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The relationship between the δ13C of dissolved inorganic carbon (DIC) and modern mollusk aragonite from rivers was calibrated for the purpose of reconstructing DIC paleochemistry from the shell record. The δ13C values of aragonitic bivalves (Dreissena polymorpha, Corbicula fluminea), prosobranch gastropods (Bithynia tentaculata, Theodoxus fluviatilis, Viviparus viviparus), and an air-breathing pulmonate gastropod (Limnea auricularia) were analyzed from several locations on the Rhone River (—13.7‰ to —6.0‰) and its major tributary, the Saone River (—11.4‰ to —10.2‰). The δ13CDIC varied from —11.5‰ to —7.5‰, and the δ13C of particulate inorganic matter (POM) varied from —31.7‰ to —25.4‰. At a given site, the δ13C of all species except the pulmonate were within 1‰ of each other. Whole-shell δ13C correlated positively with δ13CDIC, with a slope close to unity. Bioaragonite—DIC fractionations were 0–1.5‰ for bivalves and 0–2.7‰ for gastropods (excluding the pulmonates). Applying these fractionations, bivalves that live in open water are a reliable proxy, monitoring the average δ13CDIC value to within its natural ~2‰ temporal variation within the growth period. For the suspension feeders (bivalves) using POM as a food source, the δ13C of whole shells and bulk POM indicated that the incorporation of carbon derived from respiratory sources lay in the range 10–30%. Fine-scale analyses of growth increments of C. fluminea could not be related simply to δ13CDIC because metabolic and seasonal variations in δ13CDIC produced similar isotopic fluctuations (≤2.5‰).

A detailed record of sea surface temperatures in the Northern Hemisphere based on migration of marine invertebrate fauna (ammonites) and isotopic thermometry (δ18O values of shark tooth enamel) indicates a severe cooling at the Middle–Late Jurassic transition (MLJT), about 160 Ma ago. The magnitude of refrigeration (1–3°C for lower middle latitudes) and its coincidence in time with an abrupt global-scale fall of sea level documented through sequence stratigraphy are both suggestive of continental ice formation at this time. Ice sheets may have developed over the high-latitude mountainous regions of Far-East Russia. The drastic cooling just post-dated the Middle–Late Callovian widespread deposition of organic-rich marine sediments (e.g. northwestern Europe, Central Atlantic, and Arabian Peninsula). This thermal deterioration can thus be ascribed to a downdraw in atmospheric CO2 via enhanced organic carbon burial which acted as a negative feedback effect (i.e. the inverse greenhouse effect). The glacial episode of the MLJT climaxed in the Late Callovian, lasted about 2.6 Myr, and had a pronounced asymmetrical pattern composed of an abrupt (∼0.8 Myr) temperature fall opposed to a long-term (∼1.8 Myr), stepwise recovery. The glacial conditions at the MLJT reveal that atmospheric CO2 levels could have dropped temporarily to values lower than 500 ppmv during Mesozoic times.

We studied the changes in major elements and organic carbon concentrations during the initial stage of the mixing of the black (Rio Negro) and the White (Rio Solimoes) waters in the Amazon River basin to understand the geochemical processes that could control the redistribution between particulate and dissolved fractions. Water samples were collected at six stations including the Rio Negro and the Rio Solimoes and four stations downstream from the confluence. The relative contributions of the two tributaries were determined using a triple tracer approach (d 18 O, dD, Cl � ). Particulate (>0.2 Am) and dissolved (

International audience; Numerous observations indicate that faults play a major role on the migration pathways of fluids in the Bolivian sub-Andean Zone. Most oil seeps in the foothills are located on faults, but oil fields in the foredeep are closed by faults. In the foothills, analysis of cements in fractures inside and around fault zones indicates that the faults act as barriers for transversal migration but can be preferential lateral migration pathways for both hydrocarbons and water. A detailed study of these apparent contradictions suggests that the hydraulic behaviour of faults changes with depth in relation with sandstone diagenesis, but it is strain-independent. From microstructural analyses of fault zones, we suggest that the main controlling factor is temperature, which facilitates or inhibits quartz precipitation. This result implies that the same fault is a barrier for lateral and transversal migration at depths >3 km, due to sealing of fractures by authigenic quartz at T>80 °C, and is a lateral drain in its shallower parts. As a result, the various thrust sheets are isolated from a hydraulic point of view, whereas migration in the foreland may take place over long distances (>100 km).

