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1.
Denis A Wiesenburg James M Brooks Bernie B Bernard 《Geochimica et cosmochimica acta》1985,49(10):2069-2080
The composition of light hydrocarbon gases in the Orca Basin, an anoxic, hypersaline intraslope depression on the continental slope of the northern Gulf of Mexico, indicates that both methane and ethane are biogenic in nature with a ratio of 730 and a δ13C of methane of ?73%. relative to the PDB standard. The concentrations of methane (750 mM) and ethane (1300 mM) in the Orca Basin brine are higher than any other marine anoxic basin. These high levels result not from high rates of productivity, but from the long residence time of the brine in the basin, due to its high stability toward mixing with overlying seawater (). Both methane and ethane show well mixed distributions in the brine. These distributions probably result from convective mixing of the isohaline brine pool due to normal heat flow from the basin sediments. Methane and ethane maxima above the pycnocline at the brine/seawater interface reflect in situ production and/or consumption in the aerobic water column. Concurrent maxima in suspended particulate material distributions in this region suggest methane may be produced there in anaerobic microenvironments associated with the suspended matter. Reduced rates of anaerobic decomposition (including sulfate reduction) in the brine sediments are inferred from preserved Sargassum fronds in the sediments, vertical sulfate profiles in most cores, and the sediment organic carbon content which is two to three times higher in sediments below the high salinity brine than in the normal Gulf sediments nearby. 相似文献
2.
The fractionation factors () for the reduction of CO2 to CH4 by pure cultures of methane-producing bacteria are, for Methanosarcina barkeri at 40°C, 1.045 ± 0.002; for Methanobacterium strain M.o.H. at 40°C, 1.061 ± 0.002; and, for Methanobacterium thermoautotrophicum at 65°C, 1.025 ± 0.002. These observations suggest that the acetic acid used by acetate dissimilating bacteria, if they play an important role in natural methane production, must have an intramolecular isotopic fractionation () approximating the observed fractionation. 相似文献
3.
Roger A. Burke James M. Brooks William M. Sackett 《Geochimica et cosmochimica acta》1981,45(5):627-634
Light hydrocarbon (C1-C3) concentrations in the water from four Red Sea brine basins (Atlantis II, Suakin, Nereus and Valdivia Deeps) and in sediment pore waters from two of these areas (Atlantis II and Suakin Deeps) are reported. The hydrocarbon gases in the Suakin Deep brine (T = ~ 25°C, , ) are apparently of biogenic origin as evidenced by ) ratios of ~ 1000. Methane concentrations (6–8 μl/l) in Suakin Deep sediments are nearly equal to those in the brine, suggesting sedimentary interstitial waters may be the source of the brine and associated methane.The Atlantis II Deep has two brine layers with significantly different light hydrocarbon concentrations indicating separate sources. The upper brine (T = ~ 50°C, , CH4 = ~ 155 μl/l) gas seems to be of biogenic origin [], whereas the lower brine (T = ~ 61°C, , CH4 = ~ 120μl/l) gas is apparently of thermogenic origin []. The thermogenic gas resulting from thermal cracking of organic matter in the sedimentary column apparently migrates into the basin with the brine, whereas the biogenic gas is produced in situ or at the seawater-brine interface. Methane concentrations in Atlantis II interstitial waters underlying the lower brine are about one half brine concentrations; this difference possibly reflects the known temporal variations of hydrothermal activity in the basin. 相似文献
4.
