Isotopic Temperature Research Articles

Geological, mineralogical, and oxygen isotope studies of the Chandmani Uul iron oxide–copper–gold deposit in Dornogobi Province, Southeastern Mongolia

AbstractThe Chandmani Uul deposit is located in Dornogovi province, Southeastern Mongolia. Iron oxide ores are hosted in the andesitic rocks of the Shar Zeeg Formation of Neoproterozoic to Lower‐Cambrian age. Middle‐ to Upper‐Cambrian bodies of granitic rocks have intruded into the host rocks in the western and southern regions of the deposit. The wall rocks around the iron oxide ore bodies were hydrothermally altered to form potassic, epidote, and sericite–chlorite alteration zones, and calcite and quartz veinlets are ubiquitous in the late stage. Since granitic rocks also underwent potassic alteration, the activity of the granitic rocks must have a genetic relation to the ore deposit. The ore mineral assemblage is dominated by iron oxides such as mushketovite, euhedral magnetite with concentric and/or oscillatory zoning textures, and cauliflower magnetite. Lesser amounts of chalcopyrite and pyrite accompany the iron oxides. Among all these products, mushketovite is dominant and is distributed throughout the deposit. Meanwhile, euhedral magnetite appears in limited amounts at relatively shallow levels in the deposit. By contrast, cauliflower magnetite appears locally in the deeper parts of the deposit, and is associated with green‐colored garnet and calcite. Sulfide minerals are ubiquitously associated with these iron oxides. The oxygen isotope (δ18O) values of all types of magnetite, quartz, and epidote were found to be −5.9 to −2.8‰, 10.5 to 14.9‰, and 3.6 to 6.6‰, respectively. The δ18O values of quartz–magnetite pairs suggest an equilibrium isotopic temperature near 300°C. The calculated values of δ18O for the water responsible for magnetite ranged from 2 to 10‰. All the data obtained in this study suggest that the iron oxide deposit at the Chandmani Uul is a typical iron oxide–copper–gold deposit, and that this deposit was formed at an intermediate depth with potassic and sericite–chlorite alteration zones under the oxidized conditions of a hematite‐stable environment. The δ18O range estimated implies that the ore‐forming fluid was supplied by a crystallizing granodioritic magma exsolving fluids at depth with a significant contribution of meteoric water.

Performance of Adiabatic Melting as a Method to Pursue the Lowest Possible Temperature in ^{3}hbox {He} and ^{3}hbox {He}\u2013^{4}hbox {He} Mixture at the ^{4}hbox {He} Crystallization Pressure

We studied a novel cooling method, in which ^{3}hbox {He} and ^{4}hbox {He} are mixed at the ^{4}hbox {He} crystallization pressure at temperatures below 0.5,mathrm {mK}. We describe the experimental setup in detail and present an analysis of its performance under varying isotope contents, temperatures, and operational modes. Further, we developed a computational model of the system, which was required to determine the lowest temperatures obtained, since our mechanical oscillator thermometers already became insensitive at the low end of the temperature range, extending down to left( 90pm 20right) ,upmu {mathrm {K}}approx frac{T_{c}}{left( 29pm 5right) } (T_{c} of pure ^{3}hbox {He}). We did not observe any indication of superfluidity of the ^{3}hbox {He} component in the isotope mixture. The performance of the setup was limited by the background heat leak of the order of 30,mathrm {pW} at low melting rates, and by the heat leak caused by the flow of ^{4}hbox {He} in the superleak line at high melting rates up to 500,upmu mathrm {mol/s}. The optimal mixing rate between ^{3}hbox {He} and ^{4}hbox {He}, with the heat leak taken into account, was found to be about 100..150,upmu mathrm {mol/s}. We suggest improvements to the experimental design to reduce the ultimate achievable temperature further.

Stable Isotope Characteristics and Vapor Source of Precipitation in the South and North Slopes of Wushaoling Mountain

We analyze the stable isotope characteristics and vapor source of precipitation in a monsoon marginal area in the southern and northern slopes of Wushaoling Mountain, northwestern China, using 97 precipitation samples collected from October 2016 to October 2017. Correlation analysis and HYSPLIT model are used to study the characteristics of stable isotopes in precipitation, local meteoric water line equation, temperature and precipitation effects, and vapor source. The study found the following results. ① The slope and intercept of the southern slope local meteoric water line were lower than of those of the northern slope and global averages. ② Although the isotope temperature effects and seasonal effects of both slopes were obvious, the temperature effect of the northern slope was more obvious than of that of the southern slope. ③ The stable isotopes of precipitation during the summer on the northern slope and the precipitation on the southern slope<5 mm revealed that the precipitation effect was weak. There was no obvious precipitation effect in other seasons or in other precipitation levels on both slopes. ④ Vapor from the northwest and north accounted for>90% of the total. The northern slope was rarely affected by monsoon vapor, but the southern slope was affected by the southeast monsoon during the summer. Local water vapor recycling contributed to water vapor in the southern and northern slopes of Wushaoling Mountain. This study could improve the cognition of precipitation isotopic evolution in alpine regions, and lays a foundation for further research on isotope hydrology in cold and arid regions.