The analysis of macro- and microstructures and cement distribution in thrust fault zones of the Bolivian Sub-Andean Zone shows that fault zones are sealed by quartz at depths >∼2.5 km. Cementation occurred due to local silica transfer by pressure solution-precipitation activated at temperatures >80–90°C. At shallower depths, faults have remained open and could be preferential drains for lateral flow of allochthonous carbonated fluids. At a large-scale, the faults have a low transverse permeability and they separate thrust sheets with different fluid histories.

Dissolved inorganic carbon (DIC) and particulate inorganic carbon (PIC) were sampled at 20 sites on the Rhone and its main tributaries from Switzerland to the Mediterranean, in March, September and July (flood event) 1996. Flux estimation and DIC and PIC values are used to trace watershed inputs and fluvial processes affecting the inorganic carbon budget. DIC concentration and values vary between ∼1 mM at −5‰ near the Rhone's source and ∼3 mM at −10‰ near its mouth, with tributaries draining lowland, carbonate-dominated areas at ∼3.8 mM and −11‰. There is an inverse relationship between river DIC concentration and DIC . The headwaters are characterized by high DIC values and low DIC, indicating a minor input of respired CO2. DIC should be mainly produced through the reaction of carbonate with atmospheric CO2 or organic/sulfuric acids. In lowland, carbonate-dominated areas, values of ∼−11‰ are consistent with production of DIC by weathering of limestone C (≈−1‰) with CO2 derived from the oxidation of organic matter (≈−21.5‰). The evolution of the Rhone's DIC concentration and appear to be largely determined by mixing between the Rhone and its main tributaries. The CO2 fluxes and DIC mass-balance, calculated for the different segments of the Rhone, point to a net, but very limited input of fluvial respired CO2 from the oxidation of organic C (

The nature of synmetamorphic fluids and their flow is examined in the granulitic lower crust of Madagascar, part of a Precambrian crustal-scale network of vertical ductile shear zones. Based on three independent data sets - field and satellite mapping, C-, O- and H-isotope geochemistry and gravimetry - this crust is divided into three zones: outside of shear zones, minor shear zones ( 350 km long and 20–35 km wide). The major shear zones are rooted in and are controlled by the mantle. They tapped mantle-derived CO2 with carbon fluxes of the same order of magnitude as oceanic ridge degassing. One major shear zone shows abundant phlogopite-diopside-apatite-calcite mineralizations (a well known paragenesis in mantle metasomatism) due to mantle-fluid infiltration and their interaction with the crust. Carbonatitic magmas possibly collected in the major shear zones at the base of the crust and may be the source for CO2 upwellings as well as other metasomatic agents. Small-scale minor shear zones were controlled by crustal deformation processes and focused crustally-derived H2O-rich fluids. Pervasive fluid circulation was restricted to the vicinity (

An ion probe analytical procedure has been established to measure in-situ DH ratios in hydroxylated minerals on the scale of a few tens of μm with a precision of ±10‰. This technique has been applied to determine the DH ratio of amphiboles occurring as rare disseminated minerals in peridotites. These amphiboles include pargasite from the Lherz peridotite, Pyre´ne´es (France), and kaersutite and pargasite in ultramafic xenoliths and megacrysts from the Massif Central (France), Nunivak Island (Alaska) and Salt Lake Crater (Hawaii). The δD value measured in Lherz (−92 and −65) and Nunivak Island (−93 to −69) are in the accepted range for upper mantle minerals. The higher δD (−59 to −28) from the Massif Central xenoliths may involve contamination of the subcontinental lithosphere by subduction of seawater-altered oceanic crust. The very low δD (down to −125) observed for Hawaiian xenoliths could reflect the presence of a previously unidentified deep hydrogen component in the mantle. For the Massif Central and Salt Lake Crater, δD smow variations up to 70‰ were measured both on the scale of single crystals (≤200 μm) and among crystals of the same sample. Chemical variations are minor and not correlated with δD . Combining the diffusion data for hydrogen in amphiboles with these results implies that the time interval between the onset of exchange and volcanism was shorter than a few hundred years. The δD heterogeneity observed for the latter two localities probably results from incomplete equilibration between xenoliths and fluids or hydrous magmas rather than from fractionation processes.

