Redox cycling of iron and manganese in sediments of the Kalix River estuary, Northern Sweden     

Anders Widerlund  Johan Ingri 《Aquatic Geochemistry》1996,2(2):185-201

Iron and manganese redox cycling in the sediment — water interface region in the Kalix River estuary was investigated by using sediment trap data, pore-water and solid-phase sediment data. Nondetrital phases (presumably reactive Fe and Mn oxides) form substantial fractions of the total settling flux of Fe and Mn (51% of Fe_total and 84% of Mn_total). A steady-state box model reveals that nondetrital Fe and Mn differ considerably in reactivity during post-depositional redox cycling in the sediment. The production rate of dissolved Mn (1.6 mmol m^–2 d^–1) exceeded the depositional flux of nondetrital Mn (0.27 mmol m^–2 d^–1) by a factor of about 6. In contrast, the production rate of upwardly diffusing pore-water Fe (0.77 mmol m^–2 d^–1) amounted to only 22% of the depositional flux of nondetrital Fe (3.5 mmol m^–2 d^–1). Upwardly diffusing pore-water Fe and Mn are effectively oxidized and trapped in the oxic surface layer of the sediment, resulting in negligible benthic effluxes of Fe and Mn. Consequently, the concentrations of nondetrital Fe and Mn in permanently deposited, anoxic sediment are similar to those in the settling material. Reactive Fe oxides appear to form a substantial fraction of this buried, non-detrital Fe. The in-situ oxidation rates of Fe and Mn are tentatively estimated to be 0.51 and 0.16–1.7 mol cm^–3 d^–1, respectively.  相似文献   

Dissolution rates of metals in Fe oxides: implications for sampling ferruginous materials with significant relict Fe oxides     

J. Xie  A. C. Dunlop 《Journal of Geochemical Exploration》1998,61(1-3)

A study of the pattern of dissolution of synthetic and natural Fe oxides in 6 M HCl indicates that the rate of element release from synthetic Fe oxides is strongly influenced by mineralogy and the level of element incorporation. Synthetic maghemite (γ-Fe₂O₃) samples are subject to much more rapid dissolution than goethite (FeOOH) and hematite (α-Fe₂O₃). In samples dominated by hematite and maghemite, Cu, Zn and particularly Pb, in comparison to Fe, are preferentially released during the early stages of dissolution. Similar patterns are apparent from the dissolution of hematite- and maghemite-dominated samples derived from natural gossan. Comparison of XRD scans with data from the dissolution of natural gossan samples transformed by incremental heating to hematite- and maghemite-dominated assemblages suggests that the degree of crystallinity may also be a significant factor in the release of elements incorporated in the Fe oxides. Ferruginous materials made up of varying proportions of goethite, hematite, maghemite, kaolinite and quartz are important sampling materials in a range of regolith environments. These are products of complex chemical and mechanical mobilization over long periods of geological time. If the patterns of Fe oxide dissolution in 6 M HCl and the release of incorporated metals reflect stability in such weathering regimes, knowledge of the retention characteristics of incorporated metals in different Fe oxide phases, as indicated by this study, will be useful in the planning and interpretation of geochemical surveys in such regions.  相似文献   

Elucidation of different forms of organic carbon in marine sediments from the Atlantic coast of Spain using thermal analysis coupled to isotope ratio and quadrupole mass spectrometry     

Elisa Lopez Capel  Jos Maria de la Rosa Arranz  Francisco J. Gonzlez-Vila  Jos Antonio Gonzlez-Perez  David A.C. Manning 《Organic Geochemistry》2006,37(12):1983