Origin of blocky aragonite cement in Cenozoic glaciomarine sediments, McMurdo Sound, Antarctica

AbstractInorganic aragonite occurs in a wide spectrum of depositional environments and its precipitation is controlled by complex physio‐chemical factors. This study investigates diagenetic conditions that led to aragonite cement precipitation in Cenozoic glaciomarine deposits of McMurdo Sound, Antarctica. A total of 42 sandstones that host intergranular cement were collected from the CIROS‐1 core, located proximal to the terminus of Ferrar Glacier. Standard petrography, Raman spectroscopy and electron microprobe analysis reveal a prominent aragonite cement phase that occurs as a pore‐filling blocky fabric throughout the core. Oxygen isotope compositions (δ18O = −30·0 to −8·6‰ Vienna Pee‐Dee Belemnite) and clumped isotope temperatures (TΔ47 = 13·1 to 31·5°C) determined from the aragonite cements provide precise constraints on isotopic compositions (δ18Ow) of the parent fluid, which mostly range from −10·8 to −7·2‰ Vienna Standard Mean Ocean Water. The fluid δ18Ow values are consistent with those of pore water, previously identified as cryogenic brine in the nearby AND‐2A core. Petrographic and geochemical data suggest that aragonite cement in the CIROS‐1 core precipitated from a similar brine. The brine likely formed and infiltrated sediments in flooded glacial valleys along the western margin of McMurdo Sound during the middle Miocene Climatic Transition, and subsequently flowed basinward in the subsurface. Consequently, the brine forms as a longstanding subsurface fluid that has saturated Cenozoic sediments below southern McMurdo Sound since at least the middle Miocene. Aragonite cementation in the CIROS‐1 core is interpreted to reflect its proximal position to sites of brine formation and greater likelihood of experiencing brines with sustained high carbonate saturation states and Mg/Ca ratios. This unusual occurrence expands the range of known natural occurrences of aragonite cement. Given the potential for cryogenic brine formation in glaciomarine settings, blocky aragonite, as the end member of the spectrum of aragonite cement morphology, may be more widespread in glaciomarine sediments than currently thought.

Progress Towards a Universal Approach for Prediction of the Superconducting Transition Temperature

A suite of density functional theory (DFT) approaches that provide accurate and reliable superconductivity parameters without post-calculation corrections is presented. The sensitivity of phonon dispersion (PD) outputs to slight variations in calculation and external parameters enables identification of the most electron-coupled phonon mode(s). These mode(s) are directly linked, in a range of superconductors, to specific band structure characteristics and to the response of electrons to deformation potentials. These approaches are applied successfully to MgB2 under a wide range of variable external conditions, including isotopic state, metal substitutions, pressure, and temperature. This approach has also been extended to other chemical systems with significantly different composition and crystal symmetry, such as YB6, H3S under pressure, B-doped diamond, B-doped silicon, and A15 compounds, to name a few. The effectiveness of these approaches that link both PDs and electronic band structures (EBSs) is largely dependent on reliable and accurate DFT results at the meV range that resolve Fermi surface (FS) detail in close reciprocal space proximity. Such a level of meV resolution is possible only by using extremely fine k-grids and large cutoff radii, much smaller and larger, respectively, to what has typically been used in DFT calculations reported in the literature.

OXYGEN ISOTOPE PROFILES OF UPPERMOST JURASSIC VERTEBRATE TEETH AND OYSTER SHELLS: A RECORD OF PALEOENVIRONMENTAL CHANGES AND ANIMAL HABITATS

