Effects of age on the chemical structure of paleosol humic acids and fulvic acids

Humic acids and fulvic acids were extracted from six paleosols in Southern Italy. Humic acids (HAs) constituted between 96.5 and 99.2% of the total extracts; the remaining materials consisted of fulvic acids (FAs). Radiocarbon ages of the HAs ranged from about 6,000 to close to 29,000 years B.P., δ¹³C values averaged $\text{?25.6 ± 0.3‰}$ The HAs were characterized by chemical (elemental and functional group analyses) and spectroscopic (IR, ESR, ¹³CNMR, E₄/E₆ ratios) methods. FAs were characterized by chemical methods, E₄/E₆ ratios and IR spectra.The chemical and spectroscopic analyses showed practically no differences in the chemical structure and composition of the six HAs and FAs, so that age appeared to have little effect on these parameters. The paleosols were found to be closed systems with low polysaccharide and protein contents, thus providing unfavorable substrates for microbial activity. The preservation of the humic materials in the paleosols may have been due to low biological activity and/or to retention by amorphous minerals. The HAs did not appear to be affected by temperatures higher than 170–200°C over the 23,000 year period which we observed.     

Chemical studies of L-chondrites—I. A study of possible chemical sub-groups

Radiochemical neutron activation analysis of Ag, As, Au, Bi, Co, Cs, Ga, In, Rb, Sb, Te, Tl and Zn and major element data in 14 L4-6 and 3 LL5 chondrites indicates that the L-group is unusually variable and may represent at least 2 sub-groups differing in formation history. Chemical trends in the S/Fe-rich sub-group support textural evidence indicating late loss of a shock-formed Fe-Ni-S melt; the S/Fe-poor sub-group seemingly reflects nebular fractionation only. Highly mobile In and Zn apparently reflect shock-induced loss from L-chondrites. Data for L5 chondrites suggest higher formation temperatures and/or degrees of shock than for LL5 chondrites.     

Determination of hydrocarbon distributions in oils and sediment extracts by gas chromatography—high resolution mass spectrometry

The distributions of steroid and triterpenoid hydrocarbons in crude oils and sedimentary rock extracts can be routinely determined by the direct injection of the sample into a gas chromatograph coupled to a mass spectrometer (GC-MS). The mass spectrometer is operated at a resolution of about 2500 (10% valley), and only the ion intensities at selected accurate mass values, diagnostic of the structural types of interest, are monitored throughout the analysis. The distributions, so obtained, find application in the assessment of the source and thermal maturity of crude oil accumulations in the subsurface. This technique eliminates chromatographic separation steps and combines two analyses in one. Thus, more geological samples and reference mixtures may be analyzed in a given time.     

Comparison of oil shales and kerogen concentrates by 13C nuclear magnetic resonance

Six oil shales and their kerogen concentrates have been studied using ¹³C CP/MAS NMR techniques to study the distribution of organic carbon species. It is found that if the aromatic and aliphatic regions are divided at about 80 or 100 ppm, the apparent aromaticities of a raw shale and its kerogen concentrate are in good agreement. The presence of oxygen-substituted carbons in the raw shales and their depletion in the kerogen concentrates are observed and discussed.     

Phosphate beneficiation by calcination. Prediction of P2O5 in the product,mining and plant control

A method is described to predict P₂O₅ content in the product (of phosphate beneficiation by calcination) as a function of the composition of an untreated and also of a washed raw material. The method consisted of: (a) developing an on-line multielement analysis by XRF; (b) finding the elemental and mineralogical relationships in the product, by factor analysis; (c) determination of the independent variables; (d) finding the relationships between the concentrations of the impurity variables in the raw material and in the product; (e) developing a linear model to predict P₂O₅ content. The predictions are used for mining and for plant control.     

Pyrolysis-high resolution gas chromatography and pyrolysis gas chromatography-mass spectrometry of kerogens and kerogen precursors

A series of kerogens and kerogen precursors isolated from DSDP samples, oil shales and Recent algal mats have been examined by Curie point pyrolysis-high resolution gas chromatography and gas chromatography-mass spectrometry. This study has shown that the three main types of kerogens (marine, terrestrial and mixtures of both) can be characterized using these techniques. The marine (algal) kerogens yield principally aliphatic products and the terrestrial kerogens yield more aromatic and phenolic products with some n-alkanes and n-alkenes. The yields of n-alkanes and n-alkenes increase and phenols decrease with increasing geologic age, however, pyrolysis-GC cannot be used to characterize the influence of short term diagenesis on the kerogen structure.     

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.     

