The circumvention of the natural biopurification of calcium along nutrient pathways by atmospheric inputs of industrial lead     

Robert W. Elias  Yoshimitsu Hirao  Clair C. Patterson 《Geochimica et cosmochimica acta》1982,46(12):2561-2580

Biopurification factors for Ca with respect to Sr, Ba, and natural, uncontaminated Pb were measured for different nutrient-consumer pairs in a remote subalpine ecosystem. The factor for Sr is expressed as: (nutrient $\text{Sr}\text{Ca}$) ÷ (consumer $\text{Sr}\text{Ca}$). Similar expressions were used for $\text{Ba}\text{Ca}$ and $\text{Pb}\text{Ca}$. It was found that Ca was biopurified of Sr 3-fold, of Ba 16-fold, and of Pb 100-fold in going from rock to sedge leaves. In going from sedge leaf to vole, Ca was biopurified of Sr 4-fold, of Ba 8-fold, and of Pb 16-fold. In going from meadow vole to pine marten, Ca was biopurified of Sr 6-fold, of Ba 7-fold, and of Pb 1.1-fold. Similar ranges of values for these factors were obtained for detrital and amphibian food chains. Fluxes of industrial lead entering the ecosystem as precipitation and dry deposition were measured and it was found that 40% of the lead in soil humus and soil moisture, 82% of the lead in sedge leaves, 92% of the lead in vole, and 97% of the lead in marten was industrial. The natural skeletal $\text{Pb}\text{Ca}$ ratio in carnivores (4 × 10^?8) was determined by means of corrections for inputs of industrial lead, food chain relationships, and measured biopurification factors for the ecosystem studied. This represents a 1700-fold reduction of the average $\text{Pb}\text{Ca}$ ratio in igneous rocks at the earth's surface (6.4 × 10^?5) by the compounding of successive Pb biopurification factors in transferring Ca from rock to carnivore. The natural ratio is similar to the value of 6 × 10^?8 observed for $\text{Pb}\text{Ca}$ in the bones of Peruvians who lived 2000 years ago but is 1/900th of the value of about 3.5 × 10^?5 for the skeletal $\text{Pb}\text{Ca}$ ratio found in present day Americans.This study shows experimentally how the $\text{Ba}\text{Ca}$ ratio in average surface igneous rock (3 × 10^?3) has been reduced 800-fold through compounding of successive biopurification steps to provide the skeletal $\text{Ba}\text{Ca}$ ratio of about 4 × 10^?6 observed in humans. It also provides biopurification factors for Sr and Ba among a number of nutrient-consumer pairs which anthropologists can use to delineate degrees of herbivory in diets of hominids within the last 10,000 years.  相似文献   

The oxidation state of manganese in marine sediments and ferromanganese nodules     

James W Murray  Laurie S Balistrieri  Barbara Paul 《Geochimica et cosmochimica acta》1984,48(6):1237-1247

Marine sediments and ferromanganese nodules from the Pacific Ocean have been analyzed for the $\text{O}\text{Mn}$ ratio of solid manganese. We tested six chemical methods and concluded that the iodometric and oxalate methods were equivalent and were the best choice in terms of accuracy and precision on natural samples. We choose the iodometric method for most of our analyses because the oxalate procedure is a method of differences.The ferromanganese nodules that we analyzed were all from MANOP site H and had $\text{Mn}\text{Fe}$ ratios that ranged from 5.6 to 70. These nodules were invariably highly oxidized with $\text{O}\text{Mn}$ values ranging from 1.90 to 2.00. Our most precise analyses suggest that less than 1% of the total manganese is present as Mn(II).We also analyzed red clay and hemipelagic sediments from the eastern tropical Pacific (Baja borderland and MANOP site H) and carbonate ooze samples from the equatorial Pacific. These sediments are also highly oxidized ($\text{O}\text{Mn}\text{= 1.90 to 2.00}$) except when Mn(II) appears in the interstitial water. As dissolved Mn(II) increases the value of the $\text{O}\text{Mn}$ ratio in the solid phase decreases. The $\text{O}\text{Mn}$ ratio decreases to values as low as 1.40. This decrease appears to be due to a decrease in oxidized manganese by reduction, however, an increase in reduced manganese in the solid sediments by adsorption or MnCO₃ formation can not be ruled out in all cases.  相似文献   

Geochemical behavior of inorganic germanium in an unperturbed estuary     

Philip N Froelich  Gordon A Hambrick  Lisa W Kaul  James T Byrd  Odile Lecointe 《Geochimica et cosmochimica acta》1985,49(2):519-524

