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As the parent element in the U-Pb and Pb-Pb radiochronometers, uranium (U) was one of the first heavy elements whose isotopic composition was carefully determined. Thought to be constant until the end of the 20th century, the ratio of the long-lived isotopes of U (238U/235U) has since been shown to be variable at the permil to sub-permil levels in natural materials. Today, the study of U isotopes has found applications in a variety of fields including geo/cosmochronology, oceanic paleoredox reconstruction, magmatic differentiation, environmental remediation, and forensic studies. With thousands of newly reported U isotopic data each year, a real need exists for a comprehensive U isotope database. Here, we introduce a global, updatable, U isotope database (UID), which not only contains the most expansive, internally consistent U isotopic dataset to date (14,591 entries from more than 320 papers), but also includes all other sample data from the original publications, as well as the relevant metadata and sample information to facilitate further analysis. The UID is freely accessible and will be updated regularly. All data are normalized to the widely-used CRM-145 standard, and all assumptions used to convert the published data are explicitly detailed in the paper and the database itself. New data can be easily formatted and submitted for incorporation into the database. Using the UID we provide new recommended δ238U values for certified U standards and geostandards and discuss important applications and future directions for U isotope studies. • Introduce a comprehensive, freely accessible, updatable U isotope database • Already contains over 14,000 entries from more than 320 papers. • All data is consistently and transparently normalized to CRM-145. • Provide recommended δ238U for a wide range of standards and reference materials. • UID will be maintained and regularly updated. [ABSTRACT FROM AUTHOR]

Determination of the 14 C content of dissolved inorganic carbon (DIC) is useful for dating of groundwater. However, in addition to radioactive decay, the 14 C content in DIC ( 14 C DIC ) can be affected by many geochemical and physical processes and numerous models have been proposed to refine radiocarbon ages of DIC in groundwater systems. Changes in the δ 13 C content of DIC (δ 13 C DIC ) often can be used to deduce the processes that affect the carbon isotopic composition of DIC and the 14 C value during the chemical evolution of groundwater. This paper shows that a curved relationship of 14 C DIC vs. δ 13 C DIC will be observed for groundwater systems if (1) the change in δ 13 C value in DIC is caused by a first-order or pseudo-first-order process, e.g. isotopic exchange between DIC and solid carbonate, (2) the reaction/process progresses with the ageing of the groundwater, i.e. with decay of 14 C in DIC, and (3) the magnitude of the rate of change in δ 13 C of DIC is comparable with that of 14 C decay. In this paper, we use a lumped parameter method to derive a model based on the curved relationship between 14 C DIC and δ 13 C DIC . The derived model, if used for isotopic exchange between DIC and solid carbonate, is identical to that derived by Gonfiantini and Zuppi (2003). The curved relationship of 14 C DIC vs. δ 13 C DIC can be applied to interpret the age of the DIC in groundwater. Results of age calculations using the method discussed in this paper are compared with those obtained by using other methods that calculate the age of DIC based on adjusted initial radiocarbon values for individual samples. This paper shows that in addition to groundwater age interpretation, the lumped parameter method presented here also provides a useful tool for geochemical interpretations, e.g. estimation of apparent rates of geochemical reactions and revealing the complexity of the geochemical environment. [ABSTRACT FROM AUTHOR]

The dissolution of CO 2 into formation brines and the subsequent reactions of the CO 2 -charged brines with reservoir minerals are two key processes likely to increase the security of geological carbon-dioxide storage. These processes will be dependent on the permeability structure and mineral compositions of the reservoirs, but there is limited observational data on their rates. In this paper we report the cation and anion concentrations and Sr, oxygen and carbon isotopic compositions of formation waters from four extraction wells sampled at surface, over ~ 6 months after commencement of CO 2 injection in a five spot pattern for enhanced oil recovery at the Salt Creek field, Wyoming. Sampled fluids, separated from the minor oil component, exhibit near-monotonic increases in alkalinity and concentrations of cations but little change in Cl and Br concentrations and oxygen and deuterium isotope ratios. The increases in alkalinity are modelled in terms of reaction with reservoir calcite and silicate minerals as the changes in fluid chemistry and Sr-isotopic compositions are inconsistent with simple addition of injected fluids sampled over the course of the experiment. The reservoir mineral chemical and isotopic compositions are characterised by sampling core as well as surface exposures of the Frontier Formation elsewhere in Wyoming. The evolution of the fluid chemistries reflects extensive dissolution of both carbonate and silicate minerals over the course of the six months sampling implying rapid dissolution of CO 2 in the formation waters and reaction of CO 2 -bearing brines with formation minerals. Rates of CO 2 diffusion into the brines and advection of CO 2 charged brines in the reservoir are sufficiently slow that, if present, calcite should react to be close to equilibrium with the fluids. This allows estimation of the CO 2 partial pressures in the sampled fluids and comparison with the thermodynamic driving force for the relatively rapid average plagioclase dissolution rates of ~ 10 − 12 mol·m − 2 ·s − 1 . [ABSTRACT FROM AUTHOR]

