Microbiological precursors of coorongite and torbanite and the role of microbial degradation in the formation of kerogen

Permian torbanites and Recent coorongite represent fossil algal accumulations, the affinity of which as well as the extent of their biodegradation is not known. Extensive previous research has been carried out on the geochemical constituents of torbanite and coorongite. However, the study of the microbiological components has been somewhat neglected in the past. In the present study an attempt is made at improving the understanding of the nature and origin of these deposits.The major components of coorongite as observed in the present study are a diatomaceous alga and a biodegraded organism of unknown affinity. Transmission electron microscopy (TEM) also revealed a microbial assemblage most probably responsible for the degradation of the primary organic matter. Torbanites from Glen Davis, N.S.W. (TGD-1) and Carnarvon Creek, Queensland (TC-1) revealed an organism of possible cyanobacterial affinity in various stages of biodegradation. TEM studies showed the ultra-structure of the organism as well as microbial components closely resembling cysts of methanogenic bacteria; the last in the biodegradation chain to survive in the highly anoxic environment. Similar ultra-structures have been observed in the Green River shale. Geochemical evidence for the involvement of bacteria in kerogen formation in general and coorongite (Douglas et al., 1969, Geochim. Cosmochim. Acta, v. 3, p. 56–577) in particular has been reported for sometime. Selected geochemical data are reviewed in the present study and linked to the microbial assemblages observed.     

Organic geochemistry of the kerogen and bitumen from the Ohio Shale by pyrolysis-gas chromatography

An exposure of the Ohio Shale at Bristol Ridge, Ohio in the Bellefontaine Outlier was sampled into 53 channel units. Proximate and elemental (CHN) analyses were performed on these samples to determine the concentration of organic matter. The organic content averaged 6.82% with the highest both in the lower half (11.08%) and extreme upper part (10.43%) of the section.Fragmentation of the kerogen of each of the whole rock samples was accomplished by pyrolyzing for 10 s at 750°C in the injection port of a gas chromatograph with a FID detector. The concentration and distribution of the diagnostic hydrocarbons fragmented at this temperature were used to infer the molecular construction of the high molecular weight kerogens. The suite of identified hydrocarbons for each of the samples throughout the section was similar, but a very large fluctuation in the amount of pyrolysis products was observed. This fluctuation is strongly related to organic richness as defined by the proximate and elemental analyses. The identification of diagnostic normal alkanes and aromatics and SCI indicates that the kerogen assemblage is composed of both marine and terrestial components — most likely a mixed Type II kerogen. The contribution of individual aromatic and normal alkanes is variable, which suggests that there were minor fluctuations in the proportions of terrestrial and marine organic matter during decomposition.Bitumen pyrolized from the whole rock and bitumen removed by Soxhlet extraction using a 4:1 benzene/methanol solvent mixture were analyzed. Comparison of these two techniques yield similar pristane/phytane ratios and Carbon Preference Index (CPI) values. On decomposition the whole rock bitumen exhibited a mean pristane/phytane ratio of 1.5 and a mean CPI value of 1.4, whereas the Soxhlet-extracted bitumen exhibited a mean pristane/phytane ratio of 1.6 and a mean value of 1.3. The low pristane/phytane ratios from this outlier indicates a possible marine environment, with reducing conditions existing immediately below the sediment-water interface. The CPI values also indicate the sedimentary sequence is thermally immature. Reflectance of the vitrinite (%R_o 0.05) and fluorescence (Q 0.93) of the algal bodies indicate a maturation at the beginning of the oil window or at boundary between thermal immaturity and maturity.     

Changes in the composition of bitumen extracts and chemical structure of kerogen during hydrous pyrolysis

The paper presents data on the composition of biomarkers from bitumen extracts and the chemical structure of kerogen from C_org-rich sedimentary rocks before and after hydrothermal treatment in an autoclave at 300°C. Samples selected for this study are kukersite and Ordovician Dictyonema shale from the Baltics, Domanik oil shale from the Ukhta region, Upper Permian brown coal from the Pre-Ural foredeep, carbonaceous shale from the Oxfordian horizon of the Russian plate, and Upper Jurassic oil shales from the Sysola oil shale bearing region. The rocks contain type I, II, III, and II-S kerogens. The highest yield of extractable bitumen is achieved for Type II-S kerogen, whereas Type III kerogen produces the lowest amount of bitumen. The stages of organic matter thermal maturation achieved during the experiments correspond to a transition from PC_2–3 to MC_1–2. The ¹³C NMR data on kerogen indicate that the aromatic structures of geopolymers underwent significant changes.     