N. Assayag D. Jézéquel M. Ader E. Viollier G. Michard F. Prévot P. Agrinier 《Applied Geochemistry》2008
Lac Pavin (French Massif Central) is a permanently stratified lake: the upper water layers (mixolimnion, from 0 to 60 m depth) are affected by seasonal overturns, whereas the bottom water layers (monimolimnion, from 60 to 90 m depth) remain isolated and are never mixed. Hence, they are capable of storing important quantities of dissolved gases, mainly CO2. With the aim of better constraining the water balance and of gaining new insights into the carbon cycle of Lac Pavin, an isotopic approach is used. The δ18OH2O profiles lead the authors to give a new evaluation of the evaporation flow rate (8 L s−1), and to propose and characterize two sub-surface springs. The sub-surface spring located at the bottom of the lake can be deduced from the 1% isotopic difference between the upper water layers (mean δ18OH2O value: −7.3‰) and the bottom water layers (δ18OH2O=-8.4‰). It is argued that this sub-surface spring has isotopic and chemical characteristics similar to those of the magmatic CO2-rich spring (i.e. Fontaine Goyon, δ18OH2O=-9.4‰), and we calculate its flow rate of 1.6 L s−1. The second sub-surface spring is located around 45 m depth, with a composition close to those of the water surface streams (δ18OH2O<-7.6‰). 相似文献
5.
Bruce S. Hemingway Richard A. Robie James A. Kittrick 《Geochimica et cosmochimica acta》1978,42(10):1533-1543
Solution calorimetric measurements compared with solubility determinations from the literature for the same samples of gibbsite have provided a direct thermochemical cycle through which the Gibbs free energy of formation of [Al(OH)4 aq?] can be determined. The Gibbs free energy of formation of [Al(OH)4 aq?] at 298.15 K is ?1305 ± 1 kJ/mol. These heat-of-solution results show no significant difference in the thermodynamic properties of gibbsite particles in the range from 50 to 0.05 μm.The Gibbs free energies of formation at 298.15 K and 1 bar pressure of diaspore, boehmite and bayerite are ?9210 ± 5.0, ?918.4 ± 2.1 and ?1153 ± 2 kJ/mol based upon the Gibbs free energy of [A1(OH)4 aq?] calculated in this paper and the acceptance of ?1582.2 ± 1.3 and ?1154.9 ± 1.2 kJ/mol for the Gibbs free energy of formation of corundum and gibbsite, respectively.Values for the Gibbs free energy formation of [Al(OH)2 aq+] and [AlO2 aq?] were also calculated as ?914.2 ± 2.1 and ?830.9 ± 2.1 kJ/mol, respectively. The use of [AlC2 aq?] as a chemical species is discouraged.A revised Gibbs free energy of formation for [H4SiO4aq0] was recalculated from calorimetric data yielding a value of ?1307.5 ± 1.7 kJ/mol which is in good agreement with the results obtained from several solubility studies.Smoothed values for the thermodynamic functions CP0, (, , ST0 - S00, kaolinite are listed at integral temperatures between 298.15 and 800 K. The heat capacity of kaolinite at temperatures between 250 and 800 K may be calculated from the following equation: CP0 = 1430.26 ? 0.78850 T + 3.0340 × 10?4T2 ?1.85158 × 10?4T2.The thermodynamic properties of most of the geologically important Al-bearing phases have been referenced to the same reference state for Al, namely gibbsite. 相似文献
6.
