-ray fluorescence, and micro sampling, we demonstrate that methane-derived authigenic carbonates at these deep-water sites are closely associated with colocalized methane-hydrate dissolution. The isotopic composition of these authigenic carbonates are influenced by the complex mixing of different dissolved inorganic carbon (DIC) pools at various stages of isotopic re-equilibration, resulting in fine-scale isotopic variability. We propose several mixing models and stages of DIC re-equilibration to explain this isotopic variability and apply them to evaluate the contributions of the proposed sources of DIC. The isotopic domains resulting from this exercise encompass the entire range of dual isotopic values (delta O-18 and Delta(47)) ever observed in cold seeps and suggests that the isotopic diversity observed in these environments may be broader than that observed to date.

In the Gaspé Peninsula, karsts associated with subaerial exposure are interpreted to have developed either during the Silurian or the Carboniferous. Determining the timing of karst formation is valuable for economic reasons (including petroleum system characterization) and for the understanding of basin/climate evolution. In this study, a laminated calcite speleothem coating a karst wall in the McInnis cement plant quarry is studied in detail through petrographic observations, stable and clumped isotope analysis, and geochronology. The speleothem is made of laminae of different colours that are geochemically and isotopically distinct. White and red laminae have δ 18 O and δ 13 C values comparable to contemporaneous (within uncertainty) phreatic calcrete hardpans described in southern Gaspé Peninsula and northern New Brunswick, suggesting that both the speleothem and calcrete precipitated from primarily fresh groundwaters that interacted with soils. Changes in laminae colour most likely reflect different kinetics of precipitation and amounts of impurities. LA-ICP-MS in situ dating of calcite from white laminae gives a date of 331.8 ± 9.1 Ma, which is the first direct evidence that the cavity formed during the Visean (Carboniferous). From a regional point of view, subaerial exposure and karst formation during the Visean could have resulted from a glacially induced sea-level lowstand and/or from an uplift episode associated with magmatic underplating/plume-related magmatism in the offshore part of the Maritimes Basin.

Abstract Recent interlaboratory efforts have enabled methodological refinements in carbonate clumped isotope geochemistry, including the adoption of a carbonate‐based reference frame, the InterCarb Carbon Dioxide Equilibration Scale (I‐CDES). This calcite‐based standardization scheme aims at simplifying sample preparatory routines and ensuring identical treatment for all standards and unknowns. While the I‐CDES is a major step forward for the production of coherent results by laboratories for calcite, two aspects of this reference frame may only approximate but not ensure the principle of identical treatment of standards and unknowns because (a) the 90°C‐acid digestion temperature favored by I‐CDES is not achievable by all analytical setups and (b) the clumped isotope systematics of other carbonate minerals, if reported within a calcite reference frame only, may introduce uncertainties. We present an upgraded Kiel IV carbonate device—the “Franken‐Kiel”—performing acid digestions up to a theoretical 135°C, an enhancement over the factory‐default temperature of 70°C. The optimized setup considerably reduces the reaction time needed for digesting samples and yields good precision on Δ47 (i.e., long‐term standard deviations of 0.027 and 0.005‰ for calcite and dolomite standards, respectively). We further re‐evaluated the Δ47‐T relationship for calcite and dolomite directly in the I‐CDES and showed consistency between the produced temperature calibration and previous calibrations for calcite. We propose a mineralogy correction for dolomite in the I‐CDES that allows to partially reconcile theory with experimentation. Overall, the Franken‐Kiel showed excellent performance and warrants further tests on more recalcitrant carbonates, such as siderite and magnesite at higher acidification temperatures.