ABSTRACTHigh resolution oxygen isotopes profiles of well-preserved uppermost Jurassic oyster shells and vertebrate (ichthyosaur and fish) teeth from Central Poland were obtained using a microdrill and an ion microprobe (SHRIMP IIe/MC). Internal variability of δ18O values of oyster shells (-1.7 to 1.3‰ VPDB) collected from the offshore interval of the studied section is greater than that determined previously from bulk oysters. Relatively high δ18O values of the studied oysters may be linked to a slight increase in the salinity of the mid-Polish basin. Low δ18O values of co-occurring ichthyosaur tooth enamel substantiate endothermy of these reptiles. An observed ontogenetic increase in the ichthyosaur enamel δ18O values (from ∼ 19.4 to ∼ 21.6‰ VSMOW) may be a result of long distance migrations although the effect of metabolic factors at rising body mass cannot be completely excluded. It is postulated that δ18O values of the latest portion of the ichthyosaur tooth enamel can be used for the calculation of ancient water oxygen isotope composition and verification of oxygen isotope temperatures. High δ18O values of the enameloid of Caturus lungfishes (23.6 to 26.5‰ VSMOW) collected from an upper part of the studied section, which was deposited in a restricted lagoonal environment after a marine regression, are probably a result of a high evaporation rate. The fishes could have breathed atmospheric air and withstood episodes of water hypoxia. Internal oxygen isotope records of the shells and teeth are promising proxies for studies of the paleoenvironment and activity of animals.

Water isotopes – climate relationships for the mid-Holocene and preindustrial period simulated with an isotope-enabled version of MPI-ESM

Abstract. We present here the first results, for the preindustrial and mid-Holocene climatological periods, of the newly developed isotope-enhanced version of the fully coupled Earth system model MPI-ESM, called hereafter MPI-ESM-wiso. The water stable isotopes H216O, H218O and HDO have been implemented into all components of the coupled model setup. The mid-Holocene provides the opportunity to evaluate the model response to changes in the seasonal and latitudinal distribution of insolation induced by different orbital forcing conditions. The results of our equilibrium simulations allow us to evaluate the performance of the isotopic model in simulating the spatial and temporal variations of water isotopes in the different compartments of the hydrological system for warm climates. For the preindustrial climate, MPI-ESM-wiso reproduces very well the observed spatial distribution of the isotopic content in precipitation linked to the spatial variations in temperature and precipitation rate. We also find a good model–data agreement with the observed distribution of isotopic composition in surface seawater but a bias with the presence of surface seawater that is too 18O-depleted in the Arctic Ocean. All these results are improved compared to the previous model version ECHAM5/MPIOM. The spatial relationships of water isotopic composition with temperature, precipitation rate and salinity are consistent with observational data. For the preindustrial climate, the interannual relationships of water isotopes with temperature and salinity are globally lower than the spatial ones, consistent with previous studies. Simulated results under mid-Holocene conditions are in fair agreement with the isotopic measurements from ice cores and continental speleothems. MPI-ESM-wiso simulates a decrease in the isotopic composition of precipitation from North Africa to the Tibetan Plateau via India due to the enhanced monsoons during the mid-Holocene. Over Greenland, our simulation indicates a higher isotopic composition of precipitation linked to higher summer temperature and a reduction in sea ice, shown by positive isotope–temperature gradient. For the Antarctic continent, the model simulates lower isotopic values over the East Antarctic plateau, linked to the lower temperatures during the mid-Holocene period, while similar or higher isotopic values are modeled over the rest of the continent. While variations of isotopic contents in precipitation over West Antarctica between mid-Holocene and preindustrial periods are partly controlled by changes in temperature, the transport of relatively 18O-rich water vapor near the coast to the western ice core sites could play a role in the final isotopic composition. So, more caution has to be taken about the reconstruction of past temperature variations during warm periods over this area. The coupling of such a model with an ice sheet model or the use of a zoomed grid centered on this region could help to better describe the role of the water vapor transport and sea ice around West Antarctica. The reconstruction of past salinity through isotopic content in sea surface waters can be complicated for regions with strong ocean dynamics, variations in sea ice regimes or significant changes in freshwater budget, giving an extremely variable relationship between the isotopic content and salinity of ocean surface waters over small spatial scales. These complicating factors demonstrate the complexity of interpreting water isotopes as past climate signals of warm periods like the mid-Holocene. A systematic isotope model intercomparison study for further insights on the model dependency of these results would be beneficial.

