Hydrogen Isotopic Composition Research Articles

Natural gas characteristics and gas-source comparisons of the Lower Triassic Feixianguan Formation, Eastern Sichuan Basin, China

There is great controversy regarding the origin and source of natural gas in the Lower Triassic Feixianguan Formation in the Eastern Sichuan Basin. This seriously restricts the study of natural gas dynamics in the Feixianguan Formation and thus hampers natural gas exploration in the region, so further study is urgently required. Using experimental tests of natural gas composition, stable isotopes, and noble gas isotopes with gas chromatography (GC) and mass spectrometry (MS) studies of source rock and reservoir asphalt saturated hydrocarbons, the natural gas geochemical characteristics, the genetic identification and a gas-source comparison of the Feixianguan Formation were studied. Then, constrained by the thermal history, the histories of gas generation and expulsion were restored by basin simulation technology. Finally, a gas accumulation model was established for the Feixianguan Formation. The results showed that (1) the H2S-rich and H2S-poor gas reservoirs of the Feixianguan Formation are distributed on the east and west sides of the Kaijiang-Liangping trough in the Eastern Sichuan Basin, respectively. The carbon and hydrogen isotope compositions of the natural gas in the gas reservoirs are generally heavy and have typical characteristics of high-maturity dry gas reservoirs. (2) The natural gas of the Feixianguan Formation is organic thermogenic gas, which is mainly oil-type gas generated by the secondary cracking of crude oil. The gas-generating parent material is mainly type II kerogen. (3) The natural gas of the Feixianguan Formation in the Eastern Sichuan Basin was mainly generated by argillaceous source rocks of the Upper Permian Longtan Formation. (4) Natural gas accumulation occurred as follows: the paleo-structure heights were filled with crude oil in the Early Jurassic, and paleo-oil reservoirs were formed in the Feixianguan Formation; during the Middle-Late Jurassic, the paleo-oil reservoirs were cracked when the reservoir temperatures rose above 160 °C, and paleo-gas reservoirs were formed. Since the end of the Late Jurassic, the paleo-gas reservoirs have been adjusted and reformed to form the present-day natural gas reservoirs. These results provide a basis for studying natural gas accumulation dynamics of the Feixianguan Formation in the Eastern Sichuan Basin.

Temporal stability of δ2H in insect tissues: Implications for isotope-based geographic assignments

Hydrogen isotope geolocation of insects is based on the assumption that the chitin in the wings of adult migratory insects preserves the hydrogen isotope composition (δ2H) of the larval stages without influence of adult diet. Here, we test this assumption by conducting laboratory feeding experiments for monarch butterflies (Danaus plexippus) including: (1) a starvation treatment where adults were not fed and (2) an enriched treatment where adults were fed a diet isotopically enriched in deuterium (~ +78‰) compared to the larval diet. The δ2H values of adult wings were measured at different time steps along the 24-day experiment. We also investigated intra-wing differences in δ2H values caused by wing pigmentation, absence of wing scales, and presence of major wing veins. We conclude that, although the magnitude of the changes in δ2H values are small (~6‰), wing δ2H values vary based on adult diet and insect age, particularly early after eclosion (i.e., 1–4 days). We found that wing shade, wing pigmentation, and the presence of wing scales do not alter wing δ2H values. However, wing samples containing veins had systematically higher δ2H values (~9‰), suggesting that adult diet influences the hemolymph that circulates in the wing veins. We hypothesise that there is a stronger influence of adult diet on the isotope signal of wings during early adult life relative to later life because of increased metabolic and physiologic activity in young insect wings. We argue that the influence of the isotopic contribution of adult diet is generally small and is likely minimal if the wings are carefully sampled to avoid veins. However, we also demonstrated that wings are not inert tissues, and that adult feeding contributes to some of the intra-population δ2H variance. We conclude that δ2H geolocation using insect wings remains valid, but that adult feeding, butterfly age and wing vein sampling generate an inherent uncertainty limiting the precision of geolocation.