Eleven monthly estuarine profiles of dissolved inorganic germanium (Ge_i) and silica (Si) in a natural, pristine river/bay system demonstrate that Ge-removal and -input parallel the seasonal silica cycle, reflecting Ge-uptake by and -dissolution from diatoms. The Ge/Si atom ratio of the river is 0.6 ± 0.15 × 10^?6, which is near the average value for continental granites and for uncontaminated, remote, natural rivers (0.7 ± 0.3 × 10^?6). The $\text{Ge}\text{Si}$ ratio escaping this estuary to the ocean is 0.8 × 10^?6, reflecting some estuarine enhancement of the fluvial Ge-flux, probably due to release of Ge_i from fluvial particulates. Nevertheless, the post-estuarine $\text{Ge}\text{Si}$ ratio is not significantly different from the continental crustal ratio but is very different from the ratio in sea-floor hot springs and mid-ocean ridge hydrothermal plumes (4 ± 2 × 10^?6) and in oceanic basalts (2.6 × 10^?6). Thus natural estuarine processes do not obscure the contrasting $\text{Ge}\text{Si}$ signatures entering the ocean from dissolution of continental and sea-floor silicates.  相似文献   

Behaviour of strontium in subsurface calcium chloride brines: Southern Israel and Dead Sea rift valley     

E. Sass  A. Starinsky 《Geochimica et cosmochimica acta》1979,43(6):885-895

Calcium chloride brines are, as a rule, relatively rich in strontium, but the enrichment is usually limited and is found to be related to the concentration of calcium. The limiting mechanisms were evaluated as a model which comprises simple interactions between minerals and solutions. Based on the known ranges of strontium concentration in minerals, mineral solubilities and partition coefficients of strontium (both poorly known in certain cases), six fields of $\text{Sr}\text{Ca}$ molar ratios were defined in terms of participating minerals and processes: (a) 0.38?1.56 × 10^{? 3} by dolomitization of calcite; (b) 1.5?2.2 × 10^{? 2} due to dolomitization of aragonite; (c) 0.4?1.4 × 10^{? 2} as a result of solution-reprecipitation of calcite; (d)0.12?0.20 through transformation of aragonite to calcite; (e)0.10?0.60 through equilibrium of the pair calcite-strontianite; and (f)0.01?0.08 by equilibrium with gypsum and celestite.The model was applied to the analysis of two groups of brines from southern Israel which are originated in the coastal plain (group C) and in the rift valley (group R). The low $\text{Mg}\text{Ca}$ ratios of both water groups point to dolomitization as the main subsurface modifying process. $\text{Sr}\text{Ca}$ ratios of brines belonging to group C are consistent with dolomitization of aragonitic surface sediments at the beginning of their evolution. Brines of group R bear evidence to a similar pathway at the beginning of their evolution, but most of them were further affected by interaction with limestone.  相似文献   

Effect of pressure on the diffusivity of network-forming cations in melts of jadeitic compositions     

Ikuo Kushiro 《Geochimica et cosmochimica acta》1983,47(8):1415-1422

The diffusivities of network-forming cations (Si⁴⁺, Al³⁺, Ge⁴⁺ and Ga³⁺) in melts of the jadeitic composition NaAl(Si, Ge)₂O₆ and Na(Al, Ga)Si₂O₆ have been measured at pressures between 6 and 20 kbar at 1400°C. The rates of interdiffusion of Si⁴⁺-Ge⁴⁺ and Al³⁺-Ge³⁺ increase with increasing pressure at constant temperature. The results are consistent with the ion-dynamics computer simulations of Jadeite melt by Angellet al. (1982, 1983). The coefficient measured for the Si⁴⁺-Ge⁴⁺ interdiffusion is between 8 × 10^?10 and 2.5 × 10^?8$\text{cm}{}^2\text{sec}$ at 6 kbar, depending on the composition of the melt, whereas at 20 kbar it is between 7 × 10^?9 and 2 × 10^?7$\text{cm}{}^2\text{sec}$. The effect of pressure is greater for more Si-rich compositions (i.e., closer to NaAlSi₂O₆ composition). The coefficient measured for the Al³⁺-Ga³⁺ inter- diffusion is between 9 × 10^?10 and 3 × 10^?9 cm²/sec at 6 kbar and between 3 × 10^?9 and 1 × 10^?8$\text{cm}{}^2\text{sec}$ at 20 kbar. The rate of increase in diffusivity with pressure of Al³⁺-Ga³⁺ (a factor of 3–4) is smaller than that of Si⁴⁺-Ge⁴⁺ (a factor of 7–17).The Si⁴⁺-Ge⁴⁺ interdiffusion in melts of Na₂O · 4(Si, Ge)O₂ composition has also been measured at 8 and 15 kbar for comparison. The effect of pressure on the diffusivity in this melt is significantly smaller than that for the jadeitic melts. The increase in diffusivity of the network-forming cations in jadeitic melts with increasing pressure may be related to the decrease in viscosity of the same melt. The present results, as well as the ion-dynamics simulations, suggest that the homogenization of partial melts and mixing of magmas would be more efficient at greater depths.  相似文献   