Analysis of river, estuary and marine sediments from the Atlantic coast of Spain using thermogravimetry–differential scanning calorimetry–quadrupole mass spectrometry–isotope ratio mass spectrometry (TG–DSC–QMS–IRMS) was used to (a) distinguish bulk chemical hosts for C within a sediment and humic acid fraction, (b) track C pools with differing natural C isotope ratios and (c) observe variation with distance from the coast. This is the first application of such a novel method to the characterisation of organic matter from marine sediments and their corresponding humic acid fractions. Using thermal analysis, a labile, a recalcitrant and a refractory carbon pool can be distinguished. Extracted humic fractions are mainly of recalcitrant nature. The proportion of refractory carbon is greatest in marine sediments and humic acid fractions. Quadrupole mass spectrometry confirmed that the greatest proportion of m/z 44 (CO₂) and m/z 18 (H₂O) were detected at temperatures associated with recalcitrant carbon (510–540 °C). Isotope analysis detected progressive enrichment in δ¹³C for the sediment samples with an increase in marine influence. Isotopic heterogeneity in the refractory organic matter in marine sediments could be due to products of anthropogenic origin or natural combustion products. Isotope homogeneity of humic acids confirms the presence of terrigenous C in marine sediments, allowing the terrestrial input to be characterised.  相似文献   

Influence of the aging of Fe oxides on the decline of magnetic susceptibility of the Tertiary red clay in the Chinese Loess Plateau     

Xue-Feng Hu  Liang-Feng Xu  Yun Pan  Ming-Neng Shen 《Quaternary International》2009,209(1-2):22

Magnetic properties, free and active Fe oxides, grain size distribution and mineral assemblage of a Quaternary loess–Tertiary red clay (TRC) section in Lingtai County in the Chinese Loess Plateau were studied. The results suggest that the TRC of the Lingtai section shares similar aeolian characteristics with the overlying Quaternary loess-paleosol sequence (QLPS), but the former is generally more intensively weathered than the latter, as indicated by its higher citrate–bicarbonate–dithionite (CBD) extractable Fe (Fe_d), finer grain size and lower content of easily weathered primary minerals. However, magnetic susceptibility (χ_lf) and magnetic remanence (χ_arm, SIRM and SOFT etc.) of the main part of the TRC are significantly lower, implying the decline of ferrimagnetic minerals (FM). In contrast, hematite and goethite in the TRC is significantly enhanced, as indicated by its higher HIRM. The acid ammonium oxalate (AAO) extractable Fe (Fe_o) of the whole section sharply decreases with increasing age. Fe_o and Fe_o/Fe_d values of the section are significantly correlated with χ_lf. Especially in the TRC, the low values of Fe_o and Fe_o/Fe_d correspond to weak χ_lf. This suggests a significant influence of the age-related transformation of Fe oxides on the decline of FM in the TRC. Lower FM and higher hematite and/or goethite in the TRC further suggest the transformation of FM into hematite with the aging of Fe oxides during post-depositional processes, though more evidence is needed to understand the processes involved. χ_lf of the TRC in the Chinese Loess Plateau mostly cannot be regarded as a promising paleoclimatic proxy because its weak magnetism does not correlate to its strong pedogenesis.  相似文献   

Analysis of the Major Fe Bearing Mineral Phases in Recent Lake Sediments by EXAFS Spectroscopy   总被引：1，自引：0，他引：1  

Lorenzo Spadini  Markus Bott  Bernhard Wehrli  Alain Manceau 《Aquatic Geochemistry》2003,9(1):1-17