Sediment-hosted gold deposits in central Yukon have most of the diagnostic characteristics of Carlin-type gold deposits in Nevada. This study combines organic matter geothermometry with fluid inclusion microthermometry, clumped isotope data (Δ 47 ) for late ore-stage hydrothermal calcite, and apatite fission-track analyses to constrain the thermal evolution of Carlin-type gold zones in central Yukon. The Tmax parameter derived from pyrolysis analyses indicates that organic matter is overmature and records regional temperatures of > 150 °C. Calcite and fluorite associated with the waning stage of mineralization at ca. 74 Ma have mean fluid inclusion homogenization temperatures of 123–173 °C, with an average salinity of 4.8 wt.% NaCl equiv. These temperatures overlap values of 91–162 °C determined from calcite clumped isotope measurements and are similar to data from Carlin-type deposits in Nevada. Fluid mixing is suggested by a variation of the isotopic composition of the fluid in equilibrium with calcite, with the higher temperature end-member having higher δ 18 O H2O values. In thermal models based on Tmax, fluid inclusion microthermometry, clumped isotope measurements, and apatite fission-track data, a higher temperature event at approximately 220 °C is consistent with pyrobitumen reflectance measurements. This event is either related to maximum tectonic burial prior to mineralization or to the flow of acidic hydrothermal fluids early in the main ore-stage. Each analytical technique used in this study is independent of the others and records part of the thermal and chemical evolution of the Yukon Carlin-type gold deposits and their host rocks.

This study evaluates the applicability of the clumped isotope thermometry to mesothermal hydrothermal systems (5-10 km depth; 250-450 degrees C). We measured Delta(47), delta O-18 and delta C-13 of calcite as well as delta O-18 of cogenetic minerals from typical quartz-calcite +/- tourmaline +/- chlorite orogenic veins from the Neoarchean Augmitto-Bouzan orogenic gold deposits (Abitibi, Canada). Our findings show that caution is required when utilizing the clumped isotope thermometry in the study of old mesothermal deposits. Temperatures calculated from Delta(47) values are systematically and significantly shifted to low temperature, i.e., similar to 150 degrees C rather than the similar to 350 +/- 50 degrees C expected for orogenic gold deposit formation and documented using oxygen isotope equilibrium between mineral pairs. We show that the low temperatures estimates resulted from solid-state reordering that occurred in calcite grains during the cooling history of the vein-hosting rocks. Because systems are geologically unrealistic, we suggest that refractory minerals (i.e., minerals with higher blocking temperature such as magnesite, dolomite, ankerite) should be investigated to apply clumped isotope thermometry in such context.