Interstellar organic matter in meteorites     

Jongmann Yang  Samuel Epstein 《Geochimica et cosmochimica acta》1983,47(12):2199-2216

Hydrogen which is highly enriched in deuterium is present in organic matter in a variety of meteorites including non-carbonaceous chondrites. The concentrations of this hydrogen are quite large. For example Renazzo contains 140 μmoles/g of the 10,000‰ δD hydrogen. The $\text{D}\text{H}$ ratios of hydrogen in the organic matter vary from 8 × 10^?5 to 170 × 10^?5 (δD ranges from ? 500‰ to 10,000‰) as compared to 16 × 10^?5 for terrestrial hydrogen and 2 × 10^?5 for cosmic hydrogen. The majority of the unequilibrated primitive meteorites contain hydrogen whose $\text{D}\text{H}$ ratios are greater than 30 × 10^?5. If the $\text{D}\text{H}$ ratios in these compounds were due to enrichment relative to cosmic hydrogen by isotope exchange reactions, it would require that these reactions take place below 150 K. In addition the organic compounds having $\text{D}\text{H}$ ratios above 50 × 10^?5 would require temperatures of formation of < 120 K. These types of deuterium enrichments must take place by ion-molecule reactions in interstellar clouds where both ionization and low temperatures exist. Astronomically observed $\text{D}\text{H}$ ratios in organic compounds in interstellar clouds are typically 180 × 10^?5 and range between about 40 × 10^?5 and 5000 × 10^?5. The $\text{D}\text{H}$ values we have determined are the lower limits for the organic compounds derived from interstellar molecules because all processes subsequent to their formation, including terrestrial contamination, decrease their $\text{D}\text{H}$ ratios.In contrast, the $\text{D}\text{H}$ ratios of hydrogen associated with hydrated silicates are relatively uniform for the meteorites we have analyzed with an average value of 14 × 10^?5; very similar to the terrestrial value. These phyllosilicates values suggest equilibration of H₂O with H₂ in the solar nebula at temperatures of about 200 K and higher.The ${}^{13}\text{C}{}^{12}\text{C}$ ratios of organic matter, irrespective its $\text{D}\text{H}$ ratio, lie well within those observed for the earth. If organic matter originated in the interstellar medium, our data would indicate that the ${}^{13}\text{C}{}^{12}\text{C}$ ratio of interstellar carbon five billion years ago was similar to the present terrestrial value.Our findings suggest that other interstellar material, representing various inputs from various stars, in addition to the organic matter is preserved and is present in the meteorites which contain the high $\text{D}\text{H}$ ratios. We feel that some elements existing in trace quantities which possess isotopic anomalies in the meteorites may very well be such materials.  相似文献   

Concentration of Mn and separation from Fe in sediments—I. Kinetics and stoichiometry of the reaction between birnessite and dissolved Fe(II) at 10°C     

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: $\text{J = km}{}_0\text{(H}{}^{\mathrm{+}}\text{)}{}^{\mathrm{?0.45}}\text{[Fe}{}^{\mathrm{2+}}\text{]}{}^{\mathrm{\gamma }}\text{(}\text{m}\text{m}{}_0\text{)}{}^{\mathrm{\beta }}$ 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   

The Behavior of Mixed Ca–Mn Carbonates in Water and Seawater: Controls of Manganese Concentrations in Marine Porewaters     

Alfonso Mucci 《Aquatic Geochemistry》2004,10(1-2):139-169

The dissolution behavior of natural, ordered kutnahorite (Mn_1.14Ca_0.82Mg_0.04Fe_0.012(CO₃)₂) and a disordered, calcian rhodochrosite (Mn_1.16Ca_0.78Mg_0.06(CO₃)₂) precipitated in the laboratory was investigated in deionized distilled water and artificial seawater in both open and closed systems at 25 °C, one atmosphere total pressure, and various pCO₂s. Both solids dissolved congruently in distilled water in an open system and yielded identical long-term equilibration or extrapolated ion activity products, IAP_pkt = a_Ca ²⁺a_Mn ²⁺(a_{CO 3} ^2?)² = 1.7 (±0.12)× 10^?21 or pIAP_pkt = 20.77 (±0.03). This value is believed to be the thermodynamic solubility product of pseudokutnahorite. In contrast, the steady state ion concentration products, ICP_pkt = [Ca²⁺][Mn²⁺][CO₃ ^2?]², measured following the dissolution of both minerals in artificial seawater increase as the CO₂ partial pressure decreases and the [Mn²⁺]:[Ca²⁺] ratio increases. These observations are interpreted as resulting from the formation of phases of different stoichiometry in response to large variations of the [Mn²⁺]:[Ca²⁺] ratio in solution. These data and results of calcite-seawater equilibration experiments in the presence of various dissolved Mn(II) concentrations define the fields of stability of manganoan calcites and calcian rhodochrosites in seawater within Lippmann phase diagrams for the CaCO₃–MnCO₃–H₂O system. Results of this study reveal that the nature (i.e., mineralogy) and composition of manganese-rich carbonate phases that may form under suboxic/anoxic conditions in marine sediments are dictated by the porewater [Mn²⁺]:[Ca²⁺] ratio, the abundance of calcite surfaces and reaction kinetics.  相似文献   

