Heavy Isotope Content Research Articles

Composition and Content of Fatty Acids in Muscle Tissue of the Potanin Altai Osman Oreoleuciscus potanini (Cypriniformes, Actinopterigii) from Mongolian Reservoirs.

The composition of fatty acids in the muscle tissue of the unique Central Asian carp-like fish, Potanin Altai osman Oreoleuciscus potanini, was studied for the first time. The populations of these fish in the reservoirs of the semiarid zone (Durgun and Taishir) during the period of their formation are considered. It was shown that the content of eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids in O. potanini corresponds to the median of this value in the order Cypriniformes. It was established that the basis of the food web of the herbivorous form of this species consists of microalgae (diatoms, Euglena and, possibly, chrysophytes), as well as bacteria. At the same time, the levels of bacterial biomarkers, 15-17BCFA and 17:0 were significantly higher in fish in the Durgun reservoir, whereas the level of EPA (diatom biomarker) in O. potanini was higher in the Taishir reservoir. The established higher values of the heavy nitrogen isotope content in the muscles of O. potanini from the Taishir reservoir are most likely associated with the yet unformed benthic communities and with the incomplete diversification of the riverine form of the Potanin Altai osman into lacustrine forms.

Trophic characteristics of pelagic and bottom nekton in certain water masses in the western Chukchi Sea, by δ15N and δ13C data

To compare the trophic characteristics of pelagic- and bottom-dwelling fish in the western Chukchi Sea, isotopic composition of carbon and nitrogen (δ13С and δ15N) is considered separately for the Subarctic water mass (invaded from the Bering Sea) and local Arctic water mass. In summer of 2018 and 2019, the proper water mass occupied mostly the area southward from 71оN and the latter one – northward from this latitude. The isotopic composition of both pelagic and bottom nekton in the southern area was characterized by higher values of δ13C (up to 2 % higher) and low values of δ15N (up to 1 % lower) in comparison with those in the northern area. That was interpreted that in the southern area, within the water from the Bering Sea, more than 90 % of the sampled bottom fish species were linked with prey from the bottom community. In the northern area, within the Arctic water, all samples of bottom fish were characterized by minimal content of heavy carbon δ13C isotope, comparable with the values in samples of pelagic fish that indicated a significant role of pelagic prey in nutrition of the bottom nekton.

Stable isotope geochemistry and petrography of the Qorveh–Takab travertines in northwest Iran

Abstract The Qorveh-Takab travertines, which are connected to thermal springs, are situated in the northwest of the Sanandaj- Sirjan metamorphic zone in Iran. In this study, the travertines were investigated applying petrography, mineralogy and isotope geochemistry. Oxygen and carbon isotope geochemistry, petrography, scanning electron microscopy (SEM) and X-ray powder diffraction (XRD) analysis were used to determine the source of the CO2 and the lithofacies and to classify the travertines. Isotope studies, morphological and mineralogical observations and distribution of travertines revealed that the travertines of the Qorveh-Takab could be of thermal water origin and, therefore, belong to the thermogene travertine category. These travertines are usually massive with mound-type morphology and are essentially found in regions with recent volcanic or high tectonic activity. The measured δ13C values of the travertines indicate that the δ13C of the CO2 released from the water during travertine deposition, while the source of the CO2 in the water springs seems to have been of crustal magmatic affinity. These travertines are divided into two lithofacies: (1) crystalline crust travertine and (2) pebbly (phytoclastic travertine with pebble- size extraclasts) travertine. δ18O and δ13C values of travertines are -0.6 to -11.9 (‰VPDB) and +6.08 to +9.84 (‰VPDB), respectively. A probable reason for the heavy carbon isotope content observed in these deposits is the presence of algae microorganisms, which was verified by SEM images. Fissure ridges, fluvial crusts with oncoids, and mound morphological features are observed in the study area. Based on the petrographic and SEM criteria, Qorveh-Takab travertines are classified into four groups: (1) compacted, (2) laminated, (3) iron-rich spring deposit and (4) aragonite-bearing travertines. Stable isotope compositions of Turkish travertines are largely similar to the travertines in the study area.

