Some chemical structural features of coals of differing maceral distributions and stratigraphy

Six North American bituminous coals (four Carboniferous and two Cretaceous) and eight maceral concentrates from Carboniferous British seams have been heated with tetralin and hydrogen to 400°C. The hexane-soluble parts of the products were separated by column chromatography and the fractions were then analyzed by gas chromatography/mass spectrometry. In all cases the aromatic hydrocarbon fraction was a very complex mixture containing a number of alkylated biphenyls, diphenylmethanes and -ethanes, and polycyclic compounds. However single ioncchromatography (m/z = 142) showed that, in addition to these, the products from five of the six American coals contained homologous series of long chain n-alkylnapththalenes with alkyl groups extending to C₁₆. In other fractions from the American coals, homologous series of n-alkylfurans and alkylphenols were found to be major components, as also were many alkylcyclohexenones related to isophorone. Extensive homologous series of n-alkyl aromatics were not detected in products from any of six vitrinites from British seams, though series of n- and iso-alkylphenols were found in the products from two sporinite concentrates. A number of polycyclic ketones apparently related to sterols were found in the products from the British vitrinites but not from any American coals. Reasons for what appear to be systematic structural differences between the American and British coals are discussed. Differences in stratigraphy are noted and it seems not impossible that differences in source vegetation are significant.     

Geological and laboratory evidence for early generation of large amounts of liquid hydrocarbons from suberinite and subereous components

Suberinite, and subereous components of amorphous nature, comprise largely unrecognized, proficient sources of liquid hydrocarbons. Due to difficulties in recognizing the presence of subereous components and suberinite in organic sediments, the contributions of these liptinitic components to the organic input of source rocks are easily underestimated. Severe chemical alterations of suberinite in the vitrinite reflectance range of R_o = 0.35–0.60% are demonstrated. Organic geochemical data, obtained from samples subjected to natural maturation, reveal that subereous components/suberinite undergoes early thermal degradation to generate large amounts of hydrocarbons below R_o = 0.60%. Data obtained from laboratory maturation of immature, suberinite-rich coals indicate that about 50% of the potential of suberinite for generating C₁₂₊ hydrocarbons has already been exhausted during natural maturation of the samples, prior to the onset of the traditionally defined “oil window”. The present data (a) contradict the assumption that suberinite is mainly sourced by selective preservation/enrichment of a stable, highly aliphatic biopolymer, i.e. “suberan” and (b) suggest that suberinite contains appreciable amounts of aliphatic and aromatic moieties which are released at low thermal stress.     

Classification of torbanite and cannel coal: II. Insights from pyrolysis-GC/MS and multivariate statistical analysis

Petrographic and megascopic criteria have traditionally been used as the basis for the classification of torbanite and cannel coal. For this study, it was hypothesized that modern analytical organic geochemical and multivariate statistical techniques could provide an alternative approach. Towards this end, the demineralized residues of 14 torbanite (rich in Botryococcus-related alginite) and cannel (essentially, rich in organic groundmass and/or sporinite) coal samples were analyzed by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Cluster analysis performed on the Py-GC/MS data clearly distinguished the torbanite from the cannel coal, demonstrating a consistency between the chemical properties and the petrographic composition. All the torbanite samples group into one cluster, their pyrolyzates having an overwhelming predominance of straight chain hydrocarbons, a characteristic typical of Botryococcus. The presence of the C₉–C₂₆ n-α,ω-alkadiene series is the key feature distinguishing the torbanites from the other samples. The cannel coals exhibit more chemical diversity, reflecting their greater variability in petrographic composition. The Breckinridge cannel, dominated by a highly aliphatic lamalginitic groundmass, chemically fits the torbanite category. The bituminitic groundmass-dominated cannel coals fall into a cannel sub-cluster, their pyrolyzates having a characteristic predominance of n-alk-1-enes and n-alkanes (particularly the long-chain homologues), with no detectable alkadienes. The vitrinitic groundmass-dominated Ohio Linton cannel and the sporinite-rich Canadian Melville Island cannel are readily distinguishable from the other cannels by the relatively abundant aromatic and phenolic compounds in their pyrolyzates. The internal distribution patterns of alkylaromatic and alkylphenolic isomers are shown to be less significant in the classification of this sample set. Multivariate statistical analysis of the pyrolysis data not only successfully discriminated torbanites from cannel coals, but recognized subtler differences between the examples of these two coal types, in substantial agreement with the petrographic characterization. As such, these methods can substitute for or supplement the traditional microscope-based approach.     