Deccan traps mantle degassing in the terminal Cretaceous marine extinctions     

Dewey M. McLean 《Cretaceous Research》1985,6(3):235-259

Mantle degassing continually releases gases onto the earth's surface. Over geologically long time intervals, a general equilibrium probably exists between mantle CO₂ release and uptake by surficial sinks. However, during periods of rapid plate movement, or continental flood basalt volcanism, the increased rate of mantle CO₂ release may exceed that of uptake, leading to CO₂ accumulation in the atmosphere and the marine mixed layer (top 50–100 m). This in turn triggers chemical changes in the mixed layer, climatic warming, and bioevolutionary turnover. The Cretaceous/Tertiary ($\text{K}\text{T}$) transition at 65 Ma seems to have been a time of major mantle degassing which induced a perturbation of the carbon cycle. During the $\text{K}\text{T}$ transition, Deccan Traps volcanism, perhaps the greatest episode of continental flood basalt volcanism in the Phanerozoic, flooded an estimated 2.6 × 10⁶ km² of India with basaltic lavas, releasing 5 × 10¹⁷ moles of CO₂ into the earth's atmosphere over a duration 0.53–1.36 Ma at the rate of 3.9 × 10¹¹ to 9.6 × 10¹¹ moles CO₂ per year. The modern mean annual rate of mantle CO₂ release from all sources is 4.1 × 10¹² moles CO₂ per year; assuming a comparable rate of release prior to the Deccan Traps volcanism, the Deccan Traps addition would have elevated the rate of mantle CO₂ release by 10–25%. Sluggish marine circulation and warm, deep, oceans (14–15°C) would have exacerbated CO₂ buildup in the atmosphere, accounting for the Cretaceous to Tertiary drop in oxygen-18 via climatic warming, and, in the marine mixed layer (top 50–100 m), explaining the selective nature of the terminal Cretaceous marine extinctions via a pH change. The extinctions were most severe amongst the calcareous microplankton of the mixed layer; calcareous microplankton (planktonic foraminifera and coccolithophorids) begin to have pH problems at 7.8 and 7.5, respectively. Failure of the coccolithophorids would have disrupted the Williams-Riley pump (algal productivity-gravity pump of CO₂ from the atmosphere and mixed layer into the deep oceans) producing dead ocean conditions (severely reduced photosynthesis and CaCO₃ production). Failure of the Williams-Riley pump is reflected in the extinctions themselves, and in the loss of biogenic CaCO₃ to the sea floor, causing the $\text{K}\text{T}$ boundary hiatus and (or) the $\text{K}\text{T}$ boundary clay. Failure of the pump today would elevate atmospheric pCO₂ severalfold; the $\text{K}\text{T}$ failure would have responded comparably. Dead ocean conditions would, in themselves, have produced a major CO₂ buildup. Early Tertiary “Strangelove” conditions in the mixed layer, characterized by a dominance of the thoracosphaerids, braarudosphaerids and small planktonic foraminifera, were coeval with the main pulse of Deccan Traps volcanism. Overall, the record is one of gradual $\text{K}\text{T}$ bioevolutionary turnover during a period of disequilibrium between the rate of mantle CO₂ degassing and uptake by sinks. Mantle degassing during the Deccan Traps volcanism unifies the $\text{K}\text{T}$ biological and physicochemical records.  相似文献   

Chemical evidence for advection of hydrothermal solutions in the sediments of the Galapagos Mounds Hydrothermal Field     

Cynthia R.P. Maris  Michael L. Bender  Philip N. Froelich  Ross Barnes  Nile A. Luedtke 《Geochimica et cosmochimica acta》1984,48(11):2331-2346