Extended X-ray absorption fine structure (EXAFS) spectroscopy and chemical analyses were combined to determine the Fe bearing minerals in recent lake sediments from Baldeggersee (Switzerland). The upper section of a laminated sediment core, deposited under eutrophic conditions, was compared to the lower part from an oligotrophic period. Qualitative analysis of FeK EXAFS agreed well with chemical data: In the oligotrophic section Fe(II)–O and Fe(III)–O specieswere present, whereas a significant fraction of Fe(II)–S sulfides was strongly indicated in the eutrophic part. A statistical analysis was performed by least square fitting of normalized reference spectra. The set of reference minerals included Fe(III) oxides and Fe(II) sulfides, carbonates and phosphates. In the oligotrophic regime no satisfying fit was obtained using the set of reference spectra, indicating that siderite (FeCO₃) was not present in a significant amount in these carbonate-rich sediments. Simulated EXAFS spectra for a(Ca_x, Fe_1-x)CO₃solid solution allowed reconstructing the specificfeatures of the experimental spectra, suggesting that this phase was the dominant Fe carrier in the oligotrophic section of the core. In the eutrophic part, mackinawite was positively identified and represented the dominant Fe(II) sulfide phase. This finding agreed with chemical extraction, which indicated that18–40 mol% of Fe was contained in the acid volatile iron sulfide fraction. EXAFS spectra of the eutrophic section were best fitted by considering the admixture of mackinawite and the Fe–Ca carbonate phase inferred to be predominant in the oligotrophic regime.  相似文献   

Elevated naturally occurring arsenic in a semiarid oxidizing system, Southern High Plains aquifer, Texas, USA     

B.R. Scanlon  J.P. Nicot  R.C. Reedy  D. Kurtzman  A. Mukherjee  D.K. Nordstrom 《Applied Geochemistry》2009,24(11):2061-2071

High groundwater As concentrations in oxidizing systems are generally associated with As adsorption onto hydrous metal (Al, Fe or Mn) oxides and mobilization with increased pH. The objective of this study was to evaluate the distribution, sources and mobilization mechanisms of As in the Southern High Plains (SHP) aquifer, Texas, relative to those in other semiarid, oxidizing systems. Elevated groundwater As levels are widespread in the southern part of the SHP (SHP-S) aquifer, with 47% of wells exceeding the current EPA maximum contaminant level (MCL) of 10 μg/L (range 0.3–164 μg/L), whereas As levels are much lower in the north (SHP-N: 9%  As MCL of 10 μg/L; range 0.2–43 μg/L). The sharp contrast in As levels between the north and south coincides with a change in total dissolved solids (TDS) from 395 mg/L (median north) to 885 mg/L (median south). Arsenic is present as arsenate (As V) in this oxidizing system and is correlated with groundwater TDS (Spearman’s ρ = 0.57). The most likely current source of As is sorbed As onto hydrous metal oxides based on correlations between As and other oxyanion-forming elements (V, ρ = 0.88; Se, ρ = 0.54; B, ρ = 0.51 and Mo, ρ = 0.46). This source is similar to that in other oxidizing systems and constitutes a secondary source; the most likely primary source being volcanic ashes in the SHP aquifer or original source rocks in the Rockies, based on co-occurrence of As and F (ρ = 0.56), oxyanion-forming elements and SiO₂ (ρ = 0.41), which are found in volcanic ashes. High groundwater As concentrations in some semiarid oxidizing systems are related to high evaporation. Although correlation of As with TDS in the SHP aquifer may suggest evaporative concentration, unenriched stable isotopes (δ²H: −65 to −27; δ¹⁸O: −9.1 to −4.2) in the SHP aquifer do not support evaporation. High TDS in the SHP aquifer is most likely related to upward movement of saline water from the underlying Triassic Dockum aquifer. Mobilization of As in other semiarid oxidizing systems is caused by increased pH; however, pH in the SHP aquifer is near neutral (10–90 percentiles, 7.0–7.6). Although many processes, such as competitive desorption with SiO₂, VO₄, or PO₄, could be responsible for local mobilization of As in the SHP aquifer, the most plausible explanation for the regional As distribution and correlation with TDS is the counterion effect caused by a change from Ca- to Na-rich, water as shown by the high correlation between As and Na/(Ca)^0.5 ratios (ρ = 0.57). This change in chemistry is related to mixing with saline water that moves upward from the underlying Dockum aquifer. This counterion effect may mobilize other anions and oxyanion-forming elements that are correlated with As (F, V, Se, B, Mo and SiO₂). Competition among the oxyanions for sorption sites may enhance As mobilization. The SHP case study has similar As sources to those of other semiarid, oxidizing systems (original volcanic ash source followed by sorption onto hydrous metal oxides) but contrasts with these systems by showing lack of evaporative concentration and pH mobilization of As but counterion mobilization of As instead in the SHP-S aquifer.  相似文献   

