Adrian C. Hutton

Influence of alginite on the reflectance of vitrinite from Joadja, NSW, and some other coals and oil shales containing alginite

Abstract Reflectance data for vitrinite occurring in torbanites indicate that the mean maximum reflectance and the range of reflectance values are significantly lowered by the presence of alginite. This is the probable cause of apparently anomalous rank gradients in some deep oil exploration wells. Intermaceral effects need to be considered in assessing rank or maturity from vitrinite reflectance, and by inference, in most other methods. The interpretation of the cause of the effect is open to further study but the findings are highly significant in relation to coal utilization, oil and gas exploration, and studies of oil shales.

Petrographic classification of oil shales

Abstract Oil shales are a diverse group of rocks that contain mineral matter and organic matter. The organic matter is derived from terrestrial, lacustrine and marine organisms. The maceral nomeclature system of the International Committee for Coal Petrology, used widely in coal petrography and petroleum source-rock studies, is suitable for describing the organic matter in oil shales provided the terminology for organic matter derived from algal precursors is divided into two submacerals — telalginite and lamalginite. Macerals of the liptinite group, including alginite, are volumetrically important constituents of oil shales and are the major source of the shale oil that is formed during pyrolysis. Liptinite is easily characterized and quantified using fluorescence mode microscopy and thus the type and abundance of liptinite can be used as a basis for a petrographic classification of oil shales. Oil shales are grouped, using the environmental of deposition as the discriminatory criterion, into the three primary divisions of terrestrial, lacustrine and marine oil shales. Type and abundance of liptinite is then used to subdivide these three groups into cannel coal, torbanite, lamosite (further subdivided into Rundle-type lamosite and Green River-type lamosite), marinite, tasmanite and kuckersite.

Chemical, molecular and isotopic differentiation of organic facies in the Tertiary lacustrine Duaringa oil shale deposit, Queensland, Australia

Abstract Total organic matter, extractable organic matter (bitumen), and pyrolysates released on low-temperature sealed-tube pyrolysis of kerogen were analysed chemically and isotopically. Based on bulk bitumen and biomarker parameters, the sediments are immature to a depth of approx. 1300 m. Within the terrestrial and lacustrine depositional environments of the Tertiary Duaringa Basin, various organic facies have been classified according to inorganic input and maceral abundances of organic matter derived from land-plant and algal sources; the latter derived mainly from Pediastrum and with a varying Botryococcus content. The lacustrine upper lamosite is chemically and isotopically distinct from the lower lamosite due to a changing algal community, relative contributions from allochthonous land-plants and, for the lower lamosite, a slightly more saline and restricted lake environment. The lower lamosite is associated with the highest concentrations of C 28 -C 30 4-methylsteranes and 13 C depletion in TOC. In the upper lamosite, there is a strong positive correlation between Botryococcus content and 13 C enrichment. The organically lean claystones have sources nearly identical to the lamosites, but the organic matter is diluted due to rapid influx of siliciclastics. The terrestrial facies, the cannel coal and carbonaceous shales, are mainly distinguished from the lacustrine facies by higher relative proportions of C 29 steranes, C 30 4-methylsteranes and δ 13 C values for the pyrolysed hydrocarbons intermediate between the two lamosite facies. The carbonaceous oil shale has a composite geochemical signature intermediate between the two end-members, lamosite and cannel coal. Oleanane and ring-A-degraded triterpanes derived from lupane, arborane and oleanane skeletons are distributed throughout all organic facies, representing both autochthonous and allochthonous higher plant inputs. Higher concentrations of oleanane and des-A-lupane are associated with the terrestrial facies. Hopanes dominate over steranes in all organic facies and their concentration ranges are independent of facies. For the lamosites, the aliphatic biopolymer algaenan is implicated as the dominant source for n -alkanes from analysis of their yields, homologue abundances, and individual δ 13 C values. In the terrestrial facies, resinites are paraffinic and are a major source for the n -alkanes released on pyrolysis. Compound Specific Analysis of extractable and pyrolysate hydrocarbons allowed deconvolution of different source inputs to free lipids and kerogen. For the lamosites, low-molecular-weight n -alkanes in the bitumen are derived mainly from a Pediastrum source while Botryococcus is associated with waxy n -alkanes. However, the situation is reversed in the kerogen; Pediastrum algeanan has a longer average alkyl chain-length than Botryococcus algaenan. The magnitude of the isotopic differences between single n -alkanes released at different temperatures is useful in determining multiplicity of sources.