Cenozoic topographic evolution of the Southern Central Andes foreland as revealed by hydrogen stable isotopes in hydrated volcanic glass

We use the “isotope-paleotopography” method to resolve the topographic evolution of the Southern Central Andes and adjacent foreland to the east, at the latitude of 35°S. Our analysis is based on δ2H measurements from hydrated volcanic glass from 107 samples collected from a 55 to 10 Ma stratigraphic section in the Malargüe basin, and from an additional 11 samples of Quaternary tuffs. The results are supported by an analysis of a large dataset of modern meteoric water samples (n=197), which are used to characterize the relationship between orographic lifting and precipitation isotopes in the modern. Our interpretations are guided by the Orographic Precipitation and Isotopes (OPI) programs, which provide a full simulation of the flow of moist air over a specified 3D topography and the resulting condensation and fall out of rain and snow, and the isotopic fractionation associated with these processes. The OPI model is fit, in a least-squares sense, to the modern isotope data, which provides a way to test for moisture sources and to calculate how precipitation isotopes would be influenced by variations in climate.There are three important conclusions from these data: 1) OPI modeling of modern water isotopes shows that precipitation at the Malargüe study area is derived solely from the moist northeasterly winds. The isotopic fractionation along this wind path occurs by lifting over the Córdoba and San Luis basement highs, and during the initial rise up the east side of the range. Westerly moist air is able to pass over the range, but downslope flow over the east side means that this source becomes strongly undersaturated, so precipitation from this source is suppressed in this area. 2) Our volcanic glass data indicate that the hydrogen isotopic composition of precipitation, δ2H, has been strongly depleted, by −50 to −90 per mil, since 55 Ma to present. The only way to produce this depletion is by upslope flow of moist winds and associated precipitation over the eastern side of the range. The amount of isotopic fractionation remains fairly constant and similar to modern for the interval from 55 to 15 Ma, which indicates that the topography to the east of Malargüe has been fairly steady during that time interval. 3) Our δ2H record indicates that between 15 and 10 Ma, the topography upwind of Malargüe decreased by about 50%, and then increased by the same amount between 10 and 0 Ma. This subsidence event coincides with the Paranense marine transgression, and is also predicted by numerical modeling of mantle flow and dynamic topography associated with subduction of the Nazca plate.

Hydrogeochemical characteristics and genesis of Hongshuilantang Hot Spring and its water temperature anomalies during the Rushan earthquake swarm in Eastern China

Water temperatures of hot springs close to tectonic fault zones often show some variations before earthquakes, and analyses of earthquake precursors in hot springs have significant referential meaning for earthquake monitoring and forecasting. This study measured the concentration of major ions in water from the Hongshuilantang Hot Spring in 2017 and 2020. The ion composition was classified by hydrochemistry into the HCO3·SO4-Na chemical type. The composition of hydrogen and oxygen isotopes in the Hongshuilantang Hot Spring were located near the global meteoric water line (GMWL), indicating that the recharge source of the hot spring was meteoric water. The δD and δ18O values were not plotted on the Glogal Meteroric Water Line (GMWL), and there were some deviations, which suggested that hot spring water underwent water–rock interactions. Deep circulation water played an important role during the evolution process of thermal water. Water temperature showed a decreasing trend from October 2013 to June 2015 during the Rushan earthquake swarm in eastern China. Because of the occurrence of the earthquake swarm, we inferred that regional stress in this area began to be released, allowing continuous rebalancing. Free surface water appeared in some aquifers, and the seepage of low-temperature underground water into the upper aquifer led to a drop in water temperature in the hot spring. The Hongshuilantang Hot Spring and the epicenter of the Rushan earthquake swarm were located on the Muping–Jimo seismological fault zone, with the same seismotectonic system and some genesis relationships.

Мінералого-петрографічна та геохімічна характеристика відкладів середнього девону Львівського прогину в аспекті перспектив їхньої нафтогазоносності

The Middle Devonian deposits within the Lviv Depression of the Volyn-Podillya plate are largely underexplored and are of great interest for further exploration for hydrocarbons. The presence of two discovered gas fields and the occurrence of granular and fractured reservoir rocks within the entire Lviv Depression point that the deposits of this age range are prospective for further exploration works for hydrocarbons. The authors conducted mineralogical and petrographic studies of these strata in order to study different types of reservoir rocks. Petrographic studies of terrigenous rocks showed that the reservoir rocks are composed of fine-grained and medium-grained sandstones, as well as fine-grained and coarse-grained siltstones. The matrix in these rocks is contact-porous and contact, composed of dolomitized calcite (4–19 %) and hydromica (3–13 %). Regardless of the type of matrix, the pore space in rocks is formed by intergranular spaces of 0.05 to 0.5 mm size. Siltstone-sandstone deposits represent the granular-type reservoir rocks, the filtration properties of which are formed by the intergranular space, while fractures are of subordinate importance. Terrigenous rocks form gas-bearing horizons in Middle Devonian (Eiffelian and Zhivetian) in the Lokachi field of the Lviv Depression. Carbonate rocks are represented by a wide range of lithological types from slightly dolomitized biodetrital limestones to secondary dolomites. Dolomitization and recrystallization form fracture-like microcaverns with a size of up to 0.5 mm and result in a high porosity of up to 9 %. In carbonate reservoir rocks fracturing is prevailing, while porosity has a subordinate value. Studies of the molecular composition of natural gases from reservoir rocks of the Middle Devonian of the Lokachi field showed that their predominant component is methane. Its content is 92.7–95.4 vol %. The rest of the methane homologues account for 1.45–2.16 vol %. The total share of non-hydrocarbon gases – nitrogen, carbon dioxide, helium and hydrogen are 3.102–5.082 vol %. In order to clarify the origin of the Middle Devonian gases of the Lviv Depression, further studies of the carbon, nitrogen, and hydrogen isotopic composition of these gases and the study of the generation properties of the Lower and Middle Devonian rocks of the studied region are necessary.