Biological marker distribution in coexisting kerogen, bitumen and asphaltenes in Monterey Formation diatomite, California

Organic-rich (18.2%) Monterey Formation diatomite from California was studied. The organic matter consist of 94% bitumen and 6% kerogen. Biological markers from the bitumen and from pyrolysates of the coexisting asphaltenes and kerogen were analyzed in order to elucidate the relationship between the various fractions of the organic matter. While 17 alpha(H), 18 alpha(H), 21 alpha(H)-28,30-bisnorhopane was present in the bitumen and in the pryolysate of the asphaltenes, it was not detected in the pyrolysates of the kerogen. A C40-isoprenoid with "head to head" linkage, however, was present in pyrolysates of both kerogen and asphaltenes, but not in the bitumen from the diatomite. The maturation level of the bitumen, based on the extent of isomerization of steranes and hopanes, was that of a mature oil, whereas the pyrolysate from the kerogen showed a considerably lower maturation level. These relationships indicate that the bitumen may not be indigenous to the diatomite and that it is a mature oil that migrated into the rock. We consider the possibility, however, that some of the 28,30-bisnorhopane-rich Monterey Formation oils have not been generated through thermal degradation of kerogen, but have been expelled from the source rock at an early stage of diagenesis.     

煤中干酪根的成熟度与菲的吸附行为间的关系

将云南先锋褐煤采用热模拟的实验方法制得一组成熟度不同的煤,并将煤中的干酪根用于对菲的吸附研究.结果表明:随着干酪根成熟度的增加,有机质结构变得紧密、刚硬,还原性和芳香性增强.不同成熟度干酪根的内部结构和性质与菲的吸附行为间存在一定的关系.随着干酪根内部结构的刚性和芳香性的增强,吸附等温线的非线性逐渐增强.对于成熟度相对较低的干酪根,随着成熟度的增加,吸附容量逐渐增大,而对于成熟度相对较高的干酪根,随着成熟度的增加,吸附容量却减小.     

An evaluation of Rock-Eval pyrolysis for the study of Australian coals including their kerogen and humic acid fractions

Rock-Eval pyrolysis was performed on lithotype and depth profiles of Tertiary brown coals and a coalification profile of Permian bituminous coals. The humic acid and kerogen fractions from the coals are also investigated by this technique along with the effect of base extraction on the kerogen fraction. Structural variations between brown coal lithotypes are primarily reflected by changes in Oxygen Index Value. This result was supported by the results from the depth profile (same lithotype). A wide range of Hydrogen Indices (independent of depth) but similar Oxygen Indices were observed. The results from the Qualification profile show that the Oxygen Indices varied with rank, whereas Hydrogen Indices show a greater dependence on coal type. A plot of $\text{H}\text{C}$versus Hydrogen Index produced good correlations with the brown (0.77) and bituminous (0.90) samples lying on two separate lines intersecting at high H/C. This result (and higher correlation for bituminous samples) reflects the expected dependence of hydrogen index on oxygen content (present primarily as hydroxyl groups). A high correlation (0.95) between quantitative IR data (K 2920 cm mg^?1) and Hydrogen Indices supports previous conclusions regarding the dependence of Hydrogen Indices on the aliphatic structure of the samples.     

Characterization of permineralized kerogen from an Eocene fossil fern

The processes of organic maturation that occur during the permineralization of fossils and the detailed chemistry of the resulting products are incompletely understood. Primary among such processes is the geochemical alteration of biological matter to produce kerogen, such as that which comprises the cell walls of the fossils studied here: essentially unmetamorphosed, Eocene plant axes (specimens of the fossil fern Dennstaedtiopsis aerenchymata cellularly permineralized in cherts of the Clarno Formation of Oregon and the Allenby Formation of British Columbia). The composition and molecular structure of the kerogen that comprises the cell walls of such axes were analyzed using ultraviolet Raman spectroscopy (UV–Raman), solid state ¹³C nuclear magnetic resonance spectroscopy (¹³C NMR) and pyrolysis–gas chromatography–mass spectrometry (py–GC–MS).Cellularly well-preserved fern axes from both geologic units exhibit similar overall molecular structure, being composed primarily of networks of aromatic rings and polyene chains that, unlike more mature kerogens, lack large polycyclic aromatic hydrocarbon (PAH) constituents. The cell walls of the Allenby Formation specimens are, however, less altered than those of the Clarno chert, exhibiting more prevalent oxygen-containing and alkyl functional groups and comprising a greater fraction of rock mass.The study represents the first demonstration of the effectiveness (and limitations) of the combined use of UV–Raman, ¹³C NMR and py–GC–MS for the analysis of the kerogenous cell walls of chert-permineralized vascular plants.     