Variations in the chemical composition of sedimentary rocks and the nature of kerogen through geologic time were investigated in order to obtain information on biological and environmental evolution during the pre-Phanerozoic eon. Rock samples differing in lithology, depositional environment, and age were pulverized, pre-extracted with organic solvents, and analyzed for total nitrogen (N), phosphorus (P) and organic carbon (org. C or CT). Variations in the molecular structure of kerogen were measured by determining the ratio of org. C content after pyrolysis (CR) to org. C content before pyrolysis (CT), the ratio being considered an index of the degree of condensed-aromatic (as opposed to aliphatic) character. The rocks included mudstones (Early Archean (> 3 · 109 years old) to Miocene), carbonate rocks (mid-Proterozoic (1.3 · 109 years old) to Eocene), cherts (Early Archean (> 3 · 109 years old) to Late Proterozoic (0.8 · 109 years old)), and coal (Archean (> 2.7 · 109 years old) to Early Proterozoic (～1.8 · 109 years old)).The mudstones and carbonates showed progressive increase in org. C content with decreasing age, as reported by other investigators, but the cherts unexpectedly showed a decrease in org. C content with decreasing age. In all samples, a simple inverse correlation between ratio and org. C was observed, each rock type forming its own trend separate from but parallel to those of the other rock types. Thus, the older cherts tend to be richer in org. C and have lower ratios, but the older carbonates and mudstones are poorer in org. C and have higher ratios. For a given org. C concentration, chert has the highest ratio and carbonate rock the lowest, mudstone being intermediate; this may mean that chert is relatively ineffective as a catalyst for the thermal cracking of kerogen or that it inhibits cracking. N appears to be correlated with org. C. The relationship between ratio and org. C or N suggests that the concentrations of org. C and N in sedimentary rocks are largely determined by selective elimination of labile aliphatic and nitrogenous groups of kerogen during post-depositional maturation, although the nature, abundance and depositional environment of the organic source material must be taken into consideration as well. The observed secular variations of org. C, N and ratio may be ascribed to several possible causes, including age-dependent post-depositional alteration of kerogen, secular decrease in the ratio of the atmosphere and hydrosphere during pre-Phanerozoic time, secular increase in rates of accumulation of organic matter in sediments and evolutionary changes in the composition of the biological source material. The secular variations of the carbonates and mudstones could be accounted for by age-dependent cumulative effects of post-depositional alteration alone, whereas the secular variations of the cherts probably reflect changes in the nature of the biological source material and the composition of the atmosphere and hydrosphere. The available evidence suggests that primary characteristics of kerogen are better preserved in chert than in the other types of sediment.The ratios of the carbonates and cherts correlate negatively with the absorbance ratios of “humic matter” extracted from the same rock samples with benzene—methanol. Thus, the greater the degree of condensed-aromatic character of the kerogen, the greater the degree of condensed-aromatic character of the solvent-extractable bituminous “humic matter” with which it is associated. In addition, the ratio of aliphatic to carbonyl-type groups () in the extractable “humic matter” of carbonates and cherts correlates with the non-extractable org. C content of the rocks, suggesting that the org. C data are related to the degree of aliphatic character of the kerogen. The chemical similarity between extractable “humic matter” and its associated kerogen is evidence that the “humic matter” is as old as its rock matrix and can be accepted as a valid chemical fossil. It also suggests that information obtainable from kerogen may be gotten more easily, rapidly and cheaply from solvent-extractable organic matter. The mudstones showed little or no relationship between ratio and ratio, or between ratio and org. C content. The data are consistent with the hypothesis that the kerogen in the carbonates and cherts is autochthonous, whereas the kerogen in the mudstones is partly allochthonous, implying the existence of soil humus and soil organisms in pre-Phanerozoic times. Moreover, the existence of coal in Archean sediments is consistent with the existence of very shallow-water and possibly terrestrial microfloras possessing adaptations for protection against ultraviolet solar radiation.The P content of the sediments showed a complicated zig-zag pattern of variation through geologic time. All the different suites of samples gave similar results, indicating that the variations represent phenomena whose effects were worldwide and independent of local environment. P levels are low in the early pre-Phanerozoic but rise with decreasing age until ～ 1 · 109 years B.P., then fall to a minimum at (～0.7–0.8) · 109 years B.P., and rise again to a lower Paleozoic (Ediacarian?) maximum, decline to a later Paleozoic minimum, and then rise again. The low P content of early pre-Phanerozoic sediments could be due to several factors, including high CO2 content of seawater, anaerobic conditions in the sea, absence of stable-shelf environments, and low rates of primary production. The minimum in the Late Proterozoic is tentatively attributed to the Late Proterozoic glaciations. The data are consistent with the theory that the glacial episode was of worldwide extent. 相似文献
7.