Kinetics of Active Pharmaceutical Ingredient Solubility in Water with Different Hydrogen Isotopic Content

Kinetic analysis by means of low-angle laser light scattering has been used for the investigation into active pharmaceutical ingredients solubility depending on the content of heavy isotope of hydrogen 12H (D) in water. Rate constants of active pharmaceutical ingredient solubility differ approximately by ~1.5 times for the two types of water with different deuterium/protium ratios, natural deionized high-ohmic water (D/H=140 ppm) and deuterium-depleted water (D/H= 4 ppm). Results are to be utilized in order to control the quality of pharmaceutical substances with the purpose of dissolution quantitative evaluation, as well as with the aim of tackling the issue of new active pharmaceutical ingredients' low solubility while developing drugs.

Reduced biomass burning emissions reconcile conflicting estimates of the post-2006 atmospheric methane budget

Several viable but conflicting explanations have been proposed to explain the recent ~8 p.p.b. per year increase in atmospheric methane after 2006, equivalent to net emissions increase of ~25 Tg CH4 per year. A concurrent increase in atmospheric ethane implicates a fossil source; a concurrent decrease in the heavy isotope content of methane points toward a biogenic source, while other studies propose a decrease in the chemical sink (OH). Here we show that biomass burning emissions of methane decreased by 3.7 (±1.4) Tg CH4 per year from the 2001–2007 to the 2008–2014 time periods using satellite measurements of CO and CH4, nearly twice the decrease expected from prior estimates. After updating both the total and isotopic budgets for atmospheric methane with these revised biomass burning emissions (and assuming no change to the chemical sink), we find that fossil fuels contribute between 12–19 Tg CH4 per year to the recent atmospheric methane increase, thus reconciling the isotopic- and ethane-based results.

Yeast longevity promoted by reversing aging-associated decline in heavy isotope content.

Dysregulation of metabolism develops with organismal aging. Both genetic and environmental manipulations promote longevity by effectively diverting various metabolic processes against aging. How these processes converge on the metabolome is not clear. Here we report that the heavy isotopic forms of common elements, a universal feature of metabolites, decline in yeast cells undergoing chronological aging. Supplementation of deuterium, a heavy hydrogen isotope, through heavy water (D2O) uptake extends yeast chronological lifespan (CLS) by up to 85% with minimal effects on growth. The CLS extension by D2O bypasses several known genetic regulators, but is abrogated by calorie restriction and mitochondrial deficiency. Heavy water substantially suppresses endogenous generation of reactive oxygen species (ROS) and slows the pace of metabolic consumption and disposal. Protection from aging by heavy isotopes might result from kinetic modulation of biochemical reactions. Altogether, our findings reveal a novel perspective of aging and new means for promoting longevity.

Аррениусовская кинетика как критерий оценки биоактивности фармацевтически активных субстанций и вспомогательных веществ

Описывается применение закономерностей аррениусовской кинетики, в частности значений Ea для оценки биологической активности водных растворов фармацевтических веществ с разным соотношением D/H. Полученные значения энергии активации указывают на снижение токсичности/биологической активности растворов со снижением содержания тяжелого изотопа водорода дейтерия.

Isotopic composition on ground ice in Western Yamal (Marre-Sale)

The profile of Quaternary sediments near Marre-Salle polar station, Western Yamal Peninsula, has large bodies of tabular ground ice. This profile is considered strata-typical and critical in understanding of paleogeographic conditions of the Arctic in Pleistocene-Holocene. However, interpretation of the profile is under discussion. It consists of two distinct strata: upper layer of 10–15 m thick represented by continental sediments and lower one with a thickness of more than 100 m represented by marine sediments. Lower layer of saline marine clays has lenses of tabular ground ice (more than 20 m thick), the bases of which are below the sea level. Upper continental layer is characterized by syngenetic ice-wedges of different generations. Samples were collected from ice-wedges and tabular ground ice for chemical and isotope analysis. The results of the analysis allow to reconstruct paleogeographic conditions of the sedimentation and freezing of Quaternary sediments. Heavy stable isotope content and relationship between oxygen and hydrogen isotopes show that the ice bodies in the lower layer were formed in-situ within the ground. In the upper layer, heavier isotope content found in younger ice-wedges relative to the old-generation wedges. Formation of massive syngenetic Upper-Pleistocene ice-wedges occurred in conditions of colder winter temperatures than at present. Syngenetic Holocene wedges were formed after Holocene Optimum under winter conditions similar to present. Younger ice wedges formed smaller polygons, were smaller and often were developing in the locations of the degraded old wedges. Results of the isotope analysis of various types of ground ice near Marre-Sale allow reconstructing changes of marine sedimentation to continental one around Kargino time (MIS 3) and changes in climatic conditions in Arctic in Late Pleistocene and Holocene.