Evaluation of the liquid hydrocarbon potential of coal by artificial maturation techniques

In certain areas, relatively large accumulations of liquid hydrocarbons have been attributed to coals. Evaluating the source rock potential of coal requires definition of both the generative potential (quantity and composition of generated hydrocarbons), and expulsion efficiency. Hydrous pyrolysis experiments were completed using Tertiary lignites (R_o < 0.35%) from North Dakota and the Far East to evaluate the source rock potential of coal. The North Dakota lignite is vitrinite-rich (93%) and liptinite-poor (3%); the Far East lignite is liptinite-rich (32% of total maceral content). These lignites have Hydrogen Index values of 123 and 483 mg HC/g OC, respectively. Differences in oil-pyrolysate yield, composition, and temperature of maximum pyrolysate yield from hydrous pyrolysis experiments for these two lignites are related to the type and amount of liptinite and vitrinite macerals. A maximum of 48 and 158 mg oil-pyrolysate/g OC is generated and expelled from the North Dakota and Far East lignites, respectively. Although these lignites consist predominantly of gas-prone vitrinitic components, their organic-rich nature can compensate for their poor convertibility to liquid hydrocarbons. The composition of these artificially generated oil-pyrolysates are similar to some non-marine oils, suggesting that this type of organic matter can be a significant contributor to many oils. Although the overall composition of the generated products from the two lignites is similar, the distribution of these products is significantly different. Homologous series of methyl ketones and alkyl benzenes have been identified in both oil-pyrolysates. Their presence and characteristic distribution suggest that microbial degradation occurred during the formation of these lignites. Although many coals generate significate amounts of liquid hydrocarbons that are similar to naturally occurring oils, poor explusion efficiency limits their source rock potential. Significant amounts of liquid products are assimilated by the vitrinitic matrix of most coals prior to expulsion, severely limiting the amount of petroleum available for migration and reservoir accumulation. However, adequate expulsion may occur in certain liptinite-rich coals or coals occurring in unique depositional settings.     

Diversities in biomarker compositions of Carboniferous–Permian humic coals in the Ordos Basin,China

The molecular composition of Carboniferous–Permian coals in the maturity range from 0.66 to 1.63% vitrinite reflectance has been analysed using organic geochemistry to investigate the factors influencing the biomarker compositions of humic coals. The Carboniferous–Permian coal has a variable organofacies and is mainly humic-prone. There is a significant difference in the distribution of saturated and aromatic hydrocarbons in these coals, which can be divided into three types. The Group A coals have biomarker compositions typical of humic coal, characterised by high Pr/Ph ratios, a lower abundance of tricyclic terpanes with a decreasing distribution from C₁₉ tricyclic terpane to C₂₄ tricyclic terpane and a high number of terrigenous-related biomarkers, such as C₂₄ tetracyclic terpane and C₂₉ steranes. The biomarker composition of Group B coals, which were deposited in a suboxic environment, have a higher abundance of rearranged hopanes than observed in Group A coals. In contrast, in Group C coals, the Pr/Ph ratio is less than 1.0, and the sterane and terpane distributions are very different from those in groups A and B. Group C coals generally have abnormally abundant tricyclic terpanes with a normal distribution maximising at the C₂₃ peak; C₂₇ steranes predominates in the m/z 217 mass fragmentograms. The relationships between biomarker compositions, thermal maturity, Pr/Ph ratios and depositional environments, indicate that the biomarker compositions of Carboniferous–Permian coals in Ordos Basin are mainly related to their depositional environment. This leads to the conclusion that the biomarker compositions of groups A and B coals collected from Shanxi and Taiyuan formations in the northern Ordos Basin are mainly related to their marine–terrigenous transitional environment, whereas the biomarker compositions for the Group C coals from Carboniferous strata and Shanxi Formation in the eastern Ordos Basin are associated with marine incursions.     