The stable carbon isotopic analysis of tree-rings for environmental, plant physiological and archaeological applications using conventional methods is occasionally limited by physical constraints (narrow rings) or administrative concerns (requirement for non-destructive sampling) that prevent researcher access to scientifically valuable wood samples. Analysis of such archives by laser-ablation can potentially address these issues and facilitate access to restricted archives. Smaller quantities of wood are required for analysis by laser ablation, hence the approach may be considered less-invasive and is virtually non-destructive compared to standard preparation methods. High levels of intra-annual isotopic variability reported elsewhere mean that a single measurement may not faithfully represent the inter-annual isotopic signal, so before such an approach can be used with confidence it is necessary to compare the stable carbon isotopic data produced using these two methods. This paper presents stable carbon isotope (δ 13 C) data from the resin-extracted wood of dated Scots Pine ( Pinus sylvestris L.) tree-rings analysed using a modified Schulze-type laser-ablation system with results obtained using conventional manual sampling and analysis of α-cellulose prepared from the same tree-ring groups. The laser sampling system is found to perform very well against established more invasive methods. High correlations are observed between the methods for both raw and Suess corrected data ( r > 0.90 n = 50). These results highlight the potential for using laser-sampling to support the development of long isotope chronologies, for sampling narrow rings or for pre-screening cores prior to analysis using more detailed or labour intensive methods. [ABSTRACT FROM AUTHOR]

The groundwater in the Cambrian–Vendian aquifer system with its δ 18 O water values of about − 22‰ (VSMOW) and a low radiocarbon concentration is of glacial origin from the Last Ice Age. Earlier surveys have highlighted a negative co-variance of sulphate and bicarbonate content in the groundwater of the Cambrian–Vendian aquifer system, whereas the most depleted dissolved inorganic carbon δ 13 C values have been measured mainly in groundwater samples with the lowest sulphate concentrations. In this paper we studied the origin of sulphate and the factors controlling the sulphur and carbon isotope geochemistry in the aquifer system. Direct sources of sulphate were not found, but relying upon δ 18 O SO 4 measurements we suggest that the sulphate originates from oxidation of sulphide minerals whereas the δ 34 S of the dissolved SO 4 2 − in the groundwater is more enriched than the δ 34 S of the surrounding rocks. We show that bacterial activity may have caused the enrichment of δ 34 S of sulphate. [ABSTRACT FROM AUTHOR]