Pore water profiles of Ca, Mg, F, PO₄^?3 and Mn in the Galapagos Mounds Hydrothermal Field are believed to reflect, in part, upwelling of hydrothermal solutions through the sediments. Concentration-depth profiles in a low heat flow area just north of the Mounds Field display diagenetic changes typical of those found in pore waters underlying highly productive surface waters, consistent with the inference of no water flow or very slow downwelling ($\text{w < 5}\text{cm/yr}$) of bottom water through these sediments. Rates of upward advection calculated from Mounds Field pore water profiles of Ca, Mg, and F profiles agree well with each other, averaging about 1 cm/yr in the pelagic sediments near the mounds and 15–30 cm/yr within the hydrothermal mounds themselves. The upward advection also modifies the shape of PO₄^?3 and Mn profiles.Advection rates inferred from the pore water data are generally in reasonable agreement with those made from heat flow data.The higher Ca and lower Mg, F, PO₄^?3 and Mn concentrations in Mounds Field pore waters (compared with those of the low heat flow area) suggest chemical exchange between the solution and basalt prior to upwelling. Li⁺, K⁺, Rb⁺, Sr⁺⁺ and SO₄^? concentrations are indistinguishable from bottom water. This suggests very high effective water/rock ratios during the reactions which produced the upwelling solutions, perhaps due to extensive prior alteration of basalt adjacent to the flow path of water through the crust Inferred reaction temperatures are between 70–150°C.  相似文献   

Thermochemical redox equilibria of ZoBell's solution     

Darrell Kirk Nordstrom 《Geochimica et cosmochimica acta》1977,41(12):1835-1841

The redox potential of ZoBell's solution, consisting of $\text{3.33 × 10}{}^{\mathrm{?3}}$ molar K₄Fe(CN)₆, $\text{3.33 × 10}{}^{\mathrm{?3}}$ molar K₃Fe(CN)₆ and 0.10 molar KCl, has been measured by a polished platinum electrode vs a saturated KCl, Ag/AgCl reference electrode. Measurements in the temperature range 8–85°C fit the equation $\text{E(}\text{volts}\text{) = 0.23145 ? 1.5220 × 10}{}^{\mathrm{?3}}\text{(t ? 25) ? 2.2449 × 10}{}^{\mathrm{?6}}\text{(t ? 25)}{}^2$ where $\text{t}$ is in degrees Celsius. Evaluation of literature data was necessary to obtain a reliable value for the Ag/AgCl half-cell reference potential as a function of temperature. Combining the measurements from this study with the literature evaluation of the Ag/AgCl reference potential yields the temperature dependent potential for ZoBell's solution: $\text{E(}\text{volts}\text{) = 0.43028 ? 2.5157 × 10}{}^{\mathrm{?3}}\text{(t ? 25) ? 3.7979 × 10}{}^{\mathrm{?6}}\text{(t ? 25)}{}^2$ relative to the standard hydrogen potential. From these data the enthalpy, entropy, free energy and heat capacity for the ferro-ferricyanide redox couple have been calculated. The temperature equation for the potential of ZoBell's solution may be used for checking potentiometric equipment in the determination of the redox potential of natural waters.  相似文献   

Precise age determinations and petrogenetic studies using the KCa method     

B.D. Marshall  D.J. DePaolo 《Geochimica et cosmochimica acta》1982,46(12):2537-2545

High precision mass spectrometric determination of calcium isotope ratios allows the ⁴⁰K → ⁴⁰Ca radioactive decay to be used for dating a much broader range of geologic materials than is suggested by previous work. ${}^{40}\text{Ca}{}^{42}\text{Ca}$ is used to monitor enrichments in ⁴⁰Ca and can be measured to ±0.01% (2σ) using an exponential mass discrimination correction (Russell et al., 1978) and large ion currents. The earth's mantle has such a low $\text{K}\text{Ca}$ (～0.01) that it has retained “primordial” ${}^{40}\text{Ca}{}^{42}\text{Ca}\text{= 151.016}$ ± 0.011 (normalized to ${}^{42}\text{Ca}{}^{44}\text{Ca}\text{= 0.31221}$), as determined by measurements on two meteorites, pyroxene from an ultramafic nodule, metabasalt, and carbonatite. ${}^{40}\text{Ca}{}^{42}\text{Ca}$ ratios can be conveniently expressed relative to this value as ?_Ca in units of 10^?4. To test the method for age dating, a mineral isochron has been obtained on a sample of Pikes Peak granite, which has been shown to have concordant KAr, RbSr, and UPb ages. Plagioclase, K-feldspar, biotite, and whole rock yield an age of 1041 ± 32 m.y. (2σ) in agreement with previous age determinations (λ_K = 0.5543 b.y.^?1, $\text{λ}{}_{\mathrm{\beta ?}}\text{λ}{}_{\mathrm{<mtext>K</mtext>}}\text{= 0.8952}$, ⁴⁰K = 0.01167%). The initial ${}^{40}\text{Ca}{}^{42}\text{Ca}$ of 151.024 ± 0.016 (?_Ca = +0.5 ± 1.0), indicates that assimilation of high K/Ca crust was insufficient to affect calcium isotopes. Measurements on two-mica granite from eastern Nevada indicate that the magma sources had K/Ca ≈ 1, similar to intermediate-composition crustal rocks. These results show that the KCa system can be used as a precise geochromometer for common felsic igneous and metamorphic rocks, and may prove applicable to sedimentary rocks containing authigenic K minerals. The relatively short half-life of ⁴⁰K, the non-volatile daughter, and the fact that potassium and calcium are stoichiometric constituents of many minerals, make the KCa system complementary to other dating methods, and potentially applicable to a variety of geologic problems.  相似文献   