Photochemical activity and characterization of the complex of humic acids with iron(III)     

Xiaoxia Ou  Shuo ChenXie Quan  Huimin Zhao 《Journal of Geochemical Exploration》2009

This study examined the effects of humic acids (HA) and Fe(III)–HA complex on the photodegradation of atrazine, one of the most widely used herbicides. It was shown that the photolysis of atrazine proceeded via first-order reaction kinetics and that atrazine photodegradation was inhibited by the presence of HA, whereas the rate for atrazine photolysis was promoted in solutions containing both HA and Fe(III). Interactions of Fe(III) with HA were characterized by SEM, EDX, UV–Vis and FTIR, revealing that Fe(III)–HA complex was formed by ligand exchange between oxygen groups of HA and Fe(III). Using fluorescence spectrometry the stability constant (K_c) and the fraction of fluorophores available for complexation (f) were obtained as log K_c = 4.28 and f = 74%. Photoformed Fe(II) by ligand-to-metal charge-transfer (LMCT) within the Fe(III)–HA complex was the most important factor involved in photolysis of atrazine, since Fe(II) was the reactant to generate hydroxyl radical. Thus, the rate of atrazine photodegradation in natural sunlit waters is dependent on both the amount of iron present and the interaction between HA and iron.  相似文献   

1H NMR spectra of humic and fulvic acids and their peracetic oxidation products     

P Ruggiero  F.S Interesse  L Cassidei  O Sciacovelli 《Geochimica et cosmochimica acta》1980,44(4):603-609

¹H NMR spectra of humic (HA) and fulvic (FA) acids and their oxidative degradation products are reported. The HA shows the presence of -(CH₂)_n - CH₃ (n > 6) chemical fragments belonging to n-alkanes and/or n-fatty acids physically adsorbed onto the macromolecule structure. These fragments are absent in the FA fraction. Both humic fractions reveal the presence of similar amounts of aromatic protons which partly undergo exchange phenomena. The importance of this experimental observation is discussed. Oxidative degradation seems to cause partial cleavage of aromatic rings, more pronounced in the FA than in the HA. The degraded FA shows a higher total acidity and a higher phenolic OH content than the degraded HA. Both degraded fractions display some sharp singlet signals at 1.9 and 3.9 ppm arising from protons belonging to repetitive chemical fragments probably formed during the oxidation reaction. Tentative assignments of these signals are given. A general analysis of the HA and FA degraded spectra seems to indicate that the chemical fragments which undergo peracetic oxidation are substantially similar. The extent of oxidation of the two humic fractions is different. The HA degradation products reveal the presence of oligomeric structures, whereas the degraded FA appears less resistant to the oxidizing agent.  相似文献   

Kinetics of the selective extraction of iron oxides in geochemical samples. Association between Fe and Cu in acid brown soils     

P. Warnant  H. Martin  A.J. Herbillon 《Journal of Geochemical Exploration》1981,15(1-3)

The use of Tamm's reagent at 60°C and at different reaction times enables the progressive dissolution of iron oxides from the different horizons of acid brown soils. This technique is used to evaluate the association between Cu and Fe in soils from a zone mineralized in Cu. This association is quantified by the coefficient α (moles Cu/moles Fe) which represents the degree of doping of the iron oxides by Cu. For the B horizon of these soils, α values range from 5 to 10 × 10^-3 mole Cu/mole Fe.Calculation of the coefficient α (range = 0.4 to 2.0 × 10^-3) for 150 soil samples of the same type enabled the differentiation of two geochemical populations. Treatment of the total Cu values of these samples did not permit such differentiation.  相似文献   

