Iron oxide from a seasonally anoxic lake

The ferric oxide formed by oxidation of Fe(II) in Esthwaite Water, U.K., during the lake's seasonal thermal stratification and deep-water anoxia consists of amorphous particles which are approximately spherical or ellipsoidal, with diameters in the range 0.05–0.5 μm. Concentrations in the lake are 10¹¹–10¹² particles per litre, corresponding to 3 mg l^?1 Fe. Unlike iron oxides of similar chemical composition formed by oxidative mechanisms in soil-borne waters, the particles do not appear to be composed of small primary particles. This is possibly because in the lake they form slowly, at low supersaturation. The particles contain 30–40% by weight Fe. The carbon content is uncertain because of contamination but is in the range 4–18%. Humic carbon contributes at least 4–7% of the total weight. Other major elements present are P, N, Mn, Si, S. Ca and Mg, comprising between them up to 8% of the total weight.The particles are negatively charged probably because of adsorbed humic substances, and also phosphate and silicate. Their electrophoretic mobility-pH dependence is similar to those of synthetic iron oxides added to samples of surface Esthwaite Water. The calculated zeta potential is ? 27 mV, which is sufficiently high to make flocculation slow under lake conditions. The low flocculation rate partially accounts for the formation of a well-defined peak of particulate iron in the water column of the lake.     

Mixing rates in Shagawa Lake,Minnesota, sediments as determined from 106Ru profiles

Rates of surficial sediment mixing and sediment burial are measured in Shagawa Lake, Minnesota, using radionuclide tracers. Based on ¹⁰⁶Ru profiles in 16 cores, mixing rates average 13 cm²/yr within the upper 9 cm of sediment. Two other nuclides, ²¹⁰Pb and ¹³⁷Cs, provide further evidence for calculation of mixing rates. In addition, ²¹⁰Pb profiles estimate sediment burial rates (about 0.4 cm/yr). Mixing estimates are shown to be fairly insensitive both to uncertainties in sediment burial rates and to temporal patterns of ¹⁰⁶Ru deposition.     

Thermal metamorphism of primitive meteorites—IX. On the mechanism of trace element loss from Allende heated up to 1400° C

We report data for Ag, Bi, Cd, Co, Cs, Ga, In, Se, Te, Tl and Zn determined by neutron activation in Allende samples heated for one week at 100° increments in the 1000–1400°C range in a low pressure (initially 10^?5atmH₂) environment using an apparatus of novel design. In the extremes, concentrations of these trace elements—initially present at ppm-ppb levels—in unheated material are lowered even farther by factors of 10^?4–10^?5 over a broad temperature span. Loss of some elements above 1000°C extends trends evident below 1000°C; loss of others is even more extreme. On Arrhenius diagrams some elements exhibit but one apparent activation energy over the entire temperature span of loss while others exhibit 2 or 3, each operative in a particular temperature region. These discontinuities seem related to mineralogic/petrologic alteration and probably reflect differences in diffusion mechanism rather than siting differences. The extension of previous experiments into the temperature regime postulated for chondritic differentiation should lead to a better understanding of the evolution of meteoritic parent bodies.     

Polycyclic aromatic hydrocarbons in an anoxic sediment core from the Pettaquamscutt River (Rhode Island,U.S.A.)

Fifteen sections from an anoxic sediment core were analyzed for polycyclic aromatic hydrocarbons (PAH). Two types of PAH were observed: (a) those from combustion sources such as pyrene and chrysene and (b) those from natural sources such as retene and perylene. The combustion PAH levels in core sections dated between 1900 and 1970 were much higher than in earlier sections; this indicated an anthropogenic origin of these PAH at this location. The perylene and retene core profiles show significant anomalies during the period 1850–1880. Organic carbon does not fluctuate markedly but δC-13 of organic carbon shows several unexplained excursions; one of which correlates with the perylene and retene anomalies.     