A complex geochemical survey for forecasting the oil and gas potential of Gydanskii and Yuratskii Bays of the Kara Sea

The potential possibility for searching for and fore� casting of the hydrocarbon (HC) deposits using the results of the geochemical surveys of the nearbottom water layer and bottom deposits is determined by the subvertical migration of the hydrocarbon fluids and the resulting secondary geochemical anomalies. Anomalies are formed by the higher above background concentrations of HCGs including methane with an enhanced heavy carbon isotope content, methane homologs (in some cases with a high content of the butyric acid fraction in bitumens), fields with increased numbers of hydrocarbon oxidizing microor� ganisms, a high content of ferrous and copper sulfides, etc. (1, 2). The peripheril part of the anomaly is char� acterized by increased concentrations of carbon diox� ide and hydrogen. Different combinations of helium and methane are characteristic features of the mani� festation of the fluidconducting zones of the faults with displacements (3).

Snow isotopic content change by sublimation

AbstractWe present results from cold-laboratory observations of changes in isotopic (δ18O and δD) content by sublimation in snow and ice samples under nearly isothermal conditions. The results show large increases in observed δ18O and δD in snow samples within several centimeters of the surface. They contradict the assumption of a non-changing isotopic content due to layer-by-layer transport mechanisms driven by sublimation/desublimation processes. The data also do not support the idea that isotopic changes of snow and firn are limited by the possibility that the ice matrix incorporates the atmospheric water vapor and that forced water-vapor diffusion in the pore space (wind pumping) is a requirement for isotopic content change. The observations show that sublimation from ice samples results in much lower increases in heavy-isotope content in the first several millimetres near the sublimating surface over the same time period, despite sublimation intensities similar to those of the snow samples. The results suggest that continuous phase transitions inside snow (recrystallization) are the process responsible for the isotopic content change because they are the primary mass-exchange mechanism between the snow mass and the surrounding environment. Modeling the isotopic content of the ice matrix therefore requires inclusion of a two-stage process: fractionation at the ice-matrix surface due to repetitive phase transitions, and fractionation due to preferable diffusion of light water isotopes in the pore space. For interpretation of the observed natural isotopic profiles in snow, the first process can be linked to the time a snow layer undergoes recrystallization, while the second process is related to the total ice/snow mass gain/loss determined by the external environmental conditions.

Isotope effects accompanying evaporation of water from leaky containers

Laboratory experiments aimed at quantifying isotope effects associated with partial evaporation of water from leaky containers have been performed under three different settings: (i) evaporation into dry atmosphere, performed in a dynamic mode, (ii) evaporation into dry atmosphere, performed in a static mode, and (iii) evaporation into free laboratory atmosphere. The results demonstrate that evaporative enrichment of water stored in leaky containers can be properly described in the framework of the Craig–Gordon evaporation model. The key parameter controlling the degree of isotope enrichment is the remaining fraction of water in the leaking containers. Other factors such as temperature, relative humidity, or extent of kinetic fractionation play only minor roles. Satisfactory agreement between observed and predicted isotope enrichments for both 18O and 2H in experiments for the case of evaporation into dry atmosphere could be obtained only when molecular diffusivity ratios of isotope water molecules as suggested recently by Cappa et al. [J. Geophys. Res., 108, 4525–4535, (2003).] were adopted. However, the observed and modelled isotope enrichments for 2H and 18O could be reconciled also for the ratios of molecular diffusivities obtained by Merlivat [J. Chem. Phys., 69, 2864–2871 (1978).], if non-negligible transport resistance in the viscous liquid sub-layer adjacent to the evaporating surface is considered. The evaporation experiments revealed that the loss of mass of water stored in leaky containers in the order of 1%, will lead to an increase of the heavy isotope content in this water by ca. 0.35 and 1.1 ‰, for δ 18O and δ 2H, respectively.