Cu and Fe associated with humic acids in sediments of a tropical coastal lagoon   总被引：1，自引：0，他引：1  

Julio Cesar Wasserman  Fernanda B. L. Oliveira  Mnica Bidarra 《Organic Geochemistry》1998,28(12):813-822

The amount of Cu and Fe associated with humic acids was estimated in five sediment cores from a tropical coastal lagoon (Piratininga Lagoon, Rio de Janeiro, Brazil). Core samples were analysed for humic acid contents, total Fe and Cu content. Fe and Cu associated with humic acids were also measured. Results show amounts of humic acids ranging from 0.7 to 21.7% of the dry weight of sediment (average 4.6%, standard deviation 4.4%). Concentrations of Fe and Cu ranged from 0.3 to 6.0% (average 2.2%, S.D. 1.2%) and from <1.0 to 65.0 μg g⁻¹ (average 28.6 μg g⁻¹, S.D. 16.4 μg g⁻¹), respectively. The results of strongly bound metals show that while humic acids are the main carrier for Cu, Fe does not seems to be significantly associated with this organic matter.  相似文献   

Iron isotopes in acid mine waters and iron-rich solids from the Tinto–Odiel Basin (Iberian Pyrite Belt, Southwest Spain)     

M. Egal  F. Elbaz-Poulichet  C. Casiot  M. Motelica-Heino  P. Ngrel  O. Bruneel  A.M. Sarmiento  J.M. Nieto 《Chemical Geology》2008,253(3-4):162-171

The isotopic composition of Fe was determined in water, Fe-oxides and sulfides from the Tinto and Odiel Basins (South West Spain). As a consequence of sulfide oxidation in mine tailings both rivers are acidic (1.45 < pH < 3.85) and display high concentrations of dissolved Fe (up to 420 mmol l^− 1) and sulphates (up to 1190 mmol l^− 1).The δ⁵⁶Fe of pyrite-rich samples from the Rio Tinto and from the Tharsis mine ranged from − 0.56 ± 0.08‰ to + 0.25 ± 0.1‰. δ⁵⁶Fe values for Fe-oxides precipitates that currently form in the riverbed varied from − 1.98 ± 0.10‰ to 1.57 ± 0.08‰. Comparatively narrower ranges of values (− 0.18 ± 0.08‰ and + 0.21 ± 0.14‰) were observed in their fossil analogues from the Pliocene–Pleistocene and in samples from the Gossan (the oxidized layer that formed through exposure to oxygen of the massive sulfide deposits) (− 0.36 ± 0.12‰ to 0.82 ± 0.07‰). In water, δ⁵⁶Fe values ranged from − 1.76 ± 0.10‰ to + 0.43 ± 0.05‰.At the source of the Tinto River, fractionation between aqueous Fe(III) and pyrite from the tailings was less than would be expected from a simple pyrite oxidation process. Similarly, the isotopic composition of Gossan oxides and that of pyrite was different from what would be expected from pyrite oxidation. In rivers, the precipitation of Fe-oxides (mainly jarosite and schwertmannite and lesser amounts of goethite) from water containing mainly (more than 99%) Fe(III) with concentrations up to 372 mmol l^− 1 causes variable fractionation between the solid and the aqueous phase (− 0.98‰ < Δ⁵⁶Fe_{solid–water} < 2.25‰). The significant magnitude of the positive fractionation factor observed in several Fe(III) dominated water may be related to the precipitation of Fe(III) sulphates containing phases.  相似文献   

Matrix-independent Fe isotope ratio determination in silicates using UV femtosecond laser ablation     

Grit Steinhoefel  Ingo Horn  Friedhelm von Blanckenburg 《Chemical Geology》2009,268(1-2):67-73