Liquid hydrocarbon generation potential from Tertiary Nyalau Formation coals in the onshore Sarawak, Eastern Malaysia

Tertiary coals exposed in the north-central part of onshore Sarawak are evaluated, and their depositional environments are interpreted. Total organic carbon contents (TOC) of the coals range from 58.1 to 80.9 wt. % and yield hydrogen index values ranging from 282 to 510 mg HC/g TOC with low oxygen index values, consistent with Type II and mixed Type II–III kerogens. The coal samples have vitrinite reflectance values in the range of 0.47–0.67 Ro %, indicating immature to early mature (initial oil window). T _max values range from 428 to 436 °C, which are good in agreement with vitrinite reflectance data. The Tertiary coals are humic and generally dominated by vitrinite, with significant amounts of liptinite and low amounts of inertinite macerals. Good liquid hydrocarbons generation potential can be expected from the coals with rich liptinitic content (>35 %). This is supported by their high hydrogen index of up to 300 mg HC/g TOC and Py-GC (S ₂) pyrograms with n-alkane/alkene doublets extending beyond C₃₀. The Tertiary coals are characterised by dominant odd carbon numbered n-alkanes (n-C₂₃ to n-C₃₃), high Pr/Ph ratio (6–8), high T _m /T _s ratio (8–16), and predominant regular sterane C₂₉. All biomarkers parameters clearly indicate that the organic matter was derived from terrestrial inputs and the deposited under oxic condition.     

Stable carbon isotopic fractionation of individual n-alkanes accompanying primary migration: Evidence from hydrocarbon generation–expulsion simulations of selected terrestrial source rocks

The effect of isotopic fractionation during primary migration of hydrocarbons from coals is rarely noticed because it overlaps with the isotopic effects of maturation. In this research, geological chromatography-like effects and possible physical isotopic fractionation effects on n-alkanes during primary migration from four coals and one mudstone were studied through two types of generation–expulsion simulations (generation–expulsion simulations I and II). In order to monitor the kinetic isotopic fractionation effect during primary migration and to differentiate the isotopic effects of primary migration from the isotopic effects of maturation, generation–expulsion simulation was upgraded in two aspects, source rock was separated into at least five layers, and deuterated n-C₁₅D₃₂ was added to the initial layer of the source rock (simulation II). The experimental results suggested that all terrestrial source rocks exhibit significant geological chromatography-like effects in generation–expulsion simulation. Expulsion efficiencies shown by vitrinite-rich coals are much lower than algal cannel, fusinite-rich coal and mudstone. There also exist significant physical isotopic fractionation effects in hydrocarbon primary migration processes from vitrinite-rich coals, but there is no significant isotopic fractionation effect from fusinite-rich brown coal and mudstone. Pore structure and specific surface area of source rock samples were measured by gas adsorption of both N₂ and CO₂. This indicated that vitrinite-rich coals have a higher proportion of microporosity. The differences in pore structure and adsorptive capacity of source rocks may be responsible for differences in expulsion efficiencies and isotopic fractionation effects in generation–expulsion simulations. The isotopic fractionation effect due to primary migration should be considered in making oil-source correlation when vitrinite-rich coals are concerned.     

Composition of soluble organic matter in coals: relation to rank and liptinite fluorescence

Study of a series of twenty-six German high volatile bituminous B to low volatile bituminous coals of Upper Carboniferous age by recently refined analytical methods (‘flow-blending’ extraction, medium pressure liquid chromatography, HPLC, glass capillary gas chromatography and spectral fluorescence microscopy) reveals that yield and composition of soluble organic matter are strongly controlled by rank. In particular, the following points of inflection are noted in rank trends around 0.9% vitrinite reflectance: a maximum in yields of total soluble organic matter, aromatic hydrocarbons and n-alkanes; the most pronounced change in aromatic hydrocarbon composition; a trend reversal for pristane/ phytane ratios; a gradient change in the odd/even-predominance of long chain n-alkanes; appearance of a bimodal n-alkane distribution; and a sharp drop in concentration of individual n-, and isoprenoid alkanes. This discontinuity in rank trends around 0.9% Rm is interpreted to reflect a major change in reaction types, i.e. a shift from predominantly hydrocarbon generating to predominantly fragmentation reactions. Rank trends of maceral fluorescence exhibit the following pronounced changes over a similar but broader rank range: Different types of the maceral sporinite show a relatively abrupt shift of the fluorescence colour from yellow towards red between 0.8–0.9% Rm while up to about 1.0% Rm a sharp increase is recorded in the proportion of fluorescent vitrinite. This coincidence at a near-equal rank stage suggests a common cause for changes in yield and composition of the soluble organic matter and the maceral fluorescence of these coals.     