Terpenoid marker compounds derived from biogenic precursors in volcanic ash from Mount St. Helens,Washington

A volcanic-ash sample obtained after the 1980 eruption of Mount St. Helens, Washington, was analyzed for cyclic terpenoid organic compounds and polycyclic aromatic hydrocarbons using capillary gas chromatography-mass spectrometry-computer techniques. Various tricyclic diterpenoid acids and hydrocarbons were identified including dehydroabietic acid, dehydroabietin, dehydroabietane, simonellite, and retene. Preliminary evidence indicates that these compounds were derived from forest soils or atmospheric aerosols or both in the vicinity of coniferous forests. A diagenetic scheme involving three possible pathways for the conversion of abietic acid to retene is presented.     

SrCa and MgCa ratios in polygenetic carbonate allochems from a Michigan marl lake

Rapid accumulation of CaCO₃ is occurring in Littlefield Lake, a marl lake located in central Michigan. The sediment, which is 95% CaCO₃, primarily consists of eight different genetic groups of carbonate allochems. These include calcite muds, sands, algal oncoids and Chara encrustations, as well as the dominant aragonitic gastropods Valvota tricarinota. Gyraulus deflectus and Amnicola integra. and the dominant aragonitic pelecypod Sphaerium partumeium. Samples of each of these groups were analyzed for Ca, Sr and Mg. Molar $\text{Mg}\text{Ca}$ ratios are primarily controlled by allochem mineralogy, with calcitic forms having $\text{Mg}\text{Ca}$ ratios 5–10 times larger than aragonitic (shelled) forms. The $\text{Sr}\text{Ca}$ ratios are primarily controlled by biochemical fractionation, and are significantly lower than $\text{Sr}\text{Ca}$ ratios of inorganically precipitated aragonite from other settings. Partition coefficients were determined for both Sr and Mg for each carbonate allochem group and, based on comparisons with results reported by other workers, the partition coefficients determined here are generally considered ‘typical’ or representative values for biogeneous freshwater carbonates. An analysis of variance of the data indicates that most genera and species of carbonate-secreting organisms in marl lakes have highly characteristic $\text{Sr}\text{Ca}$ and $\text{Mg}\text{Ca}$ ratios. These ratios can potentially serve as geochemical tracers in future investigations of lacustrine carbonate diagenesis. Both Sr and Mg are influenced by grain size and/or surface area, probably due to the presence of these elements in non-lattice-held (exchangeable) positions.     

Thermal metamorphism of primitive meteorites—XL The enstatite meteorites: origin and evolution of a parent body

We report neutron activation data for Ag, As, Bi, Cd, Co, Cs, Cu, Ga, In, Rb, Se, Te, Tl and Zn in samples of Abee heated at temperatures of 1000–1400°C in a low-pressure environment (initially ~ 10^?5 atm H₂) and in 9 enstatite achondrites (aubrites) and the silicate portion of the unique stony-iron, Mt Egerton. Trace element losses in heated Abee progress with temperature, the lowest retention being 2.4 × 10^?6 of initial contents. These data indicate trace element loss above 1000°C via diffusion-controlled processes having apparent activation energies of 8–55 kcal/mol ; only Co exhibits a significantly higher energy. These trace element data and those for aubrites, Mt Egerton and E4–6 chondrites, and mineralogic and isotopic evidence link all enstatite meteorites to a common parent body. Volatile, mobile elements vary inversely with cobalt content in aubrites and Mt Egerton but directly in E4–6 chondrites; this is inconsistent with all genetic models positing fractionation of such elements during nebular condensation and accretion. However, the data are consistent with the idea that aubrites and Mt. Egerton reflect fractional crystallization of a magma produced from enstatite chondrite-like parent material (probably E6) and late introduction of chalcophiles and mobile elements transported by FeS-Fe eutectic from an E4–6 region experiencing open-system metamorphism. As suggested earlier, the only primary process that affected enstatite meteorites involved fractionation of non-volatile lithophiles from sulfides and metal during condensation and accretion of chondritic parent material from the nebula. If, as seems likely, volatile/mobile elements reflect secondary processes, they can only be used to establish alteration conditions within the enstatite parent body and not to estimate temperatures during primary nebular condensation and accretion.     