Constraints on N<sub>2</sub>O budget changes since pre-industrial time from new firn air and ice core isotope measurements

Abstract. A historical record of changes in the N2O isotope composition is important for a better understanding of the global N2O atmospheric budget. Here we have combined measurements of trapped gases in the firn and in ice cores of one Arctic site (North GReenland Ice core Project - NGRIP) and one Antarctic site (Berkner Island). We have performed measurements of the 18O and position dependent 15N isotopic composition of N2O. By comparing these data to simulations carried out with a firn air diffusion model, we have reconstructed the temporal evolution of the N2O isotope signatures since pre-industrial times. The decrease observed for all signatures is consistent from one pole to the other. Results obtained from the air occluded in the ice suggest a decrease of about -2.8, -2.4, -3.2 and -1.6 for δ15N, 1δ15N, 2δ15N and δ18O, respectively, since 1700 AD. Firn air data imply a decrease of about -1.1, -1.2, -1.0 and -0.6 for δ15N, 1δ15N, 2δ15N and δ18O, respectively, since 1970 AD. These results imply consistent trends from firn and ice measurements for δ15N and δ18O. The trends for the intramolecular distribution of 15N are less well constrained than the bulk 15N trends because of the larger experimental error for the position dependent 15N measurements. The decrease in the heavy isotope content of atmospheric N2O can be explained by the increasing importance of agriculture for the present atmospheric N2O budget.

High‐precision determination of the changing isotopic composition of atmospheric N2O from 1990 to 2002

High‐precision nitrous oxide (N2O) concentration and isotope ratio measurements have been carried out on archived air samples from the Antarctic station Neumayer covering the period 1990–2002. The results show that the increase in the N2O mixing ratio over this period is accompanied by a significant decrease in the heavy isotope content. The temporal isotope trends amount to (−0.040 ± 0.003)‰/yr for δ15N (the average of both nitrogen positions) and (−0.021 ± 0.003)‰/yr for δ18O. The individual trends for the terminal (position 1) and central (position 2) nitrogen atoms within the N2O molecule are (−0.064 ± 0.016)‰/yr for 1δ15N and (−0.014 ± 0.016)‰/yr for 2δ15N. The average 15N and 18O trends compare well with recent results from measurements on air extracted from polar firn and ice, confirming earlier estimates that isotopically depleted N2O, mainly from soil emissions, is responsible for a large fraction of the observed N2O increase in the atmosphere. The position‐dependent 15N determinations show a strong difference between the two positions. This is in disagreement with the firn and ice core data, which imply similar fractionations at both positions.

Global application of stable hydrogen and oxygen isotopes to wildlife forensics

Stable isotopes are being increasingly used in wildlife forensics as means of determining the origin and movement of animals. The heavy isotope content of precipitated water and snow (deltaD(p), delta(18)O(p)) varies widely and systematically across the globe, providing a label that is incorporated through diet into animal tissue. As a result, these isotopes are potentially ideal tracers of geographic origin. The hydrogen and oxygen isotope tracer method has excellent potential where (1) spatial variation of precipitation isotopes exist, and (2) strong, mechanistic relationships link precipitation and isotope ratios in biological tissue. Here, we present a method for interpolation of precipitation isotope values and use it to create global basemaps of growing-season (GS) and mean annual (MA) deltaD(p) and delta(18)O(p). The use of these maps for forensic application is demonstrated using previously published isotope data for bird feathers (deltaD(f)) in North America and Europe. The precipitation maps show that the greatest potential for applying hydrogen and oxygen isotope forensics exists in mid- to high-latitude continental regions, where strong spatial isotope gradients exist. We demonstrate that deltaD(f)/deltaD(p) relationships have significant predictive power both in North America and Europe, and show how zones of confidence for the assignment of origin can be described using these predictive relationships. Our analysis focuses on wildlife forensics, but the maps and approaches presented here will be equally applicable to criminal forensic studies involving biological materials. These maps are available in GIS format at http://www.waterisotopes.org.