The Delta(47) (paleo)thermometer has opened a new avenue to determine carbonate formation temperatures independent of the oxygen isotopic composition of the fluid from which the carbonate crystallized. A major limitation of this thermometer is related to kinetic effects if homogeneous isotopic equilibrium is not attained during carbonate precipitation. Dual clumped isotope thermometry - the high-precision analysis of Delta(48) along with Delta(47) in CO2 evolved from phosphoric acid digestion of carbonates - makes it possible to resolve temperature from the kinetic information recorded in an individual carbonate phase. Therefore, it provides a new opportunity to identify (bio)mineralization pathways and to determine carbonate formation temperatures devoid of a kinetic bias, based solely on isotopic analysis of a single carbonate phase. Identification of the nature and extent of kinetic effects as well as the reconstruction of accurate formation temperatures requires knowledge of the position of equilibrium in Delta(47) vs Delta(48) space. Here, we present Delta(47) and Delta(48) data of carbonates that were previously considered as having crystallized closest to equilibrium in a temperature range of 8 to 1100 degrees C. Across this range, the temperature dependences of Delta(47) and Delta(48) are best expressed by the following fourth order polynomials of 1/T: Delta(47) (CDES 90) (%) = 1.038 (-5.897 1/T - 3.521 103 1/T-2 + 2.391 107 1/T-3 - 3.541 109 1/T-4) + 0.1856 Delta(48) (CDES 90) (%) = 1.028 (6.002 1/T - 1.299 104 1/T-2 + 8.996 106 1/T-3 - 7.423 108 1/T-4) + 0.1245 with CDES 90 representing the Carbon Dioxide Equilibrium Scale at a reaction temperature of 90 degrees C. In its entire temperature range, our Delta(47) (CDES 90) - T - relationship agrees within 2 ppm with two previous Delta(47) (I-CDES) - T - relationships reported by Jautzy et al. (2020) and Anderson et al. (2021). Accuracy of our proposed Delta(47) (CDES 90) - Delta(48) (CDES 90) equilibrium relationship is independently confirmed by additional dual clumped isotope data of experimental and geothermal carbonates which precipitated from potentially equilibrated dissolved inorganic carbon pools at a temperature range of 25-100 degrees C. Furthermore, we reprocessed original dual clumped isotope data of natural carbonates (Bajnai et al., 2020) and compared their composition to the position of equilibrium in Delta(47) vs Delta(48) space. These results corroborate preliminary evidence that the hydration/hydroxylation reactions became rate-limiting during the calcification of a speleothem-like sample, a warm water coral, a cold water coral and a brachiopod, finally evoking significant departures of carbonate-Delta(47) and -Delta(48) from dual clumped isotope equilibrium. An anti-clumped Delta(48) value of -419 (+/- 16) ppm (95% confidence interval level) is obtained for a technical calcite that was precipitated by the injection of CO2 into a Ca(OH)(2)-saturated solution. Its negative Delta(48) value largely arises from a combinatorial effect, i.e. the carbonate oxygen derives from two sources with different bulk isotopic compositions. Besides the identification of the nature and the extent of (bio)mineralization kinetics and the reconstruction of carbonate formation temperatures unbiased by kinetics, dual clumped isotope analysis, therefore, allows tracing the isotopic heterogeneity of oxygen pools contributing to carbonate formation. (C) 2021 Elsevier Ltd. All rights reserved.

Photocatalytic reduction of CO2 into useful feedstocks has attracted more attention in recent decades. However, the effective and selective conversion of CO2 to the desired product always remains a major challenge in photocatalysis, which relies on the appropriate band edge potential and efficient separation of photogenerated charge carriers in the photocatalysts. In this direction, herein we report the construction of a keto-enamine covalent organic framework (COF) incorporated with reduced graphene oxide with increasing concentrations, rGO(x)@TpPa-1 (x = 5%, 10%, 15%, and 20%), by the in situ assembling technique to significantly boost up the charge separation thereby to improve the efficiency CO2 photoreduction. The developed rGO(15)@TpPa-1 nanocomposite showed remarkable efficiencies toward photocatalytic CO2 reduction under visible light irradiation, which yielded the CO at a rate up to similar to 200 mu mol g(-1) h(-1) and with a selectivity of 89%, which was 1.57 and 6.97 times higher as compared to the bare COF and rGO counterparts, respectively. The series of control experiments demonstrated that both TpPa-1 and rGO counterparts have a significant synergistic impact on the selectivity and efficiency toward photoreduction of CO2. Under optimized conditions, rGO(15)@TpPa-1 exhibited an apparent quantum yield of 0.5% at 420 nm, which is one of the few notable values reported in the literature. The covalent interactions between TpPa-1 and rGO facilitated the formation of band edges with required potential and thereby an improved charge separation along with rapid migration of charge carriers to the surface toward the selective reduction of CO2 to CO, which is validated by the C-13 labeling. This work could be a promising approach toward energy applications for the potential development of COFs and their analogous structures.