Groundwater recharge in Central India and its spatio-temporal variation: Insights and implications from oxygen and hydrogen isotopes

This study interprets the observed spatio-temporal variation in the oxygen and hydrogen isotopic composition (δ18O, δD) of shallow unconfined groundwater of Central India (Madhya Pradesh) in terms of changing moisture sources for the Indian Summer Monsoon rainfall, orography and hydrogeological settings.Shallow groundwater samples collected from 282 locations for both pre-monsoon (April) and post-monsoon (November) seasons were analysed for δ18O and δD. The isotopic composition of groundwater varies spatially and seasonally from pre-monsoon to post-monsoon. A clear seasonal variation in isotopic composition with different spatial characters is ascribed to different recharge sources, mixing and evaporation. Backward wind trajectory analysis confirms that the observed isotopic variation from east to west is due to different moisture sources contributing to rainfall in these regions.The isotopic composition of groundwater in most (58% of the geographical area) of the study area have lower values in the post-monsoon season compared to the pre-monsoon season suggesting seasonal recharge of groundwater by isotopically depleted Indian Summer Monsoon (ISM) rain, while 15% of the study area shows the opposite trend caused by different recharge source (irrigation return flow, allochthonous water, and evaporated surface water). Isotopic mass balance in two adjoining aquifers (Sedimentary hard rock and Volcanic rock) reveals that post-monsoon groundwater is an admixture of 39% ISM and 61% of pre-monsoon residual water in sedimentary hard rock, while in the volcanic system, it is 32% ISM and 68% pre-monsoon residual which suggest a higher rate of groundwater recharge in sedimentary hard aquifers compared to the volcanic system. This study provides new insights into the recharge characteristics in a data-poor region of central India covered by different hydrogeological units.

2H-2H clumping in molecular hydrogen method and preliminary results

We present a method for measuring the clumped isotope composition of molecular hydrogen (H2) using a high-resolution mass spectrometer, the Thermo 253 Ultra, improved to address subtle artifacts arising from instrument baselines and non-linear responses. We also present methods for purification and concentration of H2 from natural and experimental samples, tailored to this measurement. We document the accuracy of the method through comparison to established methods for the determination of δD values, and through measurements of H2 gases of widely varying D content that were driven to isotopic equilibrium with respect to their distributions of isotopologues by heating in the presence of a catalyst. Experimental reproducibility of δD and ΔDD values over months averages ±0.5 and ± 6.9 ‰, respectively (1σ) — both small fractions of common natural variations. We explore methods of gas purification and handling, and show that preferred methods result in low (0–4 ‰) changes in δD and undetectable changes in ΔDD. Our methods and data processing procedures were further tested by comparing measurements of mixtures of H2 gases that varied widely in δD and ∆DD with a model describing proportions of isotopologues in such mixtures. Application of these methods to H2 that is residual to laboratory consumption by cultured methanogens shows that metabolic ‘back reaction’ (metabolic production of H2 from water-derived protons during net H2 consumption) is responsible for driving the ΔDD value of residual H2 toward equilibrium at environmental temperatures. Finally, we report the first measurements of the clumped isotope composition of molecular hydrogen in natural geological samples collected from high and low temperature submarine hydrothermal vents (Lost city, Rainbow, Ashadze) and an intracontinental natural reservoir in Mali; initial findings suggest that ∆DD of H2 generally records temperatures of fluid venting or long-term storage, even in cases where the δD of H2 has not equilibrated with water at those temperatures. This study establishes the first clumped isotope systematics of molecular hydrogen based on both experimental and natural samples, including key processes in the biogeochemical cycle of H2.