Carbon content and carbonate ¹³C abundances in the Early Precambrian Swaziland sediments of South Africa     

Bartholomew Nagy  Steven M. Kunen  John E. Zumberge  Austin Long  Carleton B. Moore  Charles F. Lewis  Carl R. Anhaeusser  Desmond A. Pretorius 《Precambrian Research》1974,1(1):43-48

Carbon content (0.02–0.68% organic), carbonate content (0–69.7%) and carbonate ¹³C abundances (${}^{\mathrm{?}}\text{7.5?+2.3‰}$) were obtained on samples from the Swaziland sediments of South Africa, which are among the oldest known sedimentary rocks on earth (> 3·10⁹ years old). The carbon chemistry of these sediments may serve as evidence for early life and/or for products of chemical evolution. The variation of organic and carbonate carbon concentrations in different sedimentary horizons seems to be controlled by differences in depositional and diagenetic histories. The carbonate δ ¹³C values did not vary significantly from the ordinary range of Phanerozoic limestone values.  相似文献   

Kinetic and thermodynamic factors controlling the distribution of SO₃²⁻ and Na⁺ in calcites and selected aragonites     

Eurybiades Busenberg  L. Niel Plummer 《Geochimica et cosmochimica acta》1985,49(3):713-725

Significant amounts of SO₄^2?, Na⁺, and OH^? are incorporated in marine biogenic calcites. Biogenic high Mg-calcites average about 1 mole percent SO₄^2?. Aragonites and most biogenic low Mg-calcites contain significant amounts of Na⁺, but very low concentrations of SO₄^2?. The SO₄^2? content of non-biogenic calcites and aragonites investigated was below 100 ppm. The presence of Na⁺ and SO₄^2? increases the unit cell size of calcites. The solid-solutions show a solubility minimum at about 0.5 mole percent SO₄^2? beyond which the solubility rapidly increases. The solubility product of calcites containing 3 mole percent SO₄^2? is the same as that of aragonite. Na⁺ appears to have very little effect on the solubility product of calcites. The amounts of Na⁺ and SO₄^2? incorporated in calcites vary as a function of the rate of crystal growth. The variation of the distribution coefficient ($\text{D}$) of SO₄^2? in calcite at 25.0°C and 0.50 molal NaCl is described by the equation $\text{D = k}{}_0\text{+ k}{}_1\text{R}$ where $\text{k}{}_0$ and $\text{k}{}_1$ are constants equal to $\text{6.16 × 10}{}^{\mathrm{?6}}$ and $\text{3.941 × 10}{}^{\mathrm{?6}}$, respectively, and $\text{R}$ is the rate of crystal growth of calcite in mg·min^?1·g^?1 of seed. The data on Na⁺ are consistent with the hypothesis that a significant amount of Na⁺ occupies interstitial positions in the calcite structure. The distribution of Na⁺ follows a Freundlich isotherm and not the Berthelot-Nernst distribution law. The numerical value of the Na⁺ distribution coefficient in calcite is probably dependent on the number of defects in the calcite structure. The Na⁺ contents of calcites are not very accurate indicators of environmental salinities.  相似文献   

A fundamental equation for calcite dissolution kinetics   总被引：1，自引：0，他引：1  

E.L. Sjöberg 《Geochimica et cosmochimica acta》1976,40(4):441-447

A fundamental rate equation for the dissolution of calcite in a pure 0.7 M KC1 solution has been determined. Between pH 8.0 and 10.1 the kinetics of the dissolution reaction can be expressed by the equation , where d[Ca²⁺]/dt is the rate in mole cm^?3s^?1, k is the apparent rate constant in s^?1 cm^?2, A is the calcite surface area and C is the square root of the calcite solubility constant. The apparent rate constant at 20°C is 9.5 × 10^?6s^?1cm^?2. The apparent activation energy for the reaction between 5 and 50°C is 8.4 kcal mole^?1.The reaction rate is pH independent above pH = 7.5. At pH values less than 8, [CO₃^2?] becomes negligible, and the rate becomes fast and should be dependent on the calcite surface area alone, if there is no change in mechanism.The stirring coefficient between 2.8 and 11.1 rev s^?1 is 0.33. This, together with the relatively high activation energy, indicates that the reaction is mainly chemically controlled.Interpolation of the experimental results into seawater systems gives a computed rate several magnitudes greater than the observed rate, but considerably less than that calculated for a diffusion-controlled reaction.  相似文献   