Cumberland Falls chondritic inclusions—II. Trace element contents of forsterite chondrites and meteorites of similar redox state

Mineralogic study of black inclusions in the Cumberland Falls enstatite achondrite revealed that they constitute a highly unequilibrated chondritic suite distinct from other chondrite groups. This highly shocked suite, the forsterite (F) chondrites, exhibits mineralogic trends apparently produced during primary nebular condensation and accretion over a broad redox range. We analyzed these samples and possibly related meteorites for Ag, As, Au, Bi, Cd, Co, Cs, Ga, In, Rb, Sb, Se, Te, Tl, U and Zn, trace elements known to yield important genetic information. The results demonstrate the compositional coherence and distinctiveness of the F chondrite suite relative to other chondrites. The Antarctic aubrite, ALH A78113, may include more F chondrite material. Trace element contents do not vary with mineral compositions hence do not reflect redox variations during formation of F chondrite parental matter. Trace element mobilization—during secondary heating episodes in the F chondrite parent or during its disruptive collision with the enstatite meteorite parent body—is not detectable. Chemical trends in F chondrites apparently reflect primary nebular processes. Cosmochemical fractionation of lithophiles from siderophiles and chalcophiles occurred at moderately high temperatures, certainly higher than those existing during formation of primitive carbonaceous, enstatite and ordinary chondrites of petrologic type ≤3.     

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.     

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.     

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.     

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.     

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.     

The influence of minerals on the pyrolysis of kerogens

The effect of mineral matter on the laboratory pyrolysis of sediments, kerogens and coals, and of coal macerals mixed with either alumina, bentonite, kaolinite, or calcium carbonate has been investigated. Some minerals are more active than others in effecting changes in the composition of the pyrolysate. The relative content of low molecular weight pyrolysis products is higher for kerogens pyrolyzed in a mineral matrix than for isolated kerogens. Our limited data suggests that this is due to both condensation and gasification of higher molecular weight constituents in the ‘primary’ pyrolysate. Differences in the content of aromatic versus aliphatic compounds have been noted when pyrograms from coal macerals are compared with pyrograms from coal maceral-mineral mixtures. We conclude that mineralogy is important in controlling the composition of kerogen pyrolysis products.     

Demethylated hopanes in crude oils and their applications in petroleum geochemistry

Analyses of some Australian crude oils show that many contain varying concentrations of A/ B-ring demethylated hopanes. These range from C₂₆ to C₃₄ and have been identified from their retention times and mass spectral data as 17α(H)-25-norhopanes. Comparison of hopane and demethylated hopane concentrations and distributions in source-related, biodegraded oils suggests that demethylated hopanes are biotransformation products of the hopanes. Further, it appears that the process occurs at a late stage of biodegradation, after partial degradation of steranes has occurred. Demethylated hopanes are proposed as biomarkers for this stage of severe biodegradation. The presence of these compounds in apparently undegraded crude oils is thought to be due to the presence of biodegraded crude oil residues which have been dissolved by the undegraded crude oil during accumulation in the reservoir sands. The timing of hopane demethylation, relative to the degradation of other compounds, has been assessed and the progressive changes in crude oil composition with increasing extent of biodegradation have been identified. The use of demethylated hopanes as maturity parameters for severely biodegraded crude oils, and the applicability of established biomarker maturity parameters to such oils, are also discussed.     

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.     

Thermal metamorphism of primitive meteorites—VIII. Noble gases,carbon and sulfur in Allende (C3) meteorite heated at 400–1000°C

Noble gases, C and S are lost from Allende samples heated for 1 week at temperatures of 400–1000°C in a low pressure environment. In the extreme, losses of ³He and ⁴He are ~ 100 × while for C. S and Ne, Ar and Kr isotopes and ¹³²Xe. these are ≤10 ×. Except for He, these losses are less severe than those of Bi or Tl from samples heated in the same runs. Significant He. Ne and Ar isotopic fractionation during heating indicates preferential outgassing of specific reservoirs. Apparent activation energies for all species generally indicate loss controlled by a diffusive process. Next to He, ⁴⁰Ar is the most labile of those species considered here but still less so than Bi or Tl. L-group (but not H- or LL-group) chondrites may have lost mobile elements like Tl while being outgassed after late impact-associated heating. A less likely alternative possibility involving a collateral relation between condensation conditions and depth in a parent object may also explain the L-group trend.     

Chemical studies of L chondrites—II. Shock-induced trace element mobilization

Previous studies of chondrites heated in the laboratory for extended periods under conditions approximating those in shock-heated collisional debris indicate that Au, Co, Se, Ga, Rb, Cs, Te, Bi, In, Ag, Zn, Tl and Cd progress in mobility. We report data for these 13 trace elements in 14 L4–6 chondrites of established shock history and discuss these and 13 additional chondrites studied earlier. Trace element contents vary with petrologic type, $\text{S}\text{Fe}$ sub-group and shock history, the last dominating strongly. Absolute abundances and interelement relationships for the 6 or 7 most mobile elements vary with degree of shock-loading (i.e. residual temperatures) established from mineralogic/petrologic study. A tertiary process, shock-heating, previously known to have affected radiogenic ⁴⁰Ar and/or ⁴He in meteorites but not other elements, apparently was at least as effective as other open-system processes (secondary [parent body] and primary [nebular and/or accretionary] episodes) in establishing mobile trace element contents of L chondrites and probably others. If conditions during early genetic episodes are to be deduced from compositional information, shocked meteorites should be avoided or effects of later processes should be compensated for.     

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.