Comparison of Pretreatment Methods for Organic-matter Removal and their Effects on the Hydrogen Isotope (δ2H) Composition of Kaolinite

AbstractThe hydrogen isotopic composition (δ2H) of authigenic clay minerals has been used extensively in paleoclimate studies. The separation of clay minerals from sediments/soils, using various chemicals, is a prerequisite for isotope ratio measurements, where carbonate, Fe-(oxyhydr)oxides, and organic matter are removed successively from the sediments for a greater clay yield. The commonly adopted organic matter-removal method using hydrogen peroxide (H2O2) is thought to either alter directly the pristine δ2H values of the smectite clay minerals or to introduce organic hydrogen-bearing impurities through the ineffective removal of organic matter. The objective of the present study was to test whether H2O2 treatment can alter the δ2H values of kaolinite (Kln) by comparing two organic matter-removal methods, namely, H2O2 and disodium peroxodisulfate (Na2S2O8) combined with a neutral buffer. In doing so, kaolinite-rich, old (~56 Ma) sediment samples and pure kaolinite internal laboratory reference materials were used to understand the effectiveness and suitability of the above-mentioned methods in clay-sample preparation for δ2H measurements. The δ2H values of the H2O2-treated aliquots show smaller δ2H values than those for the Na2S2O8-treated aliquots. Estimated ambient water δ18O values (−4‰) from the Na2S2O8-treated aliquots agreed well with the bio-phosphate (fish vertebrae) based environmental water δ18O estimation (−3.3‰). The present study indicated, therefore, that δ2H values obtained after Na2S2O8 treatment are likely to be more realistic for paleoclimate reconstruction.

Minimum requirements for publishing hydrogen, carbon, nitrogen, oxygen and sulfur stable-isotope delta results (IUPAC Technical Report)

Abstract Stable hydrogen, carbon, nitrogen, oxygen and sulfur (HCNOS) isotope compositions expressed as isotope-delta values are typically reported relative to international standards such as Vienna Standard Mean Ocean Water (VSMOW), Vienna Peedee belemnite (VPDB) or Vienna Cañon Diablo Troilite (VCDT). These international standards are chosen by convention and the calibration methods used to realise them in practice undergo occasional changes. To ensure longevity and reusability of published data, a comprehensive description of (1) analytical procedure, (2) traceability, (3) data processing, and (4) uncertainty evaluation is required. Following earlier International Union of Pure and Applied Chemistry documents on terminology and notations, this paper proposes minimum requirements for publishing HCNOS stable-isotope delta results. Each of the requirements are presented with illustrative examples.

Quantitative reconstruction of the relative humidity by a coupled δ18O-δ2H approach during the Younger Dryas in central China

Paleoclimate records in central China reveal asynchronous hydroclimate changes to those from both northern and southern China during the Holocene. Whether such a spatial mode works for the Younger Dryas event (YD), a prominent abrupt climate change during the transition from the last glacial to the Holocene, is poorly constrained by quantitative records. In this study, we apply the novel coupled hydrogen isotope composition of leaf wax n-alkanes and oxygen isotope of hemicellulose (δ2Hn-alkane-δ18Osugar) paleohygrometer approach to reconstruct the paleo relative humidity (RH) on a peat layer spanning 13.1–10.0 cal ka BP in the Dajiuhu peatland, central China. The coupled δ2Hn-alkane-δ18Osugar approach reveals that the RH was relatively low in the period of 12.7–12.1 cal ka BP (RH avg. 79%, 1σ 4.9%) and then turned to relatively high values during 12.1–11.7 cal ka BP (RH avg. 88.6%, 1σ 3.9%). A dry interval happened from the end of the YD to 11.3 cal ka BP (RH< 80%). A general wetting trend during the YD period in central China contrasts with the prevailing drying in northern China and maybe also in southern China. The occurrence of a wetting trend during the YD period in central China probably results from the interplay between the westerlies and the East Asian summer monsoon under a context with weak summer monsoon intensity.

The Winchcombe meteorite, a unique and pristine witness from the outer solar system.

Direct links between carbonaceous chondrites and their parent bodies in the solar system are rare. The Winchcombe meteorite is the most accurately recorded carbonaceous chondrite fall. Its pre-atmospheric orbit and cosmic-ray exposure age confirm that it arrived on Earth shortly after ejection from a primitive asteroid. Recovered only hours after falling, the composition of the Winchcombe meteorite is largely unmodified by the terrestrial environment. It contains abundant hydrated silicates formed during fluid-rock reactions, and carbon- and nitrogen-bearing organic matter including soluble protein amino acids. The near-pristine hydrogen isotopic composition of the Winchcombe meteorite is comparable to the terrestrial hydrosphere, providing further evidence that volatile-rich carbonaceous asteroids played an important role in the origin of Earth's water.