Water samples collected from a slope station and two deep stations in the western basin of the Black Sea were analyzed for stenols and stanols by glass capillary gas chromatography. These results were used in conjuction with hydrographic, particulate organic carbon, and chlorophyll a data to better understand sterol sources and their transport and transformation mechanisms in anoxic basins.The total free sterol concentrations found in the surface waters were 450–500 ng/l dropping rapidly to values well below 100 ng/l at depths below the interface. In the upper 200 m of the water column a strong association of sterols with particulate matter is suggested. Structural elucidation by a gas chromatograph-mass spectrometer-computer system revealed the presence of at least sixteen different stenols and stanols in the surface waters of the Black Sea. Cholesterol, 24-methylenecholesterol and 24-methylcholesta-5,22-dien-3β-ol were the major sterols in the surface waters. Cholesterol and 24-ethylcholesterol both exhibited a subsurface maximum at the interface. In the anoxic deep waters (200–2000 m) only cholesterol and 24-ethylcholesterol were found. Two stenols were found that have not been reported in seawater: a C26 stenol with a saturated C7H15 side chain (presumably 24-norcholesterol) and 24-ketocholesterol. At least six 5α-stanols could be identified in the surface samples, each of them comprising about 10–20% of the concentration of the corresponding Δ5-stenol. From these comparatively high surface values the stanol concentrations drop rapidly to values near zero at the interface. Except for very low concentrations of 5α-cholestanol (< 4ng/l) no other stanols could be detected in the anoxic zone.From this data it appears that no detectable stenol → stanol conversion is occurring at the interface or in the deep anoxic waters of the Black Sea. 相似文献
8.
Stuart G. Wakeham 《Geochimica et cosmochimica acta》1982,46(11):2239-2257
The vertical flux and composition of wax esters, steryl esters, triacylglycerols, and alkyldiacylglycerols in particulate matter was determined in the equatorial Atlantic Ocean by deploying sediment traps at 389, 988, 3,755 and 5,068 m. Detailed compositional analyses of these lipids were carried out by high temperature glass capillary gas chromatography and gas chromatography/mass spectrometry.The distributions of these lipids are discussed in terms of potential biological sources. Zooplankton fecal matter and intact zooplankters may represent the most important input of these compounds to the shallower two traps, while the material in the deeper two traps appears to have been biogeochemically altered. The finding of these biochemically important compounds, often unsaturated, indicates that particle transit through the water column must be relatively fast.Wax esters were most abundant in the 389 m sediment trap and decreased with increasing trap depth. Compounds ranging from C28–C44 were present at all depths. The major homologs were C32, C34 and C36, most often monounsaturated. The dominant alcohol/acid combinations in the 389 m trap were and , but in the 988 m sample, was the major wax ester. A flux maximum was observed for steryl esters at 988 m. Cholesteryl esters of C14:0, C16:1 and C16:0, and fatty acids were the dominant steryl esters. For triacylglycerols, fluxes in the 389 and 988 m traps were similar, while the deeper pair of traps contained much less triacylglycerol. C46, C48, C50 and C52 compounds were the major triacylglycerols. Constituent fatty acids in the 389 m and 988 m samples were mainly C14:0, C16:1, C16:0, C18:1 and C18:0. In the 988 m material, C20:5 and C22:6 were also dominant. A homologous series of alkyldiacylglycerols was abundant in the 389 m trap material. The alkyldiacylglycerols consisted of C46–C56 compounds composed of C16:0 alkyl moieties and C14:0, C16:0, C18:1, and C18:0 fatty acids. 相似文献
9.