Recent studies using the CO2 carbonate clumped isotope (C-13-O-18-O-16, i.e., Delta(47)) paleothermometer and bulk isotopes (delta C-13, delta O-18) have brought new insights into the prevailing conditions during carbonate formation around marine methane seeps. These studies mostly revealed delta O-18 or paired delta O-18 and Delta(47) disequilibria between precipitating minerals, water and DIC species. Here, we have sampled bivalves and cements from two modern, slow-release methane seeps located in the St. Lawrence Estuary. The bivalve shells have marine isotopic signals, whereas the cements show wide Delta(47) (up to +0.05 parts per thousand) and minor delta O-18 (+0.8 parts per thousand) positive offsets relative to marine equilibrium, with a narrow delta C-13 range (-33.5 to -31.1 parts per thousand). The observed isotopic trends show that, unlike in previous studies, the aragonite shells precipitated at full isotopic equilibrium, whilst the cements suggest differential disequilibrium precipitation. We propose that the suite of results were generated by distinct Delta(47) and delta O-18 pathways, as supported by DIC-water isotopic exchange numerical experiments. The observed trends typify slow rates of methane oxidation and carbonate precipitation from residual gas with high-delta O-18 and low-delta(47) values after methane-derived CO2 diffusion. Overall, we suggest that the shells represent potential archives of seep conditions, and that the seep cements define a new Delta(47) and delta O-18 domain widening the known spectrum of marine conditions producing natural carbonates. Our results, compiled with literature data, help refine the basis for interpreting carbonate precipitation mechanisms in ancient seeps or other geological settings. Crown Copyright (C) 2021 Published by Elsevier Ltd.

This study presents noble gas characteristics of porewater in the Ordovician low-permeability drill cores, which were vacuum-sealed in Al-foil bags and collected over a decade ago on the eastern flank of the Michigan Basin. Noble gas ratios and concentrations reveal crustal noble gas features as well as radiogenic He-4, Ar-40, and Xe-136 components. The measured noble gas ratios in this study agree with measurements previously made in the Ordovician brine samples from the western flank of the Michigan Basin. However, unlike water samples from the western Michigan Basin, no mantle-featured noble gas components are found in the Ordovician rock porewater from this site. The Ordovician porewater residence time is quantitatively estimated with both He and Xe radiogenic ingrowth, yielding an average of 251 million years (m.y.). This porewater residence time estimate is comparable with the previous He accumulation time estimate at the same study site that yielded 260 m.y. The radiogenic noble gas ingrowth demonstrates long-term confinement of porewater and concomitant gases within the Ordovician low-permeability rock investigated. The remarkable preservation of gases in these well-sealed vapor-barrier Al-foil bags provides an economical and efficient possibility for noble gas out-diffusion sampling from drill cores.

The Hudson Bay sedimentary basin was overlooked geologically until two decades ago. Recent efforts to understand the palaeogeothermal history of this basin have led to the evaluation of fluid inclusion microthermometry, apatite fission track, organic matter reflectance and Rock–Eval analyses. Although apatite fission track and organic maturity indicators tend to show relatively low maximum burial temperatures (60–80°C), evidence of potential oil slicks on the sea surface and oil and gas shows in offshore wells have been reported across Hudson Bay. Fluid inclusion microthermometry in a carbonate mound sequence suggests homogenization temperatures of 118 ± 25 and 93 ± 10°C for recrystallized synsedimentary marine calcite and late pore-filling burial calcite, respectively. This sequence provides an interesting geological framework to test the application of clumped isotope thermometry against independent geothermometers. Here, we present clumped isotope data acquired on the late calcite cements and diagenetically altered early marine phases. The integration of clumped isotopic data with other thermal indicators allows the reconstruction and refinement of the thermal–diagenetic history of these carbonates by confirming an episode of heating, probably of hydrothermal origin and prior to normal burial diagenesis, that reset both fluid inclusions and the clumped isotope indicators without recrystallization.

Ring of Fire (RoF) = large mineral deposits of Ni/Cu/Zn/Cr and PGM: Located in one of the world's largest peatland system; Sensitive to climate change (Hadley et al., 2019) and anthropogenic stresses (Leclair et al., 2015) Environmental conditions: Additional knowledge required to understand how baseline conditions respond to climate change and new anthropogenic stresses (e.g., roads, mining camps,...); Natural presence and behavior of metal(loid)s in this system needs to be carefully assessed prior to any development; Changes to groundwater flow dynamic, changes in lake sediment conditions and forest fires can potentially enhance the remobilization of metal(loid)s over time; Explore and develop environmental indicators adapted to the RoF environment.