Structural relationships between a brown coal and its kerogen and humic acid fractions

A South Australian Tertiary brown coal is fractionated into humic acid and kerogen fractions. These related samples are then subjected to a number of different analytical techniques including infrared and¹³C-Nuclear Magnetic Resonance spectroscopies and pertrifluoroacetic acid oxidation. Structural conclusions are drawn from an integrated consideration of the data. Brown coal aliphatic structure is concentrated in the kerogen and the solvent soluble polar acid fractions. The humic acids are the most aromatic and contain a high degree of hydrogen bonding. Only very minor amounts of long polymethylene chain structures are observed in the humic acids, in complete contrast to the kerogen fraction. Different organic detrital origins are proposed for the coal fractions.     

Investigations into the structure of kerogen—I. Low temperature ozonolysis of Messel shale kerogen

Low-temperature ozonolysis of Messel kerogen is demonstrated to be a rather specific degradation method. The structures of the degradation products identified clearly point to specific structural elements in the kerogen network. These structural elements in turn indicate some classes of contributing species present in the paleo-ecosystem.     

Comparisons between the diets of distant taxa (teleost and cormorant) in an Australian estuary

While most studies of the utilisation of food resources in aquatic ecosystems have focused on comparing the diets of closely related taxa, the present study was aimed at elucidating whether the diets of five species, representing two distant taxa, were correlated and overlapped. We have thus compared the diets of a fish species (the flathead, Platycephalus speculator) with those of two small species of cormorant (little pied, Phalocrocorax melanoleucos, and little black, P. sulcirostris) and two larger species of cormorant (pied, P. varius, and black, P. carbo) in a temperate southwestern Australian estuary. The flathead and the two smaller cormorants consumed predominantly shrimp and small, short-lived teleosts, whereas the two larger cormorants fed almost exclusively on larger species of teleost. Although the diet of flathead were correlated with and overlapped those of the two smaller cormorant species, there was no correlation or overlap between the diets of these three species and those of either of the larger species of cormorant. Our observations of P. speculator are consistent with the results of previous studies which have shown that platycephalids are ambush predators, whereas cormorants are pursuit surface plungers, with the little pied cormorant feeding solitarily and the little black cormorant feeding communally. Flathead preyed on both demersal and mid-water teleosts. The little pied cormorant fed almost exclusively on demersal teleosts and the little black cormorant exploited predominantly mid-water schooling fish. Thus, differences in the fish components of the diets of these three predators can be related to differences in the mode of foraging and the level in the water column in which feeding takes place. The respective daily consumption of shrimp and teleosts in the estuary was estimated as 1,000 kg and 450 kg by flathead and as 180 kg and 150kg by the four species of cormorants combined. The results of this study show that, in estuaries, the degree to which diets were correlated and overlapped amongst predatory vertebrates can be greater between representatives of distant taxa than between species within the same genus.     

Evidence for the rapid incorporation of hopanoids into kerogen

Hopanoids bound into the insoluble organic matter (kerogen) of Recent sediments from a freshwater lake (Priest Pot) and an anoxic sulphidic fjord (Framvaren) were released by hydropyrolysis and examined by gas chromatography-mass spectrometry. Bound hopanoids are present in high concentration (190-1400 μg/g TOC) and represent 22 to 86% of the total analysable hopanoids (i.e., bound and solvent-soluble), this proportion increasing with depth in Framvaren Fjord. The hopanes generated by hydropyrolysis contain higher amounts of the C₃₅, C₃₂, and C₃₀ homologues, reflecting the carbon number distribution of the bound hopanoids and indicating that both biohopanoids (C₃₀ and C₃₅) and their diagenetic products (dominated by C₃₂) are incorporated into the kerogen on a timescale of only 0 to 350 years. Sequential (multiple temperature) hydropyrolysis experiments gave an indication of the relative strengths of bonds being cleaved in association with hopane generation: The hopanoids of a sediment from Priest Pot are almost entirely bound by strong covalent bonds, interpreted to be mainly ether linkages, whilst a Framvaren sediment contains hopanoids that are bound by a mixture of weak di-/polysulphide linkages and stronger ether bonds. Labelling with deuterium indicated that the strong covalent linkages dominate, even for the Framvaren sediment.     