In a soil developed on the Cretaceous chalk of the Eastern Paris basin, calcite dissolution begins at the surface. The soil water is rapidly saturated in calcite. Calcite dissolution follows two different pathways according to seasonal pedoclimatic conditions.During winter: the soil is only partly saturated in water and the CO2 partial pressure is low (Ca 10?3 atm.). As a consequence total inorganic dissolved carbon (TIDC) is a hundred times the carbon content of the gaseous phase. Equilibrium is usually observed between the two phases. It is a closed system. The measured carbon 14 activity (87,5%) and 13C content () of the drainage water are very close to theoretical values calculated for an ideal mixing system between gaseous and mineral phases (respectively characterized by the following isotopic values: ; ; ; ).During spring and summer: the soil moisture decreases, the input of biogenic CO2 induces an increase of the soil CO2 partial pressure (Ca from 3.10?3 atm to 7.10?3 atm). The carbon content of the gaseous phase is higher by an order of magnitude compared to winter conditions. Therefore the aqueous phase is undersaturated in CO2 with respect to the latter. This disequilibrium occurs as a result of unbalanced rates of CO2 dissolution and CO2 effusion toward atmosphère. It is an open system. The carbon isotopic ratio of the aqueous phase is regulated by that of the gaseous phase, as demonstrated by the agreement between measured and calculated isotopic compositions (respectively δL mes = from ?9,4%0 to ?11,5%0, δl calc = from ?9,8%0 to ?13,9%0 AL mes = 119%, AL calc = from 119% to 125%).The solutions originating from both systems (open and closed) move downwards without significant mixing together. It has also been observed that no significant variation of the TIDC isotopic composition occurs during precipitation of secondary calcite. 相似文献
10.
Polyunsaturated fatty acids (C18:2 and C18:3ω3 were analyzed in the upper 20m layer of a 200 m long sediment core taken from Lake Biwa. Concentration maxima occur in layers at depths of 0.2, 1–5, 11–12, and 16m. The vertical changes in the ratio appear to correlate with paleoclimatic condition suggested from palynological evidence. On the basis of ratios, it was suggested that it has been colder at 200, 1000–4000, 15,000 and 20,000 yr BP than at other times. 相似文献
11.
Mechanisms and kinetics of aqueous oxidation-reduction and dissolved O2 interaction in the presence of augite, biotite and hornblende were studied in oxic and anoxic solutions at pH 1–9 at 25°C. Oxidation of surface iron on the minerals coincided with both surface release of Fe+2 and by reduction of Fe+3 in solution. Reaction with iron silicates consumed dissolved oxygen at a rate that increased with decreasing pH. Both Fe+3 and O2 consumption were shown to be controlled by coupled electron-cation transfer reactions of the form; and where M is a cation of charge +z. The spontaneous reduction of aqueous Fe+3in the presence of precipitated Fe(OH)3bracketed the surface oxidation standard half cell between +0.33 and +0.52 volts. Concurrent hydrolysis reactions involving cation release from the iron silicates were suppressed by the above reactions. Calculated oxidation depths in the minerals varied between 12 and 80Å and were apparently controlled by rates of solid-state cation diffusion. 相似文献
12.
Aqueous solubilities of methane at 25°C have been determined in single-salt solutions equilibrated with a CH4 gas phase at 350, 550, and 750 psia. Measurements were made over a range of ionic strengths in NaCl, KCl, CaCl2, MgCl2, Na2SO4, K2SO4, MgSO4, Na2CO3, K2CO3, NaHCO3, and KHCO3 aqueous solutions.At 25°C and constant pressure and methane fugacity, methane solubilities were largely controlled by the stoichiometric ionic strength, I, and the cation of the salt. Except for an increased salting-out due to HCO3?, the anion effect was relatively insignificant. Different but consistent solubility trends were followed in monovalent and divalent cation salt solutions as a function of I. Solubilities increased in salt solutions having a common anion in the following cation sequence: Na+ < K+ ? Ca2+ < Mg2+.The molal salting coefficient, km, for each salt was constant under the experimental conditions of the study, km is defined by where , the molal activity coefficient, is the methane solubility ratio () measured at constant temperature, pressure, and CH4 fugacity. Single-salt km values are as follows: 0.121, NaCl (4m); 0.121, Na2SO4 (1m); 0.118, Na2CO3 (1.5m); 0.146, NaHCO3 (0.5m); 0.101, KCl (4m); 0.108, K2SO4 (0.5m); 0.111, K2CO3 (2m); 0.145, KHCO3 (0.5m); 0.071, CaCl2 (2m); 0.063, MgCl2 (2m); and 0.066, MgSO4 (1.5m) where the molalities in parentheses refer to the maximum salt concentrations used in this study. 相似文献
13.
14.