Geochemical comparisons between estuaries with non‐industrialised and industrialised catchments: The Huon and Derwent River estuaries, Tasmania

The adjacent Huon and Derwent estuaries in Tasmania have similar climatic and physical characteristics, and provide a good comparison between relatively uncontaminated and industrially polluted estuaries, respectively. Representative samples were collected from both estuaries and analysed for grainsize and trace‐element content (using X‐ray fluorescence and neutron activation analyses). The Huon estuary drains a predominantly forested and agricultural catchment and contains low (baseline) concentrations of trace elements, including lead, zinc and copper. In contrast, the Derwent estuary has a geologically similar yet larger catchment and it passes through an industrialised area in the midestuarine reach. A zinc refinery has, in the past, been a major source of trace‐element contamination. These contaminants are distributed downstream from the refinery by combined fluvial and tidal activity, while the latter also causes upstream movement of contaminants during non‐flood periods. Significant upstream contamination is limited by fluvial bottom flows remobilising contaminated fine sediment during flood periods. Maximum contamination occurs in the region around the refinery with values in the surface sediments ranging from 40 to 565 times baseline levels and from 2 to 55 times the Australian Interim Sediment Quality Guidelines high‐levels for aquatic sediments (maximum 22593 ppm Zn, 3866 ppm Pb and 1182 ppm Cu). In the lower Derwent estuary, contaminant distribution is inversely related to tidal‐flow velocities and is most prominent in the lower energy muddy substrates. Trace‐metal levels in the more recent surficial aquatic sediments are slightly lower than those recorded in a previous study from the area, possibly reflecting the stricter environmental controls now operating.

Quantitative X-ray diffraction analysis of mineral and organic phases in organic-rich rocks

Abstract Using rapid routine quantitative analyses of X-ray powder diffraction scans both the mineral and organic content of organic-rich rocks, such as coal, carbonaceous shale and oil shale, can be quantified. The minerals are quantified by the Rietveld method and the organic matter is quantified by an organic calibration curve from the same X-ray diffraction (XRD) data. For this single analysis technique, the organic content, mass absorption coefficient and density of the organic matter have to be included in the analysis to account for microabsorption effects caused by the large differences between the mass absorption coefficients of the organic matter and the inorganic fraction of the rock. The methodology was tested on rocks with up to 90wt% organic matter. Empirical calibration curves are used to relate the area of an ‘organic hump’ on an XRD trace to the organic content. These curves are calibrated by either of two calibration methods: the addition method, using mineral mixtures to which various proportions of organic matter are added, or the direct method, using XRD patterns of samples that are spiked with an internal standard. Experimental results for both calibration methods are in good agreement. The calibration curves are dependant upon organic type but, once established, each curve can be used universally for the given type of organic matter, providing the same set of diffractometer conditions are used. Errors may be introduced by: XRD background interference noise, caused by clay minerals; interference from other amorphous phases; and the presence of iron-bearing minerals. The latter is partly eliminated using either a calibration formula and intensity correction curve or by spiking the organic matter with a fixed proportion of an iron-bearing phase.

Origin, alteration and geochemical correlation of Late Permian airfall tuffs in coal measures, Sydney Basin, Australia

Abstract The Late Permian Illawarra Coal Measures of the southern Sydney Basin contain tuffs derived from altered pyroclastic airfall material. These units represent ideal stratigraphic time planes because, as the products of airfall volcanic ashes, they are distributed over wide areas in short periods of geological time. Geochemical correlation of the tuffs of the Illawarra Coal Measures with similar units in the stratigraphically equivalent Newcastle Coal Measures offers a unique opportunity to understand the temporal and spatial relations during deposition of coal-bearing units in the Sydney Basin. Thirty five core samples comprising 12 samples from each of the Burragorang and Farmborough Claystone Members and 11 samples from the Huntley Claystone Member were analysed for major and trace elements by X-ray fluorescence and instrumental neutron activation, and the results were subjected to stepwise discriminant analysis. The elements that served as the best discriminators between tuffs were, in order of atomic number, Ti, V, Sn, Hf and Th. Samples for basin-wide correlation were taken from thick interseam tuffs of the Newcastle Coal Measures and treated as unknowns in the discriminant model. The Burragorang Claystone Member shows a strong geochemical correlation with the Awaba Tuff, and the Farmborough Claystone Member correlates with the Warners Bay Tuff. The Huntley Claystone Member, however, has proved difficult to correlate with the Nobbys Tuff, the proposed stratigraphic equivalent in the Newcastle Coal Measures. Petrographic data for tuffs of the Illawarra Coal Measures indicate that they were deposited by airfall mechanisms and consist mainly of kaolinite and mixed-layer illite/smectite clays, quartz and plagioclase crystal fragments, lithic fragments and secondary calcite and siderite. Zr/TiO2 and Nb/Y ratios, tectonic discrimination diagrams and chondrite normalised REE patterns (La/Yb=3.3 to 11.9) are identical to those for tuffs of the Newcastle Coal Measures and are interpreted as being derived from magma that was calc-alkaline, rhyodacitic to rhyolitic in composition and derived from a continental volcanic-arc tectonic setting. The source of the tuffs is interpreted to be an active volcanic arc to the east of the present coastline (Currarong Orogen), but a lack of evidence from below the continental shelf makes it difficult to make concrete conclusions on its likely extent and composition.