Investigation of the thermal history of the Delaware Basin (West Texas, USA) using carbonate clumped isotope thermometry

AbstractWe utilized carbonate clumped isotope thermometry to explore the thermal history of the Delaware Basin, West Texas, USA. Carbonate wellbore cuttings from five oil/gas wells across the basin yielded clumped isotope temperatures (T(Δ47)) ranging from 27°C to 307°C, interpreted to reflect a combination of initial precipitation/recrystallization temperature and solid‐state C‐O bond reordering during burial. Dolomite samples generally record lower apparent T(Δ47)s than calcite, reflecting greater resistance to reordering in dolomite. In all five wells, clumped isotope temperatures exceed modern downhole temperature measurements, indicating higher heat flow in the past. Using modelled burial curves based on sedimentological history, we created unique time‐temperature histories by linearly applying a geothermal gradient. Applying two different thermal history reordering models, we modelled the extent of solid‐state C–O bond reordering to iteratively find the time‐averaged best‐fit geothermal gradients for each of the five wells. Results of this modelling suggest that the shallower, southwestern portion of the study area experienced higher geothermal gradients throughout the sediment history (~45°C/km) than did the deeper, southeastern portion (~32°C/km), with the northern portion experiencing intermediate geothermal gradients (~35–38°C/km). This trend is in agreement with the observed gas/oil ratios of the Delaware Basin, increasing from east to west. Furthermore, our clumped isotope temperatures agree well with previously published vitrinite reflectance data, confirming previous observations and demonstrating the utility of carbonate clumped isotope thermometry to reconstruct basin thermal histories.

Serpentinization at the Rainbow and Saldanha sites, Mid-Atlantic Ridge: Mineralogical, geochemical, and isotopic features

Abstract The Rainbow hydrothermal field (36°14′N) and the Saldanha seamount (36°34′N), in the Mid-Atlantic Ridge (MAR), are tectonic exposures of serpentinized upper mantle peridotites, both associated with significant hydrothermal activity. On the basis of detailed mineralogical and geochemical characterization of serpentinites from both sites, several serpentinization-related issues are discussed in the present work. As expected in oceanic environments, most of the sampled rocks are lizardite-chrysotile serpentinites exhibiting a variety of pseudomorphic through non-pseudomorphic textures, such textural evolution probably being related to changing water/rock ratios during this retrograde process. Oxygen isotope temperatures indicate that the serpentinization took place at 300–200 °C; on the other hand, isotopic data suggest that replacement of early pseudomorphic lizardite by lizardite ± chrysotile non-pseudomorphic textures requires that temperatures and/or water/rock ratios are high enough to promote the necessary dissolution–recrystallization processes. Mass-balance calculations for olivine-serpentine and orthopyroxene-serpentine pairs provided a basis for establishing serpentinization reactions likely to have produced the present rocks. Moreover, these calculations also showed that, notwithstanding some noticeable loss of MgO from olivine and of SiO2 from orthopyroxene, serpentinization of both minerals implies volume increases on the order of 26–27%, therefore potentially promoting the overall expansion of the rock. The geochemical and isotopic features of the studied rocks indicate that unmodified seawater was responsible for the serpentinization of the MAR peridotites. However, the mineralogy and REE patterns of some of these serpentinites indicate occasional subsequent interaction of the serpentinized rocks with seawater at much lower temperatures (seafloor alteration, characterized by carbonate deposition and negative Ce anomalies), or with high-temperature ore-forming hydrothermal fluids (ore-forming alteration, characterized by sulfide precipitation and steep positive Eu anomalies).

Dynamic Intermediate Waters Across the Late Glacial Revealed by Paired Radiocarbon and Clumped Isotope Temperature Records

AbstractPaired radiocarbon and clumped isotope temperature records from U/Th‐dated Desmophyllum dianthus corals in the North Atlantic and Southern Ocean provide unique information about the history of intermediate waters (∼1,500–1,700 m) across the late glacial and deglaciation (∼35–10 ka). These measurements allow for the construction of radiocarbon‐temperature crossplots, which help to identify water mass endmembers at different times across the deglaciation. Radiocarbon and temperature values from the late glacial fall outside the range of modern ocean data from near the sample collection sites. In the North Atlantic, radiocarbon values tend to be much older than the modern, while in the Southern Ocean, they are more often younger than the modern. Reconstructed temperatures vary around respective modern ocean values; however, warm waters are observed at the Last Glacial Maximum and across the deglaciation in the north and south. We interpret our data in the context of the modern hydrography of the Western North Atlantic and Southern Ocean, and we draw upon direct comparisons between sediment core‐derived reconstructions of ocean circulation from the South Indo‐Pacific and our deep‐sea coral data from the Southern Ocean. Our North Atlantic data support accepted patterns of reduced North Atlantic Deep Water formation during Heinrich Stadials 1 and 2. In the Southern Ocean, deep‐sea coral populations respond to changes in ocean structure that are also reflected in a depth profile of δ13C data from New Zealand, and data indicate that there was less influence of Pacific Deep Water between 1,500 and 1,700 m south of Tasmania across much of the deglaciation.