[1] Sources and fluxes of particulate organic carbon (OC) in the Ganga-Brahmaputra river system were estimated from 13C/12C ratios of bedrocks, soils, bank and suspended river sediments from a Himalayan watershed (Narayani, Nepal), and the Bangladesh floodplain. In the watershed of the Narayani, OC δ13C values for bank and suspended sediments have similar values and narrow ranges, with a mean of about −24.2‰ at the base of the Himalayas. On the Bangladesh floodplain, bank and suspended sediments are enriched in 13C (δ13C about −22.5‰) relative to those collected at the base of the Himalayas. The OC exported at the base of the Himalayan range is estimated to include about 15% from the 13C enriched C4 biomass while the C4 contribution is about 25% of the OC exported by the Ganga and Brahmaputra. A calculated total OC flux of 0.65 × 1012 molC yr−1 is exported to the ocean or trapped in the plain. In sediments of the Ganga and Brahmaputra, the clay-size fraction is depleted in 13C (

International audience; The Bolivian previous termSub-Andean Zonenext term (SAZ) corresponds to a Neogene previous termthrustnext term system that affects an about 10-km thick Palaeozoic to Neogene siliciclastic succession. The analysis of macro and microstructures and cement distribution previous termin thrust fault zonesnext term shows that they are sealed by quartz at depths >not, vert, similar3 km, due to local silica transfer by pressure-solution/precipitation activated at temperatures >70–90 °C. At shallower depths, previous termfaultsnext term have remained open and could be preferential drains for lateral previous termflownext term of carbonate-bearing previous termfluids,next term as shown by the occurrence of carbonate cements previous terminnext term fractures and their host-previous termsandstone.next term Due to decreasing burial, resulting from foothill erosion during previous termfaultnext term activity, critically buried previous termfaultnext term segments can be affected by non-quartz-sealed structures that post-date initial quartz-sealed structures. The integration of textural, previous termfluidnext term inclusion and isotopic data shows that carbonates precipitated at shallow depth (

cited By 88; A crustal-scale ductile shear zone network in the Precambrian granulite-facies crust of Madagascar is examined to determine the nature of the connections between the mantle and lower crust. Based on three independent data sets - field and satellite mapping, C- and O-isotope geochemistry and gravimetry - this crust is divided into three zones: (1) outside of shear zones; (2) minor shear zones that are 350 km long (up to 1000 km) and 20-35 km wide. The mantle is uplifted by about 10 km beneath the major shear zones. The major shear zones are rooted in and are inferred to be controlled by the mantle; they directly tapped mantle-derived CO2. The small-scale minor shear zones were controlled by crustal processes and focused crustally derived H2O-rich±CO2 fluids. The regular distribution of the shear zones on a crustal scale is in agreement with models of buckling of the continental lithosphere in a compressional context. The propagation of these mechanical instabilities promoted and channelled fluid flow. These major Pan-African shear zones thinned the crust and were reactivated during the subsequent drifting of Madagascar and opening of the Indian Ocean during Jurassic to Cretaceous times. They also controlled many of the brittle fault zones in the overlying sedimentary basins. Mantle-rooted large-scale shear zones are inferred to be a general feature of cratonic areas reactivated by shear zone systems.

Hydrogen carbon and oxygen isotope analyses were determined, where applicable, on phlogopite megacrysts (two samples), serpentine megacrysts (two), unweathered matrix (nine), carbonated granulite xenoliths (two), a carbonatite dyke and weathered yellow kimberlite from diatremes in Lesotho (Kao, Matsoku) and South Africa (Monastery, New Elands, Premier, Wesselton) and dykes and sills in Lesotho (Kaunyane) and South Africa (Benfontein, Du Plessis). The DH ratios of phlogopite megacrysts are in the range previously reported for possible upper mantle derived phlogopites: −40 to −70 per mil, SMOW. DH ratios of the serpentinized megacrysts and the hydrous phases of the matrix, dominantly serpentine and/or phlogopite, are depleted in D by 20 to 55 per mil relative to the phlogopite megacrysts from, in some cases, the same sample. Serpentine megacrysts and serpentine-rich matrix samples are depleted in 18O by up to 6 per mil relative to both phlogopite-rich and olivine-rich matrix, and “normal” ultramafic values. The H- and O-isotope data indicate that meteoric-hydrothermal fluids interacted with the kimberlite during the major serpentinization processes. The origin of fluids associated with matrix phlogopite cannot be defined specifically: magmatic, metamorphic or exchanged meteoric waters with very low water/rock ratios (< 0.2 at.% oxygen) or some combination are possible. The isotopic “thermometers” indicate very approximately that the matrix phlogopite crystallized at temperatures on the order of 200° to 500°C and serpentinization process occurred at 50° to 200°C. Carbonates from the matrix, carbonatite dykes and xenoliths have δ18O = +7 to +21 per mil, SMOW and δ13C = −3 to −7.5 per mil, PDB. The C-isotope ratios are similar to those for most diamonds and primary igneous carbonatites and are similarly variable at a single locality. They are compatible with a genetic relationship among these carbon sources. The 18O enrichment of most kimberlite carbonates is a result of the relatively low temperature of exchange with other matrix minerals and/or with meteoric-hydrothermal fluids. Loss of CO2 + H2O fluid during degassing may contribute to the H- and C-isotope variations in a kimberlite. The water content of kimberlite magmas were probably substantially less than the 5 to 10 wt.% H2O observed in many diatreme-facies kimberlites. The preservation of diamonds in a kimberlite may be critically dependent on both the initial water content of the mell and the stage and temperature at which large-scale influx of ground waters into the kimberlite occured. Weathered yellow kimberlite is isotopically distinctive from our matrix samples.