NanoSIMS as an analytical tool for measuring oxygen and hydrogen isotopes in clay minerals from palaeosols: Analytical procedure and preliminary results

Oxygen and hydrogen isotope composition of neoformed clay minerals is commonly used as a palaeoclimatic proxy. Usually, sediments and rocks (including palaeosols) contain not only neoformed clay minerals, but also detrital and/or diagenetic ones. Together with the usually small size (micro- or nanometric) of the clay minerals in these materials, this can generate difficulties during isotopic analyses by conventional spectrometry. To avoid this problem, we used nanoscale secondary ion mass spectrometry (NanoSIMS) to analyse neoformed clay minerals included in palaeosol levels in early Barremian continental profiles located in NE Spain. The bottom levels of the profiles are rich in kaolinite, whereas the top levels contain smectite (beidellite-type). The isotopic compositions of pure powder standards of kaolinite and beidellite were measured in bulk by conventional mass spectrometry to obtain reference values for calibrating the instrumental mass fractionation. Two common preparation techniques for geological samples were tested (thin sections and thick polished sections), revealing that thin sections are more suitable for NanoSIMS analysis due to their lower resin content. The high spatial resolution of the instrument allowed the elemental mapping of the samples, permitting the localization of the minerals of interest and the measurement of isotopic ratios at selected points (1 x 1 μm2) within the samples. The preliminary isotopic results allowed to distinguish a decrease in the average 18O/16O and D/H ratios from the kaolinite in the bottom levels to the smectite in the top levels, reflecting a change in the climatic conditions. The average δ18O and δD values obtained for kaolinite (δ18OSMOW=18±15‰; δDSMOW=-82±36‰ and δ18OSMOW=14±4‰; δDSMOW=-97±37‰) and smectite (δ18OSMOW=13±14‰; δDSMOW=-167±87‰ and δ18OSMOW=11±6‰; δDSMOW=-180±40‰;), respectively, are consistent with the crystallization of the clays in weathering conditions. Despite the uncertainties of these preliminary isotopic measures, the results obtained allowed to estimate an average temperature for kaolinite formation of 21-22°C, and of 16-17°C for smectite. Given suitable calibration using pure isotopic standards and adequate sample preparation, NanoSIMS can thus have a great applicability in palaeoclimatic studies involving the oxygen and hydrogen isotopic composition of nanometre-sized clay minerals from palaeosols samples.

Application of concentration and 2-dimensional stable isotope measurements of methane to constrain sources and sinks in a seasonally stratified freshwater lake

Methane (CH4) emissions from aquatic systems have recently been comprised to account for up to 50% of global CH4 emissions, with lakes representing one of the largest CH4 sources within this pool. However, there is large uncertainty associated with CH4 emissions from freshwater environments to the atmosphere, because of a lack of understanding in the spatial and temporal dynamics of CH4 sources and sinks, as well as underlying mechanisms and processes. In this study, we investigated the concentrations and stable carbon (δ13C-CH4) and hydrogen (δ2H-CH4) isotope composition of CH4 in a small eutrophic lake (Lake Willersinnweiher) with seasonal stratification and its spatial and temporal variation. We found that while supersaturation of CH4 in the entire water column was present throughout the whole year, the isotopic composition of CH4 in sediment and water column varied depending on lake stratification, physiochemical conditions, and lake depth. During the stratification period, isotopic characteristics of pelagic surface water CH4 differed from littoral and sedimentary CH4, suggesting likely mixing of CH4 from different sources including vertical and lateral input as well as groundwater input and potentially oxic methane production in the mixed surface water layer. Aerobic CH4 oxidation indicated by a strong increase in both δ13C-CH4 and δ2H-CH4 values at the bottom of the oxycline was found to significantly reduce upward migrating CH4 released at the sediment-water interface. In the sediment, stable isotope characteristics of CH4 showed an increasing dominance of the acetoclastic CH4 formation pathway from the pelagic towards the littoral area. Furthermore, the occurrence of sulfate-dependent anaerobic methane oxidation in the sediment was suggested by an increase in δ13C-CH4 and δ2H-CH4 values. During the mixing period, the isotopic CH4 composition of the water column was distinctively less negative than during the stratification period potentially resulting from a greater impact of groundwater CH4 input compared to the stratification period. Our findings implicate that the application of concentrations and dual isotope measurements of CH4 is a promising approach for constraining CH4 sinks and sources in Lake Willersinnweiher and potentially other small lakes to clearly disentangle the complex CH4 dynamics in lakes both spatially and seasonally.