Experimental paleotemperature equation for planktonic foraminifera     

Jonathan Erez  Boaz Luz 《Geochimica et cosmochimica acta》1983,47(6):1025-1031

Small live individuals of Globigerinoides sacculifer which were cultured in the laboratory reached maturity and produced garnets. Fifty to ninety percent of their skeleton weight was deposited under controlled water temperature (14° to 30°C) and water isotopic composition, and a correction was made to account for the isotopic composition of the original skeleton using control groups.Comparison of. the actual growth temperatures with the calculated temperature based on paleotemperature equations for inorganic CaCO₃ indicate that the foraminifera precipitate their CaCO₃ in isotopic equilibrium. Comparison with equations developed for biogenic calcite give a similarly good fit. Linear regression with Craig's (1965) equation yields: $\text{t = ?0.07 + 1.01}\text{t}\text{?}\text{(r= 0.95)}$ where t is the actual growth temperature and $\text{t}\text{?}$ Is the calculated paleotemperature. The intercept and the slope of this linear equation show that the familiar paleotemperature equation developed originally for mollusca carbonate, is equally applicable for the planktonic foraminifer G. sacculifer.Second order regression of the culture temperature and the delta difference (δ¹⁸Oc ? δ¹⁸Ow) yield a correlation coefficient of r = 0.95: $\text{t}\text{?}\text{= 17.0 ? 4.52(δ}{}^{18}\text{Oc ? δ}{}^{18}\text{Ow) + 0.03(δ}{}^{18}\text{Oc ? δ}{}^{18}\text{Ow)}{}^2$$\text{t}\text{?}\text{, δ}{}^{18}\text{Oc}$ and δ¹⁸Ow are the estimated temperature, the isotopic composition of the shell carbonate and the sea water respectively.A possible cause for nonequilibnum isotopic compositions reported earlier for living planktonic foraminifera is the improper combustion of the organic matter.  相似文献   

Diffusivity of oxygen in jadeite and diopside melts at high pressures     

N. Shimizu  I. Kushiro 《Geochimica et cosmochimica acta》1984,48(6):1295-1303

The diffusivity of oxygen was determined in melts of Jadeite (NaAlSi₂O₆) and diopside (CaMgSi₂O₆) compositions using diffusion couples with ¹⁸O as a tracer. In the Jadeite melt, the diffusivity of oxygen increases from $\text{6.87}{}_{\mathrm{?0.25}}{}^{\mathrm{+0.28}}\text{× 10}{}^{\mathrm{?10}}\text{cm}{}^2\text{/}\text{sec}$ at 5 Kb to $\text{1.32 ± 0.08 × 10}{}^{\mathrm{?9}}\text{cm}{}^2\text{/}\text{sec}$ at 20 Kb at constant temperature (1400°C), whereas in the diopside melt at 1650°C, the diffusivity decreases from $\text{7.30}{}_{\mathrm{?0.18}}{}^{0.29}\text{× 10}{}^{\mathrm{?7}}\text{cm}{}^2\text{/}\text{sec}$ at 10 Kb to $\text{5.28}{}_{\mathrm{?0.55}}{}^{\mathrm{+0.60}}\text{× 10}{}^{\mathrm{?7}}\text{cm}{}^2\text{/}\text{sec}$ at 17 Kb. These results demonstrate that the diffusivity is inversely correlated with the viscosity of the melt. For the jadeite melt, in particular, the inverse correlation is very well approximated by the Eyring equation using the diameter of oxygen ions as a unit distance of translation, suggesting that the viscous flow is rate-limited by the diffusion of individual oxygen ions. In the diopside melt, the activation volume is slightly greater than the molar volume of oxygen ion, indicating that the individual oxygen ion is the diffusion unit. The negative activation volume obtained for the jadeite melt is interpreted as the volume decrease associated with a diffusive jump of an oxygen ion due to local collapse of the network structure.  相似文献   

Ferromanganese oxide deposits from the Central Pacific Ocean,I. Encrustations from the Line Islands Archipelago     

Andrew C Aplin  David S Cronan 《Geochimica et cosmochimica acta》1985,49(2):427-436