The isotopic fingerprint of the pre-industrial and the anthropogenic N<sub>2</sub>O source

Abstract. We have performed high-precision measurements of the 18O and position dependent 15N isotopic composition of N2O from Antarctic firn air samples. By comparing these data to simulations carried out with a firn air diffusion model, we have reconstructed the temporal evolution of the N2O isotope signatures since pre-industrial times. The heavy isotope content of atmospheric N2O is presently decreasing for all signatures at rates of about -0.038 %o yr -1 for 1d15N, -0.046 %o yr -1 for 2d 15N and -0.025 %o yr -1 for d18O. The total decrease since pre-industrial times is estimated to be about -1.8%o for 1d15N at both positions and -2.2%o for 2d15N. Isotope budget calculations using these trends and recent stratospheric measurements allow to isotopically characterize the present and the pre-industrial global average N2O source, as well as the additional N2O emissions that have caused the global N2O increase since pre-industrial times. The increased fluxes from the depleted surface sources alone are insufficient to explain the inferred temporal isotope changes. In addition, the global average N2O source signature is calculated to be significantly depleted today relative to the pre-industrial value, in agreement with recent indications from soil emission measurements.

Short-term evaporation and water budget comparisons in shallow Arctic lakes using non-steady isotope mass balance

Shallow lakes in a continental, low Arctic setting are found to undergo substantial fluctuations in heavy-isotope content during the annual cycle due to extreme seasonality in water balance processes. Progressive isotope enrichment during the ice-free period occurs as a consequence of isotope exchange during evaporation under seasonally arid conditions, while enhanced input and flushing by heavy-isotope depleted precipitation and snowmelt during late fall and spring tend to deplete the lakes in heavy isotopes once again. Time-series sampling surveys in a group of nearby lakes, ranging in volume from 41,000 to 2,250,000 m 3, was carried out for two consecutive ice-free periods, in conjunction with a comprehensive hydrological measurement program in a detailed study lake, to assess models that describe isotopic enrichment in lakes and to test their suitability for comparing evaporation rates and water balance. From a non-steady isotope balance analysis, it is found that isotope enrichment rates in lakes during the ice-free period are determined primarily by evaporation rates and volume of the lakes, and are less sensitive to water balance variations for short time intervals when evaporation is less than 50 mm or so. A basic assessment of best-fit and step-wise models is presented which suggests that the former are useful only for predicting evaporation and water balance during month-long periods with relatively stable atmospheric and hydrologic conditions. A step-wise isotope balance approach is presented which demonstrates how isotope-based estimates of evaporation rates can be applied to effectively compare short-term (weekly) water balance in nearby lakes. Practical applications in the region include water balance assessments to assist in design and maintenance of tailings ponds for gold and diamond mining operations.

Isotopic assignment in large-molecule mass spectra by fragmentation of a selected isotopic peak.

For large ( > 5 kDa) ionic species, Fourier transform ion cyclotron resonance instruments yield by far the highest mass accuracy. However, this can be compromised by misassignment of the isotopic content based on predicted natural abundances of the isotopic peaks. As an alternative method independent of natural abundance variations, high-resolution isolation and dissociation of a single isotopic peak yields a distribution of isotopic peak abundances characteristic of the isotopic content of the precursor peak. Accuracy is enhanced if the precursor peak is abundant and of minimum heavy isotope content, and if the product species is abundant and of intermediate mass. In addition, such spectra of the highest mass products are useful for identifying complementary product pairs, a key step in sequencing proteins and nucleotides.

Isotope palaeohydrology and the prediction of long‐term repository behaviour

ABSTRACTThere are considerable, well‐recognized difficulties involved in the investigation of very low permeability rocks by conventional measurements of water potentials and spatial distribution of hydrological parameters such as permeability and effective porosity. Therefore, most studies of predictive behaviour are based on models which, when unconstrained by data, are often worse than no model at all. Geochemistry and environmental isotope geochemistry are techniques well suited for hydrological investigations of potential sites of nuclear waste isolation and for constraining predictive models.Stable isotopes constitutive of the water molecule (2H and 18O) may give information on the origin of the water, especially 2H which is practically uninvolved in isotope exchange with rock‐forming minerals. Variations in stable isotope contents can be related to palaeohydrological and palaeoclimatic conditions whereas 3H is indicative of recent recharge.The 13C content of dissolved carbon is related to its origin(s) and the 14C activity gives a time‐scale. However, the initial carbon isotope contents can be modified by various diagenetic effects such as precipitation/dissolution of secondary calcite and oxidation of reduced carbon. The heavy isotope content of the Total Dissolved Inorganic Carbon (TDIC) cannot be interpreted without a detailed knowledge of the carbon chemistry and of the mineralogy and isotope contents of secondary carbonates. Species of Dissolved Organic Carbon (DOC), with high molecular weights (HMW) can generally be attributed to soil derived compounds. Their 14C content may be measured by AMS (Accelerator Mass Spectrometry) thus providing an estimate of the time elapsed since recharge took place.Chlorine‐36 is an interesting potential tool for dating old ground waters because of its long half‐life (301 kyr) and its hydrophilic behaviour. It can be also produced in situ in significant amount if the rocks are rich (some tens of ppm) in U and Th. In such cases, this time dependent build‐up provides a more systematic radiochronometer of CI‐ residence time in the rock than the decay of cosmic input 36CI, provided no Cl‐ is leached from the rock.The isotopic composition of aqueous sulphur compounds depends on their origin and on their diagenetic evolution. The redox reactions of SO2‐4 reduction or of S2‐ oxidation are marked by strong isotope effects especially when generated by bacteria. Sulphate reduction by organic matter is a potential source of dissolved inorganic carbon and may thus interfere with 14C age interpretations.After discussion of the possible age and origin of waters and solutes, some scenarios of evolution of local and regional palaeohydrological conditions are proposed.Examples are given with special emphasis on detailed results from the Fennoscanian shield (Stripa project), and from northern Switzerland.