The Baogutu gold deposit in west Junggar, NW China: An epizonal intrusion-related gold deposit

The Baogutu gold deposit (∼4 Mt ore @ 5.5 g/t Au) in West Junggar, is hosted by Early Carboniferous volcano-sedimentary rocks and Late Carboniferous dioritic dikes. Both the dikes and gold mineralization are controlled by NE-trending faults. Two diorite dikes in direct spatial association with gold-bearing quartz veins have LA–ICP–MS zircon U–Pb ages of 316 ± 5 Ma and 314 ± 3 Ma, respectively. The emplacement ages of the dikes are a little older than reported gold mineralization ages (312–311 Ma), which is consistent with their crosscutting relationships. Gold mineralization occurs in quartz veins and stockworks in altered tuff, tuffaceous siltstone, silty mudstone, and dikes. Three gold-bearing vein stages have been identified: (I) pyrite–quartz veins in the deep part of the system; (II) stibnite–quartz veins and (III) native arsenic–quartz veins at shallower-level. Fluid inclusion study shows that the pyrite–quartz veins of stage I formed at temperatures between 345 and 265 °C from fluids with salinities of 5.1–9.1 wt% NaCl equiv, whereas the native arsenic–quartz veins of stage III formed at ∼200 °C from fluids with salinities of 1.4–3.9 wt% NaCl equiv. The ore-forming pressure is estimated to be ∼50–62 MPa, corresponding to mineralization depth of ∼3.3–4.0 km. Oxygen and hydrogen isotope compositions of the fluids (δ18OH2O = 7.9 to 11.2 ‰, δD = -88 to −96 ‰) indicate that the initial hydrothermal fluids have a magmatic source, with involvement of meteoric water in the late stage. The in-situ lead isotopic compositions of pyrite in stage I pyrite–quartz veins are similar to those of bulk sulfide minerals in the Baogutu porphyry Cu deposit, and close to the porphyry stocks, whereas the stibnite and native arsenic in stage II and III quartz veins have more radiogenic lead isotopic signatures due to water–rock exchange with the wall rocks. The Baogutu gold deposit shows affinities to epizonal gold deposits in intrusion-related gold systems (IRGS). The IRGS model suggests that, sheeted, disseminated and vein-type Au–As–Bi mineralization might be found hosted in dioritic to granitic stocks and proximal strata, and vein-type Au–As–Sb mineralization in distal faults.

Distribution of legacy and novel per- and polyfluoroalkyl substances in surface and groundwater affected by irrigation in an arid region

Frequent exchange of surface water and groundwater occurs in arid/semi-arid areas due to high evaporation and intensive irrigation activities, affecting the migration and transformation of per- and polyfluoroalkyl substances (PFASs) and threatening drinking water safety. This study analyzed legacy PFASs and potential precursors in surface water, groundwater, soil, and aquifer solid samples collected from a typical arid area, the Hetao Irrigation District of Northern China, to explore PFASs distribution and transformation between surface and ground. Total PFASs (ΣPFASs) in surface water was 29–232 ng/L, higher than 2–77 ng/L in groundwater. ΣPFASs in soil were 0.29–0.59 ng/g, higher than 0.09–0.27 in the aquifer solids. Regarding horizontal distribution, the concentration of PFASs in groundwater increased in downtowns and the areas recharged with lake water. In terms of vertical distribution, ΣPFASs decreased with the increase of depth, and more PFASs adsorbed on clay particles in the aquifer. The total oxidable precursor analysis showed that 8:2 FT and 4:2 FT were the dominant precursors of PFASs, resulting in an increment of 0.1–4 ng/L PFASs. Hydrogen and oxygen stable isotope compositions suggest similar sources between surface water and groundwater in the study area, while principal component analysis and Bayesian inference also indicate that surface water is an important source of groundwater PFASs. The annual infiltration PFASs to groundwater from Ulansuhai was estimated by the water balance approach to be 9.39 kg. Results highlight the influence of agricultural irrigation activities and lake infiltration on groundwater PFASs in the arid region.

Hydroclimate reconstruction through MIS 3 in the Middle Paleolithic site of Crvena Stijena (Montenegro) based on hydrogen-isotopic composition of sedimentary n-alkanes

This study presents a hydroclimatic reconstruction from Crvena Stijena (Montenegro, Balkan Peninsula), a rock shelter that has yielded evidence for Middle Paleolithic human occupation. The integration of lipid biomarkers, hydrogen (δD) isotopic compositions of n-alkanes, and organic elemental geochemistry in the 7-m deep vertical sedimentary sequence enables reconstruction of the main hydrological and environmental changes during the MIS 3 and their correlation with the presence at the site. We apply agglomerative hierarchical clustering and principal component analysis to the geochemical, molecular, and stable isotopic data to obtain a robust hydrological record. We find evidence of three aridity trends from the studied period, one of them correlated with the Heinrich Event 5, and humid and cold-temperate conditions in archaeology-rich layers. Our dataset also contributes to the knowledge of past hydrological variability in the Balkan Peninsula, a sensitive area to short-lived climatic shifts, and overall, in the Mediterranean region during the last glacial/interglacial cycle.