Role of coal type and rank on methane sorption characteristics of Bowen Basin, Australia coals

The effect of coal composition, particularly the organic fraction, upon gas sorption has been investigated for Bowen Basin and Sydney Basin, Australia coals. Maceral composition influences on gas retention and release were investigated using isorank pairs of hand-picked bright and dull coal in the rank range of high volatile bituminous (0.78% R_{o max}) to anthracite (3.01% R_{o max}). Adsorption isotherm results of dry coals indicated that Langmuir volume (V_L) for bright and dull coal types followed discrete, second-order polynomial trends with increasing rank. Bright coals had a minimum V_L at 1.72% R_{o max} and dull coals had a minimum V_L at 1.17% R_{o max}. At low rank, V_L was greater in bright coal by about 10 cm³/g, but as rank increased, the bright and dull trends converged and crossed at 1.65% R_{o max}. At ranks higher than 1.65% R_{o max}, both bright and dull coals followed similar trends. These competing trends mean that the importance of maceral composition on V_L varies according to rank. In high volatile bituminous coals, increases in vitrinite content are associated with increases in adsorption capacity. At ranks higher than medium to low volatile bituminous, changes in maceral composition may exert relatively little influence on adsorption capacity. The Langmuir pressure (P_L) showed a strong relationship of decreasing P_L with increasing rank, which was not related to coal type. It is suggested that the observed trend is related to a decrease in the heterogeneity of the pore surfaces, and subsequent increased coverage by the adsorbate, as coal rank increases. Desorption rate studies on crushed samples show that dull coals desorb more rapidly than bright coals and that desorption rate is also a function of rank. Coals of lower rank have higher effective diffusivities. Mineral matter was found to have no influence on desorption rate of these finely crushed samples. The evolution of the coal pore structure with changing rank is implicated in diffusion rate differences.     

Oil-generating potential of Tertiary coals and other organic-rich sediments of the Nyalau Formation,onshore Sarawak

The oil-generating potential of coals and other organic-rich sediments from the Late Oligocene–Early Miocene Nyalau Formation, the offshore extension of which is believed to be a major source rock, is evaluated. Coals of the Nyalau Formation are typically dominated by vitrinite, with moderate and low amounts of exinite and inertinite, respectively. Significant amounts of clay minerals are present in these coals and those containing between 15 to 65% mineral matter by volume are termed carbargilite. The samples analysed range from sub-bituminous to high-volatile bituminous rank, possessing vitrinite reflectance in the range 0.42% to 0.72%. T_max values range from 425°–450°C which is in good agreement with vitrinite reflectance data. Good oil-generating potential is anticipated from these coals and carbargilites with moderate to rich exinite content (15–35%). This is supported by their high hydrogen indices of up to 400 mgHC/gTOC, Py–GC (S2) pyrograms with n-alkane/alkene doublets extending beyond nC₃₀, and their being in the early to mid-mature oil-window range. Petrographically, the most significant evidence of the oil-generating potential of these coals is the generation of petroleum-like materials (exsudatinite) visible under the microscope. Exsudatinite is a secondary maceral, commonly considered to represent the very beginning of oil generation in coal, which is shown here to also have an important role to play in hydrocarbon expulsion. The precursor of exsudatinite in these coals is the maceral bituminite which readily expels or mobilizes to hydrocarbon-like material in the form of oil smears and/or exsudatinite as observed under the microscope. The maceral bituminite is considered to play a major generative role via early exsudatinite generation, which is considered to facilitate the overall expulsion process in coaly source rocks.     