Stable carbon isotope ratios in Astrangia danae: evidence for algal modification of carbon pools used in calcification

Stable carbon isotope ratios have been measured in skeletons of the temperature shallow water scleractinian coral, Astrangia danae. δ¹³C values ranging from ?5.42 to ?7.30%. revealed the expected depletion of ¹³C in skeletal carbonate relative to sea water bicarbonate. Differences among the ratios could not be attributed to collection site and were not correlated to skeletal morphology. Values of δ¹³C were directly related to zooxanthellae density for all colonies, so that as zooxanthellae concentration increased, δ¹³C valued increased. Colonies maintained under high temperature conditions were offset from the normal, exhibiting ratios less enriched in ¹³C than similar colonies from natural conditions. These trends supported the models of Weber and Goreau in which the carbon pools used in calcification are modified by algal photosynthesis. Direct evidence of physiological differences between symbiotic and asymbiotic colonies of A. danae has also been provided.     

Thermal metamorphism of primitive meteorites—III. Ten trace elements in Krymka L3 chondrite heated at 400–1000°C

Ten trace elements were determined by neutron activation analysis in Krymka (L3) chondrite samples heated for 1 week, at 100°C increments, from 400 to 1000°C in a low-pressure environment (initially 10^?5 atm H₂). As in other samples studied. Co seems unaffected by heating; ~50% of Cs and Ga are lost only at 1000°C and losses of other elements increase with temperature to extremes of ～ 25% for Se and 95–99% for Ag, Bi, In, Te, T1 and Zn. Where comparison is possible, ‘open-system’ losses are generally in the order Krymka (L3) > Abee (E4) > Allende (C3). Treating elemental mobilization as representing a kinetic process involving diffusion from spherical grains of uniform size Ag, Bi, In, Te, Tl and Zn are lost from a single host phase or by a single process. This differs from trends shown by many of these elements in Abee and Allende and terrestrial basalt BCR-1. Loss of Tl apparently involves a process with a low activation energy, perhaps desorption. Loss of other elements apparently reflects diffusion-controlled process(es).Trace element contents, patterns of statistically significant interelement relationships, factor analysis and two-element correlation diagrams for unheated and heated Krymka and ‘as-received’ L3-6 chondrites are very different. Thus, significant open-system metamorphism during the genesis of L-group chondrites are not supported by these data. This contrasts sharply with the picture for enstatite chondrites, indicating substantial differences in the origin of various chondritic groups.     

Trace elements in primitive meteorites—V. Abundance patterns of thirteen trace elements and interelement relationships in enstatite chondrites

Neutron activation analysis was used to determine As, Au, Bi, Cd, Co, Cu, Ga, In, Sb, Se, Te, Tl and Zn in 11 samples representing 9 chondrites of grades E4–6. These chondrites exhibit systematic intra- and inter-grade differences particularly for highly-variable elements, the differences being E4 ? E3 > E6 ? E5. The abundance pattern for these 13 and an additional 16 elements in E3-6 chondrites differs from those of other primitive meteorites—the carbonaceous and unequilibrated ordinary chondrites. A search for statistically-significant interelement relationships among the 13 elements (for grades E4–6) reveal that 40 elementpairs are linearly and/or exponentially correlated. Similar consideration of data for 37 elements in 12 chondrites (grades E3–6) reveals that 191 element-pairs exhibit such relationships, 170 involving linear and/or exponential correlations, the remainder involving anti-correlations. The patterns depicting these relationships—i.e. the correlation profiles—and elemental abundance patterns, factor analysis and two-element correlation diagrams are consistent with all enstatite chondrites representing a single evolutionary sequence. The primary process responsible for the chemical trends of these chondrites involved thermal fractionation accompanied by geochemical fractionation of sulfide-plus-metal from silicate, probably during condensation and accretion of solid material from the solar nebula. Chalcophile elements may have been fractionated during condensation or, after accretion, during thermal metamorphism in the parent body. No genetic model proposed thus far accounts for the detailed chemical trends, although the constrained equilibrium theory and two-component condensation theories qualitatively seem most satisfactory. The correlation profiles of enstatite, carbonaceous and unequilibrated ordinary chondrites are distinctly different, pointing to major differences in the formation conditions of these different sorts of primitive meteorites.     