Hydrogen isotope behavior during rhyolite glass hydration under hydrothermal conditions

The diffusion of molecular water (H2Om) from the environment into volcanic glass can hydrate the glass up to several wt% at low temperature over long timescales. During this process, the water imprints its hydrogen isotope composition (δDH2O) to the glass (δDgl) offset by a glass-H2O fractionation factor (ΔDgl-H2O = δDgl – δDH2O) which is approximately −33‰ at Earth surface temperatures. Glasses hydrate much more rapidly at higher, sub-magmatic temperatures as they interact with H2O during eruption, transport, and emplacement. To aid in the interpretation of δDgl in natural samples, we present hydrogen isotope results from vapor hydration experiments conducted at 175–375 °C for durations of hours to months using natural volcanic glasses. The results can be divided into two thermal regimes: above 250 °C and below 250 °C. Lower temperature experiments yield raw ΔDgl-H2O values in the range of −33 ± 11‰. Experiments at 225 °C using both positive and negative initial ΔDgl-H2O values converge on this range of values, suggesting this range represents the approximate equilibrium fractionation for H isotopes between glass and H2O vapor (103lnαgl-H2O) below 250 °C. Variation in ΔDgl-H2O (−33 ± 11‰) between different experiments and glasses may arise from incomplete hydration, analytical uncertainty, differences in glass chemistry, and/or subordinate kinetic isotope effects. Experiments above 250 °C yield unexpectedly low δDgl values with ΔDgl-H2O values of ≤–85‰. While alteration alone is incapable of explaining the data, these run products have more extensive surface alteration and are not interpreted to reflect equilibrium fractionation between glass and H2O vapor. Fourier transform infrared spectroscopy (FTIR) shows that glass can hydrate with as much as 5.9 wt% H2Om and 1.0 wt% hydroxl (OH−) in the highest P-T experiment at 375 °C and 21.1 MPa. Therefore, we employ a 1D isotope diffusion–reaction model of glass hydration to evaluate the roles of equilibrium fractionation, isotope diffusion, water speciation reactions internal to the glass, and changing boundary conditions (e.g. alteration and dissolution). At lower temperatures, the best fitting model results to experimental data for low silica rhyolite (LSR) glasses require only an equilibrium fractionation factor and yield 103lnαgl-H2O values of −33‰ ± 5‰ and −25‰ ± 5‰ at 175 °C and 225 °C, respectively. At higher temperatures, ΔDgl-H2O is dominated by boundary layer effects during glass hydration and glass surface alteration. The modeled bulk δDgl value is highly responsive to changes in the δDgl boundary condition regardless of the magnitude of other kinetic effects. Observed glass dissolution and surficial secondary mineral formation are likely to impose a disequilibrium boundary layer that drives extreme δDgl fractionation with progressive glass hydration. These results indicate that the observed ΔDgl-H2O of ∼−33 ± 11‰ can be cautiously applied as an equilibrium 103lnαgl-H2O value to natural silicic glasses hydrated below 250 °C to identify hydration sources. This approximate ΔDgl-H2O may be applicable to even higher temperature glasses hydrated on short timescales (of seconds to minutes) in phreatomagmatic or submarine eruptions before H2O in the glass is primarily affected by boundary layer effects associated with alteration on the glass surface.

Formation conditions of Sinian–Cambrian large lithologic gas reservoirs in the north slope area of central Sichuan Basin, SW China

Based on analyses of characteristics, hydrocarbon charging history and geological conditions for the formation of Sinian–Cambrian reservoirs in the north slope area of central Sichuan paleo-uplift, the natural gas origin, accumulation evolution, accumulation pattern and formation conditions of large lithologic gas reservoirs have been investigated. Through comprehensive analyses of natural gas composition, carbon and hydrogen isotopic compositions, fluid inclusions, reservoir bitumen, and geological conditions such as lithofacies paleogeography and beach body characterization, it is concluded that: (1) The natural gas in the Sinian–Cambrian of the north slope area is mainly oil cracking gas, and different contribution ratios of multiple sets of source rocks lead to different geochemical characteristics of natural gas in different reservoirs. (2) Although the both Sinian and Cambrian gas reservoirs in this area are lithologic gas reservoirs under monocline background, the former has normal-pressure and the latter has high-pressure. There are three types of source-reservoir-caprock combinations: single source with lower generation and upper reservoir, double sources with lower generation and upper reservoir or with side source and lateral reservoir, double sources with lower generation and upper reservoir or with upper generation and lower reservoir. The Permian–Triassic is the main generation period of oil, Early–Middle Jurassic is the main generation period of oil cracking gas and wet gas, and Late Jurassic–Cretaceous is the main generation period of dry gas. (3) The Sinian–Cambrian system of the north slope area has two favorable conditions for formation of large lithologic gas reservoirs, one is that the large scale beach facies reservoirs are located in the range of ancient oil reservoirs or near the source rocks, which is conducive to the “in-situ” large-scale accumulation of cracked gas in the paleo-oil reservoirs, the other is that the large scale mound-beach complex reservoirs and sealing layers of inter beach tight zones match effectively to form large lithologic traps under the slope background. The research results confirm that the north slope area has large multi-layer lithologic gas reservoirs with more than one trillion cubic meters of natural gas resources and great exploration potential.