Investigation of the biology and biochemistry of the deep subsurface provides invaluable information regarding the limit of life in extreme environments and its role in the global carbon cycle. It has been observed that subsurface microbial CH4 can form in apparent isotopic equilibrium, both with respect to methane clumped isotopic species and D/H fractionation with respect to coexisting water. This observation fostered the suggestion that methanogenic metabolisms in energy-starved environments can operate through slow and reversible enzymatic reactions. Here we present isotopic data including a vertical profile of clumped isotopic indices of methane from Paleozoic-aged pore waters in an aquiclude system from the Michigan Basin. We show evidence of both internal isotopic equilibrium of methane and intermolecular H-isotopic equilibrium between methane and co-occurring non-gaseous n-alkanes. Various mixing and microbial metabolic models were tested and allowed us to identify the possibility of the production of methane at thermodynamic equilibrium from the syntrophic degradation of sedimentary n-alkanes at ultra-slow rates. Significance Statement: The recent ability to measure the clumped isotopic composition of methane has fostered new ways of observing the deep subsurface biogeochemistry and has been proposed as a new independent geothermometer when methane is formed at or near isotopic equilibrium. In this manuscript, we present the first continuous Paleozoic sedimentary profile of clumped isotopes in pore methane (i.e. directly sampled from the pores of tight sedimentary rocks) from a paleo-bioreactor in the subsurface and show that a syntrophic metabolic network between fermentative bacteria and mainly acetotrophic methanogens can thrive in an energy limited environment. (C) 2021 Published by Elsevier B.V.

Clumped isotopes ( Δ 47 ) excess measurements in carbonates is becoming a widespread isotopic geothermometer, which also casts the precipitating fluid δ 18 O composition. The measurement of clumped isotopic abundances in authigenic carbonates near marine cold seeps has revealed an unprecedented range of isotopic ordering, and several explanations have been put forward to account for the various disequilibrium signals observed. Here we report δ 13 C, δ 18 O and Δ 47 measurements performed on two sediment core profiles from two deeply-seated cold seeps (water depth >2400 m), on the platform margin off-shore Nova Scotia. The cores contain several indications of hydrate presence. Data obtained from sub-surface depth varying between 34 and 235 cm reveal a clear CH 4 oxidation signal in the investigated calcites, associated with Δ 47 and δ 18 O values mostly in apparent disequilibrium with seafloor conditions. Here, we will discuss the observation of higher apparent Δ 47 and δ 18 O disequilibrium at depth in comparison to surficial samples. We will compare them to results from other cold seep settings and explore the possible causes of these isotopic patterns.

Clumped isotopes (Delta(47)) analysis in carbonates is becoming widespread across the geochemical community as a geothermometer that also allows for the reconstruction of the precipitating fluid delta O-18 composition. While initial Delta(47)-temperature relationship discrepancies between laboratories have been considerably reduced over the past 10 years, theoretical temperature calibration and laboratory experimental efforts have still not converged to common ground. Moreover, a lack of high temperature anchor points has weakened its application to high temperature calcite formation. Here we present a temperature calibration for carbonate clumped isotopes between 5 and 726 degrees C, using synthetically precipitated and heated calcites, to extend the calcite Delta(47) -temperature calibration to higher temperatures. By showing a strong agreement between the empirical calibration proposed here, theoretical and all recently published T-calibrations made using a full carbonate referencing scheme, this study: (1) provides a calibration allowing more precise application in high temperature geological systems, (2) further supports the improvement of inter-laboratory comparison by using carbonate standards, (3) reconciles empirical temperature calibrations with theory.