REE geochemistry and isotopic (Pb, Sr, Nd, O) compositions have been studied in up to nine separate leucogranite massifs from three structurally adjacent zones in South Brittany. Ages decrease from 340 Ma in the north to 300 Ma in the south whereas initial 87 Sr/ 86 Sr ratios increase from 0.706 to 0.710–0.717. REE abundances are relatively low (La N ∼ 20–80 × chondrites) with a strong enrichment of LREE relative to HREE (La N /Lu N = 13.4–26.6). Pb isotope ratios are homogeneous for a given massif but heterogeneous among massifs and plot very close to a normal terrestrial lead growth curve at 300 Ma ago. 18 O/ 16 O ratios are high and relatively uniform at 10.7 to 12.8, mean 11.9. U Pb studies on zircon indicate the presence of an inherited radiogenic Pb component and that the sediment-dominated source region had been metamorphosed during the Siluro-Devonian (Ligerian). Negativee Nd(T) values imply that the source region had been enriched in LREE prior to the melting episode. Based on the combined data, large-scale partial melting of crustal material, dominantly of sedimentary origin, is proposed. The model age of the source rocks is not very old (600–700 to 1200 Ma). The Pb and Sr isotopic variations observed among different massifs is probably the result of age differences in the source materials of the different leucogranites.

Hydrogen carbon and oxygen isotope analyses were determined, where applicable, on phlogopite megacrysts (two samples), serpentine megacrysts (two), unweathered matrix (nine), carbonated granulite xenoliths (two), a carbonatite dyke and weathered yellow kimberlite from diatremes in Lesotho (Kao, Matsoku) and South Africa (Monastery, New Elands, Premier, Wesselton) and dykes and sills in Lesotho (Kaunyane) and South Africa (Benfontein, Du Plessis). The D/H ratios of phlogopite megacrysts are in the range previously reported for possible upper mantle derived phlogopites: −40 to −70 per mil, SMOW. D/H ratios of the serpentinized megacrysts and the hydrous phases of the matrix, dominantly serpentine and/or phlogopite, are depleted in D by 20 to 55 per mil relative to the phlogopite megacrysts from, in some cases, the same sample. Serpentine megacrysts and serpentine-rich matrix samples are depleted in 18O by up to 6 per mil relative to both phlogopite-rich and olivine-rich matrix, and “normal” ultramafic values. The H- and O-isotope data indicate that meteoric-hydrothermal fluids interacted with the kimberlite during the major serpentinization processes. The origin of fluids associated with matrix phlogopite cannot be defined specifically: magmatic, metamorphic or exchanged meteoric waters with very low water/rock ratios (< 0.2 at.% oxygen) or some combination are possible. The isotopic “thermometers” indicate very approximately that the matrix phlogopite crystallized at temperatures on the order of 200° to 500°C and serpentinization process occurred at 50° to 200°C. Carbonates from the matrix, carbonatite dykes and xenoliths have δ18O = +7 to +21 per mil, SMOW and δ13C = −3 to −7.5 per mil, PDB. The C-isotope ratios are similar to those for most diamonds and primary igneous carbonatites and are similarly variable at a single locality. They are compatible with a genetic relationship among these carbon sources. The 18O enrichment of most kimberlite carbonates is a result of the relatively low temperature of exchange with other matrix minerals and/or with meteoric-hydrothermal fluids. Loss of CO2 + H2O fluid during degassing may contribute to the H- and C-isotope variations in a kimberlite. The water content of kimberlite magmas were probably substantially less than the 5 to 10 wt.% H2O observed in many diatreme-facies kimberlites. The preservation of diamonds in a kimberlite may be critically dependent on both the initial water content of the melt and the stage and temperature at which large-scale influx of ground waters into the kimberlite occurred. Weathered yellow kimberlite is isotopically distinctive from our matrix samples.