A diagenetic origin for isotopic variability of sediments deposited on the margin of Great Bahama Bank, insights from clumped isotopes

Abstract The clumped isotope temperature proxy has been used to investigate the diagenetic history of carbonate sediments in two cores recovered during ODP Leg 166 on the margin of Great Bahama Bank. While periplatform sediments constitute a tempting archive of paleo ocean chemistry as they are unlikely to be subducted, their primary limitation is a well-documented susceptibility to post-depositional diagenetic reworking. The crystallization temperatures reconstructed using the clumped isotope proxy, as well as the mineralogy and δ13C and δ18O values have been used to determine the relative effects of sediment mixing and sediment recrystallization. Results show that as sediments undergo diagenetic alteration at the seafloor, their initially “warm” clumped isotope composition is overprinted at cooler benthic temperatures. This process appears to occur in an environment with sufficient fluid exchange to overprint carbon isotopes; an observation confirmed in a separate study by analyses of calcium, a similarly rock-buffered element. This early reactive exchange between carbonates and fluids is likely driven by the conversion of metastable aragonite to calcite. This partially occurs within the “flushed zone”, where porewater compositions remain compositionally similar to seawater throughout the upper ∼40 meters of the sediment column. Sediments dominated by open system isotopic compositions correspond to a period of minimal sediment accumulation between 2 and 3 Ma. More deeply buried Miocene sediments of the more platform-proximal Site 1003 show evidence of subsequent recrystallization, incorporating the warmer geothermal TΔ47 values, and more as well as modified water δ18O values, likely driven by co-evolving porewater and carbonate oxygen isotopes. Reconstructed water δ18O values of these deeper sediments at Site 1003 are considerably more positive than the measured modern values, suggesting that porewater δ18O values were more positive during the Miocene. Sediments deposited at the platform distal Site 1006 between the early and middle Miocene did not show evidence for this deeper recrystallization. Differences in diagenetic behavior between the two sites cannot be solely accounted for by differences in sediment accumulation rate. To illustrate this, time-integrated models were constructed which simulated the burial of identically reactive material through the depositional history of each site, the sediments deposited at Site 1006 appear to “stabilize” after an initial phase of neomorphism, whereas the more platform proximal Site 1003 continues to recrystallize during deeper burial, apparently in the presence of a parent fluid with a more positive δ18O value than observed today. We conclude that despite consisting of the same end-member sediment sources, and being spatially separated by less than 30 km, the difference in clumped and oxygen isotopic composition between Sites 1003 and 1006 can be predominantly attributed to differences in the rate and duration of recrystallization during burial.

Sensitivity of clumped isotope temperatures in fossil benthic and planktic foraminifera to diagenetic alteration

Applying the clumped isotope (Δ47) thermometer to foraminifer microfossils offers the potential to significantly improve paleoclimate reconstructions, owing to its insensitivity to the isotopic composition of seawater (unlike traditional oxygen isotope (δ18O) analyses). However, the extent to which primary Δ47 signatures of foraminiferal calcites can be altered during diagenesis is not well known. Here, we present Δ47 data as well as high-resolution (∼10 kyr) δ18O and δ13C middle Eocene time series, measured on benthic and planktic foraminifera from ODP/IODP Sites 1408, 1409, 1410, 1050, 1260 and 1263 in the Atlantic Ocean. The sites examined span various oceanographic regimes, including the western tropical to mid-latitude North Atlantic, and the eastern mid-latitude South Atlantic. Comparing data from contemporaneous foraminifera with different preservation states, we test the effects of diagenetic alteration on paleotemperature reconstructions for the deep and surface ocean. We find that overall, primary Δ47 signatures appear similarly sensitive to diagenetic overprinting as δ18O, with differences in sensitivity depending on pore fluid chemistry and the amount of secondary calcite. Where planktic foraminifera are significantly altered, sea surface temperatures derived from Δ47 and δ18O values are biased towards cool temperatures. In comparison, Δ47 and δ18O values of benthic and well preserved planktic foraminifera are less affected by diagenesis and thus likely to yield robust foraminiferal calcification temperatures. With independent estimates of diagenetic calcite fractions, secondary overprints could be corrected for, using end-member modeling and Δ47-based temperatures from benthic foraminifera.