Chemical and mineralogical analyses of a well-controlled suite of ferromanganese encrustations from the Line Islands Archipelago (Central Pacific) suggest that they represent purely hydrogenous deposits—i.e. they have formed through the slow accumulation of trace metal-enriched oxides directly from the water-column. Mineralogically they consist predominantly of δMnO₂ and amorphous FeOOHxH₂O. Compositionally, they are similar to δMnO₂ nodules from adjoining basinal areas but are enriched in both Mn (mean = 20.4%, max = 29.3%) and Co (mean = 0.55%, max = 1.57%). δMnO₂ is the most important trace metal bearing phase; strong associations are noted between it and Co, Mo, Ni, Zn, and Cd, whilst only Be is associated specifically with FeOOH. V, Sr and Pb are partitioned between the authigenic oxide phases, whilst Ti most probably occurs as TiO₂xH₂O. Cu is contained in both aluminosilicate contaminant phases and Fe oxide phases. These relations are considered to reflect the differing scavenging behaviour of Mn and Fe oxides in the water column.Crusts from ~1–2 km are enriched in Mn and the Mn-related elements and exhibit higher $\text{Mn}\text{Fe}$ ratios than deeper crusts, which are compositionally constant. The higher $\text{Mn}\text{Fe}$ ratios may result from a supply of Mn from continental borderland sediments at these depths, which is transported horizontally by advective-diffusive processes. Since manganophile elements are enriched relative to Mn in the 1–2 km crusts, it is considered that the supply of Mn is scavenged by existing oxides, is oxidised and effectively occludes them. A higher proportion of oxide particles thus exhibit Mn oxide scavenging properties in the 1–2 km depth zone. The increased vertical flux of Mn resulting from the supply at ~1–2 km is not reflected by higher $\text{Mn}\text{Fe}$ ratios in deeper crusts, so that the vertical flux of oxides is not simply related to the standing crop. The $\text{Mn}\text{Fe}$ ratios of the crusts thus reflect the composition of suspended oxides at similar depths.  相似文献   

Gibbsite solubility and thermodynamic properties of hydroxy-aluminum ions in aqueous solution at 25°C     

Howard M. May  Philip A. Helmke  Marion L. Jackson 《Geochimica et cosmochimica acta》1979,43(6):861-868

Solubility curves were determined for a synthetic gibbsite and a natural gibbsite (Minas Gerais, Brazil) from pH 4 to 9, in 0.2% gibbsite suspensions in 0.01 M NaNO₃ that were buffered by low concentrations of non-complexing buffer agents. Equilibrium solubility was approached from oversaturation (in suspensions spiked with Al(NO₃)₃ solution), and also from undersaturation in some synthetic gibbsite suspensions. Mononuclear Al ion concentrations and pH values were periodically determined. Within 1 month or less, data from over-and undersaturated suspensions of synthetic gibbsite converged to describe an equilibrium solubility curve. A downward shift of the solubility curve, beginning at pH 6.7, indicates that a phase more stable than gibbsite controls Al solubility in alkaline systems. Extrapolation of the initial portion of the high-pH side of the synthetic gibbsite solubility curve provides the first unified equilibrium experimental model of Al ion speciation in waters from pH 4 to 9.The significant mononuclear ion species at equilibrium with gibbsite are Al³⁺, AlOH²⁺, Al(OH)⁺₂ and Al(OH)^?₄, and their ion activity products are $\text{1K}{}_{50}\text{= 1.29 × 10}{}^8$, $\text{1K}{}_{\mathrm{s1}}\text{= 1.33 × 10}{}^3$, $\text{1K}{}_{\mathrm{s2}}\text{= 9.49 × 10}{}^{\mathrm{?3}}$ and $\text{1K}{}_{\mathrm{s4}}\text{= 8.94 × 10}{}^{\mathrm{?15}}$. The calculated standard Gibbs free energies of formation (ΔG°_f) for the synthetic gibbsite and the A1OH²⁺, Al(OH)⁺₂ and Al(OH)^?₄ ions are ?276.0, ?166.9, ?216.5 and ?313.5 kcal mol^?1, respectively. These ΔG°_f values are based on the recently revised ΔG°_f value for Al³⁺ (?117.0 ± 0.3 kcal mol_?1) and carry the same uncertainty. The ΔG°_f of the natural gibbsite is ?275.1 ± 0.4 kcal mol^?, which suggests that a range of ΔG°_f values can exist even for relatively simple natural minerals.  相似文献   

Determination of the ⁸⁷Rb decay constant     

D.W. Davis  J. Gray  G.l. Gumming  H. Baadsgaard 《Geochimica et cosmochimica acta》1977,41(12):1745-1749

The decay constant ⁸⁷Rb has been redetermined by measuring the amount of radiogenic ⁸⁷Sr produced over a period of 19 years, in 20 g samples of purified RbClO₄, using isotope dilution techniques. The rubidium sample was spiked with ⁸⁴Sr and the nanogram quantities of strontium separated by coprecipitation with Ba(NO₃)₂. Analyses were carried out on a 25cm, 90° sector mass spectrometer equipped with a Spiraltron electron multiplier. Measurement of three independent ratios permitted continuous monitoring of the ion beam fractionation. The average of nine determinations gives a value for the decay constant of $\text{1.419(±0.012) × 10}{}^{\mathrm{?11}}\text{yr}{}^{\mathrm{?1}}\text{(2σ)}$. [$\text{τ}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 4.89(±0.04) × 10}{}^{10}\text{yr}$.]  相似文献