Frank J Millero 《Geochimica et cosmochimica acta》1985,49(2):547-553
The effect of ionic interactions of the major components of natural waters on the oxidation of Cu(I) and Fe(II) has been examined. The various ion pairs of these metals have been shown to have different rates of oxidation. For Fe(II), the chloride and sulfate ion pairs are not easily oxidized. The measured decrease in the rate constant at a fixed pH in chloride and sulfate solutions agrees very well with the values predicted. The effect of pH (6 to 8) on the oxidation of Fe(II) in water and seawater have been shown to follow the rate equation where k1 and k2 are the pseudo first order rate constants, β1 and β2 are the hydrolysis constants for Fe(OH)+ and Fe(OH)0. The value of αFE is the fraction of free Fe2+. The value of k1 (2.0 ±0.5 min?1) in water and seawater are similar within experimental error. The value of k2 (1.2 × 105 min?1) in seawater is 28% of its value in water in reasonable agreement with predictions using an ion pairing model.For the oxidation of Cu(I) a rate equation of the form was found where k0 (14.1 sec?1) and k1 (3.9 sec?1) are the pseudo first order rate constants for the oxidation of Cu+ and CuCl0, β1 is the formation constant for CuCl0 and αCu is the fraction of free Cu+. Thus, unlike the results for Fe(II), Cu(I) chloride complexes have measurable rates of oxidation. 相似文献
15.
16.
Dieke Postma 《Geochimica et cosmochimica acta》1985,49(4):1023-1033
Redox reactions between Fe2+ in solution and Mn-oxides are proposed as a mechanism for concentration of Mn in sediments both during weathering and diagenesis in marine sediments, e.g. the formation of Mn-nodules.If such a mechanism is to be effective, then reaction rates between Fe2+ and Mn-oxides should be fast. The kinetics and stoichiometry of the reaction between dissolved Fe2+ and synthetically prepared birnessite (Mn7O13·5H2O) were studied experimentally in the pH range 3–6.Results show a stoichiometry which at pH < 4 conforms to a simple reaction between Fe2+ and birnessite, releasing Mn2+ and Fe3+ to the solution. At pH > 4 FeOOH is precipitated and excess Fe2+ consumption compared to the theoretical stoichiometry is observed. The excess Fe2+ consumption is not due to a formation of a quantitative MnOOH layer but rather to adsorption.Reaction kinetics are very fast at pH < 4 and change at pH 4 to a slower mechanism. At pH > 4 the reaction is fast initially until 17% of the bimessite has dissolved and changes then to a slower stage. The later stage can be described by the equation: where J is the overall rate of Mn2+ release, m0 and m the mass of birnessite at time t = 0 and t > 0, β = 6.76?0.94 pH and γ has values of 0.76 at pH 5 and 0.39 at pH 6. The rate constant k is 7.2·10?7 moles s?1 g?1 (moles/1)?0.31 at pH 5 and 9.6·10?8 moles s?1 g?1 (moles/1)0.06 at pH 6.Diffusion calculations show that the rate is controlled by surface reaction and it is tentatively proposed that the availability of vacancies in octahedral [MnO6]sheets of the birnessite surface could be rate controlling. It is concluded that reactions between Fe(II) and birnessite, and probably other Mn-oxides, are fast enough to be important in natural environments at the earth surface. 相似文献
17.
Art F White 《Geochimica et cosmochimica acta》1977,41(5):613-625
The coprecipitation of Na and K was experimentally investigated in aragonite. The distribution functions were determined at pH 6.8 and 8.8 over aqueous Na and K concentrations of between 5 × 10?4and 2.0 M and temperatures of between 25 and 75°C.The mole fractions of Na and K in aragonite are related to the aqueous ratios of Na and Ca by a function of the form where C0 and C1 are constants at a given temperature. This equation was derived by a statistical model assuming a heterogeneous energy distribution for the sites of incorporation. The independence of the coprecipitation process from aqueous anion activities suggests that carbonate is the only anionic species in the solid solution. 相似文献
18.