Stable hydrogen and oxygen isotopes reveal aperiodic non-river evaporative solute enrichment in the solute cycling of rivers in arid watersheds

We investigated the spatial and temporal variations of the stable isotope composition of hydrogen (δD) and oxygen (δ18O) and the total dissolved ions (TDI) concentrations in the Okavango River in the middle Kalahari Desert. We aimed to elucidate the role of evaporation in controlling river solute enrichment from samples collected at a one- to two-month frequency from nine stations along a ∼460 km river transect for one year. We found that the δD and δ18O composition and the TDI concentrations increased downriver. Seasonal increases in the δD and δ18O composition and TDI concentrations during the hot, rainy season were subdued or decreased during the cool, dry season from pulse flooding. The δD and δ18O values of the samples plot along the Okavango Delta Evaporation Line consistent with evaporation. The effect of evaporation during river transit was related to the mean δD (δD = 0.07*River distance (km) − 37.9; R2 = 0.98) and mean d-excess (d-excess = −0.04*River distance (km) + 9.9; R2 = 0.94). The effect of evaporation on the river solute behavior is characterized by the mean d-excess and TDI concentrations (d-excess = −0.29*TDI (mg/L) + 15.0; R2 = 0.97). Some samples from this study and those compiled from published studies plot at greater than one sigma standard deviation above and below the mean TDI concentration vs. mean d-excess regression model line. We use these marked deviations from the mean TDI concentration vs. the mean d-excess regression model to suggest that additional solutes from river-floodplain-wetland-island interaction driven by pulse flooding are delivered into the river. While our findings support an evaporation-dominated solute enrichment during river transit at the seasonal scale, we conclude that intermittent hydrology (pulse flooding) plays an important role in the sub-seasonal spatiotemporal behavior of solutes in rivers in arid watersheds, which must be considered in solute cycling models.

Inverse relationships between salinity and hydrogen isotope fractionation of n-alkanes in the Aegiceras corniculatum leaves and surface sediments from Zhanjiang mangrove estuary of China

Hydrogen isotope ratios of mangrove lipids have recently gained increasing interest because of their potential for reconstructing past water salinity and paleohydrology conditions. Although it has been suggested that the deuterium fractionation in mangrove leaf lipids appears to be primarily affected by water salinity, it remains an important research topic if this inverse relationship between salinity and hydrogen fractionation in leaf wax can be universally applied. In this regard, we have investigated the hydrogen isotopic composition of n-alkanes in leaves of Aegiceras corniculatum and surface sediments and the environmental water (surface water; αn-alkane-Water), collected along a 30 ppt salinity gradient in the Zhanjiang mangrove estuary of China, aiming to evaluate the impact of water salinity on the hydrogen isotopic fractionation of leaf wax derived n-alkanes. δ2H values of A. corniculatum leaf wax n-alkanes were between −183‰ and − 127‰ for C27, C29, and C31n-alkanes, and their αn-alkane-Water values range from 0.823 to 0.887. Sedimentary δ2H values range from −171‰ to −132‰ for C27, C29, and C31n-alkanes, and their αn-alkane-Water values were between 0.832 and 0.887. Inverse relationships between αn-alkane-Water and salinity were observed in mangrove A. corniculatum and surface sediment. This relationship for mangrove A. corniculatum may result from the selective utilization of freshwater during the rain event, changes in biosynthetic fractionation, and the relatively high humidity and/or larger changes in water vapour isotopic composition. For surface sediment, the inverse relationship could be mainly attributed to the mangrove-derived organic matter input, as the principal component analysis (PCA) results demonstrated a strong connection between the studied mangrove tree and the surface sediment. The consistent negative correlations between αn-alkane-Water and salinity for mangrove leaf waxes and surface sediments provide encouraging evidence for applying the hydrogen isotopic composition of mangrove leaf wax for paleohydrological reconstruction.