A pyroclastic tuff from the Velay volcanic province in the French Massif Central contains blocks up to 30cm long of local basement rocks, lava clasts, coarse-grained cumulates and pyroclastic fragments, with more or less diffuse boundaries with the host tuff, which probably represent more consolidated parts of the tuff. All of the pyroclastics examined and approximately 10% of the cumulate xenoliths contain carbonates in variable amounts, textures and mineralogy. In some of the tuff samples, dolomite occurs in large amounts (up to 57%), principally as immiscible globules in trachytic melt (now glass), and represents the first occurrence of carbonatite reported from the Massif Central. The other carbonates, magnesiosiderite in the mafic cumulates or occasionally in some tuffs, and calcite in the felsic cumulates, are always associated with a silicate glass of trachytic composition. Coexisting feldspars and carbonates in the various types of sample are approximately in Sr isotopic equilibrium with an initial ratio of about 07042. C- and O-isotopic compositions of the carbonates covary and cover a very wide range of composition fromˇ2 9t o 3 9 %(PDB) and from 87 to 245% (SMOW), respectively; the globular dolomites have primary igneous isotopic signatures and plot within the primary igneous carbonatite field. The combined C---O ---Sr isotopic data indicate that both the dolomitic carbonatitic and silicate magmas came from a mantle source with very similar isotopic characteristics. On compositional arguments, injection of a non-cogenetic carbonatite magma into a differentiating body of felsic magma within the crust is preferred to the unmixing of a relatively late, fractionated melt to carbonatitic and trachytic magmas. The textures, high d 13 Ca nd d 18 O values of Mg-siderite and calcite and their trend are consistent with post-magmatic precipitation of these carbonates, probably by interaction between a CO2---H 2O-bearing fluid (520 mol % CO2) undergoing Rayleigh distillation processes and the minerals and glass in the cumulates. Although minimum isotopic temperatures are 4100C for the calcites and 4275C for the magnesiosiderites, the isotopic data are compatible with the chemical, solvus temperatures of 4500C for the calcites and 4500---700C for the magnesiosiderites, if the CO2 content of the fluid decreased during the distillation processes. The highly variable K2O/ Na2O ratios of some of the glasses on the scale of a few microns may be another consequence of H2O---CO2 metasomatic processes. Explosive eruption of the two immiscible magmas that entrained the xenoliths probably occurred as a result of CO2---H 2O degassing processes soon after the arrival of the carbonatitic magma in the trachytic system.

Endemics–Area Relationships (EARs)are fundamental in theoretical and applied biogeography for understanding distribution patterns and promoting biodiversity conservation. However, calculating EARs for vascular plant species from existing data is problematic because of biased knowledge of endemic species distributions and differences between taxonomies. We aimed to overcome these challenges by developing a new standardized global dataset based on expert knowledge to produce a set of global EARs. We developed a nested circle design, with grain sizes of 10 4 , 10 5 , 10 6 , 10 7 , and 10 8 km 2 , respectively, and a global distribution of plots based on a stratified random scheme. The number of vascular plant species endemic to each circle was then estimated independently by five experts randomly chosen from a pool of 23, as both a minimum and a maximum value (lower and upper bounds of the estimation), taking into account the limitations of current knowledge and varied species concepts in existing taxonomies. This procedure resulted in a dataset of 3000 expert estimates. Based on the data, we produced three global EARs for endemic species richness using minimum, maximum and average estimates. As a validation, we used all three models to extrapolate to the entire world, producing estimates of 284,493 (minimum), 398,364 (maximum)and 312,243 (average)vascular plant species. These figures conform to the range of taxonomists’ estimates. From the models, we calculated the average area needed to harbour a single endemic species as 12,875 km 2 (range 9675–20,529). The global vascular plant EARs we calculated represent the first standardized, quantitative expectations of plant endemism at any given scale (sampling unit size). These EARs allow us to provide a clear answer to a long-standing but elusive biogeographical question: how to assess whether any area on the surface of the Earth is rich or poor in endemics relative to the average.