Brecciated and mineralized coals in Union County, Western Kentucky coal field

Coals from the D-2 and D-3 boreholes in the Grove Center 7 1/2 min quadrangle, Union County, KY, have been found to be highly brecciated and mineralized. The mineralization is dominated by a carbonate assemblage with minor sulfides and sulfates. Included among the secondary minerals is the lead selenide, clausthalite. Overall, the emplacement of secondary vein minerals was responsible for raising the rank of the coals from the 0.6–0.7% R_max range found in the area to as high as 0.95–0.99% R_max.A 1.3-m-thick coal found in one of the boreholes is unique among known Western Kentucky coals in having less than 50% vitrinite. Semifusinite and fusinite dominate the maceral assemblages. The coal is also low in sulfur coal, which is unusual for the Illinois Basin. It has an ash yield of less than 10%; much of it dominated by pervasive carbonate veining. The age of the thick coal in core D-2 is similar to that of the Elm Lick coal bed, found elsewhere in the Western Kentucky coalfield. The coals in D-3 are younger, having Stephanian palynomorph assemblages.     

Isotopic and molecular composition of coal-bed gas in the Amasra region (Zonguldak basin—western Black Sea)

Previous studies on the coal-bed methane potential of the Zonguldak basin have indicated that the gases are thermogenic and sourced by the coal-bearing Carboniferous units. In this earlier work, the origin of coal-bed gas was only defined according to the molecular composition of gases and to organic geochemical properties of the respective source rocks, since data on isotopic composition of gases were not available. Furthermore, in the western Black Sea region there also exist other source rocks, which may have contributed to the coal-bed gas accumulations. The aim of this study is to determine the origin of coal-bed gas and to try a gas-source rock correlation. For this purpose, the molecular and isotopic compositions of 13 headspace gases from coals and adjacent sediments of two wells in the Amasra region have been analyzed. Total organic carbon (TOC) measurements and Rock-Eval pyrolysis were performed in order to characterize the respective source rocks. Coals and sediments are bearing humic type organic matter, which have hydrogen indices (HI) of up to 300 mgHC/gTOC, indicating a certain content of liptinitic material. The stable carbon isotope ratios (δ¹³C) of the kerogen vary from −23.1 to −27.7‰. Air-free calculated gases contain hydrocarbons up to C₅, carbon dioxide (<1%) and a considerable amount of nitrogen (up to 38%). The gaseous hydrocarbons are dominated by methane (>98%). The stable carbon isotope ratios of methane, ethane and propane are defined as δ¹³C₁: −51.1 to −48.3‰, δ¹³C₂: −37.9 to −25.3‰, δ¹³C₃: −26.0 to −19.2 ‰, respectively. The δD₁ values of methane range from −190 to −178‰. According to its isotopic composition, methane is a mixture, partly generated bacterially, partly thermogenic. Molecular and isotopic composition of the gases and organic geochemical properties of possible source rocks indicate that the thermogenic gas generation took place in coals and organic rich shales of the Westphalian-A Kozlu formation. The bacterial input can be related to a primary bacterial methane generation during Carboniferous and/or to a recent secondary bacterial methane generation. However, some peculiarities of respective isotope values of headspace gases can also be related to the desorption process, which took place by sampling.     

Occurrences and distributions of branched alkylbenzenes in the Dongsheng sedimentary uranium ore deposits,China

A series of branched alkylbenzene ranging from C₁₅ to C₁₉ with several isomers (2–5) at each carbon number were identified in sediments from the Dongsheng sedimentary uranium ore deposits, Ordos Basin, China. The distribution patterns of the branched alkylbenzenes show significant differences in the sample extracts. The branched alkylbenzenes from organic-rich argillites and coals range from C₁₅ to C₁₉ homologues, in which the C₁₇ or C₁₈ dominated. On the other hand, the C₁₉ branched alkylbenzenes dominated in the sandstone/siltstone extracts. The obvious differences of the branched alkylbenzene distributions between the uranium-host sandstones/siltstones and the interbedded barren organic-rich mudstones/coals probably indicate their potential use as biological markers associated with particular depositional environments and/or maturity diagenetic processes. Possible origins for these branched alkylbenzenes include interaction of simple aromatic compounds with, or cyclization and aromatization reactions of, these linear lipid precursors such as fatty acids, methyl alkanoates, wax esters or alkanes/alkenes that occur naturally in carbonaceous sediments. The possible simple aromatic compounds may include substituted benzenes, functionalized compounds such as phenols that are bound to kerogen at the benzyl position, and phenols that are decomposition products derived from aquatic and terrestrial sources. The distributions of methyl alkanoates and n-alkanes were found to be different between organic-rich mudstone/coal and sandstone/siltstone. From this result, it can be concluded that such differences of the alkylbenzene distributions were mainly resulting from the differences of organic precursors, although maturity effect and radiolytic alteration cannot be completely excluded.     