Geochemistry and origin of formation brines from the Paris Basin, France: 1. Brines associated with Triassic salts

Small amounts of brines associated with Triassic (Keuper) layered halite from the eastern Paris Basin have been collected during salt mining operations. Critical consideration of the possible reactions and interactions involving Br − indicates that Cl − Br − ratio values are conservative except in two cases: (1) precipitation or dissolution of solid chlorides; and (2) convective or diffusive mixing of saline solutions. Calculations suggest that halite recrystallization could be a source of aqueous Br −, but this process is probably not significant under natural conditions as Triassic salt has retained a Br − content higher than calculated for equilibrium conditions. Bromide-chloride data for the brines associated with Triassic salts are presented on a log-log diagram of Cl − Br − vs. Cl −, including the evolution of present-day marine solutions and literature values for the chloride salts between halite and tachyhydrite ((CaCl 2, 2MgCl 2)·12H 2O) deposition. This diagram allows discernment of primary or secondary origins of brines. Chemical variations of major and trace elements during the evaporative concentration of seawater are estimated from selected literature and from additional measurements of salt ponds on the Mediterranean shore. Low values of the Cl − Br − ratios in brines from Triassic salt can be reconciled with high Na + contents if the sampled solutions are mixtures of a secondary brine (halite dissolution) and a highly evolved primary brine. Mass-balance considerations indicate that the primary brine component was more concentrated than the stage of bischofite (MgCl 2·6H 2O) deposition. Contents of Br −, Cl −, Na + and K + can be accounted for by a conservative behaviour of these ions, possibly slightly affected by some precipitation of NaCl induced by the mixing of the two types of solutions. The secondary brine component would have contributed all Na + and K + through halite and sylvite (KCl) dissolution. Several hypotheses are discussed for the origin of the high contents in Li +: diagenesis, halite dissolution, global or local enrichment of Triassic seawater, and contribution from the primary brine. The high Li + concentration is attributed to the highly concentrated brine component. Rubidium would also behave conservatively after all K + has been removed by sylvite and carnallite ((KCl,MgCl 2)·6H 2O) precipitation. Boron, Ca 2+, Sr 2+, Mg 2+ and SO 2− 4 are not conservative. Mass-balance calculations indicate that the high content in Ca 2+ and in Sr 2+ imposes a diagenetic origin. The values of the 87 Sr 86 Sr isotope ratio are clearly higher than the Keuper marine values of the literature, which could be explained by a major contribution of reworked Permian evaporites with high 87Sr content. Such hypothesis would be in agreement with the low heavy-isotope content of aqueous SO 2− 4. Dolomitization, either by the primary brine or by the mixing of primary and secondary brines, would have implied Ca-sulphate precipitation, in agreement with the observed additional depletion in heavy isotopes of aqueous SO 2− 4, relative to anhydrite deposits from Triassic layers of the Paris Basin. Stable isotope contents ( 2H and 18O) of the brines can be accounted for by mixings of a secondary brine of continental origin with a primary brine enriched in 18O by evaporation. In conclusion, emphasis is put on the conservation of Li +, the near-conservative behaviour of the elements Cl −, Br −, Na +, K + and Rb +, whereas diagenetic reactions control B 3+, Mg 2+, Ca 2+, Sr 2+ and SO 2− 4.