UV femtosecond laser ablation coupled to MC-ICP-MS provides a promising in situ tool to investigate elemental and isotope ratios by non-matrix-matched calibration. In this study, we investigate Fe isotope composition in siliceous matrices including biotite, hornblende, garnet, fayalite and forsterite (San Carlos Olivine), and an oceanic Fe–Mn crust using the iron reference material IRMM-014 for calibration. To test the accuracy of the laser ablation data, Fe isotope compositions were obtained independently by solution ICP-MS after chromatographic separation of Fe. Sample materials with low Cr content, i.e. biotite, hornblende, fayalite and the Fe–Mn crust, reveal δ^56/54Fe and δ^57/54Fe values that agree with those from solution ICP-MS data within the measured precision. For high Cr concentration (⁵⁴Cr/⁵⁴Fe >0.0001), i.e. in the garnet and forsterite sample, δ^56/54Fe and δ^57/54Fe values were derived from ⁵⁷Fe/⁵⁶Fe ratios as correction of the isobaric interference of ⁵⁴Cr on ⁵⁴Fe is unsatisfactory. This approach provides accurate results for both minerals. Moreover, the garnet crystal exhibits isotopic zonation with differences of 0.3‰ in δ^56/54Fe showing that substantial heterogeneities exist in high-temperature metamorphic minerals. Multiple analyses of homogeneous sample materials reveal a repeatability of 0.1‰ (2 SD) for δ^56/54Fe and 0.2‰ (2 SD) for δ^57/54Fe, respectively. This study adds to the observations of Horn et al. (2006) who have shown that the determination of Fe isotope ratios in various matrices including iron alloys, iron oxides and hydroxides, iron sulfide and iron carbonates can be performed with high accuracy and precision at high spatial resolution using UV femtosecond laser ablation ICP-MS. These results demonstrate that femtosecond laser ablation ICP-MS is a largely matrix-independent method, which provides a substantial advantage over commonly employed nanosecond laser ablation systems.  相似文献   

As–(Ag) sulphide veins in the Spanish Central System: further evidence for a hydrothermal event of Permian age     

Toms Martín-Crespo  Elena Vindel  Jos Angel Lpez-García  Esteve Cardellach 《Ore Geology Reviews》2004,25(3-4):199-219

The Spanish Central System (SCS) has been subjected to repeated deformation and fluid flow events which have produced both sulphide-bearing and barren vein systems. Although several hydrothermal episodes took place between 300 and 100 Ma, fluid circulation during the Permian was especially important, giving rise to a range of different types of deposits. This study presents a multidisciplinary approach leading to the characterisation of the chemistry and age of the hydrothermal fluids that produced the As–(Ag) mineralised stockwork of Mónica mine (Bustaviejo, Madrid). Fluid inclusion data indicate the presence of two different fluids. An initial ore stage (I) formed from a low- to moderate salinity (3–8 wt.% eq. NaCl) H₂O–NaCl–CO₂–CH₄ fluid, at minimum trapping temperature of 350±15 °C and 0.3 kbar. A second H₂O–NaCl fluid is found in three types of fluid inclusions: a high temperature and low salinity type (340±20 °C; 0.8–3.1 wt.% eq. NaCl) also associated to ore stage I, a moderate temperature and very low salinity type (160–255 °C; 0–1.5 wt.% eq. NaCl) represented in ore stage III, and a very low temperature and hypersaline type (60–70 °C; 30–35 wt.% NaCl), unrelated to the mineralising stages and clearly postdating the previous types. ⁴⁰Ar–³⁹Ar dating on muscovite from the early As–Fe stage (I) has provided an age of 286±4 Ma, synchronous with the late emplacement phases of La Cabrera plutonic massif (288±5 Ma) and with other Permian hydrothermal events like Sn–W skarns and W–(Sn) sulphide veins. δ¹⁸O of water in equilibrium with stage I quartz (5.3–7.7‰), δD of water in equilibrium with coexisting muscovite (−16.0‰ to −2.0‰), and sulphide δ³⁴S (1.5–3.6‰) values are compatible with waters that leached metamorphic rocks. The dominant mechanism of the As–(Ag) deposition was mixing and dilution processes between aqueous–carbonic and aqueous fluids for stage I (As–Fe), and nearly isobaric cooling processes for stages II (Zn–Cu–Sn) and III (Pb–Ag). The origin and hydrothermal evolution of As–(Ag) veins is comparable to other hydrothermal Permian events in the Spanish Central System.  相似文献   