Oil-generating coals of the San Juan Basin, New Mexico and Colorado, U.S.A.

Coal beds of the Upper Cretaceous Fruitland Formation in the San Juan Basin of northwestern New Mexico and southwestern Colorado have significant liquid hydrocarbon generation potential as indicated by typical Rock-Eval Hydrogen Indexes in the range of 200–400 mg hydrocarbon/g organic carbon (type II and III organic matter). Small, non-commercial quantities of oil have been produced from the coal beds at several locations. The oils are characterized by high pristane/phytane (ca 4) and pristane/n-C₁₇ ratios (ca 1.2), abundant C₂₁₊ alkanes in the C₁₀₊ fraction with a slight predominance of odd carbon-numbered n-alkanes, abundant branched-chain alkanes in the C₁₅₊ region, and a predominance of methylcyclohexane in the C₄----C₁₀ fraction. The oils are indigenous to the Fruitland Formation coals and probably migrated at thermal maturities corresponding to vitrinite reflectance values in the range 0.7–0.8%. Although the oils found to date are not present in commercial amounts, these findings illustrate the potential of some coals to generate and expel oil under conditions of moderate thermal heating.     

Characterization of nC7-soluble fractions of the products from mild oxidation of asphaltenes

A significant quantity of hydrocarbons (including alkanes) is occluded in the skeleton of the asphaltene molecule. The hydrocarbons are probably remnants of the “original oil” which had been retained within the asphaltene matrix and protected from the secondary alteration processes that occurred subsequently in the oil reservoirs. In this work we report that oxidation of asphaltenes by stirring with 30%H₂O₂–HAc or NaIO₄–NaH₂PO₄ can release nC₇-soluble oxidized products, including the occluded hydrocarbons. Characterization of the nC₇-soluble fractions of oxidized products can be applied to highlight some geochemical problems, such as in studies of oil–oil correlation, oil–source correlation and secondary alterations of oil reservoirs. It will be especially useful to recover the original geochemical information of some oil reservoirs heavily degraded by post-depositional processes.     

Organic geochemistry and petrography of Tertiary coals and carbonaceous shales from Argentina

A series of eight Tertiary coal and carbonaceous shale samples with vitrinite reflectance values between 0.50 and 0.58% were extracted, fractionated and the saturated and aromatic hydrocarbons analysed for characteristic components by GC and GC-MS. Additionally, a microscopical study was undertaken in order to obtain a more precise picture of the samples under investigation.The saturated hydrocarbon fractions displayed the typical n-alkane distribution for coals of this rank, with CPI values between 2.0 and 3.1. Among the branched/cyclic compounds, pristane and α, β-homohopane were recognised as relevant components pointing to an oxic depositional environment. Detection of benzohopanes (C₃₂–C₃₅) in the aromatic hydrocarbon fractions suggests that bacteriohopanetetrol was a significant constituent of the coal biomass. Taking into consideration the Pr/Ph ratios, ash contents and microscopical characteristics of the samples, aspects of the possible degradation of hopanetetrol to homohopane are discussed. Resin-derived diterpenoids with the phyllocladane and kaurane skeleton were tentatively identified and, although minor compounds, they are interpreted to be a sign of the contribution of Podocarpaceae and Araucareaceae to the coal swamp.Aromatic compounds were dominated by alkylnaphthalene derivatives, presumably formed by C-ring cleavage and aromatisation of higher plant-derived pentacyclic triterpenois, which were main components in the high-boiling range of the fractions investigated. Angiosperms (especially Fagaceae) are postulated as source for these polycyclic compounds and, hence, for some of the polyalkylated aromatic bicyclics detected.     