Thermal depolymerization of kerogen and formation of immature oil

Two Chinese immature oil shales from the continental deposits of kerogen type I and II have been thermally treated combined with the technique of supercritical fluid extraction at 630–650 K and 15–25 MPa in a semi-continuous laboratory scale apparatus. Toluence is selected as the solvent. Up to 70–80% of the kerogen matrix can be converted to a thermal bitumen and extracted simultaneously. The chemical structural parameters from the NMR, IR, XRD, ESR and EA analyses of the kerogen and the thermal bitumen show striking resemblance in nature. It implies that the thermal bitumen is primarily a depolymerized product of the kerogen. Based on the GC/MS spectra of the aliphatic eluate of the thermal bitumen, the predominance of the odd/even ratio of the alkanes and the epimeric ratios, such as 20S(20S + 20R) of C-29 steranes and 22S/(22S + 22R) of C-32 terpanes, show that the maturity of the thermal bitumen from these oil shales is comparable to that of commercial immature oils from East China. The thermal bitumen is thought to be an intermediate product of the thermal degradation of kerogen.Since the thermal bitumen is mainly composed of asphaltenes and resins, it has a structure of gel. The gel-state bitumen may turn to sol-state readily due to its low aromaticity and polarity, or due to selective adsorption of asphaltenes by clay minerals. Then the migration potential of the bitumen is enhanced.Consequently, under favorable geological conditions, the thermal depolymerization of kerogen seems to be a probable mechanism to explain the formation of immature oils.     

黔西南卡林型金矿床与区域古油藏的关系:来自流体包裹体气相组成和沥青拉曼光谱特征的证据

黔西南地区是世界第二大卡林型金矿床集中区,同时也发育有大量古油藏,二者空间关系密切,但是否具有成因联系目前尚不清楚且存在较大争议。本文报道该区典型金矿床与成矿有关的热液矿物中流体包裹体的气相组成和高品位金矿石中沥青的激光拉曼光谱分析结果,以探讨含有机质流体与金成矿作用之间的关系。研究表明,虽然含砷富金黄铁矿、石英、方解石、萤石和雄黄等热液矿物形成于不同的成矿阶段,但其中流体包裹体的有机气相组分种类、含量及相对比例整体较为一致,表明成矿流体中的有机络离子团在成矿作用过程中没有发生明显的分解或重组,进而说明黔西南卡林型金矿成矿作用过程中有机质并未以有机络离子团的形式对金进行有效搬运或其搬运金的能力非常有限。在N2/Ar-CO2/CH4流体来源判别图解中,各蚀变矿物中的流体包裹体气相组成主要落在循环的大气降水区域,经大气水区域向岩浆流体区域延伸,整体上构成一条非常好的线性分布趋势,暗示成矿流体可能起源于深部岩浆但在演化过程中有大量循环大气水的加入。水银洞金矿床的1件石英样品偏离上述趋势线并向有机流体方向偏移,可能反映了流体迁移过程中有机质的加入。该区金矿床的矿石中均不同程度地发育浸染状沥青,不同矿床中沥青的激光拉曼光谱特征基本一致,说明该区金矿床中的沥青具有相同成因。根据沥青激光拉曼光谱特征地质温度计反演计算的成矿早阶段流体温度为317~336℃,明显高于区域古地温温度(160~250℃)以及区域古油藏的流体包裹体均一温度(73~175℃),说明该区卡林型金矿床的成矿热源与区域古地温无关。对区域地质及近年来地球物理与地球化学最新成果的综合分析表明,该区卡林型金矿床可能是叠加在区域古地温场之上的深部岩浆活动远端低温热液成矿作用的产物,与金矿床空间关系密切的有机质可能为来自先存古油藏并沿控矿构造发生逃逸的油气物质裂解产物,金成矿与区域古油藏之间不存在成因联系。     

Electron microscope investigation of the structure of naturally and artificially metamorphosed kerogen

The alteration of organic materials during burial is similar to thermally induced carbonization. High resolution electron microscopy shows that samples of either natural or heat-treated kerogens are formed by stacks of two aromatic layers of 5–8 Å in diameter. During catagenesis and heat-treatment, these stacks orientate themselves parallel to each other and form clusters of increasing diameter.     

Geochemical significance of lipids and lipid-derived substructures interlaced in kerogen

Young kerogens isolated from seven freshwater lakes, six river mouths and four marine surface sediments were subjected to pyrolysis in vacuo. Their pyrolysates were trapped and separated subsequently for determination of hydrocarbons, fatty acids and alcohols. The abundances, carbon number distributions of long (C₁₂) polymethylene chain lipid compounds and relative abundances of pristenes are proposed as possible indices applicable to discrimination between young kerogens from freshwater lacustrine and marine sediments. Some oil-shale kerogens of Eocene and Permian age were pyrolyzed in the same way, where the chain-length distributions of the pyrolysis products showed similar trends as those observed for the pyrolysis of young kerogens.     