E.T.C. Spooner R.D. Beckinsale P.C. England A. Senior 《Geochimica et cosmochimica acta》1977,41(7):857-871
During ocean-floor hydrothermal metamorphism of a 225 m thick allochthonous Jurassic sequence of ophiolitic pillow lavas and underlying material in E. Liguria, Italy, the rocks were hydrated, enriched in 18O and oxidised. H2O+ contents increased from ~0.3 to 3.8 wt.%, δ18O values increased from ~ +6‰ to values as high as +13.2‰, and (1) increased from 0.18 to ratios as high as 1.0. Both δ18O values and oxidation ratios decrease in the original direction of increasing depth. Pillow margins are consistently more enriched in 18O and are more oxidised than cores.These observations are qualitatively interpreted in terms of a non-isothermal, heterogeneous reaction model of interaction of basalt with oxygen-bearing sea water during flow through the packed bed of pillows. Fluid flow approximated undirectional downward motion, and occurred in the recharge part of a cycle of single pass convection. Mass transfer through the pile was by flow (infiltration metasomatism), whereas intra-pillow mass transfer was diffusional. Oxygen isotope exchange and oxidation did not occur under conditions of perfect incremental equilibrium. An integrated bulk volumetric water/rock ratio of ~2 × 103:1 is estimated from the oxidation profile. 相似文献
19.
The geochemical history of Lake Lisan, the Pleistocene precursor of the Dead Sea, has been studied by geological, chemical and isotopic methods.Aragonite laminae from the Lisan Formation yielded (equivalent) Sr/Ca ratios in the range 0.5 × 10?2?1 × 10?2, Na/Ca ratios from 3.6 × 10?3 to 9.2 × 10?3, values between 1.5 and 7%. and from ?7.7 to 3.4%..The distribution coefficient of Na+ between aragonite and aqueous solutions, , is experimentally shown to be very sensitive to salinity and nearly temperature independent. Thus, Na/Ca in aragonite serves as a paleosalinity indicator.Sr/Ca ratios and values in aragonite provide good long-term monitors of a lake's evolution. They show Lake Lisan to be well mixed, highly evaporated and saline. Except for a diluted surface layer, the salinity of the lake was half that of the present Dead Sea (15 vs 31%).Lake Lisan evolved from a small, yet deep, hypersaline Dead Sea-like, water body. This initial lake was rapidly filled-up to its highest stand by fresh waters and existed for about 40,000 yr before shrinking back to the present Dead Sea. The chemistry of Lake Lisan at its stable stand represented a material balance between a Jordan-like input, an original large mass of salts and a chemical removal of aragonite. The weighted average depth of Lake Lisan is calculated, on a geochemical basis, to have been at least 400, preferably 600 m.The oxygen isotopic composition of Lake Lisan water, which was higher by at least 3%. than that of the Dead Sea, was probably dictated by a higher rate of evaporation.Na/Ca ratios in aragonite, which correlate well with values, but change frequently in time, reflect the existence of a short lived upper water layer of varying salinity in Lake Lisan. 相似文献
20.
The partitioning of germanium between forsterite (Fo) and liquids in the diopside-anorthiteforsterite join was investigated by electron microprobe analysis of Ge-doped samples equilibrated at 1300°–1450°C. Germanium is somewhat incompatible in Fo relative to the haplobasaltic melts, with a grand mean for all simple partition coefficients (DFo-lGe) of 0.68 ± 0.06. For the melt composition range studied, DFo-lGe is virtually constant in isothermal series of experiments, and shows only minor overall temperature dependence. The exchange reaction partition coefficient ] is near unity in all cases, with a grand mean of 0.93 ± 0.11. One exploratory run at 20 kbar yielded a distinctly lower partition coefficient (DFo-lGe = 0.54 ± 0.04), which confirms the negative pressure dependence predicted by the thermodynamics of Ge ai Si exchange.These new data indicate that absolute Ge enrichment must occur in terrestrial magmas undergoing olivine fractionation, while remains nearly constant. 相似文献