Microbial lipids of an intertidal sediment—I. Fatty acids and hydrocarbons

A detailed study has been made of the solvent extractable monocarboxylic, dicarboxylic and hydroxylated fatty acids and n-alkanes in a surface intertidal sediment, and the distributions compared to microorganisms cultured from the sediment. Diatoms are shown to contribute most of the monocarboxylic acids, particularly the significant amounts of polyunsaturated acids present, and a small proportion of the n-alkanes. Bacteria contribute between 11 and 14% of the monocarboxylic acids and markers for this, including trans-monounsaturated acids, are proposed. Detritus from the sea-grass Zostera muelleri is a major source of the α-hydroxy-, ω-hydroxy and α,ω-dicarboxylic acids in the sediment and a minor contributor of n-alkanes and long-chain fatty acids.     

GC-MS characterisation of C27 and C28 triterpanes in sediments and petroleum

Earlier studies have shown that an unusual C₂₇ triterpane is abundant in sediments from the Norwegian Continental Shelf and the North Sea. This compound was assigned the tentative structures 24,28,30-trisnormoretane or 25,28,30-trisnormoretane, but we have now shown from detailed retention time measurements and a reinterpretation of the mass spectral data that its correct structure is 17α(H),18α (H),21β(H)-25,28,30-trisnorhopane. Two other triterpanes, 25,28,30-trisnormoretane and 28,30-bisnormoretane, have also been identified as minor constituents of extracts of sediments from the North Sea. Possible origins for these compounds are discussed.     

On volatile element trends in gas-rich meteorites

Study of 10 volatile elements (and non-volatile Co) in co-existing light and dark portions of 5 gas-rich chondrites indicates patterns of distinct but non-uniform enrichment of volatile elements. Only Cs is enriched in all samples; Hi and Tl enrichments covary. The observed enrichments are inconsistent with prior suggestions of admixture of C1 or C2 chondritic matter, whether pristine or partly devolatilized, but suggest that both light and dark portions of each chondrite represents a compositionally more extended sampling of parental nebular material than hitherto known.     

Trace elements in primitive meteorites—VI. Abundance patterns of thirteen trace elements and interelement relationships in unequilibrated ordinary chondrites

Neutron activation analysis was used to determine As, Au, Bi, Cd, Co, Cu, Ga, In, Sb, Se, Te, Tl and Zn in 13 different unequilibrated ordinary chondrites (UOC), i.e. those having chemicallyinhomogeneous silicates. This study together with prior data completes our coverage of this group of 23 primitive chondrites. Four elements are quite variable in UOC (Cd—20 x, In—30 x, Bi—300 x and Tl—1300 x), the others varying by 2–8 x. Three highly-depleted elements—Bi, In and Tl—are richer by 5–35 x in unequilibrated chondrites than in their equilibrated congeners. All 3 elements vary directly in characteristic fashion with disequilibrium parameters for olivine and pyroxene in UOC and generally with petrologic type 3 > 4 > 5 > 6. The data do not provide unambiguous evidence for nebular fractionation of siderophile elements. Examination of statistically-significant interelement relationships among various ordinary chondrite populations involving 34 elements reveals patterns distinct from those of other chondritic groups. These patterns reflect nebular metal-silicate fractionation which preceded or accompanied thermal fractionation. The results point to significant differences in the formation of primitive carbonaceous, enstatite and ordinary chondrites.     

Thermal metamorphism of primitive meteorites—X. Additional trace elements in Allende (C3V) heated to 1400° C

We report data for Ag, As, Cd, Cs, Co, Cu, Rb, Sb, Te, Tl and Zn in Allende samples subjected to week-long heating at 400–1400°C in a low-pressure H₂ environment. Temperatures of incipient release for these 11 and 5 additional elements tend to be ordered in a manner similar to postulated condensation sequences during cooling of nebular material but there are differences. Losses progress with temperature but neither the extent of loss nor apparent activation energies for mobilization would have been predictable to even a zeroth order approximation. Elemental retentivity trends and interelement correlation patterns for Allende (C3V) and Murchison (C2) differ markedly indicating a substantially different trace element siting, hence loss trends for these two chondrites.     