Geochemistry and origin of formation brines from the Paris Basin, France: 2. Saline solutions associated with oil fields

Oil fields from the Paris Basin are located in three geological levels: Dogger (Middle Jurassic), Rhaetian and Keuper (Upper Triassic). The origin of water and dissolved salts in saline solutions associated with oil is investigated, using the hypothesis that Cl − and Br − are conservative in solution. In a diagram of Cl − Br − ratios vs. Cl −, the points of the Dogger and the Keuper aquifers lie in the zone of primary brines whereas those of the Rhaetian are located in the zone of secondary brines. The Na + Cl − ratio is very high in all of the saline solutions, suggesting either a relatively poorly evolved brine (at the beginning of halite deposition) or some halite dissolution. All of the saline solutions, especially those from the Dogger aquifer, are clearly diluted. Dilution by meteoric waters would not alter the Cl − Br − ratio. High concentrations of lithium, rubidium and boron are attributed to the presence of an extremely evolved brine of marine origin in mixtures of secondary brines formed by dissolution of halite and small amounts of sylvite and Ca-sulphate. Mass-balance calculations of the excess of Cl − with respect to Na + + K + allows the fraction x of water derived from the primary brine to be calculated. Assumptions are that all Na + and K + is derived from the secondary brine and that the Cl − content of the primary brine is constrained by bischofite saturation at ∼ 11,000 mmol kg −1. The typical proportion of water from the primary brine waters is ∼ 0.7% in the Dogger formation and ∼ 2.4% in the Keuper. Values of the concentration factor CF, expressed as the ratio of the molal concentration of a conservative ion in the evolved brine to its concentration in seawater have been calculated for lithium. Solutions from the Dogger and Keuper aquifers have CF Li + -values of 1.8 · 10 3 and of 7.7 · 10 3, respectively. In the Rhaetian aquifer, the linear relationship between heavy-isotope contents of the brine ( 2H and 18O) and the Cl − content indicates a mixture of two water sources. The first one is meteoric water as defined by the intersection of the formation water line with the global meteoric water line ( δ 2 H = −65‰ , δ 18 O = −9.3‰ ). The other end-member is enriched in heavy isotopes and in Cl −, and is attributed to seawater that has dissolved evaporites (mainly halite). However, the presence of small amounts of an extremely evolved brine is required to account for the bromide, lithium, rubidium and boron contents of the formation brine from the Rhaetian aquifer. As this contribution is very limited in amount, it cannot affect the heavy-isotope content of the formation water. Mass-balance equations are solved for ternary mixtures of meteoric water, seawater and brine. The same constraints as above (no Na + and K + supplied by the primary brine and Cl Brine ≈ 11,000 mmol kg −1) are applied. It is also assumed that the seawater component has the same ionic contents as modern seawater and that the salt content of the meteoric component is negligible. The fraction of primary brines is x ≈ 1.4% according to the Cl − balance. This estimate agrees with that obtained from the lithium balance assuming that the primary brine component was the same as that of the Keuper formation water. Mass-balance calculations also indicate that the SO 4 2− content of the Rhaetian formation water is exclusively due to the secondary brine component. In the three saline solutions, the very high Ca 2+ contents and high Ca 2+ Mg 2+ ratios, may be attributed to reaction of the very evolved brine (free of SO 2− 4), with gypsum or anhydrite. The result is an exchange of Mg 2+ for Ca 2+, which causes a release of Ca 2+ to the solution and a precipitation of secondary Mg-sulphate. This process can also account for the high strontium contents of the analysed samples. Values of the ratio 87 Sr 86 Sr are very high in the Keuper formation water due to close contact of the solutions with the granitic basement or with granite-derived detrital deposits. Values in the Rhaetian and Dogger aquifers equal those of Upper Triassic marine deposits. The stable isotope ( 34S and 18O) content of the dissolved aqueous SO 2− 4 indicates a Triassic origin for the bulk of sulphate involved in the evolution of formation waters from the Rhaetian and from the Dogger. All geochemical indicators thus show a vertical migration of Triassic brines. However, aqueous SO 2− 4 from the Keuper has a Permian isotopic signature suggesting a reworking in solution of salts from this period.