Carbonate clumped isotope (&amp;Delta;&amp;lt;sub&amp;gt;47&amp;lt;/sub&amp;gt;) thermometry andits application in paleoelevation reconstruction

Paleoaltimetry provides crucial constraints on tectonic processes and precise paleotemperature measurement is an important component in paleoelevation reconstruction. Carbonate clumped isotope thermometry is based on homogeneous isotope equilibrium and is used to provide direct estimation of carbonate formation temperature independent of δ 18O of the parent water from which the carbonate formed. The error regarding clumped isotope temperature estimation can be reduced to ±2°C. The characteristics of temperature-dependence, and the small uncertainty using carbonate clumped isotope thermometry, greatly improve accuracy and precision in paleoelevation reconstruction. In this review, we introduce the basic theory, laboratory methodology and standardization processes underpinning carbonate clumped isotope thermometry. Theoretical calculations indicate a linear relationship between parameter Δ47 and 1/ T 2, which establishes the foundation from which carbonate clumped isotopes provide reliable paleotemperatures. The laboratory treatment of carbonate includes two systems: the modified Kiel IV device for small weight samples (0.15−0.2 mg) installed within microvolume nitrogen traps and packed microvolume columns; and a heavy sample device that is installed with McCrea/common bath acid digestion devices, nitrogen traps and packed columns. These systems are designed to remove potential interference from water and hydrocarbons in the CO2. The measurement of purified CO2 is finished on gas source isotope mass ratio spectrometry (IMRS), especially on MAT 253 and 253 Plus machines. The standardization of the Δ47 to an absolute reference frame (ARF) accounts for the non-linearity and scaling effect of the IMRS, and the ARF also enables direct comparison of data from different laboratories. The practical procedure for the standardization includes interpolating the relationship between the measured δ 47 and Δ47 of the equilibrium gases, and conversion of the measured Δ47 to theoretical values to derive an empirical transfer function. Due to the great potential for solving Earth science problems, empirical calibration of the carbonate clumped isotope thermometry has been explored over a wide range of temperature in different types of carbonates, but is still plagued by discrepancies between different calibrations, probably due to variability in acid preparation, CO2 purification and data reduction methods. We summarized all the published synthetic calcite data to ARF with the same acid fractionation factor and yield a composite empirical calibration that could resolve the discrepancies between different calibrations. However, bio-genetic carbonates still fail to yield a universal empirical calibration, even when using the same methodology. The cause of this difference is probably due to different environmental, species discrimination and vital effects. The application of carbonate clumped isotope thermometry to paleoaltimetry is based on the theory that the δ 18O of precipitation (meteoric water) decreases proportionally as elevation increases. Knowing the formation temperature and δ 18O of carbonate, we can trace back to the precise value of δ 18O in precipitation, and then, using the theoretical model, or empirical relationship, between the δ 18O of precipitation and elevation, reconstruct paleoelevation. Furthermore, clumped isotope thermometry can be used to test for diagenetic effects on pedogenic samples to ensure they retain original sedimentary isotopic compositions. We summarized previous applications of carbonate clumped isotope thermometry to accurately and precisely reconstruct the paleoelevation of the Andes mountains, Western North America and the Tibetan Plateau to provide insights into the uplift history and geodynamic process of those regions. Despite the great potential for carbonate clumped isotopes in paleoelevation reconstruction, there are still challenges regarding equilibrium mechanisms, the discrepancies between different calibrations and the broader application in different carbonates. To resolve these challenges, more theoretical research is needed, as well as improving the resolution of IMRS.

Challenges associated with the climatic interpretation of water stable isotope records from a highly resolved firn core from Adélie Land, coastal Antarctica

Abstract. A new 21.3 m firn core was drilled in 2015 at a coastal Antarctic high-accumulation site in Adélie Land (66.78∘ S; 139.56∘ E, 602 m a.s.l.), named Terre Adélie 192A (TA192A). The mean isotopic values (-19.3‰±3.1 ‰ for δ18O and 5.4 ‰±2.2 ‰ for deuterium excess) are consistent with other coastal Antarctic values. No significant isotope–temperature relationship can be evidenced at any timescale. This rules out a simple interpretation in terms of local temperature. An observed asymmetry in the δ18O seasonal cycle may be explained by the precipitation of air masses coming from the eastern and western sectors in autumn and winter, recorded in the d-excess signal showing outstanding values in austral spring versus autumn. Significant positive trends are observed in the annual d-excess record and local sea ice extent (135–145∘ E) over the period 1998–2014. However, process studies focusing on resulting isotopic compositions and particularly the deuterium excess–δ18O relationship, evidenced as a potential fingerprint of moisture origins, as well as the collection of more isotopic measurements in Adélie Land are needed for an accurate interpretation of our signals.