This paper describes numerous siderite occurrences from Nb-Zr-REY-Ga-enriched beds of tuffaceous mudstone from the Yujingshan borehole, eastern Yunnan, southwestern China. The mineral phases in the samples were identified and characterized through macroscopic observation, XRD (X-ray diffraction) analysis, optical microscopy, and FE-SEM (field emission-scanning electron microscopy). The results show that the siderite occurs in the drill core from depths of 664.07 to 729.21 m, where its content varies from 15.1 to 65.7%, 31.3% on average. Modes of occurrence of authigenic siderite include irregular banded or massive aggregates, discrete fine particles, oolitic aggregates, and double or multi-ring ellipsoid-shaped or rhombohedral aggregates. The mineralogical association with quartz, anatase, ilmenite, chromite, and zircon with sharp-edged outlines, high-temperature cracks and/or corroded embayments, and REE-bearing minerals and geochemical characteristics such as Al 2 O 3 /TiO 2 between 3 and 8, less commonly 8–23.77, indicate that abundant siderite was produced by hydrothermal alteration of airborne volcaniclastic materials. The δ 13C PDB , δ 18O PDB , and δ 18O SMOW values of siderite in the argillized tuff range from −12.56 to −1.32‰, −8.98 to −5.88‰, and 21.60 to 24.80‰, respectively. In the δ 13C PDB - δ 18O SMOW diagram, plots of the studied siderite are distributed between the fields of marine carbonate rocks, sedimentary organic matter, and carbonates of hydrothermal ores. Some siderite from the upper part of the studied borehole is isotopically close to REY carbonates from the Abramovka lignite deposit, Far Eastern Russia, which precipitated from evolved basinal waters mixed with CO 2 from a mantle source. In summary, this indicates a hybrid origin for the studied siderite including carbonate dissolution, dehydroxylation of sedimentary organic matter, and hydrothermal activity. Furthermore, the paleosalinity (Z) and paleotemperature (T) of the ore-forming fluids were calculated based on the age-corrected stable carbon and oxygen isotopic data in the samples. The Z values range from 96.65 to 121.5‰, suggesting the formation of siderite under brackish-water conditions. The T values vary from 19.47 to 47.12 °C, with some sharp fluctuations that may be due to ash falls and/or hydrothermal injections. Overall, our data support the model for critical-metal Nb(Ta)-Zr(Hf)-REY-Ga enrichment in tuffaceous deposits of southwest China including a combination of volcanic activity and terrestrial organic-rich sedimentation under warm and humid conditions, followed by low-temperature alteration evolved from acidic leaching, which is responsible for the Nb-Zr-REY-Ga enrichment, and, subsequently, formation of authigenic siderite with associated quartz, sulfide minerals, and phosphate minerals under reducing neutral/weakly alkaline conditions. • Abundant siderite is documented in the clay-altered tuffaceous horizons. • Fe was primarily derived from airborne pyroclastics. • C and O were sourced from carbonate, organic matter, and hydrotherm. • C-O isotopes show that siderite was affected by seawater and hot fluids. • A genetic model of siderite in Nb-Zr-REY-Ga deposits has been proposed. [ABSTRACT FROM AUTHOR]

The late Paleozoic ice age (LPIA) during the Carboniferous and Permian (ca. 360–260 Ma) was vegetated Earth's only recorded icehouse-to-greenhouse transition and provides a deep-time perspective for climate-glaciation-environment coevolution and future climate change. During the LPIA, changes in glacial-interglacial cycles have been closely linked to atmospheric p CO 2. In this paper, we investigate the relationship between volcanism and glacial to interglacial climate cycles during the Pennsylvanian to earliest Cisuralian in the Liujiang Coalfield from the North China Plate (NCP). We use integrated data from Zircon U-Pb dating, Hg/TOC ratios and δ13C org to recover temporal trends in volcanic intensity and relate these to fluctuations in the global carbon cycle and atmospheric p CO 2. Four new radiometric dates from tuffaceous claystones provide a precision stratigraphic framework and constrain the succession to ~322 to 301 Ma. Results date the Benxi Formation to the Bashkirian–Moscovian stages of the Carboniferous, and the Taiyuan Formation ranging from the Kasimovian stage of the Carboniferous to the Asselian stage of the Permian. Results from Hg/TOC ratios record four peaks of volcanic intensity from the Bashkirian to the Carboniferous-Permian (C-P) transition period, and two low ebbs during the early-middle Bashkirian and the early-middle Moscovian. Peaks in volcanic intensity coincide with the four negative excursions of δ13C org and correlate with volcanism in the North China Plate and NW Europe, inferring volcanic drivers for the carbon isotope excursions and perturbations in the global carbon cycle. Periods of higher atmospheric p CO 2 correlate to interglacial intervals, the two lower ebbs in p CO 2 correlate with two positive isotope plateaus, while periods of lower atmospheric p CO 2 and cooling correlate with glacial intervals C3 and C4 recognized from other sections globally. Results suggest volcanism to be a significant driver for late Pennsylvanian to earliest Cisuralian shifts in global climates from glacial to interglacial through greenhouse gas emissions and changes to the global carbon cycle. Our results represent an important contribution to the development of an accurate chronostratigraphy for the continental facies of the NCP during the Pennsylvanian and earliest Permian, enabling correlation of volcanic and climate events including glacial and interglacial cycles. [ABSTRACT FROM AUTHOR]