Electron-probe microanalysis of light elements in coal and other kerogen

Recent advances in electron microprobe technology including development of layered synthetic microstructures, more stable electronics and better matrix-correction programs facilitated routine microanalysis of the light elements in coal. Utilizing an appropriately equipped electron micro-probe with suitable standards, it is now possible to analyze directly the light elements (C, O and N, if abundant) in coal macerals and other kerogen. The analytical results are both accurate compared to ASTM methods and highly precise, and provide an opportunity to access the variation in coal chemistry at the micrometre scale. Our experiments show that analyses using a 10 kV accelerating voltage and 10 nA beam current yield the most reliable data and result in minimum sample damage and contamination. High sample counts were obtained for C, O and N using a bi-elemental nickel-carbon pseudo-crystal (2d = 9.5 nm) as an analyzing crystal.Vitrinite isolated from anthracite rank coal proves the best carbon standard and is more desirable than graphite which has higher porosity, whereas lower rank vitrinite is too heterogeneous to use routinely as a standard. Other standards utilized were magnesite for oxygen and BN for nitrogen. No significant carbon, oxygen or nitrogen X-ray peak shifts or peak-shape changes occur between standards and the kerogen analyzed. Counting rates for carbon and oxygen were found to be constant over a range of beam sizes and currents for counting times up to 160 s. Probe-determined carbon and oxygen contents agree closely with those reported from ASTM analyses. Nitrogen analyses compare poorly to ASTM values which probably is in response to overlap between the nitrogen K α peak with the carbon K-adsorption edge and the overall low nitrogen content of most of our samples.Our results show that the electron microprobe technique provides accurate compositional data for both minor and major elements in coal without the necessity and inherent problems associated with mechanically isolating macerals. Studies to date have demonstrated the level of compositional variability within and between macerals in suites of Canadian coals.     

Computer simulation of the transformation of natural living matter into kerogen

Thermodynamic simulation of the system living matter (algae, zooplankton, or green plants) + mineral matter (25% carbonates + 75% clay minerals) + standard seawater at temperatures and pressure corresponding to diagenesis indicates that kerogen can be synthesized, together with hydrocarbons and carbon dioxide, in the reaction mix. The removal of CO₂(g) and N₂(g) from the system is favorable for the reaction Δ₁C₂₉₂H₂₈₈O₁₂ (s; H/C = 0.99, O/C = 0.041) → Δ₂C₁₂₈H₆₈O₇ (s; H/C = 0.53, O/C = 0.055) + xСH₄(aq) + yCO₂(aq) + zH₂O, whose constant and stoichiometric coefficients were calculated based on the simulation results. It is demonstrated that a pressure increase is favorable, while a temperature increase is not, for the procedure of this reaction at P-T parameters of diagenesis: log K =–567 (20°C, 35 bar), 1170 (20°C, 200 bar),–1530 (20°C, 60 bar), and +1030 (20°C, 600 bar).     

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.     

Elucidation of the Alum Shale kerogen structure using a multi-disciplinary approach

The significance and validity of integrating data obtained from a variety of analytical techniques to understand, elucidate and model kerogen's complex chemical structure is reported here using degradative (open and closed system pyrolysis, chemical oxidation), non-degradative (¹³C CP/MAS NMR) and optical (incident white light and blue light) methods. Seven Cambrian Alum Shale samples, ranging in maturity from immature to post-mature with respect to petroleum generation, were studied and were chosen for their simple geological history, uniform organic matter type and high organic carbon content. The Alum Shale kerogens, which primarily consist of algal organic matter, liberate low molecular weight gaseous and aromatic compounds on pyrolysis and give mostly branched dicarboxylic acids on chemical oxidation. ¹³C NMR spectroscopy shows that the Alum Shale kerogens are anomalously rich in oxygen-bearing functional groups (such as C = O, ArCO, CHO, CH_xO), most of which apparently remain intact within the kerogen macro-molecule (KMM) through the diagenetic and catagenetic stages. Fragments released by different degradative techniques are quantified and the aromaticity (f_a), O/C and relative proportions of various carbon types estimated by ¹³C NMR. A synthesis of these data has allowed us to better understand the chemistry of the Alum Shale kerogen.