Composition of manganese nodules and manganese carbonates from Loch Fyne,Scotland   总被引：2，自引：0，他引：2  

S. E. Calvert  N. B. Price 《Contributions to Mineralogy and Petrology》1970,29(3):215-233

Manganese nodules and manganese carbonate concretions occur in the upper 10–15 cm of the Recent sediments of Loch Fyne, Argyllshire in water depths of 180–200 m. The nodules are spherical, a few mm to 3 cm in diameter, and consist of a black, Mn-rich core and a thin, red, Fe-rich rim. The carbonate occurs as irregular concretions, 0.5–8 cm in size, and as a cement in irregular nodule and shell fragment aggregates. It partially replaces some nodule material and clastic silicate inclusions, but does not affect aragonitic and calcitic shell fragments.The nodules are approximately 75% pure oxides and contain 30% Mn and 4% Fe. In the cores, the principal mineral phase is todorokite, with a Mn/Fe ratio of 17. The rim consists of X-ray amorphous Fe and Mn oxides with a Mn/Fe ratio of 0.66. The cores are enriched, relative to Al, in K, Ba, Co, Mo, Ni and Sr while the rims contain more P, Ti, As, Pb, Y and Zn.The manganese carbonate has the composition (Mn_47.7 Ca_45.1 Mg_7.2) CO₃. Apart from Cu, all minor elements are excluded from significant substitution in the carbonate lattice.Manganese nodules and carbonates form diagenetically within the Recent sediments of Loch Fyne. This accounts for the high Mn/Fe ratios in the oxide phases and the abundance of manganese carbonate concretions. Mn concentrations in the interstitial waters of sediment cores are high (ca. 10 ppm) as also, by inference, are the dissolved carbonate concentrations.  相似文献   

Changes in bulk properties and molecular compositions within New Zealand Coal Band solvent extracts from early diagenetic to catagenetic maturity levels     

T.T.A. Vu  K.-G. Zink  K. Mangelsdorf  R. Sykes  H. Wilkes  B. Horsfield 《Organic Geochemistry》2009,40(9):963-977

The bulk properties and bitumen molecular compositions of a rank-series of 38 humic coals from the New Zealand Coal Band (Cretaceous–Cenozoic) have been analysed to investigate early maturation processes affecting coaly organic matter through diagenesis to moderate catagenesis (Rank(S_r) 0.0–11.8, R_o 0.23–0.81%). The samples comprise a relatively restricted range of vitrinite rich coal types formed largely from higher land plant material under relatively oxic conditions, but with a significant contribution from microbial biomass. With increasing rank, total organic carbon contents show a general increase, whereas moisture and asphaltene contents decrease. Bitumen yields also decrease through the stages of diagenesis and early catagenesis (Rank(S_r) < 9, R_o < 0.55%), indicating partial loss of initial bitumen during early maturation. Thermal generation of hydrocarbons begins slowly at Rank(S_r)  5–6 (R_o  0.40%) as indicated by the constant occurrence and gradual increase of isoprenoids (e.g., pristane and phytane) and hopanoids in their more mature αβ configuration. This early phase of catagenesis, not previously recognised in New Zealand coals, is followed at Rank(S_r)  9 (R_o  0.55%) by the main catagenesis phase characterised by a more rapid increase in the generation of hydrocarbons, including total n-alkanes, isoprenoids and αβ-hopanes. Changes in the maturity of New Zealand coals can be traced by the Carbon Preference Index and several hopane maturity parameters, including 22S/(22S + 22R), αβ/(αβ + βα) and ββ/(αβ + βα + ββ).  相似文献