Thermal catalytic transformation of pentacyclic triterpenoids: Alteration of geochemical fossils during coalification

To elucidate the possible natural evolutionary pathways for the transformation of pentacyclic triterpenoids, three terpenoid samples, Δ²-allobetulene, tetranormethylallobetulheptaene and fernenes were heated independently at 150°C for 7 weeks with montmorillonite clay. Common products from these reactions consisted of di, tri-, tetra-, and pentacyclic hydroaromatic and aromatic hydrocarbons, which are commonly found in higher rank coals. C-ring cleaved (8,14-seco) aromatic terpenoid derivatives were also found in the thermal catalytic reaction products of Δ²-allobetulene. Such compounds could be important intermediates in the formation of bicyclic hydrocarbons from pentacyclic triterpenoids.     

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

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).     

Micro-FTIR spectroscopy of liptinite macerals in coal

Reflectance FTIR microspectroscopy has been used to investigate the chemical structure of the liptinite macerals, alginite, bituminite, sporinite, cutinite and resinite in bituminous coals of Carboniferous to Tertiary age. In comparison with the spectra of vitrinite in the same coals, the micro-FTIR spectra of liptinite macerals are characterized by stronger aliphatic CH_x absorptions at 3000–2800 and 1460–1450 cm⁻¹, less intense aromatic C=C ring stretching vibration and aromatic CH out of plane deformation at 1610–1560 and 900–700 cm⁻¹ respectively and various intense acid C=O group absorptions at 1740–1700 cm⁻¹. The peaks at 1000–900 cm⁻¹ due to aliphatic CH₂ wagging vibrations in olefins and at 730–720 cm⁻¹ due to CH₂ rocking vibration in long chain aliphatic substances ([CH₂]_n, n≥4), are characteristic of liptinite macerals. Collectively the micro-FTIR spectral characteristics indicate that liptinite is composed of greater numbers of long chain aliphatics, fewer aromatics and a broader range of oxygen-containing groups than other macerals. Marked differences exist in micro-FTIR spectra within the liptinite maceral group. Alginite has the strongest aliphatic and least aromatic absorptions followed by bituminite, resinite, cutinite and sporinite. The aliphatic components in alginite are the longest chained and least branched whereas those in sporinite are the shortest chained and most branched. Bituminite, resinite and cutinite are intermediate. Notable differences in micro-FTIR spectra of individual liptinite macerals, such as intensities and peak locations of aromatic C=C in alginite, C=O groups in bituminite and resinite and substituted aromatic CH and C–O–C groups in cutinite and sporinite, also exist, which are attributed to differences in depositional environments or biotaxonomy.     

Ge-bearing coals of the Luzanovka Graben, Pavlovka brown coal deposit, southern Primorye

Results of the study of a new Ge-bearing area of the Pavlovka brown coal deposit are presented. Ge is accumulated in bed III₂ lying at the bottom of the Late Paleogene-Early Neogene coal-bearing sequence adjacent to the Middle Paleozoic granite basement. The Ge content in coals and coal-bearing rocks varies in different sections from 10 to 200–250 ppm, reaching up to 500–600 ppm in the highest-grade lower part of the bed. The metalliferous area reveals a geochemical zoning: complex Ge-Mo-W anomalies subsequently grades along the depth and strike into Mo-W and W anomalies. Orebodies, like those at many Ge-bearing coal deposits, are concentric in plan and dome-shaped in cross-section. Coals in their central parts, in addition to Ge, W, and Mo, are enriched in U, As, Be, Ag, and Au. Distribution of Ge and other trace elements in the metalliferous sequence and products of gravity separation of Ge-bearing coals is studied. These data indicate that most elements (W, Mo, U, As, Be) concentrated like Ge in the Ge-bearing bed relative to background values are restricted to the organic matter of coals. The electron microscopic study shows that Ge-bearing coals contain native metals and intermetallic compounds in association with carbonates, sulfides, and halogenides. Coal inclusions in the metalliferous and barren areas of the molasse section strongly differ in contents of Ge and associated trace elements. Ge was accumulated in the coals in the course of the interaction of ascending metalliferous solutions with organic matter of the buried peat bogs in Late Miocene. The solutions were presumably represented by N₂-bearing thermal waters (contaminated by volcanogenic CO₂) that are typical of granite terranes.