Morphology effect of diverse ceria with active tungsten species on NH3-SCR behaviors

Abstract A series of CeO2 with diverse morphologies (hollowsphere, cube, and rod) was synthesized by hydrothermal method, while a worm-like mesoporous ceria was synthesized by evaporation-induced self-assembly (EISA) method. 5 (wt.)% of WO3 species was loaded on the above four kinds of CeO2 supports with various morphologies by impregnation method (respectively noted as four catalysts including 5%WO3/CeO2-hollowsphere, 5%WO3/CeO2-cube, 5%WO3/CeO2-rod, and 5%WO3/CeO2-mesopore). Thereafter, these solids were comparatively tested for the reaction of low-temperature selective catalytic reduction (SCR) of NO with ammonia. The physicochemical properties were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), X-ray photoelectron spectroscopy (XPS), N2 physical sorption, temperature programmed desorption of NH3 (NH3-TPD). The distinct activities of tungsten loaded on CeO2 with different morphologies were observed. 5%WO3/CeO2-mesopore especially exhibited abroad temperature window of high NO conversion (>95%, 200–420 °C), and an excellent N2 yield (>90%, 200–450 °C). Thereafter, NH3-SCR reaction was systematically studied the changes of surface acidity, active site status, and nitrite/nitrate adsorption behaviors. The surface acidity of CeO2 and 5%WO3/CeO2 were distinguishable. Lewis acid sites were commonly originated from CeO2, but WO3 greatly enhanced the amount and strength of the Bronsted acid sites based on DRIFT study. In addition, the oxygen isotopic temperature programmed exchange experiment indicated that the introduction of tungsten inhibited the surface lattice oxygen mobility and the related oxidative activity, corresponding to poor oxygen exchange ability. Furthermore, the mechanisms were deduced by the DRIFT spectra, and density functional theory (DFT) calculations. NO adspecies of 5%WO3/CeO2 could be more gaseous NO2 and asymmetric vibration bridging nitrate species, while symmetric vibration bridging and monodentate nitrates over CeO2 could be readily generated. The adsorption of NO, NO2 and NH3 on molecular facet were investigated by DFT method, which clearly showed that the crystal plane of (110) is more reactive to NO and NH3 gases with respect to the crystal plane of (111).

The burial and exhumation history of the Liuqu Conglomerate in the Yarlung Zangbo suture zone, southern Tibet: Insights from clumped isotope thermometry

The Liuqu Conglomerate, exposed along the Yarlung Zangbo suture zone (YZSZ) in southern Tibet, archives not only the process of the India-Asia collision, but also the exhumation history of the India-Asia collision zone. The burial and exhumation history of the Liuqu Conglomerate thus could potentially provide clues to the India-Asia collision and orogeny. Low-temperature thermochronometric data indicate that maximum burial temperatures of the Liuqu Conglomerate ranged from 80 to 110 °C; however, the exact burial history is not well constrained. Here, we examine the burial conditions of the Liuqu Conglomerate by applying clumped isotope thermometry to paleosol carbonates. Extensive microcrystalline recrystallization indicates that the samples have been diagenetically altered during burial. Moreover, the clumped isotope temperatures (ranging from ∼48 to ∼97 °C) are clearly above Earth surface conditions, indicating the original climatic information was overwritten by alteration at higher burial temperatures. Nevertheless, the calculated diagenetic water δ18O values represent maximum meteoric water values that can be used to broadly constrain the paleoelevation. The highest clumped isotope temperature implies that the maximum burial temperature of the Liuqu Conglomerate was at least ∼97 °C. We conclude that the Liuqu Conglomerate was buried as deeply as 3.7–4.3 km during the latest Paleocene to Eocene, and then exhumed during the Miocene (∼10–12 Ma). Incision of the paleo-Yarlung River was likely responsible for erosion and exhumation of the Liuqu Conglomerate, which suggests that the drainage system of Paleo-Yarlung River was similar to that of today and supports the model of outward growth of the Tibetan Plateau.

Clumped isotope evidence for episodic, rapid flow of fluids in a mineralized fault system in the Peak District, UK

We have used clumped isotope thermometry to study a fault-hosted hydrothermal calcite vein associated with the Mississippi Valley Type (MVT) mineralization on the Derbyshire Platform in the southern Pennines, UK. This is the first published dataset obtained using a new mass spectrometer, MIRA, optimized for clumped isotope analysis and an associated clumped isotope–temperature calibration. We analysed multiple generations of vein growth at high spatial resolution in two transects across the vein. The vein grew episodically at temperatures between 40 and 100°C. We interpret each episode of growth as being associated with an increasing flux of formation waters from deep sedimentary basins next to the mineralized platform and an accompanying increase in the precipitation temperatures. Heat is conserved in the fluid as it ascends along the fault surface and, thus, flow must have been fast and restricted to short-lived pulses. The flux could have been driven by high pore pressures associated with rapid sedimentation, hydrocarbon generation and diagenesis in the basinal facies of the Visean Bowland–Hodder group. Natural hydraulic fracturing of shale units and failure of capillary seals, possibly triggered by uplift, allowed the release of fluids into aquifers within the sediment pile. The transmission of high pore fluid pressures from the shales to the fault zone, aided by the compressibility of the gas phase in two-phase pore fluids, may have resulted in fault rupture, accompanied by enhanced fracture permeability and rapid fluid flow. Vein growth ceased as pore pressures dissipated. Such behaviour is closely related to a seismic valve type model for mineralization. Supplementary material: Details of the methods and equipment are available at https://dx.doi.org/10.6084/m9.figshare.3808329.v9