Organic Petrography of Oil Shales

The term oil shale is a misnomer and little agreement nas been possible, in the past, as to a definition of oil shale or the nature and origin of the organic matter. Many definitions of oil shale have been published but few address the fundamental feature of oil shales which is the nature and abundance of organic matter. The volume of oil produced during pyrolysis and the chemical composition and subsequent physical properties of the derived oil, are dependent on the nature and abundance of organic matter. It should be noted rocks best termed oil shale, coal, limestone and claystone may all occur in the same sequence. With respect to organic matter, all are end members of transitions, for example, oil shale->limestone and oil shale->claystone. This means that the percentage of organic matter ranges from a minimum (= 0 or at the most <<1%) in claystone and limestone to a maximum in oil shale or coal.

Chemical and petrographic characterization of the Australian Tertiary Duaringa oil shale deposit

Abstract A comprehensive set of organic-rich sediments from the upper and lower units in the Duaringa oil shale deposit, Australia, has been studied by organic geochemical and organic petrographic methods. Rock Eval, total organic carbon, elemental analysis and infrared spectroscopy have been used to investigate gross chemical features while pyrolysis-gas chromatography has been used to determine the yield and composition of the hydrocarbons evolved during the thermal breakdown of the isolated kerogens. There is very good agreement between the maceral composition of the oil shales, the chemical composition of the kerogen and the amount and type of pyrolysis product. On pyrolysis, lamalginite-rich kerogens derived mainly from the remains of the green alga Pediastrum, predominately yields straight-chain hydrocarbons with a high wax content. As the relative proportion of non-alginitic liptinite derived from terrestrial plants decreases there is a commensurate decrease in the overall yield of pyrolysate, a decrease in the percentage of straight-chain hydrocarbons in the pyrolysate and an increase in the content of aromatic hydrocarbons. In oil shales with low terrestrial liptinite and high vitrinite, pyrolysis produces abundant phenols.

Classification of Australian Oil Shales

Oil shales, a possible additional source of liquid hydrocarbons for Australia, contain abundant organic matter that is best described using coal maceral terminology. Liptinite is the dominant maceral in all the oil shales and the type and abundance of liptinite is used to divide the oil shales into cannel coal, torbanite, lamosite, marinite and tasminite. The oil shales are formed in lakes associated with peat swamps, fresh to brackish water lakes and shallow oceans. The present status of each of the five types of Australian oil shales is reviewed.

Pyrolysis of Tertiary oil shale by a dolerite intrusion, Stuart Deposit, Queensland, Australia

Abstract The mid to late Eocene oil shale sequence of the Stuart Deposit, eastern Queensland, Australia, has been intruded by an alkali dolerite laccolith. The dolerite pyrolysed the intruded sediments with the observed aureole up to 68 m thick. Petrographic studies of samples from five drill holes that intersected the aureole showed that vitrinite reflectance near the top of the aureole generally decreases with depth but closer to the contact vitrinite reflectance rapidly increases. The lowest reflectance values are associated with a zone of bitumen, derived from the thermal alteration of alginite, in each of the five drill holes. The decrease in vitrinite reflectance is accompanied by a decrease in the fluorescence intensity of alginite and a shift in fluorescence colour towards the red end of the spectrum. In the zone characterized by the rapid increase in vitrinite reflectance, the alginite was pyrolysed and pyrolytic carbon formed.