Stable hydrogen isotopes in iron oxides—II. DH variations among natural goethites

Goethite samples analyzed for this study have a δD range from ?202 to ?98 per mil with a corresponding δD range of associated waters from about ?110 to +7 per mil. Goethites with the most positive δD values are from marine environments. Goethite-water equilibrium $\text{D}\text{H}$ fractionation factors measured in this laboratory at 100°C and 145°C and estimated for sedimentary temperatures from data on natural samples have values of about 0.900 at all three temperatures. These data suggest that goethite δD values may be a direct, temperature-independent measure of the δD values of the waters with which the goethite last equilibrated. Most of the goethite δD values in this study reflect the δD values of the modern waters in the locales of origin.Substitution of Mn and/or Al for Fe in the goethite structure may affect the mineral-water fractionation factor. Manganese appears to decrease the value of α. The effect of Al substitution on α has not yet been measured, but preliminary arguments suggest that increasing Al content could increase α values.     

Evaluation of alkaline permanganate oxidation method for the characterization of young kerogen

Alkaline potassium permanganate oxidation of a young kerogen (lacustrine) and 34 model compounds (saturated and unsaturated fatty acids, hydroxy acid, aliphatic dicarboxylic acids, aliphatic alcohols, normal hydrocarbon, β-carotene, phenolic acids, benzenecarboxylic acids, carbohydrates, amino acids and proteins) were conducted, followed by GC and GC-MS analysis of the degradation products. The stability of the degradation products of kerogen in permanganate solution and the relationship between degradation products and kerogen building blocks were determined.The results showed that aliphatic acids C₁₂–C₁₆ monocarboxylic acids and C₆–C₁₀ α,ω-dicarboxylic acids) were rather susceptible to oxidation compared with benzenecarboxylic acids and the former were degraded into lower molecular weight decarboxylic acids. It was concluded that oxidation at milder conditions (60° C, 1 hr) is appropriate for qualitative and quantitative characterization of the aliphatic structure of young kerogen. It was noteworthy that benzoic acid was produced in a significant amount by oxidation of amino acids (phenylalanine) and proteins, C₁₈-isoprenoidal ketone from phytol, and C₈ and C₉ α,ω-dicarboxylic acids from unsaturated fatty acids, respectively; furthermore, 2,2-dimethyl succinic and 2,2-dimethyl glutaric acids were produced from β-carotene.     

Sulphur isotope effects in the high temperature oxidation of troilite

Troilite oxidation in air at 1200°C gives sulphur dioxide which is slightly enriched (~0.3%.) in ³⁴S. No systematic variations were seen of the isotopic compositions of product sulphur dioxide or residual troilite with extent of conversion. We speculate that the oxidation reaction takes place at the surface of the molten troilite in such a way as to inhibit mixing between the reacting outer layers and the unreacted liquid substrate so that Rayleigh behaviour with extent of reaction is not observed.     

Surface study of HF- and HFH2SO4-treated feldspar using Auger electron spectroscopy

Auger electron spectroscopy has been used to study K-feldspar that has been reacted with both aqueous 10% HF and a 50% mixture of a 10% HF/0.1 N H₂SO₄ solution. In the feldspar/HF system, the resulting feldspar surface was shown to have been fluorinated; depth profiling, using argon ion sputtering, showed the fluorination to have occurred substantially into the mineral bulk. In the feldspar/ $\text{HF}\text{H}{}_2\text{SO}{}_4$ system, the resulting surface contained both fluorine and sulfur. The fluorination had again penetrated into the bulk, but the sulfur could be removed with mild argon ion sputtering. The $\text{Al}\text{F}$ signal ratio was much lower on the feldspar surface treated with the 10% HF/0.1 N H₂SO₄ solution than the feldspar surface treated with the weaker 10% HF acid solution.