Revisiting the equable climate problem during the Late Cretaceous greenhouse using paleosol carbonate clumped isotope temperatures from the Campanian of the Western Interior Basin, USA

Greenhouse climates such as the Late Cretaceous period provide important reference frames for understanding modern anthropogenic climate change. Upper Cretaceous terrestrial climate proxies have been interpreted as evidence for “equable” climates with reduced seasonal variations in temperature. However, climate models have largely failed to reproduce these reconstructions unless parameters such as atmospheric CO2 concentrations are set to unreasonable values. To help resolve such model-proxy disagreements, we reconstruct mean annual range in temperature (MART) for the Campanian (~75 Ma) Kaiparowits (south-central Utah) and Two Medicine (northwest Montana) Formations using warmest mean monthly temperature reconstructions from the clumped isotope composition of paleosol carbonate nodules, and reconstructions of local mean annual air temperatures from other methods. An evaluation of the applicability of bulk elemental soil geochemistry temperature proxies in these deposits supports the use of previous leaf physiognomy-based estimates of mean annual temperature for our MART reconstructions. We test the validity of several common assumptions made in reconstructing MART in two novel ways. First, MART is commonly calculated as twice the difference between local mean annual air temperature and warmest mean monthly temperature, and we validate this method by estimating modern MART for a range of environments using climate reanalysis data. Second, we constrain the effect of radiative soil heating on our soil carbonate temperature estimates by showing that for most environments likely to be preserved in the geologic record, summer soil temperatures are <3 °C higher than air temperatures. Our findings suggest that warmest mean monthly temperatures were 30 to 35 ± 4 °C at the two study sites, and that MART was 21 to 29 °C for the Kaiparowits Formation, and 21 to 27 °C for the Two Medicine Formation. Mid-latitude Late Cretaceous MARTs were similar to modern ranges in mid-latitude seasonal temperature, and much (>9 °C) larger than previous proxy reconstructions of Late Cretaceous MART. These results add to a growing body of literature showing that terrestrial MART during ancient greenhouse periods was not significantly different from modern seasonal temperature variations. Finally, the similarity in MART between the Kaiparowits and Two Medicine formations suggests that latitudinal changes in MART did not contribute to the faunal provincialism that has been proposed by some paleontologists.

Taking the Temperature of Hydrothermal Ore Deposits Using Clumped Isotope Thermometry

Abstract Better tools are needed to map the thermal structure of ore deposits. Here, carbonate clumped isotope thermometry is applied for the first time in epithermal, skarn, and carbonate-hosted deposits to identify the conditions involved in metal transport and deposition. Clumped isotope temperature calibrations were tested by measurement of carbonates from three geothermal fields in the Taupo volcanic zone, New Zealand, that record growth temperatures between 130° and 310°C. Results for modern Taupo volcanic zone calcites were paired with known fluid δ18O values and these indicate precipitation in equilibrium with produced geothermal waters. Measurements carried out at the Waihi low sulfidation deposit in New Zealand, the Antamina polymetallic skarn in Peru, and the Mount Isa sediment hosted Pb-Zn and Cu deposit in Queensland, Australia, demonstrate that clumped isotope values are sensitive to temperature gradients defined using other methods. At Waihi, an andesite-hosted deposit, temperature controls the majority of variation in carbonate mineral δ18O. At Mount Isa, ~300° to 400°C temperatures were recorded in a 1.5 Ga orebody, which are consistent with fluid inclusion values, highlighting the longevity of clumped isotope archives in dolomite minerals. Collectively, these results demonstrate the potential for clumped isotopes to delineate the heat footprint around deposits that contain carbonates, and to more effectively disentangle magmatic and meteoric fluid δ18O signals.

Carbonate stable and clumped isotopic evidence for late Eocene moderate to high elevation of the east-central Tibetan Plateau and its geodynamic implications

Carbonate stable and clumped isotopic evidence for late Eocene moderate to high elevation of the east-central Tibetan Plateau and its geodynamic implications